- Email: [email protected]
Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation
DES-12215; No of Pages 7 Desalination xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Desalination journal homepage: www.elsevier.com/locate/desal
Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation Samuel Bunani a,d, Eren Yörükoğlu a, Ümran Yüksel a, Nalan Kabay b,⁎, Mithat Yüksel b, Gökhan Sert c a
Ege University, Faculty of Science, Department of Chemistry, Izmir, Turkey Ege University, Faculty of Engineering, Department of Chemical Engineering, Izmir, Turkey Ege University, Faculty of Fisheries, Izmir, Turkey d University of Burundi, Faculty of Science, Department of Chemistry, Bujumbura, Burundi b c
H I G H L I G H T S • • • •
Treatment of bio-treated urban wastewater by RO membranes Application of BWRO and SWRO membranes for wastewater reuse Blending of secondary effluent and RO permeate to obey the irrigation requirements. BWRO membrane produces high recovery and good water quality.
a r t i c l e
i n f o
Article history: Received 20 April 2014 Received in revised form 16 July 2014 Accepted 23 July 2014 Available online xxxx Keywords: Agriculture Irrigation water Municipal wastewater Reverse osmosis Water reuse
a b s t r a c t Secondary treated urban wastewater was further polished by reverse osmosis (RO) membranes and the water quality of RO permeates was assessed for their utilizations in agricultural irrigation. The performances of brackish water reverse osmosis (AK-BWRO) and seawater reverse osmosis (AD-SWRO) membranes were investigated at 10 bar as applied pressure. The AD-SWRO membrane was tested also at 20 bar. Conductivity, salinity, chemical oxygen demand (COD), total organic carbon (TOC) and color were rejected by AK-BWRO membrane with average values of 94.6%, 95.2%, 85.8%, 76.4% and 91.3%, respectively, whereas the same contaminants were rejected with average values of 98.3%, 98.3%, 84.6%, 69.7% and 86.6%, respectively with AD-SWRO membrane. Except for TOC, AD-SWRO membrane showed similar rejections at 10 bar and at 20 bar of applied pressures. Although their rejection efficiencies were similar, AK-BWRO and AD-SWRO membranes revealed differences in their permeate flux which is 38.0 L/hm2 for AK-BWRO membrane and 3.81 L/hm2 for AD-SWRO membrane. An average value of permeate flux was 14.8 L/hm2 at 20 bar for AD-SWRO membrane. Assessment of water quality of product water obtained by blending of the two effluents (secondary treated urban wastewater and RO permeate) based on salinity, electrical conductivity, specific ionic toxicity and miscellaneous hazards proved that blending of 20–30% of secondary treated effluent and 80–70% of RO permeate is a good strategy to minimize the unwanted components in treated water for its reuse in agricultural irrigation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The bio-treated urban wastewater represents a more reliable and significant source for reclaimed water as compared to wastewaters coming from agricultural return flows, storm water runoff, and industrial discharges. Since many communities are approaching the limits of their readily available water supplies, water reclamation and reuse has become an attractive option for conserving and extending available water supply [1]. The reclaimed wastewater effluents constitute an alternative source of water for a wide variety of applications, including landscape and ⁎ Corresponding author. Tel.: +90 232 3112290; fax: +90 232 3887776. E-mail address: [email protected] (N. Kabay).
agricultural irrigation, toilet flushing, industrial processing, power plant cooling, wetland habitat creation, restoration and maintenance, and groundwater recharge. Obviously, water quality refers to the characteristics of a water supply that will influence its suitability for a specific use. The chemical constituents in reclaimed water of concern for agricultural irrigation are salinity, sodium, trace elements, excessive chlorine residual and nutrients [2]. Salinity, which is the amount of salt dissolved in water, directly affects plant growth, generally has an adverse effect on agricultural crop performance, and can also affect the soil properties. Consequently, without knowledge of both soil and water salinity and correspondingly appropriate management, long-term irrigated crop productivity can decrease. Most commonly, suitability of irrigation water, with respect to salinity, is assessed on the basis of the ‘electrical conductivity’ (ECw) or
http://dx.doi.org/10.1016/j.desal.2014.07.030 0011-9164/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
2
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Nomenclature BWRO COD ECw ESP IC Jv Lp MF NF R RO RSC SAR SSP SWRO T TC TDS TOC UF
brackish water reverse osmosis chemical oxygen demand electrical conductivity (dS/m) exchangeable sodium percentage inorganic carbon (mg/L) permeate flux (L/m2h) membrane water permeability constant microfiltration nanofiltration rejection (%) reverse osmosis residual sodium carbonate sodium adsorption ratio soluble sodium percentage seawater reverse osmosis temperature (°C) total carbon (mg/L) total dissolved solids (mg/L) total organic carbon ultrafiltration
‘specific conductance’ of a water sample. For managing the salt hazard and other type of hazards for irrigation water, if an alternative water supply is available, but not fully adequate in quantity or quality, a blending of waters may offer an overall improvement in quality and reduce the potential toxicity problem. Blending is especially effective for a sodium toxicity problem since proportions of monovalent (Na+) and divalent (Ca2+) cations absorbed on the soil depend on concentration, with dilution favoring adsorption of the divalent calcium and magnesium ions rather than the monovalent sodium [3]. Often, reclaimed water system design is approached in the same way as conventional potable water system design. However, special issues arise from the water quality, reliability, variation in supply and demand, and other differences between reclaimed water and fresh water [1]. Today, technically proven water reclamation or water purification processes exist to provide water of almost any quality desired, including ultrapure water for some industries and medical uses. Among them, membrane filtration processes are recognized as the most effective technologies for wastewater reuse/reclamation due to their great performances, especially for removal of inorganic and organic micro pollutants [4]. Membranes used for water and wastewater treatment are typically classified as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) in an order of decreasing pore size. As a general rule, MF is suitable for removal of suspended solids, including microorganisms like protozoa and bacteria. UF is required for the removal of viruses and organic macromolecules down to a size of around 20 nm. Smaller organics and multivalent ions can be removed by NF while RO is even suitable for removal of all dissolved species, even monovalent ions [5]. In membrane filtration systems, membrane fouling results in decreasing of permeate flux when operated for conventionally treated municipal effluents. In such case, a significant increase of the feed pressure is required to keep the permeate flow constant. The effluents of municipal wastewaters treated by conventional activated sludge process contain high concentrations of colloidal particles, suspended solids and dissolved organics. Also a high level of biological activity exists in the treated effluents of municipal wastewater. Prior to membrane processes to be applied as advanced treatment process, this effluent is recommended to be pre-filtered to reduce concentration of colloidal and solid particles and to stop the biological activity. This will also help to reduce the membrane fouling during the membrane filtration process [6].
