Peak flux performance and microbial removal by selected membrane bioreactor systems

A pilot study was conducted over a period of 18 months at the Point Loma Wastewater Treatment Plant (PLWWTP) in San Diego, CA to evaluate the operational and water quality performance of six selected membrane bioreactor (MBR) systems at average and peak flux operation. Each of these systems was operated at peak flux for 4 h a day for six consecutive days to assess peak flux performance. Virus seeding studies were also conducted during peak flux operation to assess the capability of these systems to reject MS-2 coliphage. When operating at steady state, these MBR systems achieved an effluent BOD concentration of <2 mg/L and a turbidity of <0.1 NTU. Peak flux for the MBR systems ranged from 56 to 76 L/m²/h (liters per square meter per hour) with peaking factors in the range of 1.5-3.2. When switching from average to peak flux operation, a reversible drop of 22-32% in temperature-corrected permeability was observed for all submerged MBR systems. The percent drop in permeability increased as MLSS concentration in the membrane tank increased from 11,100 mg/L to 15,300 mg/L and was observed to be highest for the system operating at highest MLSS concentration. Such trends were not observed with an external MBR system. Each MBR system was able to sustain a 4-h-a-day peak flow for six consecutive days with only moderate membrane fouling. The membrane fouling was quantified by measuring the drop in temperature-corrected permeability. This drop ranged from 13 to 33% over six days for different submerged MBR systems. The MBR systems achieved microbial removal in the range of 5.8-6.9 logs for total coliform bacteria, >5.5 to >6.0 logs for fecal coliform bacteria and 2.6 to >3.4 logs for indigenous MS-2 coliphages. When operating at peak flux, seeded MS-2 coliphage removal ranged from 1.0 to 4.4 logs, respectively. The higher log removal values (LRVs) for indigenous MS-2 coliphage among different MBR systems were probably the result of particle association of indigenous coliphage. Differences in membrane pore size (0.04-0.2 μm) amongst the MBR systems evaluated did not have a substantial impact on indigenous MS-2 coliphage removal, but seeded MS-2 coliphage removal varied among the different MBR systems.     

Hydrogen-dependent denitrification of water in an anaerobic submerged membrane bioreactor coupled with a novel hydrogen delivery system

Hydrogen-dependent denitrification has gained significant attention due to its potential economic advantage over heterotrophic denitrification. However, effective hydrogen delivery and biomass retention under anaerobic conditions are significant challenges to implementation of this process. An innovative hydrogenotrophic denitrification system, that addresses these challenges, consisting of an anaerobic submerged membrane bioreactor (MBR) and a novel hydrogen delivery unit, was evaluated for removal of nitrate from a synthetic groundwater feed. The hydrogen delivery unit was designed to release hydrogen-supersaturated water to the reactor and was efficient in hydrogen delivery, providing complete mass transfer. The anaerobic submerged MBR was successful in both reducing nitrate from 25 mg NO(3)-Nl(-1) to below detection and separating biomass from treated water to produce effluent free of suspended solids. Nitrogen gas produced during denitrification was internally recycled to effectively achieve membrane scouring and reactor mixing. The total organic carbon was similar to that of the incoming feed water, averaging approximately 6 mgl(-1).     

Indigenous somatic coliphage removal from a real municipal wastewater by a submerged membrane bioreactor

The membrane bioreactor (MBR) features many advantages, such as its excellent effluent quality and compactness. Moreover, the MBR is well known for its disinfectant capacity. This paper investigates virus removal performance for municipal wastewater using a submerged MBR and the operational conditions affecting the virus removal using indigenous somatic coliphages (SC) as an indicator for viruses. The results revealed that the municipal wastewater acquired by the Qinghe Municipal Wastewater Treatment Plant, Beijing, contained an SC concentration of (2.81 ± 1.51) × 10⁴ PFU ml⁻¹, which varies seasonally due to spontaneous decay. In the MBR system, the biomass process dominates SC removal. Membrane rejection is an essential supplement of biomass process for SC removal. In this paper, the relative contributions of biomass process and membrane rejection during the start-up and steady operational periods are discussed in detail. The major factors affecting SC removal are biodegradation, membrane pore size, and gel layer formation on the membrane. During long-term experiments, it was demonstrated that high inoculated sludge concentration, long hydraulic retention time, moderate fouling layer, and non-frequent chemical cleaning are favorable for high SC removal in MBR systems.     

