Effect of potassium permanganate dosing position on the performance of coagulation/ultrafiltration combined process

The effects of potassium permanganate(KMnO_4)dosing position on the natural organic matter(NOM)removal as well as membrane fouling were investigated in the coagulation/ultrafiltration combined process.KMnO_4 oxidation altered the NOM characteristics in terms of hydrophobicity and molecular weight,and destroyed humic substances originated from terraneous organisms in raw water.The optimal KMnO_4 dosage was 0.5 mg·L~(-1) in the peroxidation enhanced coagulation process with respect to the dissolved organic carbon(DOC)removal.When KMnO_4 was dosed into both upstream and downstream of coagulation,namely in the proposed twoposition dosing mode,coagulation and KMnO_4 oxidation worked individually on the apparent DOC removal.However,compared to the KMnO_4 addition prior to or after coagulation,the two-position dosing mode dramatically alleviated membrane fouling and reduced fouling irreversibility.This was attributed to the change of NOM characteristics as a result of KMnO_4 addition prior to coagulation and the presence of MnO_2 on membrane surface as a result of KMnO_4 addition prior to ultrafiltration.This work may provide useful information for the application of KMnO_4 oxidation in the coagulation/ultrafiltration combined system.     

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.     

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。     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

Changes in NOM Fractionation through Treatment: A Comparison of Ozonation and Chlorination.

NOM isolation and fractionation to provide insight into the effectiveness of ozonation vs. conventional water treatment was done. In this research, the dissolved portion of natural organic matter (NOM) or dissolved organic matter (DOM) at two surface drinking water treatment plants that treat the same source water was fractionated by resin adsorption. The first treatment plant uses conventional treatment (coagulation, sedimentation, and filtration) with intermediate free chlorination and post chlorination while the second plant uses conventional treatment with pre and intermediate ozonation, and multi-media filtration unit operation. Several different sampling locations within each plant were selected for DOM isolation and fractionation into six fractions (hydrophobic acid, neutral and base, and hydrophilic acid, neutral, and base). The effectiveness of each treatment plant on the oxidation and removal of each organic fraction are discussed. Oxidation by ozone leads to better overall performance in the removal of DOM.     

循环絮凝对水中SUVA及膜污染的影响

将循环接触絮凝与膜过滤相结合组成循环接触絮凝-膜过滤（CF-MF）工艺,以传统混凝-膜过滤（C-MF）工艺为对照,考察两种工艺在延缓膜污染方面的差异。采用比紫外吸光度（SUVA）作为有机物亲/疏水特性的评价指标,分析工艺变化对SUVA的影响以及SUVA和综合膜污染指数（UMFI）之间的内在联系。结果发现,膜出水SUVA与膜污染呈很好的相关性,出水SUVA越高,膜污染越严重;在最佳工艺条件下,CF-MF出水和混凝上清液SUVA分别达到了1.74 L·mg^-1·m^-1和1.18 L·mg^-1·m^-1,去除率与C-MF工艺相比分别提高17%和29%,说明CF-MF工艺对水中疏水性物质的去除效果比C-MF更好,能够有效控制疏水性物质对膜形成的污染;与C-MF相比,CF-MF能够更有效地去除水中的有机物,当混凝剂氯化铁投加量为6 mg·L^-1、回流絮体浓度为10 mg·L^-1时,UV₂₅₄和DOC的去除率分别达到了58.75%和49.7%。     

城市污水二级出水有机物性状及对膜污染的贡献

将城市污水二级出水中溶解性有机物分为强疏水性、弱疏水性和亲水性组分,研究其对超滤膜的污染。测定结果表明,二级出水中有机物对膜污染影响程度顺序为:强疏水性有机物>亲水性有机物>弱疏水性有机物。究其原因:(1)膜污染与有机物分子量大小有关,膜选择性地截留强疏水性有机物主要是这类有机物分子量较大所致。(2)从三维荧光光谱图上看,3个组分中均含有腐殖酸类荧光峰,说明腐殖酸类物质对膜通量的衰减贡献最大。(3)强疏水性组分中所含有机物最为复杂,荧光峰最为明显,由此可见膜污染的程度不仅与组分中所含有机物的种类有关,而且与其含量有关。此外,膜被有机物污染的程度与膜对有机物的去除率有着密切的关系。总荧光强度(FLU)可作为总有机物含量的一种指标来反映有机物被膜截留的情况。     

