Preparation of poly(ether sulfone) hollow fiber UF membrane for removal of NOM

In this study, a high performance poly(ether sulfone) (PES) hollow fiber ultrafiltration (UF) membrane has been prepared for removal of natural organic matter (NOM). The membrane was spun from a dope solution containing PES/poly (vinyl pyrrolidone) (PVP 40K)/N‐methyl‐2‐pyrrolidone (NMP) by using a wet‐spinning process. Characterization of the membrane in terms of pure water flux, molecule weight cut‐off (MWCO), and retention for a model humic acid (HA) were conducted, and the fouling resistance was analyzed. The experimental results showed that the membrane had a pure water permeability of 20 × 10^?5 L m^?2 h^?1 Pa^?1 and a nominal MWCO of 6000 Da. The results also showed that the membrane retention for humic acid was over 97% and both productivity and selectivity for HA increased with increasing feed velocity. The PES membrane in this study exhibited a much lower fouling tendency than the commercial polysulfone membrane. SEM images revealed that the membrane had an outer dense skin and a porous inner surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 430–435, 2006     

Irreversible Fouling in MF/UF Membranes Caused by Natural Organic Matters (NOMs) Isolated from Different Origins

Abstract

For more efficient use of membrane technology in water treatment, it is essential to understand more about the fouling that requires chemical cleaning to be eliminated (i.e., irreversible fouling). In this study, five different MF/UF membranes and four types of organic matter collected from different origins were examined in terms of the degree of irreversible membrane fouling. Experimental results demonstrated that the extent of irreversible fouling differed significantly depending on the properties of both the membrane and organic matter. Among the tested membranes, UF membranes made of polyacrylonitrile (PAN) exhibited the best performance in terms of prevention of irreversible fouling. In contrast, MF membranes, especially one made of polyvinylidenefluoride (PVDF), suffered significant irreversible fouling. Conventional methods for characterization of organic matter such as specific ultraviolet absorption (SUVA), XAD fractionation, and excitation‐emission matrix (EEM) were found to be inadequate for prediction of the degree of irreversible fouling. This is because these analytical methods represent an average property of bulk organic matter, while the fouling was actually caused by some specific fractions. It was revealed that hydrophilic fraction of the organic matter was responsible for the irreversible fouling regardless of the type of membranes or organic matter.     

Comparison of ceramic and polymeric membranes for natural organic matter (NOM) removal

Ceramic membranes were compared with polymeric membranes with respect to natural organic matter (NOM) removal using two removal mechanisms (i.e., size exclusion and charge repulsion). NOM properties including molecular weight and molecular structure, at different charge densities, were examined, along with membrane characteristics, including molecular weight cut-off (MWCO) and surface charge. Integrated analyses of both NOM and membrane characteristics provided information for membrane evaluation of different membrane materials and configurations (i.e., tubular vs. flat sheet type). A ceramic tight-ultrafiltration (UF) membrane showed the same potential as a similar nanofiltration (NF) polymeric membrane, in terms of the minimization of haloacetic acid (HAA) formation. Moreover, a ceramic OF membrane with a MWCO of 8000 Daltons showed almost the same behavior as an equitable polymeric UF membrane with a MW CO of 8000 Daltons in terms of NOM removal.     

Colloidal organic matter fouling of UF membranes: role of NOM composition & size

The aim of this study was to fractionate pre-filtered surface water using a 3.5 and a 10 kDa dialysis membrane, and to compare the rate of fouling and the fouling reversibility/irreversibility of the NOM fractions. Trial dialyses (3.5 and 10 kDa) were carried out for 6 and 21 days with pre-filtered surface water using synthetic surface water as dialysate. The aim of the trials was to optimize the dialysis process for NOM fractionation. DOC, Ca²⁺, Mg²⁺, soluble silica and bacteria were monitored at intervals during the dialysis process. Thereafter, the various NOM fractions (with low and high Ca²⁺) were fed to a miniature UF system operated at a constant flux of 138.5 L/m2 h, filtration cycle times of 31.5 min and backwash duration of 1.75 min. A PES/PSV hollow fiber UF membrane (MWCO 100 kDa) with a surface area of 0.0125 m² was employed for the filtration tests (X-Flow). Transmembrane pressure (TMP) and UF feed and permeate (LC-OCD) were monitored at regular intervals. For a dialysate recirculation of 95 L/h, sample to dialysate ratio of 5.2:80 L and a dialysate change frequency of 3 times per 24 h, the shortest duration of dialysis was about 6–7 days for both 3.5 and 10 kDa dialyses membranes. The removal of organic carbon (OC) increased with dialysis duration and MWCO of the bags. The biopolymer fraction increased from 120% to 240% when the duration of dialysis was increased from 6 days (1.1 mg DOC/L, 151 mg Ca/L) to 21 days (0.82 mg DOC/L, 133 mg Ca/L) with the 10 kDa dialysis membrane. The increased biopolymer fraction in the NOM sample that was dialyzed for 21 days resulted in a doubling of the fouling rate from 3.5 to 6.6 mbar/min per mg DOC/L. The other NOM fractions (humics and building blocks) and the Ca/DOC ratio was more or less the same in both NOM samples suggesting that biopolymers were the major cause of UF fouling.     

