Valorization of Organic Wastes into Biochemicals

Global warming and depletion of fossil fuel resources have urged our research to enhance the utilization of renewable resources for biofuels and biochemical production. Green bio-based technologies (e.g., biorefinery) have also created growing opportunities to support agricultural industries. Agro-industrial biomass is a sustainable source of biorefinery feedstock for bioconversion into a range of value-added products. Modern biorefinery aims to utilize all the building block chemicals (cellulose, hemicellulose, and lignin) while lignocellulosic biomass is recalcitrant to biodegradation and enzymatic hydrolysis.
Therefore, our research aims to isolate and identify the xylose-utilizing bacterial strains for converting the biomass “whole sugars” into useful industrial products. As a part, the recent research project is centred on 2,3-butanediol (2,3-BDO) production. Based on the diverse chemical nature of the feedstock, strategic design of the bioprocesses, accompanied with high-throughput omics studies and sustainability analysis are demonstrated for determining the magnitude of green production of biofuels and value-added chemicals in next generation biorefinery.

Conversion of Food Waste to Biofuels

According to Hong Kong Environmental Protection Department (EPD), more than 3000 tons of food waste is generated every day in Hong Kong in 2019. This accumulating food waste is disposed by dumping into the landfill, which creates another problem. Food waste occupies majority portion of landfill in the limited space of Hong Kong and generates methane in the landfill, which is a harmful greenhouse gas. Hence, a new method to treat food waste is necessary. In our laboratory, we process food waste and convert it into valuable biofuel by enzymatic hydrolysis and fermentation. Food waste contains abundant carbohydrates, proteins, and lipids which can be transformed into hydrolysate containing rich glucose, amino acids, and fatty acids by enzymatic hydrolysis. Subsequently, the hydrolysate is used in a fermentation to produce valuable biofuels or other chemical commodities. Our laboratory promotes green biorefinery and circular economy approach using food waste to produce valuable and environmentally friendly products.

Anaerobic Digestion of High Lignocellulose Sewage Sludge

Carbon neutrality is an environmental-friendly target toward our sustainable future. Resources mining from municipal wastewater has also become an emerging goal under a global perspective. Energy-saving operation has been practiced in wastewater treatment plants (WWTPs) through careful adjustments of aeration energy supply and biogas recovery from the anaerobic digestion (AD) used for treating biosolids. Chemically enhanced primary treatment (CEPT) is a unique WWTP approach progressively adopted by mega-cities to improve energy- and land-efficiencies. The roles of enriched cellulosome-forming bacteria, abundances of cellulosome-related genes, their associations with syntrophs and methanogens, and feedback to characteristics of substrate still remain unclear. Our research aims to assess the prospects of cellulose carbon transformation and cellulolysis metabolism to methane from AD. We employ techniques such as, 16S rRNA gene and meta-genomics analyses, to elucidate the interspecies interactions, identify the cellulosome-related genes, understand cellulosic degradation pathways, and clarify the carbon flow. The findings provide essential biological insights to facilitate the stability of ADs for bioconversion of cellulose-rich substrates, i.e., food wastes, lignocellulosic biomass, and/or non-recyclable paper, which facilitate the paradigm shift of WWTPs from an energy-deficit to an energy-sustainable industry.

Conversion of Biomass to High-value chemicals

Solid waste is an emerging environmental problem associated with urbanization and is particularly serious in highly populated cities like Hong Kong. Developing biorefinery technologies to harvest renewable fuels and chemicals is a promising strategy to response the society’s awareness on sustainable development. Among the biorefinery techniques, pre-treatment is the most critical process to fractionate the plant cell wall and hence to harvest the important building block chemicals for further processing. The conventional pre-treatment approaches are carried out at elevated temperature with various chemicals to remove hemicellulose and lignin. However, the harsh reaction environment can result in lignin degradation and condensation, which can seriously reduce the yield of valuable lignin and fermentation products. The high-temperature process also requires high-profile digester and can result in high concentration of harmful by-products. Mild pre-treatment techniques are needed to facilitate the biorefinery economy. We are attempting to develop a new hybrid acid based low pressure organic solvent (using 1,4-butandiol) pre-treatment process to decompose biomass into basic monomers, i.e., 6- and 5-C sugars and monolignols.

Lignin valorization toward value-added chemicals

Until very recently, lignin was considered a waste as the material potential of lignin remains largely unused with 98% of lignin being burned. But times are changing, and tremendous amount of research has been conducted in order to unlock the full potential of lignin, addressing various aspects of lignin reactivity, chemistry and utilization with the hope to make breakthroughs in the field of lignin valorisation. Our research is aims to untap the lignin’s potential by converting lignin into value added products such as membranes, foams and other composite material that can be used for water and wastewater treatment and various other high-performance applications.

Bioconversion protocol for Food waste valorization - medium-chain fatty acids production chain elongation

One third of the food is wasted every year globally and 95% of it ends up in landfills, contributing to environmental issues like greenhouse gas emission. The Hong Kong O-Park has been operating food waste (FW) anaerobic digestion (AD) reactors, but acidification is an intrinsic problem due to the high organic content of FW. Generation of food waste digestate (FWD) is another emerging problem with food waste AD. Moreover, the product biogas from AD requires CO2 removal before applying to effective burning. Our research is focused on FW derived carboxylate chain elongation (CCE) with FWD as inoculum to address the aforementioned challenges. The chain elongation product MCFAs is a high-quality biofuel precursor with buffering capacity thus mitigates the acidification problem and reduces the hydroxide input to maintain pH during operation. MCFA is also of low solubility in water and easy to be extracted from fermentation broth. Meanwhile, as CCE is a H2-producing process, integrating CO2 fixation in this process through Wood-Ljungdahl pathway (WLP) is also explored in our work. Our study is also interested in utilizing protein in FW and FWD as extra carbon source for CCE, where its hydrolysis product amino acids could further support bacterial cell growth.

Catalyst and Photosensitizer Fabrication from Lignocellulosic Biomass for Toxic Material Detection and Value-Added Chemical Precursor Production

The devastating global environmental problems such as increasing solid waste production requires immediate mitigating measures. The heavy dependence on petroleum on the production of energies and precursors in chemical and building industries must be alleviated to reduce the continuing deterioration. Development of biomass-derived materials for converting waste to valuable products is a sustainable measure for attenuating the problems. Our research aims to develop materials from lignocellulosic biomass to produce heterogeneous catalysts, electrodes and photosensitizers for toxic substance detections and conversion of pollutants to valuable chemical precursors. Strategic catalyst design and material fabrications with high-throughput kinetic, product and mechanistic studies are being conducted for toxin detection and value-added chemicals manufacturing.