Global warming readiness: Feasibility of enhanced biological phosphorus removal from wastewater at 35°C

Abstract

Recent research has shown enhanced biological phosphorus removal (EBPR) from municipal wastewater at warmer temperatures around 30oC to be stable in both laboratory-scale reactors and full-scale treatment plants. In the context of a changing climate, the feasibility of EBPR at even higher temperatures is of interest. We operated two lab-scale EBPR sequencing batch reactors with alternating anaerobic and aerobic phases for over 300 days at 30oC and 35oC, respectively, and followed the dynamics of the communities of phosphorus accumulating organisms (PAOs) and competing glycogen accumulating organisms (GAOs) using a combination of 16S rRNA gene metabarcoding, quantitative PCR and fluorescent in-situ hybridization analyses. Stable and nearly complete P removal was achieved at 30oC; similarly, long term P removal was stable at 35oC with effluent PO43-_P concentrations < 0.5 mg/L on half of all monitored days. Diverse and abundant Ca. Accumulibacter amplicon sequence variants were closely related to those found in temperate environments, suggesting that EBPR at this temperature does not require a highly specialized PAO community. The slow-feeding strategy used effectively limited the carbon uptake rates of GAOs, allowing PAOs to outcompete GAOs at both temperatures. Candidatus Competibacter was the main GAO, along with cluster III Defluviicoccus members. These organisms withstood the slow-feeding regime, suggesting that their bioenergetic characteristics of carbon uptake differ from those of their tetrad-forming relatives. This specific lineage of GAOs warrants further study to establish how complete P removal can be maintained. Comparative cycle studies at two temperatures for each reactor revealed higher activity of Ca. Accumulibacter when the temperature was increased from 30oC to 35oC, suggesting that the stress was a result of the higher carbon (and/or P) metabolic rates of PAOs and GAOs, the resultant carbon deficiency, and additional community competition. An increase in the TOC to PO43--P ratio (from 25:1 to 40:1) effectively eased the carbon deficiency and benefited the proliferation of PAOs. In general, the slow-feeding strategy and sufficiently high carbon input benefited a high and stable EBPR at elevated temperature and represent basic conditions for full-scale applications.

Effect of the Return Activated Sludge on the Start-Up of a Lab-Scale Continuous Flow EBPR Reactor

“…Perfect phenomena of anaerobic P release and aerobic P uptake [45] both were observed in the Batch SBR tests. The 4~5 mg P/L of anaerobic P release was obviously at a low level, but its net aerobic P uptake was not low, compared with the EBPR reports [13,16,21,39]. The top 7 microorganisms, which accounted for 70.2~80.6% of the top 20 genera, showed little difference in each phase tank, and the PAOs (Candidatus Accumulibacter, Tetrasphaera and Dechloromonas) plus GAOs (Candidatus Competibacter) accounted for 7.8~12.2 % of the all genera detected (Fig.…”

“…What's more, EBPR processes often suffer from upsets, deterioration, and failures because of secondary P release and so on, and as such must rely on costly backup chemical precipitation systems [2,6,15]. In order to understand the underlying biological mechanisms and solve the above-mentioned problems for P removal, most of the conclusions of the EBPR system were drawn through operating sequencing batch reactors (SBRs) [16][17][18][19] or continuous flow full-scale WWTPs [2,13,20,21]. There had been fewer previous studies for drawing statistically reliable conclusions based on the operation of a lab-scale continuous flow EBPR reactor.…”