In Delhi, the capital, the problem becomes acute in November and December when the smoke from the burning residue adds to the city's existing pollution and blankets it in a thick black smog choking everyone.
"I have personally experienced the severe pollution days in Delhi, where using masks has been a norm much before COVID-19 to prevent smoke from damaging our lungs," says Anubhuti Bhatnagar.
The reasons for the residue burning are a short duration between harvest and preparing the soil for the new crop season, lack of financial means to purchase equipment for complete stubble removal, and high costs of transferring the lightweight crop residue for further processing. Through her research, Anubhuti Bhatnagar is interested in creating a small-scale system that may utilize locally available crop residues and turn them into high-value products on farms. Pyrolysis is one such technology that can potentially convert crop residues economically on a small scale.
Pyrolysis involves heating the residues in the absence of air at 600–700°C. Pyrolysis generates three products: a liquid called bio-oil, a solid called biochar, and a mixture of gases. Bio-oil contains multiple chemicals that can be separated to obtain intermediates for pharmaceutical and agro-industries or even transportation fuels through further refining. Biochar may be mixed with soil on farms to sequester carbon, improve the water holding capacity of the soil, or reduce fertilizer requirements during farming. It can substitute coal in power plants and be used to make carbon electrodes for batteries and adsorbents for water and air purification. The gases generated may be burnt to generate heat for the operation of the pyrolysis reactor, reducing the dependence on external electricity or fuels for heating.
Since the product composition and concentration of high-value chemicals in bio-oil depends on the composition of crop residues and the pyrolysis conditions (temperature and heating rate), Anubhuti Bhatnagar's doctoral research was related to optimizing the process conditions and evaluating the product composition in laboratory scale experiments.
“I calculated the potential of small-scale pyrolysis plants to reduce CO2 emissions over its lifecycle and the technology's economic viability, proving that this technology was environmentally and economically suitable for application on Indian farms,” she says.
Crop residue burning is a real issue in many countries, for example in parts of China, Tanzania and Malaysia. Since this technology was viable for the Indian scenario, it may be further modified to address biomass burning in other countries.
Anubhuti Bhatnagar is from India. She is currently working as a researcher at the School of Arts, Design, and Architecture at Aalto University, focusing on the issues related to post-consumer household textile waste recycling.
The doctoral dissertation of Anubhuti Bhatnagar in the field of Bio- and Circular Economy titled Crop Residue Management through Stepwise Slow Pyrolysis and Chemical Recovery will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University in auditorium Pieni Sali 1 in the Festia building (address: Korkeakoulunkatu 8, Tampere, Finland) at 12 o’clock on Friday, 30 September 2022. The Opponent will be Dr. Kimmo Rasa from the Natural Resources Institute of Finland (LUKE). The Custos will be Professor Jukka Konttinen from the Faculty of Engineering and Natural Sciences at Tampere University.
The dissertation is available online at the http://urn.fi/URN:ISBN:978-952-03-2553-4.
Photo: Sujai Banerji