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Tertiary Treatment of Pharmaceuticals and Personal Care products by Pretreatment and Membrane Processes

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A lab-scale pretreatment system and various membrane systems were investigated in their efficiencies in the removal of eight pharmaceuticals and personal care products (PPCP) compounds from secondary wastewater effluent. The targeted pharmaceutical compounds in this study included acetaminophen, atenolol, carbamazepine, clofibric acid, erythromycin-H2O, gemfibrozil, ibuprofen and sulfamethoxazole because of their high detection frequencies in municipal wastewater treatment plants. The highest PPCP concentrations in municipal wastewater secondary effluents were clofibric acid (240-296 ng L-1), ibuprofen (263-293 ng L-1) and sulfamethoxazole (255-293 ng L-1). Among the various pretreatment processes, granular activated carbon (GAC) was found to be highly-effective in removing the targeted pharmaceuticals by adsorption except for gemfibrozil, ibuprofen and clofibric acid. Microfiltration (MF) and ultrafiltration (UF) membranes are capable of removing suspended solids in wastewater, but as it is difficult to retain PPCPs by size exclusions; this contributed less than 10% removal efficiency. It was also observed that hydrophobic compounds (log Kow > 3) were difficult to remove using UF and MF membranes. The results of this study demonstrate that reverse osmosis (RO) can effectively remove nearly all of the pharmaceuticals (83-99%). In particular, the RO removal mechanisms are emphasized because of their utmost important role in eliminating micro-pollutants
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Sustain. Environ. Res., 21(3), 173-180 (2011) 173
TERTIARY TREATMENT OF PHARMACEUTICALS AND PERSONAL CARE
PRODUCTS BY PRETREATMENT AND MEMBRANE PROCESSES
Kok-Kwang Ng, Angela Yu-Chen Lin, Tsung-Hsien Yu and Cheng-Fang Lin*
Graduate Institute of Environmental Engineering
National Taiwan University
Taipei 106, Taiwan
Key Words: Pharmaceuticals, pretreatments, ultrafiltration, microfiltration, reverse osmosis
ABSTRACT
A lab-scale pretreatment system and various membrane systems were investigated in their
efficiencies in the removal of eight pharmaceuticals and personal care products (PPCP) compounds
from secondary wastewater effluent. The targeted pharmaceutical compounds in this study included
acetaminophen, atenolol, carbamazepine, clofibric acid, erythromycin-H2O, gemfibrozil, ibuprofen
and sulfamethoxazole because of their high detection frequencies in municipal wastewater treatment
plants. The highest PPCP concentrations in municipal wastewater secondary effluents were clofibric
acid (240-296 ng L-1), ibuprofen (263-293 ng L-1) and sulfamethoxazole (255-293 ng L-1). Among
the various pretreatment processes, granular activated carbon (GAC) was found to be highly-
effective in removing the targeted pharmaceuticals by adsorption except for gemfibrozil, ibuprofen
and clofibric acid. Microfiltration (MF) and ultrafiltration (UF) membranes are capable of removing
suspended solids in wastewater, but as it is difficult to retain PPCPs by size exclusions; this
contributed less than 10% removal efficiency. It was also observed that hydrophobic compounds (log
Kow > 3) were difficult to remove using UF and MF membranes. The results of this study
demonstrate that reverse osmosis (RO) can effectively remove nearly all of the pharmaceuticals (83-
99%). In particular, the RO removal mechanisms are emphasized because of their utmost important
role in eliminating micro-pollutants.
*Corresponding author
Email: cflin@ntu.edu.tw
INTRODUCTION
As human population continues to increase and
economies grow, the demand on limited water re-
sources are expected to rise tremendously in the com-
ing decades. Therefore, water recycling or water rec-
lamation will be the future development in developing
water purification technology to ensure the reliable
quantities and qualities of water for public use. None-
theless, several studies have demonstrated that various
pharmaceuticals and personal care products (PPCPs)
are persistent in the secondary effluent and in natural
waters at ng L-1 to µg L-1 concentrations [1-4]. For ex-
ample, 57 PPCP compounds were detected at four
Taiwanese wastewater treatment plants (WWTP), and
while non-steroidal anti-inflammatory drugs, estro-
gens and caffeine have higher removal efficiencies
(72-100%) by the wastewater treatment process, sev-
eral antibiotic groups are still persistent and present in
the secondary effluents [5]. If their elimination in
WWTPs is not complete, the trace level concentra-
tions may pose potential risks to human health and al-
so to the terrestrial, marine and aquatic ecosystems
[5,6] especially during water reclamation process.
