The effects of pH on the production of volatile fatty acids and microbial dynamics in long-term reactor operation.

Volatile fatty acids, intermediate products of anaerobic digestion, are one of the most promising biobased products. In this study, the effects of acidic (pH 5), neutral (without pH adjustment) and alkali (pH 10) pH on production efficiency and composition of volatile fatty acids (VFAs) and bacterial community profile were analyzed. The anaerobic sequencing batch reactors were fed cheese production wastewater as substrate and inoculated by anaerobic granular seed sludge. The results showed that acidic pH improved VFA production yield (0.92 at pH 5; 0.42 at pH 10 and 0.21 gCOD/gVS at neutral pH). Furthermore, propionic acid was dominant under both pH 10 (64 ± 20%) and neutral pH (72 ± 8%), whereas, acetic acid (23 ± 20%4), propionic acid (22 ± 3%), butyric acid (21 ± 4%) and valeric acid (15 ± 8%) were almost equally distributed under pH 5. Adaptation of bacterial community to different pH conditions might steer the acid profile: Bacteroidetes (50.07 ± 2%) under pH 10, Proteobacteria (40.74 ± 7%) under neutral pH and Firmicutes (47.64 ± 9%) under pH 5 were the most dominant phylum, respectively. Results indicated pH plays a significant role in VFA production, acid composition, and bacterial community structure. However, in order to gain a concrete understanding effects of pH, characterization of intracellular and extracellular metabolites with dynamics of the microbial community is required.