High organic content industrial wastewater treatment by membrane filtration

Desalination 162 (2004) 117–120 High organic content industrial wastewater treatment by membrane filtration Ildikó Galambosa*, Jesús Mora Molinaa,b, Péter Járaya, Gyula Vataia, Erika Bekássy-Molnára a Szent István University, Faculty of Food Science, Department of Food Engineering H-1118 Ménesi út 44, Budapest, Hungary Tel. +36 (1) 372-6232; Fax +36 (1) 372-6323; email: gildiko@omega.kee.hu b Instituto Tecnologico de Costa Rica, Sede Regional de San Carlos, Escuela de Ciencias y Letras, Apartado 223-4400, Ciudad Quesada, Costa Rica Tel. +1 (506) 475-5033; Fax +1 (506) 475-5395; email: jesusmm@costarricense.cr Received 2 July 2003; accepted 3 September 2003 Abstract The importance of wastewater treatment in the food industry is growing nowadays, because of the rising cost of water and because of environmental pollution. The aim of this study was to decrease the chemical oxygen demand (COD) of two different wastewaters originated from the food industry. If the treated water is drained into natural water, the COD has to be below 125 mgO2/L, if it is released into sewer the limit is 800 mgO2/L. Reverse osmosis and nanofiltration membranes were investigated for wastewater treatement. Experiments were carried out at constant temperature and recycle flow rate, the permeate flux, salt rejection and COD were measured continously. During concentration experiments the fouling of the membranes was observed. Keywords: Membrane filtration; Nanofiltration; Reverse osmosis; Wastewater; Drinking water; Organic compounds 1. Introduction Concerning Central European datas the industry produces 50% of the wastewater and the rest is *Corresponding author. almost exactly divided between agriculture and household. Compared with other industrial sectors the food industry needs a greater amount of water than other sections [1]. High organic contents of wastewater are mainly characteristic of food Presented at PERMEA 2003, Membrane Science and Technology Conference of Visegrad Countries (Czech Republic, Hungary, Poland and Slovakia), September 7–11, 2003, Tatranské Matliare, Slovakia. 0011-9164/04/$– See front matter © 2004 Elsevier B.V. All rights reserved 118 I. Galambos et al. / Desalination 162 (2004) 117–120 industry, and aerobic and anaerobic fermentation processes can easily decompose these. The decomposition requires big space, while its economic efficiency is low. The task of researchers is to find effective cleaning methods for the removal of organic materials from wastewater, or just to decrease the quantity of waste concentrate, then to decompose it by fermentation. For this latter task nanofiltration (NF) and reverse osmosis (RO) were selected. Both membranes are applied in the food industry and with their assistance organics, mono- and bivalent salts can be removed effectively [2–4]. Owen et al. [5] have economically estimated the possible water and wastewater treatment by membrane technology. 2. Materials and methods In our experimental investigations two different wastewaters containing organic substances and dispersed oil have been examined. The characteristics of the two wastewaters are shown in Table 1. Two different membrane filtration processes — nanofiltration and reverse osmosis — have been selected and carried out in both cases. In our experiments Dow-FilmTec membranes were used. The salt (NaCl) rejection of nanofiltration membrane (NF200, material polyamide) was 51% and of reverse osmosis (SWHR30-80, material polyamide) membrane was 99.4%. Experiments have been carried out on DDS Minilab 20 laboratory equipment using flat sheet membranes (360 cm2 active surface). The composition of the wastewaters was not known in detail at the start of the Table 1 The parameters of the examined wastewaters Wastewater 1 Wastewater 2 Chemical oxygen demand (COD), mgO2/L pH Conductivity, µS/cm Total solid content, % Fig. 1. Flow-diagram of the investigated laboratory equipment: 1, vessel; 2, thermometer; 3, pump; 4, manometer; 5, membrane module; 6, permeate; 7, rotameter; 8, valve. measurements. Fig. 1 shows the simplified flowdiagram of the equipment. Batch mode of wastewater concentration was applied. During the measurements temperature (t = 30°C) and recycle flow rate (Q = 300 L/h) were kept constant, while pressure (p) values were changed — in the case of NF p = 5, 10 and 15 bar; in the case of RO p = 10, 20 and 30 bar were settled. Permeate flux, salt rejection (with conductivity by the equipment OK-102/1), pH (by the HI 8314 pHmeter) and chemical oxygen demand (COD) (in the laboratory of Korte-Organica Rt., Budapest, Hungary) were measured and calculated constantly, while the organic material rejection was also examined. Filtration (Filt) and concentration (Conc) surveys were done, the parameters are shown in Table 2. During the concentration experiments after taking away every 500 cm3 permeate the COD of the concentrate and the permeate were