Restructuring landfills: Bhalswa follows Okhla
Test report from Okhla showed the process, overseen by IIT-Delhi expert, helped reduce the height of landfill by 30%
Having brought down the height of the Okhla landfill from 50 metres to about 38 metres and having stabilised the structure through a year-long ‘remediation’ process that started in March 2018, a similar project is now being undertaken at the Bhalswa landfill by the North Delhi Municipal Corporation.
The collapse of a portion of the East Delhi Municipal Corporation’s Ghazipur landfill in September 2017, which led to the death of two people, had shifted the focus on managing landfills to ensure safety.
While the South Delhi Municipal Corporation, which runs the Okhla landfill, received external proposals to deal with the landfill, the work was finally undertaken through departmental means, especially given that it was a lot cheaper, said executive engineer for the project Taufell Ahmed. He has now been roped into working on the Bhalswa landfill, along with Civil Engineering Professor at IIT Delhi, Manoj Datta, who is overseeing both projects.
In the first stage, the garbage undergoes re-profiling. “The process involves excavation, cutting, channelising, aeration, spreading, levelling/dressing, compaction and sorting of fluffy material such as plastic or clothes,” an SDMC project report on the Okhla landfill reads.
This involves the use of earth moving machines which tear the garbage down and turn it over multiple times. This allows the garbage, which is stuck in packed anaerobic conditions, to be aired out thus speeding up the decomposition proces. The garbage is also spread over vacant land near the site to help the decomposition. This is in turn pressed together, or compacted depending on the structural requirement. The dry bulk density of the compacted waste is 1.5 metric tonne per cubic metre, the report states. Finally, the garbage once in place, is topped with a layer of silt or some form of construction and demolition waste.
The stabilisation work itself begins with construction of 15-16 (average) metre-wide kachha road, including a three-metre open kachha drain at the bottom of the landfill, according to the report. The road helps in movement of the machines involved and for airing out the garbage and the drains help divert rainwater. This is done to reduce the amount of leachate generated which is the sludge that forms when water passes through garbage and dissolves soluble.
The first slope is 10-metres high and spread over a 27-metre long incline, in the ratio of 2.5:1, determined by the engineers to ensure stability. At the top of this slope, a six-metre wide kachha berm or a flat levelling is constructed along with another kachha drain. Similarly, three slopes of dumped material, of the same size have been constructed from top to bottom. And to trap rainwater, kachha drains have been constructed at the bottom of each slope. The final structure resembles a hill, with convex or roundish slopes so as to increase surface run off during rains, along with flat relief at two intervals where kachha drains collect the water.
Tests of the stabilised dump, carried out by Shri Ram Institute of Industrial research revealed that after stabilisation, the garbage consists of 93.72% of sand, earth, soil, bricks, concrete etc, 1.97% organic matter, 3.77% plastic and 0.54 glass and metals, the report states. The test also noted that the process reduced the height of the Okhla landfill by 30%.
The report further reads, following a site visit by a Supreme Court appointed committee in December last year, environmentalist Almitra H Patel, who is part of the committee, suggested that grass be planted where work of slope stabilisation has been completed so as to hold the earth and eliminate chances of slippage. Ms. Patel also suggested that as and when additional land is made available to the SDMC, the “biomining” of the entire dump be carried out, according to the report. A total of 5,700 square metres is to be planted with grass. While this step was expected to be completed by the end of March, the engineer in-charge Mr. Ahmed, said that the work is likely to be completed by June.
In its attempt to manage the landfill, other processes such as trapping of leachate that leaks from garbage and treating it and installation of pipes to extract trapped methane are also involved. However, so far, Mr. Ahmed said that very low methane content is found in the garbage.
The undertaking at Bhalswa, spread over 52 acres with a height of 62 metres, will be the first step on the same line. Meanwhile, the North Corporation has also invited a tender for scientific capping of the landfill. However, commissioner Varsha Joshi has said that it will take place only after all possible volume reduction and biodegradation happens.