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Anaerobic treatment differs from conventional aerobic treatment in that no aeration is applied. The absence of oxygen leads to controlled anaerobic conversions of organic pollutants to carbondioxide and methane, the latter of which can be utilized as energy source.

The main advantages of anaerobic treatment are the very high loading rates that can be applied (10 to 20 times as high as in conventional activated sludge treatment) and the very low operating costs. Anaerobic treatment often is very cost-effective in reducing discharge levies combined with the production of reusable energy in the form of biogas. Pay-back times of significant investments in anaerobic treatment technologies can be as low as two years. Anaerobic treatment of domestic wastewater can also be very interesting and cost-effective in countries were the priority in discharge control is in removal of organic pollutants.

COD is basically a measure of organic matter content or concentration. The best way to appreciate anaerobic wastewater treatment is to compare its COD balance with that of aerobic wastewater treatment, as shown in Figure below.

Anaerobic Treatment:
The COD in wastewater is highly converted to methane, which is a valuable fuel. Very little COD is converted to sludge. No major inputs are required to operate the system.

Aerobic Treatment:
The COD in wastewater is highly converted sludge, a bulky waste product, which costs lots of money to get rid of. Oxygen has to be continuously supplied by aerating the wastewater at a great expense in kilowatt hours to operate the aerators.

Anaerobic Wastewater Treatment:
Industrial wastewater anaerobic treatment of wastewater is very well suited for industries discharging highly concentrated (over approximately 1,500 mg COD/l) wastewaters, with nitrogen concentrations that are not too high. The food and food processing industry, beer breweries, soft drink producing factories and paper producing or processing factories, and some chemical industries all discharge wastewaters of this type.

Many applications are directed towards the removal of organic pollution in wastewater, slurries and sludges. The organic pollutants are converted by anaerobic microorganisms to a gas containing methane and carbon dioxide, known as “biogas”.

Two major advantages of anaerobic wastewater treatment explain its progress at the expense of the classic aerobic activated sludge treatment:

• Sludge growth is significantly less compared with the aerobic treatment
• Considerable energy saving: no costly aeration and production of energy-rich biogas.
• Depending on the system scale the biogas (> 100 Nm³/hr) may be recovered to produce heat or electricity.

Other advantages:

• Lower nutrient requirements
• Lower plan area requirements because of higher volumetric loading rates
• Lower capital investment and overall operation costs.

The appropriate choice of anaerobic reactor type depends on the composition of the effluent. Successful anaerobic wastewater treatment is only possible if the characteristics and specific problems for each individual wastewater are known in advance

How it works:
This process has been traditionally more complex and consequently harder to control than the aerobic biological process used in the classic activated sludge wastewater treatment. Better understanding of the microbiology of anaerobic processes has resulted in the successful develop­ment of new, improved and practical systems.

Anaerobic treatment is based on microbiological processes, namely methane fermentation, which occurs in an anaerobic environment.
Numerous species of bacteria have to cooperate in order to convert the organic pollution in the water to a mixture of methane (CH4)
and carbon dioxide (CO2), called biogas. The bacteria are generally present as sludge flocs or bacterial clusters (aggregates).

The main parameters determining the efficiency of the anaerobic activated sludge process are:

• Temperature
• BOD/COD ratio
• Sludge retention time
• Suspended solids concentration
• pH
• VFA/COD ratio
• Partial effluent recycle
• Nutrients
• Toxic compounds

1. Hydrolysis & Acidogenesis:
Complex particulate and solubilized polymeric substrates (e.g. polysaccharides and proteins) are hydrolysed to simpler soluble mole­cules (amino acids and sugars). These products are then further catabolized by fermentative micro-organisms, to produce mainly volatile fatty acids (VFA), aldehydes, alcohols, carbondioxide and hydrogen.

2. Acetogenesis:
The majority of the fermentation products, except H2, CO2, formate and acetate, is further degraded by the ­acetogens to yield acetate and H2 and additional CO2. The acetogens grow in close association with the ­methanogenic bacteria.

3. Methanogenesis:
The final step in the anaerobic digestion is carried out by the methanogenic bacteria and is the formation of methane­ gas from acetate and from hydrogen and carbon dioxide.

4. Bioremediation:
Anaerobic technologies are not only suitable for the removal of bulk COD they can also be utilized for the biodegradation or biotransformation of toxic priority pollutants. Microbial communities in anaerobic environments can either cause the oxidation of the pollutants resulting in its mineralization to
benign products (e.g. CO2) or they can cause the reductive biotransformation of pollutants to less toxic substances (e.g. dechlorination of polychlorinated hydrocarbons). Anaerobic bioremediation can take place in bioreactors, such as the case in the treatment of industrial effluents containing toxic pollutants. Or anaerobic bioremediation can take place in situ in groundwater or sediments at contaminated sites.

Figure: Example of a hazardous waste contaminated siteAmong the most successful applications of anaerobic treatment for the oxidation of toxic pollutants is the case of the treatment of effluent in the plastic industry containing high concentrations of terephthalate. These effluents are generally high in COD and aerobic treatment would result in excessive sludge production.

A complex microbial community of anaerobes is feasible to maintain in bioreactors permitting the total conversion of terephthalate to carbon dioxide and methane in high rate anaerobic bioreactors. Anaerobic technology has now been fully accepted as the main treatment technology for effluents of the polyethylene terephthalate (PET) industry.

Car wash effluent consists of many pollutants like Free Oil & Grease (FOG), Surfactants & Chemical Oxygen Demand (COD). There can be some particulate matter also as a result of floor washing water getting mixed with care wash effluent. A treatment for this effluent is at best tricky & treatment scheme needs to be decided carefully. The treatment depends upon the treatment goals which can be described as below:

1. Effluent discharge to Sewer
2. Effluent recycle for Car wash

• The treatment scheme in first case would entail FOG removal, COD reduction to achieve values well below the statutory limits and TSS removal for polishing. The scheme can be a Oil & Grease trap before the Effluent Storage Tank (Equalisation Tank) – DAF – AOP- PSF – ACF.
• For recycling of water, Ultrafiltration unit would be needed to remove all the suspended matter instead of Filters.

The ‘rolling seal’ actuator, together with a transducer, provides high-accuracy, gravimetric powder handling, process control, and powder and particulate flow-control, and also allows – if required – an accurate weighing capability of stored products into further process or final packing. The key attributes of the ‘rolling seal’ discharge station are:

• Fast response actuation, allowing fine control of product flow
• No flow restriction
• Hygienic design, manufactured from a handful of components
• Ease of maintenance and cleaning
• Two to three-minute remove and replace for seal and covers
• Two-year guarantee on the life of the rolling seal

CHEMICAL INDUSTRY BIG BAG DISCHARGE EQUIPMENT:

The FIBCs (bulk bag) to be used directly in process with dust containment, batch and continuous weighing direct from the FIBC, and also has the unique ability to take a partly-empty bulk bag off process without untying or retying of the outlet, or fitting of additional components to the outlet sock, thus maintaining product containment.‘big bag bin’ with cone-valve technology can be used for the dust free discharge of FIBCs, big bags, bulk bags and sacks.

CHEMICAL INDUSTRY SILO VALVES:

There are two types of silo valves: the dosing valve and the bridge breaker. The bridge breaker is usually used with the dosing valve in tandem; the dosing valve at the silo outlet and the bridge breaker is fixed with its cross frame some distance above inside the silo hopper.The bridge breaker provides head load protection to the dosing valve, which in turn controls the discharge and accurate dosing to process. The bridge breaker can have an optional internal vibrator for more cohesive products.A major benefit of the ISL silo valve system is that the dosing valve can be dismantled from below, leaving the cone-valve assembly in place even with a full silo.

cone-valve technology can be used for powder hadling and process control of powders, granules and particulates across a wide range of chemical processing industries.

COLD LIME SOFTENING

Cold lime softening process is used to reduce raw water hardness, alkalinity, silica, and other constituents. This helps prepare water for direct use as cooling tower makeup or as a first-stage treatment followed by ion exchange for boiler makeup or RO Reject recycle. The water is treated with lime or a combination of lime and soda ash (carbonate ion). These chemicals react with the hardness and natural alkalinity in the water to form insoluble compounds. The compounds precipitate and are removed from the water by sedimentation/clarification. Waters with moderate to high hardness and alkalinity concentrations (150-500 ppm as CaCO3) are often treated in this fashion.

Chemistry of Precipitation Softening

In almost every raw water supply, hardness is present as calcium and magnesium bicarbonate, often referred to as carbonate hardness or temporary hardness. These compounds result from the action of acidic, carbon dioxide laden rain water on naturally occurring minerals in the earth, such as limestone. For example:

CO2 + H2O = H2CO3

H2CO3 + CaCO3 ¯ = Ca(HCO3)2
Cold Lime Softening Lime softening accomplished at ambient temperatures is referred to as cold lime softening. When hydrated lime, Ca(OH)2, is added to the water being treated, the following reactions occur:

CO2 + Ca(OH)2 = CaCO3 ¯ + H2O

Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 ¯ + 2H2O

Mg(HCO3)2 + 2Ca(OH)2 = Mg(OH)2 ¯ + 2CaCO3 ¯ + 2H2O
If the proper chemical control is maintained on lime feed, the calcium hardness may be reduced to 35-50 ppm. Permanent calcium hardness is not affected by treatment with lime alone. If non carbonate magnesium hardness is present in an amount greater than 70 ppm and an excess hydroxyl alkalinity of about 5 ppm is maintained, the magnesium will be reduced to about 70 ppm, but the calcium will increase in proportion to the magnesium reduction. For example, in cold lime treatment of a water containing 110 ppm of calcium, 95 ppm of magnesium, and at least 110 ppm of alkalinity (all expressed as calcium carbonate), calcium could theoretically be reduced to 35 ppm and the magnesium to about 70 ppm. However, an additional 25 ppm of calcium would be expected in the treated water due to the following reactions:

MgSO4 + Ca(OH)2 = Mg(OH)2 ¯ + CaSO4

MgCl2 + Ca(OH)2 = Mg(OH)2 ¯ + CaCl2
To improve magnesium reduction, which also improves silica reduction in cold process softening, sodium aluminate may be used. The sodium aluminate provides hydroxyl ion (OH-) needed for improved magnesium reduction, without increasing calcium hardness in the treated water. In addition, the hydrolysis of sodium aluminate results in the formation of aluminium hydroxide, which aids in floc formation, sludge blanket conditioning, and silica reduction. The reactions are as follows:

Na2Al2O4 + 4H2O = 2Al(OH)3 ¯ + 2NaOH

Mg [ SO4 ] + 2NaOH = Mg(OH)2¯ + [ Na2SO4 ]
Cl2 2NaCl
Soda ash (Na2CO3) is also used to improve hardness reduction. It reacts with non-carbonate calcium hardness according to the following:

CaSO4 + Na2CO3 = CaCO3 ¯ + Na2SO4

CaCl2 + Na2CO3 = CaCO3 ¯ + 2NaCl
However, permanent magnesium hardness reduction in cold process softening requires added lime. The reactions are as follows:

MgSO4 + Ca(OH)2 + Na2CO3 = Mg(OH)2 ¯ + CaCO3 ¯ + Na2SO4

MgCl2 + Ca(OH)2 + Na2CO3 = Mg(OH)2¯ + CaCO3 ¯ + 2NaCl
In these reactions, dissolved solids (TDS) are not reduced because a solution reaction product (sodium sulfate or sodium chloride) is formed.

