Once seawater used to come inside through Matta Piyali at the uptide time. But the siltation caused by city sewage-cut off the sea water passage. Now these rivers are officially announced dead
Incoming city waste water is of about 170-200 BOD unit and ODO unit. This kind of highly polluted water carries-various heavy metal, oil & grease like materials apart from other pollutants.
After crossing two small ponds waste water passes through a bed of water hyacinth-this a 1200 ft. Long hyacinth bed. Sewage water of about 200 BOD unit-bring down to about 80 BOD unit.
Root system of hyacinth grasps most of the material ingredients, heavy metals, oil and grease like materials-make the water almost free from particle pollutants