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.     

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.     

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。     

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     

Enhancement of Coagulation Flocculation Process Using Anionic Polymer for the Post Treatment of UASB Reactor Effluent

This study was conducted for the treatment of up-flow anaerobic sludge blanket (UASB) reactor effluent by polymer assisted coagulation–flocculation process. The efficiency of alum, FeCl₃, and polyaluminum chloride (PAC) was observed alone and in coupled with anionic polymer (Synpol). The results revealed that FeCl₃ and PAC are efficient to remove 99% of turbidity, 83% of total suspended solids (TSS), 82% and 85% of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), respectively, and 99.5% removal of total coliforms (TC) and fecal coliforms (FC). The addition of anionic polymer to alum, FeCl₃, and PAC reduces the sludge volume upto 25%.     

Removal of organics and viruses using hybrid ceramic MF system without draining PAC

Ceramic microfiltration combined with powdered activated carbon adsorption (PAC-MF) was tested for organic and microbial control using river water laden with sewerage effluents. The PAC-MF was compactly configured with PAC adsorption and MF filtration zones in one reactor. It was operated with PAC addition of 20 g/L at the beginning without PAC drain. Organic matter was largely removed in the adsorption zone and then additional removal was obtained in the filtration zone. Selective adsorption of hydrophobic organic compounds onto PAC resulted in greater UV₂₆₀ removal of 90.3 ± 3.2% than DOC removal of 80.2 ± 8.6%. Efficient organic control of the PAC-MF onsiderably decreased chlorine consumption to less than 0.5 ± 0.08 mg/L, and thus THMFP was brought down to less than 8.8 ± 2.2 μg/L in permeate. Furthermore, adsorption or attraction potential of microorganisms by PAC addition as well as virus capture in the PAC cake layer also assisted ceramic MF to remove viruses to less than detection limit after 60 days of operation. Therefore, the hybrid PAC-MF is a prospective advanced water treatment process that is capable of simultaneous organic and microbial removal by adsorption and filtration mechanisms.     

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。     

Application of hybrid coagulation–microfiltration process for treatment of membrane backwash water from waterworks

A coagulation–microfiltration (MF) system was studied to treat the discharged membrane backwash water (MBW) to meet the drinking water quality requirements. The values of dissolved organic carbon (DOC) and trihalomethanes formation potential (THMFP) in MBW were higher than those in Luan River water (LRW, the raw water for a pilot-scale membrane plant, which produced MBW used in this study), and organic matter enriched in MBW distributed mainly in molecular weight (MW) > 10k Da. When 15 mg FeCl₃/L and 15 mg/L powdered activated carbon (PAC) were added into the system, the average concentration of DOC was reduced from 5.731 mg/L in MBW to 3.377 mg/L in the treated water, and the average UV₂₅₄ was reduced from 0.047 to 0.030 cm⁻¹. The removal of organic matter was main in the range of MW > 30k Da. Efficient organic removal by the hybrid coagulation–MF system resulted in significant reduction of THMFP in the treated water. Concentrations of trihalomethanes, turbidity, bacteria and coliforms in the treated water were below the limit value of the drinking water standards. The results show that the treated water from MBW is with satisfactory organic and microbiological quality.     

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.     

Effects of O3, O3/H2O2 and Coagulation on Natural Organic Matter and Arsenic Removal from Typical Northern Serbia Source Water

The objectives of this study were to investigate the effects of ozone and the O₃/H₂O₂ process on FeCl₃ coagulation efficiency for the removal of the high content of natural organic matter (NOM) and arsenic (As) from groundwater (DOC = 9.27 ± 0.92 mg/L; 51.7 ± 16.4 µg As/L). Arsenic and NOM removal mechanisms during coagulation/flocculation are well investigated. However, data concerning arsenic removal in the presence of NOM, which is the subject of this article, are still insufficient. Laboratory and pilot plant test results have shown that the competition of NOM and As for adsorption sites on the coagulant surface have great influence on coagulation/flocculation efficiency for their removal. With both oxidation pre-treatments, arsenic content after the coagulation process was less than 2.0 µg/L in treated water. Application of ozone has a lower influence on coagulation efficacy in terms of DOC reduction, compared to the O₃/H₂O₂ process with the same ozone dose.     