Reduction of Other Contaminants

Lime softening processes, with the usual filters, will reduce oxidized iron and manganese to about 0.05 and 0.01 ppm, respectively. Raw water organics (colour-contributing colloids) are also reduced. Turbidity, present in most surface supplies, is reduced to about 1.0 NTU with filtration following chemical treatment. Raw water turbidity in excess of 100 NTU may be tolerated in these systems; however, it may be necessary to coagulate raw water solids with polyelectrolyte. Oil may also be removed by adsorption on the precipitates formed during treatment. However, oil in concentrations above about 30 ppm should be reduced before lime treatment because higher concentrations of oil may exert a dispersing influence and cause floc carryover.

Equipment Employed

Continuous sludge-contact softeners are used to provide a constant flow with effluent quality superior to that obtained through batch treatment. Treating chemicals are added as a function of flow rate and water quality to the rapid mix zone of the unit. Sludge, recirculated either internally or externally to the unit, may be returned to this rapid mix zone for improved softening, softened water clarity, and silica reduction. The water then flows to the slow mix zone of the unit. Here, the precipitation reactions continue and the precipitates formed become large enough to begin settling. In the sludge-contact unit, the water flows through a bed of sludge for additional contact. The sludge level is maintained by the proper combination of sludge bed conditioning chemicals, mechanical agitation, hydraulic suspension, and sludge blowdown. A discernible line of separation between clarified water and slurry pool should exist in a properly operated unit. Effluent turbidity is usually less than 10 NTU. Flow rate is usually limited to less than 1.5 gpm/ft2 of settling area. A retention time of 1- 1.5 hrs is required to allow the softening reactions to come as close to completion as possible. Because the reactions in cold process softening are not complete, the water contaminant levels leaving the unit are unstable. With additional time and/or increased temperature, further precipitation will occur downstream of the unit. Frequently, acid or carbon dioxide is added to stabilize the water. The pH is reduced from about 10.2 to between 8.0 and 9.0, which converts the carbonate to the more soluble bicarbonate.

Limitations

Given proper consideration of raw water quality and ultimate end use of the treated water, the application of precipitation processes has few limitations. However, operational difficulties may be encountered unless the following factors are controlled: Temperature. Cold and warm units are subject to carryover if the temperature varies more than 4°F/hr (2°C/hr). Hot process units are less sensitive to slight temperature variations. Hydraulics. In any system, steady-state operation within design limits optimizes the performance of the equipment. Rapid flow variations can cause severe system upsets. Suitable treated water storage capacity should be incorporated into the total system design to minimize load swings on the softener. Chemical Control. This should be as precise as possible to prevent poor water quality. Because of the comparatively constant quality of most well waters, changes in chemical feed rates are largely a function of flow only. However, surface water quality may vary hourly. Therefore, for proper control, it is imperative that users perform frequent testing of the raw water as well as the treated effluent, and adjust chemical feed accordingly.

Aeration systems for conventional wastewater activated sludge plants typically account for 45 to 60% of a treatment facility’s total energy use. The ability to define what improvements will be most cost effective begins with understanding how to create a simplified model of the system.

The equipment used for wastewater aeration is required for the biological process and also to provide mixing to keep solids suspended for more effective treatment. Although there are many types of aeration systems, the two basic methods of aerating wastewater are through mechanical surface aeration to entrain air into the wastewater by agitation, or by introducing air or pure oxygen with submerged diffusers. The surface aeration is very energy intensive and almost obsolete nowadays.

Diffused aeration systems include a low pressure, high volume air compressor (blower), air piping system, and diffusers that break the air into bubbles as they are dispersed through the aeration tank. The most commonly used blowers are positive displacement type blowers, and centrifugal blowers (single and multi-stage).

An air diffuser or sparger diffuser is an aeration device typically is used to transfer air and with that oxygen into sewage or industrial wastewater or alternatively for mixing the large volumes. Oxygen is required by microorganisms/bacteria residents in the water to break down the pollutants. Diffusers/Spargers use either rubber membranes or plastic/ceramic elements typically and produce either fine or coarse bubbles.

A typical Disc type Diffuser System Layout

Diffusers are typically connected to a piping system which is supplied with pressurized air by a blower. This system is commonly referred to as a diffused aeration system or aeration grid.

There are two main types of diffused aeration systems, retrievable and fixed grid, that are designed to serve different purposes. In the case of a plant with a single tank, a retrievable system is desirable, in order to avoid stopping operation of the plant when maintenance is required on the aeration system. Fixed systems are typically less costly, and often more efficient because it is easier to make full use of the floor. Fixed systems can be used in multiple tanks.

The two main types of diffusers are porous & non-porous fixed orifice diffusers. The porous diffusers have types like Disc, plate or membrane (Fine Bubble). The non-porous diffusers are perforated piping, spargers & slotted tube (Course Bubble).

Diffuser Performance: The efficiency of Oxygen Transfer depends on many factors like type, size and shape of the diffuser, air flow rate, depth of submersion, tank geometry etc.

Typical Clean Water Oxygen Transfer Rates:

Course Bubble Diffusers: 2.0

Fine Bubble Diffusers: 6.5

When facilities are interested in improving aeration system efficiency to reduce energy costs, the first thought is typically “fine bubble aeration.” While this is an excellent way to improve the oxygen transfer efficiency for some aeration systems, many other considerations should be reviewed to understand how each part of the aeration process impacts energy use and the effect it may have on other facility processes.

Apparently it looks like that Fine Bubble systems are more energy efficient. Without a comprehensive model of the aeration system, energy savings calculations comparing course with fine bubble aeration systems are often skewed by not including the increased back pressure that occurs in fine bubble systems. The presence of constituents like detergents, dissolved solids and suspended solids affect the bubble size & shape & diminish Oxygen transfer efficiency.

Following points are considered when designing the Diffuser/Sparger System:

Type of wastewater being treated including any special characteristics

Proposed Tank Geometry

Type of treatment process considered

Electrical energy cost

Type and capacity of aeration components

Number and capacity of blowers

Number and configuration of proposed Aeration/Equalization Tanks

Ability to access Tanks including ability to dewater and take off-line

Economic considerations including objectives for first cost and life cycle cost

The energy costs in SWRO plants could represent up to 40 – 45% of the final costs of the water product, thus making highly efficient Energy Recovery Devices (ERD) of vital importance, as they allow for energy to be recovered from the brine stream.

There are mainly two types of ERDs available in market today.

• Energy Recovery Turbine (Pelton Turbine)
• Pressure Exchangers (Isobaric Devices)

1. Energy Recovery Turbine:
A Pelton device is a tangential flow impulse turbine. Pressurised reject is ejected through one or more nozzles is directed against a

series of spoon-shaped buckets mounted around the edge of a wheel. Each bucket reverses the flow of water, leaving it with diminished energy and the resulting impulse spins the turbine.

The buckets are mounted in pairs to keep the forces on the wheel balanced as well as to ensure smooth, efficient momentum transfer of the fluid jet to the wheel. The wheel is mounted on the high-pressure pump shaft, which together with a motor drive the pump that pressurises the SWRO system.

A modification of this is known as Hydraulic Turbo Charger. One or more nozzles direct the SWRO reject stream onto a tangential-flow pump turbine directly connected to a centrifugal impeller spinning in the SWRO feed stream. The feed stream, partially pressurised by a high-pressure pump, is boosted by the Turbocharger impeller to the SWRO feed pressure. The turbocharger and the high-pressure pump are not directly connected, providing a degree of flexibility in the operation of these devices. Also, turbochargers have a relatively small footprint and are easy to install. Currently Pump Engineering Inc.(PEI) & Fluid Equipment Development Company (FEDCO) manufacture this type of ERDs.

Pressure Exchangers:

To avoid the efficiency losses inherent to Mechanical to Pressure Energy conversion in centrifugal ERDs, the Positive displacement piston isobaric devices were developed in 80s. These devices transfer the reject pressure to low pressure feed in Equalising or Isobaric chambers. The Isobaric devices can recover up to 98% of energy in waste stream depending upon the system configuration & size.

The pressurised feed from ERD combines with discharge of HPP as feed to membranes. The HPP operates at full feed pressure but supplies only portion of total feed ~ 40% of total feed. A booster pump is needed in series with ERD to match feed pressure required for membranes.

As it can be seen in below sketch, the Isobaric devices completely decouple the ERD and the HPP. The advantage of this feature is that HPP size is not restricted by ERD size & pressure centre system SWRO can be designed. The larger HPP gives better efficiency coupled with efficiency of Isobaric device, further reducing power consumption.

