The cost of a large-scale hollow fibre MBR

A cost sensitivity analysis was carried out for a full-scale hollow fibre membrane bioreactor to quantify the effect of design choices and operational parameters on cost. Different options were subjected to a long term dynamic influent profile and evaluated using ASM1 for effluent quality, aeration requirements and sludge production. The results were used to calculate a net present value (NPV), incorporating both capital expenditure (capex), based on costs obtained from equipment manufacturers and full-scale plants, and operating expenditure (opex), accounting for energy demand, sludge production and chemical cleaning costs.Results show that the amount of contingency built in to cope with changes in feedwater flow has a large impact on NPV. Deviation from a constant daily flow increases NPV as mean plant utilisation decreases. Conversely, adding a buffer tank reduces NPV, since less membrane surface is required when average plant utilisation increases. Membrane cost and lifetime is decisive in determining NPV: an increased membrane replacement interval from 5 to 10 years reduces NPV by 19%. Operation at higher SRT increases the NPV, since the reduced costs for sludge treatment are offset by correspondingly higher aeration costs at higher MLSS levels, though the analysis is very sensitive to sludge treatment costs. A higher sustainable flux demands greater membrane aeration, but the subsequent opex increase is offset by the reduced membrane area and the corresponding lower capex.     

Physical characteristics of the sludge in a complete retention membrane bioreactor

Sludge physical characteristics play an important role in the operation of membrane bioreactors (MBR) due to their influence on filtration and their effects on handling of excess sludge. These systems are designed to maintain high solid concentrations, thus limiting sludge production and the related operational costs of the process. In this study, the sludge from a bench scale MBR operated for about 1 year with complete solid retention was investigated to assess its physical and rheological properties. Concentrations of mixed liquor suspended solids (MLSS) up to 24 gTSSL(-1) affected the diluted sludge volume index (DSVI), the capillary suction time (CST), the specific resistance to filtration (SRF) and the compressibility (s). The MBR sludge displayed similar dewatering properties of conventional waste activated sludge, suggesting that the upgrade of wastewater treatment plants with the MBR technology would not affect the behaviour of the dewatering equipment. The apparent viscosity was expressed as a function of the MLSS and the experimental data were interpreted by comparing different models. Ostwald model was chosen, and two equations for viscosity were proposed. The thixotropy of MBR sludge was also evaluated by measuring the reduced hysteresis area (rHa) and relating this parameter to the characteristics of the sludge. The evaluation of energy consumption for mixing evidenced that, under the tested conditions, the increase of solid concentration from 3 to 30 gTSSL(-1) resulted in a limited increase of energy requirements (25-30%).     

污泥驯化阶段MBR与CAS工艺特性比较

在接种污泥、进水水质、反应器尺寸及水力停留时间相同的条件下，比较了膜生物反应器（MBR）和传统活性污泥工艺（CAS）在污泥驯化期的除污效果和污泥特性。结果表明，MBR对COD的去除效果优于CAS的，两工艺对氨氮的去除效果差异不大；MBR中的污泥絮体较CAS中的分散，原生动物和后生动物的种类也较少；MBR中的污泥浓度远高于CAS工艺的，其污泥的体积平均粒径小于CAS的；两反应器中的活性污泥均表现出了较好的沉降性能。     

Feasibility of using a chlorination step to reduce excess sludge in activated sludge process

The ultimate disposal of excess sludge generated from activated sludge processes has been one of the most challenging problems for wastewater treatment utilities. Previous work has shown that excess sludge can be minimized successfully by using sludge ozonation to dissolve it into substrates to be oxidized in the aeration tank. However, this approach is a costly option. Therefore, as an alternative solution, we propose to use chlorination to replace ozonation in excess sludge minimization in the light of operational cost. To investigate the feasibility of this low cost approach, this paper mainly focuses on the effect of chlorination on sludge reduction rate, formation of trihalomethanes, sludge settleability, and effluent quality. Two identical activated sludge membrane bioreactors were continuously operated with synthetic wastewater under the same operation conditions for several months. During this period, one pilot unit was used as the reference system without chlorination of excess sludge, while another served as a testing unit, where excess sludge was taken out for conducting chlorination at a dose of 133mg/g MLSS every day and the chlorinated liquor was then returned to the aeration tank. The sludge production rate and the water quality of both the units were analyzed daily. It was observed that the sludge production could readily be reduced by 65% once the chlorination treatment was involved. However, the chlorination treatment also resulted in poor sludge settleability as well as significant increase of soluble chemical oxygen demand in the effluent, which creates potential difficulties in the operation of a conventional treatment plant with gravity clarifiers. However, it has been demonstrated that by integrating the immersed membrane into the activated sludge process these difficulties can be overcome effectively.     

