Lab and pilot scale investigations on membrane fouling during the ultrafiltration of surface water

In the combined laboratory and pilot plant investigation powder activated carbon dosing and inline coagulation were investigated for surface water from river Spree. The aim was to understand the fouling behaviour of this raw water and to understand and to identify strategies to minimize the irreversible fouling in this application. Trials with activated carbon showed significant differences in the adsorption of biopolymers on different types of carbon. Whereas the TOC removal was in the same range for both types the coarse carbon type showed very small removal of biopolymers. The effect of different types of coagulants, dosage and pH was investigated in a laboratory filtration set up. Samples were investigated by LC-OCD measurements for fractionation of DOC for raw water, flocculated water and permeate. The removal of biopolymers was possible with iron and alumina salts, however the alumina salts tend to remove humic acids as well and this results in a higher overall DOC removal. In the pilot plant the inline coagulation was investigated under actual site conditions. Whereas the results for the effect of coagulation and DOC removal were confirmed it turned out that aluminium coagulants give a significantly higher increase in differential pressure. The use of ferric coagulants at slightly acidic pH was thus identified as a robust method to achieve a stable performance of the ultrafiltration system at this site.     

Optimizing the coagulant dose to control membrane fouling in combined coagulation/ultrafiltration systems for textile wastewater reclamation

Optimal coagulation conditions need to be re-examined when coagulation is coupled to membrane filtration for wastewater treatment. This work focused on the optimization of coagulant dosing in order to control membrane fouling in ultrafiltration (UF), following coagulation for the reclamation of textile wastewater. The effects of pore size and coagulant types and dosages on flux decline were investigated using a stirred-cell UF unit. The flux was greatly enhanced for the UF membrane when a coagulant was added, whereas for the microfiltration (MF) membrane the flux decreased. This could be attributed to changes in the size of coagulated particles and their interaction with membrane pores. At a low dosage (e.g., 0.0371 mM as Al), the polyaluminum chloride (PACl) coagulant was found to control the flux decline most effectively for low ionic-strength wastewater. The optimal dose minimized the fouling and cake layer resistances, although it was sharp and dependent on influent composition. The cake layer protected the membrane from fouling, but it provided additional resistance to permeation. Analyses of turbidity, particle size, and membrane surface exhibited the characteristics of coagulated particles and their cake structures that are closely associated with flux behavior.     

Application of ultrafiltration integrated with coagulation for improved NOM removal

Alum coagulation followed by ultrafiltration was studied in order to improve water quality for surface water treatment. The influence of pH (from 5 to 10) and coagulant dose (25, 40 and 50 g alum/m³ equal to 1.795, 2.872 and 3.59 g Al/m³) on the investigated process performance was analyzed. Two ultrafiltration membranes (cut-off 30 kD) made of regenerated cellulose and polyethersulphone were used. The experiments showed that even the lowest dose of alum significantly increased the quality of permeate. The maximum NOM separation was observed at pH 6 and a further increase of solution reaction resulted in a worsening of the permeate quality.     

A statistical method for quantifying the different fouling effects of three combined water sources on an ultrafiltration membrane

A simple statistical model has been developed to explain the fouling of an ultrafiltration (UF) membrane treating three mixed feedwater matrices. A tubular UF membrane operating under dead-end conditions, based at the Millennium Dome Water Recycling Plant, was used for this study. The feedwaters comprised surface water, greywater and groundwater, all having distinct quality differences. The analysis utilises the least-squares fit regression technique. Fouling, as manifested in the diurnal change in trans-membrane pressure (TMP), is related numerically to the volumes of the feedwaters, the mean TMP and the cross product of mean TMP with water volume. It was found that the impact of the recovered greywater on TMP was not statistically significant only due to the low daily volumes of this matrix generated, compared with those of the other sources. The model that best described the data was chosen on the basis of highest R² and lowest residual mean square, and demonstrated the surface water to be more fouling than the ground water by a factor, which is a function of the mean TMP.     

Modification of polysulfone ultrafiltration membranes by CO2 plasma treatment

Carbon dioxide plasmas were used to modify hydrophobic polysulfone ultrafiltration membranes to create hydrophilic surfaces throughout the membrane structure. The water contact angle of the upstream side of the membrane (facing the plasma) decreased to zero after treatment and did not change even after several months of aging. The water contact angle of the downstream side decreased with increasing CO₂ plasma treatment time and became zero for treatment times ≥ 1 min (P = 10 W). Functional groups introduced by CO₂ plasma treatment were examined using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). For the treated membranes, the atomic concentration of oxygen increased dramatically and small amounts of nitrogen incorporation were also observed. Membrane performance was tested with water flux measurements as well as protein fouling studies. For treated membranes, the water flux recovery measured after protein fouling was significantly higher than that for control membranes, with nearly 100% recovery after gentle cleaning in water. Moreover, the amount of protein adsorption decreased by over 75% for the treated membranes compared to control membranes. This suggests the protein fouling layer is essentially completely reversible on the CO₂ plasma treated membranes.     

