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.     

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 evaluation and mathematical modelling of granular activated carbon biofiltration in wastewater treatment

Biological filtration is an effective technique for removing organic matter from wastewater. The performance of a biofilter can be influenced by a range of operational conditions. In this study the performance of biofilters was investigated for the influence of filter media depth, influent concentrations, filtrations rates and backwashing. The results show that performance of GAC filters decreased with shallower filter bed depths. In addition, the GAC performed better at lower influent concentration and lower filtration rates. The daily backwash adopted to avoid the physical clogging of the biofilter did not have any significant effect on the organic removal efficiency of the filter. The concentration, activity and characteristics of the biomass are quantified and described. A mathematical model was developed to simulate the organic removal of the GAC biofiltration system. The performance of the GAC filter under different influent organic concentration levels, filtration rates and filter bed depths was adequately simulated by the mathematical model developed for this study.     

Mathematical modeling of granular activated carbon (GAC) biofiltration system

In this study, a mathematical model of a fixed bed Granular Activated Carbon (GAC) biofiltration system was developed to predict the organic removal efficiency of the filter. The model consists of bulk transportation, adsorption, utilization, and biodegradation of organics. The variation of the specific surface area due to biofilm growth and the effect of filter backwash were also included in the model. The intrapellet diffusion and the diffusion of substrate in the biofilm were described by linear driving force approximation (LDFA) method. Biodegradation of organics was described by Monod kinetics. Sips adsorption isotherm was used to analyze the initial adsorption equilibrium of the system. The model showed that the organic removal efficiency of the biofilter greatly depends on the parameters related to the biological activities such as the maximum rate of substrate utilization (k_max) and biomass yield (Y) coefficients. Parameters such as suspended cell concentration (X_s) and decay constant (K_d) had little effects on the model simulation results. The filter backwash also had no significant impact on the performance of the biofilter.     

Adsorption Characterization for Multi‐Component Organic Matters by Titanium Oxide (TiO2) in Wastewater

Abstract

In this study, an experimental and analytical study on adsorption and adsorption kinetics of organic matters in titanium oxide (TiO₂, Degussa P25) with synthetic wastewater was investigated. In order to understand the removal of different organic sizes in detail molecular weight (MW) distribution of organics matters was examined in terms of number and weight‐average MW. The large MW (33950 dalton) of synthetic organic matters (SOMs) was significantly removed by TiO₂ adsorption and the slight decrease of the small MW (970 dalton) occurred with time. A characterization method was applied to evaluate the composition of SOMs in terms of adsorbability by adsorption of TiO₂. Several adsorption equilibrium and batch kinetics experiments were conducted with different initial concentrations of SOMs and different amounts of adsorbent. A binomial distribution(s) of SOM fraction with the Freundlich coefficient (k) was obtained. The synthetic wastewater was explained by a finite number of pseudospecies (N) identified with a Freundlich isotherm constant (k) value. These parameters were determined by the characterization procedure, together with ideal adsorbed solution theory (IAST) with the pseudospecies number method. Prediction of adsorption isotherm and kinetics derived from a binomial concentration distribution of the characterization procedure were in good agreement with experimental data conducted.     

Control of residual organic matter to reduce bacterial regrowth potential for wastewater reuse

Several problems have been reported about accumulated microorganisms in reclaimed water distribution systems. This paper presents the results of residual organic matter (OM) removal and apparent bacterial regrowth potential of treated wastewater obtained from laboratory-scale experiments using advanced biological treatments: two immobilization processes in series and a membrane bioreactor (MBR) process. Furthermore, a nanofiltration (NF) membrane process was applied to effluents of both advanced biological treatments. The immobilization process removed large molecular weight (MW) fractions >5,000 since immobilized microorganisms had sufficiently acclimated. The NF membrane was more effective in rejecting large MW fractions in the effluents of the immobilization and the MBR treatments. But it was difficult to reject small MW fractions <1,000 by NF. Neutral hydrophilic fraction of DOC was reduced by both advanced biological processes, and it can be thought that the microorganisms in the advanced processes could decompose and grow on some part of the neutral hydrophilic fraction. Quantity of attached microorganisms in the second immobilization reactor was significantly reduced compared to that in the first immobilization reactor. This suggests that apparent bacterial regrowth potential is controlled by the accumulation of effective microorganisms in the first reactor.     

Combined Use of Ozone and Granular Activated Carbon (GAC) in Potable Water Treatment; Effects on GAC Quality After Reactivation

Common processes in potable water treatment regarding dissolved organics removal (natural organic matter, NOM, and organic micropollutants, OMP) include oxidation techniques – like ozonation -and adsorption onto granular activated carbon (GAC). This paper deals with combined ozonation and GAC filtration. Effects on water quality are discussed: partial oxidation of dissolved organics by ozone, leading to changing adsorption behavior and enhanced biodegradation in GAC columns. Special emphasis is laid on long term effects of ozone on GAC quality after several thermal reactivations. Long term experience indicates that ozonation prior to GAC filtration, leading to moderate ozone concentrations in the GAC influent, does not influence GAC quality negatively, even after more than ten reactivation cycles.     

