Operation of Membrane Bioreactor with Powdered Activated Carbon Addition

Abstract

The effect of powdered activated carbon (PAC) addition to the activated sludge (AS) in a membrane bioreactor (MBR) has been investigated. The long term nature of the tests allowed the PAC to gradually incorporate into the biofloc forming biologically activated carbon (BAC). One series of tests involved 4 bench scale (2 L) MBRs operated at sludge retention times (SRTs) of 30 days with PAC inventories of 0, 1, 3 and 5 g/L and steady state biomass concentrations of 12.0±1.0 g/L. The characteristics of the mixed liquors (MLSS) from the 4 reactors were compared. Short term filtration tests, including measurement of specific cake resistance (SCR), flux decline profile, and irreversible fouling resistance in an unstirred cell and “sustainable” flux (by monitoring transmembrane pressure (TMP) rise) in a crossflow cell all showed better filtration performance for the MLSS with BAC compared with the AS alone. In terms of SCR and flux decline profile the 1 g/L PAC addition performed best, but in terms of minimizing irreversible membrane fouling and maximizing “sustainable” flux the 5 g/L PAC was best. All 4 systems showed lower total organic carbon (TOC) in the permeate compared to the bioreactors, but the lowest permeate TOC (and the best removal) was for the highest PAC loading.

The benefit of PAC addition was confirmed in a second series of tests with two 20 L MBRs with submerged hollow fibers, one operated without PAC, the MBR(AS), and the other with 5 g/L PAC, the MBR(BAC). For an SRT of 30 days (which involved 3.3% sludge wastage per day and 3.3% new PAC addition per day) and a fixed flux of 21 L/m²hr the MBR(AS) showed a TMP rise of about 2.4 kPa/day whereas the MBR(BAC) showed a rise of only 0.8 kPa/day. However when the MBRs were operated without wastage the performance of the MBR(BAC) was worse than the MBR(AS). Thus the improved performance of the MBR(BAC) requires regular replenishment of aged BAC with fresh PAC.     

膜生物反应器中膜污染机理的研究

在采用膜生物反应器（MBR）处理染料废水的过程中,通过对活性污泥进行终端过滤来反映膜污染机理,着重考察了膜过滤的形式、膜通量变化和膜污染的形成。污泥的终端过滤过程严格符合沉积过滤定律;膜通量随过滤时间呈指数衰减趋势,并在几分钟内就达到相对稳定值;扫描电镜照片也证实了膜污染主要是膜面沉积层引起的。     

Filtration characteristics of activated sludge in hybrid membrane bioreactor with porous suspended carriers (HMBR)

The suspended carriers were efficient in controlling membrane fouling in hybrid membrane bioreactor with porous suspended carriers (HMBR). The purpose of this study consisted in investigating the effect of suspended carriers on the sludge suspension, especially the filterability of sludge suspension. The filterability of sludge suspension in HMBR and general membrane bioreactor (MBR) were investigated and compared in parallel conditions by dead-end filtration for better evaluating the influence of suspended carriers on the sludge suspension. Several aspects of sludge suspension such as filtration resistance, specific cake resistance and particle size were discussed. During long-term operation the filtration resistances rose gradually in the early stage (about 100 days) and then increased rapidly, but there was a slight difference between MBR and HMBR with the prolongation of operation time. The granulometric analysis revealed that the mean particle size of sludge suspension of HMBR decreased more sharply than that of MBR, because the fluidized carriers in HMBR would impose shear stresses on sludge flocs and induce the destruction of the network of sludge zoogloea. Dead-end filtration experiments indicated that the resistance-increasing rates of three portions of sludge suspension were in the order of supernatant > dissolved organics > microbial flocs. In order to further understand the filterability of sludge suspension, the specific cake resistance (α or α.C) of sludge suspension and supernatant in HMBR and MBR were determined. During long-term operation the α and α.C increased with operation time. These results revealed that the suspended carriers in HMBR had appreciably negative effect on the biological characteristics and filterability of the sludge suspension, but they were efficient in controlling membrane fouling during continuous operation of HMBR.     

