Influence of pH control on material characteristics, bacterial community composition and BNR performance of mature aerobic granules

The influence of different pH conditions on the characteristics, nutrient removal efficiency and bacterial community structure of mature granules. Three identical sequencing batch reactors with stable granules were operated under controlled pH (≤7.0 and ≤7.5) and uncontrolled pH (initial pH = 7.5) conditions for two months. Results show that pH ≤ 7.0 significantly affected properties of the granules. Extracellular polymeric substance content decreased from 134 to 101 mg/gVSS, granules’ size decreased from 660 to 449 μm, and fraction of floccular biomass increased from 7.8 to 26.3%. However, maintaining pH ≤ 7.5 did not show significant impact on these parameters. Moreover, pH ≤ 7.0 deteriorated nitrogen removal (from 44.4 to 17.7%) by depleting the alkalinity and inhibiting the activity of nitrifying bacteria. Phosphorus removal was also significantly influenced by the pH control such that pH ≥ 7.5 improved the phosphorus removal from 90.8 to 99.6%, while pH ≤ 7.0 obtained 63.1% phosphorus removal. Results of DNA sequencing showed that pH control influenced bacterial community structure of the granules. The results confirmed the increase in the abundance of Dechloromonas, which were the main polyphosphate accumulating organisms at pH ≤ 7.5. Our results suggest that pH adjustment could alter bacterial communities of mature granules and therefore could be used to improve treatment functionality of the granules.