printing waste water treatment using a membrane

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

Desalination 190 (2006) 277286

Dyeing and printing wastewater treatment using a membranebioreactor with a gravity drain

Xiang Zheng, Junxin Liu*

Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR ChinaTel./Fax: +86 (10) 6284 9133; email: [email protected]

Received 1 June 2005; accepted 8 September 2005

Abstract

A laboratory-scale membrane bioreactor (MBR) with a gravity drain was tested for dyeing and printing wastewatertreatment from a wool mill. The MBR was operated with continuous permeate by gravity and without chemicalcleaning for 135 days. Results showed that excellent effluent quality could meet the reuse water standard in China. Theaverage concentrations of COD, BOD5, turbidity and color in the effluent were 36.9 mg l

!1, 3.7 mg l!1, 0.2 NTU and21 dilution times (DT), respectively. The average removal rates of COD, BOD5, turbidity and color were 80.3%,95.0%, 99.3% and 58.7%, respectively. The membrane flux increased with increasing of aeration intensity, and itsincreasing rate was related to pressure-heads. The higher the pressure-head, the greater the impact of aeration intensityon membrane flux. Statistical analysis also showed that both the pressure-head and aeration intensity significantlyaffected membrane flux. Due to its compact design, simple operation and easy maintenance, MBR with a gravitationalfiltration system hs low energy consumption and is cost-effective to build and operate. If the life expectancy of themembrane is set for 34 years and the membrane flux is set at 15 l/m2.h, such a MBR would be very competitive.

Keywords: Gravitational filtration; Membrane bioreactor (MBR); Dyeing and printing wastewater

1. Introduction

The textile industry is one of the most impor-tant industries in China. Many textile factories

consume considerable amounts of water in the

manufacturing process. In 2003, the total dis-

charge of Chinese industrial wastewater was

about 21.2 billion m3/y, of which 1.6 billion m3/y

was textile industry wastewater [1]. More than

80% textile wastewater was discharged by dye-

*Corresponding author.

ing and printing manufacturing facilities. Since

1996, China has tightened controls on the effluentfrom textile facilities, and about 10,000 enter-

prises in the textile industry were closed down

because they could not meet national wastewater

discharge standards. In addition, since the intro-

duction of ISO 14,000 in China, the concept of

environmental protection has become more and

more important for industry to meet the needs of

the market and consumers. All of these factors

contribute to textile companies paying more

doi:10.1016/j.desal.2005.09.008


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X. Zheng, J. Liu / Desalination 190 (2006) 277286278

attention to wastewater treatment in order to meet

national environmental standards.

Generally, effluent from textile manufacturing

facilities is highly colored, even though it is

considered to be fairly non-toxic. However, due

to the stability of modern dyes that are most often

used in the textile industry, dyeing and printing

wastewater has a low ratio of BOD5/COD and

heavy color, and becomes one of the most diffi-

cult wastewaters to be treated in China. Con-

ventional processes treating dyeing and printing

wastewater include biological, physical and

chemical methods such as oxidation, adsorption,

or coagulation by aluminum or iron salts [25].However, these processes are increasingly facing

a challenge with variability of the dye composi-

tion in the wastewater to meet the more and more

strict Chinese wastewater discharge standards.

Therefore, it is important to develop more effi-

cient technologies for dyeing and printing waste-

water treatment.

Recently, more attention has been paid to themembrane bioreactor (MBR) for wastewatertreatment because of its higher efficiency of pol-

lutant removal and excellent effluent quality [6]. Now, two types of anaerobic/oxic pilot-scale

(10 t/d) MBRs have been tested and used fortextile industry wastewater treatment in China[7,8]. One is the side-stream MBR, and the other

is the submerged MBR with a suction pump.Results showed the quality of treated water was

excellent and met the gray water reuse standards[9]. However, high capital and operating costs areassociated with the use of MBRs in these appli-

cations. The application of the side-stream MBRsystem is limited in China due to high energy

consumption (5 kWh/m3). Although high powerrequirements of the side-stream MBR can be

partially overcome by immersing the membrane

module directly into the aerobic tank, the benefitsusing the submerged suction MBR are partially

offset by more membrane area required to pro-duce the same flux.