Polyphosphate buffering by biomass with different phosphorus contents

Polyphosphate buffering is a novel application of enhanced biological phosphorus (P) removal (EBPR) for P-deficient wastewaters with influent organic load variability. This study investigated the effect of biomass P content on polyphosphate buffering using a membrane bioreactor (MBR) and conventional bioreactor (CBR). Increasing the biomass P content increased polyphosphate buffering and the COD removal capacity, but at high P content (i.e. 20% P/TSS) the effluent P levels increased and a smaller fraction of available P was used for buffering. The MBR produced lower total effluent TSS levels and lower P levels than the CBR at both medium biomass P content (i.e. 12% P/TSS) and at low P content (i.e. 5% P/TSS) when the COD removal capacity was not exceeded. At high biomass P content, the MBR and CBR produced elevated effluent P levels. This study showed that the MBR does not make polyphosphate buffering feasible at high P content.     

新型膜生物反应器的设计及其性能研究

结合无泡曝气原理和气体反冲洗方法,设计了一种新型的一体式膜生物反应器(MBR),并将其与传统MBR进行了对比.结果表明,当处理黄麻生物脱胶废水时,在相同的运行条件下,新型MBR中混合液的DO含量明显高于传统MBR,对COD的去除效果也明显好于传统MBR;另外,与传统MBR相比,新型MBR具有膜过滤压力小、膜污染轻、能耗低等优点.     

Pharmaceutical wastewater treatment using membrane bioreactor‐ozonation system

The aim of this study was to evaluate the potential use of ozonation with pharmaceutical compounds on membrane bioreactor (MBR). The result has shown that high concentrations of pharmaceutical contaminants have caused destruction of cell wall, thereby reducing mixed liquor suspended solids (MLSS). It also resulted in high amounts of biopolymers in the presence of non‐biodegradable pharmaceutical compound in MBR. As a result, biological removal decreased and membrane fouling happened. Ozonation treatment reached a chemical Oxygen Demand (COD) removal of 99.9% and caused better effluent quality. The MBR‐ozonation process could achieve an acetaminophen and fluoxetine removal of around 98.4 and 57.83%, respectively.     

The influence of aeration intensity on predation and EPS production in membrane bioreactors

Shear, in the form of vigorous aeration, is used to control fouling in membrane bioreactor (MBR) systems. However, shear also influences the physicochemical and biological properties of MBR biomass. The current study examines the relationship between the aeration intensity and extracellular polymeric substance (EPS) production in MBRs. Two identical submerged MBRs were operated in parallel but the aeration rate was three times greater in one of the MBRs. The concentrations of floc-associated and soluble EPS were monitored for the duration of the experiment. Microscopic images and floc-size measurements were also collected regularly. The membrane fouling potential of the biomass was quantified using the flux-step method. Increased aeration did not have a direct effect on soluble or floc-associated EPS production in the microfiltration MBRs. However, aeration intensity had a significant effect on predatory organisms. Large aquatic earthworms, Aeolosoma hemprichi, proliferated under lower shear conditions but were never observed in the high shear reactor. Predation by A. hemprichi resulted in increased floc-associated and soluble EPS production. Thus, the mixing conditions in the low shear MBR indirectly resulted in increased soluble EPS concentrations and higher fouling potential. This research suggests that predation can have a significant impact on the production rates of floc-associated and soluble EPS - key parameters driving membrane fouling in MBRs.     

活性污泥与悬浮填料膜生物反应器的膜污染比较

对活性污泥-膜生物反应器与悬浮填料-膜生物反应器的膜污染情况进行对比，结果表明两种反应器的除污效果无明显差别，但悬浮填料-膜生物反应器的膜污染情况较为严重。通过测定混合液的颗粒粒径分布及其比阻，说明了导致悬浮填料-膜生物反应器膜污染严重的原因是混合液中能堵塞膜孔的微小颗粒含量较高及混合液过滤性能较差。采取增大曝气强度和投加絮凝剂等措施可改善悬浮填料-膜生物反应器的膜污染程度。     

淹没式复合型MBR处理城市生活污水的效能研究

为了缓解缺水压力，在传统膜生物反应器（CMBR）的基础上开发出了一种新型城市污水处理回用工艺——淹没式复合型膜生物反应器（SHMBR），并考察了对城市生活污水的处理效果。试验结果表明，SHMBR可以在CMBR的基础上进一步提高生物量，并明显改善了对有机物和NH4^＋-N的去除效果。试验中对TN、TP的去除效果没有提高，原因可能是生物膜的厚度不够，没有在生物膜内部形成厌氧微环境。另外，SHMBR的除磷效果没有增强还可能与生物膜的SRT较长以及聚磷菌主要生活在活性污泥中有关。     