Reverse osmosis (RO) has worldwide acceptance in both water treatment and desalination applications. It is a pressure-driven process whereby a semi-permeable membrane rejects dissolved constituents present in the feed water. This rejection is due to size exclusion, charge exclusion and physicochemical interactions between solute, solvent and membrane [7,8]. The process efficiency depends on operational parameters and on membrane and feed water properties [9]. Although solution-diffusion models are used to describe the flux and rejection of salts and other inorganic species in RO systems, predictions of removal efficiencies for organic constituents are more challenging than calculations for inorganic solutes since physicochemical properties of the solutes and interactions with membrane properties significantly affect the solute mass transfer [10,11]. Most studies on the rejection of organic micropollutants have focused on neutral solutes and in particular pesticides [12,13]. For uncharged organic solutes, the literature mentions two main solute-membrane interactions that may influence solute rejection: i) a steric hindrance (sieving) effect between large solutes and the membrane matrix, and ii) hydrophobic (van der Waals) interactions between hydrophobic solutes and hydrophobic membrane surfaces [14, 15]. Experiments have shown [16] that hydrophilic molecules are better rejected compared to hydrophobic molecules of similar size. This is explained by hydrophobic–hydrophobic interactions in a way that hydrophobic solutes can diffuse into the membrane matrix more easily by the formation of H-bonds, and consequently diffuse to the permeate side. Hydrophobic solutes are thus transported to the permeate side of the membrane more easily, explaining the lower rejection values. In this work, performances of two different RO membranes in rejection of various species in secondary treated urban wastewater were investigated. Furthermore, secondary treated urban effluent and RO product water were blended in different ratios. Since irrigation water quality has a huge impact on soil and crop health, the quality of the effluent resulting from this blending was analyzed and compared to irrigation water standards to check its reusability as irrigation water. To evaluate the reusability of mixed effluent as agricultural irrigation water, salinity and reduced water infiltration, toxicity, or the effects related to a group of miscellaneous water constituents were assessed. Salinity was referred to electrical conductivity and water infiltration problems were referred to SAR (sodium adsorption ratio) with the respect to electrical conductivity (ECw). The sodium hazard was assessed based on ECw, SAR, RSC (residual sodium carbonate), SSP (soluble sodium percentage) and ESP (exchangeable sodium percentage). Other toxicity effects or miscellaneous water constituents were evaluated based on ion contents such as sodium, chloride, and nitrogen nitrate and bicarbonate. 2. Experimentals 2.1. Equipments A cross-flow flat-sheet membrane test unit (SEPA CF-II, GE) was used for membrane tests. The flow sheet of the membrane filtration system was shown in Fig. 1. 2.2. Membranes In this study, two different GE-Osmonics RO membranes with membrane effective area of 140 cm2 were used. One of them, AK-BWRO membrane is a low pressure membrane that is selected when a high rejection and low operating pressure are desired. The seawater RO membrane AD-SWRO is characterized by a good NaCl rejection. This good rejection of NaCl was achieved with AD-SWRO membrane in 500 mg/L NaCl solution at 793 kPa operating pressure, 25 °C, pH 7.5 and 15% recovery [17]. The characteristics of the membranes were summarized in Table 1.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
3
COD, phosphate-P, nitrate-N, nitrite-N, ammonium-N, color and silica were measured with a colorimeter (Spectroquant Nova 60, Merck Model). Analyses methods of COD, phosphate-P, nitrate-N, nitrite-N, ammonium-N, color and silica are analogous to ISO 15705, ISO 6878, DIN 38405-9, EPA 354.1, EPA 350.1, APHA 2120B and APHA 4500-Si E standard methods, respectively. Feed characteristics were listed in Table 2. 2.4. Methods
Fig. 1. The flow sheet of the membrane filtration test system.
