Desalination 334 (2014) 23–28

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Removal of perfluorinated compounds by membrane bioreactor withpowdered activated carbon (PAC): Adsorption onto sludge and PAC

Jing Yu, Chengda He ⁎, Xiang Liu, Jun Wu, Yang Hu, Ya ZhangCollege of Environmental Science & Engineering, Yangzhou University, 196 West Huayang Road, Yangzhou 225127, PR China

H I G H L I G H T S

• Less than 7% of PFOS and 2% of PFOA were removed by the MBR.• More than 90% of PFCs were removed by the PAC-MBR with a PAC dosage of 100 mg/L.• Biosorption onto sludge was the only PFCs removal mechanism in the MBR.• PAC adsorption was found to be the PFCs major removal mechanism in the PAC-MBR.

⁎ Corresponding author. Tel.: +86 514 87971389.E-mail address: hcd@yzu.edu.cn (C. He).

0011-9164/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.desal.2013.08.007

a b s t r a c t

a r t i c l e i n f o

Article history:Received 23 March 2013Received in revised form 17 July 2013Accepted 13 August 2013Available online 20 December 2013

Keywords:PFOSPFOAMBRPowdered activated carbonAdsorption

The comparative studywas conducted to investigate the performance and removal efficiencies of PFOS and PFOAin MBR and PAC-MBR. Solid phase extraction (SPE) followed by HPLC coupled with tandem MS (HPLC/MS/MS)was applied to quantitatively identify PFOS and PFOA in aqueous and sludge samples. Removal efficiencies ofthese two compounds were less than 7% in MBR, which suggest that MBR could not effectively remove PFCsdue to their persistent in the activated sludge process. In contrast, removal efficiencies of 77.4% for PFOS and67.7% for PFOA were observed in PAC-MBR with PAC dosage of 30 mg/L, indicating that adsorption of PFCsonto PAC plays an important role in their removal. Moreover, with the increase of PAC dosage from 30 mg/L to100 mg/L in PAC-MBR, removal efficiency for PFOS or PFOA both increased to more than 90%. Mass balance ofPFOS and PFOA was established to explore their removal mechanisms in MBR and PAC-MBR. Results show thatPAC-MBR can effectively remove these two compounds in thewastewater by PAC adsorption, which was identi-fied as themajor removal mechanism. InMBR, adsorption onto activated sludgewas the only mechanism for re-moval of PFCs.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Perfluorooctane sulfonate (PFOS, C8F17SO3−) and perfluorooctanoate

(PFOA, C7F15COO−), the terminal breakdown end-products ofPerfluorinated compounds (PFCs), have emerged as a new class of envi-ronmentally persistent pollutants due to their wide applications [1].PFOS and PFOA have been detected in a wide array of environmentalmatrices including water, sediment and sludge. Concentrations ofPFOS and PFOA in surface water that have been reported in publiclyavailable literature vary widely over several orders of magnitude,among which half of the reported concentrations have a median con-centration of 3.2 ng/L for PFOS and 3.1 ng/L for PFOA [2]. PFOS andPFOA occur in ground and surface sources of drinking water, and inraw and finished public drinking water around the world [3–5]. Inwastewater, it was observed that PFOS and PFOA were ubiquitousin effluents of wastewater treatment plants (WWTPs). PFOS and

ghts reserved.

PFOA were detected in the influent and effluent of ten WWTPs inU.S.A. In the effluents of those ten WWTPs, PFOS concentrationswere in the range of 1.1–130 ng/L, while PFOA concentrations variedfrom 2.5 to 97 ng/L [6]. In the so-called multi-city study, elevatedPFCs concentrations were found in the effluent of publicly ownedtreatment works in the range of 48–4980 ng/L for PFOS and 42–2280 ng/L for PFOA [7]. West Virginia Department of EnvironmentalProtection (WV DEP) recommended that screening levels of PFOAwere 150 μg/L for water environment and 1360 μg/L for aquatic life[8]. In drinking water, U.S. Environmental Protection Agency (USEPA)sets a “provisional health advisory” of 0.4 ppb for PFOA and 0.2 μg/Lfor PFOS as safe level [9]. Therefore, it is urgent to develop effectivetechnologies to remove PFCs from wastewater.

