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.     

Effect of intermittent back ozonation for membrane fouling reduction in microfiltration using a metal membrane

In a microfiltration system using a metal membrane for municipal raw sewage reclamation, the following research points were mainly investigated: 1) Effect of intermittent back ozonation for membrane fouling reduction, 2) effect of operational parameters for permeation flux, and 3) the estimation of optimal operational conditions using an empirical model in the case of back ozonation. Intermittent back ozonation dramatically improved the membrane fouling. The permeation flux was recovered up to 90% of initial flux with dosage of 0.27 (mgO₃/cm³/cycle). Among operational parameters, we found that ozone concentration was the most influential parameter for membrane fouling reduction. In the case of back ozonation, the optimal values of each operational parameter with respect to ozone concentration, ozone gas flow rate and injection time to satisfy 90% recovery of initial flux were 20.2 (mgO₃/L), 3.1 (L/min) and 2.1 (min), respectively. Intermittent back ozonation is believed to be an innovative and feasible technology for fouling reduction and high permeation flux in case inorganic membrane material is being used.     

Interaction of ozone and organic matter in coagulation with inorganic polymer flocculant-PACl: Role of organic components

In this study, two model waters were used to evaluate the ozone effect on aquatic organic matter (AOM) removal by coagulation with inorganic polymer flocculant (IPF)-polyaluminum chloride (PACl). Flocs formation during coagulation processes were detected by using PDA (Photometric Dispersion Analyzer). Apparent molecular weight distribution (AMWD) and resin fractionation (RF) were also performed to characterize the change of AOM as a result of pre-ozonation. The experimental results show that the dosage of O₃, characteristics and composition of AOM are the most important factors on the behavior of coagulation. Great differences have been found between the two model waters. Coagulation in model water 1 (MW1) (composed of humic acids) is impaired markedly by pre-ozonation, as more DOC (Dissolved Organic Carbon) is produced with increasing O₃ dosage. Floc formation, as exhibited from decreasing of the slopes of FI (Flocculation Index), is retarded gradually during coagulation process. Although residual turbidity is reduced with 1.15 mg/L O₃, removals of DOC and UV₂₅₄ all decreased. As for model water 2 (MW2) (composed of salicylic acid), FI is retarded also, but turbidity and DOC removals of coagulation after pre-ozonation are improved to a certain extent. Coagulation performance judged from removal of DOC is improved distinctly by pre-ozonation. Fractionation results show that molecular weight of organic matter (OM) of MW1 is converted from higher to lower; and OM becomes from more hydrophobic to more hydrophilic, which might be one of the mechanisms involved in the impairment of ozonation on coagulation effect. OM in MW2 is oxidized and mineralized to a greater extent, thus its impairment on coagulation is released. Finally, according to water properties, some proposed applications were provided for application of ozone in water treatment process.     

Effect of Ozone in UF-Membrane Flux and Dissolved Organic Matter of Secondary Effluent

The focus of this work was to determine the effect of ozone on the removal of dissolved organic matter (DOM) from a secondary effluent and its relation with the permeated flux behavior in an ultrafiltration membrane. To assess the ozone action, the DOM of the secondary effluent was fractionated into its hydrophobic, transphilic and hydrophilic fractions, using XAD-8 and XAD-4 resins. Ozone increased the hydrophilic fraction from 32% to 42%, and this percentage remained unchanged after ultrafiltration of the secondary effluent. Permeate flux dropped to 52% in the first hour of membrane operation, but when ozone was applied as a pretreatment, it could be maintained at 84% within the first hour.     

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。     

臭氧催化氧化降解煤化工生化进水有机物的实验及机理

研究了臭氧催化氧化降解煤化工生化进水有机物的工艺条件及机理。本文以新疆某煤化工生化进水为研究对象,确定废水中难降解有机物的种类及含量,开展臭氧催化氧化试验,探讨工艺条件对化学需氧量（COD）的去除率,最后以溶解性有机物（DOM）为对象,解析废水难降解有机物的降解规律。结果表明：废水中主要为苯酚及腐殖酸;最佳工艺参数为催化剂投加量1.2L/L、臭氧浓度500mg/L、臭氧通气量2.5m³/h;反应后各组分的UV₂₅₄均下降,去除率从高到低为疏水性中性物质（HoN）>亲水性碱性物质（HiB）>疏水性碱性物质（HoB）>亲水性酸性物质（HiA）>疏水性酸性物质（HoA）>亲水性中性物质（HiN）,富里酸类、腐殖酸类、蛋白质类及溶解性生物代谢产物等荧光强度均降低。     

