Question

How is the treatment of secondary effluents is done?

Answer 1

Secondary treatment of water involves removal of dissolved and colloidal compounds by different processes:

• Biofiltration is most commonly used in trickling filters. These are made of packed bed of plastic, broken rock, gravel etc. the effluent is made to pass through the bed to remove solids
  
• Aeration: This is also called as activated sludge. In this water is treated with flocculent suspension of microbes and aeration. Water is adsorbed onto the microbial aggregates and these microbes metabolize contaminants into simpler compounds.
  
• Oxidation ponds: This makes use of natural water bodies like lagoons where water is allowed to stand for about three weeks. Organic contaminants undergo decomposition and carbon dioxide, ammonia and nitrate are released for use by algal community. Organic sludge settles at the bottom and methane is finally released.