Evaluation of PAO adaptability to oxygen concentration change: Development of stable EBPR under stepwise low-aeration adaptation

Effect of return activated sludge diversion ratio on phosphorus removal performance in side-stream enhanced biological phosphorus removal (S2EBPR) process

In this study, a lab-scale continuous flow side-stream enhanced biological phosphorus (P) removal (S2EBPR) reactor was operated for 247 days treating synthetic wastewater with influent carbon to phosphorus (C/P) ratio of 25.0 g COD/g P and influent PO43--P of 7.4 ± 0.3 mg P/L. The effect of the return activated sludge (RAS) diversion ratio on S2EBPR reactor was investigated by comparing P removal performance, microbial activity, and community structure. The results showed that the RAS diversion ratio of 8.0%, by yielding a side-stream sludge retention time (SRTSS) of ∼60 h, resulted in the lowest effluent PO43--P concentration of 0.5 ± 0.3 mg P/L. The results of in situ process profiles and ex situ P release and uptake batch tests under different RAS diversion conditions showed that the more anaerobic P release was obtained in the side-stream reactor, the higher the P removal efficiency and EBPR activity were achieved. The stoichiometric ratios observed in EBPR activity tests indicated a polyphosphate accumulating organisms (PAOs) metabolism mainly dependent on the glycolysis pathway. The results of microbial ecology analysis revealed that the optimized SRTSS would give a competitive advantage to PAOs in the S2EBPR process. By obtaining statistically reliable results, this study would provide guidance for wastewater treatment plants to achieve optimal P removal performance in S2EBPR configuration.

Performance of anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal system overwhelmingly dominated by Candidatus_Competibacter: Effect of aeration time

The anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal process (AOA-SNDPR) is a promising technology for enhanced biological wastewater treatment and in situ sludge reduction. Herein, the effects of aeration time (90, 75, 60, 45, and 30 min, respectively) on AOA-SNDPR were evaluated including simultaneous nutrients removal, sludge characteristics, and microbial community evolution, where the role of a denitrifying glycogen accumulating organisms, Candidatus_Competibacter, was re-explored given its overwhelming dominance. Results revealed that nitrogen removal was more vulnerable, and a moderate aeration period of 45-60 min mostly favored nutrients removal. Low observed sludge yields (Y_obs) were obtained with decreased aeration (as low as 0.02 g MLSS/g COD), while MLVSS/MLSS got increased. The dominance of Candidatus_Competibacter was proven to be the key to endogenous denitrifying and in situ sludge reduction. This study would aid the more carbon- and energy-efficient aeration strategy for AOA-SNDPR systems treating low-strength municipal wastewater.

Mechanisms governing the dissolution of phosphorus and iron in sewage sludge by the bioacidification process and its correlation with iron phosphate speciation

In the last two decades, phosphorus (P) recovery from sewage sludge liquors gained much interest for its high-quality product potential. However, the consistently reported constraints are the low phosphorus availability and the technical-economical difficulties to increase it through chemical acidification. This article discusses the mechanisms of phosphorus dissolution by the biological acidification process (Biological acidification or acidic fermentation) as an alternative to chemical acidification. In addition, we investigate the potential correlation between the phosphorus dissolution and iron phosphate speciation of several types of sludge from different sewage treatment plants and P removal technologies. The results show that the percentage of P dissolution by bioacidification is always higher than the P dissolution by chemical acidification at equal pH for all types of sludge except for the settled primary sludge. The highest P dissolution was recorded for the sludge from the Enhanced Biological P Removal process assisted with Chemical P Removal process (EBPR-CPR) with around 65% of P dissolution. Three mechanisms were identified as contributing to the increased P dissolution by bioacidification: P release by the Polyphosphate Accumulating Organisms (PAO), P dissolution by pH decrease, and P dissolution by a biological activity at acidic pH (3.7-4) that includes iron reduction and aluminum dissolution. The principal component analysis and Pearson's correlation indicate that P dissolution by bioacidification is negatively correlated with the P-bound to ferric iron, hence positively correlated with the P-bound to ferrous iron, which characterizes the sludge from the EBPR-CPR process. This study suggests that the choice of the P removal technology significantly influences the P recovery from sewage sludge liquors.

Application of jetventurimixer for developing low-energy-demand and highly efficient aeration process of wastewater treatment

In biological wastewater treatment, the oxygen supply in an aeration tank is the most important factor for removing organic pollutants, but it takes a large amount of electricity to generate the oxygen supply required. The Jetventurimixer (JVM) is a device that applies Bernoulli’s principle, and the difference in flow rate pressure through the impeller is generated by the rotational force. Due to this physical mechanism, this device can supply oxygen in the atmosphere to the bioreactor without additional power. In this study, the JVM-based aeration process was developed for more efficient water treatment that demands lower energy. Parameters were measured for validating the efficiency and lower power demands, including the oxygen mass transfer characteristics and power efficiency. The results indicated that all parameters related to the oxygen mass transfer characteristics were advanced in performance by more than 200 % compared to those of the conventional air diffuser. In the case of power efficiency, it was confirmed that performance was 153–176 % higher. Therefore, it was confirmed that the JVM provides high-efficiency and low-energy benefits to the aeration process and, based on these advantages, the developed system seems to require further studies and validation for application to the water treatment system.