The most significant factors influencing the

capital cost for submerged suction MBR are the

costs of the membrane and control unit, which

account for about 50% and 15% of the total capi-

tal costs, respectively [10]. In China, most mem-

brane modules used in submerged suction MBR

in practice are made by Mitsubishi Rayon

(Japan). Their price is about 34 times that of

membrane modules made in China.

A new membrane bioreactor was thus deve-

loped to decrease capital and operating costs of

submerged suction MBR for dyeing and printing

wastewater treatment. In this MBR system, a

membrane module made in China is submerged

into an airlift bioreactor, and the permeate of theMBR is continuously obtained by gravity. As a

result, no suction pump and control unit are

needed. Therefore, this MBR is cost-effective,

with simple operation and easy maintenance in

comparison with conventional submerged suction

MBRs.

The MBR with a gravity drain runs according

to the constant pressure-head. Hence, it is very

important to initiate the membrane at a proper

pressure-head at which the flux remains stable ordecreases slowly. In addition, aeration intensity is

one of the key factors affecting membrane fouling

and energy consumption [11,12]. Therefore, the

objective of this paper was to test this new MBR

for the treatment of dyeing and printing waste-

water and to investigate the impact of operation

parameters (pressure-head, aeration intensity and

MLSS) on membrane flux. Meanwhile, a cost

analysis was also made for MBR applications in

dyeing and printing wastewater treatment in order

to provide useful information for potentialcustomers.

2. Materials and methods

2.1. Test system

The MBR with a gravity drain is showed in

Fig. 1. The aerobic reactor is an airlift reactor

with 16 L of maximum working volume, that can


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X. Zheng, J. Liu / Desalination 190 (2006) 277286 279

Fig. 1. Flow sheet of the experimental apparatus.

be adjusted in accordance to experimental de-

mands. An anaerobic tank was added to improve

efficiencies of COD removal and decolorization

for dyeing and printing wastewater treatment. The

working volume of the anaerobic tank was 12 L.The membrane module was set in the downside

of the aerobic reactor. The membrane flux was

driven by the pressure-head between the liquid

level in the bioreactor and the effluent pipe.

Compressed air is supplied from the bottom of

the module, and the membrane surface can be

cleaned by air turbulence.

The tested membrane module was made of

polyvinylidene fluoride hollow fibers, and its

effective surface area and pore size were 0.18 m2

and 0.22 m, respectively. The length of the

membrane module was 270 mm.

Compared to a conventional submerged MBR

with a suction pump, this MBR with gravity has

no suction pump or control unit, but is operated

by continuous permeation with gravity at a given

pressure-head. Therefore, the new MBR is easier

to operate and maintain, and can save energy

consumption during wastewater treatment.

2.2. Operating conditions

The MBR was operated at a HRT of 612 h.

The average F/M ratio and volume loading rates

in the MBR throughout the experimentaloperation period were 0.24 kg COD kgSS!1 d!1

and 0.43 kg COD m-3 d!1, respectively. Tempera-

ture of the mixed liquor varied between 14 and

29EC. In order to eliminate the influence of tem-

perature on the membrane flux, all fluxesJ(T)

measured at temperature T were corrected to

valuesJ(25) at a temperature of 25EC by the fol-

lowing equation:

J(25) =J(T) * 1.02525!T

Neither chemical cleaning of the membrane nor

sludge discharging in this MBR was carried out

throughout the operation period of 135 days. The

characteristics of the raw wastewater are sum-

marized in Table 1.

2.3. Analytical methods

Color, suspended solids (SS), mix liquid


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Table 1

Operating parameters of the membrane bioreactor

Range Avg. SD

Pressure-head, kPa

Aeration intensity,

m3m!2h!1

Temp., EC

DO, mg l!1

HRT, h

MLSS, g l!1

F:M, kg COD kgSS d!1

4.420.3

40240

1428

3.09.3

5.9234

0.43.8

0.080.80

15.0 2.7

128 40

22 5

3.8 2.3

10.0 4.3

2.2 1.0

0.30 0.15

suspended solids (MLSS) and volatile suspendedsolids (VSS) were determined according to the

Standard Methods [13]. The pH was measured

with a pH meter (pHS-3C, China). COD was

analyzed with a CTL-12 COD meter (Huatong,

China). BOD5 was determined with a BOD

TrakTM(Hach, USA). Turbidity was measured by

a turbidity meter (Model 8391-37 Turbidity,

USA). Dissolved oxygen (DO) and temperature

were measured with a portable DO meter com-

bined with a temperature probe (JBP-607 DO,

China). Statistical analysis including Pearson and

Spearmans rank correlation analysis was carried

out using the statistical software SPSS 11.0.

