Treatment of seafood processing wastewaters by ultrafiltration-nanofiltration cellulose acetate membranes

DESAHNATION ELSEVIER

Desalination 177 (2005) 43-49

www.elsevier.com/locate/desal

Treatment of seafood processing wastewaters by ultrafiltration-nanofiltration cellulose acetate membranes E. Ferjani a*, E. Ellouze b, R. Ben Amar b aD@artement de Chimie, Facultk des Sciences de Monastir, Bd. de l'Environnement, 5000 Monastir, Tunisia Tel.+216 (73) 500280; Fax +216 (73) 500278; e-mail: [email protected] bD@artement de Chimie, Facultk des Sciences de Sfax, Route de Soukra, Sfax, Tunisia TeL +216 (74) 276400; Fax +216 (74) 274439; e-mail: [email protected]

Received 17 April 2004; accepted 1 November 2004

Abstract

The wastewaters generated by the cuttlefish processing contain a high organic (COD of 20,000-35,000 mg.L-1) and inorganic (TDS of 30-40 g.L-1) load. These seafood effluents were subjected to treatment with cellulose acetate (CA) membranes synthesised according to the phase inversion process. Two preparation parameters, i.e. polymer concentration in the dope solution and annealing temperature, were varied with the objective of tailoring the membrane performances from ultrafiltration to nanoffltration with respect to the separation needs. Membrane MWCO was determined by permeation of neutral solutes (sucrose, PEG, and BSA). Permeate solutions were characterised in terms of the COD, protein nitrogen (PN) using the Lowry's method, turbidity and conductivity. The results showed that the COD was reduced up to 93% using NF membranes while the fouling index reached 80%. On the other hand, UF membranes exhibited lower fouling index and higher hydraulic permeability values (up to 45 L rn-2.h-1.MPa-1) with a COD reduction of 50-65%. Keywords: Cellulose acetate; Ultrafiltration; Nanofiltration; Seafood wastewaters treatment

region of Sfax in the South of Tunisia has actually about 30 units where processed seaThe processing industry of seafood products foods mainly consist of the kingly prawn (Penais undergoing a great development in seaside eus kerathurus), cuttle fish (Sepia officinalis), countries nowadays. In Tunisia, the main actioctopus (Octopus vulgaris) and calamary (Lolivity in this domain consists in freezing products go vulgaris). The average daily water consumpwith high trading values destined for export. The tion for this industry is estimated in the region of about 1000 m3/d. The bulk of the used water *Corresponding author extracted from the underground consists of 0011-9164/05/$- See front matter © 2005 ElsevierB.V. All fights reserved doi: 10.1016/j.desal.2004.11.015 1. Introduction

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E. Ferjani et al. / Desalination 177 (2005) 43-49

highly brackish waters with a TDS of about 60 g.L-1. Consequently, generated effluents contain a large amount of salts (TDS of 30-40 g.L-1) and a high organic load (COD of 20,000-35,000 mg.L -1) at the same time. The salinity has a beneficial effect on the seafood conservation, but it entails difficulties regarding the biological treatment of effluents [1]. The regulation on wastewaters is becoming more and more restrictive since it involves an urgent demand for appropriate and efficient treatment for such effluents. The wastewater treatments using membrane processes are well established in the food industry. However, they are just beginning to emerge in the seafood industry [2]. The success of the membrane technology lies in the recovery of potentially valuable molecules like: (a) soluble protein in the industry of surimi [3-7], prawn [8-11] and tunny [12] processing; (b) aroma from pickling brines in sea product conservation [13-15] and (c) enzyme from the clarification of enzymatic hydrolysis of juices [ 16,17]. For instance, dynamic membranes consisting of ceramic supports coated by proteins were found to recover almost 100% of the proteins with molecular weight higher than 10 KDa [18,19]. Moreover, it was proven that polysulphone and sulphonated polysulphone materials have a strong affmity for fish proteins involving severe fouling during the permeation of surimi wastewaters, but no adsorption was detected for hydrophilic materials like regenerated cellulose membranes [20-22]. Our study consists in exploring the treatment of effluents produced by cuttlefish processing in order to reduce COD of the discharged water. The aim of the present work is to determine the potential use of NF and UF membranes in this application. Fouling by proteins contained in the feed solutions is the major limitation to the use of the membrane treatment. In recent works [23-26], we have reported the desalination properties of CA NF membranes prepared by the phase inversion technique. These materials are known for their low protein binding. Therefore,

a series of CA membrane materials that has a pore size distribution from the NF to UF range were prepared and characterized through the retention of neutral solutes.