Fractionation of Pre‐Hydrolysis Products from Lignocellulosic Biomass by an Ultrafiltration Ceramic Tubular Membrane

Abstract

Development of the lignocellulosic‐biomass‐based biorefinery for making transportation fuels requires the production of valuable byproducts, minimizing the chemical consumables, and efficient water recovery and reuse. Our focus is on a liquid stream containing a variety of soluble lignin species and alkalinity that is produced by a novel extrusion reactor that was used to break down corn stover to cellulose, sugar acids, and lignin. We report on the ambient temperature fractionation of this byproduct stream with a γ‐alumina ceramic tubular membrane. There are four primary figures‐of‐merit investigated in this study: permeance decline, total organic carbon recovery (TOC) and sodium recovery, and the average molecular mass of organic compounds rejected and permeated. These fractionation results are compared relative to differing feed compositions, recovery, and flux. There was definite fractionation between organic (mostly soluble lignin) compounds. The average molar mass of the organic compounds in the permeate remained around 1000 g/mol; however, they ranged from 1500–4000 g/mol in the retentate. In contrast to the TOC, there was no rejection of sodium ions by the membrane (a desirable objective.) With respect to flux decline, the primary form of resistance (>99%), causing significant permeance decline, was a gel/deposition layer formed on the membrane surface. However, this could be flushed away with periodic rinses using water and/or 0.1 M NaOH. After operation at a cumulative filtration load of ～4.9 Mg/m² with various soluble lignin containing streams, 70% of the membrane's virgin pure water permeance could be recovered by a more vigorous cleaning with 0.1 M NaOH including soaking and permeation. Our results seem very consistent with those previously observed for membrane applications within the pulp and paper industry.     

Polyaniline membranes for nanofiltration of solvent from dewaxed lube oil

Polyaniline nanofiltration membranes were synthesized to examine a potential candidate for application of solvent recovery from lube oil. An integrally skinned polyaniline membrane was cast on a woven polyester fabric and then was chemically crosslinked with glutaraldehyde in order to further increase the membranes resistant in a methyl ethyl ketone and toluene mixture. Subsequently, membrane performance was tested under different operational conditions. The operation pressure was fixed at 35 bar and was held constant for all of the tests. The membrane demonstrated a permeate flux of 10 l/(m² h) and oil rejection of 69%.

Abbreviations: PANi: Polyaniline; PI: polyimide; MEK: methyl ethyl ketone; GA: glutaraldehyde; NMP: N-methyl-2-pyrrolidone; 4MP: 4-methylpiperidine; SEM: Scanning Electron Microscope; OSN: organic solvent nanofiltration; MWCO: molecular weight cut-off.     

Separation of Carboxylic Acids from Carboxylates by Diffusion Dialysis

Abstract

Acetic acid/sodium acetate and propionic acid/sodium propionate were separated by the diffusion dialysis technique using Neosepta AFN‐7 and Selemion DSV membranes. Accounting for molarities of carboxylic acids and salts in broths produced by the pH controlled bacterial fermentation (pH 4–6), the experiments were carried out with carboxylates in excess of acids. The sorption equilibria established for acetic acid, propionic acid, and the sodium salts of both acids (single solute experiments) revealed a high sorption of acids in both membranes and the rejection of carboxylates. The partition coefficients were found to be from unity up to 2 for the acids and 0.04–0.05 for the salts. Reflecting a high sorption, the fluxes for the acids amounted from 1.5 to 2.0 mol · m^?2 · h^?1 and only 0.07–0.08 mol · m^?2 · h^?1 for the salts (one molar solutions). The separation factors computed upon the experiments performed with the ternary solutions were found between 20 to 37 for the Neosepta AFN‐7 membrane and about 29 for the Selemion DSV membrane. Accounting additionally, for the results of the separation of lactic acid from sodium lactate reported in our earlier paper the results prove the diffusion dialysis to be applicable to the separation of mean strength and weak carboxylic acids from their salts.     

