Powdered Activated Carbon Pretreatment Research Articles

Removal of Micropollutants in Water Reclamation by Membrane Filtration: Impact of Pretreatments and Adsorption.

Organic micropollutants (OMPs) present in water and wastewater are in the spotlight because of their potentially harmful effects even at low concentrations and the difficulties of their elimination in urban wastewater treatment plants (UWWTPs). This study explores the impact of some membrane filtration processes on the removal of a group of 11 OMPs with an eye on the effects of two pretreatments (i.e., coagulation and adsorption onto powdered activated carbon (PAC)) and the adsorption of OMPs onto the membranes on the overall removal. For this purpose, ultrafiltration (UF) and nanofiltration (NF) experiments were conducted with selected OMPs spiked in ultrapure water and secondary effluents from UWWTPs. It was observed that the adsorption of OMPs onto the membranes was influenced by the characteristics of the membranes, as well as the presence of effluent organic matter (EfOM). Since adsorption was the dominant mechanism for the rejection of OMPs by UF membranes, a study of the adsorption equilibrium of the micropollutants using UF membrane pieces as the adsorbent was conducted. The adsorption isotherms for the most hydrophobic OMPs fitted the Langmuir model. The efficiency of coagulation and powdered activated carbon (PAC) adsorption coupled with UF were also investigated. Both pretreatments alleviated membrane fouling and improved the rejection of organic and inorganic matter. The PAC pretreatment significantly improved the removal of OMPs in the combined PAC/UF process. The best options for achieving reclaimed water with satisfactory physicochemical quality, nearly devoid of OMPs and microorganisms, and suitable for diverse reuse purposes are either the NF treatment or the combination of PAC/UF.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Operational performance and cost analysis of PAC/ceramic MF for drinking water production: Exploring treatment capacity as a new indicator for performance assessment and optimization

A powdered activated carbon (PAC)/ceramic microfiltration (MF) pilot was operated (24/7) in a water treatment plant during 18 months, with water from different points of the treatment line (raw, ozonated with recirculated filter-backwash waters, ozonated/pre-coagulated, filtered), the testing including MF and PAC/MF. The optimization of PAC/MF operational performance, including PAC effect analysis and pretreatment required, and a cost analysis are herein presented. A new indicator was developed and explored for performance assessment and optimization, the treatment capacity (TCp), i.e. the design flowrate normalized to membrane area and intake pressure. As expected, a higher TCp was obtained with filtered water. Non-clarified waters required alum-coagulation pretreatment to minimize membrane fouling, and achieved similar TCp results among them. PAC addition (6–24 mg/L) did not promote membrane fouling and had no or a slight positive effect on TCp. TCp integrates all key aspects of process productivity and therefore constitutes a useful indicator to balance flux, energy consumption, backwash frequency and chemical cleaning frequency. The cost functions developed for PAC/MF yielded, for the best operating conditions found for the low-turbidity, low-dissolved organic content waters tested, a total cost of 0.07–0.11€/m3 for 100,000 m3/d, including investment and operation costs.

Effect of peroxymonosulfate oxidation activated by powdered activated carbon for mitigating ultrafiltration membrane fouling caused by different natural organic matter fractions

Powdered activated carbon (PAC) adsorption has been widely applied prior to ultrafiltration membrane for potable water production. However, the impact of PAC adsorption on membrane fouling was still controversial. To solve this problem, combined PAC and peroxymonosulfate (PMS) pretreatment was proposed in this study. The application of PAC/PMS for mitigating membrane fouling by natural organic matter (NOM) has been evaluated, and compared with PMS oxidation or PAC adsorption alone. The influence of NOM fractions on the control efficiency was also investigated using humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA), and their mixture (HA-BSA-SA). The performance was examined through normalized flux decline, fouling resistances analysis, scanning electron microscopy, and model fits. The results indicated that PAC and PMS exhibited a remarkable synergistic effect in the reduction of NOM, with the DOC reduction rates of 53.6%, 24.3%, 27.1% and 31.4% for HA, BSA, SA and HA-BSA-SA, respectively. PAC adsorption exhibited limited influence on mitigating membrane fouling, and the co-existence of PAC and HA even exacerbated fouling due to the synergistic fouling effect between them. By contrast, PAC/PMS pretreatment efficiently reduced both reversible and irreversible fouling resistances. The control efficiency was closely associated with the NOM fractions in the feed water, and followed the order of SA > HA-BSA-SA > BSA > HA. The fouling mitigation by PAC/PMS was attributed to both PAC adsorption and oxidation with SO4− and OH. The experimental results are expected to provide a feasible strategy of PAC/PMS for fouling mitigation, and simultaneously solve the problem faced by PAC adsorption.

