The impact of metallic coagulants on the removal of organic compounds from oil sands process-affected water

Coagulation/flocculation (CF) by use of alum and cationic polymer polyDADMAC, was performed as a pretreatment for remediation of oil sands process-affected water (OSPW). Various factors were investigated and the process was optimized to improve efficiency of removal of organic carbon and turbidity. Destabilization of the particles occurred through charge neutralization by adsorption of hydroxide precipitates. Scanning electron microscope images revealed that the resultant flocs were compact. The CF process significantly reduced concentrations of naphthenic acids (NAs) and oxidized NAs by 37 and 86%, respectively, demonstrating the applicability of CF pretreatment to remove a persistent and toxic organic fraction from OSPW. Concentrations of vanadium and barium were decreased by 67-78% and 42-63%, respectively. Analysis of surface functional groups on flocs also confirmed the removal of the NAs compounds. Flocculation with cationic polymer compared to alum, caused toxicity toward the benthic invertebrate, Chironoums dilutus, thus application of the polymer should be limited.     

Selective coagulant recovery from water treatment plant residuals using Donnan membrane process

Fouling of membrane surfaces by particulate matter and large organic molecules is relatively common for pressure-driven membrane processes, namely, reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF). Donnan membrane process (DMP) or Donnan Dialysis is driven by electrochemical potential gradient across a semipermeable ion exchange membrane. Theoretically, DMP is not susceptible to fouling by fine particulates and/or large organic molecules. According to information available in the open literature, however, DMP has not been tried to treat slurry or sludge with relatively high concentration of suspended solids or large organic molecules. This study presents the salient results of an extensive investigation pertaining to selective alum recovery from water treatment residuals (WTR) using DMP. Water treatment plants use alum, Al2(SO4)3 x 14H2O, as a coagulant, alum being finally converted and discharged as insoluble aluminum hydroxide along with natural organic matters (NOM), suspended solids, and other trace impurities. One commercial cation exchange membrane, namely Nafion 117 from DuPont Chemical Co., was used in the study for treating WTR obtained from two different water treatment plants in Pennsylvania. A series of laboratory tests confirmed that over 70% of alum is easily recoverable, and recovered alum is essentially free of particulate matter, NOM, and other trace metals. Most importantly, after repeated usage in the presence of high concentration of NOM and suspended solids, there was no noticeable decline in aluminum flux through the membrane, i.e., membrane surface fouling was practically absent. The DMP process involves coupled transport of Al3+ and H+ across the cation exchange membrane, and intramembrane transport was the rate-limiting step. Experimentally determined aluminum-hydrogen interdiffusion coefficient (D(Al-H)) values within the membrane were quite high (approximately 10(-6) cm2/s) under representative conditions, thus confirming high alum recovery rate. DMP was also found equally effective in recovering Fe(III) based coagulants from WTR.     

三元助留体系对二次纤维的助留助滤作用

研究阳离子淀粉(CS)/阳离子聚丙烯酰胺(CPAM)/膨润土三元微粒助留助滤体系对国产废箱纸板浆料的助留助滤作用及成纸性能。用SZP06和PCD03对浆料表面电荷和溶解电荷的测定表明,取代度为0.04的CS加入量为0.4%时能较好地吸附浆料体系中的阴离子垃圾。采用正交实验的方法对三元助留助滤系统中的三种助剂进行了优化,结果表明CS、CPAM和膨润土较合适的用量分别为0.6%、0.09%和0.25%;当CS在第7s加入、CPAM在第10s加入时,浆料的留着率达到90.6%。加入CS后的三元体系与CPAM/膨润土二元体系对成纸物理性能的比较表明,三元体系手抄纸抗张指数提高20.7%,撕裂指数提高16.7%,耐折度提高33.3%。     

Effect of microfiltration concentration factor on serum protein removal from skim milk using spiral-wound polymeric membranes

