Don't burn paddy straw: IITians offer alternative

At the Indian Institute of Technology-Delhi in 2012, professors V K Vijay and Ram Chandra and doctoral fellow Abhinav Trivedi began to work towards developing technology to convert paddy straw into biogas.

Farmers in Punjab and Haryana routinely burn paddy straw after they harvest their rice crop. The practice has been a main reason for Delhi’s extreme level of pollution this year, like every year in the past 25 to 30 years, scientists say.

V K Vijay, P M V Subbarao, Ram Chandra, Abhinav Trivedi, Bhaskar Jha and Vandit Vijay – all from IIT-Delhi – provided consultancy to a biogas plant in Punjab which uses the paddy stubble to produce one megawatt of electricity for 8 to 9 hours, which is equivalent to lighting five lakh CFL bulbs, says Trivedi.

He says the facility in Fazilka district is the only biogas plant in Asia which runs exclusively on paddy straw on this scale.

In 2012, Trivedi knew that the issue of pollution and its relation with the burning of stubble in states neighbouring Delhi was going to gain more importance. Hence he chose to do his PhD in it. Presently the study is funded by the Centre for Rural Development and Technology.

Burning paddy straw releases air pollutants that have significant toxicological properties and are carcinogens.

Rice is generally double cropped in Punjab. Punjab produces about 11 million metric tonnes of rice every year, according to Trivedi’s field work.  And over 16 million tonnes of paddy straw is produced every year –  on an average 1.5 kg of straw is generated for every kilo of rice grain harvested.

Nearly 80 per cent of the straw is being burnt off in open fields to prepare them quickly for the next crop. The biogas plant in Fazilka uses about 10 tonnes of rice straw biomass every day to produce 3,000–4,000 m3/day of biogas.

This biogas produced is used to operate a gas engine for electricity generation at a rated capacity of 1 MW. Biogas produced daily is enough to generate 6,000–8,000 kWh of electricity.

A study has also begun on utilisation of paddy straw for biomethane and bioethanol production on commercial scale and to improve biomass for domestic cooking stoves.

Bioethanol is a ray of hope for replacing the fuel in existing petrol-based motor vehicles but biomethane provides an added advantage of reaping extra energy from the same amount of paddy straw. It also provides valuable manure for sustainable agriculture. Professor Vijay worked further on biomethanation.

Biomethanation is production of biogas which is methane and carbon dioxide (CO2). Biomethane has enormous potential and can replace petrol as transport fuel. If biomethane produced from paddy straw is used for electricity generation it can replace up to 96.4 per cent of the total electricity being generated from coal-based power plants in Punjab, according to Trivedi.

In return, a biogas plant creates manure which is rich in silica and can contribute to paddy cultivation.

After a few years of farming, salt gets accumulated in the topsoil. With excessive use of fertilisers, the soil becomes useless. But if manure produced in the biogas plant is used, there would be no need to import fertilisers at all after some years, says Trivedi.

He says they have approached the government and other corporations to invest in these biogas plants as there is no better way to utilise the waste paddy straw. Presently, these IITians are providing consultancy to just one company, Sampoorna Agri Venture Private Limited.

Trivedi says if the government starts investing in this technology, in the next eight to nine years 20 per cent of the problem of pollution in Delhi and NCR will be over.