Enhancing the hydrolysis of excess sludge using thermophilic Bacillus sp. Hnu under different oxygen supply conditions

Abstract

A thermophilic Bacillus strain was isolated from excess sludge in the present study. A 16S rDNA analysis indicated that this strain was a Bacillus sp. that had not been previously reported (named Bacillus sp. Hnu). The aim of the present study was to investigate the enhanced efficiency of excess sludge hydrolysis by the addition of thermophilic Bacillus sp. Hnu under different oxygen supply conditions. The results indicated that higher temperature and a greater oxygen supply were advantageous for the volatile suspended solid removal ratio, having the same effect to that of protease activity. The maximum volatile suspended solid removal ratio was achieved at 21.5, 42.5 and 54.4 % after 108 h digestion at pH 6.9 and 60 °C and increased by 17.2, 38 and 45.4 % under anaerobic, microaerobic, and aerobic conditions compared with the control test, respectively. The hydrolysis rate constants under anaerobic, microaerobic, and aerobic conditions were 3, 4.8, and 7 times (40 °C), 3.5, 9.8, and 11.8 times (50 °C) and 2.7, 7.2, and 10.3 times (60 °C), respectively. Hydrolysis performance indicated that the Bacillus sp. Hnu could accelerate the hydrolysis rate. The kinetic study showed that the hydrolysis of sludge with Bacillus sp. Hnu and the control test followed first-order kinetics except at 60 °C. © 2013 (CC) SCS.