Enhanced Biological Phosphorus Removal at High Temperature Using Different Carbon Sources - Key Microorganisms and Processes PDF Download

Author: Rogelio Ernesto Zuniga Montanez
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Languages : en
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Book Description
Municipal wastewater contains a number of constituents that can have detrimental effects if discharged to receiving water bodies. Phosphorus (P) is of specific interest as a limiting nutrient in aquatic ecosystems that can cause eutrophication. In enhanced biological phosphorus removal (EBPR), polyphosphate accumulating organisms (PAOs) store excess P intracellularly. To achieve this accumulation, the organisms are exposed consecutively to anaerobic and either aerobic or anoxic conditions. During the anaerobic phase, PAOs consume and store organic carbon with P release, followed by the aerobic/anoxic phase during which the stored carbon is oxidized and P is taken up and stored as polyphosphate. PAOs are not the only bacteria that can thrive under these cyclic conditions and they face competition from glycogen accumulating organisms (GAOs). The latter have a similar metabolism but do not accumulate P. Most research to date has focused on the use of certain volatile fatty acids (VFAs) as carbon sources and on process conditions at temperatures common in temperate climates. Much remains unknown about the potential of EBPR in tropical regions and the suitability of other carbon substrates to drive the accumulation of phosphate. The purpose of this dissertation is to contribute to the understanding of EBPR at high temperatures and with unconventional carbon sources. Three different studies were designed and conducted with the following aims: (a) to evaluate the long-term EBPR stability and key microbial community in a wastewater treatment plant (WWTP) designed to achieve P removal in Singapore, (b) to study the process efficiency, biochemical transformations and organisms involved in a laboratory-scale EBPR reactor fed by alternating the substrates acetate and glutamate, and (c) to assess the potential of using unconventional carbon sources for EBPR by testing glutamate and glucose as alternating substrates at the laboratory-scale. The research included experiments at the full- and laboratory-scale, all at a mean temperature of 30 °C. Sustained observations in all three studies served to uncover the biochemical and microbial community dynamics. In the full-scale study, I conducted a yearlong evaluation of the EBPR activity at a WWTP that had been retrofitted to facilitate EBPR in Singapore. A mean P removal efficiency of 90 % was observed throughout the sampling period, similar to temperate climate installations and contrary to earlier reports that EBPR was not feasible at high temperatures. The main PAOs present in the reactor were Tetrasphaera, Candidatus Accumulibacter (Accumulibacter) and Dechloromonas, with mean relative abundances of 1.53, 0.43 and 0.69 %, respectively. The PAO community underwent changes during the surveyed period, with a marked transition from a Tetrasphaera-dominated community to a more even one. The link between PAOs and the P released in the anaerobic compartment was supported by a statistically significant correlation between the relative abundance of these organisms and the measured P concentrations. GAOs and PAOs coexisted without compromising the EBPR activity. In one of the laboratory-scale studies, glutamate and acetate were alternated as the carbon source for a reactor operated at 30 °C. Complete and stable P removal was achieved with a predominantly glutamate-containing feed, after modifying operating parameters commonly used in VFA-fed systems to a COD/P ratio of 40:1 mg COD/mg P and a cycle duration of 8 h. Long-term EBPR with a feed dominated by glutamate in a laboratory-scale reactor has not been previously reported. The P and carbon cycling patterns were different for glutamate and acetate. Reduced P release and polyhydroxyalkanoate (PHA) accumulation happened when glutamate was fed, but not with acetate, where glutamate appeared to be stored as an unidentified non-PHA compound or as different compounds. The PAO Accumulibacter and the GAO Candidatus Competibacter (Competibacter) remained the only known EBPR bacteria during the period of good EBPR performance, at similar relative abundances. A canonical correlation analysis revealed that the relative abundance of some non-PAO organisms correlated more strongly with variables that denoted good EBPR activity than did the abundance of any of the known PAOs. In the last study, a laboratory-scale sequencing batch reactor was used to test the EBPR potential of glutamate and glucose as alternating carbon sources in a high temperature process. The recommended influent COD/P ratio and batch duration for VFA-fed systems were unsuccessful. After modifications, COD/P ratios of 20:1 and 40:1 mg COD/ mg P resulted in complete P removal, but only in the short term. The EBPR stoichiometry with these two carbon substrates differed from that of VFA-fed systems. For both, lower P and PHA cycling was observed, and intracellular carbon storage compounds that were not PHA appeared to contribute to P cycling, as shown from carbon balances. A very diverse EBPR community was present in the reactor, including Accumulibacter, Tetrasphaera and Dechloromonas PAOs, and Competibacter, Defluviicoccus, Micropruina and Kineosphaera GAOs. Most of these organisms have not been reported before in laboratory-scale EBPR reactors operated at high temperatures. The work presented in this dissertation expands the understanding of EBPR by showing that the process is possible and stable in full-scale treatment plants at high temperature, with removal efficiencies similar to those observed in temperate climates. In addition, it was shown that unconventional carbon sources, specifically, glutamate and glucose, do participate in EBPR and that complete and stable phosphorus removal can be achieved with glutamate as dominant substrate at high temperature. A core PAO and GAO community was present in the three systems, where the interactions among members were more complex than previously considered, including competition, coexistence and succession events. The results obtained from this work enhance our fundamental knowledge of EBPR as an industrial process, as well as the metabolic diversity, niches and dynamics of PAOs and GAOs. The study outcomes can inform design and operational strategies at full-scale treatment plants. Lastly, the consideration of both high temperatures and unconventional carbon sources for EBPR is expected to aid in the development of more efficient treatment processes.