2. Experimental 2.1. Materials

CA (Mw CA. 30,000 g.mol-~, 39.8 wt.% acetyl content, degree of substitution 2.5), acetone and formamide were used as received from Aldrich. Deionised water (18 MY~. cm, Milli Q) was used in the preparation of aqueous solutions. 2.2. Preparation o f cellulose acetate membranes

A series of asymmetric CA membranes were prepared by immersion into a water coagulation bath from a dope solution made of 17-20 wt.% CA and acetone/formamide (2:1) mixture. After casting on a glass plate at a thickness of 250 p.m, the forming film system was immersed without further time of evaporation into distilled water at 4°C for 1 h. The phase inversion immediately started and the film peeled off the glass plate after some time. The membranes were then annealed for 10 min in a water bath at the desired temperature varying from 60 ° to 80 ° C. The obtained materials were named M1-4. The water content was calculated from: water % = (mwetmembrane --- mdry membrane / m w e t membrane ) × 1 0 0

Table 1 summarises the main intrinsic characteristies of several membrane samples prepared under the same conditions. Table 1 Intrinsic characteristicsof prepared membranesas a function of the preparation conditions Membrane

M1

CA content, wt.% 17 Annealingtemperature,°C 60 Thickness, gm 90 Water, % 69

M2

M3

M4

17 70 79 70

18.5 20 80 80 77 82 64 67

45

E. Ferjani et al. / Desalination 177 (2005) 43-49 2.3. Characterisation o f membranes

R(%) = (1 - Cp/Cf) x 100.

The prepared membranes were characterised by their retention of neutral solutes (sucrose, M~ = 342 g.mol-~; PEG, Mw = 550 g.mol-l; BSA, M~, = 66,000 g.mo1-1) under 0.2 MPa, at 25°C. The feed solute concentration was fixed at 1 g.L-1. The solute concentration values were determined using a refractometer (IVYMEN system) for sucrose, a spectrometric titration at 535 nm after iodine complexation for PEG [27] and the Lowry's method for BSA [15].

The results obtained were compared with a commercial CA membrane (Amicon, Millipore Filter code YCO5, nominal molecular weight limit, NMWL: 500 Da). The measurement of the hydraulic resistances was achieved using a 3-step experimental method as follows: the clean membrane resistance (Rm) was measured with deionized water filtration. After the UF or NF of the effluent, the membrane was rinsed to eliminate the polarization layer. Then deionized water was filtered with the rinsed membrane. This step was used to determine the irreversible resistance (Ri) which was due to pore plugging and adsorption phenomena. The reversible fouling due essentially to the polarization layer was calculated by:

2.4. Permeation experiments

The permeation tests were carried out at 25°C under an operating pressure (AP) up to 1.2 MPa using a conventional cross-flow Amicon type cell having a total feed solution capacity of 350 mL. Dimensions and characteristics of the used cell were previously described [23]. The effective surface membrane area was of 38.5 cm2. The initial feed volume was fixed at 320 mL.T. The calculation of the wall shear (r) yielded to a 3.125 10-3 Pa value. As the effluxent was concentrated during the experiments, a linear law was considered to estimate the variation of concentration vs, the permeate volume. Every experiment was replicated three times and an average value was considered for concentration calculation. In each experiment, a 20 mL volume of permeate was gathered. Depending on the applied pressure, the experiment time varied from 20 to 40 min. Membranes were at first conditioned in the test cell with pure water by gradually increasing the pressure to 1.2 MPa for at least 1 h. Physico-chemical parameters of effluents and of permeates were determined by using the following techniques: turbidity (turbidimeter, HACH RATIO 2100A); conductivity (conductimeter, Tacussel model 123); COD (HACH DR/2010) and protein nitrogen (PN) (organic nitrogen x 6.25, Kjeldahl Gerhard apparatus). In each experiment, the volume flux (Jr) of permeate was determined and the solute retention rate (R) defined as:

Rr = R, - (Rm + Ri). 2.5. Pickling brine

Effluents for this study were provided from a processing and freezing unit of sea products, which produces 6 tons of cuttlefish daily and has an average consumption of drilling water of about 250 m3.d-1. The wastewaters are of a dark colour due to the presence of sepia ink containing melanin. An average effluent whose composition is presented in Table 2 was considered to prevent the daily fluctuation of chemical and biological effluent quality.

