Monitoring of Lactobacillus sp. inoculated in the reactor to evaluate the solubilization efficiency of primary sludge

A new approach for the solubilization of primary sludge using the fatty-acid-producing bacteria, Lactobacillus brevis, was investigated in a laboratory-scale solubilization reactor under anaerobic conditions. Compared with a non-inoculated experiment, the 10%(v/v) inoculated experiment in an anaerobic bioreactor increased SCOD by more than 59%, and led to 50.5% COD solubilization as well as the production of mixed acids (acetic acid, lactic acid, propionic acid, butyric acid, valeric acid, etc.) after 4 days of reaction time. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA fragments revealed that the inoculated L. brevis became the predominant population in the bacterial community during the anaerobic solubilization process. PCA analysis performed on the molecular weights from the DGGE band revealed that the microbial community structure of each sample was grouped by the presence of lactic acid. This suggests that bioaugmentation of the organism might be useful for enhancing the solubilization of primary sludge. L. brevis in the solubilization reactor was monitored using 16S rDNA-based quantitative real-time PCR assays. A specific probe for the detection of L. brevis was designed and no specific PCR products were amplified, as verified by the cycle threshold value.