Biological black water treatment combined with membrane separation

Separate treatment of black (toilet) water offers the possibility to recover energy and nutrients. In this study three combinations of biological treatment and membrane filtration were compared for their biological and membrane performance and nutrient conservation: a UASB followed by effluent membrane filtration, an anaerobic MBR and an aerobic MBR. Methane production in the anaerobic systems was lower than expected. Sludge production was highest in the aerobic MBR, followed by the anaerobic MBR and the UASB-membrane system. The level of nutrient conservation in the effluent was high in all three treatment systems, which is beneficial for their recovery from the effluent. Membrane treatment guaranteed an effluent which is free of suspended and colloidal matter. However, the concentration of soluble COD in the effluent still was relatively high and this may seriously hamper subsequent nutrient recovery by physical-chemical processes. The membrane filtration behaviour of the three systems was very different, and seemed to be dominated by the concentration of colloidals in the membrane feed. In general, membrane fouling was the lowest in the aerobic MBR, followed by the membranes used for UASB effluent filtration and the anaerobic MBR.     

Effect of intermittent aeration on the microbial community structure of activated sludge in a submerged membrane bioreactor

Low removal rate for total nitrogen (TN) is the main limitation of a membrane bioreactor (MBR). The effects of intermittent aeration on the removal of TN and the microbial community structure of activated sludge from a submerged membrane bioreactor (SMBR) operating at three different aeration on/off times (run 1, continuous aeration; run 2, 60/60 min aeration on/off time; and run 3, 60/75 min aeration on/off time) were studied. The results showed that the removal rates for TN under different operation conditions were 26.2% (run 1), 59.5% (run 2) and 70.7% (run 3), respectively, and significant improvements were achieved. Monounsaturated phospholipid fatty acids (PLFAs) and saturated PLFAs were dominant PLFA types in activated sludge, followed by branched PLFAs; cyclopropane fatty acid were relatively small in amount. The highest ratio of the characteristic fatty acid representing the abundance of bacteria in activated sludge was found in run 2. Aerobic prokaryotes were the predominant groups under all three operation conditions, followed by the anaerobic bacteria and the Gram‐positive bacteria group; sulphate‐reducing bacteria (SRB) and other anaerobic bacteria occupied the lowest proportion. Intermittent aeration can be used as a possible means to improve the treatment performance in an MBR.     

BSM-MBR: a benchmark simulation model to compare control and operational strategies for membrane bioreactors

A benchmark simulation model for membrane bioreactors (BSM-MBR) was developed to evaluate operational and control strategies in terms of effluent quality and operational costs. The configuration of the existing BSM1 for conventional wastewater treatment plants was adapted using reactor volumes, pumped sludge flows and membrane filtration for the water-sludge separation. The BSM1 performance criteria were extended for an MBR taking into account additional pumping requirements for permeate production and aeration requirements for membrane fouling prevention. To incorporate the effects of elevated sludge concentrations on aeration efficiency and costs a dedicated aeration model was adopted. Steady-state and dynamic simulations revealed BSM-MBR, as expected, to out-perform BSM1 for effluent quality, mainly due to complete retention of solids and improved ammonium removal from extensive aeration combined with higher biomass levels. However, this was at the expense of significantly higher operational costs. A comparison with three large-scale MBRs showed BSM-MBR energy costs to be realistic. The membrane aeration costs for the open loop simulations were rather high, attributed to non-optimization of BSM-MBR. As proof of concept two closed loop simulations were run to demonstrate the usefulness of BSM-MBR for identifying control strategies to lower operational costs without compromising effluent quality.     

