Inclining filtration and enhanced backwash for initial fouling control in microfiltration

It is believed that rapid membrane fouling generally occurs at early-stage of filtration. The operating parameters have great effects on membrane performance. As a result, conducting filtration with appropriate conditions in initial stage may improve membrane efficiency. Therefore, we propose the idea of improving membrane performance by controlling initial operating parameters. Two strategies are employed for this purpose: enhanced backwash and inclining filtration. During initial period of operation, backwash frequency is increased (enhanced backwash) or/and flux is increased from the sub-critical flux to the critical or the supra-critical flux (inclining filtration). To evaluate the effects of these strategies, synthetic water simulating a river is treated through microfiltration (MF) of polyvinylidene fluoride (PVDF) membrane at dead-end mode. The study results showed that initial enhanced backwash causes more fouling than normal backwash. Instead, filtration without initial backwash successfully reduces fouling. Inclining filtration is found effective in fouling reduction. Rapid fouling progress is successfully suppressed by employing filtration at low flux during initial operation.     

Ultrafiltration Fouling: Impact of Backwash Frequency and Air Sparging

A bench-scale study was performed to optimize backwash frequency and air sparging conditions during ultrafiltration (UF) for drinking water treatment in order to minimize hydraulically irreversible fouling as well as operating and maintenance costs. Surface shear stress representing different air sparging conditions (continuous coarse bubble, intermittent coarse bubble, and large pulse bubble) was applied in combination with various backwash frequencies (0.5, 2, and 6 hours) during UF of two natural surface waters. Results indicated that air sparging during permeation with intermittent coarse or large pulse bubbles significantly reduced the rate of irreversible fouling. This allowed for longer permeation times (up to 6 hours) between backwashing, when compared to a baseline condition which assumed a 0.5 h-backwash frequency with no air sparging during permeation. As a result, operation and maintenance cost savings estimated at > $350,000/year for a 29 MLD membrane train could be realized. This study demonstrates that optimized air sparging could serve as a cost-effective UF fouling control strategy for drinking water production.     

核桃壳过滤器超声波辅助反冲洗实验研究

基于国内油田常用的核桃壳过滤器,对反冲洗进行了深入系统的实验研究。确定单独水反冲洗的反冲洗时间为10min、反冲洗强度为12m3·.h-1,但对于滤料的再生效果不够理想,且反冲洗强度较高、耗水量大;采用正交实验,确定超声波辅助反冲洗的超声波频率为30kHz、超声波功率为0.7kW、反冲洗时间为12min、反冲洗强度为8m3·h-1;并对两种方式的反冲洗效果进行了对比,发现超声波辅助反冲洗初始过滤压降下降极为明显,反冲洗效果优于单独水反冲洗,并能延长过滤周期、减少反冲洗次数、节约能耗及用水量,应用前景广阔。     

Optimising operation of an integrated membrane system (IMS) — A Box–Behnken approach

The optimum operating conditions of an integrated membrane system (IMS), consisting of microfiltration (MF) followed by reverse osmosis (RO), has been defined using Box–Behnken design associated with generalised linear models (respectively quasibinomial logit analysis for the MF process and quasibinomial probit analysis for the RO process). Parameters studied for the MF process were the flux, backwash frequency and chloramine dose and dosing point. Parameters studied for the RO were the flux, recovery, pH and antiscalant dose. For both processes, the statistical method successfully determined an envelope of operating conditions. Results showed MF membrane fouling propensity to be mainly controlled by backwash frequency and flux, whereas fouling of the RO membrane was primarily defined by the pH and the recovery. The model was found to accurately represent the plant performance within the operating envelope studied.     

The Effects of Pre-Treated Membrane Backwash Water on the Quality of Finished Water from a Membrane System

Recovering membrane backwash water (MBW) can improve productivity and reduce the costs of membrane treatment systems. To verify a recovery scheme in which MBW is pre-treated and recycled into an equalization tank, two lab-scale flocculation-microfiltration (MF) membrane systems were constructed. One membrane system used water from the Luan River (the Luan River system), and the other used a blend of pre-treated membrane backwash water plus water from the Luan River in a 1:9 ratio (the mixed water system). The operating parameters and coagulant dosages were the same for both systems. Ferric chloride was used as a coagulant in the pre-treatment of membrane backwash water, and powdered activated carbon (PAC) was added to improve water quality.