Therefore, the monitoring and elimination of PPCPs
in WWTP effluent has become an important and
pressing matter in water reclamation treatment and
reuse.
Pretreatment technologies have been tested for
their ability to reduce membrane fouling for the poten-
tial to increase the membrane lifetime and thus de-
creases the operating costs [7,8]. Granular activated
carbon (GAC) and powdered activated carbon (PAC)
have been reported to be commonly used in the ad-
sorption of dissolved solids from the wastewater ef-
fluent [8] and are efficient in removing polar pharma-
ceutical compounds [9]. Synder et al. [10] also re-
ported that PAC and GAC have the capability to re-
move more than 90% of PPCPs in drinking water fa-
cilities. Shon et al. [8] studied microfiltration (MF),
ultrafiltration (UF) and reverse osmosis (RO) using
different physical and chemical pretreatment proc-
174 Sustain. Environ. Res., 21(3), 173-180 (2011)
esses and found that MF and UF mainly remove sus-
pended solids (SS) from the water; meanwhile, PAC
must be added to ensure that RO has sufficient filtra-
tion performance.
Numerous studies have demonstrated that the
membrane technology can be easily applied to remove
natural organic matters (NOM), inorganic compounds
and microorganisms from raw water [11,12], which
can also be used in water reclamation applications.
Currently, in the direct filtration of secondary effluent
from wastewater treatment plants, membrane tech-
nologies such as MF, UF, nanofiltration (NF) and RO
is widely utilized for the main purpose of wastewater
recycling [10,13]. The application of RO water recla-
mation has been the focus of attention of many studies.
However, many manufacturers of PPCPs and allied
industries are looking for better ways in treatment to
ultimately eliminate the presence of PPCPs in the wa-
ter environment [14,15]. Synder et al. [10] confirmed
that most of the PPCPs were hardly eliminated when
passing through the UF system. NF (> 99% removal
efficiency) and RO (90-99% removal efficiency) are
required if membrane filtration constitutes an essential
post-treatment technique. The degree of removal effi-
ciency is directly related to the membrane characteris-
tics and molecular properties associated to its targeted
compounds [10]. Moreover, the combination of MF or
UF with RO as secondary effluent post-treatment
seems to be efficient in removing the PPCPs in the
aquatic environment [4,10,16].
To our knowledge, very little information is
available on commercial pretreatment techniques us-
ing low pressure membranes combined with pretreat-
ments for the removal of PPCPs. In this study, the per-
formances of pretreatment technologies, lab scale of
MF and UF, and RO membranes in removing the
eight targeted PPCPs were investigated. The most
suitable pretreatment technologies for MF and UF
with the combination of RO membrane in eliminating
PPCPs were also evaluated.
METHODS AND MATERIALS
1. Reagents and Selected PPCPs
All chemicals and analysis standards used were
of the highest purity commercially available. In this
study, eight PPCPs were selected as the targeted com-
pounds (Table 1) purchased from Sigma Aldrich (St.
Louis, MO). All the targeted compounds were chosen
because of their high detection frequencies and high
influent concentrations in WWTPs [17].
