Sewage and sludge

The liquid wastes like sewage and sludge contains large quantities of plant nutrients and are used for growing vegetables, sugarcane, and fodder crops near large towns. Use of raw sewage is a danger to health. Sewage is allowed to stand in a septic tank to undergo a preliminary fermentation. Then it is aerated in the setting tank by blowing air through it. The sludge that settles at the bottom in this process is called as ‘activated sludge’. It brings about rapid oxidation of matter present in fresh sewage. It contains 3.0 to 6.0 % of N, about 2.0% P2O5, and 1.0% K2O in forms that can become readily available when applied in soil. However, under no circumstances should any produce grown on a sewage farm be eaten uncooked.