Electrocoagulation-integrated hybrid membrane processes for the treatment of tannery wastewater

Three different combinations of treatment techniques, i.e. electrocoagulation combined with microfiltration (EMR), membrane bioreactor (MBR) and electrocoagulation integrated with membrane bioreactor (hybrid MBR, (HMBR)), were analysed and compared for the treatment of tannery wastewater operated for 7 days under the constant trans-membrane pressure of 5 kPa. HMBR was found to be most suitable in performance as well as fouling reduction, with 94 % of chemical oxygen demand (COD) removal, 100 % chromium removal and 8 % improvement in percentage reduction in permeate flux compared to MBR with only 90 % COD removal and 67 % chromium removal. The effect of mixed liquor suspended solids on fouling was also investigated and was found to be insignificant. EMR was capable of elevating the flux but was not as efficient as HMBR and MBR in COD removal. Fouling reduction by HMBR was further confirmed by SEM-EDX and particle size analysis.     

Effect of membrane type and material on performance of a submerged membrane bioreactor

This study evaluated the impact of membrane type and material on filtration performance in a submerged membrane bioreactor (MBR) for municipal wastewater treatment. Three types of microfiltration membranes with similar pore size of 0.1 microm but different materials and types, phase-inversed polytetrafluoroethylene (PTFE), track-etched polycarbonate (PCTE) and track-etched polyester (PETE), were used. Changes in permeability with time for the PCTE and PTFE membranes appeared similarly, whereas the PETE membrane exhibited the most rapid flux decline. Lower TOC in the permeate compared to the supernatant was probably due to a combination of biodegradation by the biofilm (cake layer) developed on the membrane surface and further filtration by cake layer and narrowed pores. The faster permeability decline and higher TOC removal rate of the PETE membrane were attributed to an initial permeate flux higher than an average design flux, which led to a faster rate of fouling and thicker cake layer. Therefore, an MBR should not be operated at a flux higher than the average design flux for a specific type of membrane. A gradual increment of biomass concentration did not significantly affect membrane permeability of each membrane investigated. Dissolved organic carbon fractionation results showed that the composition of each fraction between the supernatant and permeates did not change significantly with time, suggesting that membrane hydrophobicity was not a dominant factor affecting MBR fouling in this study. The organic foulants desorbed from the PCTE membrane contained approximately 60% of hydrophobic fraction, which was probably attributable to the extracellular polymeric substances proteins released from the biomass attached to the membrane. While the total filtration resistance of the PTFE membrane was influenced by a higher surface roughness, those of the PETE and PCTE membranes, which had a similar and lower roughness, were affected by the initial operating flux.     

Simultaneous nitrification and denitrification with anoxic phosphorus uptake in a membrane bioreactor system.

The performance of an innovative membrane bioreactor (MBR) process using anoxic phosphorus uptake with nitrification and denitrification for the treatment of municipal wastewater with respect to operational performance and effluent quality is addressed in this paper. The system was operated at steady-state conditions with a synthetic acetate-based wastewater at a hydraulic retention time (HRT) of 12 hours and on degritted municipal wastewater at a total system HRT of 6 hours. The MBR system was able to achieve 99% biochemical oxygen demand (BOD), chemical oxygen demand (COD), and ammonia-nitrogen (NH4(+)-N); 98% total Kjeldahl nitrogen (TKN); and 97% phosphorus removal, producing effluent BOD, COD, NH4+-N, TKN, nitrate-nitrogen, nitrite-nitrogen, and phosphate-phosphorus of <3, 14, 0.2, 0.26, 5.8, 0.21, and <0.01 mg/L, respectively, at the 6-hour HRT. The comparison of the synthetic and municipal wastewater run is presented in this paper. Steady-state mass balance on municipal wastewater was performed to reveal some key features of the modified MBR system.     

Use of chemical coagulants to control fouling potential for wastewater membrane bioreactor processes.