2. Sample Collection and Preservation
Wastewaters (secondary effluent) were collected
from the Dihua wastewater treatment plant which is
one of the largest secondary wastewater treatment
plants in Taipei City. A total of 80 L of secondary ef-
fluent were collected and stored in ice-packed con-
tainers. After collection, the wastewater was shipped
to the laboratory immediately and fed to different
types of pretreatments such as polymer, PAC, GAC,
ion exchange (IE), fiber filter (FF) and membrane
processes (UF, MF and RO). Triplicate samples from
the selected points in the lab-scale pretreatments and
membrane processes were collected in 1-L silanized
amber glass bottles and 8 mL of 0.125 M EDTA-2Na
were added to the amber glass bottles to prevent the
adsorption of compounds on the glass. All samples
were vacuum-filtered through 0.22 µm cellulose ace-
tate membrane filters (Advantec, Toyo Roshi Kaisha,
Japan) and immediately adjusted to pH 4 with 1 N sul-
furic acid and then were refrigerated at 4 °C until
analysis.
3. Analytical Methods
For the targeted PPCP analysis, the Oasis HLB
cartridge with 500 mg of sorbent and 6 mL capacity
(Waters, Milford, MA, USA) was conditioned with 6
mL of methanol and 6 mL of deionized water (DI). A
400-mL sample was spiked with a flow rate of 3-6 mL
min-1 followed by rinsing with 6 mL of DI and then
dried by nitrogen stream. The analytes were eluted
with 4 mL of methanol and 4 mL of 50% (v/v) metha-
nol-diethyl ether. The collected elutes were concen-
trated over a continuous and constant flow of nitrogen
gas at 37 °C, reconstituted with 0.4 mL of 25% aque-
ous methanol and then filtered through a 0.45 µm
polyvinylidene fluoride membrane filter before liquid
chromatography/tandem mass spectrometry (LC-
Table 1. Target PPCP compounds
Name Acronym MW pKa
a Log Kow
b K
H (atm-m3 mol-1) Effective Diameterc (nm)
Acetaminophen ACT 151.2 9.4 0.46 6.42 × 10-13 0.59
Atenolol ATL 266.3 9.5 0.16 1.37 × 10-18 0.75
Carbamazepine CBZ 236.3 0.37 2.45 1.08 × 10-10 0.71
Clofibric acid CFA 214.6 NA NA 2.19 × 10-8 0.68
Erythromycin-H2O ERM-H2O 734.5 8.8, 8.9 3.00, 3.06 5.42 × 10-29 1.17
Gemfibrozil GEM 250.3 4.8 4.77 1.19 × 10-8 0.73
Ibuprofen IBU 206.3 4.5, 4.9 3.97, 3.50 1.58 × 10-7 0.67
Sulfamethoxazole SMX 253.3 2.0, 5.5 0.50, 0.89 6.4 × 10-13 0.73
a, bData are from references: [5,10,21].
Ng et al.: Tertiary Treatment of PPCPs 175
MS/MS) analysis. Surrogate standards (13C6-
sulfamethazine, atenolol-d7, josamycin and ibuprofen-
d3) were added to the initial samples and were fol-
lowed through the entire extraction and analytical pro-
cedures. The concentrations of the targeted pharma-
ceuticals were analysed using an Agilent 1200 module
(Agilent Technologies, Palo Alto, CA) equipped with
a ZORBAX Eclipse XDB-C18 column (150 × 4.6 mm,
5 μm) coupled to a Sciex API 4000 quadruple mass
spectrometer (Applied Biosystems, Foster City, CA)
equipped with a turbo ion spray source. All the com-
pounds have 0.5 ng L-1 quantification limits except for
atenolol, carbamazepine, and erythromycin-H2O with
1.0 ng L-1 and ibuprofen with 2.5 ng L-1. The recover-
ies of the targeted compounds were in an acceptable
range from 74 to 130%. The detailed quantification
procedure was reported by Lin et al. [5,17].
All samples were also analyzed for pH value,
chemical oxygen demand (COD), turbidity, ammonia,
nitrate, phosphate, SS, Escherichia coli and total dis-
solved solids (TDS). The pH value, TDS and turbidity
were measured with a HACH (Loveland, CO) HQ20
Portable Dissolved Oxygen/pH Meter (Cat. No.
51825-00), a HACH SecsION5 Conductivity Meter
and a HACH 2100P Turbidimeter, respectively. COD,
NH4
+, NO3
- and PO4
3- were analysed according to the
HACH closed reflux colorimetric method, Nessler
method, cadmium reduction method and persulfate di-
gestion method with the use of a HACH (DR 2800)
spectrophotometer (HACH, 2005). The concentration
of SS and E. Coli in the wastewater was analyzed us-
ing the Standard Method [18].
