Integrated valorization of the seafood residues in a (near) zero-pollution biorefinery concept

This study evaluates the near-zero-pollution biorefinery concepts coupled with valorisation processes. Nine different scenarios were developed to assess the biochar production from various waste streams, including raw mollusc waste (Sc1-2), raw fish waste (Sc3), a mix of raw fish and mollusc waste (Sc4), enzymatic hydrolysis residues from fish and mollusc wastes (Sc5-7) and alternative feedstocks (Sc8), mixture of alternative feedstock in varying proportion with raw fish waste (Sc9). Scenario comparison revealed that mollusc-based scenarios (Sc1-2) and mixed hydrolysis residue scenarios (Sc5-7) were unsuitable for biochar production due to high inert content and reduced fixed carbon. On the other hand, two suitable feedstock configurations were identified: i) pyrolysing only lignocellulosic materials (Sc8) and ii) co-pyrolysis of lignocellulosic materials with seafood waste. Effects of biochar on compost quality were assessed in a pilot-scale experiment. Pyrolysis experiments suggested that the amount of fish waste should be less than 30% of the mixture with wooden materials, as higher proportions decreased biochar yield and increased nickel concentration in the final product, which could eventually surpass the maximum limit set by EU Fertilising Products Regulation. Biochar addition to composting (10-14% by dry weight) reduced CH₄, N₂O, and total CO₂-equivalent emissions by 33%, 23% and 13%, respectively, as well as increasing carbon content to 41.5%. Biomethane yields showed secondary residues hold great potential for renewable energy (319 mL/gVS). Overall, this is one of the first studies conducted on a near-zero-pollution biorefinery concept, and the data in this study provide a realistic pathway that complies with regulatory standards for the circular valorisation of fisheries industry residues.