The worldwide aquaculture industry has shown consistent growth over the past decade. The United States ranks only 15th in aquaculture production and is the largest importer of farmed seafood. Improving aquaculture production in the United States is required in order to develop a more productive economically and environmentally sustainable industry. Aquaculture is currently the only form of animal agriculture that internalizes waste treatment without offsetting costs through integration with other agricultural crop production systems. The development of a waste treatment and reuse approach will allow for the monetization of sludge treatment and offset the operating costs associated with recirculating aquaculture systems (RAS).
Due to the high liquid content of RAS sludge, waste nutrient reuse is ideally suited for soilless crop production in hydroponic and integrated aquaponic systems. Facilitating the most effective use of treated RAS waste nutrients in aquaponic systems, and the fastest adoption into existing hydroponic cropping systems, requires achieving two goals: 1.) effective reduction of organic carbon, and 2.) maximized waste nutrient mineralization. To achieve these goals, RAS sludge digestion requires the implementation of both aerobic and anaerobic microbial processes. Organic carbon may be detrimental to plant growth, facilitates disease outbreak in hydroponic systems, and causes excessive biofilm accumulation and distribution system fouling. Maximizing nutrient mineralization requires an overall reduction in microbial biomass. However, mineralized waste sludge is high in ammonia, thus requiring subsequent oxidation to nitrate prior to use as fertilizer. As the first step to developing an optimized treatment process for wastes with high liquid content to be used as hydroponic fertilizer, the aerobic and anaerobic digestion processes must be better characterized to understand the effects on plant nutrient availability.
The University of New Hampshire agricultural engineering research program, directed by Todd Guerdat, is researching RAS waste treatment in two facilities on the Durham, NH campus: Anadromous Fish and Invertebrate Research (AFAIR) lab and the Kingman Farm Aquaponic Greenhouses. The AFAIR lab houses three replicate, pilot-scale RAS with drum screen filters and moving bed bioreactors (MBBRs) used in the growout of rainbow trout or tilapia. The UNH Kingman Farm Aquaponic Greenhouses are three replicated farm-scale (133 m2 each) research facilities as part of the New Hampshire Agricultural Experiment Stations (NHAES). Research presented will include the presence of plant-required nutrients found in RAS waste, lab-scale characterizations of aerobic and anaerobic digestion of the mineralization of solid waste from both rainbow trout and tilapia, and insight into the optimization of these processes for implementation at industrial scale.