Model-based evaluation of competition between polyphosphate- and glycogen-accumulating organisms

Many studies show that glycogen-accumulating non-polyphosphate organisms (GAOs) can compete with polyphosphate-accumulating organisms (PAOs) for organic substrate under anaerobic conditions and may indeed cause the deterioration of enhanced biological phosphorus removal (EBPR) systems. Understanding their behaviors in an anaerobic/aerobic (A/O) system at different operational conditions is essential in developing control strategies that ensure EBPR. A model-based evaluation of competition between PAOs and GAOs under different operational conditions was presented in this study. At 30 degrees C and a 10-day sludge age, the dominance of GAOs in the A/O sequencing batch reactor (SBR) was strongly dependent upon their considerable kinetic advantage in anaerobic acetate uptake. At 20 degrees C and a 10-day sludge age, the kinetic advantage of GAOs in anaerobic acetate uptake could be less, compared to that at 30 degrees C and a 10-day sludge age, leading to the relative dominance of PAOs and a stable phosphorus removal in the A/O system. At 30 degrees C and a 3-day sludge age, the parameters responsible for determining the aerobic distribution of anaerobically stored X(PHA) for both PAOs and GAOs, other than kinetic parameters of anaerobic acetate uptake, are important for them being dominant in the A/O SBR. In a situation when the q(PHA,P) value is lower than q(PHA,G) but comparable, PAOs may still be dominant in the A/O SBR, presumably because their aerobic conversion fraction of biomass production from PHA was higher than that of the GAOs.     

Advancing post-anoxic denitrification for biological nutrient removal

The objective of this research was to advance a fundamental understanding of a unique post-anoxic denitrification process for achieving biological nutrient removal (BNR), with an emphasis on elucidating the impacts of surface oxygen transfer (SOT), variable process loadings, and bioreactor operational conditions on nitrogen and phosphorus removal. Two sequencing batch reactors (SBRs) were operated in an anaerobic/aerobic/anoxic mode for over 250 days and fed real municipal wastewater. One SBR was operated with a headspace open to the atmosphere, while the other had a covered liquid surface to prevent surface oxygen transfer. Process performance was assessed for mixed volatile fatty acid (VFA) and acetate-dominated substrate, as well as daily/seasonal variance in influent phosphorus and ammonia loadings. Results demonstrated that post-anoxic BNR can achieve near-complete (>99%) inorganic nitrogen and phosphorus removal, with soluble effluent concentrations less than 1.0 mgN L⁻¹ and 0.14 mgP L⁻¹. Observed specific denitrification rates were in excess of typical endogenous values and exhibited a linear dependence on the glycogen concentration in the biomass. Preventing SOT improved nitrogen removal but had little impact on phosphorus removal under normal loading conditions. However, during periods of low influent ammonia, the covered reactor maintained phosphorus removal performance and showed a greater relative abundance of polyphosphate accumulating organisms (PAOs) as evidenced by quantitative real-time PCR (qPCR). While GAOs were detected in both reactors under all operational conditions, BNR performance was not adversely impacted. Finally, secondary phosphorus release during the post-anoxic period was minimal and only occurred if nitrate/nitrite were depleted post-anoxically.     

AOA-SBR工艺用于城市污水同步脱氮除磷

以城市污水为研究对象,考察了不同COD／N／P对厌氧／好氧／兼氧（AOA）．SBR工艺脱氮除磷效果的影响。经过3个月稳定运行,当COD：N：P-800：24：11时,AOA．SBR工艺对污水中有机物、氨氮和磷的去除率分别为100％、84％和93％。实验通过提高有机物浓度削弱聚磷菌（PAOs）与聚糖菌（GAOs）竞争底物的能力,抑制了PAOs好氧放磷速率。当COD=800mg／L时,GAOs和PAOs厌氧乙酸摄取量之比为l：9。此外,实验采用兼氧／好氧吸磷速率比,对反硝化聚磷菌数量（DNPAOs）进行估算,结果表明AOA-SBR工艺比值明显高于A20和AO工艺。因此,通过调节进水有机物浓度,可使DNPAOs在AOA-SBR同步脱氮除磷过程中发挥重要作用。     

Changes in phosphorus removing performance and bacterial community structure in an enhanced biological phosphorus removal reactor

A lab-scale-enhanced biological phosphorus removal (EBPR) reactor was operated for 204 days to investigate the correlation between phosphorus removing performance and bacterial community structure. The phosphorus removing performance was good from day 1 to 92 and from day 172 to 204. However, the removal activity was in a deteriorated state from day 93 to 171. From day 69 (2 weeks before the beginning of the deterioration) to 118 (2 weeks after the beginning of the deterioration), sludge P content decreased. The amounts of ubiquinone-8 and menaquinone-8 (H(4)) decreased during this period while the amount of ubiquinone-10 increased. The comparison of these changes and the general attribution of each quinone to the bacterial phylogenetic groups suggested that beta proteobacteria and Actinobacteria contributed to EBPR positively, and that alpha proteobacteria were related to this EBPR deterioration. Glycogen accumulating organisms (GAOs) are considered to detrimentally affect EBPR ability by outcompeting the phosphorus accumulating organisms by using aerobically synthesized glycogen as the energy source to assimilate organic substrates anaerobically to form polyhydroxyalkanoates. However, in this research, there was nearly no substrate uptake during the anaerobic period at the middle of the deteriorated performance period. This suggests that the deterioration observed in this research does not agree with the GAOs inhibition model. In this research, the excess P release at the anaerobic period was concluded to cause the deterioration.     

污水强化生物除磷的生化模型研究进展

阐述了在污水强化生物除磷过程中生化模型的建立与发展,重点介绍了与聚磷菌有关的Mino模型,强调了在理解生化模型时应该注意的问题：所有聚磷菌生化模型都只是在试图描述发生在EBPR（Enhanced Biological Phosphorus Removal）生物群中的一些生物化学变化现象和规律（多聚磷酸盐的吸收和水解、PHA的合成与再利用）.另外,还都假设所有具有EBPR能力的细菌都有着共同的代谢特征.所以,尽管这些生化模型有助于对整个EBPR过程的理解,但不应该拘泥于这些生化模型,只有通过对聚磷菌纯培养获得最终成功才能够彻底解决整个问题.     

碳源和进水pH值对聚糖菌代谢的短期影响

通过连续流A/O工艺驯化富集了聚糖菌(GAOs),在此基础上利用静态批次试验分别考察了碳源(乙酸、丙酸和葡萄糖)和进水pH值(6.5、7.0和7.5)对GAOs代谢的短期冲击影响。结果表明,在厌氧阶段,GAOs污泥可以较快的速率吸尽乙酸和丙酸,而葡萄糖仅部分被吸收。对比消耗单位碳源合成的聚-β-羟基烷酸(PHA)量,以葡萄糖为碳源时最大,以丙酸作为碳源时最小。同时,GAOs污泥吸收单位碳源所消耗的糖原量以丙酸最少;而以葡萄糖为碳源时,与乙酸和丙酸情况不同的是其在厌氧反应后期糖原量略有增加。另外,在考察进水pH值对GAOs污泥代谢的短期冲击影响时发现,随着进水pH值的升高,GAOs污泥对挥发性脂肪酸(VFAs)的吸收速率减缓,但进水pH值的短期波动对于胞内物质(糖原、PHA)代谢的影响不大。