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Potable water production from pesticide contaminated surface water—A membrane based approach
Desalination 204 (2007) 368–373
Potable water production from pesticide contaminated surface water—A membrane based approach Baisali Sarkara, N. Venkateshwarlub, R. Nageswara Raob, Chiranjib Bhattacharjeec, Vijay Kalea* a
Lipid Science & Technology Division, Indian Institute of Chemical Technology, Hyderabad-500007 b Analytical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad-500007 c Chemical Engineering Division, Jadavpur University, Kolkata-700032 Tel. þ91–40–2719–3370; Fax þ91–40–2719–3370; email: [email protected] Received 2 February 2006; accepted 17 February 2006
Abstract The aim of the present study is to obtain safe and pure drinking water from surface water, which has been polluted with pesticide. Pesticide contaminated surface water samples were prepared by spiking commonly used pesticide, Isoproturon, in different surface water samples collected from different parts of India. Attempts were made to evaluate the efficiency of different adsorbents in removing pesticide from distilled water. Dosages and contact time of the selected adsorbent, pH were varied in order to optimise the treatment parameters for maximum removal of pesticide. Langmuir and Freundlich adsorption isotherm were also established in this adsorption study. Coagulation and then adsorption studies were performed on pesticide contaminated surface water as pre-treatment to reduce membrane fouling. Nanofiltration was done on pre-treated water in a test cell in dead end mode. The NF permeate was analysed for pH, turbidity, TDS, COD, TOC, conductivity, hardness, and colony count. RO was suggested after NF if necessary. The quality of NF/RO permeate water compared well with the potable water of our laboratory. Keywords: Surface water; Isoproturon (IPU); Coagulation; Powdered activated charcoal (PAC); Nanofiltration (NF); Potable water
1. Introduction In the older days, untreated lakes, rivers and other surface water bodies were serving
most of the requirement of drinking water supply. Although surface water is characterized by low turbidity, alkalinity and salt
*Corresponding author. Presented at EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21-25 May 2006. 0011-9164/07/$– See front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.02.041
B. Sarkar et al. / Desalination 204 (2007) 368–373
content but proper treatment is required to remove colour, odour and bad taste due to high content of NOM and different types of disease causing micro-organisms. The conventional drinking water treatment methods like coagulation-flocculation, sedimentation, sand filtration and then disinfection has been proved not very effective in this modern age as use of different chemicals in the treatment system for removing suspended materials and for disinfection are not very safe for human health and might result in the production of several carcinogenic and mutagenic by-products [1,2]. Provision should be incorporated in the treatment system to arrest these harmful materials and byproducts before distribution. Beside, surface water resources now-a-days are becoming polluted with many toxic compounds due to the fall of untreated or partially treated industrial effluents and agricultural run off to these water bodies, which are difficult to remove by conventional treatment methods [3]. Pesticides are a group of such hazardous materials found in surface water bodies as a result of agricultural wash out during rainy season. Application of different types of pesticides in agriculture lands for better production of crops, made it also difficult to adopt a single treatment method for its removal from contaminated water sources. Among the various pesticides commonly used, Isoproturon (IPU), a phenyl urea derivative, is widely used as herbicide for the control of the weed Avena fatua on wheat and is harmful to animal and human beings [4]. Adsorption is a well-known technique for the removal of various organic pollutants including pesticide and is very useful in removing colour and odour of surface water [5,6]. With the advent of pressure driven membrane systems, attention has been focussed on their application in production of potable water from surface water as it covers a broad range
369