2.3. Water analyses The secondary treated urban wastewater was obtained from Municipal Wastewater Treatment Plant, Izmir, Turkey in which the advanced biological treatment is applied as the wastewater treatment process. Wastewater Treatment Plant, İzmir with its capacity of 603,000 m3/ day consists of grill, sand traps and pre-treatment structures of parshall flume with 12 pieces of primary clarifiers which have a diameter of 40 m, 6 bio-phosphorus tanks with a capacity of 8850 m3 for each tank [18]. The treatment process in the plant focuses on phosphorus and nitrogen removal to get a biologically better quality effluent. The bio-treated wastewater from the plant is discharged to the sea via a 2.5 km open canal of 8 m in width and 2 m in height. On the other hand, the plant produces an average of 600 tons/day of sludge that is stocked in the stock area built at the site of the plant [18]. For the water quality analyses of the feed and the permeate samples, TDS, conductivity and salinity measurements were performed by a portable Mettler Toledo type conductivity meter. The pH was measured by a portable digital pH meter (WTW pH 315i/SET). Bicarbonate was determined by titration method (APHA 2310B method). The analyses of chloride and sulfate ions with a method analogous to APHA 4110 were carried out using ion chromatography equipment (Shimadzu IC 10 Ai Model). The TOC contents were measured by a TOC analyzer (Shimadzu TOC-VCPH Model). The method used for TOC is analogous to APHA 5310B. The concentrations of Na, K, Ca and Mg ions were measured by an Atomic Absorption Spectrophotometer (Varian 10 Plus Model) with respect to APHA 3111B method. The turbidity measurement (with APHA 2130B method) was performed with a portable turbidimeter (Micro TPI Field Portable Turbidimeter). All other parameters such as
Table 1 Characteristics of RO membranes used [17]. Membrane type (designation)
AK-BWRO
AD-SWRO
Manufacturer Material Maximum operating pressure (bar) Maximum temperature (°C) Operating pH range Minimum NaCl rejection (%)b,c MWCO Membrane permeability (L/m2 h bar)d
GE Osmonics PATFCa 28 50 4.0–11.0 98.0 Dense 6.16
GE Osmonics PATFCa 83 50 4.0–11.0 99.2 Dense 0.85
a
Polyamide thin film composite. Average salt rejection after a 24 hour operation. Testing conditions: 500 mg/L NaCl solution at 793 kPa operating pressure, 25 °C, pH 7.5 and 15% recovery. d Tested in our laboratory with (Milli-Q®) pure water after 24 h of conditioning in pure water. b c
Membrane permeability (Lp) is defined as the amount of permeate transported through the membrane unit area per unit time by unit driving force gradient. Membrane water permeability was measured by using laboratory-grade (Milli-Q®) pure water assuming that the osmotic pressure is equal to zero. To get permeability values for each membrane, an average of collected data at different pressures was calculated. To investigate the performances of AK-BWRO and AD-SWRO membranes in treating bio-treated urban effluent, these membranes were tested at 10 bar of applied pressure during 6 h of operation period. However, for AD-SWRO membrane, operation time was set to 8 h as it had a lower flux at 10 bar than AK-BWRO membrane. The operation time was extended to 8 h for AD-SWRO to be able to get sample quantity needed for analysis. AD-SWRO was also tested at 20 and permeate water flux was seen to be four times more than that of at 10 bar. Before set-up of the experiment, membranes were soaked in the ultrapure water for 24 h for conditioning. For AK-BWRO membrane, the permeate samples were collected after each 30 min in the initial 2 hour period and after each 2 h for the last 4 hour period. Sampling for AD-SWRO membrane was made each 2 h. During sampling, the permeate flow rate was also measured. The flow rate of the concentrate stream was maintained constant as 96 L/h during the experiment. Permeate and concentrate streams were circulated back to the feed tank. 2.5. Calculations Rejection (R) performance and permeate flux (Jv) of the different membranes were derived from the following equations:
Rð%Þ ¼
Cp 2 100Jv L=hm ¼ V=S t 1− Co
Table 2 Feed characteristics. Parameters
Value (min–max)
TDS (mg/L) ECw (dS/m) T (°C) pH Salinity (psu) Turbidity (NTU) Si (mg/L) COD (mg/L) Color (Hazen) TC (mg/L) IC (mg/L) TOC (mg/L) Na+ (mg/L) Ca2+ (mg/L) K+ (mg/L) Mg2+ (mg/L) NH4-N (mg/L) HCO− 3 (mg/L) SO2− 4 (mg/L) Cl−(mg/L) PO4-P (mg/L) NO3-N (mg/L) NO2-N (mg/L)
3110–3448 6.23–6.89 23.3–24.8 8.00–8.34 3.49–3.80 0.19–0.39 12.5–13.8 30.5–34.0 21.9–23.3 89.4–91.7 79.0–80.1 10.2–13.7 1052–1107 219–226 96.8–113 148–156 0.11–0.14 426–443 261–315 1834–2095 2.28–234 8.65–10.7 0.21–0.26
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
4
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Fig. 2. Permeate flux vs. time plots for the RO membranes.
where Cp, Co, V, S, and t are concentration in the permeate, concentration in the feed, volume of the permeate, membrane area, and time, respectively. The membrane water permeability (Lp) which depends directly on the membrane structure and is derived from the following equation: Lp ¼
Jv ΔP−Δπ
where Jv is permeate flux (L/m2h), Δ Pis differential pressure applied across the membrane (bar), Δ πis the osmotic pressure difference between feed and permeate streams (bar). The calculations of SAR, RSC, SSP and ESP were achieved using the following equations: þ Na SAR ¼ shffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi i h iffi 2þ 2þ þ Mg Ca
ESP ¼
2− CO3
i
2
i h i h − 2þ 2þ þ ½HCO3 − Ca þ Mg ! þ Na
SSP ¼ 100 Ca2þ þ Mg 2þ þ ½K þ þ ½Naþ
RSC ¼
h
100ð−0:0126 þ 0:01475 SARÞ : 1 þ ð−0:0126 þ 0:01475 SARÞ
Note that all concentrations of cations and anions used in above equations are expressed in milliequivalent per liter (meq/L).
Fig. 3. Conductivity rejection vs. time plots for the RO membranes.
Fig. 4. Salinity rejection vs. time plots for the RO membranes.
3. Results and discussion Experiments were carried out by using bio-treated urban wastewater at 10 bar for AK-BWRO and the AD-SWRO membranes, and also at 20 bar for only AD-SWRO membrane. For membrane water permeability test, laboratory-grade (Milli-Q®) pure water was used as feed assuming that the osmotic pressure is zero. According toTable 1, pure water permeability was found quite different. This shows that these polyamide RO membranes have different structures. Although AKBWRO membrane is dense membrane, it tends to fall in nanofiltration range. AD-SWRO membrane is, therefore, denser than AK-BWRO membrane. Fig. 2 shows the permeate flux versus time plots for both membranes. The flux of RO product water (RO permeate) from secondary bio-treated urban effluent (RO feed) was measured and average values of 38 L/hm2, 5 L/hm2 and 14.8 L/hm2 were achieved by AK-SWRO and AD-SWRO membranes at 10 bar, and by AD-SWRO at 20 bar, respectively. As expected from their water permeability values, the AK-BWRO membrane with high pure water permeability value (Table 1) showed a high performance in permeate water flux. The effect of pressure on AD-SWRO membrane for permeate flux was also apparent. Conductivity rejections were good enough for both membranes with an average rejection of 94.6%, 98.4% and 99.3% for AK-BWRO, AD-SWRO membranes at 10 bar and for AD-SWRO membrane at 20 bar, respectively (Fig. 3). In spite of a pressure increase, there was no remarkable difference in the conductivity rejection either at 10 or 20 bar for AD-SWRO membrane. These RO membranes showed good conductivity rejections because of their high rejection properties (Table 1). Near neutral pH, thin film composite RO membranes are negatively charged due to the
Fig. 5. COD rejection vs. time plots for the RO membranes.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Fig. 6. Color rejection vs. time plots for the RO membranes.
