Optimization of the conventional hydrothermal carbonization to produce hydrochar from fish waste

Fish waste disposal is a major cause for concern for the seafood processing industries. Fish processing generates enormous quantities of waste as almost 45% of the live weight of fish is regarded as waste. Current ways of managing fish waste involves dumping in oceans, landfills, or treating them with already established strategies. Dumping these wastes without any form of treatment is far from being environmental friendly. Current utilization strategies suffer from disadvantages such as incomplete utilization of solid and liquid wastes or generation of new waste effluents that needs further processing. Therefore, there is a need to find an alternate/supplemental method of seafood utilization. Previously, we have reported the use of microwave hydrothermal carbonization (MHTC) to carbonize fish waste to hydrochar. Here, a conventional heating method such as a custom autoclave reactor is reported that could also be used to carbonize fish waste to hydrochar. Upon response surface design optimization, it was found that a maximal yield of hydrochar (~ 35%) can be achieved at a holding temperature of 180 °C and at a holding time of 120 min. We have also characterized the elemental, proximate, energy, and surface properties of hydrochar produced by conventional hydrothermal carbonization (CHTC). It was found that the quality of the hydrochar produced by MHTC is largely comparable to CHTC. This further proves that HTC could be employed to generate energy from non-lignocellulosic wastes such as fish waste while getting rid of the waste in an eco-friendly manner.