General Description :
For thousands of years, filtration has been used to reduce the level of dirt, rust, suspended matter and other impurities from water. This is achieved by passing the dirty input water (influent) through a filter media. As the water passes through the media, the impurities are held in the filter media material. Depending on the nature of impurities and the media, several different physical and chemical mechanisms are active in removing impurities from the water. Some of the equipment used to employ these mechanisms has changed dramatically over time. Other systems, such as depth filters, have undergone very little change.The fundamental physical and chemical mechanisms that occur during filtration have become better understood over the years. These advances have allowed optimization of the removal of impurities from the water. Filtration systems remove particulate matter and, because of the large surface area of filter media, they also can be used to drive chemical reactions that result in the removal of several contaminants.

Sand And Dual Media Filters :
Occlusion : removal due to the impurity’s particle size. The filtration of suspended solids by occlusion removes particles based on size. Particles are occluded, or held back, due to their inability to pass through the pores of a barrier of some sort. The barrier might be a packed bed of sand, a fiber mat, or a membrane surface. Filtration by occlusion is often called “surface filtration”, since it occurs on the surface of the filtering media. Sand and Multi-Media filters are some of the filters working on this principle.

Activated Carbon Filters: Reduction : removal of free residual chlorine through conversion to chloride ions in the presence of activated carbon media. Chlorine is often added to water as a treatment chemical (e.g., for disinfection), and some residual chlorine may remain in the water after the treatment is complete. Residual Chlorine is the total amount of free and combined chlorine that remains in water after a designated contact time. Free available residual chlorine is the chlorine that exists in the water as hypochlorous acid and hypochlorite ions. De-chlorination partially or completely reduces the residual chlorine by chemical means. Free residual chlorine is converted to chloride ions in the presence of activated carbon by the following reaction:

Activated carbon has a nearly unlimited capacity for chlorine removal due to its large surface area and the above reaction. Activated carbon is a special form of carbon that is produced by heating organic material (such as coconut shells, walnut shells or coal) in the absence of oxygen. The heat removes trapped moisture and gases and dry activate most of the remaining organic material; it also leaves the remaining material with a slightly positive surface charge.Sodium bisulfite (SBS) injection is also frequently employed for chlorine removal in some systems. These systems tend to have a much lower capital cost than the pressure vessel system that uses activated carbon. However, activated carbon filtration has the advantage of being a passive technology with no normal risk of “non-treatment”. Removal of chlorine with SBS may create side effects on subsequent treatment units such as Reverse Osmosis and was found to encourage the growth of bacteria in some cases. On the opposite side, the removal of the chlorine using activated carbon did not show such a phenomenon.

Adsorption:
removal due to the impurity’s adherence to the media. Adsorption refers to the removal of an impurity from a liquid to the surface of a solid. A water-born, suspended particle adheres to a solid surface when adsorption occurs. Adsorption differs from occlusion in that occluded particles are removed from a process flow because they are too large to pass through a physical restriction in the media. In most cases, adsorbed particles are affected by weak chemical interactions that allow them to adhere to the surface of a solid. Adsorbed particles become attached to the surface of a given media, becoming a weakly held part of the solid.One Example is activated carbon bed, which can remove minute suspended particles, colloidal particles and dissolved organics due to its ability to adsorb or electro-statically hold particles. These particles would pass between the grains of carbon if not for the weak electrostatic attraction between the positive surface charge of the carbon and the negative surface charge of the particles. Particles can also be trapped in the porous structure of the activated carbon where they are then weakly held. Note that an activated carbon filter is not very efficient at removing most organic compounds from water and is rarely used in this manner.

Birm Filters :
Oxidation: removal of iron and manganese using oxidation, precipitation and filtration in the presence of Dissolved Oxygen and Birm media.Iron and manganese are commonly present in water in their soluble ferrous (Fe2+) and manganous (Mn2+) forms. They must be removed from the water to prevent fouling of downstream equipment and processes. Reverse osmosis (RO) can remove both ions if oxygen is kept out of the system. This can be a risky proposition. Removal before RO is a safer design. Before they can be removed, the iron and manganese are oxidized to create insoluble products that precipitate out of the water with the following reactions:For Iron:

As water passes through a bed of Birm media, the ferrous and manganous ions react with the oxygen in the water catalyzed by the surface of the media grains and get oxidized. With oxidation, the iron and manganese ions are converted to their insoluble ferric (Fe3+) and manganese (Mn3+) forms. Birm is not consumed in the iron removal operation. The birm operation is enhanced by the presence of dissolved oxygen of at least 15% of the iron content and high pH (more than 6.5). The presence of chlorine and organic matter greatly reduces the Birm efficiency. Many other media are available in the market that have different application and specialized in removal and treatment of one or more of the elements in the treated water. To mention a few: – Greensand Media – Lime Stone Media – Oil Removal Media – KDF Media UnitedMas should be consulted for any desirable application in this regard.

Filtration Process:
Vessels with sand or other loose filtration media are used in UnitedMas industrial filtration applications. These filters are cleaned by backwashing the media. During a backwash cycle, the filter bed is lifted and fluidized to remove accumulated particles. After the backwash cycle, the filter bed is allowed to settle. While it settles, the filter bed media will classify with the heaviest media particles settling first, and the lightest particles settling on the top. A single media (sand) filter bed will classify differently than a multi-media filter. Since all sand particles in a single media bed have approximately the same density, the largest particles are heaviest, and the smallest are lightest. Larger/heavier particles settle at the bottom, while the smallest/lightest particles settle on top. While this does not provide very efficient filtration capacity, since filtration occurs mostly at the upper surface of the filter bed where the spaces between media particles are smallest. However, due to the formed filtration cake on the top of the filter, smaller and smaller particles can be prevented from passing through, which results in a better outlet quality. Dual media beds use two or more filtration media. The media have selected densities to ensure that the bed settles in a more efficient manner. Anthracite, the largest particle, is the lightest (least dense) and settles on top. It provides large pore spaces that trap larger particles while allowing smaller particles to travel through to the layers below. Sand is intermediate in size and density. It settles as the middle layer. The sand layer filters out particles of intermediate size while allowing smaller particles to flow through to the gravel layer. Gravel, the heaviest (most dense), settles out as the bottom layer in a filter vessel. A dual-media filter needs fewer backwashing for a given volume of water filtered. The filtering capacity is significantly increased for the same volume of media as compared to a single media bed. The whole bed filters, not just the surface.

Operating Principle:
During operation, water enters the vessel under pressure and is distributed over the top layer of the media bed by an inlet distributor. The media layers sit on top of a layer of subfill that supports the under-drain assembly. The sand fills the bottom of the vessel up to the weld seam of the straight shell with the bottom head, and covers the under-drain assembly. The subfill is not involved in water filtration. The lower distributor assembly collects the water and directs it out of the vessel through the service outlet. When a sufficient quantity of particulate matter collects in the media bed, the filter is cleaned with a backwash cycle. Valves redirect the flow of water into the vessel through the lower distributor assembly. The water flows up through the media bed and carries the impurities out of the vessel through the inlet distributor and the backwash outlet. The backwash flow rate is much higher than the service flow rate. A media filter requires the addition of sufficient freeboard to allow expansion of the media bed during the backwash cycle. An optional air scour system can also be used to clean the media bed. The air scour system is used if the impurities on the media bed are particularly difficult to break up with a normal backwash. This is often the case when polymers are added to enhance performance of the media bed. To clean the media bed, the vessel is drained and air is blown into the under-drain and up through the media bed, causing the filter particles to scrub impurities off of each other. After the air scour cycle, the vessel is refilled and a backwash cycle is performed to remove loose impurities and to re-classify the media. The backwash step that follows an air scour is shorter and uses less water than a normal backwash cycle. The following modes of operation for a multi-media filter are described below: – Normal service – Drain-down (part of air scour option) – Air scour (optional) – Backwash – Rinse

Normal Service:
The valve configuration and water flow for normal service:Service Inlet valve open (to provide a supply of water to be filtered)Service Outlet valve open (to provide filtered water to downstream equipment) – Backwash Inlet valve closed (to prevent water from flowing downstream without being filtered, in common feed/ backwash header) – Backwash Outlet valve closed (to prevent incoming water from going to drain) – Rinse Outlet valve closed (to prevent filtered water from exiting the vessel and going to drain) – Air Inlet valve for Air Scour closed (to prevent the introduction of air into the vessel)

Drain-down for Air Scour (optional):
Before the air scour system can be used on the media, the water level must be lowered to a few inches above the top of the media. The valve configuration listed below is used during the drain-down cycle of the media filter system.- Service Inlet valve closed (to prevent water from entering the vessel) – Service Outlet valve open (to provide filtered water to downstream equipment) Service Outlet valve closed (to prevent unfiltered water from going to downstream equipment) – Backwash Inlet valve closed (to prevent water from entering the vessel) – Backwash Outlet valve opened (to allow air entering as water drain from the vessel) – Rinse Outlet valve open (to allow water to go to drain and to lower the water level) – Air Inlet valve for Air Scour closed (to prevent air from entering the vessel at the wrong location) When the water reaches the proper level, the air scour cycle can be initiated. The level is set by routing the rinse outlet pipe up to the level of the top of the media bed before turning down.

Air Scour (optional):
The optional air scour cleans the media more thoroughly than a backwash cycle alone. Service Inlet valve closed (to prevent incoming water from entering the vessel during the air scour cycle) Service Outlet valve closed (to prevent dirty water from contaminating down stream equipment) Backwash Inlet valve closed (to prevent incoming water from entering the vessel during the air scour cycle) – Backwash Outlet valve opened (to allow air to exit the vessel) – Rinse Outlet valve closed (to prevent water from going to drain) – Air Scour Inlet valve open (to provide an air supply for the air scour system to operate for a specified time).
Before the air scour system is used, the vessel must be drained until the water level is just above the top of the media bed. After the air scour, the filter must be refilled with water and backwashed to remove the loosened impurities. After the air scour is complete, the vessel is refilled with water via the backwash inlet valve.

