No ULB in India has complete sewerage system to contain the sewage generated. The plants already in existence are technologically backward and were built at times when the nature of waste was biological and not chemical. As the quantity and characteristic of domestic wastewater has changed most wastewater treatment plants are obsolete and are in need of newer technology and capacity expansion. This section covers wastewater treatment technologies for sewage, grey water and industrial wastewater to keep up sanitation of the ULB and make it pollution free. It provides access of information for general public and experts.
Urban Wastewater Management
The significance of wastewater management in urban local bodies is premised on two basic urban issues – (i) the essentiality of safe and scientific management of wastewater in view of its powerful and striking impact on health, hygiene, environment and city aesthetics, and (ii) the reuse possibilities of wastewater especially grey water (domestic wastewater with low pollution load) as a freshwater substitute to reduce the increasing demand for potable water. The commercial and residential structures, which constitute the major chunk of urban water users, use about 80 % of their potable flow for non-potable or “non-drinking” purpose, resulting i n a costly and inept use of a limited resource. In select commercial applications, 75% or more of the domestic supply serves toiletry fixtures alone. Conservatively, 70% of the current urban water demand could be substituted by reclamation and reuse of water.
Every increase in water use leads to increased wastewater generation necessitating the management of higher volumes of wastewater as the depleted fraction of domestic and residential water use is only in the order of 15 to 25%. The growing wastewater volumes render a cheap and reliable alternative to many of the conventional water uses. However, in majority of the urban areas, the activities in the wastewater sector are focused mostly on wastewater disposal than recycle and reuse. Moreover, recycle and reuse of wastewater has not received much attention by the policydecision makers perhaps because of the lack of viable models with necessary research and technology support, strong policies and legal framework at the national and state levels and lack of sufficient trained manpower in the urban local bodies.
The research and study conducted by CED under the CoE program reached to the conclusion that separating grey water from black water and tapping its reuse potential could be an ideal strategy forurban wastewater management. This is because the black water, which is only 30% of the total wastewater produced, contains most of the pollution load whereas the grey water constituting 70% of wastewater has fewer pollutants in it and is easy to reuse; in certain applications it is suitable for reuse even without treatments. The blackwater should be subjected to treatment before it is disposed of. Most of the grey water reuse applications also require suitable treatment appropriate to the type of reuse. Treatment of wastewater involves a variety of technologies:
Screens, Septic Tank , Imhoff Tank , Diversion system , Confined Trench (CT) System, 4 Barrel System, Constructed Wetland Treatment System , Waste Stabilization Pond, Aerobic Treatment,Rotating Biological Contactors(RBC), Anaerobic Treatment, Chemicalprecipitation, Membrane Bio-Reactor (MBR) ,Disinfection, Sand Filter, Activated Carbon Filter (ACF)