Fig. 7. TOC rejection vs. time plots for the RO membranes.
dissociation of acidic functional groups on the membrane surface and adsorption of other ions on the membrane surface. The presence of negative charges on the membrane surface enhances solute rejection by electrostatic repulsion of co-ions according to Donnan exclusion mechanism [19]. Zeta potentials of AK-BWRO and AD-SWRO membranes are negative in solution of pH above 6 [20,21]. However, when pH decreases, the zeta potentials become positive through the protonation of amine groups. During the experiment, both permeate side and feed side of the membrane had a pH above 6 which means that the membrane
5
surface maintains the presence of negative charges. The negative charges repulse the anions resulting in high rejections of anions. At the same time, the rejection of cations is also high due the maintenance of electroneutrality requirement in solution. Consequently, since the conductivity of a solution is directly proportional to the concentrations of cations and anions, a high conductivity rejection is due to high rejections of these ions. The difference in rejection observed between AK-BWRO and ADSWRO membranes is attributed to their difference in properties such us charge density, surface roughness, hydrophilic/hydrophobic characters and contact angles. Contact angle is a measure of hydrophilicity of a surface. The lower the contact angle, the more hydrophilic is the surface. AD-SWRO membrane is more hydrophilic with a contact angle of below 40° [21] whereas AK-BWRO membrane is more hydrophobic with a contact angle value of 64.8° [22]. The salinity rejection was found to be 95.2% for AK-BWRO membrane, 98.3% for AD-SWRO membrane at 10 bar and 99.2% for ADSWRO membrane at 20 bar (Fig. 4). Both RO membranes revealed a high salinity rejection. The salinity can be referred to electrical conductivity. Then, the reasons discussed above favor to high rejection of conductivity stand for high salinity rejection as well. In addition to size exclusion mechanism, such behavior between charged solute and charged membranes resulted in a high rejection of salinity and conductivity in RO membrane applications. The results depicted in Fig. 5 reveal that COD rejections achieved by all membranes were similar with an average rejection of 84%. Kosutic and Kunst [23] characterized the pores of RO membranes with diameters varying between 0.22 and 0.44 nm. They reported that a membrane with the smallest pore size will not always have the highest solute rejection, especially for low molecular weight non-charged organics. The moderate rejection of COD for both RO membranes reflects the presence of these non-charged organics with low molecular weight. Low molecular weight non-charged organics result from the bio-degradation of organic matters during biological activities. Since the feed water for RO filtration used in this study is bio-treated urban wastewater, the presence of such organic compounds in the effluent is normal. According to Fig. 6, the color of the effluent was removed with an average rejection of 91.3% by the AK-BWRO membrane. The respective values were 86.6% and 90.1% for AD-SWRO membrane at 10 and 20 bar, respectively. The performances in color rejection of two RO membranes are considered to be sufficient. The RO membranes tested in this work were found to be less effective in TOC rejection as shown in Fig. 7. In the first hours of the experiment, the TOC rejection was low for each case, but the rejection increased and reached a steady state. The average TOC rejections after 4 h of operation were 76.4% and 69.7% for AK-BWRO and AD-SWRO membranes, respectively at 10 bar and 84.5% for AD-SWRO membrane at 20 bar. The rejections of TOC and COD were moderate in this study. In the literature, it was reported that the existence of Ca2+ ions in the feed water lowered the removal of organic micro-pollutants by NF/RO
Table 3 Water quality obtained by AK-BWRO membrane at 10 bar using various blending ratios of RO feed and RO permeate. Parameters
AK-BWRO membrane
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.89 0.10 0.11 0.13 2.85 0.01 0.35 0.19 0.34 8.97 0,14 89.6 10.6
7.18 1.22 1.31 0.40 8.15 0.64 1.01 0.24 0.93 6.38 −1.52 71.0 7.46
11.5 2.34 2.51 0.66 13.4 1.27 1.68 0.30 1.52 7.36 −3.18 67.5 8.66
15.7 3.46 3.71 0.93 18.7 1.91 2.34 0.36 2.10 8.31 −4.84 66.0 9.81
