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 Granular Activated Carbon (GAC) Adsorption and Biofiltration in the Treatment of Biologically Treated Sewage Effluent

Abstract

In this study, the performance of GAC adsorption and biofiltration systems in treating biological treated sewage effluent (BTSE) was evaluated in terms of organic removal efficiency, organic fractions, and molecular weight distribution (MW) of organic matter (OM) removed. The GAC biofilter removed 23.5% and 61% of the hydrophobic fractions and hydrophilic fractions of OM in the BTSE respectively. MW distribution studies of GAC filter and GAC adsorption revealed the following: Hydrophobic fraction of the effluent showed a peak at 345 dalton after GAC biofiltration and 256 dalton after GAC adsorption, whereas, with hydrophilic fractions, peaks at 46,178 and 345 daltons were observed after GAC biofiltration and peaks at 46,178 and 256 daltons after GAC adsorption. Transphilic fraction showed the peaks at 12,783 dalton with GAC biofiltration, and 1,463 dalton with GAC adsorption. The performance of the GAC biofilter was successfully mathematically modelled.     

Application of an ozonation–adsorption–ultrafiltration system for surface water treatment

Investigations are presented on the effect of the preliminary ozonation on ultrafiltration (UF) and powdered activated carbon (PAC) /UF process performance, especially on permeate flux decline and the effectiveness of model organics removal. Flat membranes from regenerated cellulose were used. A model solution was prepared as a mixture of humic acids and phenol. PAC dosage was equal to 100 mg/l⁻¹. The ozone dosages were in the range of 1–3 mg O₃ l⁻¹ (0.2–0.6 mg O₃/mg TOC). It was found that the most advantageous configuration was preliminary ozonation with an ozone dosage of 0.4 mgO₃/mg TOC–UF. The permeate flux reached a value equal to the pure water flux value. Moreover, a very high effectiveness of model organics removal was obtained: TOC was reduced by about 96% and UV₂₅₄ absorbance was removed completely. When PAC was added to the feed containing humic acids without ozonation, a drop in a permeate flux was observed compared to UF. Similarly, the addition of PAC to feed treated with ozone resulted in a significant drop in the permeate flux in comparison with pure water flux, regardless of ozone dosage applied.     

Role of membrane pore size in tertiary flocculation/adsorption/ultrafiltration treatment of municipal wastewater

Flocculation, adsorption onto powered activated carbon (PAC), and ultrafiltration (UF), alone and in combination, were tested for tertiary treatment of the secondary effluent from municipal wastewater treatment at the Ashkelon plant (in southern Israel). Encouraging and reliable results of total organic carbon (TOC) of <3 mg/l were achieved with a combination of 130 mg/l FeCl₃, 0.6 g/l PAC and UF. The relative contribution of the UF membrane to the reduction of TOC changed with the molecular weight cut-off (MWCO) of the membrane, from a negligible 2.9% for a 100-kDa-MWCO membrane to 17% for 10- and 2-kDa membranes. The latter membranes, however, developed significant fouling, with a 35% drop in flux during first 30 min of the filtration cycle. The flux drop for the 50- and 100-kDa membranes was in the low range of 3%. The optimal MWCO interval of 20- to 50-kDa in combination with flocculation/PAC pretreatment gave a significant reduction in organic content with minimal membrane fouling. Detailed GC–MS analysis showed that the combined treatment gave very efficient retention of organic compounds with molecular weights below 800 Da, with the consequent absence of harmful compounds in the tertiary effluent. It was therefore concluded that the recommended flocculation/adsorption protocol constitutes an effective pretreatment for UF and that the obtained tertiary effluent can be used for unrestricted irrigation.     

