The effects of glucose and fatty acids on enhanced biological phosphorus removal using a sequencing batch reactor

Two anaerobic/aerobic sequencing batch reactors (SBRs) were used to evaluate enhanced biological phosphorus removal (EBPR). The first SBR, designated the Glucose SBR, was run for a period of four months. It received a synthetic wastewater plus glucose as a supplemental carbon source. The second SBR, the Isovaleric SBR, was run for three months. During the first month, isovaleric acid was its supplemental carbon source while for the remaining time period, no supplemental carbon source was added to the feed. Steady-state data from the SBR receiving isovalerate yielded the highest phosphorus (P) removals observed during the study, with a mixed liquor volatile suspended solid (MLVSS) P content of 7.2%. The next highest removals were observed when prefermented glucose was received, which yielded a MLVSS P content of 6.4%. The lowest removals were observed when no supplemental carbon source was added to the SBR influent, with at 4.4% MLVSS P content. Batch experiments were also conducted to quantify the effect of EBPR of glucose and the volatile fatty acids (VFAs) acetic acid, propionic acid, valeric acid, and isovaleric acid. Compounds giving the largest anaerobic P release ultimately yielded the lowest effluent P concentrations. At 0.80 mmoles/l, isovaleric acid resulted in anaerobic P released 9.5 mg/l greater than an equal amount of glucose or propionic acid, but ultimately gave effluent P values roughly 4 mg/l lower than either. Ratios of aerobic P uptake/anaerobic P release were found to be roughly equal for all the VFAs when the VFAs were compared on a molar basis. Propionic acid had aerobic P uptake/anaerobic P release ratios similar to the other VFAs. It also behaved the same as all the other VFAs with respect to the effect of concentrations added to the batch experiment; however, the magnitude of its removal was significantly lower than all the other substrates. Glucose, on the other hand, behaved differently from all the VFAs. Glucose aerobic P uptake/anaerobic P release ratios varied with concentration, which was not the case for the others substrates. Also, glucose P net removals decreased at concentrations higher than 0.60 mmoles/l. Glucose also resulted in net P removals roughly 2mg/l higher than propionic acid, but ultimately gave lower net P removal than isovaleric, valeric and acetic acids