Performance And Removal Approaches Of Biological Phosphorus Removal From Wastewater In SBR Under Low Temperature

Biological phsophorus removal (BPR) process has been widely implemented in many wastewater treatment plants (WWTP) worldwide as a economical and effective method to control wastewater eutrophication. However, the lack of stability is still a noticeable problem. There were a lot of reports about the loss of phosphorus removal capability for BPR (biological phosphorus removal) processes operated at temperatures under 10 oC. Sludge characteristics, microbial community structure, kinetics and mechanism of P removal were investigated in BPR system operated at low temperature, and biological phosphate removal and biologically induced phosphorus precipitation characteristics was analysed at low temperature.In BPR reactors started up at 5°C, PAOs were acclimated in SBR when the reactor was operated at A/O mode under 5°C, and the start up time was 31d. Lower temperature resulted in longer start up time. When the BPR reactor was well started up, the phosphorus removal efficiency was ~85%. The phosphorus removal in this reactor was lower than that operated at 15°C, but larger than the reactor operated at 25°C.SRT had a great effect on performance of BPR system. For SBR operated at 5 oC, the phosphorus removal capability seriously deteriorated after the SRT reduced from 30 days to 15 days, and PAOs were simultaneously washed out from the reactor gradually. Wash-out SRT (or minimal SRT) and stable SRT for BPR at were calculated according to the model proposed by Brdjanovic. Wash-out SRT were 12 for BPR reactor operated at 5 oC, while stable SRT was 18 days. Longer stable SRT was demanded for BPR operated at lower temperature.Variation of pH had effects on PAOs metabolization characteristics in BPR operated at low temperature. Anaerobic phosphorus release capacity increased with pH at 5 oC in the range of 6 to 8.5. Anaerobic acetate uptake and PHB formation capacity enhanced with the pH increasing from 6 to 8. When the pH increased to 8.5, too much power supplied by degradation of poly-P was used to overcomeΔ? . Less poly-β-hydroxybutyrate (PHB) was synthesized in anaerobic phase inhibited consequent uptake of orthophosphate in aerobic phase. Highest phosphorus removal efficiency was obtained in batch tests at pH 8 accompany with typical phosphorus release and uptake. BPR performance and microorganisms were monitored in 5 oC SBR operated at pH 6 and 8 to investigate pH effect on microbial community structure of BPR at low temperature. Acidic condition (pH=6) favored the growths of GAOs, while PAOs take predominant roles in BPR systems at pH 8.It is the first time to investigate that extracellular polymeric substance (EPS) played an important role for phosphorus removal in BPR system. Phosphorus removed by EPS removal achieved the highest value at 5 oC (2.4 mg P per cycle). Low temperature was propitious to EPS phosphorus removal, accounting for 13 % of total phosphorus removal at 5 oC, which was much higher than that at 15℃(4.2%) and 25℃(4.8%). Phosphorus removed by intracellular absorption was demonstrated as the dominant part (>80%) in total phosphorus removal operated under different temperatures. Intracellular phosphorus contents reduced with the increase of temperature. At 15℃, the highest total phosphorus removal rate of 95 % was obtained due to the highest intracellular phosphorus absorption of 18.2 mg P in a typical cycle.Molecular techniques were applied to investigate the microbial community characteristics and founctional microbes at low temperature. Results of FISH showed that shorter SRT (15 days) was unfavorable at 5℃for BPR due to the wash-out of PAOs to some extent. At 5 oC and 30 days SRT, the highest PAOs content among total bacteria reached 64.3%. PCR-DGGE was applied to investigate the temperature effects on founctional microbes. Founctional microbes of BPR differed with temperature. Uncultured beta proteobacterium gene for 16S rRNA clone:OS1L-4.and Gemmatimonas aurantiaca existed in SBRs operated at 5, 15 and 25 oC as founctional microbes. Uncultured actinobacterium clone GCP18 existed in a large amount in BPR operated at 25 oC, while Tetrasphaera elongata, which had a large population in BPR reactor operated at 5 oC, might be the main founctional microbe at low temperature.Anaerobic specific phosphorus release rates (SPRR), specific acetate uptake rates (SCUR) and specific PHB formation rates increased with the temperature in the range of 5 to 25 oC, and decreased at 30 oC. Temperature coefficients for P-release, acetate uptake and PHB formation were 1.056, 1.047 and 1.053, respectively. Aerobic specific phosphorus uptake rates (SPUR) and specific PHB consumption rates increased with the temperature in the range of 5 to 30 oC, and temperature coefficients for these two aerobic reactions were 1.057 and 1.066.