Aquaculture America 2023

February 23 - 26, 2023

New Orleans, Louisiana USA


Christine Lepine*, Abhinav Choudhury, and Christopher Good

The Conservation Fund Freshwater Institute                                                                 1098 Turner Rd.                                                                                                Shepherdstown, WV 25443                                               


The land-based aquaculture industry has been enhanced by farming methods such as recirculating aquaculture systems (RAS), with its ability to produce more fish in limited conditions through intensive water recycling. However, intensive production also leads to a vast amount of concentrated waste. Typical waste streams include waste solids or sludge from fecal matter and uneaten feed, often treated by municipal wastewater treatment plants at a significant cost to farmers. These wastes, high in carbon, organic matter, and macronutrients nitrogen and phosphorus and low in chemical residues, are then devalued through mixing with lower quality industrial and domestic waste streams. As the RAS industry expands, establishing methods to support a circular economy by reducing or eliminating waste and creating valuable products will reduce environmental impact and increase sustainable global development.

Composting, generally defined as the intentional aerobic decomposition of organic matter, results in a highly stable humus product to be used as a nutrient-rich soil amendment or fertilizer. Finished material also enhances plant growth and development by improving soil porosity, increasing water-holding capacity, and diversifying the soil microbiome. The land-based aquaculture industry has a longstanding interest in composting aquacultural wastes but has not adopted composting practices for various reasons.

In-vessel composting offers an alternative to the traditionally utilized methods, using a tightly controlled and often automated system that is also commercially scalable. Waste materials are fed into a vessel, and operators balance the C/N ratio, moisture content, and aeration, creating favorable temperatures and conditions for optimal microbial decomposition. In-vessel systems are more biosecure and reduce heat loss while reducing odors, leachate, and energy usage. They also minimize the space needed to convert waste into a finished product.

An in-vessel lab-scale batch study at The Freshwater Institute evaluated bulking agent (i.e., carbon) particle size for composting fish waste solids produced from Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), which were dewatered on-site through the facility’s settling cones. Additionally, the study provided insights into the volume of carbon needed to reduce moisture content while maintaining an appropriate C/N ratio. Source material was characterized, including a suite of macro- and micro-nutrients, and moisture content (%), temperature (°C), and electrical conductivity (EC) were collected in real-time. Finished product was evaluated using the standard testing assurance for certified compost. Results from this study will be used to develop compost recipes for a commercial-sized industrial drum composter. A description of the industrial composter and preliminary results will also be presented.