Our objective was to determine the effect of concentration factor (CF) on the removal of serum protein (SP) from skim milk during microfiltration (MF) at 50°C using a 0.3-μm-pore-size spiral-wound (SW) polymeric polyvinylidene fluoride (PVDF) membrane. Pasteurized (72°C for 16 s) skim milk was MF (50°C) at 3 CF (1.50, 2.25, and 3.00×), each on a separate day of processing starting with skim milk. Two phases of MF were used at each CF, with an initial startup-stabilization phase (40 min in full recycle mode) to achieve the desired CF, followed by a steady-state phase (90-min feed-and-bleed with recycle) where data was collected. The experiment was replicated 3 times, and SP removal from skim milk was quantified at each CF. System pressures, flow rates, CF, and fluxes were monitored during the 90-min run. Permeate flux increased (12.8, 15.3, and 19.0 kg/m² per hour) with decreasing CF from 3.00 to 1.50×, whereas fouled water flux did not differ among CF, indicating that the effect of membrane fouling on hydraulic resistance of the membrane was similar at all CF. However, the CF used when microfiltering skim milk (50°C) with a 0.3-μm polymeric SW PVDF membrane did affect the percentage of SP removed. As CF increased from 1.50 to 3.00×, the percentage of SP removed from skim milk increased from 10.56 to 35.57%, in a single stage bleed-and-feed MF system. Percentage SP removal from skim milk was lower than the theoretical value. Rejection of SP during MF of skim milk with SW PVDF membranes was caused by fouling of the membrane, not by the membrane itself and differences in the foulant characteristic among CF influenced SP rejection more than it influenced hydraulic resistance. We hypothesize that differences in the conditions near the surface of the membrane and within the pores during the first few minutes of processing, when casein micelles pass through the membrane, influenced the rejection of SP because more pore size narrowing and plugging occurred at low CF than at high CF due to a slower rate of gel layer formation at low CF. It is possible that percentage removal of SP from skim milk at 50°C could be improved by optimization of the membrane pore size, feed solution composition and concentration, and controlling the rate of formation of the concentration polarization-derived gel layer at the surface of the membrane during the first few minutes of processing.     

Hyperbranched polyethyleneimine induced cross-linking of polyamide-imide nanofiltration hollow fiber membranes for effective removal of ciprofloxacin

This study aims to develop a positively charged nanofiltration (NF) hollow fiber membrane for effective removal of ciprofloxacin from water. A novel NF membrane was fabricated by hyperbranched polyethyleneimine (PEI) induced cross-linking on a polyamide-imide hollow fiber support. The spongy-like, fully porous membrane support provides minimal transport resistance and sufficient mechanical strengths for water permeation under high pressures. It is found that the PEI modification significantly influences NF performance through the mechanisms of size exclusion, charge repulsion, and solute-membrane affinity. Specifically, after PEI induced cross-linking, the membrane pore size is significantly reduced. The membrane surface becomes more hydrophilic and positively charged. As a result of these synergic effects, the rejection of ciprofloxacin is substantially enhanced. Furthermore, experimental results show that the molecular weight of PEI has tremendous effect on NF performance of the as-modified membrane. The NF membrane modified by a high molecular weight PEI_60K exhibits the highest rejection, the lowest fouling tendency, and keeps a constant flux over the whole pH range. This study may have great potential for developing high-performance antifouling NF hollow fiber membranes for various industrial applications.     

不同类别聚丙烯酰胺的作用原理及其助留助滤性能

聚丙烯酰胺(PAM)是一种新型高效的助留助滤剂,是一种易溶于水、几乎不溶于有机溶剂的有机高分子化合物。聚丙烯酰胺主链上有活泼的酰胺基和双键,通过采用不同的合成方法引入不同的官能团,可以得到不同分子量和不同电荷密度的聚丙烯酰胺产品。本文对阳离子聚丙烯酰胺、阴离子聚丙烯酰胺、两性聚丙烯酰胺及非离子聚丙烯酰胺这四大种类聚丙烯酰胺的特征、与纤维素表面及悬浮物之间相互作用机理及受外界条件影响分别进行了简要综述,展望了聚丙烯酰胺类助留助滤剂的发展方向与应用前景。     

Polyelectrolyte and silver nanoparticle modification of microfiltration membranes to mitigate organic and bacterial fouling

Membrane fouling remains one of the most problematic issues surrounding membrane use in water and wastewater treatment applications. Organic and biological fouling contribute to irreversible fouling and flux decline in these processes. The aim of this study was to reduce both organic and biological fouling by modifying the surface of commercially available poly(ether sulfone) (PES) membranes using the polyelectrolyte multilayer modification method with poly(styrenesulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), and silver nanoparticles (nanoAg) integrated onto the surface as stable, thin (15 nm) films. PSS increases the hydrophilicity of the membrane and increases the negative surface charge, while integration of nanoAg into the top PSS layer imparts biocidal characteristics to the modified surface. Fouling was simulated by filtering aqueous solutions of humic acid (5 and 20 mg L(-1)), a suspension of Escherichia coli (10(6) colony-forming units (CFU) mL(-1)), and a mixture of both foulants through unmodified and modified PES membranes under batch conditions. Filtration and cleaning studies confirmed that the modification significantly reduced organic and biological fouling.     

