Creating wealth from municipal solid waste

Most of us wrinkle our noses and hurry past a mound of garbage while on an evening walk. Not Vibhuti Chhabra! This research scholar with the IITB-Monash Research Academy reflects instead on how it can be disposed of safely and whether something valuable can be extracted from it. After all she is working on a project titled, ‘Thermochemical treatment of mixed municipal solid waste’.

Municipal solid waste (MSW) is a major environmental and health concern in most cities, says Vibhuti. “It not only needs to be disposed of safely and sustainably, but an attempt should be made to recover value-added commodities as part of the waste disposal process. Globally, the volume of waste generated from urban centres is around 1,300 million tonnes per year (1.2 kg/capita/day) which is expected to rise to 2,200 million tonnes per year by 2025.”

The figure shows a waste sample collected from India. It is typically composed of: Plastics - 6.26%(w/w), yard waste - 49.1%(w/w), food waste - 1.19%(w/w), paper 9.1%(w/w), textile - 4.85%(w/w),PS - 0.41%(w/w), Soil - 20.81%(w/w), Rubber - 0.32%(w/w), Inert materials (like marbles, stones, non-volatile) -1.94%(w/w), metals - 1.62%(w/w), and unidentified household waste (mostly wood + plastic components) - 4.45%(w/w).

Studies have shown that mixed municipal solid waste (MSW) can be valorised into useful products such as oil — using thermochemical processes like pyrolysis. However, pyrolysis — decomposition brought about by temperatures in inert atmosphere — is influenced by various parameters like temperature, heating rate, residence time, pressure, catalyst and type of feedstock.

“Thermochemical treatment of MSW, which includes processes from simple incineration to large scale gasification, have been proposed and also implemented at various places. However, one of the major challenges faced by these processes is the inherent variability in the supply of MSW for processing — due to different supply sources, changing weather, and storage methods,” explains Vibhuti. “This variability can manifest itself in the form of the total quantity received, as well as the quality of each batch received. These variations — which can be quite large — have a significant negative impact on the process performance, which leads to lower efficiency, higher energy wastage, and overall reduction in the cost-competitiveness. Therefore the design and operation of these processes need to be carried out by systematically considering the input uncertainties.”

Though various studies have already been performed to study the thermal breakdown of municipal solid waste, says Vibhuti, their results cannot be generalised for the Indian subcontinent, due to variation in MSW composition.

So far Vibhuti has investigated the thermal breakdown of MSW under different heating rates to study the feasibility of formation of intended products — viz. oil (from MSW). Additionally, she has also identified various aliphatic and aromatic functional groups during thermal degradation of MSW, which proves its suitability for bio-oil production. “We may even be able to produce bunker oil from this waste,” she says excitedly.

Experimental setup for slow pyrolysis of MSW

Thermal breakdown of PS (one of the component of MSW) at 30oC/min heating rates at Australian Synchrotron facility to study the feasibility of formation of intended products—viz. oil (from MSW). Various aliphatic and aromatic functional groups are identified during thermal degradation, which proves its suitability for bio-oil production

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

Says Prof Murali Sastry, CEO of the Academy, “Studies show that in India, municipal solid waste is either dumped openly or landfilled, creating health and environmental issues. A landfill should not become the final solution for MSW treatment, just a temporary storage place. The aim should be to develop treatment techniques to convert the waste to product (WtP) or waste to energy (WtE). Vibhuti and her colleague recently won the second prize in a poster slam competition in Melbourne. Their work has the potential to give a fillip to the government’s nation-wide cleanliness drive. We hope the IITB-Monash Research Academy can make a significant contribution to making our cities cleaner and healthier.”

Indeed. The next time you spot someone closely inspecting a garbage mound, you may want to stop by for a moment and thank researchers like Vibhuti Chhabra!

Research scholar: Vibhuti Chhabra, IITB-Monash Research Academy

Project title: Thermochemical treatment of mixed municipal solid waste

Supervisors: Prof Sankar Bhattacharya and Prof Yogendra Shastri

Contact details: vibhuti.chhabra@monash.edu

This story was written by Mr Krishna Warrier based on inputs from the research student, his supervisors and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.