Practicing Success
Secondary treatment or biological treatment: The primary effluent is passed into large tanks where air is pumped into it. This allows vigorous growth of aerobic microbes. While growing, these microbes consume the major part of the organic matter in the effluent. This significantly change the BOD (biochemical oxygen demand) of the effluent. The effluent in then passed into a tank a small part of the sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called sludge digesters. Here, other kinds of bacteria grow anaerobically in the sludge. The biogas produced can be used source of energy as it is inflammable. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams. |
The anaerobic sludge digester |
Supports microbial growth Digests the aerobic bacteria and fungi Sends the waste to secondary settlement tank Contains grit and stones for churning organic waste in water |
Digests the aerobic bacteria and fungi |
The correct answer is Option (2) → Digests the aerobic bacteria and fungi |