4. Membrane Reactors Set-up and Testing Units
All the membrane evaluated were performed and
operated in a lab-scale system. Table 2 summaries the
membrane specifications for low pressure membranes
(MF and UF) and high pressure membrane (RO) in
this study. The operation of the membranes was ac-
cording to the guidelines and manuals of the mem-
brane companies. The membranes were operated with
DI to reach a steady state for 8-12 h before operating
with the test solutions in order to prevent the pre-
compaction at the same pressure. The membranes
were cleaned by the relaxation process, backwashing
and clean in place process (NaOCl). The membrane
condition was checked periodically by forcing the air
inside the membrane fibres in a DI tank and the mem-
brane was changed when bubbles were detected.
5. Pretreatments
The processes of the pretreatments consist of co-
agulation by polymer (Sigma-Aldrich Corp., St. Louis,
MO), FF (Aqua-win MB-01, Watertec Co., Kaohsiung,
Taiwan) with 1 µm, IE resin (Max Water Flow, Con-
cord, ON), GAC (Flow-Pur T33-CG, Ellsworth, OH)
and PAC (Taipei Chemical Industry Co., Taipei, Tai-
wan). A series of jar tests were used for polymer co-
agulation (1-4 mL Poly(diallyldimethylammonium)
chloride, PolyDADMAC with rapid mixing (100 rpm)
for 2 min and subsequently slow mixing (30 rpm) for
20 min and allowed to settle in 30 min. PAC was
added at a dose of 10 mg L-1 with a 2-h contact time
(based on the bench scale test). The diameters of GAC
and IE column were 8 cm and GAC had a service life
of approximately 9500 L. The secondary effluent in
the 5-L amber glass bottle was pass through the FF,
GAC and IE resin respectively by means of a peristal-
tic pump separately at a filtration rate of 140 mL min-1
and the resulting effluents from the pretreatments
were collected for further studies.
The pretreatment methods were compared and
evaluated using water quality analysis as pretreatment
selection criteria for UF and MF membranes. The re-
sults are illustrated in Table 3. Among the pretreat-
ment methods in this study, FF (1 µm) and polymer
were given strong consideration as the best pretreat-
ment methods from the economic point view to the
UF and MF membranes since low pressure mem-
branes (MF and UF) are able to remove up to 80 and
55% of SS, respectively and may be able to reduce the
cake layers on the membrane surfaces [19].
Table 2. Specifications of MF, UF and RO membrane
Microfiltration (MF) Ultrafiltration (UF) Reverse Osmosis (RO)
Manufacturer Kubota GE Zenon ZW-1 DOW BW-30 1812
Membrane type Plate and frame Hollow fibers Spiral wound
Membrane material Chlorined PE PVDF Polyamide (PA)
Nominal pore size 0.4 µm 0.04 µm 0.1 nm
Membrane area (m2) 0.1 0.046 0.465
Element size (mm) L: 210 × W: 290 × T: 60 L: 172 × D: 50 L: 305 × D: 45
Designed pH range 2-11 2-11 4-11
Operating pressure (kPa) 5-10 10-55 600-1000
Design flux (L m-2 h-1) 8-20 18-40
Recovery (%)
15
176 Sustain. Environ. Res., 21(3), 173-180 (2011)
Table 3. Secondary effluent of water quality after pretreatments
Analytes Secondary
Effluent GAC PAC IE Resin Polymer
Fiber Filter
(1 µm)
pH 7.1 7.7 6.5 7.1 6.7 6.5
COD (mg L-1) 18 ± 2 14 ± 2 7 ± 1 11 ± 2 9 ± 2 16 ± 3
Turbidity (NTU) 1.9 ± 0.4 1.0 ± 0.6 1.2 ± 0.3 0.8 ± 0.2 0.6 ± 0.4 0.4 ± 0.1
NH3-N (mg L-1) 0.19 ± 0.03 0.15 ± 0.02 0.18 ± 0.03 0.16 ± 0.03 0.17 ± 0.05 0.14 ± 0.03
NO3-N (mg L-1) 4.10 ± 0.42 1.90 ± 0.28 3.20 ± 1.13 3.80 ± 1.41 3.70 ± 0.42 3.20 ± 0.28
PO4
3- (mg L-1) 2.04 ± 0.13 1.99 ± 0.42 1.75 ± 0.64 2.10 ± 0.09 1.72 ± 0.10 1.85 ± 0.18
