long-term operation of submerged membrane bioreactor for the treatment of high strength...

Desalination 191 (2006) 45–51

0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved

Presented at the International Congress on Membranes and Membrane Processes (ICOM), Seoul, Korea,21–26 August 2005.

*Corresponding author.

Long-term operation of submerged membrane bioreactor for thetreatment of high strength acrylonitrile-butadiene-styrene (ABS)

wastewater: effect of hydraulic retention time

Jing-Song Changa, Chia-Yuan Changa, Ann-Cheng Chena, Laszlo Erdeib,Saravanamuthu Vigneswaranb*

aDepartment of Environmental Engineering and Science, Chia Nan University of Pharmacy and Science,60, Erh-Jen Road, Sec. 1, Jen-Te, Tainan 717, Taiwan

bFaculty of Engineering, University of Technology, Sydney, PO Box 123 Broadway NSW 2007, AustraliaTel. +61 295142641; Fax +61 295142633; email: [email protected]

Received 14 March 2005; accepted 19 July 2005

Abstract

In this study, the feasibility and the treatment efficiency of treating ABS industrial wastewater by an aeratedsubmerged membrane bioreactor (ASMBR) was investigated. Through a long-term experiment, biomass, biologicaloxygen demand (BOD5,) chemical oxygen demand (COD), total organic carbon (TOC) and permeate flux weremeasured to evaluate the MBR performance. The results show that a hydraulic retention time (HRT) of 18 h leadsto the highest biomass concentration, a maximum mixed liquor suspended solids (MLSS) value of approximately35 g/L. Chemical membrane cleaning was employed twice, after 131 and 180 days of operation in the totalexperimental period of 204 days. The membrane bioreactor led to superior COD and BOD5 removal in ABSwastewater compared to the conventional biological treatment.

Keywords: Membrane bioreactor; Hydraulic retention time; Long-term operation; Industrial wastewater

1. Introduction

Wastewater from acrylonitrile, butadiene andstyrene (ABS) plant in Taiwan includes high total

Kjedahl nitrogen (TKN)/COD ratios as an indexof biodegradation refractory characteristics. Avail-able methods for ABS resin wastewater treatmentconsist of adsorption on activated carbon, chemic-al oxidation, and microbial degradation, with their

46 J.-S. Chang et al. / Desalination 191 (2006) 45–51

merits and limitations in applications [1–4]. Thebiological treatment of this type of wastewaterrequires long hydraulic retention times (HRT). Forexample, a wastewater treatment plant in a typicalABS manufacturing plant in the south Taiwan wasdesigned with a HRT of approximately 4 days.However, the low degradation efficiency oforganic nitrogenous compounds resulted in highconcentration of organic nitrogen and COD in theeffluent. Moreover, the industrial zone involvedis located near Erh-Jen, the main river of Taiwan.Discharge of wastewater containing untreated andtoxic pollutants into the receiving water causesserious environmental problems. Therefore, find-ing an alternative method for the treatment of ABSresin wastewater has become a critical issue tosatisfy the Taiwanese EPA effluent standard.

Membrane bioreactor (MBR) technologyoffers several advantages compared to the tradi-tional activated sludge processes [5–7], such as:• high effluent quality;• limited space requirements; and• disinfection of the effluent.

The main objective of this study was to investi-gate the feasibility and the treatment efficiencyof treating polymeric industrial wastewater by a

submerged membrane bioreactor (SMBR). Bio-mass, BOD5, COD, TOC and permeate flux werestudied for the evaluation of performance andreactor stability. The long-term experimental re-sults of the laboratory-scale membrane bioreactorare discussed below in details.