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.     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

Performance evaluation of pretreatment processes in integrated membrane system for wastewater reuse

A series of lab-scale filtration experiments were performed under various operating conditions to investigate the fouling behavior of microfiltration (MF) membranes when employing two different pretreatment methods. The secondary effluents from a biologically advanced treatment process were fed to each hybrid system, consisting of coagulation-flocculation-MF (CF-MF) and ozonation-MF processes. All experiments were carried out using a stirred-cell system, which consisted of polyvinylidene difluoride (PVDF) MF membranes with a 0.22 μm pore size. When MF membrane was used alone without any pretreatment, the permeate flux dropped significantly. However, in the case of employing polyaluminium chloride (PACl) coagulation and ozonation as a pretreatment, the extent of flux decline rates was enhanced up to 88 and 38%, respectively. In the CF-MF hybrid system, the removal efficiencies of COD and total phosphorus were significantly enhanced at a coagulant dose above 30 mg/L. With ozonation, more than 90% of the color was removed even at a low dosage of ozone (5 mg/L). Therefore, ozonation would be strongly recommended as a pretreatment in terms of removing organic matter. The permeate water quality by ozonation-MF process was in good compliance with the guidelines for wastewater reuse proposed by South Korean Ministry of Environment.     

Effects of Ozone on Resin Acids in Thermomechanical Pulp and Paper Mill Circulation Waters

The present study investigated ozonation as means to remove resin acids from pulp and paper mill circulation waters. Ozone selectively oxidizes resin acids in debarking, thermomechanical pulping (TMP), and newsprint machine (PM) circulation waters. The relative ozone dose of 0.2 mgO₃/initial mgCOD eliminated over 90% of total resin acid concentration in all tested waters, despite the initial resin acid or organic matter concentration. With that ozone dose, the removal of organic material (measured as COD) was only about 30%. Because of the different COD concentrations of tested waters, the absolute amount of ozone needed for over 90% resin acid reduction was 2000 mg/1 for debarking water, 600 mg/1 for TMP water, and 300 mg/1 for PM water, when initial COD concentrations were 10,000, 3000, and 1500 mg/1, respectively. In theory, abietane type resin acids should be more susceptible to ozone attack than pimarane type resin acids, because of their conjugated double bond structure. In the experiments, a high oxidizability of pimarane type resin acids, as compared to abietane type resin acids, was found.     

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 Ozone Pretreatment on Flux Parameters of Reverse Osmosis for Surface Water Treatment

This research details the effects of ozone pretreatment on flux of a reverse osmosis membrane. Initial tests were conducted to determine the effects of ozonation on solids removal, turbidity, and chemical oxygen demand concentrations using various doses on a simulated surface water. These initial tests showed that the best reduction of solids in the 2–5 microns range was at 0.30 mg/L of ozone. Next, a series of bench scale tests was run for 62.5 hours using a standard reverse osmosis system under constant pressure with three pre-ozonation doses and a no ozone baseline dose. Temporal models were developed using the flux data from these tests to determine the effects of operating hours and ozone dosage on flux. It was found that the laboratory data were not linear and followed power law models. Statistical analysis was used to determine the significance of each ozone dose on the four developed models. The change in flux over the 62.5 operating hours with an ozone dosage of 0.30 mg/L showed the lowest flux change. Last, the models were tested using Hermia's filtration models and resistance versus time data to determine the type of membrane fouling that existed. It was concluded that the major fouling was pore blockage. This work demonstrated that ozone pretreatment is effective prior to use with reverse osmosis since it shows a better solid and organic removal rate as well as decreased flux and resistance changes over time.     

Experimental investigation and modeling hybrid nano-porous membrane process for industrial oily wastewater treatment

The aims of this work are to construct a pilot scale purification set-up using membrane process for Tehran Oil Refining Company desalter plant wastewater. The investigation was shown that the high amount of impurities in the feed was the main reason of low permeation flux. The nano-porous membrane-powdered activated carbon (NPM–PAC) was employed to settle this problem. Results demonstrated NPM alone was ineffective in removing TSS, COD, and TOC. In the NPM process the removal of COD and TOC are around 62.5 and 75.1%, respectively, and the steady permeation flux (SPF) is around 78.7 L/(m² h). Optimum PAC dosage, which leads to less deposit layer with high porosity on the membrane surface, could increase permeation flux up to 133.8 L/(m² h), the removal of COD and TOC, 78.1% and 90.4%, respectively, and also decreased steady fouling resistance (SFR) around 46.1%. Hermia's models were employed to investigate mechanism of preventing membrane fouling. After coagulation, the kinetic constants, K_b, K_i, K_s, and K_c, showed lower amounts when NPM filtration used alone. Thus, a NPM–PAC hybrid membrane system has the potential to be an effective method to improve NPM removal efficiency in high percentages as well as to improve membrane fouling and permeation flux in desalter plant.     

