The history and the sad fate of reservoirs meant to store rainwater for use in the dry season in the Deccan, where rainfall is seasonal and often ill-distributed, is briefly given. The dangers attendant on not stemming abuse of inexpensively created, ancient storage facilities or not doing anything about setting down practicable wastewater emission standards and strongly enforcing them are highlighted.
The deleterious effects of discharge of raw sewage and industrial effluents in coastal areas, documented recently by the UN Environment Programme, are equally applicable to inland waters. The benefits of harnessing the not-too-expensive methods of natural purification of wastewater cannot be neglected.
An investigation of microbial activity leading to the natural elevation of flowing sewage to river-quality water, conducted about half a century ago by Natarajan and Pillai, disclosed that turbulence in a channel with adequate gradient facilitates the dissolution of oxygen. When once oxygen concentration reaches about 3.5 ppm, fluffy masses of ciliate protozoa (Carchesiunm, Epistylis) develop, flocculate suspended matter and microbial entities, including pathogenic ones. Since amino acids are also rapidly destroyed in the clarified sewage what underlies the development of high biological oxygen demand is removed.
How the Natarajan-Pillai findings can be adopted for rapid and inexpensive purification of sewage is delineated.

Address:     S.N. Jawaharlal Nehru Centre for Advanced Scientific Research
Bangalore, Karnataka, India
Ph: 8535710 (R)
E-mail: snb@orgchem.iisc.ernet.in

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