Effects of chemical sludge disintegration on the performances of wastewater treatment by membrane bioreactor

A new wastewater treatment process combining a membrane bioreactor (MBR) with chemical sludge disintegration was tested in bench scale experiments. In particular, the effects of the disintegration treatment on the excess sludge production in MBR were investigated. Two MBRs were operated. In one reactor, a part of the mixed liquor was treated with NaOH and ozone gas consecutively and was returned to the bioreactor. The flow rate of the sludge disintegration stream was 1.5% of the influent flow rate. During the 200 days of operation, the MLSS level in the bioreactor with the disintegration treatment was maintained relatively constant at the range of 10,000-11,000 mg/L while it increased steadily up to 25,000 mg/L in the absence of the treatment. In the MBR with the sludge disintegration, relatively constant transmembrane pressures (TMPs) could be maintained for more than 6 months while the MBR without disintegration showed an abrupt increase of TMP in the later phase of the operation. In conclusion, a complete control of excess sludge production in the membrane-coupled bioreactor was possible without significant deterioration of the treated water quality and membrane performances.     

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.     

The cost of a package plant membrane bioreactor

The capital and operating costs associated with a small package plant MBR for small-scale domestic duty has been appraised based on a medium-strength municipal wastewater. The three main membrane configurations were considered, these being multi-tube, hollow fibre and flat sheet, with the most appropriate plant design chosen for each configuration. The analysis proceeded via a consideration of the estimated amortised capital costs of the plant individual components and their installation, coupled with operating costs based largely on energy demand and residuals management. Energy demand was calculated from aeration and pumping costs, with aeration based on a combination of empirical relationships for membrane aeration and mass balance, and the modified Activated Sludge Model version 2 used for estimating tank size and sludge generation. Results indicate that it is possible to produce a single household MBR at a capital cost similar to the current market cost for package treatment plants. Desludging and maintenance of these plants is similar but power requirements for an MBR are around 4 times that associated with more conventional package plants. Economies of scale exist from 6-20 p.e. plants but above 20 p.e. there is little cost difference per head, due to the design assumptions made. CAPEX and OPEX are to some extent interchangeable; reductions in CAPEX are associated with an increase in OPEX and vice versa. Whilst costs are high, the market for package MBRs is significantly influenced by the recycling potential of the effluent produced.     

Hydraulic effects on sludge accumulation on membrane surface in crossflow filtration

Membrane filtration technology for application of wastewater treatment has been developing recently. In the application to wastewater treatment, it is major concern to remove cake layer on membrane surface effectively with crossflow shear stress. Hydraulic effect of sludge accumulation process on membrane surface in bubble and non-bubble driven crossflow filtration was studied. Maximum sludge accumulation. sludge accumulation rate, and lag phase were introduced to describe sludge accumulation process, and the effects of hydraulic conditions were clarified experimentally. Maximum sludge accumulation and sludge accumulation rate were dependent on aeration intensity, and were less depend on flow channel width and MLSS concentration. Their tendencies were explained by shear stress. Shear stress was thought to be the major hydraulic factor that influences them. Lag phase was dependent on aeration intensity, flow channel width, and MLSS concentration. A non-dimensional equation was proposed to explain dependencies of flow channel width based on consideration of hydraulic behavior of MLSS particles and shear stress.     

Oxygen transfer in membrane bioreactors treating synthetic greywater

Mass transfer coefficients (k_La) were studied in two pilot scale membrane bioreactors (MBR) with different setup configurations treating 200 L/h of synthetic greywater with mixed liquor suspended solids' (MLSS) concentrations ranging from 4.7 to 19.5 g/L. Besides the MLSS concentration, mixed liquor volatile suspended solids (MLVSS), total solids (TS), volatile solids (VS), chemical oxygen demand (COD) and anionic surfactants of the sludge were measured. Although the pilot plants differed essentially in their configurations and aeration systems, similar α-factors at the same MLSS concentration could be determined. A comparison of the results to the published values of other authors showed that not the MLSS concentration but rather the MLVSS concentration seems to be the decisive parameter which influences the oxygen transfer in activated sludge systems operating at a high sludge retention time (SRT).     