Organic compounds, as represented by UV₂₅₄ measurements, in the membrane backwash water were predominantly low molecular weight species (MW < 1 kDa), whereas the DOC fraction consisted primarily of compounds with an MW greater than 30 kDa and substances with an MW less than 1 kDa. These two fractions of organics were effectively reduced by flocculation and adsorption. No differences in the quality of treated water from the two membrane systems were observed. The results indicated that the scheme of recovering membrane backwash water was feasible.     

A comparison of hydrodynamic methods for mitigating particle fouling in submerged membrane filtration

Hydrodynamic methods are used for mitigating particle fouling and for enhancing the filtrate flux in submerged membrane filtration. In the comparison membrane blocking-cake formation filtration system, the effects of filtration pressure, aeration intensity, backwash duration and stepwise increasing pressure on the filtration resistances and filtration flux are measured and discussed. Aeration is helpful for reducing particle deposition on the membrane surface, while stepwise increasing pressure can mainly mitigate internal fouling of the membrane. Periodic backwash can significantly reduce both the resistance caused by the membrane internal fouling and by cake formation; consequently, it can effectively recover the filtrate flux. In contrast, increasing the pressure in constant pressure filtration leads the flux to be decreased due to more severe membrane blockage. According to the comparison of the long-term flux and the received filtrate volume, among these hydrodynamic methods, the periodic backwash with longer duration is the optimal strategy for the filtration.     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

Grey water treatment and simultaneous surfactant recovery using UF and RO process

The membrane-based grey water treatment for grey water reuse and surfactant recovery is presented in this research paper. Grey water from washing machine discharges having turbidity and used surfactant was processed through the polymeric ultrafiltration (UF) membrane to remove the turbidity. The UF treated grey water is further purified by reverse osmosis (RO) membrane for surfactant recovery and water reuse. The surfactant trapped inside the RO spiral wound membrane module is recovered through various membrane physical regeneration techniques such as backwashing, simultaneous backwash–back-flush and ozone back-flush. Among this, backwash–back-flush is found to be effective process for surfactant recovery. The methodology for optimising surfactant recovery is captured by studying effect of various operating parameters such as feed detergent concentration, backwash pressure, backwash temperature and back-flush flow rate. By implementing optimal process conditions, the integrated UF and RO membrane process is able to produce 300 L of reusable pure water and 80 L of concentrated detergent solution and 20 L of turbid water while treating 400 L of grey water discharges. Maximum surfactant recovery of 82% is obtained while treating grey water which consists of 720 ppm of total dissolved solids (detergent) and 45 ppm of surfactant. The extent of UF and RO membrane fouling is determined by measuring the pure water flux before and after the grey water treatment. The membrane performance is found to be stable when membrane is regenerated by backwash–back-flush technique for RO and gravity backwash for UF membrane.     

Filtering surface water with a polyurethane-based hollow fiber membrane: effects of operating pressure on membrane fouling

Membrane fouling seriously restricts applications of membrane technology. A novel strategy was ap-plied in this study to retard membrane fouling by changing operating pressure with the pressure responsibility membrane. A polyurethane-based hollow fiber membrane was used to treat surface water for evaluating the effect of operating pressure on membrane fouling. Some bench-scale tests in dead-end mode were carried out. In the experi-ments without backwashing, as operating pressure increased, severe membrane fouling occurred on membrane sur-face, while the permeate quality was improved obviously, which is considered to be due to shrinkage deformation. The total resistance, irreversible resistance and reversible resistance under different backwash pressures were de-termined in filtration/backwashing test. With the increase of backwash pressure, the total resistance decreased, and more importantly, the irreversible resistance also decreased, which implies that small particles deposited inside membrane pores and cake layers on membrane surface are effectively removed. Similar results could be obtained in mass balance tests. The results of the present study indicate that the application of pressure responsibility membrane in surface water treatment may be an effective strategy for reducing membrane fouling.     

