Biomining of a Landfill in Kumbakonam, India

Kumbakonam is a municipal town in Tamil Nadu, India, well known for its farm-based activities. It is also known as the granary of South India. As per the 2011 Census, the city has a population of 0.14 million and stretches over 12.5 sq. km.

by Kartik Kapoor, WtERT Germany

Figure 1: Landfill in Kumbakonam before and after the bioremediation.

As per the waste projections carried out by the municipality in 2015, based on population density in all the 45 wards, Kumbakonam generates 70 TPD solid waste, out of which the biodegradable content is estimated to be 65 per cent. Kumbakonam initiated the first bioremediation site in the country. The municipality faced continuous fire at the 30-year-old dumpsite spread over 32.5 acres in Thepperumanallur village. The estimated quantity of waste on the site is around 3.5 lakh tonnes.

Biomining is the process of using microorganisms to extract materials of economic interest from legacy waste. The prime process, however, is to recover soil from the decomposed mixed waste. Biomining can also be seen as a technique of extracting and segregating valuable resources from mounds of waste. The major resources extracted from the legacy waste are plastic, rubber, metal, textiles, glass, soil, construction and demolition waste. In other words, biomining is a process where previously dumped waste is dug up after loosening by harrowing and is then processed to recover valuable recyclable scrap while also recovering landfill space. The end product, likely to be soil, gets rid of toxic materials and hence becomes reusable.

The municipality awarded a contract to a private firm in 2015. With its mobile processing unit, the company was able to start its operations in July 2016 and reclaimed the entire 32.5 acres of land. The process was completed in August 2018.  In 2017, a 70 TPD processing unit that handles the mixed waste of the city was established on the reclaimed land. Also, a 5 TPD capacity biogas unit was also commissioned on the same land.

The biomining process followed at the Kumbakonam dumpsite is as below:

Figure 2: The biomining process followed at the Kumbanakonam dumpsite.

The excavated legacy waste was initially laid in the form of windrows. The size of the windrows is not standardised and can be based on the quantity of waste excavated. The legacy waste was then stabilised by adding bio-culture at regular intervals of one week, which catalysed the decomposition rate of the waste. The decomposition levels were checked every week and soil samples collected for germination testing. The waste in general stabilised in 30 days. The stabilised waste was then passed through a series of trommels of various sizes. The rejects at each stage were considered refuse-derived fuel (RDF), and the accepts acted as inputs to the next trommel. Density blowers were used to separate soil from the RDF at each stage of waste passing through the trommel. The final product was considered as recovered soil and was fit for landfilling.

There was no residue left during the process of bioremediation, and the 25-metre-high dumpsite is now completely flat. Around 500 tonnes of RDF is left on the site as of now. The RDF, mined from the legacy waste, is sent for co-processing to Dalmia Cement in Dalmiapuram, 70 km from the Kumbakonam.

The article is adapted from a publication: Dinesh Raj Bandela and Swati Singh Sambyal, 2020, Clean It Right: Dumpsite Management in India, Centre for Science and Environment, New Delhi.

published: , 4|2021
Keywords: Landfilling, India