of materials to be separated. Among the various membrane separation techniques, nanofiltration is widely used in drinking water treatment system due to its ability to remove hardness, natural organic matter and micro-organisms from feed water [7]. Pretreatment of surface water is necessary before NF in order to overcome the fouling problem [8]. In our present investigation, IPU was spiked in distilled water and in surface water and synthetically contaminated water was prepared at a particular concentration. Adsorption treatment was carried out using powdered activated charcoal, bentonite and chitosan and their removal efficiency of IPU from distilled water was estimated. Dosages, pH, and contact time of PAC were varied in order to achieve the maximum removal of IPU. Coagulation and adsorption treatments were done on IPU contaminated surface water as pre-treatment steps before nanofiltration. The pre-treated water had undergone nanofiltration in a test cell in dead end manner. The permeate water was analysed for pH, conductivity, TDS, hardness, TOC, COD, pesticide concentration and total colony count. RO was done if necessary and the NF/RO water was compared to the quality of drinking water. 2. Materials and methods Distilled water was collected from the demineralisation unit supplied by Millipore Inc., USA. The surface water samples were from different parts of India like Ganga River, Kolkata; Mula River, Pune and Hussain Sagar Lake, Hyderabad. 2.1. Reagents Isoproturon (molecular weight: 206), 99% pure, was purchased from Supelco, USA. Polyaluminium chloride (PACl) used as coagulant, was gifted by Permionics Ltd, Vadodara, India; powdered activated charcoal (LR
370
B. Sarkar et al. / Desalination 204 (2007) 368–373
grade) was purchased from S.D Fine Chem. Ltd, Mumbai, India, bentonite (commercial grade) was from Srinivasa Mineral and Bleaching Earth Co., Hyderabad, India and chitosan (LR grade) was purchased from Sigma Aldrich Inc., USA. Merck Ltd and S.D Fine Chem. Ltd, Mumbai, India supplied the HPLC grade solvents used in the experiments like cyclohexane, isopropanol (IPA) and dichloromethane (DCM). Commonly used chemicals to maintain the pH of the medium NaOH and HCl both LR grade were procured from S.D Fine Chem. Ltd, Mumbai and Ranbaxy Fine Chemicals Ltd, New Delhi, India respectively. 2.2. Membrane and membrane units Flat sheet nanofiltration membrane was supplied by Dow FilmTech, USA and reverse osmosis membrane was by Permionics Ltd, Vadodara, India. The NF and RO test cell were made of stainless steel with magnetic stirrer arrangement. The transmembrane pressure was generated by nitrogen gas. 2.3. Analytical methods 2.3.1. Estimation of IPU in water: The stock IPU solution was prepared by dissolving it in HPLC grade isopropanol (IPA) and stored in refrigerator. The standard and working IPU solutions were prepared from stock whenever required. The extraction of IPU from water solution was done by liquid–liquid extraction technique using DCM. The DCM layer was evaporated to dryness in rotary evaporator and the residual IPU was dissolved in mobile phase and analyzed by HPLC. The IPU estimation was done by HPLC (model: LC-6A) supplied by Shimadzu, Japan and equipped with UV-visible detector. The column used was Spherisorb Silica of 25 cm L 4.6 cm ID, mobile phase used
was 90:10 (v/v) cyclohexane & isopropanol (IPA), pump flow rate selected was 1 ml/ min, and detection was done at 254 nm. 2.3.2. Analysis of water samples: Raw water and treated water samples were analysed for total dissolved solid content (TDS), hardness, chemical oxygen demand (COD), total organic carbon content (TOC) according to the standard method [9]. Turbidity was measured by Digital Nephelo-Turbiditimeter 132. Zetasizer 3000HSA was used for measuring zeta potential. The digestion of water samples for COD estimation was done in COD reactor supplied by HACH, Colorado, USA. TOC estimation was done in Total Organic Carbon Analyser (model: High TOC) manufactured by Elementar, Germany. The total colony count estimation was done according to the standard method [10]. 3. Results and discussion 3.1. Optimisation of coagulant dosages Polyaluminium Chloride (PACl) was used as coagulant in the present studies in order to remove suspended and colloidal materials from the surface water [11]. Coagulant dosages were varied from 20 to 200 mg/L followed by 5 min stirring on magnetic stirrer and allowed to settle for 60 min and then filtered. The removal of suspended and colloidal materials was measured in terms of reduction of turbidity of the water. 100 mg/L dosage of PACl was found optimum where 90–97% removal of turbidity was observed for all the surface water samples without any change in pH and conductivity of water samples. No appreciable reduction in IPU content was observed after coagulation. 3.2. Selection of adsorbent and adsorbent dosages Adsorbents taken for the experiments were powdered activated charcoal (PAC),
