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Journal of Hazardous Materials 286 (2015) 416424
Contents lists available at ScienceDirect
Journal of Hazardous Materials
journa l homepage: www.e lsev ier .com/ locate / jhazmat
Organics and nitrogen removal from textile auxiliaries
wastewaterwith A2O-MBR in a pilot-scale
Faqian Suna, Bin Suna,b, Jian Hua, Yangyang Hea, Weixiang
Wua,
a Institute of Environmental Science and Technology, Zhejiang
University, Hangzhou 310058, Chinab Shanghai Electric Group Co.
Ltd. Central Academe, Shanghai 200070, China
h i g h l i g h t s
A pilot-scale A2O-MBR system treating textile auxiliaries
wastewater was assessed. Organic matter and recycle ratio strongly
affected the performance of the system. GC/MS analysis found some
refractory organics in the MBR permeate. Combination of organic
foulants and inorganic compounds caused membrane fouling.
a r t i c l e i n f o
Article history:Received 12 October 2014Received in revised form
8 December 2014Accepted 10 January 2015Available online 13 January
2015
Keywords:Textile auxiliaries
wastewaterAnaerobicanoxicaerobicMembrane bioreactorRecycle
ratioRefractory organics
a b s t r a c t
The removal of organic compounds and nitrogen in an
anaerobicanoxicaerobic membrane bioreactorprocess (A2O-MBR) for
treatment of textile auxiliaries (TA) wastewater was investigated.
The resultsshow that the average efuent concentrations of chemical
oxygen demand (COD), ammonium nitro-gen (NH4+N) and total nitrogen
(TN) were about 119, 3 and 48mg/L under an internal recycle ratio
of1.5. The average removal efciency of COD, NH4+N and TN were 87%,
96% and 55%, respectively. Gaschromatographmass spectrometer
analysis indicated that, although as much as 121 different types
oforganic compounds were present in the TA wastewater, only 20
kinds of refractory organic compoundswere found in theMBR efuent,
which could be used as indicators of efuents from this kind of
industrialwastewater. Scanning electronmicroscopy analysis revealed
that bacterial foulantswere signicant con-tributors to membrane
fouling. An examination of foulants components by wavelength
dispersive X-rayuorescence showed that the combination of organic
foulants and inorganic compounds enhanced theformation of gel layer
and thus caused membrane fouling. The results will provide valuable
informationfor optimizing the design and operation of wastewater
treatment system in the textile industry.
2015 Elsevier B.V. All rights reserved.
1. Introduction
As one of the largest industries in the world, the textile
indus-try consumes large quantities of textile auxiliaries (TA),
whichincludemore than 100 kinds of specialty chemicals, such as
soften-ing agent, phosphates, polyamide resins, acrylic chelating
agents,polyurethane coating agents and stiffening agents. In the TA
pro-duction, considerableamountsofTAwastewater aregenerated. TheTA
wastewater is very chemical-intensive and known to containhigh
concentrations of organic matter, non-biodegradable matter,toxic
substances and ammonia [13]. These compounds producelong-term
environmental impacts, it is therefore important to
Corresponding author. Tel.: +86 571 88982020; fax: +86 571
88902020.E-mail address: [email protected] (W. Wu).
remove these organics and ammonia from the TA wastewater
forreducing their harm to the environment.
TA wastewater could be treated by physicochemicaland biological
methods or suitable combinations of them.Physicochemical methods
involve adsorption, ion exchange,coagulationocculation, as well as
advanced oxidation processes(such as Fenton oxidation, ozonation,
photocatalytic oxidationand electrochemical oxidation) [46].
However, methods suchas coagulation, ion exchange, and adsorption
only transfer theorganic pollutants from one phase to another.
Advanced oxidationprocesses, such as Fenton oxidation, ozonation,
photocatalyticoxidation and electrochemical oxidation, are very
efcient andthe fastest way for destruction of organic compounds,
but theyare expensive and could not be adopted commercially.
Comparedwith physicochemical methods, biological treatment is often
themost economical alternative for pollutant removal [7].
http://dx.doi.org/10.1016/j.jhazmat.2015.01.0310304-3894/ 2015
Elsevier B.V. All rights reserved.
