BIOLOGICAL TREATMENTS OF WASTE WATER BIOLOGICAL TREATMENTS Some

BIOLOGICAL TREATMENTS OF WASTE WATER

BIOLOGICAL TREATMENTS Some of the major processes of secondary or biological processes are as follows: ØActivated sludge process ØTrickling filters ØLagoon Process The biological process of sewage is secondary treatment involving removing, stabilizing and rendering harmless very fine suspended matter, and solids of the waste water that remain even after the primary treatment has been done.

SEWAGE TREATMENT PLANT PROCESS

ACTIVATED SLUDGE PROCESS It is a type of secondary or biological treatment process for treating sewage or industrial wastewater using aeration and a biological floc composed of bacteria and protozoa.

ACTIVATED SLUDGE PLANT INVOLVES Ø Wastewater aeration in the presence of a microbial process Ø Solid liquid separation following aeration Ø Discharge of clarified effluent ØWasting of excess biomass & Ø Return of remaining biomass to the aeration tank.

STEPS INVOLVED IN APS ARE ØWastewater after primary treatment enters an aeration tank where the organic matter is brought into intimate contact with the sludge from the secondary clarifier. This sludge is heavily laden with micro-organisms which are in an active state of growth. ØAir is introduced into the tank either in the form of bubbles through diffusers or by surface aerators. ØThe micro-organisms utilize Oxygen in the air and convert organic matter into stabilized , low energy compounds such as nitrate, sulfate ion and carbon dioxide & synthesize new bacterial cells.

CONTINUED…. Ø The effluent from the aeration tank containing the flocculent microbial mass, known as sludge, is separated in a settling tank, sometimes called a secondary settler or clarifier. ØIn the settling tank, the separated sludge exits without contact with the organic matter and becomes activated. A portion of the activated sludge is recycled to the aeration tank as a seed; the rest is wasted. If all the activated sludge is recycled, then the bacterial mass would keep increasing to a stage where the system gets clogged with solids. It is therefore necessary to “waste” some of the micro organisms and this wasted sludge is the one which is processed and disposed off.

ACTIVATED SLUDGE PROCESS

ADVANTAGES ØCapable of removing 97% of suspended solids ØBiological nitrification without adding chemicals ØOxidation and nitration achieved ØBiological phosphorous removal ØSolids and liquids separation ØRemoves organics ØCost effective ØEasily maintained mechanical work ØSelf sustaining system

DISADVANTAGES ØCleaning is a hassle. ØMost plants need at least three tanks ØTemperature changes affect the tank greatly.

TRICKLING FILTER METHOD It is an attached growth process that is process in which micro organism is responsible foe treatment are attached to an inert packing material used in attached growth process include rock, slag, sand, redwood and a wide range of plastic and other synthetic materials. ØIt is the secondly commonly used biological waste treatment process. ØThey are also known as percolating filters.

STEPS INVOLVED IN TRICKLING PROCESS ØThe waste water in trickling filter is distributed over the top area of a vessel containing non-submerged packing material. ØAir circulation in the void space, by either natural draft or blowers provide oxygen for the microorganism growing as an attached biofilm. ØDuring operation, the organic matter present in the waste water is metabolized by the bio mass attached to the medium. The biological slime grows in thickness as the organic matter abstracted from the flowing waste water is synthesized into new cellular material.

CONTINUED…. ØThe thickness of the aerobic layer is limited by the depth of a penetration of oxygen into microbial layer ØThe micro organisms near the medium face enter the endogenous phase as the substrate is metabolized before it can reach the micro organisms near the medium face as a result of increased thickness of slime layer and loose their ability to cling to the media surface. ØThe liquid when washes the slime off the medium and new slime layer starts to grow. This phenomena of losing the slime layer is called “sloughing”.

CONTINUED…. The sloughed off film and treated waste water are collected by an under drainage which also allow circulation of air through filter. The collected liquid is passed to a settling tank used for solid liquid separation.

TRICKLING FILTER

LAGOON PROCESS ØLagoons play an important role as natural ecological waste water system to reduce nutrient loading to water courses. The self purification function of natural lagoons provide an opportunity for waste water treatment prior to discharge or reuse. ØLagoons are easy and inexpensive to construct and operate. ØIn this treatment method wastes are degraded by micro biological populations and pathogens can be effectively removed by aeration or exposure to sunlight.

LAGOON PROCESS

TYPES OF LAGOON SYSTEM ØAnaerobic lagoons are usually used for treatment of distillery and industrial wastes; for example, for the treatment of distillery wastewater in India. ØFacultative lagoons are usually used for removing toxic wastes. They utilize a relationship between bacteria and algae, and a balance between aerobic and anaerobic conditions to promote uptake of chemicals.

CONTINUED…. ØMaturation lagoons use micro algae and/or aquatic plants for wastewater treatment, especially for nitrogen removal. ØAerated lagoons are an extended aeration, activated sludge process without sludge recycling. These systems usually require deeper stabilization ponds than the other types of lagoons with depths varying from 3 m to 5 m. This process is usually used for treating wastewater from both agricultural and industrial sources. It is also used for removal of nitrogen from chemically contaminated wastewaters.

ØAdvantages Lagoons can protect the main freshwater body by retaining pollutants. ØDisadvantages There is a risk of exacerbating water pollution problems if the lagoons are not properly controlled, especially if natural lagoons are used. Further, the additional pollutants loadings arising from the input of wastewaters reduces the assimilative capacity of natural lagoons and their ability to buffer the larger water body from storm water pollutant loads.

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