371
B. Sarkar et al. / Desalination 204 (2007) 368–373
bentonite [12] and chitosan [13]. The dosages were varied from 20 to 1000 mg/L and added to the synthetically prepared 1 mg/L (ppm) IPU solution in distilled water. Stirring was done on magnetic stirrer for 120 min and then filtered and analysed for IPU content. The percent removal of IPU from water solution with dosages of adsorbents is given in Table 1. A sharp increase in percent reduction of IPU content was observed when PAC dosages were increased from 20 to 100 mg/L. After that, a slow increase was observed and 98–99% removal of IPU was found in the dosage range of 300–1000 mg/L. In contrast to PAC, bentonite and chitosan had shown maximum 4% and 18% separation of IPU respectively. Therefore PAC at a dosage of 300 mg/L was selected for the treatment of IPU contaminated surface water. 3.3. Effect of contact time Stirring time after 300 mg/L addition of PAC to 1 ppm IPU contaminated distilled water was varied from 15 to 480 min. 94–95% reduction of IPU content was observed after 15–60 min contact time, which was increased to 98–99% after 60 min. No further Table 1 Percent removal of IPU from distilled water with dosages of adsorbents
0 20 50 80 100 300 500 700 1000
3.4. Effect of pH In order to find out the optimum pH for the maximum adsorption of IPU on PAC surface, zeta potential measurement of PAC and IPU was done as described below. 0.2 g of PAC was added to 200 ml of distilled water and 1 ppm solution of IPU was prepared in distilled water separately. Sonication was done for 5 min. The suspensions were divided into portions and pH were adjusted individually from 2.0 to 10.0 and kept for 24 h. Then the upper layer was filtered and zeta potential was estimated. Figure 1 is showing the variation of zeta potential with pH of the medium. The figure describes that adsorption of IPU on PAC surface is pH independent indicating physical adsorption of IPU on PAC surface. 3.5. Adsorption isotherm The equilibrium data for the adsorption of IPU on PAC surface was analysed in the light of two most commonly used Langmuir and Freundlich adsorption model. The values of the con-
Percent reduction of IPU PAC
Bentonite
Chitosan
0 60.9 87.8 93 94.1 98.2 98 98.9
0 2.7 2.5 3 0.8 0.6 – 0.8 3.6
0 7.8 10.7 17.5 17.5 16.3 10.3 – 16.3
20 Zeta potential (mV)
Dosage of adsorbents (mg/L)
change in percent reduction was observed with increase in contact time after 60 min. Therefore 60 min contact time was optimised for the treatment of 1 ppm IPU contaminated surface water.
10 0 –10 0
2
4
6
8
10
12
–20 –30 –40
PAC
IPU
–50 pH
Fig. 1. Variation of zeta potential of PAC and IPU with pH of the medium.
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B. Sarkar et al. / Desalination 204 (2007) 368–373
stants were calculated from the slope and intercept of the linear plots and are as follows:
The RO permeate could be compared to the drinking water quality.
Langmuir model Freundlich model a : 104.21 mg/g n: 2.27 b : 3.2 L/g KF: 69.4 mg/g As the value of n is within the range of 1 to 10, it signifies favourable adsorption
4. Conclusion
3.6. Nanofiltration and reverse osmosis Different surface water samples was taken and synthetically 1 mg/L IPU solution was prepared. 100 mg/L PACl treatment was done and filtered. Turbidity values came down to 0.1–0.2 NTU after coagulation and colour of the raw water was improved. The filtrate after coagulation was treated with 300 mg/L dosage of PAC and filtered. Charcoal treatment removed the colour of the water completely. 98–99% pesticide content was reduced after charcoal treatment. Nanofiltration was done on all the pretreated water samples. Nanofiltration was done in a test cell using flat sheet membrane keeping the gas pressure 25–30 bar and permeate volume was collected with time. Cumulative permeate volume collected was analysed. Nanofiltration completely removed the microbial content present after charcoal treatment and reduced COD to an appreciable extent. TOC values were below detection limit in all the NF permeates. The level of pesticide content came down to 3–4 microg/L after nanofiltration when the raw water was spiked with as much as 1 mg/L IPU. If the analysed NF permeate water was beyond the desirable limit of potable water, RO treatment was done on NF permeate at a pressure of 38–40 bar and the cumulative permeate volume collected was analysed. In the present study, Hussain Sagar Lake water after NF showed high ionic content as reflected by the conductivity value of raw water and reverse osmosis was done on NF permeate.
