Biochemical Mechanism Of Microbial Acid Tolerance Response During The Enhanced Biohydrogen Process

Along with the anaerobic digestion of biomass, large amounts of organic acids would be accumulated, which resulted in an inhibitory effect on anaerobic microbiology, and the biohydrogen process. In this study, the anaerobic sludge with butyate stress was used to enhance the biohydrogen process, and to explore the glutamate decarboxylase (GAD) represented microbial acid tolerance response (ATR) within the anaerobic sludge. Moreover, effect of different concentration of acid stress on extracellular polymeric substances (EPS) component of the anaerobic sludge was also investigated. Finally, further investigation of the DNA components through DGGE analysis during the anaerobic digestion process was also conducted. The main conclusions of this paper are as followed:1. Firstly, optimization of the fermentation conditions were investigated. It was found that the accumulation of biohydrogen and organic acids reached 2240 mL and 104.08 mmol/L when substrate concentration was 0.1 mol/L, pH ranged 5.3-5.7, ratio of glucose and inoculating sludge at 1.5:1, and the concentration of Fe2+ and Ni2+ is 0.04 mg/L and 7.5 g/L.2. Secondly, anaerobic sludge with acid stress was adopted for hydrogen production. It was found that the production of butyric acid, acetic acid and hydrogen reached 107.1 mmol/L, 46.2 mmol/L and 3690 mL/mol glucose when the concentration of butyric acid reached 6.0 g/L which were 65%, 54% and 110% of the control, respectively.3. Thirdly, three different stimulators as glucose, glutamine and butyrate were used to induce the the glutamate-dependent system based microbial ATR. It was found that GAD activity decreased 9% compared with the control in the case of glucose. While the GAD activity reached 13.9μmol/(g·TS·h) when butyrate was adopted, which increased by 55% compared with the control. Following, concentration of adopted for further acid stress was 6.0 g/L, as the activity of GAD and dehydrogenase activity reached 14.7μmol/(g·TS·h) and 6982.12μgTF/(g·TS·h), which increased by 77% and 95% compared with the control, respectively.4. Finally, it indicated that the content of EPS, and loosely bound protein, loosely bound polysaccharide, tightly bound protein and tightly bound polysaccharide content were 147%, 34.8%, 35%, 21.6% higher than that of the control, respectively, with acid stress on anaerobic sludge. On the other hand, total amount of DNA was found to be increased by 11% compared with the control with appropriate acid stress. Moreover, denaturing gradient gel electrophoresis (DGGE) investigation indicated that the amplification of the DNA with 6 g/L of acid stress was intensified obviously in comparison with the control and 12 g/L stress groups. Clostridium sp. and Bacillus sp. are dominant kinds of microbials in the sludge under acid stress was 6.0 g/L.