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。     

Application of ultrafiltration hybrid membrane processes for reuse of secondary effluent

This study evaluates the factors affecting pretreatment conditions for hybrid UF membrane processes for reuse of secondary effluent from the sewage treatment plant. The experimental results obtained from the ultrafiltration (UF) membrane process showed that the particles of the size range between 0.2 and 1.2 μm caused a significant impact on membrane fouling in all cases even with or without the coagulation process. As pretreatment of UF membrane process, the coagulation significantly improved the permeate flux. Optimal flux improvement was seen at an alum dose of 50 mg/L. In addition, it was found that the permeate flux was least declined under the coagulation condition of charge neutralization (pH 5.0). Also, the powdered activated carbon (PAC) adsorption enhanced the permeate flux. Application of the direct filtration as a pretreatment of UF membrane process was also very effective in reducing the UF membrane fouling.     

PAC-UF组合系统在饮用水处理中的试验研究

试验考察了粉末活性炭(PAC)的投加对超滤膜(UF)运行性能的影响,结果表明：PAC投加到蒸馏水中使膜通量产生微小下降。单独用UF膜系统处理自来水时,膜的通量急剧下降,而PAC作为UF膜的预处理方式处理相同水量时,可以明显延长膜的运行周期;随PAC投量的增加膜稳定运行时间延长,通量下降率降低。物理清洗方式对PAC-UF组合系统中膜通量的恢复效果较好,而化学清洗方式对单独UF膜系统中膜通量的恢复效果较好。     

A combined photocatalytic slurry reactor–immersed membrane module system for advanced wastewater treatment

Photocatalysis with titanium dioxide semiconductor catalyst can effectively degrade recalcitrant organic pollutants present in biologically treated sewage effluents. Focusing on process efficiency and sustainability within a broader program, this study presents results obtained with a bench-scale hybrid treatment system. The process train comprised of a slurry (suspension) type continuous photocatalytic (CP) system and an immersed hollow fibre membrane micro-ultrafilter (MF/UF) unit. The CP reactor charged with 1 g/L P-25 catalyst removed 63% dissolved organic carbon (DOC) from a synthetic wastewater (representing biologically treated sewage effluent). The addition of 0.05 g/L of powdered activated carbon (PAC) increased DOC removal up to 76%. The start-up times to achieve 60% DOC removal were 31 min and 15 min, respectively. These results show a 16 times improvement in volumetric load over a comparable batch reactor system used in previous studies by our group.Slurry type photocatalytic reactors need subsequent particle separation to retain the catalyst in the system and allow the discharge of treated effluent. The immersed membrane module accomplished this without prior slurry settling step. Membrane feed pre-treatment with pH adjustment and particle charge neutralisation with aluminium chloride coagulant led to improved critical membrane fluxes, 15.25 L/m² h and 19.05 L/m² h, respectively. In each experiment MF/UF produced near zero turbidity permeate, completely retained the photocatalyst, and flocculation also improved the efficiency of DOC removal. Membrane fouling was controlled by particle aggregation rather than feed DOC levels, but the latter had significant impact on coagulant demand. The complete treatment train achieved up to 92% DOC reduction with 12 mg/L AlCl₃ dosage using in-line coagulation conditions. The results show that in-line coagulation offers a simple yet effective means to improve the performance of slurry type photocatalytic–MF/UF hybrid systems for advanced water and wastewater treatment applications.     

Physico‐Chemical Processes for Landfill Leachate Treatment: Experiments and Mathematical Models

Abstract

In this study, the adsorption of synthetic landfill leachate onto four kinds of activated carbon has been investigated. From the equilibrium and kinetics experiments, it was observed that coal based PAC presented the highest organic pollutants removal efficiency (54%), followed by coal based GAC (50%), wood based GAC (33%) and wood based PAC (14%). The adsorption equilibrium of PAC and GAC was successfully predicted by Henry‐Freundlich adsorption model whilst LDFA+Dual isotherm Kinetics model could describe well the batch adsorption kinetics. The flocculation and flocculation–adsorption experiments were also conducted. The results indicated that flocculation did not perform well on organics removal because of the dominance of low molecular weight organic compounds in synthetic landfill leachate. Consequently, flocculation as pretreatment to adsorption and a combination of flocculation–adsorption could not improve much the organic removal efficiency for the single adsorption process.     