The production of drinking water from pesticide contaminated surface water can be done by NF and RO treatment after proper pretreatment. PAC treatment alone can reduce IPU content upto 98–99% of the initial. Nanofiltration reduced hardness, COD, TOC, and removed microbial content completely. If the ionic content is beyond the desirable limit of drinking water, RO was done on NF permeate. The NF or RO permeate quality were found comparable to the quality of drinking water. References [1] J.P. Botes, E.P. Jacobs and S.M. Bradshaw, Long term evaluation of a UF pilot plant for potable water production, Desalination, 115 (1998) 229–238. [2] S. Xia, X. Li, R. Liu and G. Li, Study of reservoir water treatment by ultrafiltration for drinking water production, Desalination, 167 (2004) 23–26. [3] O. Griffini, M.L. Bao, D. Burrini, D, Santianni, C. Barbieri and F. Pantani, Removal of pesticides during drinking water treatment process at Florence water supply, Italy, Aqua, 48 (5) (1999) 177–185. [4] A. Ashraf, M. Shahid, M.A. Sheikh, J. Qureshi, A. Ghaffar and S. Kausar, Fate and residue analysis of isoproturon applied to control jangli jai (Avena fatua) in wheat (Triticum aestivum), Pakistan J. Plant Pathology, 1 (2–4) (2002) 76–77. [5] A. Kouras, A. Zouboulis, C. Samara and Th. Kouimtzis, Removal of pesticides from aqueous solutions by combined physicochemical processes-the behaviour of lindane, Environ. Pollut., 103 (1998) 193–202. [6] B. Ericsson and G. Tragardh, Treatment of surface water rich in humus – Membrane filtration vs conventional treatment, Desalination, 108 (1996) 117–128. [7] R. Liikanen, I. Miettinen and R. Laukkanen, Selection of NF membrane to improve quality
B. Sarkar et al. / Desalination 204 (2007) 368–373 of chemically treated surface water, Wat. Res., 37 (2003) 864–872. [8] B. Schlichter, V. Mavrov and H. Chmiel, Study of a hybrid process combining ozonation and microfiltration/ultrafiltration for drinking water production from surface water, Desalination, 168 (2004) 307–317. [9] APHA, Standard methods for the examination of water and wastewater, 20th edition, 1998. [10] R.M. Atlas, Principles of Microbiology, 2nd edition, WCB-Mcgraw Hill, (1997) pp. 72–74.
373
[11] K. Barkacs, I. Bohuss, A. Bukovszky, I. Varga and G. Zaray, Comparison of polyelectrolytes applied in drinking water treatment, Microchem. J., 67 (2000) 271–277. [12] O.R. Pal and A.K. Vanjara, Removal of malathion and butachlor from aqueous solution by clays and organoclays, Sep. Purif. Tech., 24 (2001) 167–172. [13] K. Yoshizuka, Z. Lou and K. Inoue, Silver-complexed chitosan microparticles for pesticide removal, React. Funct. Poly., 44 (2000) 47–54.
Potable water production from pesticide contaminated surface water—A membrane based approach Baisali Sarkara, N. Venkateshwarlub, R. Nageswara Raob, Chiranjib Bhattacharjeec, Vijay Kalea* a
Lipid Science & Technology Division, Indian Institute of Chemical Technology, Hyderabad-500007 b Analytical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad-500007 c Chemical Engineering Division, Jadavpur University, Kolkata-700032 Tel. þ91–40–2719–3370; Fax þ91–40–2719–3370; email: [email protected] Received 2 February 2006; accepted 17 February 2006
Abstract The aim of the present study is to obtain safe and pure drinking water from surface water, which has been polluted with pesticide. Pesticide contaminated surface water samples were prepared by spiking commonly used pesticide, Isoproturon, in different surface water samples collected from different parts of India. Attempts were made to evaluate the efficiency of different adsorbents in removing pesticide from distilled water. Dosages and contact time of the selected adsorbent, pH were varied in order to optimise the treatment parameters for maximum removal of pesticide. Langmuir and Freundlich adsorption isotherm were also established in this adsorption study. Coagulation and then adsorption studies were performed on pesticide contaminated surface water as pre-treatment to reduce membrane fouling. Nanofiltration was done on pre-treated water in a test cell in dead end mode. The NF permeate was analysed for pH, turbidity, TDS, COD, TOC, conductivity, hardness, and colony count. RO was suggested after NF if necessary. The quality of NF/RO permeate water compared well with the potable water of our laboratory. Keywords: Surface water; Isoproturon (IPU); Coagulation; Powdered activated charcoal (PAC); Nanofiltration (NF); Potable water
1. Introduction In the older days, untreated lakes, rivers and other surface water bodies were serving
most of the requirement of drinking water supply. Although surface water is characterized by low turbidity, alkalinity and salt