啤酒污泥用作城市污水厂种泥的试验研究

为考察啤酒厂污水处理站的脱水污泥（简称啤酒污泥）用作城市污水厂接种污泥的可行性，摸索污泥的培养与驯化规律，采用连续操作、全流量同步培养和驯化方法，在处理能力为500m^2／d的UNITANK池中对啤酒污泥进行了培养和驯化。试验结果表明，啤酒污泥完全可以作为城市污水处理厂的接种污泥使用，而且培养时间短，出水水质好。曝气0．5h、厌氧搅拌1h时，活性污泥增长最快。将DO控制在2mg／L左右有利于活性污泥的增长；当DO长时间在7mg／L以上时，污泥浓度下降趋势明显。污泥浓度达到2000mg／L所需的培养驯化时间仅为5d；使出水水质达到一级B标准所需的培养时间约为6d。这种培养、驯化方法和经验可为其他城市污水处理厂的建设和运行提供参考。     

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。     

低DO下曝气方式对分段进水脱氮工艺的影响

采用分段进水生物脱氮工艺处理小区生活污水,考察了在低DO条件下,不同曝气方式对硝化率及污泥沉降性能的影响。结果表明,在曝气量为0．27m^3／h、MLSS平均为2700mg／L左右、好氧区的DO为0．26～2．5mg／L的条件下,当进水氨氮为44～55mg／L时,对氨氮的去除率保持在95％以上,对COD的去除率〉90％;当控制好氧区第1、2格室的DO分别为0．5～0．7和1．0～1．2mg／L时,系统的硝化率维持在90％以上,出水中的氨氮〈2mg／L;在恒定曝气量下,向进水中投加有机碳源,当水质改变较快时,容易引起丝状菌污泥膨胀,但通过恒DO曝气控制,可使污泥的沉降性能得到改善。     

Promotion and inhibition of oxygen transfer under fine bubble aeration by activated sludge

The promotion and inhibition of inactivated and activated sludge on oxygen mass transfer (OMT) were studied using lab‐scale experiments. The results showed that the α‐values and oxygen transfer efficiency (OTE) decreased with increasing mixed liquor suspended solids (MLSS) concentration (1–10 g/L). Although OMT promotion rate by microbial respiration in activated sludge system increased from 39.8–97.5% for the α‐values and OTE, the two parameters were found to fall sharply when MLSS concentration was over 5 g/L. This indicated that the sludge concentration is a major influence factor on OMT in activated sludge system. Such results provide valuable knowledge for the operating optimization of the aeration system in wastewater treatment process.     

Identification of wastewater sludge characteristics to predict critical flux for membrane bioreactor processes

The effects of sludge characteristics on critical flux were examined using a submerged membrane bioreactor pilot plant operated under different process conditions to treat municipal wastewater. The sludge in the membrane tank was characterized by measuring colloidal particle concentration, extracellular polymeric substances (EPS), mixed liquor suspended solids (MLSS), temperature, time to filter (TTF) and diluted sludge volume index (DSVI). The colloidal particle concentration was represented by the colloidal total organic carbon (TOC), which is the TOC difference between the filtrate passing through a 1.5 microm pore size filter and the permeate collected from pilot ultrafiltration membrane modules with a pore size of 0.04 microm. The results showed that the critical flux measured by the stepwise flux method was almost solely related to the colloidal TOC despite different sludges tested. In contrast, MLSS was shown to have little impact on the critical flux within the range examined. Neither TTF nor DSVI could be used to reliably predict the critical flux. Furthermore, colloidal TOC can be attributed to soluble EPS, but not bound EPS. Therefore, it is suggested that colloidal TOC be used as a new filterability index for MBR processes in wastewater treatment.     

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.     

曝气量对膜生物反应器污泥特性和膜污染的影响

设置M1、M2和M3等3个反应器的曝气量分别为150、200和300 L/h,研究了曝气量对膜生物反应器(MBR)的运行效果和污泥特性的影响.结果表明,随着曝气量的增加,对COD和NH4+-N的去除率提高,反应器内溶解氧浓度和污泥的比耗氧速率均增加,表明增加曝气量有助于提高污泥的活性.污泥絮体的粒径变小,溶解性微生物代谢产物(SMP)浓度则由M1的46.8mg/L增加到M3的71.0 mg/L,而且其中的成分也发生了变化,蛋白质与多糖的比值随着曝气量的增加而增加,M1的为1.5,M3的则增至1.9.随着曝气量的增加则膜污染速率加快,表明膜污染以SMP污染为主.     