Chemical coagulation with ferric chloride, alum, and an organic polymer were used to control the fouling potential of mixed liquors for submerged membrane bioreactor (MBR) processes in treating municipal wastewater. Their filterability was evaluated using a submerged hollow fiber ultrafiltration apparatus operated in constant permeate flux mode. The collected transmembrane pressures over filtration time were used to calculate the membrane fouling rates. The results showed that coagulation pretreatment can reduce fouling rates when MBRs were operated above the critical flux. Even though coagulation with the organic polymer formed larger mixed liquor suspended solids particles and had shorter time-to-filtration than those with ferric chloride and alum, the filterability for membrane filtration were similar, indicating that the membrane fouling in MBR systems was mainly controlled by the concentration of smaller colloidal particles.     

A/O和A2/O工艺对膜生物反应器处理焦化废水影响的研究

为提高膜生物反应器对焦化废水的处理效果,采用A/O和A²/O两种工艺的膜生物反应器处理焦化废水,通过对比处理效果、分析膜污染情况,寻求膜生物反应处理焦化废水的最优工艺。实验结果表明：A²/O工艺系统对酚、NH₃-N、COD的去除率分别为99%、90%和95%;A/O工艺系统对酚、NH₃-N和COD的去除率分别为97%、75%和93%。A²/O膜生物反应器系统对焦化废水中NH₃-N的去除效果明显优于A/O膜生物反应器系统,其反硝化率为50%～70%。对膜污染分析表明不同工艺对膜污染的影响不显著,A²/O工艺膜通量衰减59%,A/O工艺膜通量衰减56%。研究表明在膜生物反应器中,A²/O工艺对焦化废水的去除效果要优于A/O工艺。     

MBR净化受污染地表水的自然启动及稳定运行除污染特性

为了考察膜生物反应器(MBR)净化受污染地表水自然启动过程中功能菌群的成熟规律及碱度对MBR去除水中氨氮的影响,通过构建小试规模的MBR,考察了MBR处理受污染地表水的自然启动和稳定运行除污染特性。结果表明,MBR在自然启动过程中不会出现异养菌成熟的标志,系统对进水DOC、UV254和CODMn的平均去除率分别仅为(14.5±5.1)%、(12.6±5.6)%和(31.2±7.4)%,应考虑将其他工艺与MBR联用以提高系统的有机物去除能力。启动23天后,MBR中的亚硝化细菌成熟,NH3-N去除率达到80%以上;启动31 d后,MBR中的硝化细菌成熟,出水NO2--N稳定在0.05mg/L以下。碱度对MBR去除NH3-N效能影响较大,向进水中投加30 mg/L的NaHCO3能使MBR对NH3-N的去除率由(86.1±3.7)%提高至(98.0±1.6)%。在连续曝气、10 L/(m2.h)通量、每10 min反洗15 s运行模式下,MBR的膜污染较为严重,平均TMP增长速率为0.45 kPa/d,需进一步优化相关参数以实现MBR的长期稳定运行。     

A/O和A2/O工艺对膜生物反应器处理焦化废水影响的研究

为提高膜生物反应器对焦化废水的处理效果,采用A/O和A2/O两种工艺的膜生物反应器处理焦化废水,通过对比处理效果、分析膜污染情况,寻求膜生物反应处理焦化废水的最优工艺。实验结果表明：A2/O工艺系统对酚、NH3-N、COD的去除率分别为99%、90%和95%;A/O工艺系统对酚、NH3-N和COD的去除率分别为97%、75%和93%。A2/O膜生物反应器系统对焦化废水中NH3-N的去除效果明显优于A/O膜生物反应器系统,其反硝化率为50%-70%。对膜污染分析表明不同工艺对膜污染的影响不显著,A2/O工艺膜通量衰减59%,A/O工艺膜通量衰减56%。研究表明在膜生物反应器中,A2/O工艺对焦化废水的去除效果要优于A/O工艺。     

