Enhanced post-denitrification without addition of an external carbon source in membrane bioreactors

This study investigates a post-denitrification process without the addition of an external carbon source combined with an enhanced biological phosphorus removal (EBPR) in a membrane bioreactor (MBR). Three trial plants, with two different process configurations, were operated on two different sites, and a variety of accompanying batch tests were conducted. It was shown that even without dosing of an external carbon source, denitrification rates (DNR) much above endogenous rates could be obtained in post-denitrification systems. Furthermore, the anaerobic reactor located ahead of the process had a positive impact on the DNR. Given these surprising results, the project team decided to identify the carbon source used by the microorganisms in the post-denitrification process. Batch tests could demonstrate that lysis products do not play a major role as a C-source for post-denitrification. The following hypothesis was proposed to explain the observations: the glycogen, internally stored by the substrate accumulating bacteria, if anaerobic conditions are followed by aerobic conditions could act as carbon source for denitrification in post-denitrification system. First exploratory batch tests, where the glycogen evolution was monitored, corroborate this assumption.     

A novel post denitrification configuration for phosphorus recovery using polyphosphate accumulating organisms

Enhanced biological phosphorus removal (EBPR) has been widely used to remove phosphorus (P) from wastewater. In this study we report a novel modification to the EBPR approach, namely enhanced biological phosphorus removal and recovery (EBPR-r) that facilitates biological recovery of P from wastewater using a post denitrification configuration. The novel approach consists of two major steps. In the first step, a biofilm of phosphorus accumulating organisms (PAOs) is exposed to a wastewater stream in the absence of active aeration, during which P is taken up by the biofilm using nitrate and residual dissolved oxygen as electron acceptors. Thus, P and nitrogen (N) removal from wastewater is achieved. During the second step, the P enriched biofilm is exposed to a smaller recovery stream supplemented with an external carbon source to facilitate P release under anaerobic conditions. This allows P to be recovered as a concentrated liquid. The EBPR-r process was able to generate a P recovery stream four time more concentrated (28 mg-P/L) than the wastewater stream (7 mg-P/L), while removing nitrate (denitrification) from the wastewater stream. Repeated exposure of the biofilm (10 P-uptake and release cycles) to a recovery stream yielded up to 100 mg-P/L. Overall, EBPR-r is the first post denitrification strategy that can also facilitate P recovery during secondary wastewater treatment.     

Glycerol as a sole carbon source for enhanced biological phosphorus removal

Wastewaters with low organic matter content are one of the major causes of EBPR failures in full-scale WWTP. This carbon source deficit can be solved by external carbon addition and glycerol is a perfect candidate since it is nowadays obtained in excess from biodiesel production. This work shows for the first time that glycerol-driven EBPR with a single-sludge SBR configuration is feasible (i.e. anaerobic glycerol degradation linked to P release and aerobic P uptake). Two different strategies were studied: direct replacement of the usual carbon source for glycerol and a two-step consortium development with glycerol anaerobic degraders and PAO. The first strategy provided the best results. The implementation of glycerol as external carbon source in full-scale WWTP would require a suitable anaerobic hydraulic retention time. An example using dairy wastewater with a low COD/P ratio confirms the feasibility of using glycerol as an external carbon source to increase P removal activity. The approach used in this work opens a new range of possibilities and, similarly, other fermentable substrates can be used as electron donors for EBPR.     