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F. Sun et al. / Journal of Hazardous Materials 286 (2015) 416424
417
Due to the low biodegradability and high toxicity of manytextile
chemicals, a conventional activated sludge system is inad-equate in
removing high concentrations of refractory organics andammonia. In
recentyears, themembranebioreactor (MBR), becauseof complete
biomass retention, has been successfully integratedwith an
anaerobicanoxicaerobic (A2/O) system for industrialwastewater
treatment [8]. The combined system was efcientand cost-effective in
removing refractory pollutants and ammo-nia, especially at high and
varying loading rates [9]. The use ofanaerobic process as a
pretreatment process to partially convertrefractory organics to
intermediates that are more readily degrad-able, could be
attractive for refractory wastewater treatment. Theanoxicaerobic
process is a good option for achieving biologicalnitrogen removal
via pre-denitrication and aerobic nitrication.MBR can keep a long
sludge retention time (SRT), which allows thesystem to keep a
sufcient amount of slow-growing bacteria, suchas ammonia oxidizing
bacteria and those specializing in degradingrefractory compounds
[10]. Therefore, the A2O-MBR system is veryattractive for
chemical-intensive industrial wastewater treatment.
The efciencies of organic compounds and nitrogen removal
intheA2O-MBR systemare inuencedbymany factors, such as chem-ical
characteristics of wastewater, internal recycle ratio,
hydraulicretention time (HRT)andsubstrate loading rate. [1113].
Thechem-ical characteristics of TA wastewater determined the
biodegradingcapacity of the system. Internal recycle ratio was
found to have animportant role in nitrogen removal performance of
the system. Inaddition, membrane fouling was inevitable in MBR
systems. In theprevious studies reported in the literature,
therewas little informa-tion on the nitrogen removal and behaviors
of organic compoundsin a A2O-MBR system for TA wastewater treatment
particularly atpilot-scale operation.
The objectives of the present research were: (1) to
investigatethe pollutant removal performance in a A2O-MBR system,
(2) tocharacterize in detail organic chemical composition in the
rawwastewater and the efuents, (3) to compare the performance oftwo
kinds ofmembranemodules and examine themembrane foul-ing
behaviors.
2. Materials and methods
2.1. Experimental set-up and operating conditions
Thepilot-scale experimentswere carriedout in a sequential
sys-tem (in Fig. 1) of an anaerobic reactor (A1), an anoxic reactor
(A2),followed by an aerobic membrane bioreactor (O-MBR). The
work-ing volumes of the three reactors were 3.8m3, 7.5m3 and
5.6m3,respectively. Reactor A1 was packed with bamboo carbon,
whichwasgeneratedat600 Cundera slowpyrolysisprocesswithadiam-eter
of 35mm. In the reactor A2, amechanical stirrerwas installedto
agitate its content. The O-MBR could divide into buffer zoneand
reaction zone. An internal pump was installed in the bufferzone
andmixed liquor from the bottomwas continuously pumpedto the
reaction zone. Two different kinds of membrane moduleswere immersed
and symmetrically placed in the reaction zone. Onewas a hollow ber
(HF)membranemodulemade of polyvinylideneuoride (PVDF)with anominal
pore sizeof 0.1manda totalmem-brane surface area of 12.5m2
(SMM-1013, Memstar TechnologyCo. Ltd., Singapore). The other one
was a at-sheet (FS) membrane
module with a nominal pore size of 0.1m and a total
membranesurface area of 10.4m2 (DF80, Jiangsu Dafu Membrane
Technol-ogy Co. Ltd., China). Air diffusers were installed
underneath themembrane module to provide dissolved oxygen (DO) as
well asto control membrane fouling and clogging. DO was maintained
at35mg/L in the MBR during the experiments. Membrane
ltrationthrough a suction pump was carried out in an intermittent
suc-tionmodewith 9min of suction followed by a 2min release. In
situmembrane chemical cleaning was performed to
reducemembranefouling by 0.5% NaClO for 1h when the trans-membrane
pressure(TMP) increased to 20kPa.
The sequential system was operated in a pre-denitricationmode,
which consisted of three different steps. Firstly, TAwastewater was
continuously pumped into reactor A1 for hydrol-ysis/acidication.
