E L S E V I E R Desalination 157 (2003) 81-86

DESALINATION

www.elsevier.cornBocate/desal

Comparison between nanofiltration and ozonation of biologically treated textile wastewater for its reuse

in the industry

A. Bes-Pifi, J.A. Mendoza-Roca*, L. Roig-Alcover, A. Iborra-Clar, M.I. Iborra-Clar, M.I. Alcaina-Miranda

Department of Chemical and Nuclear Engineering, Universidad Polit4cnica of Valencia, Camino de Vera s/n, 46071 Valencia, Spain

Tel. +34 (96) 387-96 33. Fax +34 (96) 387-7639; email: jamendoz@iqn.upv.es

Received 23 December 2002; accepted 30 December 2002

Abstract

This work is focused on the advanced treatment of the biologically treated wastewater of a textile plant. Nowadays the factory effluent is treated by an activated sludge process carried out after the wastewater neutralization. The wastewater treatment plant effluent is not still appropriate for its reuse because of the residual COD and conductivity. Both nanofiltration experiments at different operating conditions and oxidation reactions with ozone and ozone/UV irradiation were performed to evaluate the final water quality for its reuse.

Keywords: Nanofiltration; Ozonation; Textile wastewater; Reuse

1. I n t r o d u c t i o n

The e n v i r o n m e u t a l impact o f the tex t i l e industry is associated with its high water con- sumption as well as by the colour, variety and amount of chemicals which are released in the wastewater [1]. Conventional treatment methods

*Corresponding author.

for tex t i le w a s t e w a t e r are ma in ly p h y s i c o - chemical or biological treatments. The quality o f the t rea ted w a s t e w a t e r can be i m p r o v e d i f advanced processes are combined with them.

With adsorption, biorefractory compounds can be removed. M e m b r a n e t echno log ies (nano- filtration and reverse osmosis) are able to separate both b i o r e f r a c t o r y o rg an i c c o m p o u n d s and

Presented at the European Conference ot7 Desalination and the Environment. Fresh Water for All, Malta, 4-8 May 2003. European Desalination Society, International Water Association.

0011-9164/03/$- See fi'ont matter © 2003 Elsevier Science B.V. All rights reserved PII: S0011-9164(03)00386-2

82 A. Bes-Pidl et aL / Desalination 157 (2003) 81-86

salinity. The main problem of theses techniques is the reject stream management.

Several authors reported about the application of membrane technologies to obtain water for reuse from textile wastewater treated previously with physico-chemical or biological treatment. It has been proved that nanofiltration could be a feasible technique for this [2,3]. On the contrary, chemical oxidation does not produce may waste, degradating organic compounds. The most com- monly used oxidizers are ozone, Fenton's reagent (H202/Fe 2+) and a combination of theses oxidizers with UV irradiation.

Ozone is a powerful oxidant for water and wastewater treatment. Once dissolved in water, ozone reacts with a great number of organic com- pounds in two different ways: by direct oxidation as molecular ozone or by indirect reaction through formation of secondary oxidants like free radical species in particular the hydroxyl radical [4]. Both ozone and hydroxyl radicals are strong oxidants and are capable of oxidising compounds such as dyes.

In the bibliography a great number of refer- ences about textile wastewater ozonation before biological treatment can be found [5,6]. The aim of that is to accomplish an increase in wastewater biodegradability.

Regarding the ozone application after the biological treatment, Ciardelli et al. [7] concluded that 30 g/m 3 ozone doses were sufficient to have good results in terms ofcolour removal for contact times of about 60 lnin. This process was applied to wastewaters coming from a filling and dyeing plant used to dye fabrics, hanks, skeins, tops and flocks of different fibres.

2. Objectives

The objectives of this work were the following: • Study of the combination of activated sludge

process with nanofiltration in order to reuse water in a printing, dyeing and finishing textile plant.

• Selection of the nanofiltration membrane and the operating conditions to achieve the best permeate quality.

• Study of the combination of activated sludge with chemical oxidation using ozone and ozone/ UV radiation.

• Comparison between the two advanced treat- ments mentioned above from the point of view of the final water quality.

3. Material and methods

Firstly, wastewater from activated sludge pro- cess was prefiltered to remove suspension solids. The next step consisted in analysing the COD, conductivity mad pH of the prefiltered samples.

Nanofiltration experiments were performed in a laboratory plant with a membrane system of four plane membranes, each one with 30 cm 2 of active surface. The variation of the permeate flux and COD and conductivity removal were studied as a function of the transmembrane pressure and the feed flow rate. The membranes tested were Desal DK-5 from Osmonics and NF-90 from Dow Chemical. Fig. 1 shows a scheme of the nano- filtration plant.

2 3 14

7

8

11

13

12

Fig. 1. Scheme of NF laboratory plant, l, feed tank; 2, thermometer; 3, stirring; 4, heat exchanger; 5, regulation valve; 6, filtration system; 7, feed pump; 8, security valve; 9-9', manometer; 10, NF module; 11, permeate stream; 12, regulation valve; 13, speed control; 14, rejection stream.