Critical Review on the Effects of Mixed Liquor Suspended Solids on Membrane Bioreactor Operation

Abstract

One of the characteristics of MBRs is that they typically operate with higher mixed liquor suspended solids (MLSS) concentration than activated sludge with a conventional settling tank. While higher MLSS has obvious benefits in terms of increasing the volumetric loading or the solids retention time, it can have negative impacts on system operation and economics. We critically evaluate three hypotheses on how high MLSS may adversely affect MBR operation:

• (1)?reduced membrane flux with high MLSS,

• (2)?decreased aeration alpha (α) value with high MLSS, and

• (3)?poorer thickening characteristics of excess sludge wasted from an MBR based on the Sludge Volume Index (SVI) and the Capillary Suction Time (CST).

The results support the first and second hypotheses, but not the third. Increasing MLSS decreases the critical permeate flux, but the effect is strong only for MLSS<～5 g/L. For the typical MLSS zone (>～5 g/L), flux‐management techniques to prevent serious cake formation are more important than MLSS. The aeration α decreases with increasing MLSS concentration, although the strength of the correlation depends on system‐specific factors that are poorly understood. Thickening properties of IMBR sludge are not significantly poorer than those of traditional activated sludge, based on available CST tests.     

Biofilm Structure and Extracellular Polymeric Substances in Low and High Dissolved Oxygen Membrane Bioreactors

Abstract

This paper discusses the effect of dissolved oxygen (DO) on the biofilm structure in membrane bioreactor (MBR) and their consequence on membrane permeability and EPS. Two MBRs under high DO (6.0 mg/L, HDO) and low DO (<0.1 mg/L, LDO) were operated in parallel under same hydrodynamic conditions. The microbiological aspects in MBR systems were explored through a series of analysis techniques including PCR‐DGGE, gel filtration chromatography (GFC), confocal laser scanning microscope (CLSM), and image analysis.

The rate of membrane fouling for the LDO MBR was 5 times faster than that for the HDO MBR. The microbial communities between HDO and LDO MBR were quite different, which is likely to be the reason for different structures and permeabilities of the biofilms. The specific biofilm resistance in HDO MBR was lower to that in LDO MBR. This is attributed to relatively lower porosity and higher amount of EPS for the biofilm in LDO MBR. The distributions of cell and EPS were not uniform in the biofilms in both HDO and LDO MBR. The biofilm in LDO MBR contained larger amount of EPS than that in HDO MBR. The ratio of protein to polysaccharide was also higher for biofilm in HDO MBR than in LDO MBR.     

Sludge Water Characteristics Under Different Separation Methods from a Membrane Bioreactor

The concept of sludge water was proposed to integrate the relative terminologies and its characteristics under different separation methods from a membrane bioreactor (MBR) were investigated in this study. Based on chemical oxygen demand (COD) and three-dimensional fluorescence excitation-emission matrix (F-EEM), and compared with the control (gravitational sedimentation), some suspended particulate organics or biopolymer clusters (mainly proteins) were released from sludge flocs into the supernatant after centrifugation under low to middle centrifugal forces (10–4000 g) and then aggregated into a pellet under high centrifugal forces (10000–20000 g). Filtration (1.2 µm glass fiber filter) produced sludge water with a lower biopolymers concentration than the control (gravitational sedimentation followed by filtration) due to cake layer formation during filtration. As for centrifugation followed by filtration, low to middle centrifugal forces did not significantly affect sludge water characteristics but high centrifugal forces reduced the concentrations of some proteins in sludge water from advanced analytical protocols including F-EEM and liquid chromatography with on-line organic carbon detection (LC-OCD), demonstrating a low to middle centrifugal force suitable for MBR sludge water separation. From LC-OCD, the main fractions of sludge water were humic substances and building blocks, low molecular weight neutrals and biopolymers (mainly proteins rather than polysaccharides). Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science and Technology to view the supplemental file.     