An Insight into Dissolved Organic Matter Removal Characteristics of Recycling Filter Backwash Water: A Comparative Study

It is necessary to put all aspects,,namely raw water characteristics, corresponding FBWW, and coagulation mechanisms, i.e., charge neutralization and sweep flocculation together to make clear the dissolved organic matter (DOM) removal characteristics and the fate of fractionations in recycle design. The DOM characteristics of molecular weight (MW) distribution, hydrophobicity, and fluorescence in source water W1 (synthesized water) and W2 (“Longtan” lake water), FBWW and treated water samples therefore are identified, and three recycling ratios of 2%, 5%, and 8% as compared to control (0%) are conducted. It is found that DOM within FBWW becomes more hydrophilic and lower MW as compared to corresponding source water. Recycling trials indicate that higher DOM concentrations and more low-MW fractions are not of any benefit to enhance UV₂₅₄ and DOC removal. Hydrophobic acid can be further eliminated in case recycling particles mainly produced by sweep flocculation, while weakly hydrophobic acid and hydrophilic fraction can be enhanced and removed under recycling particles mainly formed by charge neutralization. Higher molecular weight fraction (>30 kDa) exhibits potentially enhanced removal at preferred recycling ratio of 5%. Fluorescent characteristics analysis demonstrate that recycling FBWW can effectively improve humic-like substances removal, but the protein-like matters are resistant to be eliminated with unvaried structure.     

MIEX和PAC对微污染水源水的水质净化效果比较

研究了MIEX和PAC两种水处理吸附剂对微污染水源水的水质净化性能。实验分别考察了MIEX和PAC对DOC和UV₂₅₄的去除效率,并通过凝胶渗透色谱和三维荧光光谱分析,研究了MIEX和PAC对不同相对分子质量区间以及不同种类有机物的去除规律。在正常的吸附剂投加量下(MIEX 5~8 ml·L^-1,PAC 30~50 mg·L^-1),MIEX对DOC和UV₂₅₄的平均去除率比PAC高23%和20%。但随着吸附剂投加量的增加,两者去除效率差别逐渐减小,MIEX对DOC和UV₂₅₄的最大去除率仅比PAC高6%~8%。与PAC相比,MIEX去除的有机物相对分子质量分布范围更广,特别是对中等分子量(5000~50000)有机物,其去效率明显高于PAC。MIEX对腐殖酸和富里酸类有机物的去除率略高于PAC,而对蛋白质类有机物的去除率则远高于PAC。动力学分析表明,MIEX和PAC对DOC的吸附去除过程符合准二级动力学,MIEX对有机物的吸附速率是PAC的40倍左右。     

常规处理与深度处理工艺对南京长江原水中有机物去除效能比较

以长江南京段原水为研究对象,通过常规处理及深度处理工艺(强化过滤工艺和生物活性炭工艺)对长江南京段水源水中有机物的去除效能进行对比研究。结果表明常规工艺对CODMn、UV254、DOC及BDOC的去除率分别为30%、41%、27%及25%。强化常规工艺和生物活性炭工艺各指标的去除率分别为34%和52%、48%和50%、37%和40%及74%和82%。强化过滤工艺及生物活性炭工艺对1,2,4-三氯苯的去除效果明显,能显著提高出水水质。常规工艺对MW大于5 kDa的有机物去除效果明显,强化过滤工艺对MW小于1 kDa的有机物去除率大于25%,生物活性炭工艺对各个分子量区间的去除效果都比较好,特别是对原水中占多数的MW小于1 kDa的有机物去除率大于30%。     

改性沸石耦合活性炭强化混凝处理微污染源水

采用静态吸附和六联搅拌烧杯实验进行组合改性沸石粉(MZ)耦合粉末活性炭(PAC)强化混凝去除微污染源水氨氮(NH3-N)、耗氧量(CODMn)、UV254和浊度等效能研究。结果表明,组合改性后沸石粉的比表面积和平均吸附孔径增加,对NH3-N交换去除能力增强。MZ和PAC联用吸附对去除NH3-N具有协同作用,对去除CODMn略有拮抗作用。而MZ耦合PAC强化混凝则显著提高了NH3-N, CODMn, UV254和浊度的去除效果,出水NH3-N<0.5 mg/L, CODMn<3.0 mg/L, 浊度<1 NTU。MZ和PAC不同投加方式显著影响强化混凝处理效果,其中最佳投加方式为絮凝初期投加PAC和MZ,避免絮体包裹MZ,加强PAC对有机物的去除,进一步提高MZ对NH3-N的去除效果。耦合强化混凝使Zeta电位的绝对值降低,胶体间斥力减少,絮体粒径增大,粘黏现象明显,抗冲击能力更强。     

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.     