,4. Bes-Pid et al. / Desalination 157 (2003) 81-86 83

For each membrane, experiments with three different transmembrane pressures (0.10, 0.15 and 0.20 MPa), and three different feed flow rates (0.2, 0.3 and 0.4 m3/h) at 25°C were performed. The cross flow velocities related to these flow rates are 1.11, 1.66 mad 2.22 m/s respectively. The series of nanofi ltration experiments was carried out using an experimental design obtained from Statgraphics Plus 4.0. The duration of each experiment was long enough to reach the steady state conditions (ap- proximately 8 h). The per-meate fluxes Jp (L/m2h) and salt retentions R~A~, r (%) were determined. In addition, at the end of each experiment, COD was analysed.

The ozonation experiments were carried out in a laboratory plant consisting of three ozone generators with a maximum ozone production of 4 g/h each one and a contact reactor of 25 L. The ozone generators were fed with pure oxygen and the operat ing temperature was 25°C. Redox- potential was measured to control the oxidation reactions. In each experiment 45 L &biologically treated wastewater were ozonated. Furthermore, the plant was equipped with a monochromatic lamp (254 nm) IS-2700. Fig. 2 shows a photo- graph of the plant, indicating its main elements.

or

potential rement

Fig. 2. Photograph of the laboratory oxidation plant.

Table 1 Characterisation of biologically treated wastewater from a textile plant

pH 7.8 8.2 Conductivity, mS/cm 2.8-3.3 COD, mg/L 200400

treated textile wastewater. It can be observed that , conductivity and COD are still too high to reuse the water.

4. Results and discussion 4.1. Nanofiltraton experiments

Table 1 shows the variation ranges o f the In Table 2 salt rejections (RsAL.c) and permeate measured parameters values of the biologically fluxes (@) at the steady state conditions for the

Table 2 Salt rejections and permeate fluxes at the steady state conditions in the different experiments

Operating conditions NF-90 DK-5

Feed pressure, bar Feed flow rate, L/h Rs~L> % Jp, L/m2h Rsw.T, % Jr, L/mZh

10 200 70.30 3.33 38.18 18.50 10 300 76.36 3.50 43.80 19.20 l0 400 63.15 2.31 36.64 18.70 15 200 78.29 6.10 47.53 28.00 15 300 80.00 5.82 47.45 27.20 15 400 81.40 5.55 51.40 30.30 20 200 82.92 8.38 50.91 40.40 20 300 81.56 8.94 56.62 45.00 20 400 86.75 9.19 57.06 47.00

84 A. Bes-Pi6 et al. / Desalination 157 (2003) 81-86

tested membranes can be observed. Figs. 3 and 4 show the standardized Pareto

charts for permeate flux of the membranes tested. These Pareto charts display a frequency histogram where the length of each bar is proportional to the estimated effect and interactions of the feed flow rate (B) and feed pressure (A) on permeate flux. The cross line indicates the significance of each parameter.

For NF-90 and DK-5, it can be seen that only feed pressure influenced significantly on permeate flux. No influence of feed flow rate (in the studied range) on permeate flux was found.

Fig. 5 illustrates the obtained results with the membranes tested. The graphs only show the

A:P

AB

BB

B:Q

AA

i . . . . ~ . . . . , . . . . i . . . . i . . . . , . . . . i

,~.,:,:,, , ~,~, N~? ~ ,,~ ';<~:.

N

0 5 10 15 20 25 30

Standardized effect

Fig. 3. Standardized Pareto chart for permeate flux of NF-90.

A A ~

B:Q

BB , . . . . i . . . . . . . . . . . . , . . . . i . . . .

0 5 I0 15 20 25 30

Standardized effect

Fig. 4. Standardized Pareto chart for permeate flux of DK-5.

6 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

• NF-90 7K DK-5 50

40

30

• ~ 20

lO

0 ~

5 10 15 20 25

P (bar)

Fig. 5. Influence of feed pressure on permeate flux in NF-90 and DK-5.

evolution of permeate flux with feed pressure P, since only this variable was significant according to the Pareto charts. The permeate flux values correspond with the average values calculated for the tested feed flow rates.

It can be observed that DK-5 yielded penneate flux rates substantially higher than NF-90. At 20 bar, the average permeate flux was 44 L/(mZh).

Similarly, the obtained salt rejection values have been studied using the same types of graphs. Figs. 6 and 7 show the standardized Pareto charts for retention salts of the membranes tested. In both cases salts retentions did no depend on the feed flow rate.

In Fig. 8, it is shown that for both membranes the variation of salt retentions with the feed pressure was very similar, reaching higher values with NF-90 (approximately l 5% higher than with DK-5).

Related to permeate COD, the measured values were lower than 50 mg/L in all experiments for both lnembranes.