Backwash:
The backwash cycle is used to remove impurities that have collected in the media bed. During the backwash cycle, the valves are oriented to reverse the flow of water from normal operation. With sufficient flow, impurities are loosened from the media bed and carried out of the vessel through the inlet distributor and service inlet. The media bed must be expanded by 30% for the backwash to be effective. To prevent filter media particles escaping from the vessel, the inlet distributor must be sufficiently higher than the top of the expanded bed. – In case of manual filter the operator does backwash process initiation manually. In case of automatic filter the backwash process is generally initiated through the timer or differential pressure switch. In UnitedMas standard automatic filter, timer based backwash is provided. – The following valve configuration is used during the backwash cycle of the media filter system: Service Inlet valve closed (to prevent incoming water from flowing against the backwash water flow) Service Outlet valve closed (to prevent dirty backwash water from contaminating downstream equipment) – Backwash Inlet valve open (to supply water to backwash the media bed). – Backwash Outlet valve open (to set the flow rate and carry away the dirty back wash water to drain) – Rinse Outlet valve closed (to prevent water from going to drain) – Air Scour Inlet valve closed (prevent air from entering system)
After the backwash cycle is complete, the vessel is rinsed and can then return to normal service.

Rinse:
The rinse cycle is used to remove any residual backwash water in the media bed. The rinse mode is the same as the service mode, except the water is sent to drain instead of to service. The valve configuration listed below is used during the rinse step of the multi-media filter system:- Service Inlet valve open (to provide a supply of water for the rinse step) – Service Outlet valve closed (to prevent dirty water from contaminating down stream equipment)
– Backwash Inlet valve closed (to prevent incoming water from entering the vessel at the wrong location) – Backwash Outlet valve closed (to prevent water from leaving the vessel during the rinse step) – Rinse Outlet valve open (to carry away the dirty rinse water to drain) – Air Scour Inlet valve closed (to prevent air from entering system) After the rinse cycle, the vessel can be returned to normal service.

Type Of Filters :
Unitedmas Industrial Series Filters are mainly classified according to media used-such as : – Sand Filters – Dual Media or Sand / Anthracite Filters – Activated Carbon Filters – Birm Filters. Depending upon mode of operation, these filters can further be classified as: – Manual IF Filters – Automatic IF Filters.
Applications :-

Sand Filters:
Removal of turbidity and suspended solids from lightly contaminated water sources such as deep wells and municipality water supplies. Used frequently upstream of reverse osmosis and demineralization systems.

Dual Media or Sand / Anthracite Filters: emoval of turbidity and suspended solids from heavily contaminated water sources such as gray water and domestic sewage tertiary treatment. Also used as a roughening-filters a head of two stage filtration systems.

Activated Carbon Filters:
Removal of free chlorine upstream of RO or Softening plants and removing from smell and odor from lightly contaminated water supplies.

Brim Filters:
Removal of Iron and Manganese from contaminated water supplies.
For applications other than above & if you require help in proper selection, please consult UnitedMas & we will be happy to assist you.

The floating decanter utilizes a circular weir for decanting supernatant liquid and a flotation device for buoyantly supporting the weir within the basin. The floatation device also acts as a baffle to prevent scum from being withdrawn during the decant step. For the successful operation of an SBR, the decanter must be designed to prohibit Mixed Liquor Suspended Solids (MLSS) from entering the decanter during non-decant sequences as well.

Early decanters were simple pipes with drilled holes along the bottom and sides. Unfortunately during the Fill & Settle phase solids plugged the holes & pipes resulting in discharge of these trapped solids in Decant stage. The development of new solids decanters corrected the problem. The solutions were:

• Fixed decanters which were Air filled except during the Decant phase.
• Mechanically closed Decanters by either Electric Motor or Hydraulics
• Decanter design with spring loaded solids excluding valve that is opened by hydraulic differential during decant phase.
• Decanters which are removed from the reactor & reintroduced during the Decant phase.

Though many types of decanters are used most commonly used is Floating Decanter or adjustable weirs. The decanter withdraws around 15 -20” below the water surface & rate of decantation is controlled by Automatic valves or by pumping.

Typically 25% of volume of SBR is decanted during decant phase. This leaves nearly all of the Activated sludge within reactor. Around 40 – 50 minutes of Decant phase is required normally. The decant phase should not interfere with settled solids and also should not cause vortex resulting into floating of solids.

In order for reduced or limited withdrawal of solids from the SBR during the Decant phase, the following operational as well as design guidelines need to be followed.

The decanter should draw the treated supernatant from below the water surface & exclude foam & scum.
An adequate zone of separation between the sludge blanket & decanter should be maintained at all times during Decant Phase.
A means for excluding solids from entering decanter during React as well as Settle phase should be provided.

Hydrothermal Hydrolysis process includes oxidation of organic matter in Water (sub critical or supercritical) as a reaction medium.
The hydrothermal oxidation could be performed by two processes.

1. Sub critical water oxidation (SubCWO), including wet air oxidation (WAO);
2. Supercritical water oxidation (SCWO).

Wet air oxidation (WAO) is a relatively low temperature (120ºC to 300ºC) and low pressure (1–10 MPa) process. The process brings together the waste and the oxidant Streams under suitable oxidizing conditions. Sludge’s can be conditioned at low temperatures and oxidized to high level of destruction (80–85%) at higher temperatures. In WAO, the proteins, lipids, starch and fibers that make the sludge solids are converted into simpler dissolved compounds, such as sugars, amino acids, fatty acids and ammonia.

WAO TECHNOLOGY DESCRIPTION:
WAO is an aqueous phase process in which soluble or suspended oxidizable Constituents are oxidized by dissolved oxygen. Oxidation reactions take place in the Aqueous environment where the water is an integral part of the reaction. Water provides a medium for the dissolved oxygen to react with the organics and can also react in part with the organics. It is theorized that the chemistry of wet oxidation involves free radical formation with oxygen derived radicals attacking the organic compounds and resulting in the formation of organic radicals.51,52 Catalysts, such as homogeneous Cu2+ and Fe3+, their heterogeneous counterparts, or precious metal catalysts can be used to enhance the effectiveness of the WAO reaction.28,49,53-60.
A noteworthy characteristic of wet oxidation chemistry is the formation of Carboxylic acids in addition to the primary end-products, CO2 and H2O. The yield of these carboxylic acids varies greatly depending on the design of the WAO system, but typically 5-10% of the total organic carbon (TOC) from the feed stream remains as carboxylic acids by-products, predominantly acetic, formic, and oxalic acid. Should These compounds are undesirable, and then a more rigorous treatment at high temperature and/or catalytic operation can be used. As a practical matter however the carboxylic acids are biologically degradable and conventional biological post treatment of the WAO effluent is often the most cost effective approach. If present, the elements, nitrogen, phosphorus, sulfur, and chlorine are usually reacted to NH3, PO43-, SO42-, and Cl- respectively.
The chemistry of wet oxidation has some attractive properties with regards to the Off-gas produced. The off-gas from a WAO reaction has negligible NOx, and SOx and Negligible particulates. Volatile organic compounds (VOCs), such as aldehydes, ketones, and alcohols may be in the off-gas depending on the composition of the feed stream.
When VOCs are present, thermal oxidation is usually used for treatment of the off-gas.

GENERAL WAO PROCESS DESCRIPTION:
1. The waste is pumped through a high-pressure pump; this can be a standard Reciprocating diaphragm pump for liquids or a more exotic high pressure pump for Slurries. The oxygen for oxidation is supplied by either air or pure oxygen and in this General flow scheme an air compressor is shown. The air is combined with the liquid and they pass through a feed/effluent (F/E) heat exchanger (HX) where the fluid is heated to near reaction temperatures. The two phase fluid then flows into the bubble reactor where the exothermic reaction takes place. The usual retention time in the reactor is 1 hour.
The oxidized effluent and off-gas then pass through the hot side of the F/E HX to be Cooled while simultaneously heating the influent. Auxiliary heaters and coolers are also employed (not shown). Depending on material of construction constraints, steam balance desires, or other factors, separate heat exchangers rather than an F/E HX have been used.
After cooling, the wet oxidized effluent then passes through a pressure control Valve that controls the pressure on the WAO system. A separator downstream of the Pressure control valve allows the depressurized and cooled vapor to separate from the liquid. The liquid is discharged, typically to conventional biological treatment facilities for final treatment. The gas is usually vented to some form of thermal oxidation such as a boiler or a dedicated flare header.

WET OXIDATION TEMPERATURE AND APPLICATION SPECTRUM:
The wet oxidation reactions usually take place between 100°C and 372°C at Elevated pressures to maintain water in the liquid phase. This temperature range can be further subdivided into low (100-200°C), medium (200-260°C), and high temperature (260-320°C) operation. Higher temperature (320-372°C) systems can be designed as well but are rarely used due to the high capital cost. Due to the necessity to maintain water in the liquid form, the system pressure is maintained above the steam pressure. Because steam pressure increases with temperature, the terms such as high temperature and high pressure are used interchangeably. Figure 2 is a diagram of the typical no catalytic WAO waste treatment application spectrum.

General WAO process Flow Diagram:
The SCWO process occurs at temperatures and pressures above the critical point (374.2ºC and 22.1 MPa). Water becomes a supercritical fluid at temperatures and pressures above the critical point. Supercritical water (SCW) may be viewed as a transition state between the liquid and gas phases. Within the critical zone, the liquid and gaseous phases merge resulting in one phase, or supercritical fluid. The supercritical fluid has unique characteristics, some of which are highly useful for the hydrolysis and oxidation of complex organic waste streams. Oxygen is completely miscible in SCW .
SCW also has a high ability to dissolve organic matter and facilitate mass transport of dissolved matter. The process brings together reactants in an intimate contact in a highly oxidizing environment that rapidly achieves near complete destruction of organic waste streams. Compared to sub critical water, SCW thus has a superior ability to dissolve organic matter and oxygen. Unlike WAO and SubCWO reactions in which the liquid and gas phases remain separate and distinct, reactions in SCW occur in a single phase. The unique characteristics of SCW result in rapid oxidation reactions that are not hindered by oxygen availability or mass transfer limitations
The initial SCWO research efforts were focused on developing an effective hazardous Organic waste treatment process capable of achieving 99.9999% removal efficiencies.