PFOS and PFOA are considered stable and persist in environmentwithout natural degradation. Studies on fate and behavior of these pol-lutants inWWTPs implied that they could not be effectively removed bybiological treatment process [10–12]. Various physico-chemical treat-ment processes including adsorption [13], sonochemical treatment[14], reduction with zero-valent iron in subcritical water [15] and

24 J. Yu et al. / Desalination 334 (2014) 23–28

membrane filtration [16] have been studied to remove these com-pounds. Activated carbon adsorption is one of the most promisingmethods to remove PFCs in aqueous stream due to the effectivenessand low cost. It was reported that PFCswere effectively removed by ad-sorption onto the activated carbon at high and low equilibrium concen-trations [13,17]. It was reported that PFOS could be effectively removedby granular activated carbon (GAC) and Freundlich isothermwas appli-cable at high and low equilibrium concentrations [13]. Furthermore,PAC was found to possess significantly higher adsorption rate and ca-pacity for both PFOS and PFOAwith spiked samples in the concentrationrange 20–250 mg/L as compared to GAC [18], which indicates that PACcould be a promising adsorbent for PFCs removal. The adsorption ofPFCs onto PAC followed pseudo-second order kinetics and intraparticlediffusion was found to be the rate-controlling step in the PFCs adsorp-tion process in the absence and presence of effluent organic matters(EfOM) [19,20].

The addition of powdered activated carbon (PAC) to a membranebioreactor (MBR) (referred to as PAC-MBR in this study) has been ap-plied to wastewater treatment due to its better performance in termsof effluent quality, stability and membrane fouling rate. PAC-MBR tech-nology integrates adsorption and biodegradation of organicmatterwithmembrane filtration in one unit, which has been proved to be a simpleand highly efficientway to remove compounds inwastewater. In partic-ular, PAC addition increases the removal of organic matters with lowmolecular weight by adsorption; it also serves as a supporting mediumfor attached bacterial growth [21]. Even thoughMBRmay not be able tosignificantly remove PFOS and PFOA, combination ofMBR and PAC tech-nologies could effectively remove these compounds while adsorptiononto PAC occurs. However, little data is available on the removal ofPFCs in PAC-MBR process till now.

The objective of this study was to investigate the performance andremoval efficiencies of PFCs in PAC-MBR process as compared to MBRprocess. Mass balance of PFOS and PFOA was established to exploretheir removalmechanism inMBRand PAC-MBR. Furthermore, the effectof PAC dosage on the PFCs removal was also studied to explore the op-timum operation in PAC-MBR process.

2. Materials and methods

2.1. Chemicals and reagents

Standards of PFOS (≥98%), PFOA (96%), methanol (99.8%) and am-monium acetate (97%) were purchased from Sigma-Adrich. Oasis HLBsolid phase extraction (SPE) cartridges (500 mg, 6 cc) were purchasedfrom Waters (Milford, USA). PAC was obtained from Sigma-Adrich(China) and dosed into PAC-MBR. The characteristics of PAC used aregiven in Table 1. High density polyethylene (HDPE) bottles were usedfor all adsorption experiments.

2.2. PAC-MBR experimental setup and operation

Experiments were performed in the lab-scale submerged MBR andPAC-MBR as illustrated in Fig. 1. Except for the PAC dosage system,PAC-MBR was identical to MBR. MBR consisted of regular tank with anoperating volume of 16 L and a microfiltration (MF) membrane

Table 1Characteristics of PAC used in this study.

Primary micropore volume(b8 Å) 0.24 cm3/gSecondary micropore volume (8–20 Å) 0.18 cm3/gMesopore volume (20–500 Å) 0.07 cm3/gParticle size (nominal) ≤40 μm (75%)BET surface area 763.8 m2/gMean pore diameter 12.7 Å

module submerged in the tank. The membrane module was madeof polyvinylidene fluoride (PVDF) hollow fibre membrane with apore size of 0.2 μm and filtration area of 0.4 m2, which was mountedbetween two baffle plates located above an air diffuser in MBR. Twobaffle plates were mounted above the air diffuser to optimize thecontact between the air bubbles and the membrane surface. Com-pressed air (36 L/h) was supplied through the air diffuser to providegood mixing of the activated sludge and cross flow action for effec-tive scouring of the membrane surface. The membrane flux waskept constant at 10 L/m2·h and followed a suction cycle of 8 minon and 2 min off. Two water level sensors were installed at thehigh and low water levels respectively to maintain a constantwater level in the bioreactor. Both the bioreactor and the storagetank were initially filled with the synthetic wastewater. The storagetank was reloaded everyday with the fresh wastewater to ensure thecontinuous supply to MBR over the entire experimental period. Tominimize the variation of wastewater characteristics, the storagetank was thoroughly cleaned every two days to reduce the growthof microorganisms.

