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If incessant sewage inflow, unchecked encroachments and poor maintenance threaten to kill the city’s remaining lakes, there is one big reason: Lake restoration efforts have become mere cosmetic beautification projects focussed only on the periphery and surface, ignoring the decay underneath.
An entirely different approach is now on the horizon, with a pilot project proposed to dramatically boost the oxygen content of Ulsoor Lake through a technique called “aeration and bioremediation.”
Centrally located, with a catchment area of about 11 sq.km and a volume of 1,100 million litres, the lake is definitely high on Bangalore’s eco-agenda. But the water body is in very poor shape, thanks to heavy inflow of soilage, effluents and sewage.
Seven traps (waste weirs) to prevent this muck from getting out of the 6.2-acre sedimentation tank and entering the 119.35-acre lake, has not worked well especially during rains. Experts have analysed that the water body has turned toxic, with high concentrations of organic matter triggering formation of ammonia, methane, hydrogen sulphide and more.
So here’s the Rs. 9.31-crore plan, as proposed to the Karnataka State Pollution Control Board, the BBMP and the Lake Development Authority by an agency called Randhawa Brosons Enterprises: The aeration process will oxidise the undesired organic and inorganic matters; reduce the fecal coliform count (produced by human and animal fecal waste) in the lake waters and its sediments, and restore the entire aquatic ecosystem.
Micro-bubbles of oxygen
To inject oxygen into the water body, 7,700 feet of 0.75 inch micro-bubble tubing will be laid at ideal depths in various parts of the lake. The tubing will have two rows of holes about half an inch apart. Air will be forced into the tubing from 10 blowers, housed in six stations rooms to be set up on the islands of the lake.
The air inside the tubing will then escape into the lake bottom as thousands of tiny bubbles slowly rising to the surface and increasing the dissolved oxygen content. The bubbles will be released at the rate of over 800 cubic feet per minute. Solid core ballasts attached to the tubing will ensure that they are firmly sunk to the lake bottom.
By substantially increasing the oxygen content, the aeration process will increase fish and other aquatic animal habitat, prevent fish kills and nuisance algal blooms, besides removing the stink.
Introducing native fish
Under the bioremediation process that follows, various native fish will be introduced into the lake. One key variety will be the Grass carp that eats the undesirable water weeds. Incidentally, most species of fish had gone extinct in the Lake by early 2003. In November 2003, on the recommendations of the University of Agricultural Sciences, 61,500 Grass carp, Silver carp, Katla Katla, major Indian carp and Mirgal fish were introduced into the lake.
But within a year, all were dead due to lack of oxygen. The dead fish and other aquatic creatures killed in the process settled at the bottom, forming the anaerobic muck.
1 Micro-bubble tubing injects oxygen
into the water body
2 The tubing has two rows of holes about half an inch apart
3 Air is forced into the tubing from 10 blowers, housed in six station rooms
4 The air escapes into the lake bottom as thousands of tiny bubbles slowly rise to the surface and increase the dissolved oxygen content
5 Oxygen content rises substantially. So does the aquatic animal habitat. Fish deaths and algal blooms are prevented and the stink is removed
6 Madras Engineer Group personnel
desilting Ulsoor lake