IS IT PAO-GAO COMPETITION OR METABOLIC SHIFT IN EBPR SYSTEM? EVIDENCE FROM AN EXPERIMENTAL STUDY
Abstract:The reduced EBPR performance in full and bench-scale EBPR studies was linked to the proliferation of GAOs but often time with the lack of any evidence. No study has been performed to show whether the reduced EBPR performance was a result of a major metabolic shift or the competition between PAOs and GAOs. In this study, a detailed enzymatic study was coupled with batch tests and electron microscopy results for a realistic explanation. Two bench-scale modified UCT systems operated at 20 and 5°C, fed with acetate and exhibiting very robust EBPR performance were used in the experiments. First, sludge taken from the anaerobic and aerobic stages of each UCT system was investigated under transmission electron microscopy (TEM). Second, enzyme assays were performed on all key enzymes involved in EMP Pathway, PP Pathway, ED Pathway, Glyoxylate Shunt, TCA Cycle, Branched TCA Cycle, Reverse TCA Cycle and Succinate-Propionate Pathway. Third, EBPR mixed liquor with enriched poly-P pool and depleted poly-P pool was exposed to anaerobic/aerobic cycling to determine PHA and glycogen storage and consumption patterns. The results eliminated the possibility of population shift from PAO to GAO or other non- PAO due to the short batch test period provided (<12 hrs) which would not allow a population shift and further justified with the electron microscopy results. The results also indicate that glycogen serves not only as source of reducing power for PHA production but also serves as an alternative energy source when the poly-P pool of the PAOs is depleted. Slow generation of ATP via glycolytic pathway at 5°C cannot satisfy energy requirements of EBPR cells to complete several cell functions including acetate uptake and PHA storage. However, the glycolytic pathway is efficiently operable at warm temperatures (>20°C). The reduced performance of enhanced EBPR facilities operated at warm temperature may not be a result of GAO proliferation; instead it may be related the efficient use of the glycolytic pathway by PAOs which results in more glycogen storage and less P uptake, thereby reducing the phosphorus removal performance of the facility.
Document Type: Research Article
Publication date: January 1, 2007
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