Fouling behaviors correlating to water characteristics during the ultrafiltration of micro-polluted water with and without the addition of powdered activated carbon

The aim of this paper was to investigate the effects of powdered activated carbon (PAC) pretreatment on the fouling behavior of an ultrafiltration (UF) membrane during micro-polluted water treatment. The results of this study demonstrated that PAC had a positive influence on fouling mitigation. Specifically, PAC-pretreated water had lower fouling resistances (FRs) and fouling indexes (FIs) than raw water. Liquid chromatography combined with peak-fitting analyses of raw water with and without PAC pretreatment suggested that PAC adsorption was much effective in reducing the contents of the low molecular weight acids and building blocks (LMWA&BB) and the humic substance (HS) fractions in raw water. Principal component analysis (PCA) was also used to identify the fouling behaviors associated with the characteristics of the water samples. Significant correlations (r2) of LMWA&BB with hydraulic reversible resistance (Rre), hydraulic irreversible resistance (Rir), total fouling index (TFI) and the hydraulically irreversible index (HIFI) were found (0.7534, 0.8430, 0.6297 and 0.7015, respectively), indicating that LMWA&BB contributed more significantly than biopolymers(BP) and HS to membrane fouling. The likely mechanism by which the PAC alleviated fouling was the reduction of the LMWA&BB fraction’s presence at the membrane surface and pores. These results suggest that the application of the PAC pretreatment preceding passage through the UF membrane is a promising approach for membrane fouling mitigation.

Impact of PAC Fines in Fouling of Polymeric and Ceramic Low-Pressure Membranes for Drinking Water Treatment.

This study assessed the issue of membrane fouling in a Hybrid Membrane Process (HMP) due to the export of powdered activated carbon (PAC) fines from a pretreatment contactor. Two parallel pilot-scale ceramic and polymeric membranes were studied. Reversible and irreversible foulings were measured following three cleaning procedures: Physical backwashing (BW), chemically enhanced backwashing (CEB) and Clean-in-Place (CIP). The impacts on fouling of membrane type, operation flux increase and the presence/absence of the PAC pretreatment were investigated. Membranes without pretreatment were operated in parallel as a control. In addition, CIP washwaters samples were analyzed to measure organic and inorganic foulants removed from the membranes. It was observed that for the polymeric membranes, fouling generally increased with the presence of the PAC pretreatment because of the export of fines. On the contrary, the ceramic membranes were not significantly impacted by their presence. The analysis of CIP washwaters showed a greater total organic carbon (TOC) content on membranes with a PAC pretreatment while no similar conclusion could be made for inorganic foulants.

Effect of chemical pretreatment on the silt density index of brackish water from north and south Kuwait

In this study, the effect of chemical pretreatment with powdered activated carbon (PAC), ferric chloride, and aluminum chloride at the different concentrations of 10, 30, and 60 ppm on the silt density index (SDI) value of brackish water was examined. Generally, PAC pretreatment was found to be the best pretreatment method. Pretreatment with 10 ppm of PAC resulted in the lowest SDI value of 3.5, which is approximately 44.4% lower than untreated brackish water. After pretreatment with PAC, scanning electron microscopy (SEM) of the filter surface showed large graphite-like particles. An intermediate blocking mechanism produced the best fit for the filtration data from PAC pretreatment. The SEM images of the filter surface show a thick cake layer formation in the aluminum chloride and ferric chloride pretreatments. The cake filtration blocking mechanism was the best fit for brackish water treated with aluminum chloride and ferric chloride.