3. Results and discussion

3.1. Removal of pollutants

The characteristics of the pollutants in influent

and effluent of the MBR are shown in Table 2

and Fig. 2. Results clearly showed that the efflu-ent quality of the MBR was excellent, and could

meet with the reuse water standard of China [9].

Although the influent COD concentration varied

from 128 to 321 mg l!1, the average effluent COD

concentration was stable at 36.9 mg l!1. The ave-

rage COD and BOD5 removal efficiencies were

80.3% and 95.0%, respectively. This implies that

the biodegradable pollutants in the wastewater

were almost removed by the system.

The average color in the effluent was

decreased to 30 DT compared with that in the

influent changing between 30 DT and 70 DT. The

effluent turbidity was lower than 0.4 NTU, and its

average was 0.24 NTU when the turbidity of in-

fluent varied from 15 to 84 NTU. The ratio of

MLVSS and MLSS was stable at 0.740.81,

which means few inert solids accumulated in the

biomass, though no sludge was discharged

throughout the operation period except samples

taken for analysis.

In order to investigate the effect of the mem-

brane on COD removal and the influence of

organic matter in mixed liquor on membranefouling, COD concentration in the supernatant of

the MBR was measured. The supernatant was

collected after the mixed liquid samples from the

MBR settled for about 30 min. Compared with

low COD values of the membrane effluent, the

changes of COD values in the supernatant were

higher than those in effluent (Fig. 3). A possible

explanation is that the accumulated recalcitrant

organic matter due to its poor biodegradation and

the released organic matter from dead biomass orthe microbial metabolic products may contribute

to a rise in COD in the supernatant. In addition,

this phenomenon showed that the membrane cut-

off played a very important role in the COD

removal in this MBR for dyeing and printing

wastewater treatment.

3.2. Impact of operating parameters on mem-

brane flux

Unlike most membrane process operations,fouling was rapid at the initial stages of filtration.

Many researchers reported that the clogging of

pores inside the membrane matrix contributes

significantly to an increase of membrane resis-

tance [1416]. The higher the initial flux, the

faster the clogging inside the membrane matrix.

The initial membrane flux in this study was

therefore set at a low value of 6 2.5 l m!2 h!1 at

12.7 kPa in the first 35 days. The membrane flux


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Table 2

Characteristics of influent and effluent in the experimental MBR system

COD, mg@l!

1 BOD5, mg@l!

1 Turbidity, NTU Color, DT SS, mg@l!

1

Influent:

Average SD 195.9 45.1 74.8 21.8 74.8 17.5 51 10

Range 128321 3695 1584 3070

Effluent:

Average SD 36.911.1 3.7 5.3 0.2 0.1 21 5 n.d.

Range 1559 0.014 0.10.3 1530 n.d.

Removal rate:

Average SD 80.3 7.9 95.0 8.9 99.3 0.4 58.7 8.5 100

Range 54.390.7 80.6100 98.299.7 42.975.0 100

Reuse water standarda:

Flush water 15 10 30 Car washing 10 5 30

Irrigation 20 10 30

aWater reuse standards in China [9].

Fig. 2. Pollutant removal in the MBR system.


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Fig. 3. Variation of the supernatant COD concentration.

Fig. 5. Influence of aeration intensity on the membrane

flux.

was stepped in increments to about 12 l m!2 h!1

from a low value at the same pressure before the

64th day. Along with a pressure-head increase,

the membrane flux increased to 15 2.5 l m!2 h!1

at 17.4 kPa from the 65th to the 114th day. How-

ever, membrane flux did not increase correspond-

ingly with increasing the pressure-head from

17.4 kPa to 20.3 kPa after 114 days (Fig. 4).The influence of aeration intensity on mem-

brane flux at different pressures was investigated

(Fig. 5). Results clearly showed that the mem-

brane flux increased with increasing aeration

intensity. The increasing rate of membrane flux

was also related to the pressure-heads. The higher

the pressure, the more the influence of aeration

intensity on membrane flux. At optimal aeration

intensity, it is effective to limit sludge deposition

Fig. 4. Performance of flux and pressure-head..

