Alternate anoxic/aerobic operation for nitrogen removal in a membrane bioreactor for municipal wastewater treatment

A large pilot-scale membrane bioreactor (MBR) with a conventional denitrification/nitrification scheme for municipal wastewater treatment has been run for one year under two different aeration strategies in the oxidation/nitrification compartment. During the first five months air supply was provided according to the dissolved-oxygen set-point and the system run as a conventional predenitrification MBR; then, an intermittent aeration strategy based on effluent ammonia nitrogen was adopted in the aerobic compartment in order to assess the impact on process performances in terms of N and P removal, energy consumption and sludge reduction. The experimental inferences show a significant improvement of the effluent quality as COD and total nitrogen, both due to a better utilization of the denitrification potential which is a function of the available electron donor (biodegradable COD) and electron acceptor (nitric nitrogen); particularly, nitrogen removal increased from 67% to 75%. At the same time, a more effective biological phosphorus removal was observed as a consequence of better selection of denitrifying phosphorus accumulating organisms (dPAO). The longer duration of anoxic phases also reflected in a lower excess sludge production (12% decrease) compared with the standard pre-denitrification operation and in a decrease of energy consumption for oxygen supply (about 50%).     

Impact of different recirculation schemes on nitrogen removal and overall performance of a laboratory scale MBR.

For membrane bioreactors (MBR) with enhanced nutrients removal, rather complex recirculation schemes based on the biological requirements are commonly recommended. The aim of this work was to evaluate other recirculation options. For a laboratory scale MBR, four different recirculation schemes were tested. The MBR was operated with COD degradation, nitrification, post-denitrification without carbon dosing and biological phosphorus removal. For all configurations, efficient COD, nitrogen and phosphorus removal could be achieved. There were no big differences in elimination efficiency between the configurations (COD elimination: 96.6-97.9%, nitrogen removal: 89.7-92.1% and phosphorus removal: 97.4-99.4%). Changes in the degradation, release and uptake rates were levelled out by the changes in contact time and biomass distribution. With relatively constant outflow concentrations, different configurations are still interesting with regard to oxygen consumption, simplicity of plant operation or support of certain degradation pathways such as biological phosphorus removal or denitrification.     

Development of MBR with reduced operational and maintenance costs.

To reduce MBR O&M costs, a new MBR process that conducts efficient simultaneous biological nitrogen and phosphorus removal (BNR) was developed. In the development of this process, various approaches were taken, including reduction of power demand, chemical consumption and sludge disposal costs. To address power demand reductions, air supply requirements for membrane cleaning were reduced. The process adopted an improved membrane that requires less air for cleaning than conventional membranes. It also introduced cyclic aeration, which alternately supplies washing air to the two series of membrane units. Adoption of biological phosphorus removal eliminated chemical costs for phosphorus removal and contributed to the reduction of sludge disposal costs. By combining these technologies, compared to conventional MBR processes, an approximately 27% reduction in O&M costs was achieved.     

Treatment of slaughterhouse plant wastewater by using a membrane bioreactor

The use of a membrane bioreactor (MBR) for removal of organic substances and nutrients from slaughterhouse plant wastewater was investigated. The chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations of slaughterhouse wastewater were found to be approximately 571 mg O2/L, 102.5 mg/L, and 16.25 mg PO4-P/L, respectively. A submerged type membrane was used in the bioreactor. The removal efficiencies for COD, total organic carbon (TOC), TP and TN were found to be 97, 96, 65, 44% respectively. The COD value of wastewater was decreased to 16 mg/L (COD discharge standard for slaughterhouse plant wastewaters is 160 mg/L). TOC was decreased to 9 mg/L (TOC discharge standard for slaughterhouse plant wastewaters is 20 mg/L). Ammonium, and nitrate nitrogen concentrations of treated effluent were 0.100 mg NH4-N/L, and 80.521 mg NO3-N/L, respectively. Slaughterhouse wastewater was successfully treated with the MBR process.     

Application of membrane bioreactor system with full scale plant on livestock wastewater.

A full-scale plant of an MBR system treating livestock wastewater has shown impressive results. The Cheorwon County Environmental Authorities adopted the MBR process with UF membrane for retrofitting the old plant, which removes organic matter, nitrogen and phosphorus at a high level. According to 6 months operation data, BOD and SS removal were about 99.9% and COD(Mn), TN and TP removal were 92.0%, 98.3% and 82.7%, respectively. It is considered that the temperature at the bioreactor has to be controlled to be below 40 degrees C so as to ensure sufficient nitrification. It appeared that the MBR system is competitive with other conventional technologies for treatment of livestock wastewater such as piggery waste.     

In-situ characterization of microbial community in an A/O submerged membrane bioreactor with nitrogen removal.