Integration of Photocatalysis and Microfiltration in Removing Effluent Organic Matter from Treated Sewage Effluent

An integration of photocatalysis with low-pressure submerged membrane has attracted growing interest for its synergic advantages in water and wastewater treatment. In this study, the adsorption and photocatalytic oxidation of organic compounds by UV light responsive titanium dioxide (TiO₂) were investigated. First, the adsorption behavior of the TiO₂ was examined by the adsorption isotherm and kinetics experiments. The photocatalytic reactivity of the catalysts was then compared at different operating conditions. The results indicate that the Freundlich model described well the adsorption capacity of both materials. The photocatalytic kinetics showed that the highest removal of effluent organic matter (EfOM) was achieved at an optimum concentration of 1.0 g/L of TiO₂. In addition, it was found that the pre-photosensitization with titanium dioxide/ultra-voilet radiation (TiO₂/UV) could effectively reduce membrane fouling and enhance the permeate flux of the submerged membrane reactor when it was used as a post-treatment. An increase of 10% in organic removal efficiency was achieved by the posttreatment of membrane filtration. The sustainable flux of the membrane reactor increased from 25 up to 40 L/m²·h when the pretreatment of photocatalysis was used.     

Tannery Waste Treatment: Leaching,Filtration and Cake Dewatering Using a Membrane Filter Press (a Pilot Plant Study)

Abstract

In Alcanena (Portugal) the waste water treatment plant (WWTP) receives tannery waste, after a pretreatment for sulphides and the tanning exhaust baths have been sent to a recovery unit and the municipal waste water from Alcanena residential area. Physical, chemical, and biological treatment processes are involved, and the end products are sludge of ～71% moisture containing mainly organic matter, sulfides, iron, chromium, and other metals. The sludge is dumped, after stabilization, in a specially designed hazardous waste landfill.

In this study, tannery mixed sludge (from chemical and biological treatments) was leached and filtered. Leaching was carried out using sulfuric acid (pH 0.5) to release residual sulfides and metals from the slurry. Hydrogen sulfide (H₂S) was flushed out into an oxidation trap (hypochlorite/alkaline tank) in which H₂S transforms to soluble sulfate. The acidified sludge was fed into a membrane filter press where it was filtered, acid‐washed, water–washed, membrane‐squeezed, and vacuum‐dried reaching lower moisture levels (20–30%). The process cycle is approximately 101–137 min in our experiments; however, from this work, a cycle of 90 min to produce cakes with 0.9 cm thickness in the industrial scale through cutting some operational time, reaching final moisture of ～20% at the end of the dewatering cycle, can be estimated. Filtration was carried out at different feed pressure (3–5 bar) with and without diatomite precoating. The effect of different amounts of diatomite body‐feed was studied. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite precoating and the increased amounts of diatomite body feed. Cake washing was accomplished using 0.05 M H₂SO₄ (acid washing), to remove residual metals, followed by water washing, to remove cake acidity. Cake dewatering via membrane squeezing was applied using hot water (65°C), and cake moisture was dropped from ～71% before squeezing to 42% after squeezing. With vacuum application over the hot cakes, for 30 min, cake moisture decreased to ～20% for cakes with an average thickness of 0.9 cm. Cake chemical analysis showed chromium levels lower than 1000 mg/kg (the maximum Cr concentration allowed by the Portuguese legislation in a solid residue for use in agricultural soil). In addition, produced cake (without diatomite body feed) has a calorific value of 11,000 kJ/kg and accordingly it can be used as a source of energy.     

Separation Characteristics of Dimethylformamide/Water Mixtures through Alginate Membranes by Pervaporation,Vapor Permeation and Vapor Permeation with Temperature Difference Methods

Abstract

In this study permeation and separation characteristics of dimethylformamide (DMF)/water mixtures were investigated by pervaporation (PV), vapor permeation (VP), and vapor permeation with temperature difference (TDVP) methods using alginate membranes crosslinked with calcium chloride. The effects of membrane thickness (30–90 µm), feed composition (0–100 wt%), operating temperature (30–50°C) on the permeation rates and separation factors were investigated. The permeation rate was found to be inversely proportional to the membrane thickness whereas separation factor increased as the membrane thickness was increased. It was observed that the permeation rates in VP and TDVP were lower than in PV however the highest separation factors were obtained with TDVP method. Alginate membranes gave permeation rates of 0.97–1.2 kg/m² h and separation factors of 17–63 depending on the operation conditions and the method. In addition, sorption‐diffusion properties of the alginate membranes were investigated at the operating temperature and the feed composition. It was found that the sorption selectivity was dominant factor for the separating of DMF/water mixtures.     