20.0 4.58 4.92 1.20 24.1 2.54 3.00 0.42 2.69 9.19 −6.49 65.2 10.8
24.3 5.70 6.12 1.47 29.4 3.17 3.67 0.48 3.28 10.0 −8.15 64.7 11.8
28.6 6.82 7.32 1.74 34.7 3.80 4.33 0.53 3.87 10.8 −9.81 64.1 12.6
32.9 7.94 8.52 2.01 40.0 4.44 4.99 0.59 4.46 11.5 −11.5 64.0 13.4
37.1 9.06 9.73 2.28 45.3 5.07 5.66 0.65 5.05 12.1 −13.1 63.8 14.1
41.4 10.2 10.9 2.55 50.6 5.70 6.32 0.71 5.64 12.8 −14.8 63.7 14.8
45.7 11.3 12.1 2.81 55.9 6.33 6.98 0.76 6.23 13.4 −16.4 63.5 15.4
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3 (meq/L) NO3-N (meq/L) EC (dS/m) SAR RSC SSP ESP
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
6
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Table 4 Water quality obtained by AD-SWRO membrane at 10 bar using various blending ratios of RO feed and RO permeate. Parameters
AD-SWRO membrane
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.80 0.06 0.09 0.09 0.87 0.01 0.35 0.03 0.34 2.97 0.20 77.6 2.99
7.70 1.72 1.97 0.50 9.59 0.99 1.39 0.13 1.30 5.67 −2.34 64.8 6.56
9.99 2.28 2.59 0.64 12.5 1.32 1.73 0.17 1.62 6.41 −3.19 64.5 7.49
14.6 3.39 3.85 0.91 18.3 1.98 2.43 0.23 2.25 7.67 −4.89 64.2 9.05
19.2 4.50 5.10 1.18 24.1 2.63 3.12 0.30 2.89 8.76 −6.59 64.0 10.3
23.8 5.60 6.35 1.46 29.9 3.29 3.81 0.36 3.53 9.73 −8.29 63.9 11.5
28.4 6.71 7.61 1.74 35.8 3.94 4.50 0.43 4.17 10.6 −9.99 63.9 12.5
33.0 7.82 8.86 2.01 41.6 4.60 5.19 0.49 4.81 11.4 −11.7 63.8 13.4
37.6 8.93 10.1 2.29 47.4 5.25 5.88 0.56 5.45 12.2 −13.4 63.8 14.2
42.2 10.0 11.4 2.56 53.2 5.91 6.57 0.63 6.09 12.9 −15.1 63.8 14.9
46.8 11.2 12.6 2.84 59.0 6.56 7.26 0.69 6.73 13.6 −16.8 63.7 15.6
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3(meq/L) NO3-N(meq/L) EC (dS/m) SAR RSC SSP ESP
membranes [13]. Therefore, the moderate removal of TOC and COD by RO membranes in our study is explained by the presence of Ca2 + in the feed. In addition, non-charged organics with low molecular weight resulting from biological degradation of macro-organics in municipal wastewater could be another reason for getting such result.
3.1. Product water quality evaluation Tables 3, 4 and 5 show the quality of product waters obtained by RO membranes and the results of blending of secondary treated effluent and RO product water qualities at various ratios. According to Table 4, AD-SWRO membrane gives the best water quality compared to AKBWRO membrane (Table 3) at the same pressure of 10 bar. Increasing applied pressure to 20 bar for AD-SWRO results in increasing of product water quality (Table 5) and quantity. Based on evaluation of salinity, infiltration, toxicity and miscellaneous hazards for the suitability of RO feed (secondary treated effluent) and permeate water (RO product water), neither secondary treated effluent nor permeate water is suitable for agricultural irrigation. Secondary treated effluent is unsuitable because of its high salinity measured as electrical conductivity (ECw) and its specific ion toxicities compared to irrigation water guidelines in Table 6. The RO permeate is also unsuitable because of the infiltration problem caused by unbalanced removal of the Na+, Ca2 + and Mg2 + which impact on the SAR values. The blending of 20–30% of secondary bio-treated effluent with 80–70% of RO permeate water gives a SAR value of 7.36–8.31 with an ECw varying from 1.52 to 2.10 dS/m for AKBWRO membrane (Table 3). In this case, the infiltration hazard is resolved since the guideline for a good water infiltration is ECw N 1.9 dS/m for a SAR range of 6–12. This blending ratio results in a SAR value of
6.41–7.67 with an ECw value of 1.62–2.25 dS/m for AD-SWRO membrane at 10 bar (Table 4). The SAR and ECwvalues are 6.39–7.75 and 1.42–2.10 for AD-SWRO at 20 bar (Table 5). Thus, for both membranes, blending from 20% to 30% of bio-treated effluent (RO feed) with product water (RO permeate) between 80 and70% results in good water quality effluent suitable for agricultural irrigation. The water quality assessment based on SAR, SSP, ESP and Na+ concentration in the above suggested blending ratio results in reduction of sodium hazard and specific ionic toxicity and miscellaneous hazards (Table 3–6). The sodium hazard related to RSC is completely resolved by this blending strategy. RSC values become negative which is required for agricultural irrigation water. The positive values of RSC remove Ca2+ ions from the soil causing increase of SAR values.
