Molecular characterization of the microbial community structure in two activated sludge systems for the advanced treatment of domestic effluents

Although activated sludge systems with enhanced biological phosphorus removal (EBPR) represent state-of-the-art technology for phosphate removal from wastewater it is still unknown which species of bacteria are responsible for the EBPR process. The aim of this study was to compare the bacterial composition of activated sludge from two laboratory plants with different modes of operation, anoxic/oxic- (EBPR, no nitrification) and Phoredox-system (EBPR, nitrification and denitrification) with particular emphasis on microorganisms responsible for EBPR process. In addition to fluorescence in situ hybridization (FISH), we applied further rRNA-based molecular techniques like terminal restriction-fragment length polymorphism analysis and comparative 16S rDNA analysis to yield additional information and to verify the results from FISH analysis, like e.g. for the identification of polyphosphate accumulating organisms (PAO). Despite the different modes of operation only minor differences in the bacterial composition were detected by FISH analysis based on the probes used in this study. In contrast T-RFLP analysis yielded characteristic community fingerprints for each of the investigated plants and comparative 16S rDNA analysis indicated highly diverse microbial communities in both plants suggesting substantial differences in the microbial structure. The results obtained by FISH analysis with specific probes for PAOs support the presumption that not only one specific organism is responsible for the EBPR. In our case Tetrasphaera spp. dominated the PAO community, but other possible PAOs, like Microlunatus spp. and members of the Rhodocyclus group, were also detected.     

The effect of pH on the competition between polyphosphate-accumulating organisms and glycogen-accumulating organisms

In enhanced biological phosphorus removal (EBPR) processes, glycogen-accumulating organisms (GAOs) may compete with polyphosphate-accumulating organisms (PAOs) for the often-limited carbon substrates, potentially resulting in disturbances to phosphorus removal. A detailed investigation of the effect of pH on the competition between PAOs and GAOs is reported in this study. The results show that a high external pH ( approximately 8) provided PAOs with an advantage over GAOs in EBPR systems. The phosphorus removal performance improved due to a population shift favouring PAOs over GAOs, which was shown through both chemical and microbiological methods. Two lab-scale reactors fed with propionate as the carbon source were subjected to an increase in pH from 7 to 8. The phosphorus removal and PAO population (as measured by quantitative fluorescence in situ hybridisation analysis of "Candidatus Accumulibacter phosphatis") increased in each system, where the PAOs appeared to out-compete a group of Alphaproteobacteria GAOs. A considerable improvement in the P removal was also observed in an acetate fed reactor, where the GAO population (primarily "Candidatus Competibacter phosphatis") decreased substantially after a similar increase in the pH. The results from this study suggest that pH could be used as a control parameter to reduce the undesirable proliferation of GAOs and improve phosphorus removal in EBPR systems.     

Understanding the detrimental effect of nitrate presence on EBPR systems: effect of the plant configuration

The interaction between enhanced biological phosphorus removal (EPBR) and biological nitrogen removal may result in EBPR failure in full‐scale wastewater treatment plants (WWTPs). This work studies one of the common causes of this failure: the presence of nitrate in the anaerobic phase, which may act as an inhibitor for polyphosphate accumulating organisms (PAO) activity or may activate the competition between PAO and denitrifying bacteria for the carbon source. Several batch experiments were performed with different carbon sources (acetic acid, propionic acid and sucrose) at different nitrate concentrations using PAO‐enriched sludge from two different pilot plants: an anaerobic/aerobic sequential batch reactor (SBR) and an anaerobic/anoxic/aerobic (A²/O) continuous plant. The results imply that the operational conditions of the A²/O pilot plant selected a PAO population capable of i) coexisting with nitrate without an inhibitory effect and ii) outcompeting denitrifying bacteria for the carbon source, in contrast to the SBR pilot plant where nitrate had an inhibitory effect on EBPR. Copyright © 2012 Society of Chemical Industry     