吸附-预沉淀MBR工艺处理生活污水及膜污染控制效果

膜污染是限制膜生物反应器（MBR）广泛应用的主要因素之一。针对MBR处理生活污水过程中存在的硝化效果不稳定与膜污染问题,提出了一种新型的MBR系统：通过吸附-预沉淀实现进水中碳氮的分离和单独处理,不仅提高了污染物去除效果,且能够有效控制膜污染。研究结果表明,吸附-预沉淀可以去除进水中约89.7%的有机物,系统出水COD、NH₄⁺-N平均浓度为24 mg/L、0.78 mg/L,去除率分别为95.9%和98.1%。MBR中碳氮比的降低和硝化细菌比例的增加大大降低了MBR内MLSS、EPS和SMP含量,平均浓度分别为5 185 mg/L、41 mg/g MLSS和2.62 mg/g MLSS。在膜通量为4 L/（m²·h）条件下,TMP可稳定保持在20 kPa左右。通过吸附-预沉淀过程可有效控制MBR中的膜污染。     

膜蒸馏处理糖精钠生产废水

采用直接接触式膜蒸馏(DCMD)工艺处理糖精钠生产废水。分析了经过活性炭吸附预处理前后,膜蒸馏连续循环运行的效果。实验结果表明,未经预处理的废水在膜蒸馏过程中,废水中所含有机物不仅导致膜材料的润湿,引起产水电导率升高及膜孔润湿,促进盐晶体在膜表面附着,使产水通量下降。经吸附预处理后,膜蒸馏过程中产水通量介于10.40～11.24 kg/(m2.h)。吸附预处理能有效减缓产水通量的衰减,提高产水水质。废水经过活性炭预处理后进行膜蒸馏浓缩处理,当浓缩倍数达到5倍时,通量保持在10.55 kg/(m2.h)左右;产水水质稳定,截留率在99.5%以上。研究结果表明,吸附-膜蒸馏工艺可以应用于糖精钠生产废水的回用处理,有明显的应用前景。     

混凝沉淀前处理对丙烯酸丁酯废水陶瓷膜过滤膜污染的影响

采用混凝沉淀-双层滤料过滤-陶瓷膜过滤组合工艺去除丙烯酸丁酯废水中浊度物质。结果表明,废水pH值、混凝药剂投加量、混凝沉淀水力条件不仅对丙烯酸丁酯废水混凝沉淀出水和双层滤料过滤单元出水浊度具有重要影响,而且对后续陶瓷膜过滤单元膜污染均具有重要影响。双层滤料过滤出水浊度与陶瓷膜污染阻力具有明显的正相关关系,双层滤料过滤出水浊度越高,陶瓷膜污染阻力越大。废水pH在7.0~10.0范围内、混凝药剂PAC或PAM投加过量、废水流量过高都会造成双层滤料过滤出水浊度偏高,导致陶瓷膜污染严重。     

Design and startup of a membrane-biological-reactor system at a Ford-engine plant for treating oily wastewater.

A wastewater-treatment facility at Ford (Dearborn, Michigan) was recently upgraded from chemical de-emulsification to ultrafiltration (UF) followed by a membrane-biological reactor (MBR). This paper describes the design, startup, and initial operational performance of the facility. Primary findings are as follows: (1) the MBR proved resilient; (2) the MBR removed approximately 90% of chemical-oxygen demand (COD) after primary UF; (3) the removal of total Kjeldahl nitrogen by MBR appeared to be more sensitive to operating conditions than COD removal; (4) nitrification and denitrification were established in one month; (5) the MBR removed oil and grease and phenolics to below detection levels consistently, in contrast to widely fluctuating concentrations in the past; (6) permeate fluxes of the primary and MBR UF were adversely affected by inadvertent use of a silicone-based defoamer; and (7) zinc concentrations in the effluent increased, which might have been a result of ethylenediaminetetraacetic acid used in membrane washing solutions and/or might have been within typical concentration ranges.     

