Molecular Evidence of Internal Carbon-driven Partial Denitrification in a A-B Stage Pilot System Coupled with Sidestream EBPR

To tackle the energy-intensive issue of the conventional wastewater treatment plants (WWTPs), A-B processes are developed where the A-stage is designed for COD capture for energy recovery and B-stage is for nutrient removal and recovery (Liu et al., 2019). At B-stage, short-cut nitrogen removal via nitrite are preferred, which combined partial nitrification (PN)/partial denitrification (PDN) with Anammox processes. However, the efficient NOB out selection under mainstream condition is still challenging (Cao et al., 2017). PDN provides a promising alternative to achieve the nitrite accumulation for Anammox with low COD/N ratio applied, but still at its earlier stage based on lab-scale study (Zhang et al., 2019). Previous study observed that nitrate was reduced with the PHA degradation during the denitrification process, but no sufficient molecular evidence was provided to find out the specific functional bacteria and prove that PHA can serve as the internal carbon to perform PDN. In this study, the short-cut nitrogen removal performance was investigated in a pilot-scale A-B process integrated with sidestream EBPR (fermentation of return activated sludge) for municipal wastewater treatment. Partial denitrification coupled with nitrite accumulation was observed with simultaneous P removal. The objective of this study is to provide the molecular evidence to prove that PHA can serve as the internal carbon for PDN. In addition to batch tests performed to evaluate the activity of nitrogen conversion, 16S rRNA gene amplicon sequencing was applied to identify the dominant microorganism, and real-time PCR technique was performed to determine the relative abundance of conventional nitrifiers (AOB and NOB). Furthermore, single-cell Raman microspectroscopy was applied to elucidate the role of intracellular carbon polymers in partial denitrification with nitrite accumulation.