Effects Of Ozone On The Production Of Biodegradable Dissolved Organic Carbon (BDOC) During Water Treatment

This article deals with the oxidation effect of ozone on the increasing fraction of biodegradable organic matter with the “ozotest” method, a laboratory technique which simulates the effect of ozonation and allows a complete oxidation assessment. Ozone treatment was performed on river water samples and sand filter effluent samples. Ozone consumption, reduction of UV absorbance and BDOC formation were monitored with applied ozone doses from 0 to 10 mg/L and with contact times from 0 to 60 min. The BDOC formation was optimum at an applied ozone dose of 0.25-0.5 mg O₃ per mg DOC (contact time = 5 min) corresponding to apparition of traces of residual ozone and maximum UV reduction. Maximum ozone consumption, UV reduction and BDOC formation occurred simultaneously during the first two minutes of treatment. Concerning BDOC formation, applied ozone dose showed a greater effectiveness than contact time. For the same quantity of consumed ozone, a short contact time associated with a high ozone dose was preferable to a long contact time and a low ozone dose.     

Short-term fouling propensity and flux behavior in an osmotic membrane bioreactor for wastewater treatment

The short-term fouling behavior of forward osmosis (FO) membrane in an osmotic membrane bioreactor (OMBR) was investigated, using NaCl or MgCl₂ as the draw solutions. The effect of membrane orientation, mixed liquor suspended solids (MLSS) concentration and draw solution (DS) osmotic pressure on water flux and membrane fouling behaviors was examined, along with the effects of simulated elevated salinity on sludge properties and on membrane fouling. Water flux and membrane fouling were not significantly affected by both MLSS concentration (4.91–12.60 g/L) and osmotic pressure (3.0–15.0 MPa), but were severely affected by elevated salinity, due to changes in activated sludge properties, in particular the increase in extracellular polymeric substances (EPS) and sludge hydrophobicity. MgCl₂ as the DS showed more significant influence on activated sludge properties and membrane fouling than NaCl but gave rise to lower salt accumulation. Analyses of the membrane foulants showed that small sludge floc/particles and EPS (in particular, proteins) were enriched in the fouling layer. UPLC–MS/MS analyses of the proteins showed that hydrophobic proteins were the main cause of membrane fouling.     

The relationship between disinfection by-products formation and characteristics of natural organic matter in raw water

The influence of the characteristics of natural organic matter (NOM) on disinfection by-product formation was investigated for Maeri raw water, located in downstream of Nakdong river and Hoedong reservoir at Busan in Korea. The NOM was chlorinated and analyzed for trihalomethanes (THMs), 5 haloacetic acids (HAA-5) and total organic halide (TOX). Aromatic contents determined by specific UV absorbance at 254 nm (SUVA) correlated well with THMs, HAA-5 and TOX formation for the NOM in the Maeri raw water and Hoedong reservoir. Especially, THMFP/DOC showed better correlation with SUVA than HAAFP-5/DOC and TOXFP/DOC with SUVA. Chloroform formation showed good correlation with SUVA for Maeri raw water, but poor correlation with SUVA for the Hoedong raw water. In addition, TCAA formation potential showed good correlation with SUVA for both raw waters. In contrast, a lack of correlation was observed for DCAA formation for both raw waters. THM formation per unit DOC concentration was 70.2–81.1% and 18.9–29.8% for hydrophobic and hydrophilic organic matter in the Maeri raw water, respectively, in which the hydrophobic organic matter had much higher THM formation. In contrast, HAA-5 formation per unit DOC concentration varied seasonally for Maeri raw water. THM formation in the Maeri raw water had a good correlations with SUVA regardless of the ratio of hydrophobic and hydrophilic fraction, and THM formation per unit DOC concentration was higher for the order of humic acid>fulvic acid>hydrophilic organic matter. HAA-5 formation per unit DOC concentration for the hydrophilic organic matter was about 30 μg per mg DOC regardless of SUVA values, but HAA-5 formation per unit DOC concentration for the hydrophobic organic matter was proportionally increased with increasing SUVA values. However, the HAA-5 formation per mg DOC was the highest for the hydrophilic organic matter.     

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。     

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%。     

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.     

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.