SS (mg L-1) 16 ± 1 9 ± 1 12 ± 1 13 ± 3 7 ± 4 3 ± 0
E. coli (CFU 100 mL-1) 3800 3500 NA 3700 3700 3200
TDS (mg L-1) 301 285 146 150 146 141
NA = Not Available
RESULTS AND DISCUSSION
The results for PPCP removal by various pre-
treatments and low pressure membranes is depicted in
Table 4. The presence of compounds in the secondary
effluent indicated their incomplete removal and also
showed that residuals persisted after the WWTP
treatment process. Clofibric acid (240-296 ng L-1),
ibuprofen (263-293 ng L-1) and sulfamethoxazole
(255-293 ng L-1) in the municipal wastewater secon-
dary effluent were detected in relatively higher con-
centrations. Activated carbon (GAC and PAC) can
eliminate the PPCPs effectively and the main removal
mechanism is based on hydrophobic interaction which
is suited for non-polar organic compounds [3]. In the
study described here, both GAC and PAC which could
significantly remove the PPCPs, and GAC was found
to be highly-effective in eliminating the targeted
PPCPs (acetaminophen, atenolol, carbamazepine,
erythromycin-H2O and sulfamethoxazole) by more
than 95%. The removal efficiency of the PAC was
less than that of the GAC possibly because the PPCP
removal efficiency might be depend on the PAC dose
and contact time in the water [10]. The IE resin, po-
lymer and FF did not show good removal efficiencies,
but a slightly higher degree of removal efficiency was
observed for atenolol and erythromycin-H2O while the
rest of the PPCPs were not removed by the IE resin
and FF.
The results in Table 4 show that the MF and UF
had little capability in removing PPCPs. The removal
mechanisms might be attributed to hydrophobic ab-
sorption on the membrane surface area [20], however
the targeted PPCPs in this study did not follow the
removal mechanism; therefore, this led to less than
10% of the initial compound removal in the permeate
except for acetaminophen (< 25%). MF and UF have
the capability to remove SS and could disinfect
wastewater, but it is hard to retain PPCPs by size ex-
clusions [3,10]. The effective diameters of these
PPCPs compounds are in the range of 0.6-1.2 nm (Ta-
ble 2). Hence, MF and UF membrane with a nominal
size of 400 and 36 nm, respectively, are not able to
remove all the targeted PPCPs compounds. Moreover,
it was found that the hydrophobic compounds (log
Kow > 3) were difficult to remove with MF and UF
membranes. The finding shows that the GAC and
PAC were more effective in removing the targeted
compounds than other pretreatments and low pressure
membranes (MF and UF) and all the pretreatments
and low pressure membranes (MF and UF) have to be
combined with the RO to achieve better removal effi-
ciency of the PPCPs.
Table 5 clearly shows that the RO membranes
were effective on reducing the concentration of PPCPs.
Trace levels of compounds were still detectable in the
RO permeates. In the presence of RO, target PPCPs
compounds removal efficiencies were excellent (83-
99%), indicating that the RO membrane was sufficient
to remove these pollutants with any combination of
pretreatments or low pressure membrane (MF and UF).
The results shows the RO membrane had greater re-
tention than the MF and UF membranes, which was
presumably because more size exclusion contributed
to the retention for the RO membrane (0.1 nm). Since
almost all the PPCP compounds have a molecular
weight (MW) of greater than 0.5 that necessitates the
use of RO in order to reduce PPCPs concentration in
wastewater [21].
