Methane and hydrogen sulfide production from the anaerobic digestion of fish sludge from recirculating aquaculture systems: Effect of varying initial solid concentrations

Authors: CHOUDHURY, ABHINAV - Freshwater Institute; LEPINE, CHRISTINE - Freshwater Institute; GOOD, CHRISTOPER - Freshwater Institute

Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2023
Publication Date: 1/20/2023
Citation: Choudhury, A., Lepine, C., Good, C. 2023. Methane and hydrogen sulfide production from the anaerobic digestion of fish sludge from recirculating aquaculture systems: Effect of varying initial solid concentrations. Fermentation. (9)2:94. https://doi.org/10.3390/fermentation9020094.
DOI: https://doi.org/10.3390/fermentation9020094

Interpretive Summary: Land-based recirculating aquaculture systems (RAS) can treat and reuse over 95% of the water from fish culture tanks through a series of mechanical and biological unit processes. One of the primary challenges to increased adoption of RAS is the disposal and treatment of a large volume of waste sludge composed of fish fecal matter and some uneaten feed. One possibility for the valorization of the organic matter in the sludge may be anaerobic digestion, a method that provides a sustainable and productive solution to organic matter degradation and could assist RAS facilities in reducing energy costs. This study examined the effect of increasing solids concentration in sludge from a RAS on production of methane-rich biogas using anaerobic digestion. Overall, the study demonstrated that increasing the solids concentration can significantly enhance methane-rich biogas production without affecting the stability of the digestion process. This study demonstrates that anaerobic digestion of fish sludge presents a unique waste-to-value opportunity through production of methane gas that can be used to generate heat and electricity .

Technical Abstract: Recirculating aquaculture systems (RAS) are efficient at solid waste capture and collection, though the concentrated waste stream still requires disposal, often at a high cost to the farmer. Anaerobic digestion for biogas production could be one potential treatment option for land-based recirculating aquaculture facilities. However, the concentration of organic matter in the sludge can significantly affect the biogas quality (methane and hydrogen sulfide concentrations). Using a biochemical methane potential test, this study evaluated the effect of fish sludge (FS) solid concentration on biogas quality. Three FS treatments consisted of different initial solid concentrations (1.5%, 2.5%, and 3.5%) from a mixture of sludge produced by Atlantic salmon (Salmo salar) and Rainbow trout (Oncorhynchus mykiss). Methane (CH4) production was measured, quantified, and normalized on a volatile solids (VS) basis. The highest solid concentration treatment produced 23% more CH4 than the lowest solid concentration (519 mL/g VS versus 422 mL/g VS, respectively). Peak CH4 production occurred earlier for the lowest solid concentration (Day 7; 78.2 mL/day), while the highest FS concentration peaked later (Day 11; 96 mL/day). Peak hydrogen sulfide (H2S) concentrations ranged from 1803 – 2074 ppm across treatments, signifying the requirement of downstream unit processes for H2S removal from biogas prior to its utilization for energy generation. Overall, the study demonstrated that increasing the FS concentration can significantly enhance CH4 production without affecting the stability of the digestion process.