Sludge destruction mechanisms:
The various organic components of sludge undergo two major hydrothermal reactions: decomposition (mainly hydrolysis) and oxidation. Hydrothermal decomposition of the complex organic component of sludge results in the formation of simpler organic products, such as sugars, amino acids, and fatty acids. Hydrothermal oxidation results in the formation of oxygenated intermediates and final oxidation products, such as CO2 and H2O. The model in Figure 1 represents hydrothermal decomposition and oxidation. The final hydrothermal oxidation products of the initial complex organic matter (represented by C, H, N, O, P, S, CI) are shown in Eq. 1. The process raises the P, S, and Cl atoms in the waste to their highest oxidation state. Nitrogen products may include ammonia, nitrogen gas, nitrates, and nitrites depending on the original form of nitrogen in the waste and the reaction conditions such as temperature and pH.

C, H, N, O, P, S, Cl+O2®CO2+H20+PO43–+ Cl– +SO42–+(N2+NH4 +NO2 –+NO3 –)+Heat (1) Mass and settled-volume reduction.

The destruction of the solid organic component of sludge, which mainly consists of proteins, lipids, hydrocarbons, and crude fiber, is rapid and proceeds through hydrolysis and oxidation. Hydrothermal treatment can result in significant mass reduction, depending on the organic component of sludge (typically 60–80% VS/TS).

A simplified schematic of a hydrothermal treatment system is presented in Fig . The System utilizes a pre-heater, reactor, solid-liquid separator, and cooling/energy recovery exchanger. The pre-heater utilizes some of the energy in the effluent to heat the influent.

Introduction of the oxidant into the preheated waste stream causes a rapid rise in temperature and an aggressive oxidizing environment within the reactor. The heat exchange/ recovery units are particularly susceptible to scaling and corrosion. The corrosion issue may not be a major concern with sludge’s compared with halogenated waste streams. SCWO In general, the most suitable materials for SCWO reactions are expensive and usually lack structural integrity. However, the acceptable corrosion resistant materials can serve as reactor liners. In addition to corrosion, pressure letdown devices are susceptible to erosion as a result of suspended solids in treated effluents. Solids separation prior to effluent discharge can help reduce erosion of pressure letdown devices. Another challenge associated with process development relates to scaling. The deposition of salts on the walls of the reactor and heat exchange devices results from the inability of the low density SCW to dissolve inorganic salts, which drop out of solution treatability testing to select the most suitable range of reaction temperatures, pressures, residence times, and oxidants. As with incineration, SCWO can achieve virtually complete oxidation of the organic component of sludge. However, the major advantages of SCWO as compared to incineration relate to applicability to relatively dilute waste streams and quality of air emissions.

The process can meet stringent regulatory requirements for air emissions without the need for extensive air pollution control devices.

This feature reduces the operating costs of SCWO compared to incineration. The SCWO process is best suited to treat waste streams that contain adequate organic content to generate enough heat to sustain the reaction temperatures. Highly concentrated waste streams can result in overheating. Sludge’s thickened to 5–10% solids content can provide the best treatment economics as thickening reduces the required reactor volume and allows the generation of enough heat to sustain the reaction. On the other hand, sludge incineration requires efficient dewatering and drying of sludges and the addition of auxiliary fuels to sustain the reaction temperature.

1. Scheme A: No feed segregation: mixed sludge to the TH unit.
2. Scheme B: Feed segregation: only secondary sludge to the TH unit.
3. Burning the biogas in a boiler to produce power.
4. Burning the biogas in an engine or turbine to produce power and generate electricity

The waste is pumped through a high-pressure pump; this can be a standard Reciprocating diaphragm pump for liquids or a more exotic high pressure pump for Slurries. The oxygen for oxidation is supplied by either air or pure oxygen and in this General flow scheme an air compressor is shown. The air is combined with the liquid and they pass through a feed/effluent (F/E) heat exchanger (HX) where the fluid is heated to near reaction temperatures. The two phase fluid then flows into the bubble reactor where the exothermic reaction takes place. The usual retention time in the reactor is 1 hour.

The oxidized effluent and off-gas then pass through the hot side of the F/E HX to be Cooled while simultaneously heating the influent. Auxiliary heaters and coolers are also employed (not shown). Depending on material of construction constraints, steam balance desires, or other factors, separate heat exchangers rather than an F/E HX have been used. After cooling, the wet oxidized effluent then passes through a pressure control valve that controls the pressure on the WAO system. A separator downstream of the pressure control valve allows the depressurized and cooled vapor to separate from the liquid. The liquid is discharged, typically to conventional biological treatment facilities for final treatment. The gas is usually vented to some form of thermal oxidation such as a boiler or a dedicated flare header.

The term membrane bioreactor (MBR) defines a combination of an activated sludge process and WW separation by means of membranes.The MBR process was introduced in the late 1960s, as soon as commercial scale ultra filtration (UF) and micro filtration (MF) membranes were available. The original process was introduced by Dorr-Olivier Inc. and combined the use of an activated sludge bioreactor with a cross flow membrane filtration loop, see Figure 1. The flat sheet membranes used in this process were polymeric and featured pore sizes ranging from 0.003 to 0.01 μm.

The breakthrough for the MBR came in 1989 with the idea of Yamamoto and co-workers to submerge the membranes in the bioreactor. Until then, MBRs were designed with the separation device located external to the reactor (side stream MBR) and relied on high trans-membrane pressure (TMP) to maintain filtration. See Figure 2, with the membrane directly immersed into the bioreactor, submerged MBR systems are usually preferred to sides tream configuration, especially for domestic wastewater treatment. The submerged configuration relies on coarse bubble aeration to produce mixing and limit fouling. In submerged configurations, aeration is considered as one of the major parameter on process performances both hydraulic and biological. Aeration maintains solids in suspension, scours the membrane surface and provides oxygen to the biomass, leading to a better biodegradability and cell synthesis. This led to a further development of MBR system. A sample configuration of a developed process is shown in figure 3a and Figure 3b shows the water circulation of three submerged modules with perspective view of the modules depicting components inside.

The popularity of MBR technology lies in following advantages: (over conventional processes)

1. Most important aspect of MBR technology is production of very high quality effluent consistently.
2. Compliance with International stringent discharge norms.
3. Complete independent control of HRT (Hydraulic Retention Time) and SRT (Sludge Retention Time), which allow more complete reduction of COD, and improved stability of processes such as nitrification.
4. Reduced Sludge Production
5. Process intensification through high Biomass concentration with MLSS (Mixed Liquor Suspended Solids) over 8000 – 10000 ppm.
6. Ability to treat high strength wastewater.
7. Lower footprint than Conventional Activated Sludge Process, since Clarifier/Filters are eliminated.
8. Reduction in Post disinfection requirements.

Due to above advantages & recent technical innovations and significant cost reductions the applicability of MBR technology in municipal wastewater treatment has sharply increased in Europe, America, Middle East & China. MBR system is now widely used in industrial applications equally. Large MBR systems are normally built with Hollow Fiber or Tubular membranes & smaller installations prefer Flat Sheet membranes.

MBR applications:

• Residential development projects
• Commercial projects
• Mining camps and other remote installations
• Emergency response
• Military installations
• Sports facilities
• Recreation parks
• Schools
• Shopping centers
• Office parks

WHAT IS MIXED BED UNITS:
Mixed Bed Units are an ion exchange method used where superior water quality is needed. They are typically the last treatment step in the water treatment process train. They are normally positioned downstream of either individual two-bed working ion exchange units or reverse osmosis systems, further treating the effluent of these demineralizers. For low TDS (Total Dissolved Solids) waters, they can be used as stand alone ion exchange units. In this application they are often referred to as “Working Mixed Beds”. In condensate polishing applications, you can use Mixed Bed Ion Exchange to remove condensate contamination before reuseMixed Beds are ion exchangers that have both Cation and Anion resins, mixed in a single vessel. The resin bed is in the both H-OH form. These units are normally designed so that they can be automatically operated, with all the necessary internals, instruments, components and controls. Each unit is mounted on a rigid, structural steel skid base.The last traces of TDS and silica can be removed on a resin bed where highly regenerated strong acid cation and strong base anion resins are mixed.Mixed bed units deliver an excellent treated water quality, but are complicated to regenerate, as the resins must first be separated by back washing before regeneration. Additionally, they require large amounts of chemicals, and the hydraulic conditions for regeneration are not optimal. Therefore, mixed beds are usually only used to treat pre-demineralised water, when the service run is long.Mixed bed polishing produces water with less than 1.0 µS/cm conductivity a conductivity of less than 1.0 µS/cm. With a sophisticated design and appropriate resins, the conductivity of pure water

WORKING:
During the service cycle, water enters the unit through the inlet distributor at the top of the vessel, and is evenly distributed across the resin bed. As the water flows through the resin bed, its ionic contaminants are exchanged for H and OH ions on the resin beads. This removes the ionic contaminants from the water, producing highly purified Demineralized water. The treated water then passes through the false bottom under drain strainers to the outlet piping at the bottom of the Unit. When the unit’s capacity is exhausted, regeneration begins. The resin is backwashed and hydraulically classified based on their densities, and after the bed settles, regeneration is carried out. Caustic Sodium hydroxide is introduced through the downflow.

regenerant distributor, and acid is introduced through the upflow regenerant header. The interface collector receives spent acid and caustic for disposal. A slow rinse displaces regenerant acid and caustic, then the full bed is rinsed with service water. The vessel is drained until the water level is just above the bed surface. The resins are then re-mixed with air. The vessel is refilled and the bed is rinsed before the unit is returned to service.

A Summary of Regeneration Steps is given below:

• Backwash – Classify
• Settle Bed
• Acid & Caustic Injection
• Acid & Caustic Displacement
• Drain Down
• Air Mix
• Refill
• Rinse

Typical Applications:

• Treatment of water pre-demineralised with ion exchange resins
• Polishing of reverse osmosis permeate
• Polishing of sea water distillate
• Treatment of turbine condensate in power stations
• Treatment of process condensate in various industries
• Production of ultra-pure water for the semi-conductors-industry

Nanofiltration is a relatively recent membrane process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter.