Fouling effects of humic and alginic acids in nanofiltration and influence of solution composition

The objectives of this research were to investigate the combined and individual influence of hydrophobic and hydrophilic fractions of NOM on the fouling of thin-film composite nanofiltration (NF) membranes, and also the roles of solution chemistry on the permeate flux and fouling. Combined fouling is compared to the individual fouling behaviors (i.e., alginate or humic acid alone).Experiments were conducted using a “cross-flow” pilot-scale membrane unit with a full circulation mode. Fouling experiments were performed with individual and combined humic acid and alginate.The results demonstrated that increasing organic concentration increased greatly the rate and extent of flux reduction. Individual alginate fouling was more detrimental than individual humic acid fouling, and alginate exhibited greater flux decline than humic acid fouling alone at the same conditions. A higher flux decline was observed with increasing proportions of aliginate in combined fouling. In other word, there are antagonistic effects during combined fouling because the charge functional groups of two above foulants are negative and increase electrostatic repulsion between two foulants and also foulant-membrane. The flux reduction increased with increasing ionic strength, foulant concentrations, and with lower pH. This observation implies the importance of interaction between various foulants for deeper understanding of fouling phenomena. The membrane fouling was largely dependent on organic properties and fractions.     

Optimization of NOM Removal during Water Treatment

Abstract

The aim of this paper is to describe the removal efficiency of individual fractions of natural organic matter (NOM) and the aluminum transformation during treatment of two types of surface water with an increased concentration of NOM of various origins. The coagulation conditions (dose of destabilization reagent and reaction pH value) were optimized for the best NOM and aluminum removal. The results show that the NOM removal efficiency depends on the NOM character, using destabilizing reagents and reaction conditions. The optimized doses of destabilization reagents influence especially the removal of hydrophilic charged (CHA) and very hydrophobic acids (VHA) fractions during treatment of both types of raw water. In contrast to this, the removal of hydrophilic neutral (NEU) fraction is very low (? _NEU =0.13–0.22). The optimal destabilization reagent dosage is characterized by the lowest content of the total reactive aluminum concentration and relatively low concentration of dissolved organic aluminum.     

Investigation of Ozone Reaction in River Waters Causing Instantaneous Ozone Demand

Ozone consumption by water can be characterized by the instantaneous ozone demand (IOD) and a pseudo first order decay constant. Utilizing the flow injection analytical system for measuring IOD, the instantaneous ozone demand characteristics of two river waters (Korea) were investigated, utilizing a ?OH probe compound and ?OH scavenger, and were compared with those of two commercial humic acids (the Suwannee River humic acid and Aldrich humic acid). The major findings were as follows; (1) The IOD in river waters was found to be mainly due to the reaction of the ozone with natural organic matter (NOM), which constituted approximately 0.26–0.29?mg/mg DOC, and was responsible for the consumption of more than 40% of the applied ozone. Whereas, the IOD of the two commercial humic acids were three times more than those of the river waters. (2) The IOD in the river waters was mainly caused by the direct ozone reaction with dissolved organics, not from the ?OH mediated ozone reaction. However, for the two commercial humic acids, more than 40% of the IOD came from the ?OH mediated ozone reaction. (3) The hydrophobic fractions of the dissolved organics in the river waters were mainly responsible for the IOD. The IOD of the hydrophobic organics was approximately ten times larger than that of the hydrophilic organics. Although the exact magnitude of the IOD, and the relative importance of the direct/indirect ozone reaction with river water may vary greatly depending upon the source of the NOM, the characteristics of the IOD compromise a significant fraction of the ozone dose need (especially in achieving good ozone disinfection) in water treatment plants.     

Combined Adsorption/Ultrafiltration of Secondary Effluents Using Powdered Zeolites

The performance of powdered zeolite (PZ) adsorption/ultrafiltration (UF) with real secondary effluents is investigated. With the assistance of PZs, the membrane fouling rate was reduced and the permeate flux recovery as well as the advanced treatment of the secondary effluents were enhanced. 3D excitation emission matrix (3D‐EEM) fluorescence spectra indicate that the removal of fluorescence intensity for aromatic proteins, fulvic acid‐like materials, soluble microbial by‐product‐like materials, and humic acid‐like organics could be improved by PZs. UF membranes with PZs can increase the removal efficiency of organics, especially of those with low molecular weight. The characteristics of the cake layer on the surface of an UF membrane were determined by scanning electron microscopy and electron energy‐dispersive X‐ray spectroscopy for the combined adsorption/UF membrane.     

