Sludge Watch ==> India - Cooking Gas from Sewage

[maureen.reilly at sympatico.ca]

Sludgewatch Admin:

India is looking at decentralized sewage treatment in this experimental 
site.
It would be great if we could harness our home and rural subdivision sewage 
in a
localized way to generate power...

................................
Times of India

Cooking gas from sewage
Pooja Virendra Kumar
Sunday, May 21, 2006


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BANGALORE: Generate cooking gas from sewage water! That is the latest 
experiment the Central Pollution Control Board (CPCB) has undertaken to 
generate resources from waste.

The procedure will not only generate methane as cooking gas, but also make 
the sewage water fit for secondary purposes.

The new procedure, termed Decentralise Waste Water Treatment System 
(DEWATS), is being initiated at a colony for beedi workers in Kengeri and at 
a home for mentally retarded in Bannerghatta.

It is also being used by a tea manufacturer in Yeshwantpur and even in a 
community toilet in Ullaru. "Since the new procedure DEWATS adopts natural 
methods, like using anaerobic bacteria and upflow movement of sludge in 
gravel filters, it is far more economical compared with the prevalent, 
centralised method of treatment," CPCB zonal officer D C Sharma said.

Shortcomings of the centralised system are: Sewage needs to be flown through 
underground pipes and s a result, the pipelines sometimes are placed as deep 
as 30 feet at the treatment site.

A lot of power is consumed to pump the sewage from that level. "Considering 
that the sewers laid by Bangalore Water Supply and Sewerage Board (BWSSB) 
cover 5,200 km to carry tonnes of sewage every day, a lot of money is 
required to get the water to the site, apart from the cost of getting it 
treated," a BWSSB official said.

DEWATS involves three steps. First the sewage is collected in a biogas 
digester (a pot-shaped structure made of earth, built underground).

The digester is built at a juncture where a locality's or an industry's 
sewage flows. Then the anaerobic bacteria are released, which convert 
biodegradable (BOD) mass into methane gas. The gas generated is collected 
through a pipe.

At this step, almost 75 per cent of BOD is converted into methane gas as the 
sewage is given an upflow anaerobic sludge blanker treatment.

To decompose remaining 25 per cent of the BOD mass, the sludge is passed 
through 'planted gravel filter' units. It serves two purposes - that of 
killing the anaerobic bacteria and also purifying the water.