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混凝防止膜污染的研究 总被引:3,自引:0,他引:3
试验主要研究混凝改善膜通量和防止膜污染的效果。试验的每个工况均为0.1MPa过滤压力,连续膜过滤8h,观察膜通量的变化情况。结果表明:在直接过滤原水的情况下,反冲洗后的膜通量恢复率仅为初始通量的40%;而投加了混凝剂4mg/L和10mg/L(以Al计)后,反冲洗后的膜通量得到了完全的恢复。混凝防止膜污染取决于过滤过程在膜表面形成的滤饼层的性能。在过滤混凝液的情况下,膜表面会形成滤饼层,从而有效地防止膜污染,而在过滤上清液的情况下,无法被混凝去除的中性亲水性的有机物沉积在膜表面,造成膜污染。 相似文献
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PVDF 膜污染及清洗试验研究 总被引:4,自引:0,他引:4
考察了采用膜混凝反应器处理滦河原水后膜污染情况及几种清洗方法。试验结果表明膜污染主要由铁污染和有机污染组成,碱洗能去除大部分的有机污染,而无机污染主要由酸洗去除。为使系统在较高通量下长期稳定运行,需依靠定时在线化学清洗及时恢复跨膜压力,在长期运行中持续投加1200mg/L次氯酸钠及时清除有机污染,当跨膜压力较高时再投加1.5%盐酸执行一次。进行化学清洗时氢氧化钠、次氯酸钠和盐酸三种清洗剂结合清洗效果很好,此外,水温、加药量及清洗时间是决定化学清洗效果的重要因素。 相似文献
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构建了一种新型的超滤系统,利用运行膜组产水作为反冲洗膜组供水,取消了反冲洗水泵及反冲洗水箱,简化了超滤反冲洗系统;研究了NaCl反冲洗和NaClO反冲洗等强化水力反冲洗措施的膜污染控制效果。研究结果表明,不同膜通量条件下新型超滤中试系统具有极佳的除浊效能,对COD_(Mn)、DOC和UV_(254)等有机物均有一定的去除效果。提高膜通量可使跨膜压差增长速率增加,膜比通量下降速率加快,不可逆膜污染程度更加严重。腐殖酸类物质造成的是可逆膜污染,可通过常规水力反冲洗进行有效控制;蛋白质类有机物是造成不可逆膜污染的主要原因,采用NaCl反冲洗或NaClO反冲洗均可不同程度减轻蛋白质类有机物造成的不可逆膜污染,NaClO反冲洗可更有效地洗脱大分子溶解性蛋白质类物质。与常规反冲洗相比,NaCl反冲洗和NaClO反冲洗可以更有效地洗脱相对分子质量小于1 000和大于100 000的DOC。 相似文献
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膜生物反应器中膜的堵塞与清洗的机理研究 总被引:26,自引:1,他引:25
对一体式膜生物反应器处理生活污水进行了研究。当进水COD在 336~ 80 8mg/L时 ,COD的去除率最高可达 99% ;当进水NH3-N在 15 87~ 35 13mg/L时 ,NH3-N的去除率最高可达 10 0 %。较详细地论述了纤维丝间污泥的淤积、膜表面凝胶层的形成、膜表面垢的形成三种膜污染的基本类型。认为膜清洗的先后顺序应为先用自来水冲洗 ;后用 0 0 33%的次氯酸钠浸泡 12h ,自来水冲洗 ;最后用 0 33%硫酸浸泡 6h ,自来水冲洗。并且考察了三种方式清洗后膜通量的恢复情况 ,即用清水冲洗可使通量恢复 11% ;用 0 0 33%的次氯酸钠浸泡 ,自来水冲洗后通量恢复 2 3% ;用0 33%硫酸浸泡 ,自来水冲洗后通量恢复 31%。在此基础上提出膜生物反应器的三种运行方式 相似文献
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五种预处理方式对超滤膜处理松花江水的效能比较 总被引:1,自引:1,他引:0
采用中试对比考察了不同预处理方式(包括混凝、砂滤、混凝-砂滤、高锰酸钾-混凝-砂滤、粉末活性炭)对超滤膜渗透性能及其对去除松花江水中污染物的影响.结果表明:以松花江水为原水,在超滤膜之前进行预处理是必要的.其中单独混凝会使膜通量降低,投加高锰酸钾使膜通量显著增加,并可延缓膜通量的下降速度,投加粉末活性炭对提高膜通量作用不大;不同预处理均能保证超滤膜出水浊度低于O.3 NTU,大于2 μm颗粒数少于10个/mL;此外,不同的预处理均能提高超滤膜对水中有机物的去除效果,高锰酸钾-混凝-砂滤-超滤对DOC、UV254的去除率分别为37.5%、28%. 相似文献
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Membrane filtration is adequate for producing disinfected clear water suitable for various kinds of applications. However, fouling of membranes is the main limitation. The scope of the present study is to examine the effect of iron coagulation of primary wastewater effluent on membrane filtration, in parallel to fouling characterization of the iron itself. The fouling of ultrafiltration membranes by colloidal iron hydroxide-oxide has been studied by measuring the pore streaming potential of PES UF membrane. pH 5.5 (charge neutralization zone) provided better removal and lower fouling intensity than pH 7.8 (sweep coagulation zone), but the internal clogging at acidic pH was higher. Fouling of the membrane as measured by flux reduction was usually accompanied by a positive change in zeta potential and iso-electric point (IEP) of the membrane. An initially large change in zeta potential (without charge reversal) was seen even after relatively small amounts of iron solution were filtered through the membrane. A control experiment showed this is not due to iron adsorption equilibrium, but should probably be attributed to fouling. Change in zeta potential, can be used as an indicator for commencement of fouling even for small flux reductions. UF membrane critical flux after iron filtration can be evaluated more accurately by zeta potential than pressure drop or change in iron concentration. 相似文献
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Particle count and size alteration for membrane fouling reduction in non-conventional water filtration. 总被引:1,自引:0,他引:1
A Adin 《Water science and technology》2004,50(12):273-278
If coagulation is not completely successful and produces aggregates which are too small, fouling may increase. In some cases, a deep-bed filter could perhaps provide a solution. The paper examines these effects using experimental results for different waters. Activated sludge effluents, stormy seawater containing microalgae and spent filter backwash water (SFBW) were coagulated by alum or ferric chloride. Sand filtration tests were carried out. Tests were performed in a membrane filtration stirred cell, filtration pilot plant equipped with SDI analyzer (seawater) and pilot UF plant (SFBW). For activated sludge effluent, alum residual ratio curves of turbidity and total particle count (TPC) followed one another. With ferric chloride, low coagulant dosage showed negative turbidity removal. Contact granular filtration reduced membrane fouling intensity. Increasing the dose resulted in higher improvement in membrane flux. For seawater, a filter run period under storm conditions reached 35 hours with satisfactory filtrate quality. An iron chloride dose of 0.3 mg/l during normal conditions and 0.5 mg/l for stormy condition should be injected, mixed well before the filters, while maintaining 10 m/hr filtration rate and pH 6.8 value. For SFBW, alum flocculation pretreatment of SFBW was effective in reducing turbidity, TPC, viruses and protozoa. SFBW settling prior to flocculation did not enhance turbidity and TPC removal. The largest remaining particle fraction after alum flocculation was 3-10 microm in size, both Cryptosporidium and Giardia are found in this size range. Coagulation enhanced the removal of small size particles, a positive impact on reducing membrane fouling potential. 相似文献