Performance of adsorption pretreatment in mitigating humic acid fouling of ultrafiltration membrane under environmentally relevant ionic conditions

This study comprehensively investigated humic acid (HA) fouling of ultrafiltration (UF) membrane and the efficiency of adsorption pretreatment in its control under environmentally relevant ionic conditions. Two types of adsorbents, mesoporous adsorbent resin (MAR) and powdered activated carbon (PAC), were examined, and the ionic conditions investigated included ionic strength varying from 1mM to 500mM and different ionic composition at three ionic strength levels. HA fouling decreased at first and increased afterwards as the ionic strength rose, and the influence of ionic composition varied between different levels of ionic strength. Moreover, the efficiency of physical cleaning (imposing surface shear stress and backwashing) decreased with the elevation of ionic strength and calcium ions because of the intensification of the HA-membrane and HA–HA interactions. With the increase of ionic strength and calcium concentration, HA removal efficiency of MAR pretreatment increased more rapidly than that of PAC pretreatment. Meanwhile, due to the characteristics of the adsorbents' pore structure, MAR pretreatment efficiently removed HA that would deposit on/within the membrane while PAC pretreatment preferentially adsorbed HA that would pass through the membrane. Therefore, MAR pretreatment significantly outperformed PAC pretreatment in HA fouling control under most environmentally relevant ionic conditions.

Control of natural organic matter fouling of ultrafiltration membrane by adsorption pretreatment: Comparison of mesoporous adsorbent resin and powdered activated carbon

This paper focused on the effects of mesoporous adsorbent resin (MAR) and powdered activated carbon (PAC) pretreatments on ultrafiltration (UF) membrane fouling caused by natural organic matter (NOM). Three model foulants, humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA), were adopted to represent different NOM fractions in natural waters. Moreover, the impact of the presence of adsorbent particles in UF feed water on membrane fouling was also evaluated. The results indicated that MAR adsorption exhibited remarkable performance in alleviating HA and BSA fouling, no matter whether MAR particles were removed before UF or not. In contrast, PAC pretreatment slightly ameliorated HA fouling when PAC particles were removed before UF, whereas HA fouling was exacerbated by PAC pretreatment with PAC particles present in UF feed water. BSA fouling was moderately controlled by PAC adsorption irrespective of the presence or absence of PAC particles in UF feed water. However, neither of these two pretreatments visibly influenced SA fouling. Overall, the results obtained in the current research would provide relevant information on adsorbent selection and process design of the hybrid adsorption/UF process according to the composition and properties of NOM.

Effect of PACs pretreatment on UF performance for NOM removal

AbstractThis paper investigated the effect of various powdered activated carbon (PAC) pretreatment on ultrafiltration (UF) performance for the removal of natural organic matters (NOM) from Taihu Lake. The hydrophilicity/hydrophobicity and molecular weight (MW) distribution of NOM were analyzed to understand the correlation between PAC adsorption and NOM characteristics. Experimental results demonstrated that PAC addition into raw water could enhance NOM removal efficiency of UF, whereas PAC-NOM particles could increase the trans-membrane pressure slightly. PAC was able to adsorb organics with small MW while UF alone could retain large MW. Fractionation results showed that UF could retain strongly hydrophobic acids (SHA) and neutral hydrophilic compounds (NEU), both of which could also be removed by PAC absorption. Fluorescence excitation–emission matrix spectra showed that PAC pretreatment could decrease extracellular protein-like organics and soluble microbial products significantly from the raw water.

Effects of super-powdered activated carbon pretreatment on coagulation and trans-membrane pressure buildup during microfiltration

As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment.