Comprehensive bench- and pilot-scale investigation of trace organic compounds rejection by forward osmosis

Forward osmosis (FO) is a membrane separation technology that has been studied in recent years for application in water treatment and desalination. It can best be utilized as an advanced pretreatment for desalination processes such as reverse osmosis (RO) and nanofiltration (NF) to protect the membranes from scaling and fouling. In the current study the rejection of trace organic compounds (TOrCs) such as pharmaceuticals, personal care products, plasticizers, and flame-retardants by FO and a hybrid FO-RO system was investigated at both the bench- and pilot-scales. More than 30 compounds were analyzed, of which 23 nonionic and ionic TOrCs were identified and quantified in the studied wastewater effluent. Results revealed that almost all TOrCs were highly rejected by the FO membrane at the pilot scale while rejection at the bench scale was generally lower. Membrane fouling, especially under field conditions when wastewater effluent is the FO feed solution, plays a substantial role in increasing the rejection of TOrCs in FO. The hybrid FO-RO process demonstrated that the dual barrier treatment of impaired water could lead to more than 99% rejection of almost all TOrCs that were identified in reclaimed water.     

Novel functionalized nano-TiO2 loading electrocatalytic membrane for oily wastewater treatment

Membrane fouling is a critical problem in membrane filtration processes for water purification. Electrocatalytic membrane reactor (ECMR) was an effective method to avoid membrane fouling and improve water quality. This study focuses on the preparation and characterization of a novel functionalized nano-TiO(2) loading electrocatalytic membrane for oily wastewater treatment. A TiO(2)/carbon membrane used in the reactor is prepared by coating TiO(2) as an electrocatalyst via a sol-gel process on a conductive microporous carbon membrane. In order to immobilize TiO(2) on the carbon membrane, the carbon membrane is first pretreated with HNO(3) to generate the oxygen-containing functional groups on its surface. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) analyses are used to evaluate the morphology and microstructure of the membranes. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements are employed to illustrate the eletrochemical activity of the TiO(2)/carbon membrane. The membrane performance is investigated by treating oily wastewater. The oil removal rate increases with a decrease in the liquid hourly space velocity (LHSV) through the ECMR. The COD removal rate was 100% with a LHSV of 7.2 h(-1) and 87.4% with a LHSV of 21.6 h(-1) during the treatment of 200 mg/L oily water. It suggests that the synergistic effect of electrocatalytic oxidation and membrane separation in the ECMR plays a key role.     

Effect of membrane property and operating conditions on phytochemical properties and permeate flux during clarification of pineapple juice

The effects of membrane property on the permeate flux, membrane fouling and quality of clarified pineapple juice were studied. Both microfiltration (membrane pore size of 0.1 and 0.2 μm) and ultrafiltration (membrane molecular weight cut-off (MWCO) of 30 and 100 kDa) membranes were employed. Membrane filtration did not have significant effects on the pH, reducing sugar and acidity of clarified juice whereas the suspended solids and microorganism were completely removed. The 0.2 μm membrane gave the highest permeate flux, total vitamin C content, total phenolic content and antioxidant capacity as well as the highest value of irreversible fouling. Based on these results, the membrane with pore size of 0.2 μm was considered to be the most suitable membrane for the clarification of pineapple juice. The optimum operating conditions for the clarification pineapple juice by membrane filtration was a cross-flow velocity of 3.4 ms⁻¹ and transmembrane pressure (TMP) of 0.7 bar. An average flux of about 37 lm⁻² h⁻¹ was obtained during the microfiltration of pineapple juice under the optimum conditions using batch concentration mode.     

Unified membrane fouling index for low pressure membrane filtration of natural waters: principles and methodology

Membrane filtration is considered an important technology that can contribute to the sustainability of water supplies. However, its continued development necessitates the establishment of proper techniques for the assessment of membrane fouling. Unified Membrane Fouling Index (UMFI) was developed in this study in order to quantify and assess the fouling of low-pressure membranes (LPM) observed at various scales of water treatment. The foundation of UMFI is a revised Hermia model applied to both constant pressure and constant flux filtration. The adoption of UMFI makes it possible to simplify and standardize the bench-scale testing of membrane fouling potential by directly using the commercial LPM of interest. This approach can overcome a major challenge to fouling assessment, i.e., the membrane-specificity of fouling potential, which has not been wholly addressed by existing fouling indices. The fundamentals of UMFI are presented in this paper, together with the methodology for bench-scale testing. The application of UMFI to the assessment of the fouling of a LPM by a natural surface water is also discussed. Good agreement between bench-scale UMFI and pilot-scale UMFI was found, suggesting the validity of this new scientific concept for environmental applications.     