Nanofiltration (NF) is one of the four membrane technologies, which utilize pressure to effect separation of contaminants from water streams. The other three are microfiltration, ultrafiltration and reverse osmosis (RO). All of these technologies utilize semi-permeable membranes that have the ability to hold back (reject) dissolved and/or suspended solids from a water stream containing these contaminants.

Nanofiltration is also becoming more widely used in food processing applications such as dairy for simultaneous concentration and partial (monovalent ion) demineralization.

This mechanism depends upon the valence of the salt ion in question. Recognize that a salt is a compound of two or more ions with an electronic charge. Valence is the number of charges on the ions that form the specific salt, which is not always sodium chloride (NaCl); sodium and chloride are monovalent ions because they have only one charge, whereas ions such as calcium and sulfate are multivalent because they have more than one charge. A defining characteristic of NF membranes is that they reject multivalent ions to a significantly greater degree than monovalent ions. The specific rejection of ions varies from one membrane manufacturer to another, but a multivalent ion rejection of 95 percent with a monovalent ion rejection of only 20 percent isn’t unusual for NF membranes.

Most of these membranes available today are in spiral wound construction only, although it’s expected that capillary fiber nanofilters will soon be on the market. Figure 1 illustrates NF in terms of its removal efficacy.

In much of the developing world, clean drinking water is hard to come by, and nanotechnology provides one solution. While nanofiltration is used for the removal of other substances from a water source, it is also commonly used for the desalination of water. As seen in a recent study in South Africa, tests were run using polymeric nanofiltration in conjunction with reverse osmosis to treat brackish groundwater. These tests produced potable water, but as the researchers expected, the reverse osmosis removed a large majority of solutes. This left the water void of any essential nutrients (calcium, magnesium ions, etc.), placing the nutrient levels below that of the required World Health Organization standards. This process was probably a little too much for the production of potable water as researchers had to go back and add nutrients to bring solute levels to the standards levels for drinking water. On another note, providing nanofiltration methods to developing countries, to increase their supply of clean water, is a very inexpensive method compared to conventional ones. However, there remain issues as to how these developing countries will be able to incorporate this new technology into their economy without creating a dependency on foreign assistance.

To dissolve air for flotation, three types of pressurized systems are used. Full-flow or total pressurization is used when the wastewater contains large amounts of oily material. The intense mixing occurring in the pressurization system does not affect the treatment results. Partial-flow pressurization is used where moderate to low concentrations of oily material is present. Again, intense mixing by passage through the pressurization systems does not affect treatment efficiency significantly. The recycle-flow pressurization system is for treatment of solids or oily materials that would degrade by the intense mixing in the other pressurization systems. This approach is used following chemical treatment of oil emulsions, or for clarification and thickening of flocculent suspensions.

In the schematic drawing of dissolved-air flotation system shown in the figure, The solids-laden or oily-water influent mixture enters the flotation vessel, and the air-solids mixture rises to the liquid surface. The air-solids mixture has a specific gravity less than water. Solids having a specific gravity greater than water tend to settle to the bottom and are removed by a rotating scraper arm. Attached to the same shaft is a rotating skimmer blade that removes the floating matter from the surface of the vessel into a skimming hopper. Clean water passes underneath a skirt and then must leave the vessel through a launder, which is located in the peripheral region.

Some typical applications for Nanofiltration are:

• Desalination of food, dairy and beverage products or byproducts
• Partial Desalination of whey, UF permeate or retentate as required
• Desalination of dyes and optical brighteners
• Purification of spent clean-in-place (CIP) chemicals
• Color reduction or manipulation of food products
• Concentration of food, dairy and beverage products or byproducts
• Fermentation byproduct concentration.

Nanofiltration and softening : Water softening generally involves the removal of hardness ions, specifically calcium and Magnesium. Because these ions are multivalent, they’re preferentially removed by NF membranes.

As a matter of fact, NF has been used for a number of years for municipal softening, particularly in Florida. The advantage of NF over RO, the other membrane technology that rejects ions, is that NF has a higher flux rate. This means that fewer membrane elements are required and it operates at a lower pump pressure—pounds per square inch (psi) or bars—thereby offering savings in operating costs.

The particular advantage of membrane technology in this application is that no chemicals are required to facilitate the removal of hardness ions, whether soda lime for municipal softening or common salt (sodium chloride) in the case of regeneration of typical residential water softeners. Sodium ion exchange, the standard technology for residential water softening for more than 50 years, utilizes ion exchange resin (in the sodium form) that adsorbs hardness ions from water passing through a bed of such resin, and releases sodium ions in exchange. Because this technology requires sodium or potassium chloride for regeneration of the resin, these are released into the sewer (or septic tank) with every regeneration cycle.

Recent legislation has been enacted to limit these discharges, based upon concerns ranging from excessive chlorides to total dissolved solids (TDS) contamination,
and it appears that an increasing number of communities will prohibit the installation of traditional residential water softeners in the future.

Pump stations are used wherever water (drinking water or wastewater) has to be transported across long distances or wherever significant height differences have to be overcome. The size and therefore the power of the pumps used depends on throughput, height difference and the magnitude of the losses in the relevant network.

In addition to drinking water networks and wastewater networks, pumping stations are used increasingly in agricultural irrigation systems.

Granular Activated Carbon (GAC):

premium virgin activated carbons made from high quality bituminous coal, coconut shell and anthracite coal raw materials for liquid and vapor phase applications.

We offer high quality virgin-carbons for liquid and vapor phase applications.  Some of the applications we specialize in include:

Liquid phase:

–  Removal of trace organic contaminants
–  Pesticide removal
–  MTBE removal
–  Disinfection by-product (DBP) removal
–  Drinking water treatment
–  Industrial process water treatment
–  High purity water applications
–  Home water filtration systems

Vapor phase:

–  Chemical process applications
–  VOC control from air strippers, soil vapor extraction and air sparge systems
–  Control of tank vent emissions
–  HVAC
–  Odor control
–  Solvent recovery of low boiling point solvents

Liquid Phase Carbon Treatment Equipment and Systems:

Water Technologies provides activated carbon adsorbers and systems to filter and remove contaminants from liquid streams for industrial, municipal or commercial applications. Our systems are permanent, hard-piped as well as options for removable adsorber equipment.

UnitedMas Technologies offers liquid phase adsorber equipment and systems for the treatment of various treatment applications, including:

– Decolorization
– Process water filtration
– Groundwater remediation
– Wastewater filtration
– Tank rinse water treatment
– Pilot testing
– Underground storage tank clean up
– Leachate treatment
– Dechlorination
– Spill cleanup
– Food grade
– Drinking water

Vapor Phase Carbon Treatment Equipment and Systems:

activated carbon adsorbers and systems to treat malodorous, VOC and other industrial plant emission problems.

Our systems are permanent, hard-piped as well as options for removable adsorber equipment.

– API separator vents

– VOC control from soil vapor extraction (SVE) systems and air strippers
– Wastewater and product storage tank vents
– Process vents
– Refinery and chemical plant wastewater sewer vents
– Laboratory hood exhausts
– Soil vapor extraction (SVE) remediation system off-gases
– Controling emissions from waste processing oprations (i.e., tank cleaning)
– Backup VOC control device for thermal oxidizers

Hot Water Sanitization for Activated Carbon Adsorbers:

Hot-water sanitation effectively protects against detrimental bacterial growth in the activated carbon bed, thereby limiting carbon replacement costs and the associated system downtime.

Many industries such as pharmaceutical, food and beverage are turning to, chemical-free, hot-water sanitization to meet product quality requirements and save time and resources. Hot-water sanitization effectively protects against detrimental bacterial growth in the activated carbon media bed, thereby limiting carbon replacement costs and the associated system downtime.

Powdered Activated Carbon (PAC) media, Equipment and Systems:

powdered activated carbons have been specifically developed for the removal of a broad range of organic contaminants from potable, waste and process waters.

Powdered activated carbon (PAC) has a relatively smaller particle size when compared to granular activated carbons and consequently, presents a large surface to volume ratio.

As such, PAC is not commonly used in a dedicated adsorber vessel, due to the high headloss that would occur. Instead, PAC is generally added directly to other process units, such as raw water intakes, rapid mix basins, clarifiers, and gravity filters.

Applications for powdered activated carbon include:

– Dechlorination/chloramine reduction
– Removal of organic contaminants
– Taste and odor reduction
– Disinfection-by-product (DBP) removal
– Pesticide removal
– Landfill leachate
– Drinking water treatment
– Groundwater remediation
– Wastewater treatment

Solid Liquid Seperation :

Bag Filters and Accessories:

Suspended solids and other fine particles can be removed from liquid streams by passing them through filters.

Bag filters are a convenient and economical choice for applications that require gross particulate removal.  Particulates are trapped in the bag for quick disposal. Bag filters are available for low flow and come in welded or sewn styles. They have multiple micron removal efficiencies

Housings for bag filters are stainless steel and polypropylene.

We are the industry leader in providing components and cartridge filters, including replacement cartridges for filters that are manufactured by other vendors.

Cartridge Filters and Accessories:

Depending upon the application and water treatment requirements, filtration systems use a variety of media to remove contaminants.

We provide a wide range of media, from sand, anthracite and quartz to conditioned media for iron and manganese removal, activated carbon, and replacements for membranes and cartridge filters. Our filtration systems include cartridge, gravity, greensand, walnut shell, fine sand and multimedia.

Cloth Type Filter Systems:

Woven polyester pleated panel design disc filters increase treatment capacity and is an ultimate barrier for suspended solids in tertiary treatment processes.  The inside-out filtration design allows for a higher operating headloss capability, ensuring a more sustainable operation in terms of more throughput, better feed distribution, and fewer backwash frequencies.  Applications include; water reuse, tertiary filtration and process water filtration.

Granular Media Filter Systems – Gravity Type:

Filtration technology, from simple media filters to advanced membranes, is central to municipal and industrial water treatment systems. Interest in these technologies will grow in the future as shrinking water supplies and rising water costs put pressure on the market.  Suspended solids and other fine particles can be removed from liquid streams by passing them through filters.

