MU Connect issue 7 (page 16 to 17)

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As Hong Kong strives to reduce waste, food waste comes under the spotlight as it makes up around 30% of the city's solid waste. Fortunately, food waste is biodegradable; it can even be converted into biogas for generating electricity through anaerobic digestion — that is, making use of microorganisms to break down organic materials in an oxygen-free environment. The question is how to do this effectively.

At the School of Science and Technology, Assistant Professor Dr Chen Jianlin and his team have recently invented a microfluidic analytical device — a microchip with tiny channels designed for studying small amounts of liquids — to monitor the bioactivity of microorganisms in this process, real-time. Equipped with a built-in chemical dye called resazurin, the device gives a fluorescent response to the microbial activity of droplets generated from the waste materials. Operators can then evaluate the effectiveness of microorganisms in decomposing the waste based on the intensity of the fluorescent signal.

Currently, the Hong Kong Government is experimenting with the anaerobic co-digestion of food waste and sewage sludge. Dr Chen's team thus analysed the microbial activity of this co-digestion process in particular. They have confirmed that co-digestion does indeed produce more biogas than digesting food waste or sewage sludge alone, although adding too much food waste can upset the pH balance of the system and inhibit microbial activity. Repeated testing has allowed the team to determine the optimal food waste to sewage sludge ratio to be 1:3.

Dr Chen's project was funded by the Environmental and Conservation Fund in 2021 to support the Environmental Protection Department's Food Waste / Sewage Sludge Anaerobic Co-digestion Trial Scheme, and the research details and outcomes have been published in TrAC Trends in Analytical Chemistry and Biosensors. Compared with traditional lab testing, microfluidic technology has the advantage of producing realtime response, thereby allowing instantaneous adjustments of the system concerned. “We hope microfluidic technology can be extended to other areas and make further contributions to waste management,” says Dr Chen.