The composition of the synthetic wastewater used in this study islisted in Table 2. The influent COD concentration was 600 ± 20 mg/L(TOC: 225 ± 7.7 mg/L) with the ratio of COD: N: P maintained at100:10:1. Seed sludge was obtained from the aeration tank of a localpilot MBR for municipal wastewater treatment. After transferring intothe lab-scale MBR and PAC-MBR, the sludge was allowed to acclimateto the synthetic wastewater for 35 d. MBR and PAC-MBRwere operatedat the SRT of 30 d. For PAC-MBR, it was performed in three phasesaccording to the change of PAC dosage in the order of 30, 80 and100 mg/L. Before transferring to a new phase, a period of at least 60 dwas provided for system stabilization. In each phase, a steady state offour weeks was maintained, during which measurements were evenlyconducted for parameters of interest.

The hydraulic retention time (HRT) of 8 h and DO concentration ofaround 5 mg/Lweremaintained during the entire experimental period.MBRs were operated under ambient temperature (28 ± 2 °C) and thepH was controlled within a range of 6.8–7.5. Membrane cleaning wascarried out when the suction pressure increased beyond 26 kPa.

2.3. PFCs mass balance calculation

The mass balance in PAC-MBR or MBR was shown in Fig. 2. Massflow of PFC was calculated by the following equations for PAC-MBRand MBR:

Removed PFC mass ¼ Q0 C0−QeCe ð1Þ

Q0 C0−QeCe−PFCWAS ¼ 0 ð2Þ

PFCWAS ¼ PFCs−WAS þ PFCa−WAS: ð3Þ

The equation below was only applied for PAC-MBR:

PFCs−WAS ¼ PFCPAC þ PFCsug ð4Þ

where Q0 andQe are the flow rate of influent and effluent, and C0 and Ceare PFCs concentration in influent and effluent. PFCWAS, defined as PFCsmass in the WAS (waste activated sludge), is consisted of PFCs massin the solid phase of WAS (PFCs−WAS) and aqueous phase of WAS(PFCa−WAS). Mass flow in the solid phase of WAS (PFCs−WAS) includesPFCs mass on the surface of activated sludge (PFCsug) and PAC (PFCPAC)for PAC-MBR, while it only refers to PFCs mass in the activated sludge(PFCsug) for MBR.

Magneticstirrer

Syntheticwastewaterstorage tank

Feedingpump

PACdosingpump

PAC tank

Suctionpump

Pressureguage

Flowmeter

Air

MF membranemodule

Air diffuser

Baffles

PAC dosage system

Fig. 1. Schematic diagram of lab-scale PAC-MBR and MBR (no PAC dosage system).

25J. Yu et al. / Desalination 334 (2014) 23–28

2.4. Model simulation for sludge biosorption

Biosorption of PFOS and PFOA to the activated sludge was found tofit the Linear isotherm (r2 N 0.9) in our previous study [22], which isdefined by the following equation:

Cs ¼ Kd � Ce ð5Þ

where Kd and Cs are the partition coefficient and PFCs concentration onthe sludge surface, respectively.

The partition coefficient Kd was found to be 729 L/kg for PFOS and154 L/kg for PFOA, respectively, which was adopted to estimate theamount of PFOS or PFOA that adsorbed onto activated sludge in PAC-MBR (PFCsug) in this study.

2.5. Analytical methods

Chemical oxygen demand (COD) and specific oxygen uptake rate(SOUR) were determined in accordance with Standard Methods(APHA-AWWA-WEF, 1998). Total organic carbon (TOC) was measuredby 1010 Total Organic Carbon Analyzer (O.I. Analytical, USA). Biomassconcentration was measured as mixed liquor suspended solids (MLSS)

Table 2Composition and concentration of synthetic wastewater.

Components Concentration (mg/L)

PFOS 0.2PFOA 0.2CH3COONa 768.75(NH4)2SO4 284KH2PO4 26CaCl2·2H2O 0.368MgSO4·7H2O 5.07MnCl2·4H2O 0.275ZnSO4·7H2O 0.44FeCl3 1.45CuSO4·5H2O 0.391CoCl2·6H2O 0.42Na2MoO4·2H2O 1.26Yeast extract 30

and volatile suspended solids (VSS) in accordance with StandardMethods (APHA-AWWA-WEF, 1998).