Comparative analysis for fouling characteristics of river water,secondary effluent,and humic acid solution in ceramic membrane ultrafiltration

Ceramic membrane ultrafiltration experiments were performed with 7-channel tubular membrane (molecular weight cutoff = 300 kD) at a constant transmembrane pressure and crossflow rate under recirculation mode. In the experiments, the fouling characteristics of river water (RW, dissolved organic carbon (DOC) = 3.4 mg/L) were compared with humic acid solution (HA1, DOC = 3.7 mg/L). Also, the fouling behaviors of secondary effluent (SE, DOC = 7.9 mg/L) were compared with HA2 (DOC = 8.5 mg/L). Fluorescence excitation-emission matrix, modified Hermia’s model, and resistance-in-series model were used to analyze the fouling characteristics. Results demonstrated that RW and SE could cause ceramic membrane fouling more rapidly due to their hydrophilic organic compositions in comparison with hydrophobic HA.     

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.     

Comparative Studies on Coagulation and Adsorption as a Pretreatment Method for the Performance Improvement of Submerged MF Membrane for Secondary Domestic Wastewater Treatment

Abstract

Membrane fouling is the main limitation of water and wastewater treatment. Coagulation and adsorption can remove organic materials which play an important role in fouling phenomena. Thus, this study focused on the comparison of the hybrid process of coagulation and adsorption coupled with microfiltration (MF) membrane for the secondary domestic wastewater from an apartment complex in Gwangju city, South Korea. Coagulation and adsorption were adopted as a pretreatment method prior to MF treatment. Three different powdered activated carbon (PAC) and ferric chloride were used as an adsorbent and as a coagulant. MF was operated in a submerged mode using hollow fiber polyethylene membrane with pore size of 0.4 µm for the separation of suspended organic solids resulted from coagulation or PAC particles, which are used for adsorbing organics dissolved in wastewater. Prior to study on the hybrid system, the performance of coagulation and adsorption processes were optimized individually for the removal of organics. Then, the overall performance for the hybrid system of coagulation/MF and PAC/MF was evaluated based on TOC removal, turbidity removal, and flux decline. It was found that the combined coagulation/MF and PAC/MF showed similar performance for TOC removal while coagulation/MF resulted in a significant decrease of the flux decline.     

Application of hybrid photocatalysis systems coupled with flocculation and adsorption to biologically treated sewage effluent for organic removal

The application of a photocatalysis hybrid system coupled with flocculation and adsorption in treating biologically treated sewage effluent (BTSE) was investigated. The removal of organic matter was studied in terms of dissolved organic matter (DOC), removal of hydrophobic (HP), transphilic (TP) and hydrophilic (HL) fractions, and molecular weight (MW) distribution. The photooxidation removed the majority of MW (263, 580, 865, and 43109 daltons) within the first 30 minutes of operation. The removal of MW range of organic matter of 330 daltons was low. DOC removal of HP and TP was high (80%). DOC removal from HL fraction was, however, minimum. The photocatalytic system with simultaneous PAC adsorption and FeCl₃ flocculation removed the effluent organic matter (EfOM) up to 90%. Therefore, photocatalysis with the ferric chloride (FeCl₃) flocculation and PAC adsorption hybrid system can be a possible option in the removal of DOC from BTSE for water reuse.     

Performance of Flocculation and Adsorption Pretreatments to Ultrafiltration of Biologically Treated Sewage Effluent: the Effect of Seasonal Variations

Abstract

The effect of seasonal variations on ultrafiltration (UF) following pretreatment was investigated in terms of organic removal, removal of fraction, and molecular weight (MW) distribution. The MW range of effluent organic matter (EfOM) in biologically treated sewage effluent during winter (BTSE‐W) consisted of large MW. However, the MW ranged from 3000 to 200 daltons in biologically treated sewage effluent in the summer (BTSE‐S). During filtration experiments of BTSE‐S, the UF NTR 7410 filter showed rapid flux decline with time without pretreatment. FeCl₃ flocculation removed the hydrophobic (HP) and hydrophilic (HL) fractions with different trends. In winter the HP fraction was removed up to 68.5%, whereas during the summer season, the HL fraction was removed by up to 59.8%. Flocculation removed large MW organics together with small MW, while PAC removed the majority of small MW organics. The flux decline with adsorption was also more severe than that with flocculation. Considering MW distribution, when large MW was removed by flocculation, the flux decline was minimized, whereas PAC adsorption which removed small MW still decreased the permeate flux.     

