A new study on municipal solid waste (MSW) generated by the city offers important pointers towards construction of safe and re-usable landfills. Calculations reveal that if scientific management of our landfills is adopted, the life of the landfills during filling need to be prolonged so that there is no pressure on space for landfilling and the whole process can be scientific. It should also be noted that only the waste generated after 3Rs (Reduce, Reuse and Recycle) need to go to landfills. Ideally, there should not be landfills or waste should be minimum which was the case about a few decades ago. However, in the current scenario, this is not possible and Bengaluru faces a garbage crises regularly, this is a promising result.
The enormous quantity of waste generated by the city every day is typically sifted for compostable, recyclable material and rejects. Trash that cannot be recycled or that survives composting, also known as compost reject, ends up in landfills along with other waste. Dumping trash on open land is not only environmentally hazardous but also potentially lethal for communities living in close proximity on account of leachate and gas emissions. This can change radically if our landfills are scientifically constructed and their performance is monitored with time.
In many countries across the globe, landfill sites consist of trapezoidal pits lined with materials to prevent toxic by-products of waste from leaching into the ground. These constructed pits are then filled with compacted trash in multiple layers. On filling up, they are covered with soil and turf as well as sealing material to create an artificial mound. However, over time, they decompose and ‘settle down’, such that the surface begins to cave in. The degree of their settlement depends on the properties of the waste matter in them.
In this context, Prof. G. L. Sivakumar Babu and his team from the Indian Institute of Science evaluated properties of Bengaluru’s landfill waste using samples obtained from the Mavallipura site. They used these measurements to calculate its stability as well as settlement over time, in a hypothetical case of a filled pit. The team developed a comprehensive mathematical model that calculates the long-term stress & strain effects of bio-degradation of waste, its immediate loading as well as gradual buckling under its own weight.
Computational results forecast that landfill pits filled with city waste can undergo large volume reduction over time if biodegradables or compost rejects are present. In BBMP, there are plans to have parks and other recreational facilities on dumps. However due to significant expected settlements as well as methane gas, it is important characterise landfill material, leachate as well as gases before considering the possibility of re-use of the landfill site. “Bengaluru city waste, including its compost-reject, has a significant component of biodegradables,” points out Babu, citing the primary cause behind these dramatic results.
For long term usage, constructing landfills to be safe from collapse and other failures is an important part of their engineering design. Stability of a landfill is indicated by the factor of safety value, which is mathematically evaluated in this study by considering all the long-term stress & strain mechanisms. The study clearly shows that as more and more waste gets degraded over time, the site becomes increasingly stable. Additionally, if the waste is densely compacted in each layer, its safety factor increases in value.
“The idea is that landfills have to be used for a large period of time,” says Babu, making a strong case for scientific landfill construction through this study. In the last 5 years itself, multiple city landfills had to be shut down. With the city bursting at its seams, civic authorities need a long term solution to trash disposal. Babu and his team provide us a blueprint not only for future landfill sites, but also for salvaging existing sites.
G. L. Sivakumar Babu is a Professor at the Department of Civil Engineering at the Indian Institute of Science (IISc), Bangalore, India.
Ms. Pinom Ering, also a co-author of this study, is currently pursuing doctoral studies at IISc.
Prof G. L. Sivakumar Babu can be contacted at +91 80 2293 3124.
About the publication:
This study was published in the International Journal of Geomechanics by the American Society of Civil Engineers. The abstract can be accessed at