The correct option is C Both A and B
Waste water including sewage can be treated in an integrated by utilizing a mix of artificial and natural processes. The cleaning occurs in 2 stages (a) the conventional sedimentation, filtering, and chlorine treatments are given. After this stage, lots of dangerous pollutants like dissolved heavy metals still remain. To combat this, an innovative approach was taken and (b) biologists developed a series of six connected marshes over 60 hectares of marshland. Appropriates plants, algae, fungi, and bacteria were seeded into this area, which neutralizes, absorb and assimilate the pollutants. Hence, as the water flows through the marshes, it gets purified naturally.