How is solid waste treated?

Management of solid waste begins with the segregation of garbage into various categories at source. The variety of processes that are undertaken to effectively deal with each of these categories encompasses what we call ‘treatment’. For example: paper, glass and some plastics can be reused or recycled. Household food waste like vegetable peels, bones and leftovers are biodegradable and they can be composted right at home. This happens via aerobic composting, a biochemical process mediated by naturally occurring microorganisms which break down wet waste into an organic fertiliser called compost.

Food waste from vegetable markets and restaurants can be treated in the same way, however whole vegetables, fruits and cooked food degrade at a very fast rate. “This gives off foul smells and hence needs a more efficient system” explains Mani. This category of wet waste is more suited for anaerobic decomposition, where the waste is subjected to microbial degradation in the absence of oxygen. This process releases methane-rich biogas which can be used as a fuel or to generate electricity. It takes place in biomethanation or biogas plants, sometimes referred to as waste-to-energy plants.

Though the smallest in percentage, hazardous waste - comprising sanitary and chemical wastes – is arguably the toughest to treat. The other major challenge is non-recyclable plastic. While there are technologies that can manage plastic waste such as reverse catalysis which can potentially convert simple plastics back to petroleum, and paving roads with melted plastic waste, both these technologies have problems.

There are prescribed treatments available for various types of waste, however, none of this means anything unless solid waste is segregated at source. Despite the hype around several cleanliness campaigns, this is not done in most of our country. Subsequently, mixed waste is collected from door to door and deposited in open landfills or sometimes taken to incinerators or biomethanation plants.

What happens if solid waste is not treated?

According to Soumya Prasad, who researches the impact of garbage on health and ecology at Nature Science Initiative in Dehradun, the first casualty of garbage dumps is animal life. “It’s a place where large quantities of food are available, so in the first 24 to 48 hours, all kinds of wildlife, from flies and dogs to cows, monkeys, leopards and elephants start congregating,” she said.

Studies show that a staggering proportion of our livestock have plastic in their guts; this seriously affects the health of the animals, reduces their milk production and increases their maintenance costs. Similarly, a large number of reptiles, birds and fishes die from getting entangled in plastic waste. Garbage pileups also increase the frequency of human-wildlife conflicts. The economic costs are expected to be significant, but estimates are hard to come by.

What happens to waste in a landfill?

Waste collected from our homes usually ends up in landfills that are situated on river and lake beds as these are open and unclaimed areas. The odours and fumes from these dumps seriously affect communities living close by. Sometimes, the landfills catch fire and this exacerbates the issue. Groundwater is affected too. “The liquid part of the waste, known as leachate, seeps into the ground and enters aquifers quickly,” Prasad says. Indeed, a study co-authored by Mani in 2018 showed that groundwater samples from residential areas around the Okhla landfill site in New Delhi were unfit for human consumption.

Burning of mixed waste at low temperatures, which is what happens in most incinerators, results in the incomplete breakdown of solids points out Prasad. Organic pollutants, which are toxic and permanent, are released into the atmosphere. Incineration at higher temperatures, such as in brick kilns and cement factories, allows for a more complete breakdown and release of smaller molecules such as carbon dioxide.

Whatever it is, Mani emphasises that incineration has to be seen as the very last resort, meant only for waste that cannot be treated in any other way. “They make sense only for cold countries like Sweden, where they double up as boilers used to heat up their homes,” she said.

According to Prasad, in the absence of source segregation, all that happens is the transfer of garbage from homes to the roadside, from roads to the hillside, from hills to the forest, and ultimately to the ocean. “The scale of our garbage generation is so high that it is idiotic to think that transportation (from site to site) or transition (from solid to gas) will solve the problem,” she said.

So, what can help? She points to the example of individuals such as Poonam Bir Kasturi, Founder of Daily Dump, who passed away recently and is credited with having started a compost revolution in the country. “If individuals are able to create such an impact, then surely it’s possible for government agencies, too,” she says.