Research and applications of membrane bioreactors in China: Progress and prospect

In the past 15 years, remarkable progress has been achieved on the research and commercial applications of membrane bioreactor (MBR) technology in China. The objective of this paper is then to critically review the research achievements and to specifically present commercial applications of MBR in China. A total of 722 scientific papers published in peer-reviewed journals (600 Chinese papers and 122 English papers) written by Chinese authors from 1991 to 2006 and 254 full-scale MBR plants constructed in China were used as the analysis database. The number of articles published in journals together with organizations involved in MBR research saw a significant increase from 2001 to 2006, and much research progress was made during this period. From geographic distribution of these studies, it was found that the majority of the studies were carried out in North China, East China and North-East China. The research mainly focused on biomass separation MBR (BSMBR) with limited studies on extractive MBR (EMBR) and membrane aeration bioreactor (MABR), etc., and research contents included MBR configuration and type, membrane material and module, membrane fouling and control, characteristics of various wastewater treatment and other aspects like gas removal and microbial fermentation, etc. For commercial applications in China, a total of 254 MBR plants for municipal and industrial wastewater treatment were constructed by a lot of home-grown companies such as Tianjin Motimo Membrane Technology Co., Ltd. and Beijing Origin Water Technology Co., Ltd. and overseas-funded companies like Toray (Japan), Zenon (Canada), Mitsubishi-Rayon (Japan), etc. MBR plants with large treatment capacity will be built in future especially in North China due to the great need of water reclamation and reuse. Potential areas of MBR application include surface/drinking water treatment, gas diffusion and removal, membrane assisted fermentation for biological substance transformation and production, etc.     

Application of MBR for hospital wastewater treatment in China

In China, the number of hospitals has increased to 19,712 in 2008, with the production of hospital wastewater reaching 1.29 × 10⁶ m³/d. Membrane bioreactor (MBR) technology presents a more efficient system at removing pathological microorganism compared with existing wastewater treatment systems. In the past 8 yr, over 50 MBR plants have been successfully built for hospital wastewater treatments, with the capacity ranging from 20 to 2000 m³/d. MBR can effectively save disinfectant consumption (chlorine addition can decrease to 1.0 mg/L), shorten the reaction time (approximately 1.5 min, 2.5-5% of conventional wastewater treatment process), and attain a good effect of inactivation of microorganism. Higher disinfection efficacy is achieved in MBR effluents at lower dose of disinfectant with less disinfection by-products (DBPs). Moreover, when capacity of MBR plants increases from 20 to 1000 m³/d, their operating cost decreases sharply.     

Membrane bioreactor technology for wastewater treatment and reuse

Treatment technology for water recycling encompasses a vast number of options. Membrane processes are regarded as key elements of advanced wastewater reclamation and reuse schemes and are included in a number of prominent schemes world-wide, e.g. for artificial groundwater recharge, indirect potable reuse as well as for industrial process water production. Membrane bioreactors (MBRs) are a promising process combination of activated sludge treatment and membrane filtration for biomass retention. This paper will provide an overview of the status of membrane bioreactor applications in municipal wastewater reclamation and reuse in Europe and will depict their potential role in promoting more sustainable water use patterns. Particular attention will be paid to the impact of MBR technology on emerging pollutants. A case study will be presented on a full-scale MBR plant for municipal wastewater which is operated by Aquafin in Belgium.     

MBR module design and operation

Membrane Bioreactor (MBR) technology is widely accepted today for wastewater treatment providing superior effluent quality, opportunities for water reuse, smaller footprint, and better process control. In the following paper, the development and application of hollow fibre submerged membrane modules in Membrane Bioreactors will be discussed. Early MBR systems used tubular cross flow micro-filtration (MF) or ultra-filtration (UF) membrane modules but the huge energy demand for cross flow technology limited it to heavily polluted niche applications. In the late 80’s the development of submerged membrane technology reduced the energy consumption by using aeration to induce a cross flow and withdrawing purified water by slight vacuum allowing the adoption of MBR technology to more conventional applications. Based upon the m² of membrane area sold/used worldwide, hollow fibre membrane technology is today the most successful submerged MBR technology.     