Potential method to improve the treatment efficiency of persistent contaminants in industrial wastewater

The objective of this work was to evaluate a potential method for improving the treatment efficiency of persistent contaminants in industrial wastewater. Adsorption with powdered activated carbon (PAC) was applied as pre-treatment and operational conditions as pH, temperature, carbon concentration and time were investigated in laboratory scale for different streams generated in a fine chemical industry. Chemical oxygen demand (COD) removal efficiencies of 63 and 50% were attained for two important industrial streams, Product C after acid treatment and precipitation and Influent, at pH 7, room temperature and with 5 and 15 g l −1 of PAC, respectively. Biodegradation assays showed that PAC adsorption enhanced COD removal efficiency. PAC pre-treatment increased the COD removal of Product C after production stream from 15 to 80% and improved the biodegradability of the Influent stream by 50%.

Upgrading of the biotreatment in a pharmaceutical industry with activated carbon addition

The impact of powdered activated carbon (PAC) on the biotreatment of a chemical synthesis wastewater emerging from a pharmaceutical industry was studied. The aim of this addition was to decrease inhibitory and non-biodegradable organics. In the first step, PAC was directly added to activated sludge. In the next step, the wastewater was first contacted with PAC and then treated in an activated sludge reactor. COD, oxygen uptake rate (OUR) and ultraviolet-visible (UV-Vis) spectral measurements were carried out for the evaluation of performance. Direct PAC addition and PAC pretreatment led to similar results, but direct PAC addition was considered more practical than pretreatment with PAC. With the addition of PAC, the level of non-biodegradable matter and the colour of the wastewater were significantly reduced. In any case, the addition of PAC increased the OUR of activated sludge, indicating that inhibition could be decreased. The combined evaluation of OUR, spectral parameters and COD gave a better insight into the processes taking place than the COD parameter alone.

Powdered activated carbon‐assisted biotreatment of a chemical synthesis wastewater

AbstractThe effect of powdered activated carbon (PAC) on the biotreatment of an industrial wastewater taken from a chemical plant synthesising drugs for the pharmaceutical sector was studied. Industrial and domestic wastewaters were combined at laboratory scale and the effect of PAC addition was tested in aerobic reactors. The aim of this addition was to decrease inhibitory and non‐biodegradable organics. Two different procedures were applied in testing the effectiveness of PAC. First, PAC was directly added to activated sludge mixed liquor. In the second case, industrial wastewater was first contacted with PAC and then treated biologically. In the evaluation of performance, COD measurements, oxygen uptake rate (OUR) measurements and measurements in the ultraviolet‐visible (UV‐Vis) spectra were taken into consideration. Both direct PAC addition and PAC pretreatment led finally to similar results. In both cases, the concentration of non‐biodegradable matter could be lowered. In particular, the colour of the wastewater was significantly reduced. Direct PAC addition appeared to be more practical and plausible. In any case, PAC addition to activated sludge increased the OUR of the sludge, indicating that inhibition could be decreased. The study also pointed out that in the assessment of PAC performance, the combined evaluation of OUR, spectral parameters and COD would be much more informative than the COD parameter alone.© 2001 Society of Chemical Industry

Influence of NOM composition on nanofiltration

Hydrophilic NOM caused little permeate flux decline and was poorly rejected compared with hydrophobic NOM.The influence of natural organic matter (NOM) composition on the rejection of total organic carbon (TOC), permeate water flux, and the strength and amount of NOM association with the membrane was examined in bench‐scale nanofiltration studies. NOM composition was manipulated by fractionation into hydrophilic and hydrophobic components and by powdered activated carbon (PAC) pretreatment with subsequent dilution to control for TOC concentration. Hollow‐fiber nanofilters made of negatively charged polysulfone were used in a batch recycle system. Hydrophobic NOM was shown to be responsible for nearly all permeate flux decline and was more highly rejected by the membrane than hydrophilic NOM. Using membrane‐feed solutions with the same TOC concentration, the authors found that the NOM remaining in solution after PAC pretreatment caused greater permeate flux decline and was more poorly rejected than the original mixture of NOM. NOM recovered from the membrane after nanofiltration was predominantly high‐molecular‐weight material (i.e., > 30,000 daltons).