Secondly, the water passed to reactor A2, wheredenitrication took
place and a fraction of organic matter wasdegraded by heterotrophic
bacteria. Thirdly, the water passedto the O-MBR where nitrication
and degradation of remainingorganic matter occurred, and the
permeate water was separatedby membrane modules while nitrate was
recycled to A2 by par-tial recirculation. The inoculating sludge
was drawn from theanaerobic sludge in a conventional TA wastewater
treatment plant(Hangzhou, China). During the study, different
internal mixedliquor recycle ratios from O-MBR to A2 were employed
to assesschemical oxygen demand (COD) and nitrogen compounds
removalof the system. Recycle ratios ranged from 0.5 to 2.5 of the
inu-ent ow rate. At the start-up period (Phase I), the inuent
owrate was kept at 250 L/h, and the recycle ratio was controlled
atabout 0.5. The system was operated stably for 20 days.
Afterwards,the recycle ratio was changed to about 1.5 and the
system wasthen operated in this condition for 74 days (day 2194,
Phase II).Fromday 95 onward, the recycle ratiowasmaintained at 2.5
(PhaseIII) and methanol at a equivalent concentration of about
240mg/LCOD was supplemented as an organic source in the A1
efuent.Because the recycle ratio was high at all times, mixed
liquor sus-pended solids (MLSS) concentrations in the reactors were
similar.During the whole period of the study, no sludge was
removedfrom the plant except for some incidents with accidental
sludgeloss. MLSS concentration in the O-MBR and the A2 uctuated
at35005000mg/L. Theexperimentwas conductedunder
anambienttemperature of 2025 C. Furthermore, parameters such as
tem-perature, level of the tanks, TMP, ow rates of partial
recirculationand the permeate inside the O-MBR were measured
automaticallyand registered continuously in a database with the aid
of Realinfosoftware (Realinfo., China).
2.2. Characteristics of TA wastewater
TA wastewater was collected from Transfar Chemicals Co. Ltd.,one
of the largest TA manufacturing factories located in the south-east
of China. Itwasrstlypumped into an intermediate tankbeforebeing
continuously pumped into the bioreactor. A summary of theinuent
characteristics at different experimental phases are shownin Table
1. The raw wastewater had a highly variable composi-tion. It can be
seen that the average COD concentrations in thethree phaseswere
657, 944 and 828mg/L, while total nitrogen (TN)concentrations were
115, 106 and 121mg/L, respectively.
Table 1Characteristics of TA wastewater observed during the
experiments.
Phase pH COD (mg/L) NH4+N (mg/L) TN (mg/L) COD/TN Number of data
points
I 7.299.37 657 127 87 5 115 7 6.9 1.8 10II 7.428.71 944 163 90
19 106 19 8.0 2.0 35III 7.508.74 828 216 94 21 121 31 6.0 1.3
23
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418 F. Sun et al. / Journal of Hazardous Materials 286 (2015)
416424
Fig. 1. Schematic diagram of the pilot-scale A2O-MBR system.
2.3. Analytical methods
Ammonium nitrogen (NH4+N), nitrite nitrogen (NO2N) andnitrate
nitrogen (NO3N) were analyzed according to the stan-dardmethods for
the examination ofwater andwastewater (APHA,1998). COD and TN were
measured by the Hach COD kits and HachTN kits, respectively (Hach,
USA). The pH was measured with a pHmeter (SG2,Mettler-Toledo,
Greifensee, Switzerland) and DO by anoxygen probe (YSI 550A, YSI,
Ohio, USA). MLSS was determined byvacuum ltration of 10mL of sludge
and then dried at 105 C for2h.
Gas chromatographmass spectrometer (GCMS) was used toanalyze of
the samples with liquidliquid extraction pretreatmentusing CH2Cl2
(chromatogrampure grade, Tianjin Chemical Factory,Tianjin, China).
Subsequently a 200mL sample was extracted using10mL of CH2Cl2
(chromatogram pure grade, Fisher, USA) three
times at neutral, alkaline and acidic conditions, respectively
[14].Then, a 1mL pretreated sample was analyzed by 6890N/5975BGCMS
system (Agilent Corporation, USA). A DB-5MS capillary col-umn with
an inner diameter of 0.25mm and a length of 30m wasused in the
separation system. The GC column was operated in atemperature
programmed mode by maintaining the temperatureat 40 C for 4min,
then increasing to 300 C with an increment of8 C/min, and total run
timewas46min. Theelectron impact energywas set at 70 eV. Organic
compounds analysiswas undertakenwithreference to the instrument
library (NIST 05. L) database.