Comparison of removal of pharmaceuticals in MBR and activated sludge systems

Membrane bioreactors (MBRs) nowadays attract serious attention for the treatment of municipal wastewater, due to recent technical innovations and drastic cost reductions of the employed membranes. Especially the high biomass concentrations and long sludge retention times are favorable for the biodegradation of organic pollutants, resulting in high rate treatment systems. These characteristic features of MBR technology are not merely advantageous for organic matter removal, but also likely promote a higher biodegradation efficiency of refractory organic pollutants. The increasing concern about the potential accumulation of micro-pollutants such as pesticides, pharmaceuticals and personal care products, in the aquatic environment triggered many investigations into their biological degradation or fate in wastewater treatment systems. In this work a short overview is presented on the current knowledge of removal of pharmaceuticals in MBRs compared to their removal in conventional activated sludge treatment system. In general, for slowly degradable pharmaceuticals the removal in MBRs is better due to the relatively long sludge ages, which leads to the development of distinct microbial communities in MBRs compared to activated sludge plants. Nevertheless, from the literature results it could not be concluded that pharmaceutical removal in MBR reactors is better as many other factors have been indicated that may affect biodegradation rates, which are not directly related to the reactor configuration.     

Biological modelling of MBR and impact of primary sedimentation

Within the AMEDEUS European project, a work package is dedicated to biological modelling of Membrane Bioreactors (MBR) processes as well as the impact of a pre-treatment by primary sedimentation on sludge production, sludge characteristics and permeate quality. The supposed interest of this pre-treatment is to decrease sludge production and to improve oxygen transfer by decreasing sludge concentration.Two MBR pilots were operated side by side under the same operating conditions, one fed by screened (1 mm screen) raw municipal wastewater and the other by primary settled raw municipal wastewater. This side by side operation allows a true comparison of the performances and model calibration. In average, screened water was observed to contain 30% more solids than settled water. In this study, the sludge age was fixed at 40 days and then modified to 15 days to calibrate the model on a broad range of operating conditions in order to validate and identify the biological activated sludge model (ASM) limits.With a sludge retention time (SRT) of 15 days, sludge production is less important in the pilot fed by settled water because of better bio-accessibility behaviour of settled water. In comparison with ASM1 default parameter values, calibrated parameters are quite different concerning nitrification and denitrification because of an improvement of oxygen transfer induced by lower floc size distribution (K_OA = 0.25-0.3 g O₂/m³, K_OH = 0.1 g O₂/m³). With a SRT of 40 days, model calibration is not validated and the pilot fed with screened water has a sludge production reduction that is less important than the one of the pilot fed by settled water where accumulation of inert organic matter is observed.     

Membrane bioreactors: Two decades of research and implementation

Membrane bioreactor technology is widely recognised as offering a key option for enhanced wastewater treatment or reuse. This brief review of the technology incorporates four key aspects: (a) market growth, (b) research areas, (c) product supply diversity and specifications, and (d) practitioner needs. Market growth and research topics were assessed through an examination of the appropriate literature and databases, specifically Scopus for the latter. Available MBR membrane products were identified from the Internet and other searches and the specifications verified through contact with the suppliers. Appropriate practitioners were identified through networking and verified as either being active in the operation and maintenance of full-scale MBRs or with an extensive experience of them within the industrial community. Results indicate that the footprint of modules normalised against membrane area changes significantly across the currently commercially-available product range, notwithstanding generically similar construction, such that opportunities for interchanging may be limited. The survey of research papers revealed the most comprehensively researched topic to be at odds with its practical constraints as identified by the practitioners.     

膜生物反应器(MBR)技术及其工程应用探讨

膜生物反应器(MBR)废水处理技术开发始于20世纪90年代,近年来MBR技术的应用在世界上维持着每年高于10%的增长率。随着对水资源利用水平要求的不断提高,我国已经成为世界上MBR工程应用增长最快的国家。特别是2005年以来,处理能力5 000m3/d以上的新建大中型MBR项目均保持大于100%的年增长率。作者介绍了膜生物反应器(MBR)污水处理技术工程应用的主要类型及特点,总结了膜污染的机理、主要影响因素及当前工程上对膜污染的主要控制手段,给出了当前几种典型的生活污水及工业废水MBR工艺的工程应用的技术经济情况,显示出MBR工艺的应用前景。     

Long-term experience with an automatic process control for nitrogen removal in membrane bioreactors

The alternating processes applied in membrane bioreactors for municipal wastewater treatment may be an attractive option to reduce the energy consumptions and optimize carbon and nitrogen removal. However, the knowledge of these systems is often based on empirical results so to discourage the plant operators for its adoption. This paper discusses and compares the empirical evidence coming from two different alternating membrane bioreactors, a demonstration and a full-scale one. The two plants treat two real municipal wastewaters, rather different for both C:N ratio and degree of biodegradability of the influent organics. Nine steady-state runs have been carried out in the demonstration plant, while a one whole year operation has been considered for the full-scale system. Combining the results of the two MBRs, it was found that the alternating process was able to adjust automatically and adequately the aeration of the biological reactor with a nitrogen loading rate in the range 0.05–0.18 kgN m⁻³ d⁻¹ and C:N mass ratios greater than 5–6. As a result, the use of the available carbon source, with concern to the total nitrogen removal, was as low as 0.1 kg of total nitrogen removed per kg of total influent COD. Effluent total nitrogen met the standard for reuse with specific energy consumptions in the range 85–109 gTN_removed per kWh_consumed. Considering the usual loading conditions of the municipal wastewater treatment plants in Italy, membrane bioreactors operating alternating processes may be implemented to increase the nitrogen treatment capacity of existing plants and achieve the standards for reuse.     