*Corresponding author. Presented at EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21-25 May 2006. 0011-9164/07/$– See front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2006.02.041
B. Sarkar et al. / Desalination 204 (2007) 368–373
content but proper treatment is required to remove colour, odour and bad taste due to high content of NOM and different types of disease causing micro-organisms. The conventional drinking water treatment methods like coagulation-flocculation, sedimentation, sand filtration and then disinfection has been proved not very effective in this modern age as use of different chemicals in the treatment system for removing suspended materials and for disinfection are not very safe for human health and might result in the production of several carcinogenic and mutagenic by-products [1,2]. Provision should be incorporated in the treatment system to arrest these harmful materials and byproducts before distribution. Beside, surface water resources now-a-days are becoming polluted with many toxic compounds due to the fall of untreated or partially treated industrial effluents and agricultural run off to these water bodies, which are difficult to remove by conventional treatment methods [3]. Pesticides are a group of such hazardous materials found in surface water bodies as a result of agricultural wash out during rainy season. Application of different types of pesticides in agriculture lands for better production of crops, made it also difficult to adopt a single treatment method for its removal from contaminated water sources. Among the various pesticides commonly used, Isoproturon (IPU), a phenyl urea derivative, is widely used as herbicide for the control of the weed Avena fatua on wheat and is harmful to animal and human beings [4]. Adsorption is a well-known technique for the removal of various organic pollutants including pesticide and is very useful in removing colour and odour of surface water [5,6]. With the advent of pressure driven membrane systems, attention has been focussed on their application in production of potable water from surface water as it covers a broad range
369
of materials to be separated. Among the various membrane separation techniques, nanofiltration is widely used in drinking water treatment system due to its ability to remove hardness, natural organic matter and micro-organisms from feed water [7]. Pretreatment of surface water is necessary before NF in order to overcome the fouling problem [8]. In our present investigation, IPU was spiked in distilled water and in surface water and synthetically contaminated water was prepared at a particular concentration. Adsorption treatment was carried out using powdered activated charcoal, bentonite and chitosan and their removal efficiency of IPU from distilled water was estimated. Dosages, pH, and contact time of PAC were varied in order to achieve the maximum removal of IPU. Coagulation and adsorption treatments were done on IPU contaminated surface water as pre-treatment steps before nanofiltration. The pre-treated water had undergone nanofiltration in a test cell in dead end manner. The permeate water was analysed for pH, conductivity, TDS, hardness, TOC, COD, pesticide concentration and total colony count. RO was done if necessary and the NF/RO water was compared to the quality of drinking water. 2. Materials and methods Distilled water was collected from the demineralisation unit supplied by Millipore Inc., USA. The surface water samples were from different parts of India like Ganga River, Kolkata; Mula River, Pune and Hussain Sagar Lake, Hyderabad. 2.1. Reagents Isoproturon (molecular weight: 206), 99% pure, was purchased from Supelco, USA. Polyaluminium chloride (PACl) used as coagulant, was gifted by Permionics Ltd, Vadodara, India; powdered activated charcoal (LR
370
B. Sarkar et al. / Desalination 204 (2007) 368–373
grade) was purchased from S.D Fine Chem. Ltd, Mumbai, India, bentonite (commercial grade) was from Srinivasa Mineral and Bleaching Earth Co., Hyderabad, India and chitosan (LR grade) was purchased from Sigma Aldrich Inc., USA. Merck Ltd and S.D Fine Chem. Ltd, Mumbai, India supplied the HPLC grade solvents used in the experiments like cyclohexane, isopropanol (IPA) and dichloromethane (DCM). Commonly used chemicals to maintain the pH of the medium NaOH and HCl both LR grade were procured from S.D Fine Chem. Ltd, Mumbai and Ranbaxy Fine Chemicals Ltd, New Delhi, India respectively. 2.2. Membrane and membrane units Flat sheet nanofiltration membrane was supplied by Dow FilmTech, USA and reverse osmosis membrane was by Permionics Ltd, Vadodara, India. The NF and RO test cell were made of stainless steel with magnetic stirrer arrangement. The transmembrane pressure was generated by nitrogen gas. 2.3. Analytical methods 2.3.1. Estimation of IPU in water: The stock IPU solution was prepared by dissolving it in HPLC grade isopropanol (IPA) and stored in refrigerator. The standard and working IPU solutions were prepared from stock whenever required. The extraction of IPU from water solution was done by liquid–liquid extraction technique using DCM. The DCM layer was evaporated to dryness in rotary evaporator and the residual IPU was dissolved in mobile phase and analyzed by HPLC. The IPU estimation was done by HPLC (model: LC-6A) supplied by Shimadzu, Japan and equipped with UV-visible detector. The column used was Spherisorb Silica of 25 cm L 4.6 cm ID, mobile phase used