Filtration, typically used as a “polishing” step, refers to the capture of particles by passing water over or through one or more media. Filtration is the key to producing high-quality effluents required for modern regulatory compliance or reuse.

Filtration system technologies used in modern advanced treatment are mostly well established. Changes in the marketplace are steadily moving these new methods from specialty applications to the mainstream. Two trends are largely responsible, reduced water supplies and stricter regulations.

We design and install water and wastewater gravity filters of all kinds–shallow bed, traveling bridge, deep bed, packed filters, pressure filters, precoat filters and more, which use a variety of filtration media including sand, gravel, activated carbon, and other granular media.

Our membrane filtration systems accomplish microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.

Gravity Filter Systems:

Suspended solids and other fine particles can be removed from liquid streams by passing them through gravity filters.

We design and install gravity filters of all kinds–shallow bed, traveling bridge, deep bed, packed filters, pressure filters, precoat filters and more, which use a variety of filtration media including sand, gravel, activated carbon, and other granular media.

Media – GFH, Greensand, Walnut Shell & Specialty:

Depending upon the application and water treatment requirements, filtration systems use a variety of media to remove contaminants.

We provide a wide range of media, from sand, anthracite and quartz to conditioned media for iron and manganese removal, activated carbon, and replacements for membranes and cartridge filters. Our filtration systems include cartridge, gravity, greensand, walnut shell, fine sand and multimedia.

Packaged Water Treatment Plants:

Packaged drinking water treatment plants are safe, reliable and cost effective, specifically geared for the needs of small communities. We know it is sometimes difficult to comply with current and future regulations. That’s why we have developed packaged water treatment systems that take the guesswork out of solving your contaminated drinking water problems.

The right package treatment technology for your water needs is dependent on a number of factors, including raw water source, flowrate and effluent requirements.  In order to determine what type of water treatment technology accurately suits your situation, it is important that you first analyze the quality of your incoming water supply.  This ensures the water treatment equipment you purchase will meet your specific water quality needs.  If you need help to determine your water analysis, we can assist in analyzing and reporting on your water sample.

Deionizer/ Demineralizer/ Dealkalyzer Products:

Deionization is the use of ion exchange to remove ionic substances from a solution. Ion exchange is a chemical process that uses ion exchange resin to attract dissolved contaminants, leaving pure water.

We offer complete systems to produce pure water for rinsing, boiler feed or any other application where our quality engineered and manufactured deionizers will produce the quantity and quality of water needed for your application.

Mixed Bed Deionizers: Commercial and Light to Medium Industrial Applications – When you need higher quality water with a more neutral pH than separate bed systems, as well as enhanced silica and CO2 removal, mixed bed deionizers are the appropriate deionization systems to use.

Two Bed Deionizers: Commercial and Light to Medium Industrial Applications – An acid regenerated cation vessel piped in series with a caustic regenerated anion vessel enables our two bed deionizers to provide high-quality water over the length of the service cycle.

Packed Bed Deionizers: Industrial Applications – Using ion exchange membranes, resins and electricity, our packed bed system produces water of high purity. These chemical-free systems are especially suited for utility in general, pharmaceutical and microelectronics industries.

Circular Clarifiers:

Circular clarification technologies designed to treat water or wastewater to remove particles and reduce total suspended solids (TSS) to low levels.

Clarifiers – Plate:

To meet your liquids/ solids separation needs, we supply a full range of separator devices, such as skimmers, decanters, and other ancillary equipment.

Flotation Equipment and Systems – (DAF, IAF):

Dissolved air flotation and induced air flotation are two separation methods used to separate liquid from solids.

Rectangular Clarification Technologies:

Rectangular clarification is a separation process commonly used in very large or confined municipal and industrial spaces to remove contaminants from liquids, because it makes the most out of the available space.

  Traveling Water Screens:

debris removal for power plants, municipal drinking water intakes and other screening applications.

Decanter Centrifuge, Decanters, Centrifuges Decanter Decanter Centrifuge range provides an effective, low-maintenance solution to continuous liquid clarifying and / or solids dewatering with advanced process and mechanical performance

features.

Decanter Centrifuge Advantages

The hydraulic scroll drive also provides significant processing advantages:

Automatically maintains constant torque load and pressure on the scroll during operation

Automatically adjusts and compensates for changes in the feed material

Provides three easy to use settings controlling

Scroll pressure

Scroll differential speed

Scroll speed boost

Scroll can be turned when the bowl is stopped

Scrolls can be operated in a “leading” or “lagging” condition

Sulfate Separation system controls scale formation:

Where seawater contains sulfate and formation water contains barium and strontium, the result is the potential for significant barium and strontium sulfate scaling and possible reservoir souring. Scale deposits are a common problem in water injection, the type and severity of scaling varying between fields.

In the 1980s Dow Chemical Company developed these membranes to reject selectively sulfate ions in seawater while allowing sodium and chloride ions to pass through. Since then in addition to minimizing the potential for scale formation and associated well workover and squeeze treatment costs, the reduced sulfate levels are so low that the potential for reservoir scouring can be reduced. Today the third generation membranes are in use on offshore platforms which have a 25% increase in membrane surface area, allowing increased throughputs and thus decreasing space and weight requirements of the sulfate removal facility on an oil platform.

General Flow Diagram,

Hydrocyclones for Potato Starch Recovery:

small diameter hydrocyclones are being used at potato crisp and chip manufacturing plants to recover starch solids from the plant effluent water. Recoveries of around 80% starch are being achieved. More than 90% of the process water can be reclaimed. The use of Hydrocyclones instead of settling tanks and centrifuges reduces the separation time substantially. Washing and thickening duties also utilize these hydrocyclones.

Hydrocyclones for Corn Starch Treatment:

The corn starch wet milling industry uses 600mm ( 24″ ) and 200mm (8″) cyclones for stone and grit removal; 150mm (6″) cyclones for germ separation.  12mm cyclones are used extensively in starch washing circuits where their high capacity and exceptional gluten removal efficiency makes them an ideal choice. 10 mm cyclones are used in starch recovery and thickening duties.

  LIQUID / LIQUID Seperation:
Liquid / Liquid Coalescer Packs:
The coalescer packs are placed in the liquid

section of horizontal separators in order to assist with effective separation of water & oil.

Two basic fluid dynamic principles, as well as innovative physical dimensioning, govern the operation of separating liquid phases. Laminar, stable flow maintained between the corrugated plates, allows conventional settling (i.e. in accordance with Stoke’s Law) to be much more efficient. Decreasing the travel distance to an interface (and subsequent removal) reduces the retention time required to effectively treat a given volume of water. This can improve existing separator performance or decrease the vessel size in new designs.

Desalter / Electrostatic Treater Internals:

Electrostatic treaters are utilized to remove water from oil to high efficiencies (below 1.0% BS&W). Electrostatic separators additionally act as desalters as they remove water that contains salt.  Some times desalters consist of a upstream mixing device in which fresh water is used to wash the crude or desalters can have one or two satge desalters in order to minimize dilution water requirements. AMR Process Inc. offers various designs of electrostatic treaters and desalters and provide the process internals, proprietary transformer hook up electrical materials together with a process guarantee.

Electrostatic oil dehydrator configurations:

Advanced Treater – This is a horizontal vessel with vertical oil flow through electrostatic grids which effective dehydrate oil.

Desalter – This is an electrostatic oil dehydrator that additionally reduces the salt content of the export oil, utilizing dilution water.

Heater Treater – A fire tube is included in the electrostatic vessel for heating of bulk fluid, with initial stage separation of water/oil/gas, before passing through an electrostatic grid.

Electro-Mechanical Treater – Combines the high efficiency mechanical separation of a coalecser plate pack with the high efficiency separation of an electrostatic grid. This design can be problematic if used with waxy oils and solid loadings but is advantageous at breaking problematic emulsions.

Types of electrostatic fields:

AC-Plus – Three phase AC converted to single phase AC high voltage field. Excellent for breaking emulsions, low API oils and high inlet water contents.

AC-Direct – Three phase AC converted to DC high voltage field. Improved oil throughputs providing smaller vessel sizing.

AC-Tri – “Scott” connection, three phase hook AC up converted to two phase AC high voltage field. Excellent at balancing loads on electrical generation equipment.

Liquid Gas Sepeartion

Cyclonic Demisters

Another method of removing liquid particles from the gas stream in a separator utilizes centrifugal force. The gas stream enters a multi-cyclone or cyclonic bundle that spins the gas, forcing the liquid to the cyclone wall. The liquid drains out of the cyclone at a low pressure recycle opening, whilst the gas turns around upon itself and flows free of liquid out the bottom of the cyclone tube.

The cyclonic demister provides more efficient removal of liquid particles than the mesh pad or vane pack demister at steady state flows, and also provides smaller diameter vessels. This makes the cyclonic demister very cost competitive, especially for high pressure applications. The cyclone demister also effectively removes solids. The cyclone demister does however have a limited turndown to around 25% of design flow, as the performance is dependent on the centrifugal force that is reduced as gas flow decreases.

Plate Scrubbers:

Plate scrubbers are a highly efficient means of particulate removal, absorption of contaminants and gas cooling. In this type of scrubber (see photo) the gas passes upwards through a number of small holes in one or more plates. Liquor enters on the top plate, flows across it and through a down-comer to the plate below. Intimate gas liquid contact is obtained as the gas bubbles through the liquid on the plate.

In the target plate design a “target baffle” is located over each hole in the plate. As the gas passes through the perforations the dust particles impinge on the “targets” and they are collected by the liquor. For increased dust removal performance a venturi scrubber can be incorporated into a tray design in the form of a venturi slot plate.

Venturi Scrubbers:

Venturi scrubbers are an effective means of removing sub micron particulates. The contaminated gas is accelerated in the converging section before entering the throat (see photo). Scrubbing liquor enters around the top of the converging section and completely flushes the wall. In addition, liquor enters through a spray to fill the throat with droplets.

In the venturi throat, the high velocity gas atomizes the liquid droplets with trap the solid particles. The scrubbed gas and liquid droplets leave the venturi throat and pass through the diverging section where further agglomeration takes place to produce larger droplets. The liquor droplets are then separated from the gas stream in a cyclonic entrainment separator.

