Optimization of Enzyme Hydrolysis of Seafood Waste for Microwave Hydrothermal Carbonization

Hydrothermal carbonization (HTC) is a promising technique that converts wet biomass into a coal-like material and has a wide application to the fields of energy, material science, and nanotechnology. HTC has been primarily used to treat a limited number of feedstocks, mainly lignocellulosic biomass such as wood. Recently, the HTC process has been utilized to treat high-moisture-containing complex waste streams, a mixture of lignocellulosic: and nonlignocellulosic biomass, such as sewage and municipal waste. However, there is limited knowledge on the effectiveness of HTC on purely nonlignocellulosic industrial waste like seafood waste. Processing of seafood generates enormous amounts of waste in the form of solid residues and liquid effluents. Currently there is a demand for attractive seafood waste utilization strategies that minimize environmental pollution while recovering products that are of commercial interest to the industry. In this study, we have devised one such strategy where seafood waste is pretreated by enzymatic hydrolysis for subsequent HTC to produce hydrochar and biocrude liquor. Enzyme hydrolysis conditions including enzyme concentration; incubation time, and enzyme ratios were carefully optimized for maximal hydrolysis of seafood waste. By using an enzyme cocktail-of Viscozyme, Lipase, and Protease, it was found that an enzyme ratio of 1:1:1 (w/w/w), and an enzyme concentration of 10-20% with a treatment time of 16 h, resulted in maximal hydrolysis of fish and shrimp -waste. Subsequently, hydrochar and biocrude liquor were generated from hydrolyzed fish and shrimp waste by microwave hydrothermal carbonization (MHTC) using a high-pressure Mini WAVE Digestion Module (SCP Science, Canada) with quartz vessels at conditions of 150 degrees C for a 1 h reaction time. The results of this study show for the first time that MHTC can be successfully employed to produce valuable products from pure nonlignocellulosic waste like seafood waste. This would pave the way for effective utilization of other moisture-rich nonlignocellulosic industrial wastes.