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Immersed membrane systems, and those with in-line coagulation, have been extensively applied in drinking water systems. Sedimentation is usually replaced by membrane processes in both systems. In these systems, voluminous flocculent aggregates formed during coagulation could be potential foulants. When raw waters with high turbidity are introduced, particle loadings to membrane due to coagulation pretreatment are enormous and thus could increase fouling. In general, during the rainy season, the turbidity of the Han River water, which supplies drinking water for the City of Seoul, Korea, is more than a hundred times higher than usual. Therefore, effects of floc on membrane fouling were investigated with highly turbid waters. Two turbidity concentrations, 40 and 200 NTU, were formulated by the addition of kaolin (used as a natural particle surrogate) to the Han River raw water. The results showed that the flux decline behaviours of the highly turbid waters were different from those of natural raw water. Coagulation pretreatment was very effective at reducing membrane fouling. Flocculent aggregates showed a negative effect on the flux decline but a positive effect on the membrane cleaning efficiency. 相似文献
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Membrane fouling can be divided into two types: reversible fouling and irreversible fouling. The former can be easily canceled by physical cleaning (e.g., backwashing) while the latter needs chemical cleaning to be mitigated. For more efficient use of membranes, the control of irreversible membrane fouling is of importance. In this study, the effectiveness of pre-coagulation/sedimentation on irreversible membrane fouling was investigated, based on the pilot-scale operation of the membrane unit installed at an existing water purification plant. The membrane employed was a low-pressure ultrafiltration (UF) membrane made of polysulfone and having a molecular weight cut-off of 750,000 daltons. Although pre-coagulation/ sedimentation significantly mitigated membrane fouling mainly through the reduction of reversible membrane fouling, the degree of irreversible fouling was not reduced by the pre-treatment. This was because the irreversible fouling observed during this study was mainly attributed to polysaccharides/protein like fractions of organic substances that cannot be efficiently removed by coagulation/sedimentation. Aluminium used as coagulant was thought to cause irreversible fouling to some extent but did not in the pilot operation, which could probable be explained by the fact that coagulation was conducted at relatively high pH (7.0) in this study. 相似文献
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为提高膜蒸馏在处理垃圾渗滤液膜浓缩液时渗透通量的稳定性,设计了一种新型的超声强化直接接触膜蒸馏(US-DCMD)装置,试验研究了超声对膜渗透通量的影响,并采用电子显微镜、X射线能量色散光谱等手段分析超声对膜面污染层的影响。试验结果表明:在60W的超声辐照条件下,渗透通量最高提升19.4%,并在膜溶液浓缩系数达到4时,相对渗透通量最高维持在77.1%,而未施加超声的相对渗透通量在膜溶液浓缩系数为2时降至20.7%;膜面的主要污染物为CaCO_(3)及腐殖酸,其中CaCO_(3)是限制膜渗透通量的主要因素;超声使污染层钙的质量分数从25.6%降至15.0%,并且不会引起有机物的降解或改性;超声辐照使膜面污染层不均匀且存在裂隙,减少了污染层厚度,维持了渗透通量的稳定。 相似文献
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Recently, the membrane bioreactor (MBR) process has become one of the novel technologies to enhance the performance of biological treatment of wastewater. Membrane bioreactor process uses the membrane unit to replace a sediment tank, and this can greatly enhance treatment performance. However, membrane fouling in MBR restricts its widespread application because it leads to permeate flux decline, making more frequent membrane cleaning and replacement necessary, which then increases operating and maintenance costs. This study investigated the sludge characteristics in membrane fouling under sub-critical flux operation and also assessed the effect of shear stress on membrane fouling. Membrane fouling was slow under sub-critical flux operation. However, as filamentous microbes became dominant in the reactor, membrane fouling increased dramatically due to the increased viscosity and polysaccharides. A close link was found between membrane fouling and the amount of polysaccharides in soluble EPS. The predominant resistance was the cake resistance which could be minimized by increasing the shear stress. However, the resistance of colloids and solutes was not apparently reduced by increasing shear stress. Therefore, smaller particles such as macromolecules (e.g. polysaccharides) may play an important role in membrane fouling under sub-critical flux operation. 相似文献