An HP1100 liquid chromatograph (Agilent Technologies, USA)interfaced with a triple quadrupole MS/MS spectrometer (AppliedBiosystems, USA) was applied to determine the concentrations of PFCsin the electrospray negative ionization mode. Solid phase extractionwas conducted to remove matrix components which may enhance orsuppress electrospray ionization of perfluorinated analytes and lead toconsiderable inaccuracy [23]. Detailed information about the extractionprocedure and analytical method for PFOS and PFOA was given in ourprevious study [12]. Teflon bottles, teflon-lined caps, and any suspectedfluoropolymer materials were avoided throughout the analysis.

3. Results and discussion

3.1. Performance of MBR and PAC-MBR

The overall performance of MBR and PAC-MBR is summarized inTable 3. The COD removal efficiencies were excellent and stable withan average of over 95% for bothMBR and PAC-MBR. Our results are gen-erally consistentwith those reported in the literature such as [24]. In ad-dition, effluent quality of PAC-MBR in terms of TOC concentration wasbetter than that of MBR. It suggests that PAC adsorption of organic mat-ters improved the overall performance in comparison with MBR. MLSSof PAC-MBR was much higher than that of MBR, while their biomass

PAC-MBR(MBR)

Q0, C0 Qe, Ce

(Q0-Qe),Ce

WAS

Aqueous phase

Solid phase

Fig. 2. Mass balances of PFCs in the PAC-MBR or MBR. WAS: waste activated sludge.

Table 3Performance, biomass concentration and metabolic activity in the MBR and PAC-MBR.

Reactor COD removal (%) Effluent TOC (mg/L) MLSS (g/L) VSS (g/L) VSS/SS (%) SOUR (mgO2/gVSS h)

MBR 96.5% ± 1.3 6.4 ± 0.6 7.78 ± 1.17 7.32 ± 2.69 94.1 ± 2.3 6.45 ± 1.03PAC-MBR 98.3% ± 1.0 4.3 ± 0.8 16.55 ± 2.43 6.93 ± 0.92 41.7 ± 2.1 6.0 ± 0.88

26 J. Yu et al. / Desalination 334 (2014) 23–28

concentration (VSS)was slightly different. The increase inMLSS of PAC-MBRwould be due to the addition of a certain amount of PAC to the bio-reactor, which is confirmed by the comparable MLVSS between MBRand PAC-MBR. The ratio of VSS/SS for MBR (94.1%) was significantlyhigher than those of municipal STPs [25], which implies no considerableaccumulation of inorganic matter in MBR since synthetic wastewaterwas used as feed rather than real wastewater. Furthermore, the SOURof PAC-MBR was close to that of MBR, suggesting no discernible differ-ence in metabolic activity of sludge was observed between these twosystems.

3.2. Removal of PFOS and PFOA in MBR

In order to investigate the behavior of PFCs in MBR, filtration ex-periment was conducted with MBR membrane module to study PFCsremoval efficiency by membrane separation. As can be seen (Fig. 3),negligible amount of PFCs was removed by MBR membrane, whichcould be due to the membrane adsorption. The result is expected asmembrane pore size (0.2 μm) used is much bigger than molecularsize of PFCs. It was reported that PFOS and PFOA molecules areabout 1 nm in length [26]. In MBR, removal efficiencies of thesetwo compounds were less than 7%, which suggest MBR could notbe effectively remove PFCs due to their persistent in the activatedsludge process. It was reported that some micropollutants, such asendocrine disruptors compounds (EDCs) or pharmaceuticals couldbe biodegraded when the activated sludge treatment process (e.g. MBR)was operated with long SRT [27]. PFOS and PFOA are not biodegradedin the activated sludge process due to their exceptionally thermal andchemical stability. It is expected that removal efficiency of these com-pounds would not be improved in MBR with longer SRT. Therefore,these two compounds can only be removed by adsorption onto activatedsludge. It suggests that adsorption onto the sludge would be the onlymechanism for PFCs removal in MBR. Adsorption of PFCs on activatedsludge was reported to be strongly affected by solution pH as surfacecharge of activated sludge is dependent on the solution pH [28]. Effect

PFCs removal bythe MBR and membrane module

Fig. 3. PFCs removal by the MBR and membrane module.

of solution pH on the PFCs removal is expected to be weak in this studyor typicalWWTPs as variation in pH of wastewater is small. Low removalefficiency of PFCs inMBR indicates PFCs cannot be efficiently removed byactivated sludge process, which is also confirmed by studies on fate andbehavior of PFCs in WWTPs [10–12].