was 90:10 (v/v) cyclohexane & isopropanol (IPA), pump flow rate selected was 1 ml/ min, and detection was done at 254 nm. 2.3.2. Analysis of water samples: Raw water and treated water samples were analysed for total dissolved solid content (TDS), hardness, chemical oxygen demand (COD), total organic carbon content (TOC) according to the standard method [9]. Turbidity was measured by Digital Nephelo-Turbiditimeter 132. Zetasizer 3000HSA was used for measuring zeta potential. The digestion of water samples for COD estimation was done in COD reactor supplied by HACH, Colorado, USA. TOC estimation was done in Total Organic Carbon Analyser (model: High TOC) manufactured by Elementar, Germany. The total colony count estimation was done according to the standard method [10]. 3. Results and discussion 3.1. Optimisation of coagulant dosages Polyaluminium Chloride (PACl) was used as coagulant in the present studies in order to remove suspended and colloidal materials from the surface water [11]. Coagulant dosages were varied from 20 to 200 mg/L followed by 5 min stirring on magnetic stirrer and allowed to settle for 60 min and then filtered. The removal of suspended and colloidal materials was measured in terms of reduction of turbidity of the water. 100 mg/L dosage of PACl was found optimum where 90–97% removal of turbidity was observed for all the surface water samples without any change in pH and conductivity of water samples. No appreciable reduction in IPU content was observed after coagulation. 3.2. Selection of adsorbent and adsorbent dosages Adsorbents taken for the experiments were powdered activated charcoal (PAC),
371
B. Sarkar et al. / Desalination 204 (2007) 368–373
bentonite [12] and chitosan [13]. The dosages were varied from 20 to 1000 mg/L and added to the synthetically prepared 1 mg/L (ppm) IPU solution in distilled water. Stirring was done on magnetic stirrer for 120 min and then filtered and analysed for IPU content. The percent removal of IPU from water solution with dosages of adsorbents is given in Table 1. A sharp increase in percent reduction of IPU content was observed when PAC dosages were increased from 20 to 100 mg/L. After that, a slow increase was observed and 98–99% removal of IPU was found in the dosage range of 300–1000 mg/L. In contrast to PAC, bentonite and chitosan had shown maximum 4% and 18% separation of IPU respectively. Therefore PAC at a dosage of 300 mg/L was selected for the treatment of IPU contaminated surface water. 3.3. Effect of contact time Stirring time after 300 mg/L addition of PAC to 1 ppm IPU contaminated distilled water was varied from 15 to 480 min. 94–95% reduction of IPU content was observed after 15–60 min contact time, which was increased to 98–99% after 60 min. No further Table 1 Percent removal of IPU from distilled water with dosages of adsorbents
0 20 50 80 100 300 500 700 1000
3.4. Effect of pH In order to find out the optimum pH for the maximum adsorption of IPU on PAC surface, zeta potential measurement of PAC and IPU was done as described below. 0.2 g of PAC was added to 200 ml of distilled water and 1 ppm solution of IPU was prepared in distilled water separately. Sonication was done for 5 min. The suspensions were divided into portions and pH were adjusted individually from 2.0 to 10.0 and kept for 24 h. Then the upper layer was filtered and zeta potential was estimated. Figure 1 is showing the variation of zeta potential with pH of the medium. The figure describes that adsorption of IPU on PAC surface is pH independent indicating physical adsorption of IPU on PAC surface. 3.5. Adsorption isotherm The equilibrium data for the adsorption of IPU on PAC surface was analysed in the light of two most commonly used Langmuir and Freundlich adsorption model. The values of the con-
Percent reduction of IPU PAC
Bentonite
Chitosan
0 60.9 87.8 93 94.1 98.2 98 98.9
0 2.7 2.5 3 0.8 0.6 – 0.8 3.6
0 7.8 10.7 17.5 17.5 16.3 10.3 – 16.3
20 Zeta potential (mV)
Dosage of adsorbents (mg/L)
change in percent reduction was observed with increase in contact time after 60 min. Therefore 60 min contact time was optimised for the treatment of 1 ppm IPU contaminated surface water.