对强化生物除磷机理与工艺认识误区的剖析

结合国际上生物除磷机理与工艺的最新进展，分析了目前我国在污水生物除磷工艺研发和运行中存在的一些认识误区。基于成熟的生物除磷生化代谢机理，指出反硝化除磷菌（DPB）是一种广泛存在于一些强化生物除磷（EBPR）工艺中的聚磷菌（PAOs），无需特殊培养；对于市政污水，EBPR工艺中出现的聚糖原茵（GAOs）一般不会成为聚磷茵（PAOs／DPB）的竞争者而严重影响系统的除磷功能。针对强化生物除磷工艺的认识误区，指出污泥龄（SRT）是设计的关键参数，在最不利细菌生长的冬季，控制SRT〉12 d即可使EBPR保持较好的硝化与脱氮除磷效果；在污水生物处理除磷工艺选择上，“厌氧池＋氧化沟”只是污水处理升级而演变出的一种被动型工艺，并非最佳的EBPR工艺选择；此外倒置A^2／O工艺由于忽略了聚磷菌所需的进水碳源及DPB的作用，并不一定能改进EBPR的生物除磷效果。     

Characteristics of nitrogen and phosphorus removal in SBR and SBBR with different ammonium loading rates

Laboratory scale experiments were conducted to study the deterioration of enhanced biological phosphorus removal (EBPR) due to influent ammonium concentration, and to compare the performance of two types of sequencing batch reactor (SBR) systems, a conventional SBR and sequencing batch biofilm reactor (SBBR). Both in SBR and SBBR, the total nitrogen removal efficiency decreased from 100% to 53% and from 87.5% to 54.4%, respectively, with the increase of influent ammonium concentration from 20 mg/l to 80 mg/l. When the influent ammonium concentration was as low as 20 mg/l (C: N: P=200: 20: 15), denitrifying glycogen-accumulating organisms (DGAOs) were successfully grown and activated by using glucose as a sole carbon source in a lab-scale anaerobic-oxic-anoxic (A₂O) SBR. In the SBR, due to the effect of incomplete denitrification and pH drop, the nitrogen and phosphorus removal efficiency decreased from 77% to 33.3% when the influent ammonium concentration increased from 20 mg/l to 80 mg/l. However, in the SBBR, simultaneous nitrification/denitrification (SND) occurred, and the nitrification rate in the aerobic phase did not change remarkably in spite of the increase in influent ammonium concentration. Phosphorus removal was not affected by the increase of influent ammonium concentration.     

强化生物除磷工艺富集聚磷菌及其微生物菌群分析

为了研究聚磷菌的生长机理和菌种特性,在序批式SBR反应器中,以普通活性污泥富集聚磷菌,在厌氧/好氧条件下,以乙酸钠/丙酸交替作为碳源富集高浓度聚磷菌,采用FISH结合DGGE的分子生物学手段研究了富集周期内系统微生物种群结构的变化.DGGE结果表明:试验前后微生物种群结构发生了明显改变,其菌群的多样性指数、丰富度指数和条带数具有一致的变化趋势,在运行第2阶段末期达到最高值,进入稳定运行阶段,这3项指数下降,优势度上升.聚类分析表明,稳定运行期间种群群落相似度较高.FISH结果表明:在启动和负荷提高阶段聚磷菌与聚糖菌呈现共同增长的趋势,在第71天分别达到41%和39%;在稳定运行阶段聚磷菌成为明显的优势菌属,占总菌群的89%,反应器内仅存在少量聚糖菌.     