Stoichiometric relationship in the coagulation of melanoidins-dominated molasses wastewater

Batch experiments of coagulation/flocculation of biologically treated molasses wastewater were conducted to investigate the stoichiometric relationship between the concentration of melanoidins-dominated organics and the dosage of hydrolyzing metal salts (ferric chloride and aluminum sulfate). Wastewater samples were first fractionated by ultrafiltration. Jar tests were conducted to evaluate coagulation efficiency by measuring zeta potential, removal rates of color and chemical oxygen demand (COD). Experimental results indicate that the dissolved organic fraction accounts for predominant portion of the organic compounds present in biologically treated molasses effluent. A stoichiometric relationship exists between the concentration of melanoidins-based organic compounds and coagulant demand. When the change in solution conditions is proportional to that in organic concentration, such stoichiometric relationship still exists. On the other hand, no stoichiometry was observed between the concentration of melanoidins-dominated organics and the metal dosage when substantial changes in the nature of organics or solution conditions occur. The optimal dosage of ferric chloride expressed in terms of the ratio of metal to organic carbon removed was calculated as 0.73-0.81 g Fe³⁺/g COD.     

Removal of sodium dodecyl benzene sulfonate and phenol from water by a combined PAC adsorption and cross‐flow microfiltration process

The removal of sodium dodecyl benzene sulfonate (SDBS) and phenol from water by a combined process of PAC (powdered activated carbon) adsorption and cross‐flow microfiltration (PAC–MF) was investigated. Batch PAC adsorption studies were made to obtain the isotherm data. The PAC–MF experiments were performed as a function of PAC dose (0.2–1.0 g dm^?3), solution pH (2.5–11.2), transmembrane pressure (10–30 psi), and cross‐flow velocity (4.7–8.3 mm s^?1). A compromise between removal efficiency of the organics and the permeate flux in the PAC–MF process was needed to select a suitable PAC dose. The role of pH in the PAC–MF process mainly depended on the acid–base nature of the organics being removed. A comparison of PAC–MF and fixed bed processes was also made, and the application potential of this PAC–MF process for continuous removal of relatively high‐molar‐mass organics such as SDBS from waste effluents was demonstrated. Copyright © 2004 Society of Chemical Industry     

超滤在饮用水处理中的应用和研究进展

介绍了超滤在饮用水处理中的应用和研究进展;研讨微絮凝+超滤组合工艺、粉末活性炭(PAC)+超滤组合工艺,以及膜污染及其防治技术;从处理效果、经济性能上对超滤工艺与常规过滤工艺进行对比。认为超滤工艺必将成为未来饮用水最重要最有效的处理技术之一;而混凝+超滤工艺比较适合我国国情,具有很好的发展前景。     

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.     

Cleaning secondary effluents with organoclays and activated carbon

BACKGROUND: Flocculation, adsorption and ultrafiltration, alone and in combination, were tested for tertiary treatment of Beer Sheva (southern Israel) municipal wastewater. The focus was on the adsorption of soluble organics with powdered activated carbon (PAC) and with organoclays. RESULTS: Adsorption on 0.6 g L^?1 octadecyltrimethylammonium bromide (ODTMA) ‐ bentonite and flocculation with 130 mg L^?1 FeCl₃ reduced the dissolved organic carbon (DOC) level by 46%, and that was the highest DOC retention obtained with the organoclays. Retention achieved with 0.6 g L^?1 PAC and 130 mg L^?1 FeCl₃ was 65%. Filtration through a more hydrophobic PVDF‐30 membrane for 30 min resulted in 35–40% flux drop. A reasonable 6–7% flux reduction was obtained with filtration through a more hydrophilic PS‐50 membrane. CONCLUSION: Oganoclays at low doses are a good target adsorbent for single low molecular weight molecules. On average, higher TOC retention was achieved with PAC. Introduction of adsorption as a pre‐treatment step can lead to minimization of flux losses, reduced demand for flocculation and improved economics of the entire treatment. Copyright © 2011 Society of Chemical Industry     

Integration of immersed membrane ultrafiltration with the reuse of PAC and alum sludge (RPAS) process for drinking water treatment