At the end of ltration, a piece of membrane was cut fromthe
middle of the membrane modules. The sample was xed with3.0%
glutaraldehyde in 0.1M phosphate buffer at pH 7.2. The sam-ple,
dehydrated with ethanol and silver-coated by a sputter, wasobserved
using the scanning electronmicroscopy (SEM) (JEOL JSM-5600LV,
Tokyo, Japan). Inorganic elementary analysis was carried
Fig. 2. Variation of COD concentrations in the pilot-scale
A2O-MBR system during the 3 phases of operation.
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F. Sun et al. / Journal of Hazardous Materials 286 (2015) 416424
419
out on an Elementary Vario El (Germany) system. Wavelength
dis-persive X-ray uorescence (WD-XRF) data were obtained from
aBruker S4 Explorer spectrometer.
3. Results and discussion
3.1. COD removal
The COD removal of the pilot-scale A2O-MBR during the
wholeoperation period is presented in Fig. 2. It shows that the
A2O-MBRperformed well in organic matter removal. COD concentration
inthe TA wastewater was in the range of 3721291mg/L with anaverage
value of 879mg/L. In the reactor A1, about 100mg/L CODwas steadily
removed. The relatively low COD removal efciencyimplied organic
compounds with macromolecular structure andlarge molecules in the
raw wastewater were partially convertedinto small-molecule
substrates through hydrolysis-acidicationprocesses in an anaerobic
environment. A drop in mean pH of 0.7unit appears to support this
(datanot shown). In the reactorA2,CODconcentration was diluted by
mixed liquor recirculation. The aver-age COD concentration of A2
efuent was 320mg/L. In the O-MBR,most of the COD was removed.
Despite the uctuations of inuentCOD concentrations, the average
efuent COD concentration was131mg/L, with an average total COD
removal of 85%. Moreover, itwas also observed that efuent
CODconcentrationwas not affectedwhen the recycle ratio was
increased from about 0.5 to 2.5. Theseresults indicated the system
could maintain a consistently goodperformance of COD removal. The
efuent could meet the nationaldischarge standard ofwater pollutants
for industrial wastewater inChina (COD
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420 F. Sun et al. / Journal of Hazardous Materials 286 (2015)
416424
Fig. 3. Proles of internal recycle ratio, ammonia and TN
concentration in the A2O-MBR system.
not promote the increase innitrogen removal. Thesedata show
thatthe limited denitrication capacity is attributable to the
oxidationof organicmatter in the anoxic reactorwith the oxygen of
the inter-nal recycle at high ratios. High DO concentration (above
5mg O2/L)present in the recycle mixed liquor deteriorated TN
removal ef-ciency [15,22]. Therefore, it could be concluded that a
recycle ratioaround 1.5 should be recommended to provide a proper
comprisebetween removal efciency and cost under normal
conditions.
3.3. Behavior of organic compounds
In order to gainmore insight into the organic composition of
TAwastewater and the removalmechanisms for these organics duringthe
treatment process, GCMS analysis was carried out. The
chro-matograms of the raw wastewater and the efuent from each
unitof A2O-MBR are shown in Fig. S1. It could be seen that, at
least 121types of organic components were present in the TA
wastewater,which contained 92 kinds of alkanes and 29 other kinds
of organ-ics belonging to chemical additives and their derivatives.
Aftertreatment by anaerobic reactor, the categories of organic
com-pounds decreased to 90. These organics were more readily
degraded in the subsequent anoxic stage with the categories
fur-ther decreasing to 55. At last, only 20 different kinds of
organiccompounds were found in the permeate from MBR.