高锰酸钾对维生素B1生产废水强化混凝作用的试验研究

通过对维生素B1生产废水混凝试验中是否投加高锰酸钾的试验研究，发现高锰酸钾是一种高效的强化混凝药剂。同时研究了投药顺序、投药量、转速、搅拌时间、pH值、温度等因素对混凝效果的影响，得到了处理维生素B1废水的最佳混凝条件。     

Prefiltration of wastewater effluent: Effects on foulants and performance during dead end ultrafiltration

An important trend in the development of ultrafiltration (UF) of wastewater effluent is the integration of pretreatment to improve the performance of membranes. In this paper the results of a study on the effect of three prefiltration techniques (multimedia filtration, granulated activated carbon filtration and biological activated carbon filtration) on foulants and performance of UF are presented. The objectives of the study are: (1) to establish the different effect of three prefiltration configurations on performance of UF and foulants of wastewater effluent and (2), to determine in which particle size range the most particles or colloidals are removed after the three prefiltration configurations.From all of the filters, the biological granulated activated carbon filter (BGAC) presented the highest increase of filterability. During this study, the specific ultrafiltration resistance (SUR) value of the filtrate is always below 5 · 10¹² m^− 2 independent on the incoming SUR value. From all the foulants especially the proteins and humic substances are removed by granulated activated carbon filter (GAC) and BGAC. BGAC is the only prefiltration technique that shows significant removal of the fraction between 0.1 µm and 0.2 µm.     

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.     

Coagulation pretreatment for a large-scale ultrafiltration process treating water from the Taihu River

A large-scale ultrafiltration (UF) system integrated with coagulation was applied to produce drinking water from the highly turbid Taihu River. This UF installation could produce 10,000 m³ drinking water per day. In this study, the effect of FeCl₃ coagulant on the performance of the UF system was evaluated. Results showed that with the integration of coagulation, not only qualified drinking water was obtained from the high turbidity raw water, but also high UF specific flux was maintained, ca.190 200 L/m²·hr·bar, and the chemical cleaning period was largely prolonged. The natural organic matter removal mechanism by coagulation was also discussed.     

Temporal evolution of resistances in the ultrafiltration of humic substances

Many ultrafiltration-related studies have emphasized fouling mechanisms, but few works have been done on resistance modeling. This study investigated the temporal variation of different resistances including membrane intrinsic resistance, fouling resistance, and concentration polarization resistance, based on a well established resistance--in-series model. The various resistances were determined at an early stage of ultrafiltration operation. During the initial operation period, the total filtration resistance for ultrafiltration of humic substance solution ranged from 1.9×10⁹ to 2.2×10⁹Pa·/m. The principal resistance of ultrafiltration is from intrinsic membrane resistance, accounting for more than half of the total resistance (56-85%).     

Study on the cleaning of new ultrafiltration spiral-woundmodules to prevent membrane fouling (including biological fouling)

A study of cleaning a Bulgarian OF 60 PAN spiral-wound module was carried out on an ultrafiltration unit(Millipore, USA). Chemical cleaning of the membrane with a 0.25% solution of sodium metabisulfite did not prevent biological fouling. When treated with a 1% solution of formaldehyde, membrane fouling was diminished and the ultrafiltrate obtained contained a significantly lower number of microorganisms and colloid formations including iron and humic acids. After treatment with the two cleaning agents, the membrane maintained its flux for the water studied within a range of 1.58 to 1.64 m³/m²/d. The effect on the contaminants to be removed was also found to be comparatively constant. Membrane selectivity remained constant at different permeate yields.     

