Composting converts household biodegradable waste into valuable manure. But decomposing household waste through natural means takes 40–300 days. The humongous quantities of kitchen waste produced in urban areas create environmental and public health problems.
Decentralised composting in plastic drums where the waste is periodically mixed speeds up the process, reducing the problem. Including passive aeration and a one-time addition of a cocktail of microbes not only further accelerates the process but improves the quality of compost, claim Indian researchers.
Anurag Garg and team from IIT Bombay along with Rakesh Kumar, NEERI Nagpur recently came up with a new drum composting method to make composting inexpensive and to produce good quality manure faster.
They used six 100 litre capacity plastic drums of about half a metre diameter and a little more than half a metre height. On the periphery of five drums, they drilled small holes of about one centimetre and, in the sixth, used as control, there were no holes.
The team collected waste from the hostel kitchen and gardens of IIT Bombay. They added six kilos of waste to the control drum and to three other drums for 12 consecutive days. In the next two drums, they added about two and a half kilos of waste for 15 days. They turned the waste in the drums every day to mix the old and fresh wastes.
In four of the drums they added a commercially available soup of microbes, containing yeast, lactic acid bacteria and phototrophic bacteria. The waste was then mixed every six days for the first four drums and every six days for the other two, till decomposition started.
The researchers observed that, in all the drums with holes, the temperature increased to 55 degrees, required for destroying any pathogens. This thermophilic period was longer in drums that had garden waste. During this phase, the bacteria and fungi added by the researchers showed high growth. Though the fungal populations did go up much, their presence is important in breaking down the lignocellulosic materials during this period, say the researchers.
While the control drum without holes emitted bad odour, the drums that received the microbial soup showed rapid increase in pH and reduced smell. This is perhaps due to the action of microbes that produce lactic and other organic acids, say the researchers.
Soluble salts that can inhibit seed germination were also lower in compost from the experimental drums. There was also less moisture than in compost from the control drum.
The team grew cress seeds in soils mixed with different amounts of the compost and found that compost from the aerated drums with microbial inoculation showed about 80 to 90 per cent germination while compost from the control drum showed a maximum of about 20 per cent germination.
To make quality manure in minimal time, Anurag and collaborators suggest using this modified drum-based technique. The ideal weight of household waste for the technique is less than three kilos per day, says Anurag, IIT Bombay. This amount of waste is usually produced in college hostels and condominiums. Two drums with holes can alternate every month to produce good quality compost. And the initial investment is only about 2000 rupees.
Decentralised processing of this waste to produce high quality compost will be a boon for the rooftop vegetable gardens that are becoming popular in Indian towns and cities.
J. Cleaner Production, 2226: 233-241 (2019);
Central University of Kerala
* This is a revised version of a report that was published in the 25th July issue of Current Science, in a column titled Science Last Fortnight.