4.2. Oxidation experiments'

After previous experiments with ozone, the operating time was fixed at 3.5 h and it was decided to work with two ozone generators (maximum ozone production of 8 g/h) due to the estimated O3/COD ratio necessary for the oxidation. In Table 3, the results of the chemical oxidation with

A. Bes-Pifi el a/. ..' Desalination 157 (2003) 81-86 85

% ~%%?; A:P :~;:

ELf B:Q

a A

i , , , I . . . . i . . . . i . . . . i . . . . i . . . . i

0 5 10 15 20 25 30

Standardized effect

Fig. 6. Standardized Pareto chart for salts retention of NF-90.

A:P

AB

B:Q

BB

AA N 0 2 4 6 8

Standardized effect

Fig. 7. Standardized Pareto chart for salts retention of DK-5.

g

100

80

60

40

20

0

• NF-90 )K DK-5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 10 15 20 25

P (bar)

Fig. 8. Influence of feed pressure on salts retention in NF-90 and DK-5.

Table 3 Experiments results in the chemical oxidation of the biologically

ozone and ozone/UV are shown. It can be seen the significant influence o f the UV irradiation on the COD elimination. 111 fact, after 30 min the COD was already lower than 50 mg/L. However,

only with ozone, the COD was 286 m g / L after the same time. In this experiment it was observed

that COD decreased substantially after 90 rain. In addition, the table shows the lneasured

redox potential values, which indicate the evolu-

tion of the oxidation reactions. It can be observed that final measured value was very similar in the two experiments (--_320 mV).

Table 4 compares the final effluent quality of the two treatments applied. It can be observed that better results were achieved with nanofiltration. However, the management of the reject stream of the lnembrane process must be studied.

treated textile wastewater

Time, rain Experiment with O;

COD, mg/L Redox potential, nlV

Experiment with OJUV

COD, mg/L Redox potential, mV

15 326 209 - - -- 30 286 244 <50 209 45 276 264 - - - 60 184 266 <50 225 90 63 276 <50 239

120 84 302 <50 297 150 98 307 <50 320 210 70 319 <50 325

86 A. Bes-Pidl et al. / Desalination 157 (2003) 81--86

Table 4 Comparison between the treated effluents with nano- filtration and oxidation

Process COD, Conductivity, mg/L mS/cm

Nanofiltration (NF-90) P = 20 bar; Q = 200M00 L/h <50 0.39-0.51

Ozone + UV after 30 min <50 3.04

The combination of UV irradiation with ozone led to a significant reduction in the operat ing t ime to reach the same COD removal effici-

ency.

A c k n o w l e d g m e n t

We thank Colortex 1967 S.L. for its support in the investigation project.

5. C o n c l u s i o n s

It can be concluded that: • N a n o f i l t r a t i o n o f the b io log ica l ly t rea ted

wastewater o f a printing, dyeing and finishing textile plant produced perineates with very low COD (<50 rag/L).

• Salt rejection was higher for NF-90 than for DK-5. Though the permeate flux rates o f NF- 90 were lower than for the other, this was the selected membrane since the salt rejections were substantially higher than for the other membrane . NF-90 permeates could be reused as r inse w a t e r in the text i le p lant ( C O D <100 mg/L and conductivity <1.0 mS/cm).

• Salt rejections and permeate flux rates were dependent basically on feed pressure. How- ever, for the studied feed flow rate range, no influence was found on the studied variables.

• A high C O D remova l was ach ieved with chemical oxidation with ozone and with ozone/ UV. The advantage of this technique in com- parison with nanofiltration is that there is no reject s t ream generation. Never theless , the ox ida t ion does not reduce the water con- ductivity. Thus, the reuse o f the treated water is not possible.

R e f e r e n c e s

[1] C. O'Neill, F. Hawkes, S. Esteves, D. Hawkes and S.J. Wilcox, Anaerobic and aerobic treatment of a simulated textile effluent. J. Chem. Technol. Biotechnol., 74 (1999) 993-999.

[2] A. Bes-Pifi, J.A. Mendoza-Roca, M.I. Alcaina- Miranda, A. Iborra-Clar and M.I. Iborra-Clar, Reuse of wastewater of the textile industry after its treatment with a combination ofphysico-chemical treatment and membrane technologies. Desalination, 149 (2002) 169-174.

[3] M. Marcucci, G. Ciardelli, A. Matteucci, L. Ranieri and M. Russo, Experimental campaigns on textile wastewater for reuse by means of different membrane processes. Desalination, 149 (2002) 137-143.

[4] S. Baig and P.A. Liechti, Ozone treatment for bio- refractory COD removal. Wat. Sci. Tech., 43(2) (200 l) 197-204.

[5] J. Perkowski, L. Kos and S. Ledakowicz, Application of ozone in textile wastewater treatment. Ozone: Sci. Eng., 18(1) (1996) 73-85.

[6] F. Gahr, F. Hermanutz and W. Oppermann, Ozonation - - an important technique to comply with new Gemaan laws for textile wastewater treatment. Wat. Sci. Tech., 30(3) (1994) 255-263.

[7] G. Ciardelli, G. Capannelli and A. Bottino, Ozone treatment of textile wastewaters for reuse. Wat. Sci. Tech., 44(5) (2001) 61~57.