Activated Sludge Process

The term activated sludge refers to the brownish flocculent culture of organisms developed in an aeration tank under controlled conditions. Also, sludge floc produced in raw or settled wastewater by the growth of bacteria and other organisms in the presence of dissolved oxygen. A good quality of activated sludge is shown by brown colour, good settling characteristics, and DO (Dissolved Oxygen) present.The process consists of aeration and agitation of wastewater in the presence of flocculated suspension of microorganisms on particulate organic matter. Vigorous mixing and incorporation oxygen into effluent is achieved using bubble diffusers,paddles, stirrers, surface aerators, etc. The effluent passes through this aerator after it spends required residence time in the aerator to a secondary sedimentation tank for removal of flocculated solids. Part of the sludge from this sedimentation tank is recycled to the aeration tank to maintain biological activity. The other part is sludge waste, which goes into sludge treatment process. The process is schematically represented in figure

Schematic diagram of Activated Sludge Process

The start up process includes, aeration of the effluent in the aeration tank and seeding with cow-dung. Further seeding maybe required till the micro-organisms get accustomed (acclimatized) for taking the dairy waste organics as food material.The main control in this treatment is the micro-organism population for which the measure is Mixed Liquor Suspended Solids (MLSS) which can be determined by analyzing effluent from the aeration tank daily by settling test. If the population is more, MLSS will be higher and vice-versa. Remember that any upset due to acidic effluent condition would mean repetition of the start up procedure and plant may take one to one and half months to mature. Avoid such an eventuality. Change of sludge colour or settling ability is another indication of undesirable conditions; dark brown colour and easy settling sludge is the best in an aeration tank