The bacterial community involved in removing nitrogen from sewage and their preferred DO environment within an anoxic/oxic membrane bioreactor (A/O MBR) was investigated. A continuously operated laboratory-scale A/O MBR was maintained for 360 d. At a sludge age of 150 d and a C/N ratio of 3.5, the system was capable of removing 88% of the influent nitrogen from raw wastewater through typical nitrogen removal transformations (i.e. aerobic ammonia oxidation and anoxic nitrate reduction). Characterization of the A/O MBR bacterial community was carried out using fluorescence in situ hybridization (FISH) techniques. FISH results further showed that Nitrosospira spp. and Nitrospira spp. were the predominant groups of ammonia and nitrite oxidizing group, respectively. They constituted up to 11% and 6% of eubacteria at DO below 0.05 mg/l (low DO), respectively, and about 14% and 9% of eubacteria at DO between 2-5 mg/l (sufficient DO), respectively, indicating preference of nitrifiers for a higher DO environment. Generally low counts of the genus Paracoccus were detected while negative results were observed for Paracoccus denitrificans, Alcaligenes spp, and Pseudomonas stutzeri under the low and sufficient DO environments. The overall results indicate that Nitrosospira spp., Nitrospira spp. and members of Paracoccus spp. can be metabolically functional in nitrogen removal in the laboratory-scale A/O MBR system.     

Six years of operation of a fluidised bed reactor for denitrification.

At Himmerfj?rden wastewater treatment plant, a fluidised bed reactor for nitrogen removal has been operated since 1997. Despite its small footprint, the system enables a far-reaching nitrogen removal. The current nitrate reduction in the reactor is 95%. The reduction of total nitrogen at the wastewater treatment plant is 80-90% at normal operation. The concentration of nitrate in the effluent is easily controlled by changing the dose of carbon. As part of a series of full-scale experiments, the plant has, for the last two years, been operated without denitrification for a couple of months during spring/summer, in order to benefit a favourable N/P-ratio in the recipient and to counteract the growth of nitrogen fixing blue-green algae, When resuming the dosage of carbon, full denitrification was re-established in about two weeks. Important factors to take into consideration when operating the fluidised bed reactor are the abrasive characteristics of the carrier material (sand), the increased concentration of suspended solids in the effluent, and the importance of a suitable N/P-ratio in the influent, as lack of phosphorus might cause an uncontrolled microbiological growth.     

Optimal but robust N and P removal in Sbrs: a model-based systematic study of operation scenarios.

A systematic approach to determine the optimal operation strategy for nitrogen (N) and phosphorus (P) removal of sequencing batch reactors (SBRs) has been developed and applied successfully to a lab-scale SBR. The methodology developed is based on using a grid of possible scenarios to simulate the effect of the key degrees of freedom in the SBR system. The grid of scenarios is simulated using a calibrated ASM2dN model developed and calibrated in a previous study. Effluent quality in combination with a robustness index for each of the scenarios is used to select the best scenario. With the best scenario, it is possible to improve/increase the current performance of the SBR system by around 54% and 74% for N and P removal respectively.     

Phosphorus removal under anoxic conditions in a continuous-flow A2N two-sludge process.

The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-P bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD/TN ratio, Sludge Retention Time (SRT), Bypass Sludge Flow rate (BSF) and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed at about 26-33% of influent flow rate.     

Effects of solid retention time on the performance of submerged anoxic/oxic membrane bioreactor.

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were used simultaneously to investigate the effects of solids retention time (SRT) on organic and nitrogen removal in MBR for treating domestic wastewater. COD removal efficiencies in all reactors were consistently above 94% under steady state conditions. Complete conversion of NH(4+)-N to NO(3-)-N was readily achieved over a feed NH(4+)-N concentration range of 30 to 50 mg/L. It was also observed that SRT did not significantly affect the nitrification in the MBR systems investigated. The average denitrification efficiencies for the 3, 5, 10 and 20 days SRT operations were 43.9, 32.6, 47.5 and 66.5%, respectively. In general, the average effluent nitrogen concentrations, which were mainly nitrate, were about 22.2, 27.6, 21.7 and 13.9 mg/L for the 3, 5, 10 and 20 days SRT systems, respectively. The rate of membrane fouling at 3 days SRT operation was more rapid than that observed at 5 days SRT. No fouling was noted in the 10 days and 20 days SRT systems during the entire period of study.     

