Improving Anaerobic Digestion Processes with Bioaugmentation: Case Study for Sustainable Bioenergy Production from Aquaculture Wastes

Anaerobic digestion processes are typically operated such that natural selection determines the community of organisms that predominate in the reactor. However, it is possible to shift the naturally occurring community of organisms through bioaugmentation, which supplements the microbial population with particular species that have preferable characteristics and/or increases the fraction of organisms that are responsible for a rate-limiting step in the digestion process. In this study, we demonstrated improved performance of a bioaugmented anaerobic digestion system used to treat an aquaculture waste from the bottom of fish tanks, which primarily consists of fish feces and excess fish food. This waste stream has a high organic content as indicated by a chemical oxygen demand (COD) of 70,000 ± 5,000 mg/L, total solids content of 44,000 ± 3,000 mg/L, and volatile solids content of 33,000 ± 3,000 mg/L. Bench-scale experiments were conducted in both semi-batch mode and semi-continuous mode (also called sequencing batch) at mesophilic temperatures (i.e. 40°±2°C). In the semi-batch experiments, bioagumentation with a proprietary blend of facultative organisms increased the total methane yield (ml/g VSadded) by 18% and also increased the rate of methane production significantly. In the semi-continuous experiments, our results showed that bioaugmentation outperformed a non-augmented control run by 22%-35% in total methane yield at a hydraulic retention time of 16 days. Another advantage of bioaugmentation was hydrogen sulfide concentrations that were 13-22% lower than non-augmented control runs.