PPCPs can be removed by RO because the nega-
tive charged membrane possibly plays a role in charge
exclusion mechanism. For example, negatively
charged pharmaceutical compounds such as car-
bamazepine, gemfibrozil, sulfamethoxazole and clofi-
bric acid were recorded with higher removal efficien-
cies (> 90%) as compared to more positively charged
PPCPs which may be due to the interactions with the
membrane surface [22]. The results are also supported
by Xu et al. [23] who showed that negatively charged
compounds were easy to eliminate on a negatively
charged membrane surface. Besides, speciation of mo-
lecules, i.e., the charged property of PPCPs is highly
dependent on solution pH value. For example, while
the solution pH level is above the isoelectric point of
the membranes, the membrane is negatively charged
and it may increase the rejection of negatively
Ng et al.: Tertiary Treatment of PPCPs 177
Table 4. Percentage of PPCPs removal by various pretreatments and low pressure membranes
Sec. Eff. GAC PAC IE Resin Polymer Fiber Filter
(1 µm) UF MF
Process
Cpd.
Mean ± SD
(ng L-1)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
ACT 32 ± 12 0.6 ± 0.5
(98)
9 ± 8
(73)
4 ± 2
(87)
17 ± 7
(46)
24 ± 6
(23)
24 ± 6
(25)
36 ± 16
(NR)
ATL 124 ± 8 ND
(> 99)
53 ± 6
(58)
ND
(> 99)
80 ± 18
(36)
89 ± 12
(36)
121 ± 10
(2)
119 ± 17
(4)
CBZ 83 ± 29 ND
(> 99)
31 ± 26
(63)
59 ± 2
(29)
103 ± 2
(NR)
97 ± 3
(NR)
95 ± 6
(NR)
102 ± 5
(NR)
CFA 268 ± 28 72 ± 41
(73)
230 ± 13
(14)
321 ± 8
(NR)
227 ± 1
(15)
287 ± 4
(NR)
273 ± 2
(NR)
281 ± 21
(NR)
ERM-H2O 15 ± 2 ND
(> 99)
ND
(> 99)
ND
(> 99)
16 ± 1
(NR)
ND
(> 99)
15 ± 1
(5)
16 ± 2
(NR)
GEM 14 ± 2 3 ± 2
(81)
9 ± 2
(36)
19 ± 1
(NR)
13 ± 2
(11)
19 ± 2
(NR)
14 ± 2
(2)
14 ± 3
(2)
IBU 283 ± 20 121 ± 90
(57)
209 ± 10
(26)
362 ± 8
(NR)
279 ± 1
(5)
315 ± 8
(NR)
271 ± 21
(4)
264 ± 10
(7)
SMX 274 ± 19 ND
(> 99)
116 ± 101
(58)
242 ± 1
(12)
234 ± 4
(15)
238 ± 23
(13)
243 ± 34
(11)
258 ± 15
(6)
Cpd. = compound; Sec. Eff. = secondary effluent; GAC = granular activated carbon; PAC = powder activated carbon; IE = ion
exchanger; UF = ultrafiltration; MF = microfiltration; avg. = average concentration; SD = standard deviation; RE = removal
efficiency; ND = not detected; NR = not removed
Table 5. Percentage of PPCPs removal by membranes filtration
UF + RO MF + RO FF + UF + RO FF + MF + RO P + UF + RO P + UF + RO Process
Cpd.
