Characterization of anaerobic fermentation of rainbow trout (Oncorhynchus mykiss) effluent sludge using mixed anaerobes for reutilization

Abstract

Sludge degrading strains were screened and examined for their acidogenic ability. Two strains isolated from pond-bottom soil and identified as Alcaligenes faecalis strain HCB2- A1 and Alcaligenes faecalis A2 were determined to be useful sludge degrading strains. Strain A2 exhibited the highest acidogenic ability compared to A1 however the acidogenic ability of both strains were improved when cultured together producing a maximum of 6632 mg/L total volatile fatty acids. A gas chromatographic analysis done on the culture supernatant revealed that propionic and butyric acid were the dominant volatile fatty acids. The fermentation of rainbow trout sludge substrate revealed a steadily digesting system with total solids for the substrates being reduced by between 42-58%. With 50PS:50SS mixture exhibiting the greatest reduction in total solids percentage. Chemical oxygen demand removal was also revealed in all substrates with removal efficiency in all the substrates ranging between 40-80% with 50PS:50SS having the highest (80%). This was also shown with the gradual decline in total nitrogen % and C:N ratio with digestion stabilizing around C:N ratio of 20:1. The volatile fatty acids production was also very high with toxicity levels being controlled by buffering thereby increasing and stabilizing the digestion process. This report is the first description of optimizing and balancing between secondary and primary sludge mixtures in an anaerobic digestion process. It demonstrates that a primary/secondary co-mixture digestion process is feasible and can eventually resolve the various environmental pollution problems associated with aquaculture sludge management.