Comparative Coagulant Demand of Polyferric Chloride and Ferric Chloride for the Removal of Humic Acid

Abstract

This paper is concerned with the potential advantages of the use of polyferric chloride as a coagulant for the removal of natural organic matter (e.g., humic acid) in water treatment. In particular, this paper assesses the effects of the basic nature of polyferric chloride, the type of water, and the coagulation pH on the humic acid removal performance. The comparative dose demand of polyferric chloride and ferric chloride was assessed in terms of a good humic acid removal efficiency (> 50%) achieved. It was found that a polyferric chloride with a basic ratio of 0.3 can achieve the best humic acid removal. The water having both humic acid and colloidal particles was favorable to the floc development and a better humic acid removal. For the same coagulation conditions, the dose demand of polyferric chloride was 50% less than that of FeCl₃ for a > 50% humic acid removal.     

Determination of residual organic matter in extracted oil sands using a low temperature ashing method

The application of a low temperature ashing method for estimating total residual organic matter (toluene insolubles) in oil sands is described. A linear correlation exists between organic carbon content and loss on ignition at 400 ± 10 °C of solvent extracted oil sands. The ratio between total organic carbon and the weight loss on ignition (CT/LOl) owing to the removal of residual organic matter is much lower than that obtained for toluene soluble bitumen fractions, indicating very different chemical composition for the residual organic matter. The measured carbon content of the residual organic matter in oil sands suggests that this material could be a mixture of various fractions contained in resins, asphaltenes, asphaltic acids and humic acids.     

天然有机物提取及表征技术近期发展动态

在阐述天然有机物(NOM)来源和危害的基础上,对NOM的提取、分离和表征技术的近期发展动态进行了全面综述。介绍了NOM的各种提取和分离方法,对各种提取方法的优缺点和产率进行了分析比较,指出以反渗透、大孔树脂和膜分离为核心的工艺为目前最主要的提取分离手段。此外,详细列举了包括光谱、色谱、核磁共振、原子力显微成像等在内的NOM表征方法,对各分析结果所对应的NOM的结构特征和物化性质进行了阐述。     

Evaluation of the performance of tight-UF membranes with respect to NOM removal using effective MWCO, molecular weight, and apparent diffusivity of NOM

Concepts for the effective MWCO of tight-UF membranes, and apparent diffusion coefficients for NOM, were introduced to determine the mechanisms influencing NOM removal and to explain the various behaviors of NOM removal by UF membranes with different hydrophobicities, permeability, and surface charges. Colloidal NOM (COM) and non-colloidal hydrophobic NOM (NCD HP) constituents were chosen for the evaluation of two different UF membranes. For a relatively hydrophobic, relatively high permeability, and less negatively charged UF membrane, the hydrophobic fractions of COM were preferentially removed and were also removed by a size exclusion mechanism (i.e., both hydrophobic interaction and size exclusion mechanisms). The NCD HP exhibited no such preferential removal of the hydrophobic fractions, but could be removed by a size exclusion mechanism (i.e., only size exclusion mechanism). With a relatively hydrophilic, relatively low permeability, and more negatively charged UF membrane, COM exhibited no preferential removal of the hydrophobic fractions, but could be removed by a size exclusion mechanism (i.e., only size exclusion mechanism). Whereas the hydrophobic fractions of the NCD HP were preferentially removed, these could not be removed by a size exclusion mechanism (i.e., only hydrophobic interaction mechanism). The apparent diffusion coefficients of NOM, as determined from NOM diffusion experiments using a diffusion cell equipped with a regenerated cellulose membrane, were much lower than those calculated by the Stokes-Einstein relation. The diffusion coefficient of NOM is expected to be used to predict and explain NOM transport behaviors in tight-UF membranes.     

Problems with and local solutions for organic matter management in Vietnam

Soil organic matter plays a major role in sustainable agricultural development in Vietnam. A general soil evaluation shows that the content of organic matter in most soil units in Vietnam ranges between 0.5 to 3.0% soil organic matter (in the A and B horizon only) with lower levels especially on sloping land. Most upland soils (70% that contain ≤ 2% soil organic matter) are in danger due to imminent soil erosion. Soil organic matter is lost very quickly due to erosion, lack of organic manure and poor farming techniques in these areas. Using green hedgerows along contour lines and intercropping with legume species to cover the soil are technological options to control soil erosion and improve soil organic matter content on sloping land. Green hedgerows significantly reduce soil and organic matter loss by 50–70%, compared to sloping land without hedgerows. Intercropping with legume species reduces soil loss by 40–50%, and can provide the soil with 2.5–12 tons of green manure/ha/year. However, more studies are needed to identify the best technologies for managing soil organic matter in upland areas. This revised version was published online in June 2006 with corrections to the Cover Date.     