Themass balance of PFOS and PFOA inMBRwas established bymea-suring their concentrations in aqueous and solid phases of influent, ef-fluent and WAS according to Fig. 2. Mass flows of removed PFCs inMBR are shown in Fig. 4. It can be seen that total removed PFCs amountwas 686 μg/d for PFOS and 240 μg/d for PFOA, among which mass flowin theWASaccounted for 81.5% for PFOS and 94.2% for PFOA, respective-ly. Errors in the establishedmass balance could be due to the sludge SPEextraction and other analytical errors. The amount of PFCs in solid phaseof WAS was determined by its concentration on the sludge surface andmass flow of sludge inWAS. As can be seen, PFOSmass flow of 459 μg/dwas adsorbed onto sludge and discharged with WAS, while only120 μg/d PFOA was removed by adsorption onto sludge in WAS. Themass flow of PFOS on sludge in WAS was more than 3.5 times of thatof PFOA. The result is consistent with our previous study which foundthat adsorption capacity of PFOS (Kd: 729 L/kg) was more than 3times higher than that of PFOA (Kd: 154 L/kg) [22]. Other studies alsoobserved that Kd value for PFOS was much higher than that of PFOA.For example, Kd values for PFOS were in the range of 200–4050 L/kg,while much lower Kd values ranging from 150 to 350 L/kg for PFOAwere observed [28]. Based on above findings, it is clear that morePFOS would be adsorbed onto the activated sludge, which could resultin different behavior in activated sludge process in comparison withPFOA.

3.3. Removal of PFOS and PFOA in PAC-MBR

In PAC-MBR, PFOS and PFOA can be effectively removed at appropri-ate PAC dosage. Fig. 5 shows the PFCs removal efficiency in PAC-MBRoperated at SRT of 30 d with PAC dosage varied from 30 to 100 mg/L.With the increase of PAC dosage, the removal efficiency increased

100

105

459

120

686 µg/d 240 µg/d

0%

20%

40%

60%

80%

100%

PFOS PFOA

Dis

trib

utio

n of

PFC

s m

ass

flow

rem

oved

in M

BR

(%

)

aqueous sludge error

Fig. 4.Distribution of PFCsmass flow removed in theMBR. The value on the top of columnrepresents the total mass flow (μg/d) removed in theMBR; the value in columns indicatesthe mass flow of PFCs (μg/d) in aqueous and solid phases of the WAS.

30 mg/L 80 mg/L 100 mg/L0%

20%

40%

60%

80%

100%

PAC dosage

PFC

s re

mov

al in

PA

C-M

BR

(%

)

PFOS PFOA

Fig. 5. PFCs removal in the PAC-MBR operated with different PAC dosages.

Fig. 6. Distributions of removed PFCs mass flow in PAC-MBR with different PAC dosage:(a) PFOS; and (b) PFOA. The value on the top of column represents the total mass flow re-moved in the PAC-MBR.

27J. Yu et al. / Desalination 334 (2014) 23–28

from 77.4% to 94.8% for PFOS and from 67.7% to 90.6% for PFOA. In con-trast, insignificant removal efficiencies for these two compounds wereobserved inMBRwith the same SRT (30 d), which suggests that adsorp-tion of PFCs onto PAC can play an important role in their removal inPAC-MBR, instead of biosorption onto the activated sludge. Further-more, more PFCs were removed by PAC-MBR at PAC dosage of100 mg/L in comparison with that of 30 mg/L, indicating the removalefficiency of PFCs depends on the PAC dosage.