Baffled membrane bioreactor (BMBR) for efficient nutrient removal from municipal wastewater

Submerged membrane bioreactors (MBRs) are now widely used for various types of wastewater treatment. One drawback of submerged MBRs is the difficulty in removing nitrogen because intensive aeration is usually carried out in the tank and the MBRs must therefore be operated under aerobic conditions. In this study, the feasibility of treating municipal wastewater by a baffled membrane bioreactor (BMBR), particularly in terms of nitrogen removal, was examined. Simultaneous nitrification/denitrification in a single and small reaction tank was possible by inserting baffles into a normal submerged MBR as long as wastewater was fed in the appropriate way. To examine the applicability of the BMBR, pilot-scale experiments were carried out using real municipal wastewater. Although neither external carbon addition nor mixed liquor circulation was carried out in the operation of the BMBR, average removal rates of total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) reached 85%, 97% and 77%, respectively, with the hydraulic retention time (HRT) of 4.7h. Permeability of the membrane could be maintained at a high level throughout the operation. It was found that denitrification was the limiting step in removal of nitrogen in the BMBR in this study. Various types of monitoring carried out in the BMBR also demonstrated the possibility of further improvements in its performance.     

Drinking water denitrification by a membrane bio-reactor

Drinking water denitrification performance of a bench scale membrane bio-reactor (MBR) was investigated as function of hydraulic and biological parameters. The reactor was a stirred tank and operated both in batch and continuous mode. The mixed denitrifying culture used in the batch mode tests was derived from the mixed liquor of a wastewater treatment plant in Erzincan province in Turkey. But the culture used in the continuous mode tests was that obtained from the batch mode tests at the end of the denitrification process. The nitrate contaminated water treated was separated from the mixed liquor suspended solids (MLSS) containing active mixed denitrifying culture and other organic substances by a membrane of 0.2 microm average pore diameter. The results indicated that the use of a membrane module eliminated the need for additional post treatment processes for the removal of MLSS from the product water. Concentration of nitrite and that of MLSS in the membrane effluent was below the detectable limits. Optimum carbon to nitrogen (C/N) ratio was found to be 2.2 in batch mode tests. Depending on the process conditions, it was possible to obtain denitrification capacities based on the reactor effluent and membrane effluent up to 0.18kgm(-3)day(-1) and 2.44 kg m(-2) day2(-1) NO(3-)-N, respectively. The variation of the removal capacity with reactor dilution rate and membrane permeate flux was the same for two different degrees of [MLSS]0/[NO3-N]0 (mass) ratios of 25.15 and 49.33. The present MBR was able to produce a drinking water with NO(3-)-N concentration of less than 4 ppm from a water with NO3-N contamination level of 367 ppm equivalent to a NO(3-)-N load of 0.310 kgm(-3) day(-1). The results showed that MBR system used was able to offer NO(3-)-N removals of up to 98.5%. It was found that the membrane limiting permeate flux increased with increasing MLSS concentration.     

射流曝气MBR工艺处理城市污水的研究

传统膜生物反应器(MBR)的能耗较大、运行费用较高,为此开发了射流曝气MBR工艺。采用其处理某开发区污水,在进水COD为60～300 mg/L、氨氮为3～30 mg/L、总磷为0.8～5 mg/L、水力停留时间为2 h的条件下,出水COD、氨氮、总磷的平均值分别为25、1.27、1.66 mg/L,平均去除率分别为84%、93%、46%。反应器采用射流曝气方式,提高了氧的转移效率,大幅降低了能耗,与常规MBR相比则节能达70%。近一年的运行表明,射流曝气对膜丝的正常工作没有任何影响,其清洗周期保持不变。     

Post-treatment of upflow anaerobic sludge blanket effluent by combining the membrane filtration process: fouling control by intermittent permeation and air sparging

In this study, the membrane filtration process was proposed as a post-treatment process to treat the upflow anaerobic sludge blanket (UASB) effluent. The flat-sheet membrane modules were submerged into the UASB reactor to retain the suspended solids in the UASB effluent under intermittent permeation and air sparging conditions. The results indicated that intermittent permeation enhanced the sustainability of the submerged membrane and an idle time of 4 min with a 10-min filtration was optimal for reducing membrane fouling under the experimental conditions. Air sparging could also alleviate membrane fouling, and the lowest transmembrane pressure (TMP) change rate (dTMP/d t ) was achieved at the moderate aeration rate of 2 L/min. It appears to be effective to alleviate membrane fouling and achieve high effluent production at a flux of 25 L/m² h and an idle time of 4 min with a 10-min filtration considering the energy consumption.     