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
Mean ± SD
(ng L-1)
(RE, %)
ACT 5.3 ± 0.1
(83)
ND
(> 99)
ND
(> 99)
ND
(> 99)
ND
(> 99)
ND
(> 99)
ATL 3.4 ± 0.3
(97)
6.0 ± 0.2
(95)
ND
(> 99)
0.8 ± 0.2
(> 99)
10 ± 1
(92)
6 ± 1
(95)
CBZ ND
(> 99)
ND
(> 99)
ND
(> 99)
5 ± 1
(95)
ND
(> 99)
ND
(> 99)
CFA 11 ± 4
(96)
6 ± 3
(98)
5 ±4
(98)
5 ± 3
(98)
32 ± 2
(88)
24 ± 1
(91)
ERM-H2O ND
(> 99)
ND
(> 99)
ND
(> 99)
ND
(> 99)
ND
(> 99)
ND
(> 99)
GEM ND
(> 99)
ND
(>99)
ND
(> 99)
2 ± 1
(85)
ND
(> 99)
ND
(> 99)
IBU ND
(> 99)
4 ± 1
(98)
23 ± 12
(92)
32 ± 5
(89)
4 ± 1
(99)
17 ± 1
(94)
SMX 13.3 ± 0.3
(95)
27 ± 1
(90)
ND
(> 99)
5 ± 2
(98)
26 ± 2
(91)
25 ± 3
(91)
Cpd. = compound; Sec. Eff. = secondary effluent; UF = ultrafiltration; MF = microfiltration; RO = reverse osmosis; FF = fiber filter;
P = polymer; avg. = average concentration; SD = standard deviation; RE = removal efficiency; ND = not detected
charged solutes due to the electrostatic repulsion with
membrane surface [4,23]. As documented by Bellona
et al. [24], membrane properties, feed composition
and operating conditions could affect the rejection of
solute on NF/RO membranes. Size exclusion, charge
exclusion and physico-chemical interactions between
solute, solvent and membrane are the basic mecha-
nisms or explanations for RO rejection.
Hydrophobicity leads to PPCP adsorption onto
the membrane surface and inside the pores; it can dif-
fuse through the RO membrane polymer [25]. In most
cases, the RO membranes may absorb many hydro-
178 Sustain. Environ. Res., 21(3), 173-180 (2011)
phobic compounds (Log Kow >3) and the removal effi-
ciency will increase with the increase of Log Kow val-
ue, which shows that retention of hydrophobic mem-
brane is generally influenced by hydrophobic interac-
tion [24]. For example, erythromycin-H2O, gemfibro-
zil and ibuprofen (Log Kow > 3) are considered as ab-
stemiously hydrophobic and thus the removal effi-
ciency of these three pharmaceuticals was more than
95% and the result was consistent with that obtained
by Al-Rifai et al. [26]. On the contrary, the removal
efficiency of polar charged compounds (lower log Kow)
was found to be better removal in the RO process due
to the interactions with membrane [22,24,27] and the
convection of molecules in hydrophilic charged com-
pounds [28] which depends on the membrane material
and feed solution pH. Additional studies, however, are
needed to validate this observation at pilot-scale or
full-scale membrane utilities to understand the role of
membrane material toward PPCP compounds.
On the other hand, the rejection of hydrophilic
and uncharged molecules (acetaminophen) should be
highlighted, considering their greater affinity towards
water. It was presumed that the adsorption of trace
compounds in the structure of RO would possibly not
occur completely because the RO was new and did not
achieve the steady-state operation for the membrane
material [21]. Therefore, this may explain its limited
rejection on RO membranes (> 83%). In order to
avoid erroneous results especially in the trace concen-
trations of PPCPs, a longer time of membrane filtra-
tion would be required to achieve membrane equilib-
rium.
Throughout the duration of experiments, the ob-
served results suggest that the combination of FF, UF
with and RO had achieved an excellent removal for
nearly all the target compounds (> 98%) except for
ibuprofen (< 92%). FF has lower removal efficiency
in eliminating PPCPs, but it is able to remove the sus-
pended matters and colloid particles in the wastewater
before the wastewater enters UF membrane. FF is a
very promising pretreatment in terms of controlling
and reducing UF fouling, and it requires less cleaning
and is being economical to operate. The results give
us a good criterion for selecting pretreatment methods
for the further membrane analysis to remove the
PPCPs and also to reduce the fouling of membrane.
RO was thus shown to be the main application that
was capable of significant rejection of nearly all the
targeted compounds, though compounds at trace lev-
els were detectable in permeates. Consequently, the
fundamental approach can be utilized to evaluate the
potential of PPCP removal by identification of the
compounds in water.