2. Experimental

2.1. Membrane system

The experimental system has two compart-ments with a total volume of 6.3 L, consisting ofa biological compartment (2.8 L), and a secondbiological unit with membrane solid–liquid sepa-ration (3.5 L) (Fig. 1). The hollow-fiber mem-brane used in the second reactor is made of high-density polyethylene (Mitsubishi) with an averagepore diameter of 0.4 µm. The total surface area ofthe hollow fiber membrane used in this study was0.0283 m2. Compressed air was introduced at thebottom of the reactors for aeration. Air bubblesprovided both aeration for biological reactions andreduction of fouling of membranes. For physicalcleaning, air backflush was used every 12 minfor 1 min duration. Once the transmembrane pres-sure difference exceeded 20 kPa, the membrane

Fig. 1. Diagram of the MBR system.

J.-S. Chang et al. / Desalination 191 (2006) 45–51 47

module was cleaned with water or chemicals. Thesuction pump was operated intermittently towithdraw the effluent, and its rate was adjustedaccording to HRT requirements. The sludgeretention time (SRT) of the system was set at 30days. Membrane performance was studied at 12,18, 24 and 30 h of HRT.

2.2. Physicochemical characteristics of ABS resinwastewater

In this study, the COD in the influent flowvaried in the range of 2950–4410 mg L–1. TheCOD/BOD5 ratio was approximately 2.8. Thecharacteristics of influent samples are listed inTable 1.

Table 1Characteristics of ABS resin manufacturing wastewater

COD, mg/L 2950–4410 pH 6.2–7.5 Turbidity, NTU 102–173 TSS, mg/L 131–152 BOD5, mg/L 1200–1600 TOC, mg/L 820–880 Temperature, °C 25–35

2.3. Analytical determinations

Organic compounds were measured using aTOC analyzer (SHIMADZU TOC-5000A). CODwas measured by the standard method (APHA,1992). Suspended solids (SS) concentration wasdetermined by drying at 105°C and weighing theresidue.

3. Results and discussion

3.1. Effect of hydraulic retention time on biomassconcentration

The biomass concentration was measured interms of MLSS and mixed liquor volatile sus-pended solids (MLVSS). The variations of MLSSand MLVSS in the membrane tank are shown inFigs. 2 and 3. The results indicate that the HRTsignificantly affects the concentration of MLSS.As shown in Figs. 2 and 3, a HRT of 18 h gavethe highest biomass concentration of approximate-ly 35 g/L.

Similar trends of MLSS variation were ob-served both in the biological and membrane tanks.According to Fig. 2, MLSS and MLVSS concen-trations in the membrane tank were higher than

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

35

40HRT=30hHRT=12hHRT=18hHRT=24h

MLS

S (g

/L)

Time (d)

Biological tank Membrane tank

Fig. 2. Effect of HRT on MLSS.

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20


MLV

SS (g

/L)

Time (d)


Fig. 3. Effect of HRT on MLVSS.


in the biological tank, at higher HRT values (18and 24 h). At HRTs of 12 and 30 h, the MLSS andMLVSS concentrations are almost the same inboth tanks, or even lower than that in the biologicaltank.

One can also see that the prolonged aerationof 24 h rapidly reduced the biomass concentration.In this MBR system a HRT of 18 h has led to thehighest biomass concentration. Past research re-sults indicate that the MLSS concentration shouldbe kept in the range of 10~20 g/l to prevent thefouling of membrane. Considering the implicationof that finding, a HRT of 24 h was used instead of18 h.

The MLVSS/MLSS ratios were also calculatedboth in the biological and membrane tanks. In thecase of biological reactor, the highest value ofMLVSS/MLSS (in the range of 0.91~0.96) wasobtained at a HRT of 24 h. Since microorganismsutilize oxygen to decompose organic compoundsin biological treatment processes, their biologicalactivity can be characterized by specific oxygenuptake rates (SOUR). SOUR were measured usinga Winkler bottle method, using the followingequation:

SOUR (mg O2/g MLSS h) = O2 consumption rate (mg O2/l min) × MLSS–1 (l/g) × (60 min/h)

The SOUR values were found in the range of117~121 mg O2/g h for the biological reactor, andbetween 73~76 mg O2/g h for the membrane reac-tor. These values are much higher than the com-mon values of 30~70 mg O2/g h observed in tradi-tional activated sludge systems used in sewagetreatment. This finding indicates a high sludgeactivity in this MBR system, even though thewastewater contained large amounts of refractoryorganic compounds.