两级序批式MBR膜污染控制方法研究

针对MBR在实际应用过程中存在的同步脱氮除磷效果不佳、膜污染严重等问题,提出两级序批式MBR工艺,对该工艺的膜污染影响因素及控制方法进行了试验研究.结果表明,在MBR中保持适宜的污泥质量浓度对于膜污染的控制有重要的作用,当污泥质量浓度稳定在6～7g·L~(-1)时,膜比流量基本稳定,随着污泥质量浓度的增加,膜比流量逐步降低,当污泥质量浓度超过10g·L~(-1)以后,膜比流量直线下降;投加PAC至1 g·L~(-1)可以增加污泥粒径,减少大分子有机物在膜表面沉积,从而有助于延缓膜污染;序批式间歇运行与空曝相结合的运行方式可以有效降低泥饼层污染及凝胶层污染,使系统在更高膜通量下运行,而膜污染速率却远低于连续流单级好氧MBR系统.     

PF-MBR处理城市生活污水膜污染特性研究

在膜生物反应器处理污水过程中,广泛存在膜污染问题。自制膜生物反应器,向其中添加磁性铁氧体粉末,组成铁氧体粉末膜生物反应器(PF-MBR),并用其处理城市生活污水;研究了添加磁性铁氧体粉末对膜污染的影响,并进行机理分析。研究结果表明,添加磁性铁氧体粉末能一定程度上延缓膜污染。不加磁性铁氧体粉末的MBR-B运行到第30天时膜过滤压差达到22.9 kPa,而添加磁性铁氧体粉末的MBR-A膜过滤压差只有17.2 kPa;MBR-A的膜过滤阻力比MBR-B的低1.65×1012m-1。临界通量测定结果也表明,向膜生物反应器中添加磁性铁氧体粉末能减缓膜污染。机理分析表明,向膜生物反应器中加入磁性铁氧体粉末改变了活性污泥絮体的结构和性质,降低了膜生物反应器运行过程中膜表面泥饼层产生的阻力及膜孔堵塞与吸附产生的阻力,从而有效缓解了膜污染。实验采用自制的磁性铁氧体粉末,可实现废物的资源化利用。     

基于小孔径PVDF内衬膜A/O-MBR膜污染分析

为研究膜生物反应器膜污染问题,在缺氧-好氧一体式膜生物反应器中,对模拟生活污水的处理效果进行考察,考察了4种不同孔径聚偏氟乙烯(PVDF)内衬膜对膜污染的影响规律。结果表明,基于小孔径PVDF膜的MBR工艺对模拟生活污水中COD、NH3-N的去除率分别达到96%、90%,出水浊度在0.35 NTU以下;在操作条件固定的情况下,随着膜孔径增加,临界通量逐渐降低;孔径越小,跨膜压差上升越缓慢,膜污染较轻。膜污染模型分析结果显示:无论何种孔径的膜,在MBR系统中,滤饼层和凝胶层污染所占的比例都最大(>80%),因此,在使用过程中减缓滤饼层及凝胶层的形成至关重要。     

膜生物反应器中污泥特性对膜污染的影响研究

膜生物反应器(MBR)是膜技术与污水生物技术的组合工艺，与传统污水处理工艺相比具有许多优点，但膜污染目前仍是限制MBR广泛应用的突出问题。有效的膜污染防治技术，可以增加膜通量，增强系统稳定性，减少系统维护和运行费用。在膜过滤过程中，污泥混合液的特性对于膜污染具有重要作用。近年来围绕污泥特性对膜污染的防治问题取得了许多研究成果，膜污染的数学模型研究也得到了很大发展。     

Modeling of Particle Fouling and Membrane Blocking in Submerged Membrane Filtration

Abstract

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo‐steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data.     