Adaptation of denitrifying bacteria to acetate and methanol in activated sludge

Adaptation of denitrifying bacteria to the external carbon sources acetate and methanol was studied in bench-scale sequencing batch reactors. The reactors were seeded with sludge from a full-scale pre-denitrifying activated sludge plant and operated in cycles consisting of a 23.5 h anoxic period followed by 23 h aeration. A control reactor received no additional carbon. Potential denitrification rate, measured with the acetylene inhibition technique, and the most probable number of bacteria denitrifying with the specific carbon source were followed for 52 days. Actual rates in the reactors were estimated from cumulative gas production during anoxic operation. A period of adaptation was necessary when methanol or acetate was the supplemental carbon source. Adaptation to acetate was also observed in the control reactor. The acetate sludge was, however, probably better adapted to acetate as evidenced by the greater increase in activity per bacterium. The increase continued even after the maximum denitrification rate was reached. During adaptation to methanol the methanol denitrifying capacity per bacterium was fairly constant while the potential rate increased after an initial lag-phase. Sewage water without external carbon did not cause an increased methanol activity that could be interpreted as adaptation. We suggest that the bacteria denitrifying with acetate could be the same as those using the electron donors in the sewage. The bacteria in the methanol reactor seemed to consist of one population denitrifying with methanol and another with compounds in the sewage.     

利用储碳活性污泥强化反硝化脱氮研究

为提高脱氮效果,在SBR进水的缺氧操作结束后取出部分储碳污泥并加以保存,待好氧末返投储碳污泥作为碳源来强化缺氧反硝化反应.结果表明:对TN的去除率可达98%左右,远高于以缺氧/好氧方式运行的SBR;在好氧段的污泥浓度约为3 000 mg/L的情况下,选择缺氧搅拌段的污泥浓度为5 000 mg/L左右能使TN基本全部被去除.SBR经改造后,能有效实现取、返储碳污泥,提高了脱氮效果.     

改善MSBR系统脱氮效果的试验研究

MSBR工艺是连续流与序操作 相结合的新型生物脱氮除磷技术,由于它的后置反硝化设计,碳源不足制约了系统的脱氮效果。为了改善这种状况,进行了将部分原水分流至缺氧区的试验。结果表明：引入原水后,缺氧区的反硝化速率常数提高了一倍,系统的反硝化速率和脱氮率相应提高。与此同时,分流造成了厌氧区的碳源不 足,加之厌氧区的回流增加,引入了较多的硝酸盐,使磷的释放和过量吸收受到影响,除磷效果下降。另外,针对中间沉淀区暴露出的运行和设计问题提出了一些改进措施。     

The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal

The presence of nitrate in the theoretical anaerobic reactor of a municipal WWTP aiming at simultaneous C, N and P removal usually leads to Enhanced Biological Phosphorus Removal (EBPR) failure due to the competition between PAO and denitrifiers for organic substrate. This problem was studied in a continuous anaerobic-anoxic-aerobic (A²/O) pilot plant (146 L) operating with good removal performance and a PAO-enriched sludge (72%). Nitrate presence in the initially anaerobic reactor was studied by switching the operation of the plant to an anoxic-aerobic configuration. When the influent COD composition was a mixture of different carbon sources (acetic acid, propionic acid and sucrose) the system was surprisingly able to maintain EBPR, even with internal recycle ratios up to ten times the influent flow rate and COD limiting conditions. However, the utilisation of sucrose as sole carbon source resulted in a fast EBPR failure. Batch tests with different nitrate concentrations (0-40 mg L⁻¹) were performed in order to gain insight into the competition for the carbon source in terms of P-release or denitrification rates and P-release/C-uptake ratio. Surprisingly, no inhibitory or detrimental effect on EBPR performance due to nitrate was observed. A model based on ASM2d but considering two step nitrification and denitrification was developed and experimentally validated. Simulation studies showed that anaerobic VFA availability is critical to maintain EBPR activity.     

The efficiency of enhanced biological phosphorus removal from real wastewater affected by different ratios of acetic to propionic acid