Treatment of ampicillin‐loaded wastewater by combined adsorption and biodegradation

BACKGROUND: This study investigated the treatment of ampicillin (AMP)‐loaded wastewater in airlift reactors where biofilms were developed on granular activated carbon (GAC). A series of batch experiments were thus carried out in order to differentiate potentials of adsorption and biodegradation which would jointly contribute to the AMP removal. RESULTS: Results showed that almost all influent AMP was removed in two reactors supplemented with 4 and 8 mg L^?1 AMP, respectively. Batch experiments revealed that the percentage of the AMP removed through biodegradation increased along with the development of biofilms on GAC. For the mature biofilm‐covered GAC, adsorption accounted for about 60% of the observed AMP removal, whereas the other 40% could be attributed to biodegradation. Possible degraders of AMP were also identified, such as Acinetobacter sp., Flavobacterium sp., Pseudoxanthomonas sp., Delftia sp. and Sphingobium sp. CONCLUSION: The airlift biofilm reactor with GAC as carrier would be a feasible technology for treating AMP‐loaded wastewater due to the joint action of adsorption and biodegradation of AMP by the biofilm‐covered GAC. Copyright © 2010 Society of Chemical Industry     

颗粒活性炭催化臭氧氧化法降解焦化废水有机物

以COD和挥发酚作为焦化废水中有机物的指标,探讨了颗粒活性炭催化臭氧氧化法对有机物的处理效果、活性炭的催化效果和最佳投加量。结果表明添加颗粒活性炭能有效提高臭氧对焦化废水中的COD和挥发酚的降解效果,颗粒活性炭投加量为20g／L时,COD的去除率提高了20％。通过颗粒活性炭吸附试验可以明确颗粒活性炭在臭氧,活性炭系统中的主要作用是催化作用,活性炭的吸附作用只是催化反应的中间过程,基本不会影响有机物的最终去除率。活性炭投加量（10—25g／L）越大,其催化效果越好,但考虑到费用与效益,以20g／L为宜。活性炭作为催化剂重复使用四次后,其催化效果未明显下降。     

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。     

不同颗粒活性炭去除微污染水中有机物的性能研究

随着饮用水水质标准的不断提高,颗粒活性炭在水净化工艺中得到了广泛关注。选用不同类型的颗粒活性炭对去除微污染水中有机物的性能进行了研究。首先,通过静态吸附实验筛选出合适的活性炭炭种;然后,通过动态吸附实验考察了该活性炭在不同滤速下对于原水中CODMn,UV254及浊度的去除特性。结果表明山西的煤质颗粒活性炭在滤速15．59m／h时去除效果显著。     

A Neural Network Model for Prediction of Binary Adsorption Using Single Solute and Limited Binary Solute Adsorption Data

Abstract

A simple neural network model was used to predict binary solute adsorption onto granular activated carbon (GAC). While some data on binary adsorption were required, the neural network could be effectively trained using predominately single solute adsorption data, and only a limited number of data sets (<10) were necessary for effective performance. Once trained, the network was capable of predicting binary solute adsorptions even for systems showing nonideality.     

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.     

REMOVAL OF TOLUENE AND DICHLOROMETHANE FROM AQUEOUS PHASE BY GRANULAR ACTIVATED CARBON (GAC)

Chlorinated hydrocarbons and aromatics constitute the major class of volatile organic compounds that contaminate groundwater. In this study, the equilibrium uptake and column dynamics for the adsorption of dichloromethane (as a typical chlorinated hydrocarbon) and toluene (as a representative of aromatic compounds) from aqueous phase on coal-based granular activated carbon (GAC) were investigated. The adsorption isotherms were measured in a temperature range of 20–40°C. The experimental data obtained were correlated with several adsorption isotherm models. The Langmuir model was well adapted to describe the dichloromethane adsorption on GAC, while the adsorption of toluene on GAC was found to be well described by the Langmuir-BET hybrid model in the stated temperature range with R-squared value of about 0.99. The variations in adsorption breakthrough curves of toluene and dichloromethane with respect to operational parameters such as initial concentration, flow rate, column length, and temperature were investigated. The experimental breakthrough curves of both adsorbates are well fitted by Yan's model with high accuracy (R-squared value of 0.98–99) in most cases.     