MLSS concentration: Still a poorly understood parameter in MBR filterability

In this paper Membrane Bioreactor (MBR) activated sludge is obtained from full scale MBRs and submitted to cross-flow filtration using always the same membrane and operational conditions. Samples are diluted in order to create suspensions with different Mixed Liquor Suspended Solids (MLSS) concentrations. MLSS values varied between 3.6 and 18.3 g/L. Contrary to literature results filterability did not present a continuous increase with decreasing MLSS concentrations. Activated sludge with MLSS concentration exceeding 10 g/L originated dilution samples with worse filterability. The dilution caused an increase of particles in the range 10 to 20 μm and a decrease in the range 30 to 100 μm. The activated sludge samples had non- Newtonian viscosity and Soluble Microbial Products (SMP) concentrations varied between 60 and 11 mg/L. Activated sludge samples with MLSS concentrations exceeding 10 g/L are entrapping particles smaller than 20 μm in the activated sludge bulk that therefore are not contributing to the increase of resistance on the membrane. Activated sludge samples with lower MLSS concentrations do not show the capability to entrap particles. These different behaviours suggest that are optimal MLSS concentration ranges for MBR operation.     

A Review of Membrane Fouling in MBRs: Characteristics and Role of Sludge Cake Formed on Membrane Surfaces

Abstract

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs.     

膜生物反应器在废水处理中的应用

膜生物反应器 (MembraneBio -Reactor ,MBR)是一种传统活性污泥法的改进技术 ,它应用于给水和废水处理的研究发展过程。介绍了膜生物反应器的发展状况、结构形式、优点和应用领域。     

Novel MBRs for the removal of organic priority pollutants from industrial wastewaters: a review

Organic pollutants which are commonly discharged by the 21 industrial groups identified by the US EPA are regulated under the toxic and priority pollutants list. Novel membrane bioreactor (MBR) systems developed in the last two decades, such as the high‐retention MBRs (HR‐MBRs) and extractive MBRs (EMBRs), could be applied in the retention/extraction of targeted organics from point‐source industrial wastewater to meet stringent regulatory requirements. This paper combines previous reviews and studies conducted on the individual novel MBRs to discuss the potential in applying these technologies in the removal of targeted organic pollutants from industrial wastewater by providing a summary of the technologies and discussing the research gaps that currently hamper their commercialization. Future research should focus on long‐term operation with real industrial wastewaters to identify membrane, operational and biodegradation limitations for further optimization. This includes advances in microbiology and the application of novel membranes to boost the biodegradation and removal capabilities of these novel MBR systems. Energy and economic analyses of the MBRs operated at the pilot/demo scale are required to compare their benefits with conventional treatment systems. © 2015 Society of Chemical Industry     

改善污泥性质控制MBR膜污染的研究进展

膜生物反应器(MBR)具有高效,出水水质好的特点,在生活污水和工业废水处理中得到了应用,但膜污染是MBR广泛应用的主要障碍.介绍了污泥混合液中胞外聚合物(EPS)对膜污染的影响,详细总结了改善活性污泥混合液性质的途径,包括投加添加剂、优化运行参数和培养好氧颗粒污泥.提出了投加天然高分子混凝剂改善污泥性质的方法.     

MARKET REPORT: MBR Technology

Membrane bioreactor (MBR) technology is finally beginning to show some of its initial market promise and is attracting the attention of municipal and industrial facilities in search of effective wastewater recycling processes.     

Potential for reuse of high cellulose containing wastewater after membrane bioreactor treatment