Effect of Hydraulic Retention Time on Sludge Properties,Cake Layer Structure,and Membrane Fouling in a Thermophilic Submerged Aerobic Membrane Bioreactor

Sludge properties, cake layer structure, and membrane fouling in a membrane bioreactor were studied under various hydraulic retention times (HRT). A decrease in HRT resulted in an increase in extracellular polymeric substance production in bulk sludge and changes in cake layer structure from gel layer to one or two cake layers. Particle size distribution in cake sludge changed with respect to HRT. An evolution in cake layer thickness and porosity was observed with trans-membrane pressure (TMP) jump. The change in cake layer structure might bear more responsibility for the TMP jump than the quantity of cake layer.     

The Impact of Intermittent Aeration on the Operation of Air‐Lift Tubular Membrane Bioreactors under Sub‐Critical Conditions

Abstract

An air‐lift sidestream polymeric multi‐tube membrane module has been investigated to compare the hydraulic performance of an MBR challenged with municipal wastewater and landfill leachate. In both cases the MBRs were operated under the same conditions of membrane aeration rate and sludge retention time, but with hydraulic retention time for the leachate set by scoping trials based on porous pots to 48 hours. Operation under conventional continuous aeration conditions yielded critical flux values, based on classical flux step experiments, of 36–42 l m^?2 hr^?1 for the sewage‐fed trial compared with ～24 l m^?2 hr^?1 for the leachate‐fed trial. Substantial improvements in operating flux, between 20 and 100%, were obtained when operating with air pulsing (1s on/s off). Intermittent operation under more conventional conditions (5s on/5s off) yielded no improvement.     

缺氧-好氧MBR工艺及膜性能的研究

研究了缺氧-好氧MBR工艺处理生活污水的特性.考察了系统的处理效果,系统对于浊度、COD、氨氮、总磷等指标表现出高且稳定的去除效果.通过对系统膜过滤压差变化的长期测定,在膜丝内部负压和膜面紊流形成的剪切力双重作用下,活性污泥在膜外表面局部沉积下来形成致密的滤饼,膜表面的滤饼层和凝胶层是引起膜污染的主要因为.空曝气和化学...     

Membrane bioreactors for hospital wastewater treatment: recent advancements in membranes and processes

Discharged hospital wastewater contains various pathogenic microorganisms, antibiotic groups, toxic organic compounds, radioactive elements, and ionic pollutants. These contaminants harm the environment and human health causing the spread of disease. Thus, effective treatment of hospital wastewater is an urgent task for sustainable development. Membranes, with controllable porous and nonporous structures, have been rapidly developed for molecular separations. In particular, membrane bioreactor (MBR) technology demonstrated high removal efficiency toward organic compounds and low waste sludge production. To further enhance the separation efficiency and achieve material recovery from hospital waste streams, novel concepts of MBRs and their applications are rapidly evolved through hybridizing novel membranes (non hydrophilic ultrafiltration/microfiltration) into the MBR units (hybrid MBRs) or the MBR as a pretreatment step and integrating other membrane processes as subsequent secondary purification step (integrated MBR-membrane systems). However, there is a lack of reviews on the latest advancement in MBR technologies for hospital wastewater treatment, and analysis on its major challenges and future trends. This review started with an overview of main pollutants in common hospital wastewater, followed by an understanding on the key performance indicators/criteria in MBR membranes (i.e., solute selectivity) and processes (e.g., fouling). Then, an in-depth analysis was provided into the recent development of hybrid MBR and integrated MBR-membrane system concepts, and applications correlated with wastewater sources, with a particular focus on hospital wastewaters. It is anticipated that this review will shed light on the knowledge gaps in the field, highlighting the potential contribution of hybrid MBRs and integrated MBR-membrane systems toward global epidemic prevention.     

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.     