活性红染料染色漂洗废水的混凝脱色

将无机高分子混凝剂聚合硅酸氯化铝(PSAC)与阳离子型聚季铵盐絮凝剂按比例复配，用于处理活性红染料漂洗废水。在试验废水pH值为7，室温，复合混凝剂投加量为1mL／L，助凝剂PAM投加量为2mg／L的条件下，脱色率高达98．8％，CODCr去除率为77．8％；出水水质能达到国家一级排放标准，并能满足一般生产回用水水质的要求。     

Nanofiltration for trace organic contaminant removal: structure, solution, and membrane fouling effects on the rejection of perfluorochemicals

The use of nanofiltration (NF) membranes for water recycling requires an improved understanding of the factors that govern rejection of potentially harmful organic trace contaminants. Rejections of 15 perfluorochemicals (PFCs)--5 perfluorinated sulfonates, 9 perfluorinated carboxylates, and perfluorooctane sulfonamide (FOSA)--by four nanofiltration membranes (NF270, NF200, DK, and DL) were measured. Rejections for anionic species were >95% for MW >300 g/mol. FOSA (MW = 499 g/mol), which is uncharged at the pH of deionized water (5.6), was rejected as little as 42% (DL membrane). Decreasing the pH to less than 3 decreases rejection by up to 35%, effectively increasing the MWCO of NF270 by >200 g/mol, while a 2500 mg/L NaCl equivalent increase in ionic strength reduces rejections <1%. An alginate fouling layer increases transmission, where quantifiable, by factors of 4-8. Accumulation of PFCs on membranes was measured after the completion of rejection experiments. Based on rejection kinetics and the extent of sorption, we infer that two different sorption processes are significant: charged species adsorb quickly to the membrane surface, whereas the uncharged FOSA absorbs within the membrane matrix in a much slower process.     

Identification of Fouling Mechanism During Ultrafiltration of Stevia Extract

Stevioside is one of the naturally occurring sweetener, which can be widely applied in food, drinks, medicine, and daily chemicals. Membrane separation has potential application in clarification of stevioside from pretreated stevia extract by ultrafiltration. In the present study, namely 5-, 10-, 30-, and 100-kDa molecular weight cutoff membranes have been used. Quantification of membrane fouling during ultrafiltration is essential for improving the efficiency of such filtration systems. A systematic analysis was carried out to identify the prevailing mechanism of membrane fouling using a batch unstirred filtration cell. It was observed that the flux decline phenomenon was governed by cake filtration in almost all the membranes. For 100 kDa membrane, both internal pore blocking and cake filtration are equally important. Resistance in series analysis shows that the cake resistance is several orders of magnitude higher than the membrane resistance. The cake resistance is almost independent of transmembrane pressure drop, which indicates the incompressible nature of the cake. A response surface analysis was carried out to quantify the development of cake resistance with time during ultrafiltration of various membranes. Quality parameters show that the 30-kDa membrane is better suited for clarification purposes. Identification of the fouling mechanism would aid in the process of design and scaling up of such clarification setup in future.     

Decolorization of vegetable oils by membrane processing

Membrane decolorization studies of chlorophyll added sunflower oil and crude soybean oil were conducted in a batch membrane cell using two polymeric composite membranes (NTGS-2100 and NTGS-1100), and one polyethylene microfiltration membrane (PE-30). NTGS-2100 membrane could remove up to 96% and 72% chlorophyll from the undiluted and oil-hexane (50 wt%) solutions, respectively. Permeate oil flux was very low when undiluted oil was used as feed, but improved many fold by diluting with hexane. NTGS-1100 membrane gave higher permeate flux compared to NTGS-2100, but showed reduced rejection. Absorbance spectra of crude soybean oil and the permeate in the 350-550 nm range showed a greater degree of decolorization by polymeric composite membranes. PE-30 membrane showed insignificant rejection of color compounds. The permeate of conventionally bleached soybean oil showed a reduction in extinction coefficients at 232 and 270 nm, indicating possible rejection of dienes and trienes by the composite polymeric membranes. The membrane process was effective in reducing the color compounds in crude vegetable oils besides offering many advantages over the conventional process.     