10 0 –10 0
2
4
6
8
10
12
–20 –30 –40
PAC
IPU
–50 pH
Fig. 1. Variation of zeta potential of PAC and IPU with pH of the medium.
372
B. Sarkar et al. / Desalination 204 (2007) 368–373
stants were calculated from the slope and intercept of the linear plots and are as follows:
The RO permeate could be compared to the drinking water quality.
Langmuir model Freundlich model a : 104.21 mg/g n: 2.27 b : 3.2 L/g KF: 69.4 mg/g As the value of n is within the range of 1 to 10, it signifies favourable adsorption
4. Conclusion
3.6. Nanofiltration and reverse osmosis Different surface water samples was taken and synthetically 1 mg/L IPU solution was prepared. 100 mg/L PACl treatment was done and filtered. Turbidity values came down to 0.1–0.2 NTU after coagulation and colour of the raw water was improved. The filtrate after coagulation was treated with 300 mg/L dosage of PAC and filtered. Charcoal treatment removed the colour of the water completely. 98–99% pesticide content was reduced after charcoal treatment. Nanofiltration was done on all the pretreated water samples. Nanofiltration was done in a test cell using flat sheet membrane keeping the gas pressure 25–30 bar and permeate volume was collected with time. Cumulative permeate volume collected was analysed. Nanofiltration completely removed the microbial content present after charcoal treatment and reduced COD to an appreciable extent. TOC values were below detection limit in all the NF permeates. The level of pesticide content came down to 3–4 microg/L after nanofiltration when the raw water was spiked with as much as 1 mg/L IPU. If the analysed NF permeate water was beyond the desirable limit of potable water, RO treatment was done on NF permeate at a pressure of 38–40 bar and the cumulative permeate volume collected was analysed. In the present study, Hussain Sagar Lake water after NF showed high ionic content as reflected by the conductivity value of raw water and reverse osmosis was done on NF permeate.
The production of drinking water from pesticide contaminated surface water can be done by NF and RO treatment after proper pretreatment. PAC treatment alone can reduce IPU content upto 98–99% of the initial. Nanofiltration reduced hardness, COD, TOC, and removed microbial content completely. If the ionic content is beyond the desirable limit of drinking water, RO was done on NF permeate. The NF or RO permeate quality were found comparable to the quality of drinking water. References [1] J.P. Botes, E.P. Jacobs and S.M. Bradshaw, Long term evaluation of a UF pilot plant for potable water production, Desalination, 115 (1998) 229–238. [2] S. Xia, X. Li, R. Liu and G. Li, Study of reservoir water treatment by ultrafiltration for drinking water production, Desalination, 167 (2004) 23–26. [3] O. Griffini, M.L. Bao, D. Burrini, D, Santianni, C. Barbieri and F. Pantani, Removal of pesticides during drinking water treatment process at Florence water supply, Italy, Aqua, 48 (5) (1999) 177–185. [4] A. Ashraf, M. Shahid, M.A. Sheikh, J. Qureshi, A. Ghaffar and S. Kausar, Fate and residue analysis of isoproturon applied to control jangli jai (Avena fatua) in wheat (Triticum aestivum), Pakistan J. Plant Pathology, 1 (2–4) (2002) 76–77. [5] A. Kouras, A. Zouboulis, C. Samara and Th. Kouimtzis, Removal of pesticides from aqueous solutions by combined physicochemical processes-the behaviour of lindane, Environ. Pollut., 103 (1998) 193–202. [6] B. Ericsson and G. Tragardh, Treatment of surface water rich in humus – Membrane filtration vs conventional treatment, Desalination, 108 (1996) 117–128. [7] R. Liikanen, I. Miettinen and R. Laukkanen, Selection of NF membrane to improve quality
B. Sarkar et al. / Desalination 204 (2007) 368–373 of chemically treated surface water, Wat. Res., 37 (2003) 864–872. [8] B. Schlichter, V. Mavrov and H. Chmiel, Study of a hybrid process combining ozonation and microfiltration/ultrafiltration for drinking water production from surface water, Desalination, 168 (2004) 307–317. [9] APHA, Standard methods for the examination of water and wastewater, 20th edition, 1998. [10] R.M. Atlas, Principles of Microbiology, 2nd edition, WCB-Mcgraw Hill, (1997) pp. 72–74.
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