Sewage Treatment Plants

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ACTIVATED SLUDGE PROCESS

The activated sludge process is a type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.
The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: An aeration tank where air (or oxygen) is injected in the mixed liquor. This is followed by a settling tank (usually referred to as "final clarifier" or "secondary settling tank") to allow the biological flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water.

MOVING BED BIO REACTOR SYSTEM(MBBR)

MBBR system consists of an aeration tank (similar to an activated sludge tank) with special plastic carriers that provide a surface where a biofilm can grow. The carriers are made of a material with a density close to the density of water (1 g/cm3). An example is high-density polyethylene (HDPE) which has a density close to 0.95 g/cm3. The carriers will be mixed in the tank by the aeration system and thus will have good contact between the substrate in the influent wastewater and the biomass on the carriers.[2] To prevent the plastic carriers from escaping the aeration it is necessary to have a sieve on the outlet of the tank. To achieve higher concentration of biomass in the bioreactors, hybrid MBBR systems have also been used where suspended and attached biomass co-exist contributing both to biological processes.[4] There are also anaerobic MBBRs that have been mainly used for industrial wastewater treatment.[5] Recently, a combination of anaerobic (methanogenic) MBBR with aerobic MBBR was applied in the laboratory for municipal wastewater treatment with simultaneous production of biogas.[6] The MBBR system is considered a biofilm process. Other conventional biofilm processes for wastewater treatment are called trickling filter, rotating biological contactor (RBC) and biological aerated filter (BAF). Biofilm processes in general require less space than activated sludge systems because the biomass is more concentrated, and the efficiency of the system is less dependent on the final sludge separation. A disadvantage with other biofilm processes is that they experience bioclogging and build-up of headloss.

SEQUENTIAL BATCH REACTOR (SBR)

Sequencing batch reactors (SBR) or sequential batch reactors are a type of activated sludge process for the treatment of wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. Oxygen is bubbled through the mixture of wastewater and activated sludge to reduce the organic matter (measured as biochemical oxygen demand (BOD) and chemical oxygen demand (COD)).

The treated effluent may be suitable for discharge to surface waters or possibly for use on land.While there are several configurations of SBRs, the basic process is similar. The installation consists of one or more tanks that can be operated as plug flow or completely mixed reactors. [1] The tanks have a “flow through” system, with raw wastewater (influent) coming in at one end and treated water (effluent) flowing out the other. In systems with multiple tanks, while one tank is in settle/decant mode the other is aerating and filling. In some systems, tanks contain a section known as the bio- selector, which consists of a series of walls or baffles which direct the flow either from side to side of the tank or under and over consecutive baffles. This helps to mix the incoming Influent and the returned activated sludge (RAS), beginning the biological digestion process before the liquor enters the main part of the tank.

MEMBARANE BIO REACTOR

Membrane bioreactor (MBR) is the combination of a membrane process like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. It is now widely used for municipal and industrial wastewater treatment.

The water resource scarcity implies the need to reuse water, once it has been properly treated, thus guaranteeing environmental protection. Among the
treatment technologies available to regenerate wastewater, those that use membranes stand out for their capacity to retain solids, salts and even disinfect
water, producing water suitable for reuse in irrigation and other applications. A membrane is a material that allows the selective flow of certain substances. In case of the water purification or regeneration, the aim is for the water to flow through the membrane, retaining
undesirable species on the other side. Depending on the type of membrane it is possible to get better pollutant
retention.

When used with domestic wastewater, MBR processes can produce effluent of high quality enough to be discharged to the coastal, surface, or brackish waterways or to be reclaimed for urban irrigation. Other advantages of MBRs over conventional processes include small footprint, easy retrofit, and upgrading old wastewater treatment plants.

It is possible to operate MBR processes at higher mixed liquor suspended solids (MLSS) concentrations compared to conventional settlement separation
systems, thus reducing the reactor volume to achieve the same loading rate The easy installation enables immediate operativity of the plant and its modularity makes a parallel installation possible thus being able to reach are quired potential. The plants are equipped with a plumbing and electric system, they are insulated, air-conditioned and with indoor lighting. Sodai has been a supplier of, amongst others the US Army since 2003 in Iraq and Afghanistan, the UNO in Central Africa and on loan plants in Italy, South America and East Europe.