Fig. 6. Relationship between membrane resistance and

aeration intensity.

on the membrane surface, thus maintaining stable

membrane flux. Equations from the results of

Fig. 6 are summarized in Table 3. When aeration

intensity increased from 40 m3 m!2 h!1 to 200 m3

m!2 h!1, membrane resistance decreased from

6.98E+12 to 4.24E+12 at 12.7 kPa and from

6.58E+12 to 3.29E+12 at 17.4 kPa, respectively

(Fig. 6). These results showed that the aerationintensity played an important role in removing

external deposits on the membrane surface and

preventing the compaction of a cake layer, and

thus had a great impact on membrane flux. Statis-

tical analysis confirmed that both the pressure-

head and the aeration intensity significantly

affected membrane flux, but MLSS had no

impact on membrane flux (Table 4). Hence, it is

possible to maintain high and stable long-term


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Table 3

Relativity between aeration intensity and flux

Pressure(kPa)

Aeration intensity (x)and flux (Y)

R2

4.4 Y= 0.0104x + 5.9933 0.9624

12.7 Y= 0.0260x + 5.8475 0.9797

17.2 Y= 0.0461x + 5.4353 0.9979

20.3 Y= 0.0365x + 8.1850 0.9820

membrane flux through controlling different

operation parameters.

3.3. Economic assessment

In this study the MBR (240 m3/d) treating

dyeing and printing wastewater was set for cost

analysis, and its operating parameters were

chosen from this study and other studies about

large-scale MBRs [1719]. The designed mem-

brane flux affects not only capital costs but also

the membrane replacement costs, which is an

important component of operating costs. There-

fore, according to previous studies, 8 L/m2.h and

10 L/m2.h were set as the lower and upper limits

of membrane flux, respectively [20,21]. The

selected membrane module for submerged MBR

was from Motian Membrane Technology (China).

Two types of costs in this cost analysis were

considered: capital and operating. Capital costs

include membrane units and non-membrane unit

costs (fixed costs); non-membrane units costs

include all mechanical and electrical items, con-

trol equipment and associated civil engineeringcosts. The cost of land acquisition was not inclu-

ded in the capital costs of MBR. Operating costs

comprise depreciation of fixed costs, membrane

replacement, labor costs, chemical requirement

and energy consumption. In the operating cost

analysis, depreciation of fixed costs was based on

values of 15 years of operation. Depreciation of

membrane unit costs was based on a membrane

life expectancy of 2 years with which manufac-

Table 4

Correlations between operation parameters and mem-

brane flux

Operating

parameters

Range Pearson

correlations

Spearman

rank

correlations

Pressure-head,

kPa

4.420.3 .709a .713a

Aeration intensity,

m3m!2h!140240 .703a .631a

MLSS, g l!1 1.03.8 .169b .173b

aCorrelation is significant at the 0.01 level (two-tailed).bCorrelation is significant at the 0.05 level (two-tailed).

turers usually provide a warranty for membranes.

A unit energy consumption of 0.8kWh/m3 was

chosen from previously reported pilot studies

[20,21]. Due to its compact design and degree of

automation, it was assumed that the MBR system

only requires one person for maintenance and

repair. The annual salary of a worker is assumed

to be RMB 12,000 in 2004. The annual con-

sumption of chemicals (NaOH) used in mem-

brane cleaning was 50 kg/y (4 RMB/kg), and its

cost could be ignored compared with labor costs.

Capital requirements and operating costs for a

MBR system of 240 m3/d are shown in Table 5.

