It is estimated that the city will have to build an additional 4,000 km of pipes to the existing 4,000 km to collect sewage from all households, writes S. Vishwanath
As much as the city faces a challenge in providing water to all its citizens it also faces the challenge of managing the water supplied after it is used. Typically about 80 per cent of the water supplied to the city ends up as wastewater flow. While the city of Bangalore would get about 900 million litres per day as supply it can be expected to have to manage 720 million litres every day flowing as wastewater. This sewage needs to be collected, conveyed and treated before being let into the ecosystem.
In addition, there is a lot of water pumped from borewells for use. This may be as high as 500 million litres per day. This too enters the waste-water stream. Especially on the city outskirts this represents a hazard to our lakes. Inside the city, from broken links and uncollected sewage, most of the stormwater drains act as sewage lines and the sewage has percolated to the deep aquifers, polluting groundwater to a depth of 600 ft. in over a third of the borewells in the city.
It is estimated that the city will have to build an additional 4,000 km of pipes to the existing 4,000 km to collect the sewage from all the households. This is extremely expensive capital infrastructure and over and above this treatment plants will have to be built and run. This clearly will be financially unsustainable and alternatives have to be urgently found.
A series of 10 per cent solutions, instead of a single 100 per cent solution, are emerging which look like the best way to manage sewage in the city. Clearly the existing large underground lines will need to be upgraded and repaired. The new ones being laid will need to be connected to a set of decentralised sewage treatment plants.
In addition, large consumers of waters such as apartments, institutions, industries and new layouts will need to have their own sewage treatment plants planned, designed and integrated into the land use of the layout.
Individual homes on the outskirts will have to have neatly designed septic tanks and sewage collection pits which are regularly and frequently emptied using vacuum trucks called honey-suckers. This emptied sludge will have to be carefully composted and reused as manure.
A clear database needs to be generated for each household and building in Bangalore identifying the modes of access of water and the mode of disposal of wastewater. Building bye-laws will need to clearly identify the permitted ways of sewage disposal in the absence of a main sewage line. This will need to be checked at the time of giving an occupancy certificate. A regular system of checking the condition of sewage treatment plants by the authorities will need to be put in place.
A stronger emphasis on design, construction and maintenance of wastewater treatment systems will preserve the quality of our surface and groundwater bodies as well as maintain public health. It is about time institutional emphasis shifts to this aspect of wastewater management.