Optimization of coagulation-flocculation process for palm oil mill effluent using response surface methodology

The coagulation-flocculation process incorporated with membrane separation technology will become a new approach for palm oil mill effluent (POME) treatment as well as water reclamation and reuse. In our current research, a membrane pilot plant has been used for POME treatment where the coagulation-flocculation process plays an important role as a pretreatment process for the mitigation of membrane fouling problems. The pretreated POME with low turbidity values and high water recovery are the main objectives to be achieved through the coagulation-flocculation process. Therefore, treatment optimization to serve these purposes was performed using jar tests and applying a response surface methodology (RSM) to the results. A 2(3) full-factorial central composite design (CCD) was chosen to explain the effect and interaction of three factors: coagulant dosage, flocculent dosage, and pH. The CCD is successfully demonstrated to efficiently determine the optimized parameters, where 78% of water recovery with a 20 NTU turbidity value can be obtained at the optimum value of coagulant dosage, flocculent dosage, and pH at 15 000 mg/L, 300 mg/L, and 6, respectively.     

The effect of ultrasound waves on the efficiency of membrane clarification of pomegranate juice

Pomegranate juice has a turbid appearance, which poses difficulties in its concentration process. Membrane clarification can be used to clarify pomegranate juice; however, membrane fouling reduces the permeate flux, limiting its effectiveness. Ultrasound at 30 kHz was used to reduce membrane fouling. Results were compared with the data obtained for membrane clarification without ultrasonic treatment at the same temperature. Results showed that permeate flux increased with ultrasonic treatment. Evaluation of different membrane fouling characteristics showed that the total membrane resistance fell due to the reduction in irreversible fouling and cake resistance. However, ultrasound did not affect the thick caking produced in membrane processing at low feed‐flow rates. Evaluation of the physicochemical properties of pomegranate juice showed that ultrasound can decrease antioxidant activity due to the reduction in total anthocyanin content. Also, total soluble solid content and acidity of pomegranate juice changed with ultrasonic treatment.     

硫酸铝和聚合氯化铝性能的比较

添加硫酸铝和聚合氯化铝的纸浆的电荷特征,是决定铝化物发挥功效的重要因素。本文利用胶体滴定技术,从电荷分析的角度,比较了硫酸铝和聚合氯化铝的性能。研究了它们对纸浆pH值的电导率的影响;用量对纸浆电荷的影响;研究了pH值对添加相同量硫酸铝和聚合氯化铝的纸浆的电荷的影响;最后比较了两者的助留、助滤和施胶效果。结果表明,聚合氯化铝是一种比硫酸铝更有效的阳离子聚集剂。     

Ultrafiltration fouling of amylose solution: Behavior, characterization and mechanism

Applications of ultrafiltration membrane often deal with feed streams containing amylose starch. This paper describes a detailed investigation of amylose fouling during ultrafiltration. Commercial membranes made of polysulfone and fluoro polymer were used. Both adsorptive and ultrafiltration fouling were investigated. Experiments using different membrane characteristics, feed concentrations and trans-membrane pressures were carried out. The resulting fouling was characterized by water flux and contact angle measurements and was visualized by scanning electron microscopy (SEM). The results suggest that solute adsorption has occurred as noticed by significant water flux reductions as well as changes in membrane characteristics. Further, both reversible and irreversible fouling have occurred during ultrafiltration with irreversible fouling was more dominant. Apparently, cake layer formation initiated by either adsorption due to hydrophobic–hydrophobic interactions or pore blocking is the dominant fouling mechanism. However, pore narrowing instead of pore blocking was also observed for the membrane having large and relative uniform pore structure or for the ultrafiltration using low trans-membrane pressure or low solute concentration. Membrane autopsy using SEM confirmed the formation of solute layer on the membrane surface.     

氢氧化镁铝胶体微粒与纤维和阴离子聚丙烯酰胺的吸附

利用透射电镜和离心分离法对氢氧化镁铝胶体微粒与纤维和阴离子聚丙烯酰胺的吸附作用进行了研究.结果表明,带有正电荷的氢氧化镁铝胶体与阴离子聚丙烯酰胺和纤维、细小纤维之间具有强烈的吸附作用,并且在纤维中加入阴离子聚丙烯酰胺可提高氢氧化镁铝的吸附量.