Biological Unit Processes

Biological treatment process generally aims at removal or reduction of the concentration of organic and inorganic compounds from the industrial wastewater. Biological treatment process can take many forms but all are based around microorganisms, mainly bacteria. These microorganisms consume the effluent components for their survival and indoing so break them down to less complex and less hazardous compounds. In this process the microorganisms increase in number.

There are two main types of processes, these involve suspendedmicrobial growth (e.g. activated sludge) and attached microbial growth (e.g. fixed film). With both approaches large populations of microorganisms are brought into contact with effluent in the presence of an excess oxygen. In both systems the microbial population has to be retained in a tank referred to as the reactor.

With suspended growth systems microbes grow in small aggregates or“flocs” (this is known as activated sludge). Activated sludge (AS) leaves the reactor with the treated effluent but is settled out in a clarifier andreturned to the aeration unit to recycle the bacteria. If the amount of AS is excessive some may be disposed off rather than being recycled.