The details of organic compounds are summarized in Table 3 .It
appears that the alkanes and butylated hydroxytoluene
(BHT),corresponding to 47.6% and 26.6% of the total integration
area,respectively, dominated the organic matter in the TA
wastewater.BHT, a commonantioxidant,was likely to come from the
rawchem-icals used for TA production [23]. Certain compounds, such
as pyri-dine, tetramethylbutanedinitrile (TMSN),
butoxytrimethylSilane,p-xylene and 1,3-dimethylbenzene, which each
covered morethan1%of integration area,were the sub-dominant organic
species,whereas other compounds were the minor species. These
organiccompounds in the inuent are generally composed of
synthesis-related chemicals and their derivatives. After the
treatment byanaerobic tank, most of organic compounds have
decreasedslightly, such as alkanes, BHT, pyridine and
butoxytrimethylSi-lane. Compared to the alkanes with higher
molecular weights,alkanes with low molecular weights were removed
with rela-tively high efciency. Meanwhile, some new intermediates
wereproduced. For instance, several alkaneswere probably converted
to
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F. Sun et al. / Journal of Hazardous Materials 286 (2015) 416424
421
Table 3Main organic compounds present in the inuent and the
efuent by GCMS analysis.
No Organic compounds Relative mass percentage (%) Total removal
efciencya(%)
TA wastewater A1 efuent A2 efuent MBR permeate
1 Alkanes 47.63 40.23 44.17 8.44 982 Butylated hydroxytoluene
26.57 16.73 8.8 6.05 983 Pyridine 4.81 0.77 1004
Tetramethylbutanedinitrile 4.61 5.1 15.59 34.02 195 Silane,
butoxytrimethyl- 2.95 0.52 1006 1,2-Benzenedicarboxylic acid,
mono(2-ethylhexyl) ester 1.72 1.52 3.18 2.06 877 p-Xylene 1.45 2.06
0.43 1.87 868 Benzene, 1,3-dimethyl- 1.11 1.69 1009 Acetamide,
2,2,2-triuoro-N-(trimethylsilyl)- 0.94 100
10 Ethylbenzene 0.88 1.9 0.68 0.57 9311 Acetic acid,
(trimethylsilyl)- 0.83 0.28 10012 Methane, dimethoxy- 0.77 1.05
10013 Sulfur 0.64 0.47 10014 Benzene, 1,2,4,5-tetramethyl- 0.51
0.33 0.36 10015 Naphthalene, decahydro-2-methyl- 0.44 10016 Styrene
0.41 0.79 1 3.65 217 Cyclotetrasiloxane, octamethyl- 0.4 10018
Bis(trimethylsilyl) triuoroacetamide 0.39 10019 Phosphorous acid,
tris(decyl) este 0.37 10020 2H-Benzotriazole, 2-ethyl- 0.36 0.43
0.61 1.22 6321 Hexa(methoxymethyl) melamine 0.32 0.43 0.92 1.94
3422 Silanamine, N-methoxy-1,1,1-trimethyl-N-(trimethylsilyl)- 0.3
10023 Naphthalene, decahydro-2,6-dimethyl- 0.3 10024 Morpholine,
4-methyl- 0.26 0.72 10025 3-Methyl-2-(2-oxopropyl) furan 0.25 10026
Formamide, N,N-dimethyl- 0.21 0.51 10027 Toluene 0.2 0.21 0.24 0.87
5228 Propanoic acid, 2-methyl-, trimethylsilyl ester 0.19 10029
1,4-Dioxane 0.18 0.15 0.95 1.63 130 d-Limonene 7.16 31
Bicyclo[410]hept-2-ene, 3,7,7-trimethyl- 5.57 32 Hexanoic acid,
2-ethyl- 3.28 33 Hydrazine, 1-methyl-1-(2-propenyl) 2.09 10.1 17.3
34 Benzene, 1-methyl-2-(1-methylethyl)- 2.05 35 Benzene,
1-ethyl-2,4-dimethyl- 0.81 36 Cyclohexene,
1-methyl-4-(1-methylethylidene)- 0.64 37 6-Tetradecanesulfonic
acid, butyl ester 0.6 1.07 38 Tridecanol, 2-ethyl-2-methyl- 0.56 39
2-Ethylhexanoic acid, trimethylsilyl ester 0.3 40 Phenol,
3-(1,1-dimethylethyl)-4-methoxy- 1.86 41 Dodecane, 4,6-dimethyl-
0.65 42 Decane, 3,7-dimethyl- 0.56 43 Pentadecane 0.5 44
3-tert-Butyl-4-hydroxyanisole 1.86 3.46 45
2,4-Dimethoxy-N,N-dimethylbenzylamine 5.28 14.6 46 Others 1.05 1.09
2.32
Total 100 100 100 100
a Total removal efciency was calculated according to the peak
area under the same condition.
