Development of Digested Sludge-Assimilating and Biohydrogen-Yielding Microflorae

Digested sludge (DS) is a waste product of anaerobic digestion that is produced during the biodegradation of excess sludge. It cannot be used as a substrate for further biogas production owing to its recalcitrant nature. In the present study, we used a heat treatment technique to convert DABYS microflora (DABYS = digested sludge-assimilating and biogas-yielding soil microflora), which degraded DS and produced methane gas, to a microflora that could produce hydrogen gas from DS. Heat treatment at 80 and 100 degrees C inactivated the methanogens that consume hydrogen for methane production but did not affect the thermotolerant bacteria. We developed three microflorae (DABYS-A80, DABYS-A100, and DABYS-80B) to exclusively produce hydrogen gas. They included representatives from the anaerobic eubacterial families Clostridiaceae and Enterobacteriaceae. Pseudomonas sp. was also present in DABYS-A80 and DABYS-A100. It is thought that bacteria in the Enterobacteriaceae family or Pseudomonas genus survive heat treatment because they are embedded in microgranules. Enzymatic analysis suggested that the microflorae hydrolyzed DS using cellulase, chitinase, and protease. Under optimum culture conditions, DABYS-A80, -A100, and B-100 produced gas yields of 8.0, 7.1, and 2.6 mL, respectively, from 1.0 g of dried DS.

Automated summary

In this study, a heat treatment technique was used to convert DABYS microflora, which degrades digested sludge (DS) and produces methane gas, into a microflora that can produce hydrogen gas from DS. The inactivation of methanogens that consume hydrogen was achieved by heat treatment at 80 and 100 degrees C, while thermotolerant bacteria remained unaffected. Three microflorae were developed, including representatives from the families Clostridiaceae and Enterobacteriaceae, as well as Pseudomonas sp. in DABYS-A80 and DABYS-A100.