Assessing the performance of polyphosphate accumulating organisms in a full-scale side-stream enhanced biological...

Phosphorous (P) removal in wastewater treatment is essential to prevent eutrophication in water bodies. Side-stream enhanced biological phosphorous removal (S2EBPR) is utilized to improve biological P removal by recirculating internal streams within a side-stream reactor to generate biodegradable carbon (C) for polyphosphate accumulating organisms (PAOs). In this study, a full-scale S2EBPR system in a water resource recovery facility (WRRF) was evaluated for 5 months. Batch experiments revealed a strong positive correlation (r = 0.91) between temperature and C consumption rate (3.56-8.18 mg-COD/g-VSS/h) in the system, with temperature ranging from 14°C to 18°C. The anaerobic P-release to COD-uptake ratio decreased from 0.93 to 0.25 mg-P/mg-COD as the temperature increased, suggesting competition between PAOs and other C-consumers, such as heterotrophic microorganisms, to uptake bioavailable C. Microbial community analysis did not show a strong relationship between abundance and activity of PAO in the tested WRRF. An assessment of the economic feasibility was performed to compare the costs and benefits of a full scale WRRF with and without implementation of the S2EBPR technology. The results showed the higher capital costs required for S2EBPR were estimated to be compensated after 5 and 11 years of operation, respectively, compared to chemical precipitation and conventional EBPR. The results from this study can assist in the decision-making process for upgrading a conventional EBPR or chemical P removal process to S2EBPR. PRACTITIONER POINTS: Implementation of S2EBPR presents adaptable configurations, exhibiting advantages over conventional setups in addressing prevalent challenges associated with phosphorous removal. A full-scale S2EBPR WRRF was monitored over 5 months, and activity tests were used to measure the kinetic parameters. The seasonal changes impact the kinetic parameters of PAOs in the S2EBPR process, with elevated temperatures raising the carbon demand. PAOs abundance showed no strong correlation with their activity in the full-scale S2EBPR process in the tested WRRF. Feasibility assessment shows that the benefits from S2EBPR operation can offset upgrading costs from conventional BPR or chemical precipitation.