The food to microorganism ratio (F/M) ispresented in Fig. 4. Neglecting the unstable stateat the beginning of operation of the system (atHRT = 24 h), the F/M ratio of biological tank wasin the range of 0.24~0.37 kgBOD5/kg MLVSS d

0 20 40 60 80 100 120 140 160 180 2000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0HRT=30hHRT=12hHRT=18hHRT=24h


F/

M r

atio

(kg

BOD

5/kg

MLV

SS-d

ay)

Time (d)

Fig. 4. Effect of HRT on F/M ratio.

for the HRTs of 18 and 24 h. However, the sameHRTs caused a very low F/M ratio in the mem-brane tank, since most of the organic carbon wasconsumed in the biological tank. This result alsoimplies that nitrification took place in the mem-brane tank.

3.2. Effect of hydraulic retention time on removalefficiency

The treatment performance of the MBR systemwas measured in terms of BOD5, COD and TOCremoval. Right from the start, even when theMLSS was still below 1 g/L, the effluent BOD5concentration was less than 100 mg/L (Fig. 5) thatsatisfies the Taiwanese standard for industryeffluent discharge. The removal efficiency exceed-ed 90%, and with increasing MLSS concentrationit reached 98%, resulting in effluent concentra-tions of about 40 mg/L. The volumetric loadingof this system could be as high as 2.0 kg BOD5/m3.d. In spite of the influent BOD5 fluctuations,the effluent BOD5 remained remarkably stable.The effect of HRT was minimal on organic re-moval, since even a HRT of 12 h did not affectthe effluent concentration in a significant manner.

In completely mixed reactors, the concentra-tion of pollutants in the reactor or in the effluent


should be the same. However, in this experimentalset-up, the suction of the effluent from the mem-brane filtration was intermittent. Even when thesuction pump was stopped, the liquid transferpump still continued to pump the treated waste-water from the biological tank to membrane tank.Hence, the BOD5 concentration in the membranetank was slightly higher than in the effluent.

Fig. 6 shows that COD removal was above92% except for a HRT of 12 h that gave an 87%removal. This removal efficiency is high com-pared to the conventional treatment plants (typic-ally 75~85% at low F/M ratios). This improvementcan be attributed, first, to the retention of particu-late COD (which caused by raw monomer mate-rials or by the raw materials that failed to poly-merize) by the membrane. Secondly, the biomasscan adapt to the wastewater characteristics. Underthese conditions, specialized microorganisms canestablish themselves which are able to removeslowly degradable pollutants. As also observedin this study, the high COD removal efficiencies(between 90 and 98%) reported by variousresearchers is one of the major advantages ofmembrane bioreactors [8].

Fig. 7 represents the profile of TOC concentra-tion. The influent TOC concentration was gene-rally stable but fluctuated from day 159 to day

0 20 40 60 80 100 120 140 160 180 2000

200400600800

1000120014001600180020002200

HRT=30hHRT=12hHRT=18hHRT=24h

BOD

5 (mg/

L)

Time (d)

Influent Biological tank Membrane tank Effluent

Fig. 5. Effect of HRT on BOD removal.

0 20 40 60 80 100 120 140 160 180 2000

250500750

10001250

2500275030003250350037504000

HRT=30hHRT=12hHRT=18hHRT=24h

CO

D (m

g/L)

Time (d)


Fig. 6. Effect of HRT on COD removal.

0 20 40 60 80 100 120 140 160 180 2000

200

800

1000

1200


TOC

(mg/

L)

Time (d)


Fig. 7. Effect of HRT on TOC removal.

179. TOC removals were very high, in the rangeof 88~94% for all the four HRT values studied.This observation is useful for the design ofnitrification and denitrification in MBR systems.