Feasibility study of moving-fiber biofilm membrane bioreactor for wastewater treatment: process control

Non-biodegradable solid wastes of non-intact membrane fibres/flatsheets and modules disposed from membrane bioreactor (MBR) plants are in a great concern for environmental impact. Estimated cumulative amount of the module solid wastes from European countries in the next five years should be larger than 1000 tons in which a proper management strategy and reuse for the disposed solid waste are urgently required. This article was aimed to propose an alternative to make uses of the non-intact membrane fibres for the aerobic biofilm supports and to study the feasibility on process operation of novel moving-fiber biofilm MBR. A system of moving-fiber biofilm membrane bioreactor was designed and evaluated experimentally, including an upflow anaerobic sludge reactor, an aerobic moving-fiber biofilm reactor, and a submerged membrane filtration unit. Start-up method and operating conditions to control the biofilms growing on the moving fibers were investigated. Organic removal rates, optimum operating conditions for the system, and membrane fouling rates at various membrane aeration rates and permeate fluxes were monitored to evaluate the performance of the proposed BF-MBR process.     

Impact of solids residence time on biological nutrient removal performance of membrane bioreactor

Impact of long solids residence times (SRTs) on nutrient removal was investigated using a submerged plate-frame membrane bioreactor with anaerobic and anoxic tanks. The system was operated at 10, 25, 50 and 75 days SRTs with hydraulic retention times (HRTs) of 2 h each for the anaerobic and anoxic tanks and 8 h for the oxic tank. Recirculation of oxic tank mixed liquor into the anaerobic tank and permeate into the anoxic tank were fixed at 100% each of the influent flow. For all SRTs, percent removals of soluble chemical oxygen demand were more than 93% and nitrification was more than 98.5% but total nitrogen percent removal seemed to peak at 81% at 50 days SRT while total phosphorus (TP) percent removal showed a deterioration from approximately 80% at 50 days SRT to 60% at 75 days SRT. Before calibrating the Biowin^® model to the experimental data, a sensitivity analysis of the model was conducted which indicated that heterotrophic anoxic yield, anaerobic hydrolysis factors of heterotrophs, heterotrophic hydrolysis, oxic endogenous decay rate for heterotrophs and oxic endogenous decay rate of PAOs had the most impact on predicted effluent TP concentration. The final values of kinetic parameters obtained in the calibration seemed to imply that nitrogen and phosphorus removal increased with SRT due to an increase in anoxic and anaerobic hydrolysis factors up to 50 days SRT but beyond that removal of phosphorus deteriorated due to high oxic endogenous decay rates. This indirectly imply that the decrease in phosphorus removal at 75 days SRT may be due to an increase in lysis of microbial cells at high SRTs along with the low food/microorganisms ratio as a result of high suspended solids in the oxic tank. Several polynomial correlations relating the various calibrated kinetic parameters with SRTs were derived. The Biowin^® model and the kinetic parameters predicted by the polynomial correlations were verified and found to predict well the effluent water quality of the MBR at 35 days SRT.     

Fate of antibiotics in activated sludge followed by ultrafiltration (CAS-UF) and in a membrane bioreactor (MBR)

The fates of several macrolide, sulphonamide, and trimethoprim antibiotics contained in the raw sewage of the Tel-Aviv wastewater treatment plant (WWTP) were investigated after the sewage was treated using either a full-scale conventional activated sludge (CAS) system coupled with a subsequent ultrafiltration (UF) step or a pilot membrane bioreactor (MBR) system. Antibiotics removal in the MBR system, once it achieved stable operation, was 15-42% higher than that of the CAS system. This advantage was reduced to a maximum of 20% when a UF was added to the CAS. It was hypothesized that the contribution of membrane separation (in both systems) to antibiotics removal was due either to sorption to biomass (rather than improvement in biodegradation) or to enmeshment in the membrane biofilm (since UF membrane pores are significantly larger than the contaminant molecules). Batch experiments with MBR biomass showed a markedly high potential for sorption of the tested antibiotics onto the biomass. Moreover, methanol extraction of MBR biomass released significant amounts of sorbed antibiotics. This finding implies that more attention must be devoted to the management of excess sludge.     

悬浮填料生物系统处理炼油废水试验

为了提高A／O工艺的脱氮效果，采用悬浮填料生物系统来处理炼油废水。试验结果表明，当装填30％反应器容积的悬浮填料、进水NH3-N和COD分别为54～75mg／L和420～570mg／L、水力停留时间为24h时，对NH3-N和COD的去除率分别达96％和88％以上，出水水质达到了排放标准。此外，在悬浮填料曝气池中还发生了同步硝化反硝化现象。