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In wastewater treatment, micro- and ultra-filtration membranes are used for the separation of the activated sludge (biomass) from the treated water. This offers the advantages of a complete removal of solids and bacteria, as well as most of the viruses, namely those attached to the suspended solids. Compared to the conventional activated sludge process (CAS) this technology allows a much higher biomass concentration (MLSS) whereby the reactor volume and the footprint decreases. With increasing MLSS, the viscosity of the sludge increases, which leads to reduced oxygen transfer rates. Depending on the type of membrane and membrane module, the pre-treatment has to be more sophisticated to prevent clogging and sludging of the modules. Due to fouling and scaling, the flux through the membranes will decrease with time. The decrease depends on the water quality as well as on the measurements taken to minimize fouling. Mainly, three strategies are available: lowering the flux, increasing the "crossflow" and cleaning of the membranes. Different strategies including backwash and chemical cleaning "in situ", "on air" and "ex situ" can be applied. It has been proven more effective to apply preventive regular cleaning. Besides the energy demand for oxygen supply--which is typically in the range of 0.3 kWh/m3 for municipal wastewater--the energy for fouling prevention is substantial. Immersed membranes need approximately 0.4 to 1 kWh/m3 for the coarse bubble aeration, whereas tubular modules require 1 to 4 kWh/m3 pump energy. For proper design of industrial wastewater treatment, the verification of applicability and the development of adequate cleaning strategies, it is a precondition to run pilot tests for a sufficient period of time with the wastewater to be treated. More than 100 industrial wastewater treatment membrane bioreactors (MBR) are in operation in Europe. Data of three case studies for a sewage sludge dewatering plant in UK (12,000 m3/d), a plant for the treatment of pharmaceutical wastewater in Germany (3600 m3/d), as well for revamping of an chemical WWTP >2000 m3/d in Italy, are given. MBRs will be used in future wherever high quality effluent is required, because of a sensitive receiving water body or due to the fact of water reuse as process water. MBRs are a perfect pre-treatment in industrial applications when further treatment with nanofiltration or reverse osmosis is considered. The technique is advanced and can be applied both in municipal and industrial wastewater treatment. Higher operational costs must be balanced by superior effluent quality. 相似文献
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Microcystis aeruginosa was cultured in biologically treated municipal effluent to simulate blue-green algal bloom conditions in a treatment lagoon. The effect of algae in the early, mid and late phases of growth on membrane fouling, chemical coagulation (alum or aluminium chlorohydrate (ACH)) and hydraulic cleaning on the microfiltration of this effluent was investigated. The effect of M. aeruginosa in the early phase was negligible and gave a similar flux profile and permeate volume to that of effluent alone. The increase in M. aeruginosa concentration for the mid and late phases caused a significant reduction in permeate volume compared with the early phase. Full flux recovery was achieved with an alum dose of 1 mg Al3+ L(-1) (early phase) and 10 mg Al3+ L(-1) (mid phase), demonstrating that membrane fouling was hydraulically reversible. For the late phase, the highest flux recovery was 89%, which was achieved with an alum dose of 5 mg Al3+ L(-1). Higher alum dosages resulted in a reduction in flux recovery. The use of 1.5 pm pre-filtration after alum treatment showed little improvement in water quality but led to a drastic reduction in flux recovery, which was attributed to diminishing the protective layer on the membrane surface, thus enabling internal fouling. The performance of ACH was comparable to alum at low dissolved organic carbon (DOC) and cell concentration, but was not as effective as alum at high DOC and cell concentration due to the formation of more compact ACH flocs, which resulted in a higher cake layer specific resistance, leading to the deterioration of performance. 相似文献