4. Conclusions The results from this study show that management of conventionally bio-treated wastewater and its RO effluent could be helpful to produce reliable and significant source of reusable water. The product water quality assessment revealed that it is suitable for agricultural irrigation when blended with secondary treated urban effluent. Management of both effluents consisted in finding in which ratio they can be blend to meet specific water reuse guidelines. The optimum blending ratio regardless of soil properties was found to be 20–30% of secondary treated urban effluent with 80–70% of its RO product water for agriculture irrigation. The new effluent which results from this bending ratio suggested in this work is, however, susceptible to vary since the crop productivity depends on soil and water quality. Then, knowledge of soil properties is required to specify at which ratio blending can be
Table 5 Water quality obtained by AD-SWRO membrane at 20 bar using various blending ratios of RO feed and RO permeate. Parameters
AD-SWRO membrane (20 bar)
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.33 0.01 0.02 0.01 0.02 0.01 0.23 0.01 0.05 2.44 0.20 82.3 2.26
5.12 1.11 1.31 0.66 1.31 0.66 0.94 0.08 0.73 4.65 −1.48 65.2 5.25
9.89 2.20 2.59 1.32 2.59 1.32 1.64 0.16 1.42 6.39 −3.15 64.7 7.47
14.7 3.29 3.88 1.97 3.88 1.97 2.34 0.23 2.10 7.75 −4.83 64.5 9.14
19.5 4.39 5.16 2.63 5.16 2.63 3.05 0.30 2.79 8.90 −6.50 64.5 10.5
24.2 5.48 6.45 3.28 6.45 3.28 3.75 0.37 3.47 9.92 −8.18 64.4 11.7
29.0 6.58 7.73 3.93 7.73 3.93 4.46 0.45 4.15 10.8 −9.85 64.4 12.7
33.8 7.67 9.02 4.59 9.02 4.59 5.16 0.52 4.84 11.7 −11.5 64.4 13.7
38.6 8.76 10.3 5.24 10.3 5.24 5.86 0.59 5.52 12.5 −13.2 64.3 14.5
43.4 9.86 11.6 5.90 11.6 5.90 6.57 0.66 6.21 13.2 −14.9 64.3 15.3
48.1 11.0 12.9 6.55 12.9 6.55 7.27 0.73 6.89 13.9 −16.6 64.3 16.0
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3 (meq/L) NO3-N (meq/L) EC (dS/m) SAR RSC SSP ESP
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
7
Table 6 Guidelines for interpretations of irrigation water quality [3]. Potential irrigation problem
Units
Salinity(affects crop water availability) ECw TDS
Slight to moderate
Severe
b0.7 b450
0.7–3.0 450–2000
N3.0 N2000
N0.7 N1.2 N1.9 N2.9 N5.0
0.7–0.2 1.2–0.3 1.9–0.5 2.9–1.3 5.0–2.9
b0.2 b0.3 b0.5 b1.3 b2.9
SAR me/L
b3 b3
3–9 N3
N9
me/L me/L
b4 b3
4–10 N3
N10
mg/L me/L
b5 b1.5
5–30 1.5–8.5
N30 mN8.5
dS/m mg/L
Infiltration (affects infiltration rate of water into the soil. Evaluate using ECw and SAR together) SAR =0–3 ECw = =3–6 = =6–12 = =12–20 = =20–40 = Specific ion toxicity (affects sensitive crops) Sodium (Na) Surface irrigation Sprinkler irrigation Chloride (Cl) Surface irrigation Sprinkler irrigation Miscellaneous effects (affects susceptible crops) Nitrogen (NO3-N) Bicarbonate (HCO3) (overhead sprinkling only) Other paramers for sodium toxicity RSC [24] SSP [25] ESP [26] pH
done to give appropriate management for long-term irrigation for a given site. Salinity and reduced water infiltration, toxicity, or the effects related to a group of miscellaneous water constituent hazards were minimized or completely removed by this management strategy for both unsuitable effluents (secondary treated urban effluent and its RO product effluent) in agricultural irrigation. Although both membranes exhibited high performance in pollutant rejection, effluent from AKBWRO membrane is suggested to be more suitable than effluent from AD-SWRO membrane since AK-BWRO membrane gives good water quality with higher water recovery (regarding higher permeate flux) at a low applied pressure. Acknowledgments This work was partly supported by Ege University Scientific Research Project (EU-2011-FEN-089). We acknowledge Izmir Metropolitan Municipality, Directorate of IZSU for giving us a sample of biotreated wastewater from Çiğli Grand Canal Biological Treatment Plant. We thank M. Akçay for AAS analyses and G.Serin for TOC measurements. References [1] T. Asano, F.L. Burton, H.L. Leverenz, R. Tsuchihashi, G. Tchobanoglous, Water Reuse, Issues, Technologies, and Applications, McGraw Hill, New York, 2007. [2] U.S. Environmental Protection Agency, Guidelines for Water Reuse, EPA/625/R-04/ 108, Washington, DC, 2004. [3] R.S. Ayers, D.W. Westcot, Water quality for agriculture, FAO Irrigation and Drainage Paper 29, FAO, Rome, 1985. [4] Jarusutthirak, G. Amy, Membrane filtration of wastewater effluents for reuse: effluent organic matter rejection and fouling, Water Sci. Technol. 43 (2001) 225–232. [5] T. Wintgens, T. Melin, A. Schafter, S. Khan, M. Muston, D. Bixio, C. Thoeye, The role of membrane processes in municipal wastewater reclamation and reuse, Desalination 178 (2005) 1–11. [6] M. Wilf, S. Alt, Application of low fouling RO membrane elements for reclamation of municipal wastewater, Desalination 132 (2000) 11–19 (TA). [7] J. Radjenovic, M. Petrovic, F. Venturac, D. Barcelo, Rejection of pharmaceuticals in nanofiltration and reverse osmosis membrane drinking water treatment, Water Res. 42 (2008) 3601–3610. [8] C. Bellona, J. Drewes, The role of membrane surface charge and solute physicochemical properties in the rejection of organic acids by NF membranes, J. Membr. Sci. 249 (2005) 227–234.