Variations in backwash efficiency during colloidal filtration of hollow-fiber microfiltration membranes

A series of filtration experiments was performed systematically to investigate physical and chemical factors affecting the efficiency of backwashing during microfiltration of colloidal suspensions. In this study, all experiments were conducted in dead-end filtration mode utilizing an outside-in, hollow-fiber module with a nominal pore size of 0.1 μm. Silica particles (mean diameter = 0.14 μm) were used as model colloids. Using a flux decline model based on the Happel's cell for the hydraulic resistance of the particle layer, the cake structure was determined from experimental fouling data and then correlated to backwash efficiency. Modeling of experimental data revealed no noticeable changes in cake layer structure when feed particle concentration and operating pressure increased. Specifically, the packing density of the cake layer (1-cake porosity) in the cake layer ranged from 0.66 to 0.67, which corresponds well to random packing density. However, the particle packing density increased drastically with ionic strength. The results of backwashing experiments demonstrated that the efficiency of backwashing decreased significantly with increasing solution ionic strength, while backwash efficiency did not vary when particle concentration and operating pressure increased. This finding suggests that backwash efficiency is closely related to the structure of the cake layer formed during particle filtration. More densely packed cake layers were formed under high ionic strength, and consequently less flux was recovered per given backwash volume during backwashing.     

Influence of Ca and Na ions in backwash water on ultrafiltration fouling control

The effect of calcium and sodium in backwash water on the fouling control of ultrafiltration is investigated on a bench scale. Besides permeate of ultrafiltration and demineralized water, solutions with different calcium or sodium concentrations were used for backwash. The results show that backwashing with demineralized water is better than with permeate of ultrafiltration. The backwash efficiency decreases when calcium and sodium are added in demineralized water for backwash. That is probably because the presence of calcium and sodium in backwash water increases the Ca-bridging effect between the negatively charged membrane and the negatively charged NOM, and compresses the double layer of the membrane and the NOM, leading to a strong adhesion force on the membrane.     

A/O-MBR处理生活污水影响因素研究

采用A/O-MBR对模拟高浓度生活污水处理效果进行研究,考察曝气量、HRT及回流比等因素对COD、氨氮处理效果的影响,以确定其最佳运行参数.结果表明,系统对COD具有相对稳定的去除效果,氨氮受各因素影响较大；Qf=1200 L/h,HRT=8 h,R=300％时运行效果最佳,出水满足《城市杂用水水质标准》（GB/T18920-2002）.     

一种改进的热泵供暖系统动态实时优化策略

基于经济性目标的热泵供暖动态优化操作具有重要意义，但在操作区间内环境温度和模型参数变化的不确定性会对实际优化操控带来很大挑战。在完善热泵供暖系统模型的基础上，提出了一种改进的动态实时优化控制策略以改善系统的实际节能效果。该方法首先建立以压缩机和送水泵运行频率为控制变量的热泵供暖系统的非线性动态关系模型，并得到以24 h为周期、以综合性能指标最低为目标的动态实时优化命题。然后，在给定24 h环境温度预测情况下通过求解该优化命题得到热泵压缩机和送水泵的最优运行频率轨线，并以当前时间点的最优控制量对热泵供暖系统进行控制；接着，基于天气逐时预测和模型参数最新校验结果对环境温度轨线或者模型参数进行更新，不断地求解原优化命题以更新最优控制轨线，并不断地采用当前点的最优控制量对热泵供暖系统进行控制，直到当前时间点达到第24 h。实例计算结果表明：采用本文提出的方法可以进一步改善热泵供暖系统的动态优化操控效果，并能够很好地满足给定终端约束要求。本方法对于具有周期性和不确定参数的动态实时优化问题求解具有一定的借鉴意义。     

场作用下的滤料反冲洗技术及发展

深床过滤技术是油田污水处理领域的重要环节,影响其运行关键在于滤床的有效反冲洗过程。通过对反冲洗理论和技术现状分析,提出反冲洗中场的概念,探讨反冲洗中场的作用形式,用场的视角来分析反冲洗技术。并基于不同功能场构建旋流场和重力场耦合的复合场反冲洗体系,提出的一种轴向动态复合场反冲洗理论,该理论丰富和发展滤料水力反冲洗方法,并为解决油田高含聚滤料反洗再生提供一种新途径。     