生态塘对稻田降雨径流中氮磷的拦截效应研究

农田养分的大量流失已成为农业面源污染的主要来源之一,生态塘兼具排水和生态湿地双重功效,研究其对稻田排水氮磷的拦截效应对于防治农业非点源污染具有重要意义。针对降雨径流条件下生态塘对降雨径流中氮磷的动态拦截效应以及降雨径流结束后氮磷在静水中的去除效应有待明了的需求,本文选取太湖西岸何家浜流域典型农田作为研究对象,并将该区域的塘堰改造为生态塘,研究了生态塘对水稻生长期内的三场降雨径流氮磷的拦截去除效果及降雨径流结束后氮磷在静水中的去除效应。研究结果表明:(1)在三场降雨过程中,生态塘对总氮(TN)的平均去除率为34.7%,总磷(TP)的平均去除率为34.8%;(2)生态塘对降雨径流中不同形态氮磷的去除率大小排序为氨氮(NH_4~+-N)颗粒态氮(PN)硝态氮(NO_3~--N),颗粒态磷(PP)溶解态磷(DP),且径流状态下水体垂向分层氮磷浓度分布随降雨进行而变化,总体分布规律为底层氮磷浓度大于表层氮磷浓度;(3)降雨径流结束后,TN在生态塘中的去除率为50.4%,TP在生态塘中的去除率为52.3%,塘2对TN、TP的去除率大于塘1与塘3,生态塘表现了较强的抗冲击自修复性。     

Outcomes of a 2-year investigation on enhanced biological nutrients removal and trace organics elimination in membrane bioreactor (MBR).

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m3 each. Both configurations included an anaerobic zone ahead of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or post-denitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50 microgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring a low dose of ferric salt ferric salt < 3 mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1 mg of phosphorus was biologically eliminated for 10 mg BOD5 in the influent. The post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.     

Biological nutrient removal in membrane bioreactors: denitrification and phosphorus removal kinetics.

The impact of including membranes for solid liquid separation on the kinetics of nitrogen and phosphorus removal was investigated. To achieve this, a membrane bioreactor (MBR) biological nutrient removal (BNR) activated sludge system was operated. From batch tests on mixed liquor drawn from the MBR BNR system, denitrification and phosphorus removal rates were delineated. Additionally the influence of the high total suspended solids concentrations present in the MBR BNR system and of the limitation of substrate concentrations on the kinetics was investigated. Moreover the ability of activated sludge in this kind of system to denitrify under anoxic conditions with simultaneous phosphate uptake was verified and quantified.The denitrification rates obtained for different mixed liquor (ML) concentrations indicate no effect of ML concentration on the specific denitrification rate. The denitrification took place at a single specific rate (K(2)) with respect to the ordinary heterotrophic organisms (OHOs, i.e. non-PAOs) active mass. Similarly, results have been obtained for the P removal process kinetics: no differences in specific rates were observed for different ML or substrate concentrations. From the P removal batch tests results it seems that the biological phosphorus removal population (PAO) consists of 2 different sets of organisms denitrifying PAO and aerobic PAO.     

Comparative study of MBR and activated sludge in the treatment of paper mill wastewater.

The study was based on a full scale activated sludge plant (AS) compared to a parallel operated pilot membrane bioreactor (MBR) with flat sheets membranes. Both systems received their influent from an anaerobic bioreactor treating paper mill wastewater. MBR produced an effluent of much better quality than AS in terms of suspended solids, containing 1 mg/L or less in 80% of the monitoring time, while the AS effluent contained 12 mg/L. This could save the necessity of further treatment by filtration in the case of MBR. Other effluent quality parameters, such as organic matter (COD and BOD), phosphorus and ammonia nitrogen, did not indicate substantial differences between AS and MBR. Calcium carbonate scaling and formation of a bacterial layer on the membrane caused severe flux reduction. The membrane blockage because of scaling and biofouling proved to be very serious, therefore, it required proper and more complicated maintenance than the AS system. This study leads to the conclusion that in the case of paper mill wastewater, after anaerobic biotreatment, if there is no need for excellent effluent quality in terms of suspended solids, the replacement of the AS by the MBR would not be strongly justified, mainly because of maintenance cost.     

A novel wastewater treatment process: simultaneous nitrification, denitrification and phosphorus removal.

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen concentration (DO, 0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHA), accompanied with phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to less than 0.5 mg/L at the end of the cycle. Ammonia was also oxidised during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis found that the final denitrification product was mainly nitrous oxide (N2O) not N2. Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms rather than denitrifying polyphosphate-accumulating organisms were responsible for the denitrification activity.     

Enhanced nutrient removal MBR system with chemical addition for low effluent TP

A pilot study was conducted to test an membrane bioreactor (MBR) process for combined biological and chemical P removal to achieve a very low effluent total phosphorus (TP) concentration of 0.025 mg P/L. With the data from the pilot test, a simulation study was performed to demonstrate that: (1) the pilot system behaviour (effluent quality, MLSS, etc.) can be modelled accurately with an activated sludge model combined with a chemical precipitation model; and (2) with the calibrated model, simulation scenarios can be performed to further understand the pilot MBR process, and provide information for optimizing design and operation when applied at full-scale. Results from the pilot test indicated that the system could achieve very low effluent TP concentration through biological P removal with a limited chemical addition, and chemical addition to remove P to very low level did not affect other biological processes, i.e., organic and nitrogen removal. Simulation studies indicate that the process behaviour can be modelled accurately with an activated sludge model combined with a chemical precipitation model, and the calibrated model can be used to provide information to optimize system design and operation, e.g., chemical addition control under dynamic loading conditions is important for maintaining biological P removal.     