活性污泥法合成PHB的研究进展

PHB是许多微生物在非稳态条件下积累的一种生物聚合物,可作为微生物的胞内碳源和能源内储物,还可用作优良的可生物降解塑料、生物相容性材料和环保高分子材料。主要综述了活性污泥法合成PHB的最新研究进展。重点介绍了SBR工艺、强化生物除磷工艺、微好氧/好氧活性污泥工艺等不同工艺的PHB合成机制和研究水平;以及营养配比条件(如碳源、C/N比、氮源和磷源),工艺运行控制条件(如DO浓度、pH、污泥龄和温度),以及底物/生物量比等因素对合成PHB的影响。提高现行活性污泥法合成PHB水平是降低PHB的生产成本,实现活性污泥资源化的前提条件。研发能够同步实现氮磷等污染物的高效去除以及PHB资源化的新工艺,以及实现PHB资源化的活性污泥工艺运行控制条件的优化研究是今后活性污泥法的发展趋势之一。     

Effects of integrated fixed film activated sludge media on activated sludge settling in biological nutrient removal systems

Integrated fixed film activated sludge (IFAS) is an increasingly popular modification of conventional activated sludge, consisting of the addition of solid media to bioreactors to create hybrid attached/suspended growth systems. While the benefits of this technology for improvement of nitrification and other functions are well-demonstrated, little is known about its effects on biomass settleability. These effects were evaluated in parallel, independent wastewater treatment trains, with and without IFAS media, both at the pilot (at two solids residence times) and full scales. While all samples demonstrated good settleability, the Control (non-IFAS) systems consistently demonstrated small but significant (p < 0.05) improvements in settleability relative to the IFAS trains. Differences in biomass densities were identified as likely contributing factors, with Control suspended phase density > IFAS suspended phase density > IFAS attached phase (biofilm) density. Polyphosphate content (as non-soluble phosphorus) was well-correlated with density. This suggested that the attached phases had relatively low densities because of their lack of anaerobic/aerobic cycling and consequent low content of polyphosphate-accumulating organisms, and that differences in enhanced biological phosphorus removal performance between the IFAS and non-IFAS systems were likely related to the observed differences in density and settleability for the suspended phases. Decreases in solids retention times from 8 to 4 days resulted in improved settleability and increased density in all suspended phases, which was related to increased phosphorus content in the biomass, while no significant changes in density and phosphorus content were observed in attached phases.     

模糊控制强化生物除磷SBR系统的除磷过程

采用在线ORP和pH仪对两个平行的强化生物除磷(EBPR)SBR反应系统的厌氧放磷、缺氧吸磷和好氧吸磷过程进行监测。针对聚糖菌(GAO)和聚磷菌(PAO)的竞争和影响PAO和反硝化聚磷菌(DPAO)的各种因素,验证了以氧化还原电位(ORP)和pH作为除磷过程模糊控制参数的可行性和有效性。在此基础上,确立了厌氧／好氧(A／O)SBR系统和厌氧／缺氧(A2)SBR系统除磷过程的模糊控制策略。对ORP和pH的在线检测不仅可以模糊控制厌氧放磷、缺氧吸磷和好氧吸磷过程所需时间,节约能源优化处理效果,而且可以指示系统运行效果和功能微生物种群的竞争行为。     

Could polyphosphate-accumulating organisms (PAOs) be glycogen-accumulating organisms (GAOs)?

Polyphosphate (poly-P) is known to be a key compound in the metabolism of polyphosphate-accumulating organisms (PAOs). In this study, a sludge highly enriched (80%) in Candidatus Accumulibacter phosphatis (hereafter referred to as Accumulibacter), a widely known PAO, was used to study the ability of these microorganisms to utilize acetate anaerobically under poly-P-limiting conditions. The biomass was subject to several anaerobic and aerobic cycles, during which the poly-P pool of PAOs was gradually emptied by supplying feed deficient in phosphate and washing the biomass at the end of each anaerobic period using media containing no phosphorus. After three cycles, phosphorus was hardly released but PAOs were still able to take up acetate and stored it as polyhydroxyalkanoates (PHA), as demonstrated by post-FISH chemical staining. Glycogen degradation increased substantially, suggesting PAOs were using glycogen as the main energy source. This is a key feature of glycogen-accumulating organisms (GAOs), which are known to compete with PAOs in enhanced biological phosphorus removal (EBPR) systems. The ratios between acetate uptake, polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) production, and glycogen consumption agree well with the anaerobic models previously proposed for GAOs.