Natural organic matter and formation of trihalomethanes in two water treatment processes

The investigation involved the study of performance of two local plants' slightly different treatment processes for the removal of natural organic matter (NOM) which comprises trihalomethane (THM) precursors. Ultrafiltration separated the contained NOM into various apparent molecular weight (AMW) fractions to reveal the two processes NOM removal efficiencies, in terms of dissolved organic carbon (DOC), UV absorbance (UV254) and THM formation potential (THMFP). DOC and UV254 levels of source water at both plants tested low and they concentrated in the portion with AMW less than 3,000 Daltons. The combined expression of UV254 with DOC as specific ultraviolet light absorbance (SUVA) indicated that the source water of Macau had a value less than 3 L/mg-m. Therefore the main DOC content was fulvic in character, which is difficult to remove and favors the formation of brominated THMs. Low DOC removal percentages recorded in both processes confirm this observation. However, both processes showed similar removal efficiency of around 50% on humic substances and THM precursors quantified by measurements of UV254 and THMFP, respectively.     

磁性离子交换树脂强化水源中有机物去除性能研究

在调查某水厂水源水质及传统工艺处理效能的基础上,对比探讨了粉末活性炭和磁性离子交换树脂分别以预吸附、预吸附-混凝、混凝沉淀-吸附等不同工艺对水源水中溶解性有机物的去除效能,确定了最佳工艺。该水源存在季节性有机物污染,亲水性有机质占比80%。水厂传统工艺对有机物的去除能力约20%~30%。与其他工艺相比,树脂预吸附-混凝对有机物的去除功效最好,DOC和UV254的去除率分别达到41.48%和80.0%,与单独强化混凝相比,该工艺可将DOC和UV254的去除效率分别提高17.7和35.49个百分点,且可减少86.67%的混凝剂投加量。Langmuir等温线模型和拟二级动力学方程可定量描述树脂吸附有机物平衡和动力学。磁性离子交换树脂预吸附可作为该水厂强化去除水源中溶解性有机物的可靠技术。     

Effect of hydrophilic/hydrophobic fractions of natural organic matter on irreversible fouling of membranes

Natural organic matter (NOM) has been identified as a major factor affecting membrane processes performances, but its impact is difficult to quantify from global parameters such as organic carbon content. The extent of fouling due to the different fractions of NOM from surface water has been examined in dead-end ultrafiltration using criteria such as flux decline and irreversibility in regard with organic matter rejection. The most important flux decline was observed during the filtration of the hydrophilic acids fraction whereas fulvic acids led to the most irreversible fouling. Furthermore, the hydrophilic fraction lost its fouling character when mixed with other fractions underlining that interactions between numerous components are possibly more important than the composition itself.     

pH adjustment for seasonal control of UF fouling by natural waters

Natural surface waters in Algarve, Portugal, have important seasonal variations in natural organic matter (NOM) content, that influences ultrafiltration (UF) performance. This paper addresses the evaluation of the pH adjustment for seasonal control of UF fouling at a laboratory scale, using a plate and frame polysulphone membrane of 47 kDa MWCO. Results of two types of natural water (clear water, 3-5 NTU, and turbid water, 33-34.6 NTU) and three different water pH values (acid, neutral and basic) demonstrated that the pH adjustment could be used for seasonal control of UF fouling: when the water has less NOM (in dry periods, clear water), the acid pH will improve the UF performance, while during and after intense rainfall periods (turbid water with high NOM concentration) basic pH will be advantageous, because it minimizes membrane fouling. This behaviour is explained for clear water in terms of charge effects on membrane size. For turbid water, the electrostatic repulsion between membrane surface and NOM and turbidity particles is reduced at pH 4.13 and protonation of the NOM functional groups decreases the hydrodynamic radii of humic substances while increasing their hydrophobicity and their tendency to adsorb. Therefore, a dense fouling layer develops and flux is lower at pH 4.13 than at pH 8.33. These results together with the observed raw water feed concentrations decline and rejection decrease with WRR confirm the extensive adsorption on the membrane enhanced by the moderate hardness cation of this water.