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Nobody's backyard: managing municipal solid waste

In 2010, for the first time in modern India's history, rural Indians numbered fewer than their urban counterparts. This phenomenon of urbanization comes with many challenges, and one of the biggest is the management of  municipal solid waste. With limited landfill acerage and mounting garbage levels, smart and innovative solutions for waste management become imperative. Scientists from the Civil Engineering Department at the Indian Institute of Science, Bangalore have come up with estimates for how long different municipal solid waste components take to settle. Published in the journal of Waste Management and Research, this study is the first of its kind and has many lessons for city planners, especially in rapidly urbanizing India.

We think very little about our garbage once we have put it in our dustbins, but the reality is that each bit of refuse goes through a series of manual and semi-automatic processes wherein biodegradable material is allowed to decompose, large bits of reusable and recylable material is seperated and very small particles (less than half a centimeter) are packed and sold as compost. Landfills are composed of garbage that is not picked up in any of these processes – either too big to be salvaged or too small to be used as compost. Over time, landfills shrink and could potentially make room for more garbage, thereby saving space. Led by Dr. Sivakumar Babu and Dr. Lakshmikanthan, the team examined how landfill material settled (or 'shrank') in laboratory conditions. They examined how much of this shrinking was due to primary consolidation (or simple collapsing because of gaps), mechanical creep (bucking under its own weight and weight of the material above it) and biodegradation (the formation of biogas in an closed environment).

The team found that irrespective of how big or small the particles were, biodegradation played a strong role in the settling of landfill material. More than 40% of all the waste was due to biodegredation.  They found that primary settlement was greater for larger particles, and mechanical creep  accounted for about a fifth of the total settling. This was also subject to how thick the landfill was, how much strain it exterted, and what the duration between two filling intervals was.

“This a first-of-its-kind study that looks at landfill waste segregation”, said Dr. Sivakumar Babu, the lead author on the study. “The high amount of biodegradable matter means our current mechanical procedures of segregation are not being done well. Although Asian countries do have more biodegredable matter in their waste, its composition is evolving over time and is a difficult matter to study.”

“Replicating the experiment to note field response will be ideal”, said Dr. Babu. “We tried contacting the BBMP and Pollution Control board and other authorities but didn’t get any response. We continue to be interested in collaborating with them with respect to opportunity and funding.” Despite being lab experiments, the results have been very insightful. The result – that more than 40% is biodegradable waste – gives scope for bioreactor landfills. These have the option of generating gas, and can help better manage the waste. “The settlement is is fast and the stabilization is quicker”, added Dr. P. Lakshmikanthan, a co-author on the study. “Landfills under the bioreactor model take 5 to 8 years to stabilize, as against the 30 years taken by conventional landfills”.

This study was conducted as a part of testing several characteristics of landfills – strength, optimal conditions for gas generation, shear, etc. With more funding and support, these results can be incorporated in creating solutions to tackle one of the biggest challenges the country's planners will face in the years to come.

About the authors:

GL Sivakumar Babu is a Professor at the Department of Civil Engineering, Indian Institute of Science, Bangalore. L Laxmikanthan is a PhD student at the Department of Civil Engineering, Indian Institute of Science, Bangalore

Tel: 080 – 22933124; Email: gls@civil.iisc.ernet.in