Table 2 Characteristics of the average cuttlefish processing wastewater used in this study Turbidity,NTU

600--700

pH Conductivity,mS COD, mg/1 Dissolved proteins, rag/1

7 54 20,000-35,000 1,200

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E. Ferjani et al. / Desalinatlon 177 (2005) 43-49

Table 3 Rejection rates o f solutes for the studied membranes

Membrane M.W. Da BSA PEG Sucrose

M1

66,000 81 550 77 342 --

M2

M3

M4

M5

90 8I 51

98 92 63

99 95 93

99 94 66

3. Results and discussion

3.1. Molecular weight cut-off The MWCO was determined to check its influence on the recovery efficiency of organic molecules and on permeation parameters for the prepared membranes. We assumed that a retention higher than 90% for the smallest studied solute was indicative of the membrane MWCO [28]. The solute rejection rates obtained for the prepared membranes (M1-M4) were compared to those for the commercial one (M5), as shown in Table 3. These results show that M2, M3 and M4 had MWCO values of CA. 66 kDa, 550 Da and 342 Da, respectively. It should be noted that MWCO could not be determined for the M1 membrane. BSA was only rejected at 81%, meaning a MWCO higher than 66 kDa. These data were confirmed by the observed values of the commercial membrane M5 whose MWCO is given to be 500 Da. From the data gathered in Table 3, it appears that M1 and M2 membranes were efficient in the UF range whereas M3, M4 and M5 membranes can be considered as nanofilters.

3.2. Water permeability determination The hydraulic permeability is an intrinsic feature of a non-fouled membrane. This is de-

termined from the measurements of permeation flux variation of pure water (Jw) vs. the transmembrane pressure (AP). Prior to the first filtration experiment, the membrane samples were conditioned by using a procedure already described [23]. The conditioning involved a decrease of water permeability due to compaction and densification of the filtrating layer. The maximum applied pressure during this step was altered according to the membrane filtration range. We proceeded by increasing AP until 0.6 MPa for M1 and M2 ultrafilters and until 1.2 MPa for M3, M4 and M5 nanofilters. Using these operating conditions, Jw increased linearly with AP and the hydraulic permeability values Lp ° obtained from the slope of Jw = f(AP) were proven to be reproducible. As expected, Lp ° was found to increase with an increase of the membrane MWCO (Table 4). It can be seen that the tailor-made membrane M3 and the commercial one M5 having a similar MWCO exhibited a close hydraulic permeability. On the other hand, we note that the ultrafiltration membranes M1 and M2 showed only fair Lp ° values. We assumed that this behaviour is related to the crushing of the membrane structure during conditioning at 0.6 MPa. The Lp ° values reported in Table 4 were considered as the starting membrane state before its use in effluent treatment.

3.3. Membrane performance and efficiency for the cuttlefish effluent treatment Fig. 1 illustrates the permeation flux variation Jeff vs. AP for the prepared membrane samples. Two kinds of behaviour were observed regarding the filtration range given by the

Table 4 Membrane hydraulic permeability after conditioning Membrane MWCO, Da Lp°, L.m-2.h-l.MPa-1

M1 >66,000 128

M2 66,000 75

M3 Ca 550 52

M4 <342 30

M5 500 60

47

E. Ferjani et al. / Desalination 177 (2005) 43-49 3O

a

3o-

b

2.5-

.J 20-

15.

15-

10.

10.

5-

5

01

i

i

,

,

2

4

6

O.

