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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #421733
Research Project: Support the Viability and Expansion of Land-Based Closed-Containment Aquaculture

Location: Cool and Cold Water Aquaculture Research

Title: Co-composting aquaculture sludge at full-scale: Two case studies evaluating process performance and compost quality

Author
item LEPINE, CHRISTINE - Freshwater Institute
item CHOUDHURY, ABHINAV - Freshwater Institute
item RYLAND, KAID - Freshwater Institute
item BELL, JACOB - Freshwater Institute
item GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2026
Publication Date: 7/8/2026
Citation: Lepine, C., Choudhury, A., Ryland, K., Bell, J., Good, C. 2026. Co-composting aquaculture sludge at full-scale: Two case studies evaluating process performance and compost quality. Aquacultural Engineering. 115. Article 102778. https://doi.org/10.1016/j.aquaeng.2026.102778.
DOI: https://doi.org/10.1016/j.aquaeng.2026.102778

Interpretive Summary: Composting fish sludge (FS) from land-based recirculating aquaculture systems (RAS) could present an opportunity for farmers to create a sellable product from the waste. Two studies on composting FS in a commercial scale rotary drum composter were conducted to assess the feasibility of the process. In the first study, kiln dried wood flakes and mushroom soil (a by-product of mushroom farming) were added to optimize the moisture content and carbon:nitrogen ratio for composting. In the second study, the mushroom soil was replaced by fish mortalities as that can be another waste product from a RAS farm. Both studies suggested that FS can be readily composted in two weeks as long as the moisture content and carbon:nitrogen ratio are kept within optimal conditions. The compost products from both studies after an additional six months of curing did not show any plant toxicity in lab tests and had heavy metal concentrations well below EPA limits. The compost was rich in nitrogen and phosphorus that could be used as a soil amendment or as a mulch product.

Technical Abstract: Two in-vessel compost studies were conducted to assess the feasibility of composting dewatered fish waste sludge (FS) from recirculating aquaculture systems (RAS) using a commercial rotary drum composter (3.15 m3 working volume; 14-day retention time). The FS was co-composted with additional substrates to maintain the moisture content and carbon:nitrogen (C:N) ratio within optimal ranges. Study 1 co-composted FS and mushroom soil (MS) with dried wood flakes (WF), while Study 2 substituted MS with fish mortalities (FM), another potential waste product from RAS facilities. Study 1 exhibited high temperatures throughout the study, with an average of 58.8 ± 0.6 °C in the hottest zone. Study 2, however, had lower temperatures, with an average of 51.9 ± 1.0 °C in the hottest zone, likely due to colder ambient temperatures, a more heterogeneous mixture, and more frequent drum rotations to alleviate ammonia odor concerns. Maturity and stability testing indicated that the Study 1 compost (C1) did not require a curing phase, while the Study 2 compost (C2) needed an additional two months of curing to minimize phytotoxic effects. After six months of curing, the final C:N ratio of C1 and C2 were 19 ± 2 and 40 ± 6, respectively. Both C1 and C2 were rich in nutrients and passed EPA standards for heavy metals and pathogens. Additionally, these studies demonstrated that RAS waste products were transformed into valuable nutrient-rich compost suitable for soil amendment, erosion control, or mulch.