Combination of waste management methods will work for city: IIT study

If there is one issue the city has grappled with for decades, it is dealing with the mountain of solid waste it generates each day: over 9,000 tonnes. Most of the waste ends up at an open dumping site at Deonar and a bioreactor landfill in Kanjur Marg.

Researchers at the Centre for Environment Science and Engineering at the Indian Institute of Technology, Bombay, suggest that combining waste management methods instead of merely dumping waste can reduce the impact on our environment. “Nearly 70% of Mumbai’s waste is dumped in the open, while 30% is treated,” said Bhupender Sharma, PhD scholar and co-author of the study. The waste is often burnt in the open, causing respiratory problems, cardiovascular diseases and adverse birth defects in the surrounding areas.

Life cycle impact

“Not many studies are done in India regarding waste management. This study analyses the life cycle environmental impacts under an integrated waste management approach,” said professor Munish Chandel, co-author of the study.

Under the life cycle impact study, the researchers tracked the waste from generation at source to its final disposal. They compared six waste management scenarios with dumping in a landfill. Under these scenarios, different proportions of waste were directed to recycling, composting and anaerobic digestion (degradation in the absence of oxygen), based on the composition, recyclable portion and type of waste. The researchers also analysed the global and local environmental impact using 27 parameters, which were clubbed under the categories of global warming, acidification, eutrophication (excess growth of algae in water bodies due to phosphate and nitrate-rich pollutants), and human toxicity.

No single solution

Although open dumping emitted the least amount of acid gases, it still contributed to maximum eutrophication. Incineration, on the other hand, was low on greenhouse gas emissions, but emitted toxic and acid gases. Composting was found to have the lowest impact when it came to eutrophication and human toxicity, but could not be applied to all kinds of waste.

Hence, the researchers recommend an integrated approach that combines composting, anaerobic digestion and landfill dumping, which might help in an overall reduction in pollution.

“Indian policymakers should be able to decide which technology is better by considering the life cycle environmental impacts of different waste management options,” Mr. Chandel said.

Importantly, they found that 16% of the city’s waste is recyclable. Further, most waste contained moisture and was biodegradable. “Composting and anaerobic digestion are the most reliable options for these. As far as dry waste is concerned, recycling and thermal treatment are the options,” Mr. Sharma said.

The biological option

Incineration, wherein organic waste is burnt and the inorganic residue turns into ash, can be used too, with the heat generated utilised in thermal power plants. However, Mr. Sharma said, emissions during the process — heavy metals, dioxins and furans — need to be taken into account. “Since the waste we generate has a lot of moisture and is biodegradable, we need to focus on the biological option,” he said.

Landfills, too, can be considered, provided they are scientific ones with soil capping to ensure emissions do not enter the atmosphere and leeches are contained. “They are already doing this at Kanjur Marg, where about 3,000 tonnes waste is dumped a day,” he said.

More than anything else, he emphasised segregation at source. “It’s the first thing we need to do, before we even examine treatment options. A greater awareness of this is required.”