8 AP (10~Pa)

4

6

8

10

12 14 AP (10~Pa)

Fig. 1. Permeation flux as a function of the applied pressure for the treatment of cuttlefish wastewaters; a) ultrafiltration membrane: • - - M1, • - - M2; b) nanofiltration membrane: • - - M3, • - - M4, • - - M5. Table 5 Resistance towards mass transfer across the M1 and M2 membranes under 0.4 MPa and across the M3-M5 membranes under 1 MPa Entry

Membrane

M1

M2

M3

1

Rm* 10 -7,

2.2

3.7

5.3

9.3

4.6

2

Rr + Ri* 10 -7, m-1

3

Ri* 10 -7, m -1

3.7 3.5

5.1 4.3

7.3 7.1

19.8 18.5

18.5 14.6

4

Rr* 10 -7, m -1

0.2

0.8

0.15

1.3

3.9

m -I

M4

M5

Rm-- membrane resistance; Rr--reversible resistance; R~--irreversible resistance

MWCO values. UF materials M1 and M2 gave a non-linear variation curve reaching out a limiting flux for high pressures. This trend was assumed to be related to the concentration polarisation usually observed in an ultrafiltration process. This phenomenon leads to an accumulation of solutes near the interface that limit the mass transfer across the membrane. This is especially true for highly loaded effluents as in the case o f seafood processing wastewaters. The observed fouling may result from the formation o f a gel layer and the solute adsorption on the membrane surface. An increased resistance due to the pore blocking during the transfer of solutes across the membrane can also account for the flux decline. The starting water flux can be partly recovered

by washing the membranes after wastewater treatments. The second behaviour relates to membranes with a MWCO under 66 kDa (M3, M4 and M5) and shows a limitation of fluxes whose value reaches 0.35 MPa by osmotic pressure. This phenomena is related to dense UF or NF membranes. Mass transfer resistances at each step were calculated using the serial resistance model from Darcy law to evidence the proportion o f the irreversible fouling for the different studied membrane (Table 5). The intrinsic membrane resistance (entry I) was calculated from the starting water flux experiments. The reversible and irreversible mass transfer resistances for the effluent permeation (entry 2) were inferred from

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E. Ferjani et al. / Desalination 177 (2005) 43-49

the subtraction of the intrinsic membrane resistance from the total resistance. The water flux after membrane washing allowed us to discriminate the irreversible fouling (entry 3) from the reversible one (entry 4). 3.4. Efficiency: retention o f pollutant matters

Fouling index determination, involving reversible and irreversible resistances, assembled in Table 5, attains some high values for NF as for UF membranes. On the other hand, the use of the serial resistance model from Darcy law leads to the result that high values of irreversible resistance illustrate that membrane fouling is not only determined by an adsorption phenomena (UF membranes) but at the same time by the formation of a depositing layer composed of fine particles and low molecular weight macromolecules (NF membranes). The higher values obtained in the case of M4 and the commercial M5 membranes are related to their lower molecular cut-off (respectively 342 and 500 Da). This hypothesis is confirmed by the turbidity determination of filtrate (Table 6) obtained for both processes, which leads to lower values for nanofiltration (with a minimum for M4 and M5 membranes). At the same time, it seems that turbidity depends on membrane thickness (case of M5). The retention rate of CDO increases with size pore diminution and seems much higher in the case of nanofiltration than in that of ultrafiltration (8%93% for NF against 55-62.5% for UF). In fact, more particles with lower molecular weight are retained in the case of M3-M5 Table 6 Membrane efficiency for treatment of cuttle-fish effluent Membrane

M1

M2

M3

M4

M5

Rcoo, % RpN,% Turbidity, NTU Conductivity,

48 55 10.5 42

65 62.5 10.3 41

85 52 4.5 38

87 54 4 37

93 86.5 2 35

ms

membranes. The obtained CDO values respond thoroughiy to the enforced norms. However, nitrogen retention obtained for prepared membranes seems slightly higher in the case of UF. This result may be explained by the pore obstruction with fine particles and adsorption phenomena in the case of UF membranes. Trade membrane marked an important value of nitrogen retention in relation to its higher thickness. 4. Conclusion

CA membranes, prepared in our laboratory, were successfully used for experiments of seafood processing wastewater treatment. With regard to membrane MWCO, two kinds of membranes can be distinguished in relation to two filtration processes: ultrafiltration and nanofiltration. The obtained retention rates of COD and PN suggest that the NF process was more efficient in terms of retention of organic and biological matters, but UF results showed higher permeate fluxes. The distinction between the two phenomena has been basically determined by the concentration polarisation observed for UF membranes and by evidence of an osmotic pressure of about 0.35 MPa on NF membranes. To reduce the high values of reversible and irreversible fouling of membranes, a combination between the two membrane processes should be considered as well as the selection of membranes with the best properties. Pre- and post-treatment may also be envisaged in order to improve the whole treatment efficiency. Performance comparison with a trade membrane with 500 Da of MWCO and more important thickness showed a slightly higher retention rate for comparable filtration fluxes. References

[1] M.J. Higgins and J.T. Novak, Water Environ. Res., 69 (1997) 215-224. [2] M.D. Afonso and R. Borquez, Desalination, 142 (2002) 29-45.