In‐line Flocculation‐Submersed MF/UF Membrane Hybrid System in Tertiary Wastewater Treatment

Abstract

Coagulation/flocculation pre‐treatment of feeds can successfully mitigate the drawbacks of membrane micro‐ and ultra filtration processes: fouling and limited ability to remove organic pollutants. Laboratory experiments conducted with a synthetic wastewater (representing biologically treated secondary effluent) using 0.1 µm pore size hollow fiber membrane showed that simple in‐line flocculation pre‐treatment with inorganic coagulants dramatically reduced membrane fouling rates. The hybrid system also ensured over 70% organic matter removal in terms of dissolved organic carbon (DOC). In the experiments in in‐line flocculation outperformed clarification pre‐treatment at optimum coagulant dosages. Differences in floc characteristics and elevated suspended solids concentrations in the membrane tank may explain this finding, but the exact causes were not investigated in this study. The beneficial effects of in‐line flocculation pre‐treatment to MF/UF separation were also confirmed in the treatment of septic tank effluent in a membrane bioreactor (MBR). The fouling rate of the 0.4 µm pore size (flat‐sheet) membrane was substantially reduced with 10–100 mg L^?1 ferric chloride coagulant doses, and total dissolved chemical oxygen demand (DCOD) removal also increased from 66% up to 93%. These findings are consistent with the results of other experimental studies and show that pre‐treatment controls submersed MF/UF filtration performance.     

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.     

Affinity Separation of Trypsin from Goat Pancreatic Extract Using a Polyethersulfone Ultrafiltration Membrane

Abstract

Ultrafiltration of goat pancreatic extract to obtain trypsin, using Soybean Trypsin Inhibitor as affinity ligand and a 30 kDa MWCO polyethersulfone membrane, is studied by examining the effect of varying transmembrane pressure and pancreatic extract: wash buffer ratio on active trypsin yield and flux/throughput profiles. For all process conditions considered, no detectable trypsin activity is found in the washing-phase permeates confirming excellent ligand-trypsin binding. Maximum trypsin yield obtained, at 1:1 feed ratio and 4 kg/cm² pressure, is 74%. Mass flux of eluted protein as well as of washed-off impurities are also maximized under these conditions.     

水中残留有机物分子量分布特征和对膜性能的影响

本试验分析了城市二级处理水的残留有机物分子量分布特征及对超滤膜过滤透水性能的影响，并利用混凝法，活性炭吸附，臭氧-活性炭吸附进行了处理。研究结果表明：（1）城市污水厂二级出水中溶解态有机物主要集中在〈2k分子量区间上；（2）混凝处理后，高分子量有机物低分子化效果明显；PAC吸附能有效去除小分子量有机物；臭氧-PAC联用，大分子量有机物和小分子量有机物所占比例均有所下降，表明臭氧氧化与PAC吸附联用在去除有机物方面具有很好的互补性；（3）分子量分布对原水的透水通量影响较大；选择混凝、PAC或臭氧-PAC等作为膜法处理的预处理单元，对城市污水再生处理具有重要价值。     

投加粉末活性炭对超滤膜去除海水中有机物的影响

超滤膜的有机污染问题是膜法海水预处理技术在海水淡化工程应用面临的重要挑战,粉末活性炭吸附是目前常用的膜前预处理手段之一。本文对比分析了直接超滤和投加粉末活性炭后对海水中有机物的截留能力,利用三维荧光光谱分析了投加粉末活性炭对超滤膜截留有机物的影响机制,并考察了海水超滤过程中通量变化及膜污染情况。研究结果表明,投加粉末活性炭能够强化超滤膜对海水浊度和有机物的去除,当粉末活性炭投量为200mg/L时,整个系统对海水中DOC去除率从直接超滤时的55.1%提高到77.6%。利用粉末活性炭的吸附作用及其在超滤膜表面形成的疏松滤饼层能够显著提高超滤系统对海水中腐植酸类有机物的去除能力。与直接超滤相比,粉末活性炭-超滤系统对改善膜通量的作用有限,但粉末活性炭形成的滤饼层能够避免超滤膜与有机物直接接触,可显著减缓超滤膜的不可逆污染。