MBR工艺处理城镇污水处理厂污泥水中试研究

将平板膜组件与传统脱氮除磷工艺相结合,构建了膜生物反应器强化生物脱氮除磷中试系统,并用于处理城镇污水处理厂的污泥系统废水。结果表明,出水CODCr、BOD5、NH3—N、TN和TP的平均浓度分别为70.8 mg/L、8.7 mg/L、15.1 mg/L、29.7 mg/L和0.38 mg/L,达到或接近了《城镇污水处理厂污染物排放标准》(GB 18918—2002)的一级标准。     

生态沟渠对水稻不同生长期降雨径流氮磷的拦截效应研究

农田养分的大量流失已成为农业面源污染的主要来源之一,研究生态沟渠对稻田降雨径流氮磷拦截效应具有重要意义。针对水稻不同生长期内的降雨以及降雨的不同时段下生态沟渠对稻田径流氮磷的动态拦截效应研究缺乏的现状,本文选取太湖西岸何家浜流域典型农田作为研究对象,将该流域的自然排水沟渠改造为生态沟渠。研究了生态沟渠对水稻不同生长期内的3场降雨径流的氮磷去除效果。研究结果表明:(1)在3场不同强度的降雨过程中,生态沟渠对TN(总氮)的平均去除率为31.4%,TP(总磷)的平均去除率为40.8%;(2)生态沟渠对降雨径流不同形态氮磷的去除率大小为NH4+-N(氨氮)PN(颗粒态氮)NO3--N(硝态氮),PP(颗粒态磷)DP(溶解态磷),且PN和PP的去除率随沟渠径流量的增大而呈现下降趋势;(3)生态沟渠底泥总氮、总磷浓度在水稻的生长周期内呈现先增加后降低的趋势,说明生态沟渠具有一定的自净能力,对氮磷的拦截去除具有可持续性。     

Membrane bioreactor (MBR) sludge inoculation in a hybrid process scheme concept to assist overloaded conventional activated sludge (CAS) process operations

This study analyzes the effect of inoculating membrane bioreactor (MBR) sludge in a parallel-operated overloaded conventional activated sludge (CAS) system. Modelling studies that showed the beneficial effect of this inoculation were confirmed though full scale tests. Total nitrogen (TN) removal in the CAS increased and higher nitrate formation rates were achieved. During MBR sludge inoculation, the TN removal in the CAS was proven to be dependent on MBR sludge loading. Special attention was given to the effect of inoculation on sludge quality. The MBR flocs, grown without selection pressure, were clearly distinct from the more compact flocs in the CAS system and also contained more filamentous bacteria. After inoculation the MBR flocs did not evolve into good-settling compact flocs, resulting in a decreasing sludge quality. During high flow conditions the effluent CAS contained more suspended solids. Sludge volume index, however, did not increase. Laboratory tests were held to determine the threshold volume of MBR sludge to be seeded into the CAS reactor. Above 16-30%, supernatant turbidity and scum formation increased markedly.     

A comparison between the theory and reality of full-scale step-feed nutrient removal systems.

Capacity enhancement and volume reduction benefits of step-feeding fully aerobic bioreactors has been well documented. Application of step-feed technology to biological nutrient removal (BNR) systems, particularly those removing nitrogen alone or both nitrogen and phosphorus, is relatively new to the industry. In recent years, a number of full-scale step-feed facilities have been brought into service. This paper reviews nine full-scale step-feed biological nutrient removal systems--both nitrogen removal alone, and nitrogen and phosphorus removal. The objective is to compare the theoretical benefits of such systems with their actual operation. The predicted benefits of reduced bioreactor volume or increased process capacity, reduced energy usage, more robust nitrification performance, and the flexibility to tune (or de-tune) nitrification efficiency were verified in full-scale systems. Equations are also presented that may be used in the prediction of step-feed benefits. There are two primary drivers for considering a step-feed biological reactor system: 1. Reduced bioreactor volume for a defined capacity or performance or increased process capacity given a fixed bioreactor volume. 2. More robust nitrification performance. Full-scale operation of these step-feed nutrient removal systems provides a real world basis for the claimed benefits of step-feed operation. These systems have uniformly shown additional capacity. A number of them have also exhibited more robust performance, especially during storms. Where possible, side-by-side comparisons of full-scale step-feed systems with non-step-feed systems have exhibited greater process reliability and flexibility.