高锰酸钾安全强化预氯化工艺消毒效能的研究

预氯化是一种传统的应用比较广泛的预氧化技术,但其处理有机物浓度较高的水源水时不但生成大量对人体健康有害的消毒副产物,而且消毒性能下降,不利于多级屏障作用的发挥。因此,对受污染水源水进行预氯化处理时．安全强化其消毒效能是十分必要的。以受污染水为试验水样．从微生物安全性及化学安全性两个方面考察高锰酸钾与氯联用预处理工艺的消毒效能以及对三卤甲烷的控制作用。结果表明．高锰酸钾与氯联用预处理工艺的消毒效能要明显好于它们单独使用的情况,经Berenbaum公式计算证实高锰酸钾与氯在降低微生物指标上具有协同作用;与投药总量相同的预氯化工艺相比,高锰酸钾与氯联用预处理工艺处理受污染水时,在消毒效能上相当．而在副产物生成上,能够减少近60％的三卤甲烷的生成量。此项研究为受污染水的预处理提供了一个安全预氯化的新途径。     

Fouling of nanofiltration and ultrafiltration membranes applied for wastewater regeneration in the textile industry

Textile effluents usually contain high concentrations of inorganics as well as organics, and the therefore difficult to treat. Membrane processes can be used for many of these wastewaters in the textile industry. Two typical examples are discussed: (1) the use of nanofiltration for the treatment of exhausted dye baths, in view of water recycling, and (2) the use of ultrafiltration for the removal of spin finish from waste water resulting from rinsing of textile fibres. Both applications are in principle feasible, but in practice the process is negatively influenced by membrane fouling. In the first application, fouling is assumed to be caused by (ad)sorption of organic compounds, which has a large influence because of the high concentrations used in textile dyeing. Furthermore, the high salt concentrations result in a decrease of the effective driving force because of the high osmotic pressures obtained for typical dye baths. Experimental results are discussed, and the applicability of nanofiltration is related to the characteristics of the dye baths for different dyeing methods. In the second application, the concentration of organic compounds is relatively low, but because of the hydrophobic nature of the spin finish compounds, a significant effect of membrane fouling is expected. An improvement is suggested by using nanofiltration membranes instead of ultrafiltration membranes.     

Decolorization of azo dye Orange II by ferrate(VI)-hypochlorite liquid mixture, potassium ferrate(VI) and potassium permanganate

Ferrate(VI)-hypochlorite liquid mixture was prepared using hypochlorite, an industrial by-product, via wet oxidation method. Its oxidizing ability was investigated by decolorizing azo dye Orange II in batch experiments, and compared with potassium ferrate(VI) and potassium permanganate. Effects of the oxidant concentration, dye concentration, initial pH of dye solutions and UV 254 nm irradiation were examined. The color removal by potassium permanganate, potassium ferrate(VI) and the ferrate(VI)-hypochlorite liquid mixture at 30 min reached 17.7%, 62.0% and 95.2%, respectively. The ferrate(VI)-hypochlorite liquid mixture maintained a high decolorization efficiency over a wide pH range from 3.0 to 11.0, indicating that the initial solution pH had little impact on its oxidizing power. However, the decolorization efficiency by potassium permanganate was proved to be highly pH dependent and the lowest efficiency was observed at neutral pH. UV 254 nm irradiation did not enhance the decolorization efficiencies significantly for both the ferrate(VI)-hypochlorite liquid mixture and potassium permanganate over a wide pH range.     

Effects of ultrasound parameters on ultrasound-assisted ultrafiltration using cross-flow hollow fiber membrane for Radix astragalus extracts

In this study, the effects of ultrasonic parameters on permeate flux and fouling resistances in the ultrasound-assisted ultrafiltration (UAUF) process of Radix astragalus extracts with hollow fiber membrane (HFM) was investigated. Ultrasonic parameters such as frequency, power and irradiation mode all can significantly affect the flux and fouling during the UAUF process, though the ultrasound power intensity was attenuated to be 10% only from generator. Concentration polarization and cake layer were decreased effectively by the ultrasound irradiation, resulting in a high flux performance. Meanwhile, HFM was susceptible to the irradiation at high power and low frequency compared with a flat sheet membrane. Ultrasound can not only enhance the permeate flux in UAUF but also cause breakage of HFM at an unsuited ultrasound field. It can be applied to the ultrafiltration process with HFM at an appropriate power and frequency.     

高锰酸钾氧化安息香的实验研究

研究了不同条件下,高锰酸钾对安息香的氧化规律。当反应条件控制为2.1 g(0.01 mol)安息香,1.5 g(0.01 mol)高锰酸钾,15 mL冰醋酸,反应温度85～95℃回流1.5 h,高锰酸钾能将安息香氧化裂解为苯甲酸。当反应条件为4.32 g(0.02 mol)安息香,1.5 g(0.01 mol)高锰酸钾,6 g(0.11 mol)碱A,12 mL水,反应温度在80～90℃,高锰酸钾将安息香氧化生成二苯乙二酮;碱量增加至12 g时,二苯乙二酮重排为二苯乙醇酸,产率高达98%。     

Application of combined coagulation-ultrafiltration membrane process for water treatment