Degree of restriction on use None
b0 0–1 b60 60–80 2–10 10–40 Normal range 6.5–8.4
N1 N80 N40
[9] L. Malaeb, M.A. George, Reverse osmosis technology for water treatment: state of the art review, Desalination 267 (2011) 1–8. [10] B. Van der Bruggen, C. Vandecasteele, Modeling of the retention of uncharged molecules with nanofiltration, Water Res. 36 (2002) 1360–1368. [11] M.E. Williams, J.A. Hestekin, C.N. Smothers, D. Bhattacharyya, Separation of organic pollutants by reverse osmosis and nanofiltration membranes: mathematical models and experimental verification, Ind. Eng. Chem. Res. 38 (1999) 3683–3695. [12] Y. Kiso, A. Mizuno, R.A.A. Othman, Y.J. Jung, A. Kumano, A. Ariji, Rejection properties of pesticides with a hollow fiber NF membrane (HNF-1), Desalination 143 (2002) 147–157. [13] K.V. Plakas, A.J. Karabelas, T. Wintgens, T. Melin, A study of selected herbicides retention by nanofiltration membranes — The role of organic fouling, J. Membr. Sci. 284 (2006) 291–300. [14] Y. Yoon, P. Westerhoff, S.A. Snyder, E.C. Wert, Nanofiltration and ultrafiltration of endocrine disrupting compounds, pharmaceuticals and personal care products, J. Membr. Sci. 270 (2006) 88–100. [15] L.D. Nghiem, S. Hawkes, Effects of membrane fouling on the nanofiltration of pharmaceutically active compounds (PhACs): mechanisms and role of membrane pore size, Sep. Purif. Technol. 57 (2007) 176–184. [16] L. Braeken, R. Ramaekers, Y. Zhang, G. Maes, B. Van der Bruggen, C. Vandecasteele, Influence of hydrophobicity on retention in nanofiltration of aqueous solutions containing organic compounds, J. Membr. Sci. 252 (2005) 195–203. [17] GE Water & Process Technologies, GE Osmonis Desal Membranes, http://www. lenntech.com/products/membrane/osmonics/osmonics.htm (date of access: on 12 January 2013). [18] İZSU, http://www.izsu.gov.tr (date of access: on 02 July 2014). [19] A.R.D. Verliefde, Rejection of Organic Micropollutants by High Pressure Membranes (NF/RO), (PhD Thesis) Water Management Academic Press, Netherlands, 2008. [20] T. Hoang, G. Stevens, S. Kentish, The effect of feed pH on the performance of a reverse osmosis membrane, Desalination 261 (2010) 99–103. [21] A. Widjaya, T. Hoang, Geoff W. Stevens, Sandra E. Kentish, A comparison of commercial reverse osmosis membrane characteristics and performance under alginate fouling conditions, Sep. Purif. Technol. 89 (2012) 270–281. [22] O. Akin, F. Temelli, Probing the hydrophobicity of commercial reverse osmosis membranes produced by interfacial polymerization using contact angle, XPS, FTIR, FE-SEM and AFM, Desalination 278 (2011) 387–396. [23] K. Kosutic, B. Kunst, Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities, Desalination 142 (2002) 47–56. [24] K.E. Williams, T.W. Ley, Tree Fruit Irrigation: A Comprehensive Manual of Deciduous Tree Fruit Irrigation Needs, Good Fruit Grower Publishing (Washington State Fruit Commission), Yakima, WA, 1994. [25] D.K. Todd, Groundwater Hydrology, John Wiley & Sons, Inc., 1960 [26] D.W. James, R.J. Hanks, J.H. Jurinak, Modern Irrigated Soils, John Wiley & Sons, NY, 1982.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
Contents lists available at ScienceDirect
Desalination journal homepage: www.elsevier.com/locate/desal
Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation Samuel Bunani a,d, Eren Yörükoğlu a, Ümran Yüksel a, Nalan Kabay b,⁎, Mithat Yüksel b, Gökhan Sert c a
Ege University, Faculty of Science, Department of Chemistry, Izmir, Turkey Ege University, Faculty of Engineering, Department of Chemical Engineering, Izmir, Turkey Ege University, Faculty of Fisheries, Izmir, Turkey d University of Burundi, Faculty of Science, Department of Chemistry, Bujumbura, Burundi b c
H I G H L I G H T S • • • •
Treatment of bio-treated urban wastewater by RO membranes Application of BWRO and SWRO membranes for wastewater reuse Blending of secondary effluent and RO permeate to obey the irrigation requirements. BWRO membrane produces high recovery and good water quality.
a r t i c l e
i n f o
Article history: Received 20 April 2014 Received in revised form 16 July 2014 Accepted 23 July 2014 Available online xxxx Keywords: Agriculture Irrigation water Municipal wastewater Reverse osmosis Water reuse
a b s t r a c t Secondary treated urban wastewater was further polished by reverse osmosis (RO) membranes and the water quality of RO permeates was assessed for their utilizations in agricultural irrigation. The performances of brackish water reverse osmosis (AK-BWRO) and seawater reverse osmosis (AD-SWRO) membranes were investigated at 10 bar as applied pressure. The AD-SWRO membrane was tested also at 20 bar. Conductivity, salinity, chemical oxygen demand (COD), total organic carbon (TOC) and color were rejected by AK-BWRO membrane with average values of 94.6%, 95.2%, 85.8%, 76.4% and 91.3%, respectively, whereas the same contaminants were rejected with average values of 98.3%, 98.3%, 84.6%, 69.7% and 86.6%, respectively with AD-SWRO membrane. Except for TOC, AD-SWRO membrane showed similar rejections at 10 bar and at 20 bar of applied pressures. Although their rejection efficiencies were similar, AK-BWRO and AD-SWRO membranes revealed differences in their permeate flux which is 38.0 L/hm2 for AK-BWRO membrane and 3.81 L/hm2 for AD-SWRO membrane. An average value of permeate flux was 14.8 L/hm2 at 20 bar for AD-SWRO membrane. Assessment of water quality of product water obtained by blending of the two effluents (secondary treated urban wastewater and RO permeate) based on salinity, electrical conductivity, specific ionic toxicity and miscellaneous hazards proved that blending of 20–30% of secondary treated effluent and 80–70% of RO permeate is a good strategy to minimize the unwanted components in treated water for its reuse in agricultural irrigation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction The bio-treated urban wastewater represents a more reliable and significant source for reclaimed water as compared to wastewaters coming from agricultural return flows, storm water runoff, and industrial discharges. Since many communities are approaching the limits of their readily available water supplies, water reclamation and reuse has become an attractive option for conserving and extending available water supply [1]. The reclaimed wastewater effluents constitute an alternative source of water for a wide variety of applications, including landscape and ⁎ Corresponding author. Tel.: +90 232 3112290; fax: +90 232 3887776. E-mail address: [email protected] (N. Kabay).