Distributions of removed PFCs mass flow in PAC-MBR at SRT of 30 dwith different PAC dosages were estimated and shown in Fig. 6. As thePFCs concentrations on PAC surface cannot be measured, PFCPAC wascalculated by Eq. (4). For both PFOS and PFOA, their mass flow in theaqueous phase ofWAS only accounted for less than 1% of total removedmass flow, which cannot be properly shown in Fig. 6. With the increaseof PAC dosage, more PFOS or PFOA was removed by adsorption on thePAC and activated sludge. However, mass flow in the solid phase ofWAS only increased by 22% for PFOS and 33% for PFOA even thoughPAC dosage increased from 30 to 100 mg/L. Based on the PACmass bal-ance, PAC concentrations were 2.7, 7.2 and 9.0 g/L in the bioreactor. Itseems adsorption capacity of PAC decreased significantly as PAC con-centration in the bioreactor increased greatly. Furthermore, it can beseen that more than 98% of removed PFCs mass was in the solid phase(including activated sludge and PAC) of WAS. Compared to MBR, mostof the PFCs in the solid phase of WAS seems to be adsorbed onto thePAC instead of activated sludge. For example, 459 mg/d of PFOS and120 mg/d of PFOA were removed by adsorption onto the activatedsludge of MBR, while mass flows in solid phase of WAS of PAC-MBRwith PAC dosage of 30 mg/L were 7430 mg/d for PFOS and 6499 mg/dfor PFOA at same SRT (30 d). It suggests adsorption on PAC was an effi-cient and predominant process in the removal of PFCs in activatedsludge processes. PAC adsorption would be much more effective thanbiosorption for the removal of PFCs in the wastewater treatment eventhough its adsorption capacity was significantly reduced by organicmatters in the effluent (EfOM). Other study also confirmed that PACcan be an effective adsorption medium for PFC removal from contami-nated groundwater even though natural organic matters greatly re-duced PAC adsorption capacity [29].

3.4. Effect of PAC dosage on PFOS and PFOA removal in PAC-MBR

In order to explore the effect of PAC dosage on the PFCs removal inPAC-MBR, linear isotherm for sludge biosorption mentioned above wasapplied to calculate the concentrations of PFCs on the sludge surface inthe WAS by their aqueous concentrations and partition coefficients

(Kd). PFCsug was estimated by PFCs concentrations on the sludge surfaceand sludge amountwasted out of PAC-MBR. Table 4 shows the results ofcalculations based onmass balance, inwhich PAC surface concentrationwas obtained by normalization of PFCPAC on the amount of PAC dailywasted out of PAC-MBR. It can be seen that PFOS concentration onPAC surface decreased from 5157 μg/g to 1896 μg/g as PAC dosage in-creased from 30 to 100 mg/L, while it decreased from 4511 μg/g to1811 μg/g for PFOA. According to the PAC adsorption study in our pre-vious study [15], PFCs adsorption on PAC fitted Freundlich isothermswith the presence of organic matters in the effluent, which predictedthat PAC would have lower adsorption capacity at higher PAC dosage.In addition, PFOA concentrations on PAC at different PAC dosageswere slightly lower than those of PFOS even though significant differ-ence was seen between these two compounds on the sludge surfaceeven though PAC adsorption capacity of PFOS was much higher thanthat of PFOA. It could be due to the fouling effect of sludge and EfOMon the PAC which significantly reduced the difference in PFCs adsorp-tion onto PAC [13].

Table 4Effect of PAC dosage on the PFCs removal in the PAC-MBR.

Mass Flow PAC dosage

30 mg/L 80 mg/L 100 mg/L

PFOS PFOA PFOS PFOA PFOS PFOA

PFCs−WAS (ug/d) 7431 6499 8597 8083 9101 8693PFCsug (ug/d) 133 40 61 20 31 12PFCPAC (ug/d) 7298 6459 8535 8064 9070 8681Normalization of PFCs mass on PAC (ug/g) 5157 4511 2239 2105 1896 1811

28 J. Yu et al. / Desalination 334 (2014) 23–28

4. Conclusions

The removal efficiencies of PFOS and PFOA in MBR and PAC-MBR,which both were operated at SRT of 30 d, were investigated in thisstudy. The removal efficiency of these two compounds was less than7% in MBR, while more than 90% PFOS or PFOA were removed in PAC-MBRwith a PAC dosage of 100 mg/L. Mass balance of these compoundswas established by measuring their concentrations in aqueous andsludge samples. PAC adsorption was the major removal mechanism inPAC-MBR, while sludge adsorption could be the only removal mecha-nism in MBR. Our study suggests that PAC-MBR is an effective processto remove PFCs fromwastewater. Dosage of PAC should be carefully se-lected with the consideration of significantly reduced PAC adsorptioncapacity for the PFCs removal. Solid waste from the treatment processincluding wasted activated sludge and PAC should be treated carefullyto avoid the contamination of water environment.

Acknowledgment

We acknowledge the financial support from Yangzhou University(0574790015596) and National Natural Science Foundation of China(51208450).

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