The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biological phosphorus removal (EBPR) from real wastewater supplemented with volatile fatty acids (VFAs) was investigated. Two sequencing batch reactors (SBRs) were used to acclimate two types (SBR1 and SBR2) of biomass. They were cultured and studied using real wastewater with an average propionic to acetic acid carbon molar ratio of 0.16 and 2.06, respectively. The laboratory results showed that for a given long-term cultured biomass the more the soluble ortho-phosphate (SOP) was released in the anaerobic stage, the higher the SOP was taken up in the aerobic phase. However, the SBR2 biomass had a much greater SOP uptake to release ratio than SBR1, which resulted in a higher SOP removal efficiency than SBR1 (average 87.3% versus 76.9% in SBRs experiments, and 93.5% against 68.1% in batch tests). The SBR2 biomass therefore had a higher SOP uptake ability than the SBR1 for a given amount of SOP release. In addition, the SBR1 had a higher secondary SOP release following VFAs uptake. It was found that the SBR2 biomass synthesized and utilized less observable polyhydroxyalkanoates (PHAs) during the anaerobic and aerobic stage respectively than SBR1. The apparent PHAs utilization efficiency for SOP uptake with the SBR2 biomass was much greater than with the SBR1, and the SBR2 biomass synthesized less glycogen during aerobiosis than SBR1, which might mean a higher PHAs fraction was used for SOP removal, resulting in the increased efficiency with the long-term cultured SBR2 biomass. Higher propionic acid content led to superior EBPR in long-term cultivation, but was transiently detrimental in the short term.     

Polyhydroxyalkanoates form potentially a key aspect of aerobic phosphorus uptake in enhanced biological phosphorus removal

Eighteen anaerobic/aerobic batch experiments were conducted with a variety of volatile fatty acids (VFAs) on a sequencing batch reactor (SBR) population displaying enhanced biological phosphorus removal (EBPR). A statistically significant (P < 0.01 for all variables) correlation between aerobic phosphorus uptake and polyhydroxyalkanoates (PHAs) quantity and form was observed. The results suggest that poly-3-hydroxy-butyrate (3HB) results in significantly higher aerobic phosphorus (P) uptake per unit mmoles as carbon (mmoles-C) than poly-3-hydroxy-valerate (3HV). The results showed that acetic and isovaleric acids resulted in higher P removals (relative to propionic and valeric acids) during EBPR batch experiments not because of higher PHAs quantity, but largely because the predominant type was 3HB rather than 3HV. In contrast propionic and valeric acids resulted in 3HV, and showed much lower aerobic P uptake per unit PHAs.     

SBR无厌氧段生物强化除磷的诱导研究

采用SBR工艺处理人工配水,考察了进水COD及氨氮浓度、C/N值、好氧时间对诱导无厌氧段生物强化除磷的影响.结果表明,当以醋酸钠为碳源、进水COD和氨氮分别为100和5mg/L、C/N值为20时,对在A/O运行方式下表现为厌氧释磷、好氧超量吸磷的SBR,逐渐缩短其厌氧时间且保持好氧时间为135 min后,好氧吸磷现象并不会消失,仅是吸磷量略有降低.该除磷现象的发生是系统微生物经过特定诱导的结果.     

SBR工艺对低碳量城市污水的反硝化除磷研究

广州地区的城市污水含碳量低，碳、氮、磷浓度比例失调，采用传统工艺处理很难达到理想的脱氮除磷效果，为此采用SBR工艺对其进行处理，考察了该工艺的反硝化除磷效果。结果表明，在厌氧／缺氧／好氧的运行模式下，采用逐步增加缺氧段运行时间的方法可有效提高污泥的反硝化除磷性能；在试验进水水质条件下，反应器厌氧运行30min、缺氧运行3h、好氧运行1h可保证对磷的稳定高效去除，出水TP〈1mg／L；ORP值无法指示缺氧反硝化与吸磷过程，pH值可作为缺氧吸磷结束的指示参数，而ORP和pH值均可作为好氧吸磷结束的控制参数。     

Endogenous metabolism of Candidatus Accumulibacter phosphatis under various starvation conditions

