On top of this went ribbed, wavy plastic netting, designed to hold a 45cm thick layer of soil on which the grass was planted.
It sounds straightforward enough, but on a mound with an area of many hundreds of square metres, it was a mammoth task.
Twenty boreholes extending to depths of between 15m and 25m were then drilled across the mound, in which 15cm wide pipes were placed. These pipes, with slits running along their length, would collect the landfill gases.
To prevent garbage from choking these slits, a layer of gravel was placed around the pipes. The top of each pipe was then sealed shut.
The gas wells were then connected to each other. A slight vacuum created by a fan connected to this network is enough to draw the gases out, says T Nandakumar of GAIL’s research department.
High moisture content is essential for the production of the methane, and to achieve this the thick contaminated sludge that leaches down to the base of the landfill is pumped back to the top. It is released under the impermeable plastic casing to percolate down again.
Currently, the gases are fed into a ‘flaring tower’, a 30-foot-high metal pipe surrounded by gauges and machinery, in a small lot adjoining the mound. Here they are burnt, converting methane (which is 21 times more damaging a greenhouse gas than carbon dioxide) into carbon dioxide. This, however, is just an interim measure.
In a few months time, the gases will be sent to a purification system where methane will be separated from other gases like hydrogen sulfide and carbon dioxide. It will then be concentrated into compressed natural gas (CNG) for use as fuel.
The only precedent to this project in India is a project at the Gorai landfill on the outskirts of Mumbai. There, however, the landfill was closed entirely; and the captured gases were flared to produce electricity. But, Nandkumar says, “variations in gas output made electricity generation erratic. As a result, electricity could not be fed into the grid.”
In a little over a month that the gas wells at Ghazipur have been operational, production has been ramping up steadily — starting from 100 cubic metres an hour, now up to 300 cubic metres an hour. Nandakumar expects this to reach 500 cubic metres by the end of April. Half of this will be natural gas. That, compressed, will yield over 2,000 litres of CNG per hour.
However, landfill gas production is temperature sensitive, and there are likely to be large seasonal variations in output. Here, unlike in the case of the Gorai landfill, that won’t be a problem since the gases will be stored.
Once complete, the project will be eligible for carbon credits under the UN’s Clean Development Mechanism (CDM). In a document submitted to the UN GAIL claims that it will, till 2022, lead to a greenhouse gas reduction equivalent to 22,306 tonnes of carbon dioxide annually.
“Not only will we earn credits for converting methane to less damaging carbon dioxide,” says Nandakumar, “we will also get credits for replacing petrol and diesel with the CNG produced.”
These credits will offset part of the 33 crore cost of the project, but for Nandakumar, it’s the environmental benefits that are more important.
Dr Mohammad Emran Khan of Jamia Millia Islamia University, an expert on energy recovery from waste, also believes that the most important aspect of this project is to test “technical viability under Indian conditions rather than economic viability”. According to him, the technologies for purification of landfill gases are commercially established in other parts of the world, but have not yet been tried in India (where waste is not segregated).
Atop the experimental mound, the fresh grass is being watered. A couple of rag picker girls have wandered across from an adjacent smoldering mountain of garbage. Where will they go if all of Ghazipur is reclaimed? “We’ll have to move somewhere else I guess,” says one pausing. They don’t seem to have given this eventuality much thought.
For now, however, this green hill, the first of the nascent Ghazipur range, is a miraculous respite. Up here, the bustle of Delhi seems far away. The girls settle down on the grass and start splashing each other with water.
akshai@tehelka.com