To ensure high scrubbing efficiencies, even with varying gas flows, the throat can be made adjustable, thus maintaining the required scrubber pressure drop, even at reduced throughputs.

The liquor from the separator is recycled via pumps to the venturi scrubber with a small bleed being discharged to control the build up of solids in the circulating liquor.

Packed Towers:

Wetted packed towers are the simplest and most commonly used approaches to gas scrubbing. The principle of this type of scrubber is to remove contaminants from the gas stream by passing the stream through a packed structure which provides a large wetted surface area to induce intimate contact between the gas and the scrubbing liquor. the contaminant is absorbed into or reacted with the scrubbing liquor.

The packing of the tower is normally a proprietary loose fill random packing designed to encourage dispersion of the liquid flow without tracking, to provide maximum contact area for the ‘mass transfer’ interaction and to offer minimal back pressure to the gas flow. The reactivity between the contaminant and the scrubbing liquor influences the system designer’s determination of gas and liquor flow and the height and diameter of the packed bed.

A demister is fitted at the top of the tower to prevent entrainment of droplets of the scrubbing liquor into the extraction system or stack.

Wetted packed towers can be designed for very high efficiencies with relatively low capital and running costs. The low pressure drop associated with packed bed scrubbers permits the use of smaller more economical fans. Although efficiency may be affected, a packed tower will usually function when gas or liquor flows vary from its original design parameters.

Air Strippers:

Dissolved gases such as hydrocarbons ( VOC’s), carbon dioxide, ammonia and hydrogen sulfide can be removed from water by stripping (desorbing) by contacting the water with ambient air in a packed column. The water to be treated enters the top of a packed tower and is distributed over the top of a packed bed and flows down through the packing. Fans blow ambient air into the base of the tower and this flows up through the packing where it contacts the water stripping out the VOC contaminants. The air containing the stripped VOC’s passes through a demister to remove water droplets and is vented to atmosphere. The stripped water collects in the base of the stripping tower from where it is discharged. The efficiency of the VOC removal depends on the vapor pressure of the specific VOC compounds, the temperature of operation and the packed height of the tower. The materials of construction of the stripping towers would be either stainless steel or glass reinforced polypropylene. The internals would be manufactured from polypropylene.

Gas / liquid vertical separator filter:

The Plenty Vertical Filter Separator will remove 100% of all droplets 8-10 microns and larger and 99.5% of all droplets ½-8 microns in size. It will also remove 100% of all solid particles, 3 microns and larger 99% of all particles ½-3 microns in size. These operating efficiencies apply over the entire flow range from maximum design down to virtually zero flow. The first stage of the filter separator consists of a number of glass fibre coalescer /filter elements through which the wet gas passes. The small liquid drops carried in the gas stream are trapped within the glass fibres of the element and coalesce to form drops 100 to 200 times larger than the original size. These drops pass through the element wall and are carried forward by the gas stream to the second stage vane type separator. The second stage consists of a vane type impingement separator, which operates exactly as described for vane separator.

Its maintaining the required scrubber pressure drop, even at reduced throughputs.

The liquor from the separator is recycled via pumps to with a small bleed being discharged to control the buildup of liquor.

Thermal treatment is a term given to any waste treatment technology that involves high temperatures in the processing of the waste feedstock. This commonly, although not exclusively involves the combustion of waste materials.

Systems that are generally considered to be thermal treatment include:

–    Gasification
–    Incineration
–    Pyrolysis

Gasification:

Gasification can be seen as between Pyrolysis and combustion in that it involves the partial oxidation of a substance. This means that oxygen is added but the amounts are not sufficient to allow the fuel to be completely oxidised and full combustion to occur. The temperatures employed are typically above 650°C. The process is largely exothermic but some heat may be required to initialise and sustain the gasification process. The main product is a syngas, which contains carbon monoxide, hydrogen and methane. Typically, the gas generated from gasification will have a net calorific value (NCV) of 4 – 10 MJ/Nm3. The other main product produced by gasification is a solid residue of non-combustible materials (ash) which contains a relatively low level of carbon. For reference, the calorific value of syngas from Pyrolysis and gasification is far lower than natural gas, which has a NCV of around 38 MJ/Nm3.

Incineration: Incineration usually involves the combustion of unprepared (raw or residual) MSW. To allow the combustion to take place a sufficient quantity of oxygen is required to fully oxidise the fuel. Typically, incineration plant combustion (flame) temperatures are in excess of 850ºC and the waste is converted into carbon dioxide and water. Any non-combustible materials (e.g. metals, glass) remain as a solid, known as Bottom Ash, that contains a small amount of residual carbon.

Pyrolysis: In contrast to combustion, pyrolysis is the thermal degradation of a substance in the absence of oxygen. This process requires an external heat source to maintain the temperature required. Typically, relatively low temperatures of between 300ºC to 850ºC are used during pyrolysis of materials such as MSW. The products produced from pyrolysing materials are a solid residue and a synthetic gas (syngas). The solid residue (sometimes described as a char) is a combination of non-combustible materials and carbon. The syngas is a mixture of gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other VOCs). A proportion of these can be condensed to produce oils, waxes and tars. The syngas typically has a net calorific value (NCV) of between 10 and 20 MJ/Nm3. If required, the condensable fraction can be collected by cooling the syngas, potentially for use as a liquid fuel.

Typical Reactors & Applications are given below.

Reactor	Typical Application	Operating Conditions
Rotating Kiln	Pyrolysis	Typically operate at temperatures of between 300 – 850oC. Unit can accommodate large size feed material (200 mm). Kiln is heated externally and waste is fed in from one end of the kiln which slowly rotates creating a tumbling action. This mixes the waste and ensures contact with the heating surface and gases inside the kiln.
Heated Tube	Pyrolysis	The tubes are heated externally and temperatures as high as 800 C are used. The process can accommodate large size feed material. The waste passes through the tube at a set speed to ensure the pyrolysis process is complete.
Surface Contact	Pyrolysis	Small size feed material required and therefore significant pre-treatment is necessary. Process operates at high temperatures and the small size of the feed gives high heating rates. The application of this technology is to maximise the rate of pyrolysis.
Fluidised Bed	Gasification	Fluidised bed technology may be used for gasification or combustion processes. The bed is a mass of particles (typically alumina) that has similar characteristics to a moving fluid. This is achieved by blowing hot gases through the bed of particles. This system provides good mixing and heat transfer to the incoming waste. Waste is pre-treated to remove large sized material. This technology is well suited to the gasification of refuse derived fuels.
Fixed Bed	Gasification	There are a range of different reactor types that come under this heading. A typical example is a grate system where the feed passes along the grate and hot gases pass through the bed of waste heating it.

The removal of dissolved gases from boiler feedwater/heating plants is an essential process in a steam system. The presence of dissolved oxygen in feedwater causes rapid localized corrosion in boiler tubes. Carbon dioxide will dissolve in water, resulting in low pH levels and the production of corrosive carbonic acid. Low pH levels in feedwater causes severe acid attack throughout the boiler system. While dissolved gases and low pH levels in the feedwater can be controlled or removed by the addition of chemicals, it is more economical and thermally efficient to remove these gases mechanically. This mechanical process is known as deaeration and will increase the life of a steam system dramatically.

Deaeration is based on two scientific principles. The first principle can be described by Henry’s Law. Henry’s Law asserts that gas solubility in a solution decreases as the gas partial pressure above the solution decreases. The second scientific principle that governs deaeration is the relationship between gas solubility and temperature. Easily explained, gas solubility in a solution decreases as the temperature of the solution rises and approaches saturation temperature. A deaerator utilizes both of these natural processes to remove dissolved oxygen, carbon dioxide, and other non-condensable gases from boiler feedwater. The feedwater is sprayed in thin films into a steam atmosphere allowing it to become quickly heated to saturation. Spraying feedwater in thin films increases the surface area of the liquid in contact with the steam, which, in turn, provides more rapid oxygen removal and lower gas concentrations. This process reduces the solubility of all dissolved gases and removes it from the feedwater. The liberated gases are then vented from the deaerator.

APPLICATION:

A vacuum deaerator is used for treatment of circulating water in heating plants. The circulating water should not contain oxygen as this increases the risk of corrosion on the system. The oxygen is dissolved in the make-up water and thereby enters the tank together with the make-up water, which normally contains 6-8 mg/l oxygen. The oxygen content can be reduced to under 0.2 mg/l with a vacuum deaerator.

Vacuum Deaerator is especially useful when:

1. In installations with many branches and low flow rates

2. For small temperature differences between supply and return. A vacuum degasser is not limited by fluid temperature

3. If a through-flow deaerator cannot be mounted on the installation for practical reasons. A vacuum degasser can be connected in almost every part of an installation.

THEORY OF OPERATION:

The oxygen-containing make-up water, preheated to 40-90 °C, is led to the upper section of the deaeration tank. In order to optimize the removal of oxygen, the deaeration tank is equipped with fillers for division of the water into fine particles. The vacuum pump creates the necessary vacuum so that the make-up water boils. When the water boils, the oxygen is liberated and removed by means of the vacuum pump. The deaerated water is separated into two streams, which are pumped partly into the district heating network, partly recycled over the deaeration tank.

A vacuum deaerator consists of three main components: A vacuum deaerator, a vacuum pump unit and a pump unit.

DEAERATION TANK:

The deaeration tank is constructed in galvanized or stainless steel. Inside the tank is equipped with an intermediate bottom, under which a reservoir for deaerated water is mounted. Fillers are installed on top of the intermediate bottom. The system is provided with requisite instrumentation for level control and is delivered for foot/wall-mounting.

VACUUM PUMP UNIT:

The vacuum pump unit consists of a vacuum pump (liquid ring pump) as well as a valving arrangement for setting of cooling water quantity and vacuum force. The vacuum pump is delivered on bracket for wall-mounting.

PUMP UNIT:

The pump unit consists of a centrifugal pump and of a pipe system with valves for setting of the make-up water quantity and the circulating quantity. The pipe system can be in galvanized or stainless steel, and the pump in stainless steel.