The endogenous processes of Candidatus Accumulibacter phosphatis (referred to as Accumulibacter), a known polyphosphate-accumulating organism (PAO) responsible for enhanced biological phosphorus removal systems (EBPR), were characterized during 8-day starvation under anaerobic, anoxic, aerobic and intermittent aerobic–anaerobic conditions. A lab-scale EBPR culture with Accumulibacter representing over 85% of the entire bacterial population as quantified with fluorescence in-situ hybridization was used in the study. Cell decay rates were found to be negligible under anaerobic and anoxic conditions and may be ignored in activated sludge models. The decay rate under aerobic conditions was determined to be 0.03/d at 22 °C, considerably lower than the values commonly used in activated sludge modeling. Polyphosphate and glycogen were utilized simultaneously under anaerobic and anoxic conditions for maintenance energy production, with glycogen being the primary energy source until the glycogen content reached very low levels. Glycogen was used by Accumulibacter as the primary source of energy for maintenance under aerobic conditions in the absence of polyhydroxyalkanoates. However, Accumulibacter did not seem to use polyphosphate for energy production during aerobic starvation, clearly contrasting the anaerobic and particularly the anoxic case. Intermittent aerobic–anaerobic storage resulted in not only negligible cell decay rate, but also slower rates of glycogen and polyphosphate utilization, and may therefore be an effective strategy for long-term storage of EBPR sludge.     

Endogenous processes during long-term starvation in activated sludge performing enhanced biological phosphorus removal

In many biological wastewater treatment systems, bacterial growth and the amount of active biomass are limited by the availability of substrate. Under these low growth conditions, endogenous processes have a significant influence on the amount of active biomass and therefore, the overall system performance. In enhanced biological phosphorus removal (EBPR) systems endogenous processes can also influence the levels of the internal storage compounds of the polyphosphate accumulating organisms (PAO), directly affecting phosphorus removal performance. The purpose of this study was to evaluate the significance of different endogenous processes that occur during the long-term starvation of EBPR sludge under aerobic and anaerobic conditions. Activated sludge obtained from a laboratory sequencing batch reactor was used to perform a series of batch starvation experiments. Under aerobic starvation conditions we observed a significant decay of PAO (first-order decay rate of 0.15/d) together with a rapid utilization of polyhydroxyalkanoates (PHA) and a slower utilization of glycogen and polyphosphate to generate maintenance energy. On the other hand, anaerobic starvation was best described by maintenance processes that rapidly reduce the levels of polyphosphate and glycogen under starvation conditions while no significant decay of PAO was observed. The endogenous utilization of glycogen for maintenance purposes is currently not included in available EBPR models. Our experimental results suggest that mathematical models for in EBPR should differentiate between aerobic and anaerobic endogenous processes, as they influence active biomass and storage products differently.     

Denitrification on poly-beta-hydroxybutyrate in microbial granular sludge sequencing batch reactor

Microbial granules were successfully cultivated in an alternating aerobic-anaerobic sequencing batch reactor (SBR) for removing organic carbon and nitrogen. It was found that almost all input ammonium was converted to nitrite and nitrate in the aerobic phase, while the efficiency of denitrification was highly related to the availability of external carbon source in the anaerobic phase. Complete denitrification was achieved with sufficient supply of external carbon, while only partial denitrification was observed with no addition of external carbon. Results showed that in the absence of external carbon source, pre-accumulated poly-beta-hydroxybutyric acid (PHB) in microbial granules could be utilized for cell maintenance and denitrification. With supply of external carbon but no addition of nitrate, PHB accumulation accounted for the main mechanism of the organic removal. Under balanced growth conditions (with organic carbon and nitrogen supply), external organic carbon was consumed simultaneously for denitrification, PHB storage as well as for cell functions. It was revealed that the potential role of PHB for denitrification by microbial granules was very limited, i.e. less than 28 mg nitrate-nitrogen l(-1) was found to be denitrified with internally accumulated PHB. This study for the first time shows the limiting capacity of PHB as reducing power for denitrification by microbial granules.     

Denitrification with methanol: Fundamental study of the growth and denitrification capacity of Hyphomicrobium sp

Hyphomicrobrium spp was found as dominant organism in a two-sludge nitrifying-denitrifying wastewater treatment system with methanol as external carbon source. The optimal pH for growth was found to be 8.3 and the organism seemed to be rather temperature sensitive (Q₁₀ = 3.3). The denitrification rate was expressed as a function of pH and temperature since it was almost independent on the concentrations of methanol and nitrate-nitrogen. Identical growth rates are found when using either nitrate- or nitrite-nitrogen; the nitrite consumption rate, however, is twice the nitrate reduction rate. Nitrate to nitrite reduction is the rate limiting step in denitrification reaction and some inhibition by high concentrations of nitrite on the nitrate reduction is measured. The methanol/nitrate-N ratio is 2.55 and increasing to 3.5 at extreme pH values. The endogenous denitrification rate is only 10% of the normal denitrification rate measured.     