Effect of Support Material Properties on Dynamic Membrane Filtration Performance

A dynamic membrane is defined as a cake layer which forms on a support material, for example, filter cloth or mesh when the liquid to be filtered includes suspended particles. Formation of an effective dynamic cake layer is highly related with the retention of particles on the support material surface. Therefore, support material properties are considered to be of prime importance in the performance of dynamic membrane treatment systems. This study investigates the effect of support material properties including pore size and structure of the material on dynamic membrane formation and performance. In this concept, a comparative evaluation was made between support materials which have different yarn types. The results showed that high total suspended solids removal efficiency (>98%) could be achieved by using dynamic membrane filtration technology. Mono-monofilament and staple filter cloths were determined as the most appropriate materials in terms of the critical fluxes which were 9.2 L/m² · h and 17–19 L/m² · h for mono-mono filament and staple materials, respectively. However, considering the results of more long-term experiments, mono-monofilament filter cloth was found more suitable for cake layer accumulation. Therefore, we postulate that mono-monofilament cloth can be used in dynamic membrane filtration systems as an alternative to traditional membranes in anaerobic membrane bioreactors.     

Influence of Mechanical Mixing Rates on Sludge Characteristics and Membrane Fouling in MBRs

Abstract

The influence of shear intensity (G) induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in membrane bioreactors (MBRs) was investigated. Four MBRs were operated at different mechanical mixing conditions. The control reactor (MBR₀) was operated with aeration only supplemented by mechanical stirring at 150, 300, and 450 rpm in MBR₁₅₀, MBR₃₀₀, and MBR₄₅₀, respectively. It was found that the MBR₃₀₀ demonstrated minimum rate of membrane fouling. The fouling potential of the MBR₃₀₀ mixed liquor was lowest characterized by the specific cake resistance and the normalized capillary suction time (CST_N). Moreover, it was found that the mean particle size reduced with an increase in the shear intensity. These results reveal that membrane fouling can be significantly mitigated by appropriate shear stress on membrane fibers induced by mechanical mixing condition.     

双酚A在膜生物反应器中的去除及转化分析

通过小试考察了MBR去除双酚A(BPA)的机理及转化规律。结果表明,BPA的加入未对MBR的运行产生明显影响。随着MBR运行压力的升高,出水BPA含量呈现下降的趋势。出水初期平均压力为4.8 kPa,出水平均BPA的质量浓度为3.98 mg/L,运行后期出水平均压力为46.4 kPa,出水平均BPA的质量浓度为1.67 mg/L。对反应池内污泥、膜清洗洗脱液中BPA的检测发现,BPA在反应池内污泥、膜滤饼层和凝胶层中具有很高的含量分布。BPA的3种主要降解产物在反应器中的含量与出水含量相差不大,但在膜面的凝胶层和滤饼层中有一定程度的积累。在70 d的运行时间内,MBR去除BPA的主要机理是膜面滤饼层和凝胶层通过截留已吸附BPA的污泥而形成强化去除作用。只有部分BPA通过生物降解作用转化为其产物,生物降解作用在本研究中属于次要地位。     

Influence of Water Compositions and Conditioning on Flux Enhancement in an Immersed Membrane System

Abstract

The objective was to quantify the importance of operational conditions, aeration, and physico‐chemical conditioning on membrane fouling intensity. The suspension filterability was also analysed by using frontal filtration and a cake filtration model. Results pointed out the moderated role of aeration to reduce compound accumulation on the membrane surface. It did not appear as a determining criterion to prevent membrane fouling. In contrast, the physico‐chemical conditioning appeared as a determining criterion to increase critical flux. According to the experimental conditions 200 l/m²/h/bar membrane permeability could be maintained transmembrane pressure (TMP) when filtering stored rainwater. This permeability value was 2–3 times higher than the values obtained without conditioning. Moreover, according to the low turbidity of such stored rainwater and because of the high selectivity of the membrane, the coagulation step, a very low amount of 10 mg/l FeCl₃, was sufficient to intensify the filtration step. This conditioning interest appeared less significant when filtering salted water in immersed membrane systems, but a 20 mg/l FeCl₃ addition appeared sufficient to double the value of critical flux. Nevertheless filtration in frontal mode pointed out the significant impact of physico‐chemical conditioning in reducing the cake deposit hydraulic resistance.