Anaerobic digestion (AD) is a naturally occurring biological process where microorganisms degrade organic matter to produce methane (CH4), carbon dioxide (CO2), and trace gases like hydrogen sulfide (H2S). An anaerobic digester is an engineered system where this process is controlled and optimized, and the gas mixture, also known as biogas, can be captured to generate renewable energy. While AD can be a suitable technique for waste solids treatment from a recirculating aquaculture system (RAS), the components of the waste may lead to several challenges that inhibit the stable functioning of biological processes within a digester. These challenges include low solids content, high salinity, low carbon-to-nitrogen (C:N) ratio, high fat content, and high sulfur content. Typically, all these issues affect the biogas quality and quantity, leading to reduced energy recovery from the waste, increased downtime, and longer return on investment.
In the last few years, researchers at The Conservation Fund Freshwater Institute and around the world have conducted more in-depth studies on AD to understand and overcome some of these challenges. Studies have investigated thickening to concentrate the waste solids as a pretreatment, co-digestion to alleviate inhibition due to the low C:N ratio and high fat content, acclimated microbes to reduce the negative effects of salinity, different reactor setups to enhance biogas production, and biochar addition to minimize H2S production. In this presentation, the results of these studies will be discussed. Future research directions for further resource recovery will also be presented.