Effect Of Different Ratios Of Acetate To Glycerol On Biological Phosphorus Removal In Sequencing Batch Reactor Operated As Oxic/Extended-idle Regime

Traditional biological phosphorus removal theory believes that the presence of anaerobic phase is essential for good phosphorus removal efficiency while aerobic/extended-idle regime can still achieve under aerobic/extended-idle condition. Due to its simple process, low cost and stable water out, aerobic/extended-idle regime has received lots of attention in recent years. Currently, organic carbon source used in aerobic/extended-idle regime mainly is the VFAs such as acetic acid, propionic acid, etc. Though the material is easy to be absorbed by PAOs, but the cost is higher, therefore, to explore a economic and reliable carbon source for biological phosphorus removal has become a pressing demand.Taking the synthetic wastewater as target, the effect of different acetate/glycerol ratios on biological phosphorus removal performance in aerobic/extended-idle regime were investigated in five lab-scale sequencing batch reactors(SBR1,SBR2,SBR3,SBR4,SBR5).A acetate/glycerol mixture was separately added to the reactors in ratios of 4:0, 4:1, 1:1, 1:4 and 0:4. The results showed that the acetate/glycerol mixture in the ratios of 4:1 and 1:1 could induce better performance of biological phosphorus removal than that of the other ratios. The average efficiency of phosphorus removal were 90.1%, 92.5%, 97.3%, 65.7% and 53.4% respectively. The typical cycle study found that most of the PHAs were synthesized to provide more energy for the subsequent absorption of phosphorus and poly-P synthesis when the ratio of acetate/glycerol was 1:1. This phenomenon indicated that the low content of glycerol can promote the absorption of VFAs and the synthesis of PHAs, which then strengthen the absorption of phosphorus during the extended-idle period. More lactic acid was generated with the increase of glycerol, which resulting in lower pH, less amount of PHAs synthesis, large amount of glycogen synthesis and the phosphorus removal performance was weaken. Different glycogen levels at the end of the aeration leaded to different levels of phosphorus release during extended-idle period and different phosphorus removal performance were achieved because of different dependence degree on the poly-P.Subsquently, the acetate/glycerol mixture in ratios of 4:1 and 1:1 which can reach good phosphorus removal performance were operated in A/O(SBR6, SBR7) and O/EI regime(SBR6#, SBR7#) at the same time. The average efficiency of phosphorus removal were 88.4%, 73.2%, 91.3%, 96.5% respectively. The typical cycle study found that only a few VFAs were absorbed in SBR7 and less PHAs were synthesized compared with SBR6. Under the same acetate/glycerol ratio conditions, although the PHAs accumulation in A/O regime was higher than that of the O/EI regime, but less were used for phosphorus uptake; The higher phosphorus uptake/phosphorus release and the lower MLVSS/MLSS showed that the ability of phosphorus accumulation and the dependence on the poly-P were stronger in the O/EI regime. Therefore, the phosphorus removal performance of O/EI regime was better than that of A/O regime when the acetate/glycerol ratio was the same.