E. Ferjani et al. / Desalination 177 (2005) 43-49

[3] E.H. Pavia and A.D. Tyagi, Saafe ASME, NY, 1972. [4] T. Tsuchiya and J. Takahashi, Fish Sausage, Gyoniku Soseji, 215 (1983) 3. [5] D.P. Grenn, L. Tzou, A.C. Chao and T.C. Lanier, Proc. 39th Industrial Waste Conf., Purdue University, West Lafayette, IN, Butterworth, Boston, 1984, p. 565. [6] D.P. Grenn, UNC Sea Grant Publication (88-04), 1988, pp. 357-368. [7] P. Jaouen and F. Qu6m6neur, in: G.M. Hall, ed., Fish Processing Technology, Blackie and Son Ltd., Glascow, UK, oh. 8, 1992, pp. 212-248. [8] S.N. Jhaveri, PhD dissertation, Rhode Island University, USA, 1984. [9] C. Sentad and K.A. Almas, in: Muzzarelli, ed., 3rd Int. Conf. on Chitini/Chitosan, Ancona, Italy, 1985. [10] C.Y. Shiau and T.J. Chai, Proc. 12th Annual Conf. Tropical and Subtropical Fisheries, Technological Society of the Americas, Orlando, USA, 1988. [11] S.I. Kuznetsov, Rybnoe Khozyaistvo, 4 (1988) 87. [12] P. Byskov, Rensing av vann fra fiskeforedling, STF 21, F78146, SINTEF, Norwegian Institute of Technology, Trondheim, Norway, 1978. [13] K. Ninomiya, T. Ookawa, T. Tsuchiya and J.J. Matsunoto, Bull. Jap. Sco. Sei. Fish., 51 (1985) 7. [14]T.C. Swafford, Proc. Pacific Fisheries Technol. Meeting, Monterey, CA, USA, 1987. [15] F. Jacobsen, Meeting of the Scientific Committee, Int. Ass. Fish Meal Manufacturers, London, 1984.

49

[16] D.J. Pauson, R.L.Wilson and D.D. Spatz, Food Technol., 38 (1984) 77. [17] Y. Joh and L.F. Hood, J. Food Sci., 44(6) (1979) 1612. [18] A. Watanabe, T. Ohtani, H. Horikita, H. Ohya and S. Kimura, Food Eng. Proc. Appl., 2 (1986) 225. [19] A. Watanabe, T. Shoji, M. Nakajima, H. Nabetani and T. Ohtani, Nippon Nogeikagaku Kaishi, 62 (1988) 1055. [20] P. Jaouen, PhD dissertation, ENSM, Nantes University, France, 1989. [21] F. Qu6m6neur and P. Jaouen, Key Eng. Mater., 61-62 (1991) 585. [22] P. Jaouen and F. Qu6m6neur, in: G. M. Hall, ed., Fish Processing Technology, Blackie Academic and Professional, London, 1992, pp. 212-248. [23] E. Ferjani and M.S. Roudesli, Eur. Polym. J., 36 (2000) 35-49. [24]E. Ferjani, M. Majdoub, M.S. Roudesli, M.M. Chehimi, D. Picard and M. Delamar, J. Membr. Sci., 165 (2000)125-133. [25] E. Ferjani, R. Hajlajimi, A. Deratani and M.S. Roudesli, Desalination, 14 (2002) 325-330. [26]E. Ferjani, M.S. Roudesli and A. Deratani, Desalination, 162 (2004) 103-109. [27] A.D. Sabde, M.K. Trivedi, V. Ramachandhran, M.S. Hanra and B.M. Misra, Desalination, 114 (1997) 223-232. [28] S. Lee, G. Park, G. Amy, S.-K. Hong, S.-H. Moon, D.-H. Lee and J. Cho, J. Membr. Sci., 201 (2002) 191.