沉淀-超滤工艺膜反洗水的回收处理

在处理以地表水为水源的沉淀池出水时,超滤技术存在产水率较低的问题,反洗水的回收可以有效地提高系统的产水率和降低运行成本。试验设计了两套小试微滤膜系统,将膜反洗水经过预处理后按1∶9比例与滦河水混合作为一套小试膜系统进水,另外一套小试膜系统处理滦河水。试验考察了两种预处理方式对于混配水膜系统的出水水质及膜污染的影响。结果表明,在膜反洗水中投加混凝剂和粉末活性炭（PAC）后,相对仅投加混凝剂的预处理方式,混配水系统的出水水质得到改善,UV₂₅₄和COD_Mn的去除率分别提高了9%和6.3%,预处理方式对于混配水系统出水浊度没有影响,比通量衰减速率降低了16.6%。在反洗水经混凝和PAC吸附后,混配水和滦河水系统出水水质与膜污染状况未见显著差异。     

变频器在滤池反冲洗鼓风机上的应用与节能

叙述了变频器在滤池反冲洗鼓风机上的参数设置和控制系统方法 ,该技术先进 ,功能齐全 ,节电效果显著 ,是一种理想的调速控制方式。     

反渗透/纳滤膜剖检分析与膜污染诊断研究进展

反渗透（RO）/纳滤（NF）膜元件在长期运行过程中会不可避免地发生膜污染,当产水水质无法满足应用指标时,就需要对膜元件进行更换。膜剖检分析是研究和确定膜污染最直观有效的方法,通过膜剖检分析及膜污染诊断可以为膜元件的日常维护、膜系统运行优化和膜性能修复提供有效依据。但是,目前对于膜剖检分析的实践及膜污染诊断研究还不系统、不全面。本文针对RO/NF膜剖检分析及膜污染诊断相关研究,介绍了膜元件剖检分析流程和各类膜污染分析方法,分析了实际应用中存在的问题,并根据膜剖检分析的意义和价值,重点综述了膜污染成分诊断、膜污染分布情况诊断、不同应用场景膜污染情况对比和不同膜材料的污染情况对比研究进展,以期为膜污染机制研究、膜污染预防控制和膜系统运行改善提供参考。     

Analysis of hollow fibre membrane systems for multicomponent gas separation

This paper analysed the performance of a membrane system over key design/operation parameters. A computation methodology is developed to solve the model of hollow fibre membrane systems for multicomponent gas feeds. The model represented by a nonlinear differential algebraic equation system is solved via a combination of backward differentiation and Gauss–Seidel methods. Natural gas sweetening problem is investigated as a case study. Model parametric analyses of variables, namely feed gas quality, pressure, area, selectivity and permeance, resulted in better understanding of operating and design optima. Particularly, high selectivities and/or permeabilities are shown not to be necessary targets for optimal operation. Rather, a medium selectivity (<60 in the given example) combined with medium permeance (∼300–500 × 10⁻¹⁰ mol/s m² Pa in the given case study) is more advantageous. This model-based membrane systems engineering approach is proposed for the synthesis of efficient and cost-effective multi-stage membrane networks.     

超滤阀门内漏对膜设备的危害及控制措施

反渗透进水中如果含有次氯酸钠,会造成膜的氧化,影响膜的性能和寿命。由于超滤阀门的阀板选材不当,发生腐蚀内漏,在超滤进行加次氯酸钠反洗时,将含有次氯酸钠的反洗水漏进超滤水箱,从超滤水箱出来的水进入反渗透时,导致反渗透膜被氧化,降低了反渗透的脱盐率。目前把铜材阀板均改为不锈钢阀板,并经过调整试验,控制反渗透进水余氯为1～10μg/L,氧化还原电位(ORP)为350～450mV,既避免了微生物滋生污堵反渗透膜,也能保证反渗透膜免遭氧化。     

双极膜法制酸碱工艺参数的试验研究

本文对利用双极膜水解离技术将盐转化为相应酸和碱的多种工艺参数进行了探索，讨论了电流效率、转化主经、电流密度、膜平衡、能耗等因素对双极膜应用的影响。根据试验研究结果，提出了双极膜法将盐转化为相应酸和碱的最佳工作条件。