生物制剂对MBR中无纺布膜组件过滤性能的影响

研究了生物制剂对浸渍式膜生物反应器(submerged membrane bioreactor,SMBR)中聚丙烯无纺布(non-wov-en fabric,NWF)膜组件过滤性能的影响。结果表明,能减少膜组件表面附着污泥胞外聚合物(extra-cellular polymeric sub-stances,EPS)的含量及污泥的沉积,减缓膜通量的衰减速率和膜污染,无纺布膜组件的过滤性能得到明显改善,表现出一定的耐污染性。生物制剂能改善污泥的沉降性能,有效防止污泥膨胀;对MBR的COD去除率基本没有影响,但略微增大了处理水的浊度。     

水力停留时间对膜生物反应器复合工艺污水处理特性的影响

开发了厌氧-多级好氧/缺氧-膜生物反应器复合工艺,在不同水力停留时间(HRT)下,考察了系统对污染物去除效果及其膜污染的特性.结果表明,在试验选定的HRT范围内,系统对TN和TP的去除率随着HRT的降低而升高,当HRT为8.70、6.96、4.97 h时,系统对TN和TP的平均去除率分别为73.15%、79.76%、81.98%和67.79%、80.99%、92.16%.但是,较低HRT条件下膜通量较高,会加剧膜污染进程.解决这一问题的措施是增加膜组件个数,从而在不提高膜通量的情况下使系统保持较低的HRT,保证系统高效稳定的污染物去除效果.     

改性PES膜在MBR中膜阻力分析及膜污染机理研究

以聚醚砜(PES)、醋酸纤维素(CA)和纳米二氧化钛(TiO2)为膜材料,采用L-S相转化法制备共混改性PES膜。在24℃、0.2 MPa的操作条件下,制得的PES膜纯水通量为300 L/(m2.h)左右,CA改性PES膜为660 L/(m2.h)左右,TiO2改性PES膜为840 L/(m2.h)左右。通过膜生物反应器中膜阻力的测定,表明膜污染主要由浓差极化层及凝胶层引起的;通过活性污泥对膜污染机理的研究,判断出污泥的过滤过程基本符合沉积过滤定律。在MBR中运行时,改性PES膜稳定通量高于未改性膜,总阻力低于未改性膜;TiO2改性膜稳定通量高于CA改性膜,总阻力低于CA改性膜;通过扫描电镜分析,改性PES膜沉积层的厚度均比未改性膜薄,TiO2改性膜沉积层厚度小于CA改性膜,表明改性膜的抗污染性能提高了,TiO改性膜抗污染性能更优。     

Treatment of municipal wastewater by membrane bioreactor: a pilot study

The operational performance of a submerged hollow fibre Membrane Bio-Reactor (MBR) for treatment of municipal wastewater on pilot scale was investigated. The experimental results indicated that the removal efficiency for SS, COD, NH₄-N, turbidity, bacterium, iron (Fe²⁺) and Manganese (Mn²⁺) was 100%, 94.5%, 98.3%, 99.7%, lg6, 99%, 92.3%, respectively. The water quality of the effluent was quite good. The reclaimed water could be reused either directly or indirectly for municipal or industrial purposes. The MBR had a strong ability to resist loading shock and DO was a crucial factor to membrane fouling.     

Aerobic and anaerobic membrane bioreactors for municipal wastewater treatment.

An aerobic bioreactor and an anaerobic bioreactor, each coupled with a microfiltration membrane filter (MBR), were operated at different hydraulic retention times (HRTs) with primary effluent from the City of Elmhurst, Illinois, municipal-wastewater-treatment plant. The soluble chemical oxygen demand (COD) removal performance of the anaerobic MBR system was similar to that of the aerobic MBR under the same operational conditions, without the added cost of aeration. The results indicated that the solids deposition rate on the membrane surface was lower in the case of anaerobic MBR compared to the aerobic MBR, indicating possible lower loss in water-flux rates. This research found that an anaerobic MBR is a feasible and economical option for municipal-wastewater-treatment plants seeking COD removal by a biological process followed by a separate nitrification and denitrification system.     