It is difficult to adequately treat wastewater with a high cellulose content with the traditional anaerobic and aerobic activated sludge processes. In this study we used microfiltration (MF) and reverse osmosis (RO) membranes combined with an anaerobic or aerobic activated sludge process to treat high cellulose containing wastewater for different hydraulic retention times (HRTs). The potential target applications for reuse of the treated wastewater are also compared. Six bioreactors, which were configured as anaerobic sequencing batch reactor (ANSBR), aerobic sequencing batch reactor (ASBR), aerobic membrane bioreactor (AMBR), AMBR plus RO (AMBR/RO), anaerobic activated sludge plus aerobic MBR (AOMBR), and AOMBR plus RO (AOMBR/RO), was operated in this study. The experiment results showed that, as expected, no effluents from the ASBR or the ANSBR could meet the Taiwan EPA criteria for effluent and wastewater reuse, no matter what the HRT was. However when the HRT was 12 h or more, the effluent from the AMBR and AOMBR processes did meet the criteria for effluent, but still did not meet the treated wastewater reuse criteria , primarily due to the color, total alkalinity, and total dissolved solid parameters. Finally, the effluents from the AMBR/RO and AOMBR/RO processes did meet the Taiwan criteria for both effluent and treated wastewater reuse when the HRT for the AOMBR/RO and AMBR/RO processes was equal to or longer than 12 h and 8 h, respectively. For the HRT of 4 h for both the AOMBR/RO and AMBR/RO process, and an HRT of 8 h for the AOMBR/RO process, neither the effluent criteria nor the treated wastewater reuse criteria were met.     

An integrated wastewater treatment and reuse concept for the Olympic Park 2008, Beijing

In a Sino-German research project, a joined developed sustainable water reclamation concept was developed for different applications of municipal water reuse at the Olympic Green 2008. The concept combines advanced technological processes like membrane bioreactors, specific phosphorus (P) adsorption columns and ultrafiltration (UF) with nature-based treatment processes like wetland and bank filtration mechanisms. The project’s approach is not only to comply with the reclamation requests of the Olympic Green 2008, but also to give an example for better, adapted and energy efficient reuse applications throughout China. The study shows that fixed-bed granular ferric hydroxide (GFH) adsorbers after a membrane bioreactor (MBR) can maintain a total phosphorus (TP) concentration of <0.03 mg L⁻¹. A low P concentration will be necessary to control eutrophication in the artificial Olympic Lake filled with treated wastewater. With an adsorption capacity of approx. 20 mg g⁻¹ d.m. at a corresponding equilibrium concentration of 1 mg L⁻¹ P, GFH reaches long operation times and can be repeatedly regenerated by caustic solutions with an efficiency of 50%. Apart from scenic impoundments, treated wastewater will be used for irrigation and toilet flushing. The latter requires a superior quality that will be delivered by low pressure UF treatment after lake (bank) filtration. A crucial reduction of fouling potential for dead-end UF is expected.     

膜生物反应器中的膜污染及其调控措施

膜生物反应器(MBR)是一项高效的污水处理与回用新技术,膜污染是MBR的主要问题,它限制了MBR的推广和应用.从膜性质、操作条件和活性污泥混合液性质3方面系统论述了MBR中膜污染的影响因素,着重针对各影响因素总结减缓膜污染的调控措施.并指出采取有效、合理的调控措施可有效减缓膜污染,使其在污水处理与回用领域得到更广泛的应...     

A comparative study of tertiary membrane filtration of industrial wastewater treated in a granular and a flocculent sludge SBR

Membrane fouling has been identified by many researchers as an inconvenience for the industrial application of membranes in wastewater treatment plants. Membrane fouling decreases permeability and therefore permeates flow, increasing costs. Although fouling is the result of complex phenomena not completely known, it can be said that fouling takes place by the presence of three different kinds of compounds in the water: suspended solids, colloids and solutes. In this sense, the characteristics of the suspended solid aggregates might be an important aspect in order to diminish the impact of suspended solids on membrane fouling. The main objective of this study was to compare the operation of two similar tertiary membrane filtration units treating the effluent of two different SBRs, respectively: A granular sludge SBR (GSBR) and a membrane flocculent sludge SBR system, at laboratory scale. Two PVDF microfiltration membrane modules were used for tertiary filtration of the effluent treated in the SBRs. Both reactors were used for treating the wastewater generated in a factory of the fish freezing sector. COD of the wastewater was between 700 and 1100 mg/L, total nitrogen concentration was between 110 and 180 mg N/L and total phosphorus ranged around 110 mg P/L. The chemical characteristics of both permeates were similar. Moreover, the presence of either granules or flocs in the tertiary membrane filtration systems did not have an appreciable impact on the membrane filtration. Nevertheless, it was observed that the operation of the membrane on the flocculent system tends to be more instable, showing a major tendency to achieve critical flux.     

Economical evaluation of the fluoride removal by nanofiltration

Economic evaluation was carried out for a plant of fluoride removal by nanofiltration having a capacity of 2400 m³/d (100 m³/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium. The design of this plant was carried out for the predetermined optimized conditions corresponding to a recovery rate of 84%, a fluoride rejection of 97.8% and a pressure pump of 10 bar. The capital cost was estimated to 748,003 € and the calculated operating cost to 0.212 €/m³. These costs were briefly compared to other ones.