Bacteriophage MS-2 removal by submerged membrane bioreactor

A membrane bioreactor (MBR) may serve as a pre-disinfection or disinfection unit, in addition to its solid/liquid separation and biological conversion functions, to produce sewage effluent of high quality. This bench-scale pilot study focuses on investigating the performance of a submerged MBR in pathogen removal and the factors affecting the removal, using a 0.4-microm hollow-fiber membrane module submerged in an aeration tank and bacteriophage MS-2 as the indicator organism. Removal of the MS-2 phage was found to be contributed by physical filtration by the membrane itself, biomass activity in the aeration tank and bio-filtration achieved by the biofilm developed on the membrane surface. The membrane alone gave poor virus removal (0.4+/-0.1 log) but the overall removal increased substantially with the presence of biomass and the membrane-surface-attached biofilm. The contributions of the suspended biomass and attached biofilm to the phage removal are dependent on the inter-related parameters including the concentration of mixed liquor suspended solids (MLSS), the sludge retention time (SRT) and the food to mass (F/M) ratio. The correlations between effluent flux/trans-membrane pressure and virus removal give evidence that phage removal in the MBR is most likely susceptible to both biological and physical factors including the quantity and property of the biomass and the biofilm and the membrane pore size reduction.     

Analysing the influence of operating conditions on the performance of algal–bacterial granular sludge processes for wastewater treatment: A review

This article discussed the effect of the main operating parameter involved in the operation of algal–bacterial granular sludge (ABGS) systems as promising biological processes for wastewater treatment. The focus was on the operational ranges reported in the literature capable of achieving better granule properties, good stability and high removal capacities. This review identified that hydraulic retention time (HRT), light intensity (LI) and light/dark periods were the most influential operating factors on the formation, stability, settleability and organic pollutant removal efficiency of ABGS. The discussion argued that ABGS systems enhance industrial and domestic wastewater treatment due to additional advantages that provide the symbiotic interactions to process performance, maintaining lesser operating costs concerning aerobic granular sludges (AGS) and microalgae consortia. This review will improve the understanding of the operation of ABGS systems and thus further expand possible operating combinations that help to enhance microbial interactions, microalgae growth and external aeration self-sufficiency in further research with a focus on its scaling up.     

膜生物反应器在污水深度处理中的技术研究

试验研究了以膜生物反应器(MBR)为核心的单元式再生水处理装置(处理能力为30m3/d)在设置成A/O型MBR和A2/O型MBR两种工艺组合和不同运行条件下(如安装BS填料、投加PAC、改变原水条件和增减膜组件数量等)对城市污水的深度处理效果。试验结果表明单元式再生水处理装置具有较高的污泥浓度(MLSS=10000～12000mg/L)和较强的抗冲击负荷(温度、水质变化等)能力。在不同工况下CODcr、BOD5、NH3-N、TN、SS、浊度、色度和粪大肠菌群数等指标均达到或优于国家一级A标准。优化的A2/O型MBR工艺的各项出水指标达到或优于国家一级A标准。BS填料可明显提高生物脱氮效率。     

Economic evaluation of alternative wastewater treatment plant options for pulp and paper industry

Excessive water consumption in pulp and paper industry results in high amount of wastewater. Pollutant characteristics of the wastewater vary depending on the processes used in production and the quality of paper produced. However, in general, high organic material and suspended solid contents are considered as major pollutants of pulp and paper industry effluents. The major pollutant characteristics of pulp and paper industry effluents in Turkey were surveyed and means of major pollutant concentrations, which were grouped in three different pollution grades (low, moderate and high strength effluents), and flow rates within 3000 to 10,000 m³/day range with 1000 m³/day steps were used as design parameters. Ninety-six treatment plants were designed using twelve flow schemes which were combinations of physical treatment, chemical treatment, aerobic and anaerobic biological processes. Detailed comparative cost analysis which includes investment, operation, maintenance and rehabilitation costs was prepared to determine optimum treatment processes for each pollution grade. The most economic and technically optimal treatment processes were found as extended aeration activated sludge process for low strength effluents, extended aeration activated sludge process or UASB followed by an aeration basin for medium strength effluents, and UASB followed by an aeration basin or UASB followed by the conventional activated sludge process for high strength effluents.