气-水联合反冲洗膜污染防治技术研究

采用气水联合反冲洗技术,考察了气水比(Qg/Ql)、反冲洗周期及其对膜污染的防治效果。结果表明,气水联合反冲洗较单独气或水反冲洗效果好;在过滤周期20min,反冲洗时间1min,气水比1.5时,气水联合反冲洗能够恢复膜通量到膜清水通量的80%以上。此法可大幅度清除沉积在膜表面的泥饼层,恢复膜通量,维持膜过滤性能的稳定,是一种较为有效的膜污染防治技术。     

MFC-MBR耦合系统运行效果

膜生物反应器(MBR)是一种高效的污水处理工艺,而微生物燃料电池(MFC)能有效降解污泥中的胞外生物有机质(EBOM)并回收电能.将MFC与MBR联用,建立了一套能够有效抑制膜污染同时回收电能的新系统——MFC-MBR耦合系统,MBR的剩余污泥经MFC处理后回流.以传统MBR为对照,对耦合系统中污水处理效果、膜污染情况和污泥混合液的性质进行研究.研究表明,耦合系统的污水处理效果没有明显恶化,COD去除率为94％,NH4+-N的去除率为92％.耦合系统能够有效减缓膜污染的发生,清洗周期延长了28％.污泥混合液的MLVSS/MLSS稳定在80％ ～ 88％,系统内几乎没有无机颗粒积累.松散结合态胞外聚合物(LB-EPS)降低了48％,使污泥混合液性质得到改善.较低的污泥比阻(2.69×1012m/kg)和标准化毛细吸水时间(1.67 s·L/g MLSS),证明耦合系统污泥混合液脱水性能提高了.     

Prediction of membrane fouling using artificial neural networks for wastewater treated by membrane bioreactor technologies: bottlenecks and possibilities

Membrane fouling is a major concern for the optimization of membrane bioreactor (MBR) technologies. Numerous studies have been led in the field of membrane fouling control in order to assess with precision the fouling mechanisms which affect membrane resistance to filtration, such as the wastewater characteristics, the mixed liquor constituents, or the operational conditions, for example. Worldwide applications of MBRs in wastewater treatment plants treating all kinds of influents require new methods to predict membrane fouling and thus optimize operating MBRs. That is why new models capable of simulating membrane fouling phenomenon were progressively developed, using mainly a mathematical or numerical approach. Faced with the limits of such models, artificial neural networks (ANNs) were progressively considered to predict membrane fouling in MBRs and showed great potential. This review summarizes fouling control methods used in MBRs and models built in order to predict membrane fouling. A critical study of the application of ANNs in the prediction of membrane fouling in MBRs was carried out with the aim of presenting the bottlenecks associated with this method and the possibilities for further investigation on the subject.     

Parameters governing permeate flux in an anaerobic membrane bioreactor treating low-strength municipal wastewaters: a literature review.

The objective of this review was to conduct a comprehensive literature survey to identify the parameters that govern the permeate flux in an anaerobic membrane bioreactor (AnMBR) treating municipal wastewater. Based on the survey, research to date indicates that the optimal membrane system for an AnMBR consists of an organic, hydrophilic, and negatively charged membrane with a pore size of approximately 0.1 microm. The use of both external and submerged membrane configurations shows promise. The operating parameters that affect permeate flux in an external membrane system are transmembrane pressure (TMP) and cross-flow velocity. The operating parameters that affect permeate flux in a submerged membrane system are TMP, sparging intensity, and duration of the relaxation period. Both cross-flow velocity and sparging intensity impart a significant amount of shear force on the biomass in an AnMBR. High shear forces can reduce the microbial activity in an AnMBR. In addition, high shear forces can reduce the size of the biosolids in the mixed liquor and increase the release of soluble microbial products. In this respect, external and submerged membrane systems are expected to perform differently because the magnitude of the shear forces to which the biomass is exposed in an external membrane system is significantly greater than that in a submerged system. The size of the biosolid particles and concentration of soluble microbial products in the mixed liquor affect permeate flux. Higher concentrations of soluble microbial products may be present in the mixed liquor when an AnMBR is operated at relatively low operating temperatures. Aerobic polishing following anaerobic treatment can potentially significantly reduce the concentration of some components of the soluble microbial products in the mixed liquor. It is not possible to remove the foulant layer on an organic membrane with caustic cleaning alone. Acidic cleaning or acidic cleaning followed by caustic cleaning is required to remove the foulant layer. This suggests that both biological/organic and inorganic material contribute to membrane fouling.