2-ethyl-hexanoic acid, and 6-tetradecanesulfonic acid, butyl
ester,and consistent with the general decrease of pH in the
anaerobictank due to hydrolysis/acidication.
After the treatment in theanoxic tank, it canbe seen
fromTable3that a considerable amount of benzene series organics and
alka-nes, which were hardly biodegraded at the anaerobic stage,
weredegraded. Pyridine, butoxytrimethylSilane, 1,3-dimethyl
benzene,were completely removed. Furthermore, most of new
interme-diates produced from the anaerobic tank were consumed atthe
anoxic stage, probably leading to a satisfactory denitri-cation
performance. By contrast, some new compounds, suchas
3-(1,1-dimethylethyl)-4-methoxy-phenol,
2,4-dimethoxy-N,N-dimethylbenzylamine etc. were produced.
Therefore, in order totreat TA wastewater or other refractory
wastewater, it is desir-able to have an anaerobic unit as a
pretreatment method for betterdenitrication performance [24].
Most of the residual compounds in the anoxic efuents werefurther
degraded at the aerobic stage. In order to make aquantitative
comparison of the relative removal of organiccompounds from the TA
wastewater, the areas of the peaks under
the chromatograms were determined under the same conditions.It
can be observed that, alkanes, the main components in TAwastewater,
were reduced by 98%, and only 6 types of alkanescould be detected
in the MBR efuent. Similarly, BHT, the sub-dominant component, was
reduced by 98%, which is better thanthat reported in municipal
wastewater treatment using a com-bined systemofUASB and two
constructedwetlands (1030%) [25].Although the majority of the
organic pollutants were removed,there were still a few refractory
contaminants present in the nalefuent. It seems that some
compounds, such as TMSN, styrene andhexa-methoxymethylmelamine,
were quite stable in the A2O-MBRsystem and often used as organic
indicators of industrial efuentsfrom certain chemical production
industries [26]. In addition, 1,4-Dioxane, a well-known hazardous
pollutant, was hardly removedin the system. Despite the fact that
1,4-Dioxane biodegradationwas achieved through bioaugmentation and
the use of enrichedmicrobial pure cultures [27], this compound
could not be oxi-dized effectively by conventional biological
process due to its highresistance to biotransformation, and could
only be removed effec-tively by the advanced oxidation processes
[28,29]. Suh and
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422 F. Sun et al. / Journal of Hazardous Materials 286 (2015)
416424
Fig. 4. TMP evolution during 88-d continuous ltration operation
in the MBR.
Mohseni [29] found that O3/H2O2 could be used to
eliminate1,4-Dioxane, and the oxidation rate was rst order at the
diox-ane concentrations lower than 50mg/L. Therefore, much
attentionshould be paid attention to some refractory contaminants
remain-ing in the nal efuent.
3.4. Membrane fouling behavior
Themembrane foulingof twodifferentkindsofmembranemod-ules (HF
and FS) were observed bymonitoring TMP throughout theoperation of
MBR. The variations of permeation ux and TMP are
Fig. 5. SEM micrographs showing the surfaces of clean membranes
and fouled membranes. (a) New FS membrane surface, (b) fouled FS
membrane surface, (c) new HFmembrane surface, (b) fouled HF
membrane surface (FS =at sheet, HF=hollow ber).
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F. Sun et al. / Journal of Hazardous Materials 286 (2015) 416424
423
Table 4Components of membrane foulants measured by WD-XRF.
Element Atomic ratio (%)
C F Si S Cl Ca Ti P N Na Mg Al K FeClean FS 61.17 38.74 0.01
0.01 0.03 0.01 0.03 Fouled FS 73.41 5.01 0.46 0.19 0.06 0.12 0.04
0.52 19.28 0.10 0.12 0.62 0.02 0.05Clean HF 44.21 41.48 0.01 0.01
8.24 5.01 1.02 0.02 Fouled HF 49.60 27.61 0.07 0.10 0.02 0.12 0.34
21.65 0.21 0.04 0.12 0.01 0.11
presented in Fig. 4. During the operation, the average
permeationux of HF and FS in the MBR system were 8.52 and 9.74
L/(m2 h),respectively. As shown in Fig. 4, noticeable membrane
fouling ofHF was rst observed on day 56 when the fouling was
removedby on-line chemical cleaning. Subsequently, themembrane
foulingof HF was observed on days 87 and 102. The trend of
membranefouling of FS was very similar to that of HF. However, the
TMP ofHFwas alwaysmuch higher than that of FS. On day 102, the TMP
ofFS decreased almost to its initial level after the chemical
cleaning,implying that the fouling in the FSwas smaller andmore
reversiblethan fouling observed in the HF.
