Cold anaerobic digestion viable, according to new study

A new study has demonstrated the viability of using anaerobic digestion in a low-temperature (20°C) environment to convert solid food waste into renewable energy and organic fertiliser.

Researchers from Concordia’s Department of Building, Civil and Environmental Engineering (BCEE) in collaboration with Bio-Terre Systems Inc. have been using ‘cold-loving’ psychrophilic bacteria to break down food waste in a specially designed bioreactor. The outcome was the production of a specific methane yield comparable to that of more energy-intensive anaerobic digestion processes.

The study, written by Rajinikanth Rajagopal, David Bellavance and Mohammad Saifur Rahaman, is published in the journal Process Safety and Environmental Protection.

"There is enormous potential here to reduce the amount of fuel that we use for solid waste treatment," Rahaman explained in a statement from Concordia University.

"Managing and treating food waste is a global challenge, particularly for cold countries like Canada where the temperature often falls below -20°C and energy demands related to heating are high."

Most common forms of anaerobic digestion require large amounts of energy to heat bioreactors and maintain temperatures for the bacteria’s optimal performance.

"What we've learned is that we can now use adapted psychrophilic bacteria to produce a level of methane comparable to those more common forms, while using less energy." Rahaman continued.

With the level of global municipal waste expected to reach 2.2 billion tonnes by 2025, the greenhouse gas produced as the waste biodegrades is set to pose a serious climate threat. The researchers behind the new study claim that this gas can be captured through engineered anaerobic digestion techniques and turned into renewable energy.

The feeding process for the low temperature bioreactor is unique, involving a semi-continuously fed constant volume overflow approach: the amount of food waste fed into the bottom opening necessitates the removal of an equal amount of treated effluent from the top.

Various tests were carried out on the extracted material to determine its physiochemical characteristics as well as to monitor the biogas quality and quantity.

"There aren't many studies that look into developing new applications for treating food waste," Rajagopal says. "We hope that this study will mark the beginning of a promising new research direction."