Characterization of acidogenesis occurring on rainbow trout (Oncorhynchus mykiss) sludge by indigenous Alcaligenes faecalis

Abstract

For the efficient treatment of sludge accumulated on a rainbow trout farm, two novel strains were isolated that possessed the ability for acidogenic digestion. The strains were identified as Alcaligenes faecalis HCB2-A1 and Alcaligenes faecalis A2, respectively, and there was synergism between the two strains. Acidogenic digestions using the mixed culture of the two isolates were performed on various sludge mixtures under examinations of changes in major reaction parameters. Among the sludge mixtures, the most stable acidogenic digestion was observed on 1:1 mixture of primary and secondary sludge. During this acidogenesis, pH and ORP dropped to 6.5 and -274 mV within 1 day and then increased steadily. At the same time total solids, COD, and total nitrogen were reduced 58, 79.3 and 42.7%, respectively, with the COD removal rate of 13,017 mg/L/day. The C: N ratio changed from 27:1 to 10:1 as the sludge was digested, and total volatile fatty acids of 6065.3 mg/L was produced for 7 days. The results demonstrated an efficient means to treat aquaculture sludge, which is the alternative to the discharge of the sludge into the river.