Development of a 2-sludge, 3-stage system for nitrogen and phosphorous removal from nutrient-rich wastewater using granular sludge and biofilms

A novel 2-sludge 3-stage process using a combination of granular sludge and biofilm was developed to achieve biological removal of nitrogen and phosphorus from nutrient-rich wastewater. The system consists of a granular sequencing batch reactor (SBR) working under alternating anaerobic/anoxic conditions supplemented with a short aerobic phase and an aerobic biofilm SBR. The wastewater is first fed to the granular SBR reactor, where easily biodegradable carbon sources are taken up primarily by polyphosphate accumulating organisms (PAOs). The supernatant resulting from quick settling of the granular sludge is then fed to the biofilm SBR for nitrification, which produces oxidized nitrogen that is returned to the granular reactor for simultaneous denitrification and phosphorus removal. While maximizing the utilization of organic substrates and reducing operational costs, as do other 2-sludge processes previously reported in literature, the proposed system solves the bottleneck problem of traditional 2-sludge systems, namely high effluent ammonia concentration, due to its high-volume exchange ratios. An ammonia oxidation rate of 32 mg N/Lh was achieved in the biofilm SBR, which produced nitrite as the final product. This nitrite stream was found to cause major inhibition on the anoxic P uptake and also to result in the accumulation of N(2)O. These problems were solved by feeding the nitrite-containing stream continuously to the granular reactor in the anoxic phase. With a nitrogen and phosphorus removal efficiency of 81% and 94%, respectively, the system produces an effluent that is suitable for land irrigation from a wastewater stream containing 270 mg N/L of total nitrogen and 40 mg P/L of total phosphorus.     

Mixed carbon sources for nitrate reduction in activated sludge-identification of bacteria and process activity studies

Mixtures of methanol and acetate as carbon source were investigated in order to determine their capacity to enhance denitrification and for analysis of the microbial composition and carbon degradation activity in activated sludge from wastewater treatment plants. Laboratory batch reactors at 20 degrees C were used for nitrate uptake rate (NUR) measurements in order to investigate the anoxic activity, while single and mixed carbon substrates were added to activated sludge. Microautoradiography (MAR) in combination with fluorescence in situ hybridisation (FISH) were applied for microbial analysis during exposure to different carbon sources. The NUR increased with additions of a mixture of acetate and methanol compared with additions of a single carbon source. MAR-FISH measurements demonstrated that the probe-defined group of Azoarcus was the main group of bacteria utilising acetate and the only active group utilising methanol under anoxic conditions. The present study indicated an improved denitrification potential by additions of a mixed carbon source compared with commonly used single-carbon additions. It is also established that Azoarcus bacteria are involved in the degradation of both acetate and methanol in the anoxic activated sludge.     

新型UniFed SBR生物除磷脱氮工艺

介绍了新型UniFed SBR工艺的运行方式、在除磷脱氮方面的特点及其在实际污水处理厂的应用实例.其特点是在SBR运行周期的沉淀和排水阶段,将进水均匀地引入沉淀污泥层,以取得反硝化和厌氧放磷所需的适宜条件.与复杂的连续流生物脱氮除磷工艺相比,该工艺采用单池运行,不需物理分区和污泥回流即可达到较高的除磷脱氮效率,还可减少基建投资.     

提高SBR工艺中脱氮除磷处理效果的措施

利用序批式反应器(SBR)试验装置对城市生活污水进行处理研究，讨论了影响SBR脱氮除磷的碳源、pH值、好氧曝气等因素，并对SBR工艺中脱氮除磷的相互影响进行了探讨，提出了可以同时脱氮除磷的一种SBR的运行方式。     

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.