The objectives of this research are to identify the membrane fouling potential due to different fractions of NOM and correlate the physicochemical properties of NOM and membranes with the adsorption of humic substances on membrane and investigate the mechanism of coagulation affecting UF, and find the optimum conditions of the combined of coagulation with UF membrane filtration for NOM removal. For Nakdong river water, the humic acid fraction was the most reactive precursor fraction for the formation of the ratio of THMFP/DOC (STHMFP) and TOXFP/DOC (STOXFP). The result of adsorption kinetics tests showed that hydrophobic organics adsorbed much more quickly than hydrophilic organics on both membranes. Thus, hydrophobic compounds exhibited a preferential adsorption onto membrane. In case of the effect of membrane properties on the adsorption of organic fractions, the adsorption ratio (C₁/C_e) was greater for the hydrophobic membrane than for the hydrophilic membrane regardless of the kind of organic fractions. For combined coagulation with membrane process, flux reduction rate showed lower than the UF process alone. Also, the rate of flux decline for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Applying the coagulation process before membrane filtration showed not only reduced membrane fouling, but also improved removal of dissolved organic materials that might otherwise not be removed by the membrane. That is, during the mixing period, substantial changes in particle size distribution occurred under rapid and slow mixing conditions due to the simultaneous formation of microflocs and NOM precipitates. Therefore, combined pretreatment using coagulation (both rapid mixing and slow mixing) improved not only dissolved organic removal efficiency but also DBP (Disinfection By-Product) precursor's removal efficiency.     

Simultaneous removal of SO2 and NOx by microwave with potassium permanganate over zeolite

Simultaneous sulfur dioxide (SO₂) and nitrogen oxides (NO_x) removal from flue gas can be achieved with high efficiency by microwave with potassium permanganate (KMnO₄) over zeolite. The experimental results showed that the microwave reactor could be used to oxidation of SO₂ to sulfate with the best desulfurization efficiency of 96.8% and oxidize NO_x to nitrates with the best NO_x removal efficiency of 98.4%. Microwave accentuates catalytic oxidation treatment, and microwave addition can increase the SO₂ and NO_x removal efficiency by 7.2% and 12.2% separately. The addition of zeolite to microwave potassium permanganate increases from 16.5% to 43.5% the microwave removal efficiency for SO₂, and the NO_x removal efficiency from 85.6% to 98.2%. The additional use of potassium permanganate to the microwave zeolite leads to the enhancement of SO₂ removal efficiency up from 53.9% to 95%, and denitrification efficiency up from 85.6% to 98.2%. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and denitrification are 259 W and 0.357 s, respectively. SO₂ and NO_x were rapidly oxidized in microwave induced catalytic oxidation reaction using potassium permanganate with zeolite being the catalyst and microwave absorbent.     

Integration of immersed membrane ultrafiltration with coagulation and activated carbon adsorption for advanced treatment of municipal wastewater

A pilot-scale hollow-fiber ultrafiltration unit was installed in the wastewater treatment plant of Rethymno, Crete, Greece. The system was fed with treated unchlorinated effluent. Three sets of experiments were conducted. At first, the UF pilot unit was operated as a direct filtration unit. During the second phase, ultrafiltration was combined with the addition of a coagulant (alum). The last phase of the experiments involved the addition of activated carbon (either powdered or granular) into the system. During direct filtration, the average COD removal was 19%, while the average DOC was removed to a similar extent (25%). Effluent turbidity was practically independent of the influent turbidity with an overall average removal of 90%. Faecal and total coliform were also removed efficiently reaching average removals of 99.94% and 99.96%, respectively. Removal of heavy metals in particulate form also took place. When ultrafiltration was combined with in-line coagulation, the results were similar to those exhibited without coagulation. Combining ultrafiltration with powdered activated carbon resulted in DOC removal as high as 60%. However, after the addition of the PAC, the transmembrane pressure increased rapidly due to the formation of PAC cake on the membrane surface. Application of granular activated carbon resulted in 36% reduction of DOC without causing an increase to the trans-membrane pressure. Heavy metals present in the secondary effluent were also removed very efficiently by the GAC in the UF tank.     

高锰酸钾复合药剂对水中邻氯酚去除效能的研究

本文以水中的邻氯苯酚为研究对象,在实验基础上,考察了高锰酸钾及高锰酸钾复合药剂对纯水中微量邻氯酚的去除效果,用可见分光光度计分析,对二者的除酚效果进行了对比。结果表明:高锰酸钾复合药剂对水中微量邻氯酚具有较好的去除能力。同时还考察了水样pH值,高锰酸钾及其复合药剂投加量,反应水温,反应时间等因素对邻氯酚去除效果的影响。