Effects of PAC and alum sludge generated from water treatment process on the effluent quality and fouling of immersed UF membrane were systematically investigated with representative source of natural water and the efficiency of coagulation, PAC adsorption and RPAS to treat natural surface water prior to UF were compared. It was found that the average turbidity removal by RPAS could reach up to 80.2%, and the turbidity removal of immersed membrane UF was independent of the influent, which could be kept at 99%. Particulates were reduced after being pre-treated by different processes, and particles with sizes ranging from 0.5 to 3.5 μm and larger than 13.5 μm were effectively removed by RPAS. UF coupled with RPAS pre-treatment got the best removal for DOM compared to other processes with average DOC and UV₂₅₄ removal 54.1% and 47.2% due to the high removal in the influent of UF. The residual alum content in the effluent of RPAS with UF was less than coagulation and bacteria were almost all removed by membrane. The membrane-fouling was mitigated by pre-treatment processes at different degrees, TMP of UF coupled with RPAS process was relatively stable in 15 d of run, the adsorption of PAC and large number of Al(OH)₃ complexes and precipitates for the foulant molecules might be an important mechanism.     

用活性炭吸附强化超滤过程脱除废水中染料的研究(英文)

In this study, orange G dye was efficiently removed from aqueous solution by ultrafiltration (UF) mem-brane separation enhanced with activated carbon adsorption. The powdered activated carbon (PAC) was deposited onto the UF membrane surface, forming an intact filter cake. The enhanced UF process simultaneously exploited the high water permeation flux of porous membrane and the high adsorption ability of PAC toward dye molecules. The influencing factors on the dye removal were investigated. The results indicated that with sufficient PAC incor-poration, the formation of intact PAC filtration cake led to nearly complete rejection for dye solution under opti-mized dye concentration and operation pressure, without large sacrificing the permeation flux of the filtration process. Typically, the dye rejection ratio increased from 43.6% for single UF without adsorption to nearly 100% for the en-hanced UF process, achieving long time continuous treatment with water permeation flux of 47 L·m 2·h 1. The pre-sent study demonstrated that adsorption enhanced UF may be a feasible method for the dye wastewater treatment.     

活性炭UF膜分离污水中COD的实验研究

试验考察了粉末活性炭的投加对超滤膜运行性能的影响,结果表明:随粉末活性炭投量的增加膜稳定运行时间延长,通量下降率降低。粉末活性炭的投加对膜过滤阻力影响不大。在此基础上又对PAC-UF组合系统去除有机物的效果进行了进一步研究,主要是对比研究了不同PAC投加量对5种不同配置水样中有机物的去除效果。得出如下结论:在相同PAC投加量下,CODMn值大的水样的CODMn平均去除率高,且出水CODMn值相近。说明了PAC-UF组合系统出水稳定,受水质差异的影响不大。     

絮凝剂复配处理城镇生活污水的实验研究

以实际生活污水为实验对象,利用絮凝剂PAC、PFS、CTS、阴离子PAM和阳离子PAM进行两组分或三组分复合,找出复配方案在提高COD去除率的同时降低PAC的用量。在5min搅拌,15min沉淀的短时絮凝实验中,絮凝剂复配后的絮凝效果普遍比单独加PAC好,PAC和阳离子PAM复配的COD去除率比单独加PAC高18%,成本下降40%。通过合理的絮凝剂复配能提高絮凝效果,减少絮凝剂用量,降低出水的铝离子浓度。     

PAC/AC与超滤组合去除水中有机物效果的研究

分别以粉末活性炭(PAC)和活性焦(AC)作为超滤(UF)前处理材料,考察了PAC-UF和AC-UF两种组合工艺对水中不同分子质量大小有机物的去除能力,并对两种吸附材料对膜污染的影响进行了评价。实验结果表明:PAC和AC均可有效吸附水中分子质量为1~10 k Da的有机物,并能有效缓解膜污染;AC表现出了良好的吸附性能,可在再生水的深度处理中作为替代PAC的吸附材料。     

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.