measured and the yield was calculated: 9500 1160 Yield = (volume of permeate)/(volume of feed) × 100% 7.64 1320 0.25 7.34 1010 0.44 In the experiments the problem to be solved was to remove the organic contamination from the feed solution in one step. First we have measured I. Galambos et al. / Desalination 162 (2004) 117–120 119 Table 2 Parameters for the filtration and concentration of the two types of wastewaters Nanofiltration Q = 300 L/h, t = 30°C Wastewater 1 Wastewater 2 Wastewater 1 Wastewater 2 Filt Conc Filt Conc Filt Conc Filt Conc 5, 10, 15 1600 — — 15 3800 890 76.6 5, 10, 15 2500 — — 15 2500 292 88.3 10, 30, 50 2500 — — 40 2200 700 68.2 10, 30, 50 2500 — — 40 2200 300 86.4 the fluxes of the RO and NF membranes, as a function of pressure, at constant temperature (t = 30°C) and recirculation flow rate (Q = 300 L/h) (Table 2). 3. Results and discussion 50 40 Flux (L/m2h) Pressure, bar Feed, cm³ Concentrate, cm³ Yield, % Reverse osmosis Q = 300 L/h, t = 30°C 30 20 10 Wastewater 2 0 Wastewater 1 5 10 15 Pressure (bar) Fig. 2. Influence of pressure on permeate flux with different wastewaters on NF membrane. 20 Flux (L/m2h) Some measured results are shown in Fig. 2 and Fig. 3. From the diagrams it can be seen that the flux increases with the increase in the pressure. During the nanofiltration the flux was higher in the second wastewater sample (COD = 1160 mgO2/L) than in the first one (COD = 9500 mgO2/L), but using the reverse osmosis this difference is negligible. The next two diagrams in Fig. 4 and Fig. 5 show the results of the concentration surveys. The first sample of the wastewater (COD = 9500 mgO2/L) was filtered by RO. In this case the COD values of the permeate were lower than 100 mgO2/L, while the COD of the concentrate was 22800 mgO2/L. After nanofiltration of the same sample the COD values in the permeate were 300–500 mgO2/L and concentrate values were 14550 mgO2/L. Treating the second sample (COD = 1160 mgO2/L) with RO membrane the permeate had 20–30 mgO2/L and concentrate 3100 mgO2/L COD values, while the nanofiltration of the permeate had 70–100 mgO2/L and the concentrate 2600 mgO2/L COD values. During concentration experiments the flux of RO was already constant, while in the case of 15 10 5 Wastewater 2 0 10 Wastewater 1 30 50 Pressure (bar) Fig. 3. Influence of pressure on permeate flux with different wastewaters on RO membrane. NF experiments the flux significantly decreased with increasing the retentate concentration. The fouling was greater in the case of NF, so frequent 120 I. Galambos et al. / Desalination 162 (2004) 117–120 COD (mgO2/L) 25000 20000 15000 10000 41 5000 RO 370 0 Feed NF Concentrate Average permeate Fig. 4. Results of concentration survey in case of the first wastewater (feed COD = 9500 mgO2/L). COD (mgO2/L) 3000 2500 2000 1500 25 500 RO 93 0 Feed NF Concentrate Acknowledgements The authors express their gratitude to the Ministry of Education (NKFP/OM–00308/02), to the OTKA Foundation (T 037848), to the ITCR (Instituto Tecnologico de Costa Rica), to the MICIT (Ministerio de Ciencias y Tecnologia) and to the CONICIT (Consejo Nacional de Investigaciones Cientificas y Tecnologicas). 3500 1000 into the process/technology. Also the fouling was irrelevant. On the other hand the permeate of NF has higher COD, than that of RO, the permeate can be released into sewer only, where a next purifying step is necessary. The retentate having high content of organics should be treated by evaporation to minimize the quantity of waste or as another solution membrane bioreactors can be applied where the biological method is combined with ultrafiltration or microfiltration. The final decision should be made after an economical efficiency study. Average permeate Fig. 5. Results of concentration survey in case of the second wastewater (feed COD = 1160 mgO2/L). backwashing was necessary with 0.1% NaOH and 0.1% HNO3 solutions. 4. Conclusions As the main result of this study we concluded that for the investigated wastewaters — originated from the food industry — the application of RO can be proposed. The permeate of RO can be drained into natural waters, or can be recycled References [1] V. Mavrov and E. Belieres, Reduction of water consumption and wastewater quantities in the food industry by water recycling using membrane processes, Desalination, 131 (2000) 75–86. [2] A.J. Karabelas, S.G. Yiantsios, Z. Metaxiotou, N. Andritsos, A. Akiskalos, G. Vlachopoulos and S. Stavroulias, Water and materials recovery from fertilizer industry acidic effluents by membrane processes, Desalination, 138 (2001) 93–102. [3] J. Schaefer, Reliable water supply by reusing wastewater after membrane treatment, Desalination, 138 (2001) 91. [4] K. Belafi-Bako, Ed., Integration of membrane processes into bioconversions. Kluwer, New York, 2000. [5] G. Owen, M. Bandi, J.A. Howell and S.J. Churchouse, Economic assessment of membrane processes for water and wastewater treatment, J. Membr. Sci., 102 (1995) 77–91.