CONCLUSIONS
In this work, various pretreatments and mem-
branes (UF, MF and RO) were applied in the removal
of PPCPs from a municipal WWTP with the aim of
water reclamation. PPCPs could be removed by GAC
with the adsorption mechanisms but the MF and UF
membranes had little removal efficiency on the se-
lected PPCPs (< 30%) which were generally governed
by hydrophobic adsorption. Hydrophobic compounds
(log Kow >3) were difficult to remove by pretreatments
and low pressure membranes (MF and UF membrane)
and this led to the poor removal efficiency of the
PPCPs. The mechanism of size exclusion for RO
brought about high rejections (> 83%) for these mi-
cropollutants that have a greater MW cut-off than that
of RO membranes. Besides, the highest removal effi-
ciency in RO process was recorded for negatively
charged pharmaceutical compounds of gemfibrozil,
sulfamethoxazole and clofibric acid. Furthermore, a
steady-state operation for the membrane must be
achieved in order to avoid erroneous results especially
in the trace concentrations of PPCPs. In addition, the
combination of FF, UF with RO membrane had
achieved an excellent removal efficiency (90-99%) in
all the target compounds. The results in this study
provide several additional data although this is a
short-term study using the pretreatments and mem-
brane systems. Therefore, future research efforts
should focus on the studies of the transport of animal
and endocrine disrupting compounds in membrane fil-
tration to establish additional meaningful treatment
goals.
ACKNOWLEDGMENTS
The authors would like to thank Water Resource
Agency, Ministry of Economic Affairs of the Repub-
lic of China for financially supporting us in this re-
search under Contract No. MOEAWRA 0980045 and
Contract No. MOEAWRA 0990020.
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... MF and UF membranes are efficient in removing solid particles in wastewater, but as it is hard to sustain PPCPs by size exclusions, this contributed less than 10% removal efficiency. It was also noticed that hydrophobic compounds (log Kow > 3) were less likely to be removed by UF and MF membranes [65]. ...
... NF and RO, on the other hand, showed a higher removal efficiency-up to 90%-99% in some cases. The degree of removal efficiency was directly related to the membrane characteristics and molecular properties associated with its targeted compounds [65]. However, even though NF has demonstrated such a promising efficacy, it suffers, in addition to the other three classes of membranes, from the following crucial challenges that hinder their full-scale applications in the environmental field to remove PhACs. ...
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Pharmaceuticals and personal care products, and endocrine disruptive compounds, have arisen as a new class of emerging organic micropollutants imposing a great risk on the health of both human and aquatic ecosystems. In spite of the advancements accomplished so far in conventional membrane for water purification, none can be considered as a membrane of choice as each of them is inhibited by at least one drawback or trade-off relating to flux, selectivity, stability, or high cost of fabrication; above all, the critical fouling issue exacerbates the situation and comes to the fore, here. Huge efforts have been made to overcome these obstacles, for instance, by modifying membrane surfaces by chemical grafting with hydrophilic monomers; however, satisfactory antifouling properties have not yet been achieved. By exploiting the distinctive features of nanotechnology, blending membranes with nanoparticles, carbon nanomaterials, nanofibers, self-assembled two-dimensional layer materials, their composites, etc. are proven to exceed all the limitations and attain a satisfactory sustainable membrane technology. Even better, employing the functionalized type of nanomaterials may far surpass their original counterparts in terms of mechanical strength, antifouling tendency, rejection for micropollutants, and antitrade-off between permeability and selectivity. This chapter attempts to shed some light on the nanotechnologies novelties and endeavors notably found in the state-of-the-art membrane-based micropollutant removal technologies.
... Advanced treatment processes usually follow high-rate secondary treatment, which is sometimes referred as tertiary treatment procedures. However, sometimes advanced treatment processes can be combined with primary or secondary treatment or used in place of secondary treatment [23]. The most popular advanced treatment methods are membrane filtration and advanced oxidation. ...
... Different treatment processes, including activated carbon [1,17], nanofiltration [18,19], and reverse osmosis [20] have been reported as effective treatment options for removing different types of pharmaceuticals. However, these treatment processes are considered temporary solutions, as they only move or transfer the pharmaceuticals to the solid phase or concentrate them in a small volume of aqueous solution, which then requires further treatment. ...
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