The performance of the membrane bioreactorcan thus be summarized as shown in Table 2.

3.3. Effect of hydraulic retention time on perme-ate flux

The variation of permeate flux and the cleaningfrequency of membrane is presented in Fig. 8. In


Table 2The performance of the membrane bioreactor

0 20 40 60 80 100 120 140 160 180 2000

10

20

30

40

50

60


Chemical cleaning

Flux Pressure

Time (d)

Flux

(L/m

2 -hr)

0

10

20

30

40

50

60

70

Pressure (cm H

g)

Fig. 8. Effect of HRT on permeate flux.

HRT, h 12 18 24 30 MLSS in biological tank, g/L 22.8–24.7 25.4–27.2 11–12 7.2–7.6 MLSS in membrane tank, g/L 23.2–24.2 30.1–34.5 16–18 6.12–6.4 MLVSS in biological tank, g/L 14.2–16.6 16.9–18.9 10–12 4.6–4.7 MLVSS in membrane tank, g/L 14.6–16.2 20.0–21.1 12–14 5.1–5.3 BOD removal efficiency, % 91 98 95 97 Influent BOD value, mg/L 1711 1373 1293 1275 COD removal efficiency, % 87 92 96 93 Influent COD value, mg/L 3157 3375 3449 2888 TOC removal efficiency, % 88 94 93 89

this study, when the transmembrane pressure dif-ference exceeded 20 kPa, the membrane modulewas cleaned by water or chemicals. However, inthis experiment the production period lasted for120 days without any chemical cleaning, andmembrane fouling could be controlled by watercleaning only. The high flux decline rate could bedue to the high value of permeate flux (up to45 L/m2. h) initially adopted. Chemical cleaningwas carried out twice during the experimentalperiod of 204 days, after 120 and 158 days ofoperation. The membrane cleaning frequency isshown in Table 3. In general, the cleaning wasmore frequent at lower HRT values.

4. Conclusions

The conclusions of this study can be sum-marized as follows:1. The effect of HRT on MLSS concentration was

significant. A HRT of 18 h leads to the highestbiomass concentration, approximately 35 g/Lmaximum MLSS value.

2. The membrane bioreactor treated ABS waste-water efficiently, achieving significantly betterCOD and BOD reduction than conventionalbiological treatment.

3. TOC removal was very high, in the range of88~94% for all HRT values. This observation


Table 3The frequency of membrane cleaning

Water cleaning Chemical cleaning HRT (h)

Run (d)

MLSS (g/L) Cleaning frequency

(d) Numbers of wash during the experiment

Cleaning frequency (d)

12 38 23.9 6.3 6 38 18 30 30.9 6 5 30 24 90 15.5 22.5 4 no cleaning 30 46 6.3 15.3 3 no cleaning

is useful for the design of nitrification and de-nitrification in MBR systems.

4. Membrane cleaning was more frequent andchemical cleaning was required at lower HRTvalues.

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Tech., 10 (1996) 35–41.[2] D.B. Harper, Biochem. J., 165 (1977) 309.[3] N. Chekhovskaya, Ambient Waste Quality Criteria:

Acrylonitrile, USEPA, Washington, DC. C-10-15,1980.

[4] J.W.B. Diane and R.E. Speece, J. WPCF, 63 (1991)198–206.

[5] A.D. Bailey, G.S. Hansford and P.L. Dold, Wat. Res.,28 (1994) 297–301.

[6] T. Ueda, K. Hata and Y. Kikuoka, Wat. Sci. Tech.,34 (1996)189–196.

[7] K. Yamamoto and K.M. Win, Wat. Sci. Tech., 21(1991) 43–54.

[8] T. Stephenson, S. Judd, B. Jefferson and K. Brindle,Membrane Bioreactors for Wastewater Treatment.IWA Publishing, 2000.

long-term operation of submerged membrane bioreactor for the treatment of high strength...

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