The total capital costs of the MBR are 400,000

430,000 RMB, including RMB 280,000 of non-

membrane units costs and 120,800150,000

RMB of membrane units costs. The costs of the

membrane unit accounted for 27.934.9% of the

total capital costs.The unit operating costs of the MBR are 1.45

1.62 RMB per m3 of wastewater. An analysis of

MBR operating costs indicates that the membrane

replacement cost is the dominant factor for the

submerged MBR, 47.653.1% of total operating

costs. A sensitivity analysis on membrane re-

placement cost also suggests that it is sensitive to

the set membrane flux, membrane life expectancy

and the membrane price [22,23]. In the declining


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Table 5

Costs of MBR facilities with different membrane fluxes (240 m3/d)

Gravitational filtration Gravitational filtration

Design and operating parameters:

Membrane module Motian (China) Motian (China)

Operation mode Continuous flux Continuous flux

Control unit Auto-control Auto-control

Designed membrane flux, Lm!2h!1) 8 10

Designed membrane area, m2 1250 1000

Unit membrane module price, RMB/m2 120 120

Unit energy consumption, kWh/m3 0.8 0.8

Unit energy cost, RMB/kWh 0.5 0.5

Membrane life expectancy, y 2 2Non-membrane life expectancy, y 15 15

Capital costs:

Non-membrane costs, RMB10,000 28 28

Membrane costs, RMB10,000 15 12

Total capital costs, RMB10,000 43 40

Unit capital costs, RMB/m3 1792 1667

Operating costs:

Depreciation of assets, RMB/m3 0.21 0.21

Membrane replacement, RMB/m3 0.86 0.69

Energy cost, RMB/m3 0.40 0.40

Other, RMB/m3 0.15 0.136

Total operating costs, RMB/m3 1.62 1.45

Notes: Energy price is estimated as 0.5 RMB/kWh (1 US$ = 8.27 RMB).

Areamembrane, designed membrane area (m2); CapacityMBR treatment, MBR treatment capacity (m

3/d); CostMembrane, Membrane

costs (RMB); CostNon-membrane, Non-membrane costs (RMB); CostTotal, Total capital costs; CostOperating, Total operating costs

(RMB/m3); DepreciationAssets, Depreciation of assets (RMB/m3); DepreciationMembrane replacement, Membrane replacement cost

(RMB/m3); EnergyMBR, Unit energy consumption of MBR (kWh/m3); Flux, designed membrane flux (Lm!2h!1);

LifeNonmembrane, nonmembrane life expectancy (y); LifeMembrane, membrane life expectancy (y); PriceMembrane module, unit

membrane module price (RMB/m2); PriceEnergy, Energy price (RMB/kWh).


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trend of membrane module price, it dropped from

RMB 150 m!2 in the year 2000 to about RMB

120 m!2 at present, and could be reduced as low

as approximately RMB 100 m!2 in the year 2006.

In contrast with the declining price of mem-

brane modules, water prices are being gradually

raised in many cities in China because of both the

aggravation of water pollution and shortages of

water. For example, the water price in Beijing has

been increased from 0.12 RMB/m3 (US $0.015)

in 1990 to 2.9 RMB m3 (US $0.35) in 2003, with

an annual growth of 25.6%. It is expected to be

about 5 RMB/m3 (US $0.60) in 1 or 2 years.

Therefore, there is an increasing economic driv-ing force for using the new MBR for wastewater

treatment and reuse. If the membrane life expec-

tancy reaches 34 years and stable membrane

flux is maintained at 15 L/m2.h, MBRs with

gravitational filtration will be more competitive

in the near future.

4. Conclusions1. The new MBR with a gravity drain was

feasible and effective for dyeing and printing

wastewater treatment. The quality of treated

water was excellent, i.e., 36.9 mg COD/l, 3.7 mg

BOD5/l, 0.2 NTU of turbidity, and 21 DT of

color, respectively, and meets the reuse water

standard [9].

2. Statistical analysis showed that both the

pressure-head and aeration intensity significantly

affected membrane flux. Membrane flux in-creased accordingly with increasing both the

pressure-head and aeration intensity. The increase

rate of membrane flux also related to pressure-

heads.

3. A cost analysis of the MBR shows that it is

increasingly considered as a competitive method

to dyeing and printing wastewater treatment since

membrane prices have gradually declined and

water prices are being raised in China.

Acknowledgenents

The research was funded by the National

Natural Science Foundation of China and ChineseSaving Energy and Investment Company

(No. 50238050), and the National Hi-Tech

Development Plan (863) (2002AA601310).

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printing waste water treatment using a membrane

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