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.     

Immobilized titanium dioxide/powdered activated carbon system for the photocatalytic adsorptive removal of phenol

Titanium dioxide (TiO₂) and powdered activated carbon (PAC) were fabricated via a layer by layer arrangement on a glass plate using a dip-coating technique for the photocatalytic-adsorptive removal of phenol. Thinner TiO₂ layer coated on PAC sub-layer has larger surface area and better phenol removal than the thicker TiO₂ layer. The system obeyed the Langmuir isotherm model, which exhibited a homogeneous and monolayer adsorption with a maximum capacity of 27.8 mg g^-1. The intra-particle diffusion was the rate-limiting step as the linear plot crossed the origin, while the adsorption was unfavorable at elevated temperature. Under light irradiation, the TiO₂/PAC system removed phenol two-times more effectively than the TiO₂ monolayer due to the synergistic effect of photocatalysis by TiO₂ top layer and adsorption by PAC sub-layer. The COD removal of phenol was rapid for 10mg L^-1 of concentration and under solar light irradiation. It was shown that the PAC sub-layer plays a significant role in the total removal of phenol by providing the adsorption sites and slowing down the recombination rate of charge carriers to improve the TiO₂ photocatalytic oxidation performance.     

Effluent organic matter removal from reverse osmosis feed by granular activated carbon and purolite A502PS fluidized beds

Applying pre-treatments to remove dissolved organic matter from reverse osmosis (RO) feed can help to reduce organic fouling of the RO membrane. In this study the performance of granular activated carbon (GAC), a popular adsorbent, and purolite A502PS, an anion exchange resin, in removing effluent organic matter (EfOM) from RO feed collected from a water reclamation plant located at Sydney Olympic Park, Australia were evaluated and compared through adsorption equilibrium, kinetics and fluidized bed experiments. The maximum adsorption capacity (Q_max) of GAC calculated from the Langmuir model with RO feed was 13.4 mg/g GAC. The operational conditions of fluidized bed columns packed with GAC and purolite A502PS strongly affected the removal of EfOM. GAC fluidized bed with a bed height of 10 cm and fluidization velocity of 5.7 m/h removed more than 80% of dissolved organic carbon (DOC) during a 7 h experiment. The average DOC removal was 60% when the bed height was reduced to 7 cm. When comparing GAC with purolite A502PS, more of the later was required to remove the same amount of DOC. The poorer performance of purolite A502PS can be explained by the competition provided by other inorganic anions present in RO feed. A plug flow model can be used to predict the impact of the amount of adsorbent and of the flow rate on removal of organic matter from the fluidized bed column.     

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.     

Removal of residual organic matter from secondary effluent by iron oxides adsorption

Residual organic matter (ROM) removal is an important issue in wastewater reclamation and reuse processes. Use of iron oxide particles (IOPs) as adsorbents for further treatment of the secondary effluent was investigated to mainly remove non-biodegradable residual organic matter under various operating conditions. ROM removal by IOP adsorption was evaluated in terms of the changes of UV absorbance, COD, and DOC concentrations in feed (secondary effluent) and treated water. The respective relationship of UV removal with COD and DOC removal efficiencies exhibited somewhat different profiles, possibly due to the influence of ROM properties on adsorptive removal mechanisms by IOP, such as hydrophobicity and coordinative capability. The types of IOPs such as ferrihydrite, geothite, and hematite were compared, and it was found that amorphous ferrihydrite was most effective in ROM removal. Maximum ROM removal was occuring at a solution pH of approximately 6.0, which might be ascribed to the ability of ligand exchange related to the association and dissociation of ROM molecules and IOPs at differing pH levels. Substantial reduction in the oxidation state (OS) of the treated water at high ROM removal indicated the coordination of highly oxidized groups in ROM at the IOP surface, such as carboxylic groups.