The cake layerwas obviously observed on FSmembrane surface,while
itwasnotevident forHF.Afterushing thecake layerwith tapwater, the
gel layer was seen on both membranes. SEM images ofclean and fouled
membranes were taken to determine the depositmorphology of the gel
surface. The membrane pores were clearlyseen on the new membranes
(Fig. 5a and c), whereas, gel layerswere observed blocking the
membrane pores on the fouled mem-branes and seemed to be more
foulants accumulation (Fig. 5b andd).
WD-XRF was also used to measure the chemical componentson the
clean and fouled membrane surface. Table 4 shows that therelative
contents of C and N on the fouled membrane surfaces (HFand FS)
weremuch higher than those on cleanmembrane surfaces,indicating
that membrane fouling wasmainly governed by organicfouling.
Moreover, several inorganic elements, such as Al, P, S, Si,Ca and
Mg, were found on the fouled membrane. It is well knownthat metal
ions may bridge the deposited cells and biopolymers,resulting in
ahighly fouling layer and substantial TMP increase [30].Although
the relative contents of these elements were small, theyplayed an
important role in fouled layer formation [31]. The com-parison of
chemical components between fouledHF and FS impliedthat FS
exhibited more foulants accumulation than HF on mem-brane surface.
In fact, SEM of longitudinal direction of membraneshowed that the
gel layer of FS and HFwere about 60mand 5min thickness (Fig. S2).
It could be deduced that gel layer and cakelayerwere easily formed
on FSmembrane, and the cake layer couldprotect the gel layer from
being removed by aeration from below.Fan and Huang [32] reported
that the gel layer was indispensableand played a key role in the
dynamic MBR rejection capacity ofthe ne particles. It was observed
that small colloids and macro-molecules may adsorb on the thin gel
layer of the membrane andresult in severely clogged pores [33].
These might be the reason ahigher ux under lower TMP could be
obtained in the FSmembranemodule. Therefore, the chemical cleaning
method using a combi-nation of acids and oxidizing agents is
recommended for fouledmembrane caused by organic foulants and
inorganic compounds.
4. Conclusions
Results suggest that the A2O-MBR system is very efcient
insimultaneousorganicmatter andnitrogen removal in
thechemical-intensive TA wastewater treatment. An increase of
internal recycleratio from 0.5 to 1.5 had a greater effect than an
increase from1.5 to 2.5 in the nitrogen removal performance. Some
refrac-tory compounds present in the MBR permeate, such as
TMSN,
styrene, hexa-methoxymethylmelamine and 1,4-Dioxane, shouldbe
discharged into municipal sewage treatment plant for
furthertreatment. The bridging between organic foulants and
inorganiccompounds was a signicant contributor to membrane
fouling,and the combination of acids and oxidizing agents could be
a goodoption for chemical cleaning of fouled membrane.
Acknowledgements
Thisworkwas nancially supported by Fuji Electric Co. Ltd., andby
Open Project of Zhejiang Province Key Laboratory of Environ-mental
Pollution Control Technology. We thank Ms. Lijuan Maothe technician
of 985-Institute of Agrobiology and Environmen-tal Sciences of
Zhejiang University, for the assistance in using6890N/5975B GCMS
system. The authors would like to thankemeritus professor Goen Ho
of Murdoch University for his contri-butions to improve the
manuscript.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,in
the online version, at
http://dx.doi.org/10.1016/j.jhazmat.2015.01.031.
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Organics and nitrogen removal from textile auxiliaries
wastewater with A2O-MBR in a pilot-scale1 Introduction2 Materials
and methods2.1 Experimental set-up and operating conditions2.2
Characteristics of TA wastewater2.3 Analytical methods
3 Results and discussion3.1 COD removal3.2 Nitrogen removal3.3
Behavior of organic compounds3.4 Membrane fouling behavior
4 ConclusionsAcknowledgementsAppendix A Supplementary
dataReferences