Effect of Ozone and GAC Process for the Treatment of Micropollutants and DBPs Control in Drinking Water: Pilot Scale Evaluation

To improve the quality of water supplied to the City of Seoul in Korea, a pilot-scale evaluation of how the conventional treatment process could be upgraded was conducted. Three candidate processes were evaluated and compared: a conventional process (consisting of coagulation, sedimentation, and rapid sand filtration) plus GAC (Train A); a conventional process plus ozone and GAC (Train B); and a process consisting of coagulation, sedimentation, intermediate ozone, sand filtration, and GAC (Train C). Treatment efficiency of the unit process and overall treatment trains were evaluated using several parameters such as turbidity, dissolved organic carbon (DOC), UV absorbance at 254 nm (UV₂₅₄), specific ultraviolet absorbance (SUVA), micropollutants (pesticides, benzenes, and phenols), disinfection by-products (trihalomethanes (THMs), haloacetic acids (HAAs) and aldehydes), and total organic halogen (TOX). Results showed that ozone and/or GAC was effective for removing micropollutants and controlling chlorinated by-products such as THMs and HAAs. However, any synergistic effect of ozonation (adsorption and biodegradation) on GAC was observed due to the low concentration of aldehydes in raw and process water.     

Pilot study of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption

The objective of this pilot study was to evaluate the performance of a GAC postfilter-adsorber for the removal from the drinking water of Athens, Greece, of the two main groups of chlorination by-products, trihalomethanes (THMs) and haloacetic acids (HAAs), as well as of dissolved organic carbon (DOC). The analyses performed during the whole operation period (638 days) showed that the GAC breakthrough capacity for DOC was much higher than the capacity for total HAAs, which was higher than that for total THMs. The removal of THMs and the most part of the removal of HAAs and DOC should be attributed to adsorption by GAC, while that of a smaller part of HAAs and DOC may be attributed to biodegradation in the adsorber bed, where dechlorination, caused catalytically by the carbon surface, favoured microbial growth. Additionally, the GAC postfilter-adsorber showed a much higher adsorption efficiency than a GAC filter-adsorber, due to the smaller size of the carbon and the lower hydraulic loading rate. Also, observed desorption incidents of THMs (mainly) and HAAs, especially during the postfilteradsorber operation, were favoured by the same factors. Formation of THMs within the GAC bed was also indicated by the mass balance of total THMs during the whole cycle.     

MnOx/GAC复合材料制备及其在苯酚废水处理中的应用

以商业颗粒活性炭(GAC)为载体,乙酸锰为锰源,采用等体积浸渍法制备系列MnO_x/GAC复合材料。通过X-射线粉末衍射、透射电镜、拉曼光谱等对改性前后活性炭材料进行微观分析,并探讨锰负载量、反应温度、反应时间等对MnO_x/GAC复合材料处理苯酚模拟废水性能的影响。结果表明,MnO_x/GAC复合材料的活性物种主要以Mn_3O_4、Mn_2O_3和MnO_2为主,呈现均匀分散纳米晶态。在20 mL 1 500 mg·L~(-1)苯酚废水中加入1 g Mn质量分数为8%的MnO_x/GAC复合材料,反应温度50℃,反应时间240 min条件下,苯酚转化率99.88%,COD降解率97.80%,吸附动力学遵循准二级动力学模型。     

Effect of Media on Biofilter Performance Following Ozonation of Secondary Treated Municipal Wastewater Effluent: Sand vs. GAC

Ozone has been shown to be effective in the transformation of several chemicals of emerging concern that escape the wastewater treatment process, but there is concern whether toxic transformation products are formed. Two parallel biofilter columns with granular activated carbon (GAC) and filter sand following a pilot-scale ozone unit to treat secondary treated municipal wastewater were studied. Results show reduced wastewater genotoxicity following ozonation and further reduction following biofiltration. The BAC biofilter outperformed the sand biofilter in terms of reduction in both organics and genotoxicity. Biofilter performance correlated with biological indicators (dissolved oxygen reduction and effluent E. coli counts) but not with ATP bioactivity measurements. Limited bacterial (E. coli) regrowth was observed in treated effluent from both biofilters.     

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。     

Simultaneous pentachlorophenol decomposition and granular activated carbon regeneration assisted by microwave irradiation

This paper describes an integrated granular activated carbon (GAC) adsorption/microwave (MW) irradiation process used for the treatment of high concentration pentachlorophenol (PCP) wastewater. Firstly, PCP in water was adsorbed onto GAC, then the PCP was decomposed and GAC regenerated by MW irradiation. The liquid and gas produced during irradiation were collected through condensing, and absorbed by a 0.1 mol l⁻¹ NaOH solution, respectively. The determination of the PCP concentrations in the distillate, absorption solution and GAC was accomplished by a HPLC. The results suggested that when irradiated with 850 W MW for 10 min, most of the PCP adsorbed by GAC and whatever fragments formed were decomposed to CO₂, H₂O and HCl or tightly bound to GAC, and less than 2% of PCP was transformed into intermediates in the distillate. Some dechlorination and dehydroxylation products were identified by the GC/MS analysis, and the degradation mechanism was proposed. It was also confirmed that GAC could be reused after several adsorption/MW regeneration cycles and its adsorption capacity could maintain a relatively high level, even higher than that of virgin GAC, as indicated by BET results, iodine values and PCP adsorption isotherms.