agricultural irrigation, toilet flushing, industrial processing, power plant cooling, wetland habitat creation, restoration and maintenance, and groundwater recharge. Obviously, water quality refers to the characteristics of a water supply that will influence its suitability for a specific use. The chemical constituents in reclaimed water of concern for agricultural irrigation are salinity, sodium, trace elements, excessive chlorine residual and nutrients [2]. Salinity, which is the amount of salt dissolved in water, directly affects plant growth, generally has an adverse effect on agricultural crop performance, and can also affect the soil properties. Consequently, without knowledge of both soil and water salinity and correspondingly appropriate management, long-term irrigated crop productivity can decrease. Most commonly, suitability of irrigation water, with respect to salinity, is assessed on the basis of the ‘electrical conductivity’ (ECw) or
http://dx.doi.org/10.1016/j.desal.2014.07.030 0011-9164/© 2014 Elsevier B.V. All rights reserved.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
2
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Nomenclature BWRO COD ECw ESP IC Jv Lp MF NF R RO RSC SAR SSP SWRO T TC TDS TOC UF
brackish water reverse osmosis chemical oxygen demand electrical conductivity (dS/m) exchangeable sodium percentage inorganic carbon (mg/L) permeate flux (L/m2h) membrane water permeability constant microfiltration nanofiltration rejection (%) reverse osmosis residual sodium carbonate sodium adsorption ratio soluble sodium percentage seawater reverse osmosis temperature (°C) total carbon (mg/L) total dissolved solids (mg/L) total organic carbon ultrafiltration
‘specific conductance’ of a water sample. For managing the salt hazard and other type of hazards for irrigation water, if an alternative water supply is available, but not fully adequate in quantity or quality, a blending of waters may offer an overall improvement in quality and reduce the potential toxicity problem. Blending is especially effective for a sodium toxicity problem since proportions of monovalent (Na+) and divalent (Ca2+) cations absorbed on the soil depend on concentration, with dilution favoring adsorption of the divalent calcium and magnesium ions rather than the monovalent sodium [3]. Often, reclaimed water system design is approached in the same way as conventional potable water system design. However, special issues arise from the water quality, reliability, variation in supply and demand, and other differences between reclaimed water and fresh water [1]. Today, technically proven water reclamation or water purification processes exist to provide water of almost any quality desired, including ultrapure water for some industries and medical uses. Among them, membrane filtration processes are recognized as the most effective technologies for wastewater reuse/reclamation due to their great performances, especially for removal of inorganic and organic micro pollutants [4]. Membranes used for water and wastewater treatment are typically classified as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) in an order of decreasing pore size. As a general rule, MF is suitable for removal of suspended solids, including microorganisms like protozoa and bacteria. UF is required for the removal of viruses and organic macromolecules down to a size of around 20 nm. Smaller organics and multivalent ions can be removed by NF while RO is even suitable for removal of all dissolved species, even monovalent ions [5]. In membrane filtration systems, membrane fouling results in decreasing of permeate flux when operated for conventionally treated municipal effluents. In such case, a significant increase of the feed pressure is required to keep the permeate flow constant. The effluents of municipal wastewaters treated by conventional activated sludge process contain high concentrations of colloidal particles, suspended solids and dissolved organics. Also a high level of biological activity exists in the treated effluents of municipal wastewater. Prior to membrane processes to be applied as advanced treatment process, this effluent is recommended to be pre-filtered to reduce concentration of colloidal and solid particles and to stop the biological activity. This will also help to reduce the membrane fouling during the membrane filtration process [6].
Reverse osmosis (RO) has worldwide acceptance in both water treatment and desalination applications. It is a pressure-driven process whereby a semi-permeable membrane rejects dissolved constituents present in the feed water. This rejection is due to size exclusion, charge exclusion and physicochemical interactions between solute, solvent and membrane [7,8]. The process efficiency depends on operational parameters and on membrane and feed water properties [9]. Although solution-diffusion models are used to describe the flux and rejection of salts and other inorganic species in RO systems, predictions of removal efficiencies for organic constituents are more challenging than calculations for inorganic solutes since physicochemical properties of the solutes and interactions with membrane properties significantly affect the solute mass transfer [10,11]. Most studies on the rejection of organic micropollutants have focused on neutral solutes and in particular pesticides [12,13]. For uncharged organic solutes, the literature mentions two main solute-membrane interactions that may influence solute rejection: i) a steric hindrance (sieving) effect between large solutes and the membrane matrix, and ii) hydrophobic (van der Waals) interactions between hydrophobic solutes and hydrophobic membrane surfaces [14, 15]. Experiments have shown [16] that hydrophilic molecules are better rejected compared to hydrophobic molecules of similar size. This is explained by hydrophobic–hydrophobic interactions in a way that hydrophobic solutes can diffuse into the membrane matrix more easily by the formation of H-bonds, and consequently diffuse to the permeate side. Hydrophobic solutes are thus transported to the permeate side of the membrane more easily, explaining the lower rejection values. In this work, performances of two different RO membranes in rejection of various species in secondary treated urban wastewater were investigated. Furthermore, secondary treated urban effluent and RO product water were blended in different ratios. Since irrigation water quality has a huge impact on soil and crop health, the quality of the effluent resulting from this blending was analyzed and compared to irrigation water standards to check its reusability as irrigation water. To evaluate the reusability of mixed effluent as agricultural irrigation water, salinity and reduced water infiltration, toxicity, or the effects related to a group of miscellaneous water constituents were assessed. Salinity was referred to electrical conductivity and water infiltration problems were referred to SAR (sodium adsorption ratio) with the respect to electrical conductivity (ECw). The sodium hazard was assessed based on ECw, SAR, RSC (residual sodium carbonate), SSP (soluble sodium percentage) and ESP (exchangeable sodium percentage). Other toxicity effects or miscellaneous water constituents were evaluated based on ion contents such as sodium, chloride, and nitrogen nitrate and bicarbonate. 2. Experimentals 2.1. Equipments A cross-flow flat-sheet membrane test unit (SEPA CF-II, GE) was used for membrane tests. The flow sheet of the membrane filtration system was shown in Fig. 1. 2.2. Membranes In this study, two different GE-Osmonics RO membranes with membrane effective area of 140 cm2 were used. One of them, AK-BWRO membrane is a low pressure membrane that is selected when a high rejection and low operating pressure are desired. The seawater RO membrane AD-SWRO is characterized by a good NaCl rejection. This good rejection of NaCl was achieved with AD-SWRO membrane in 500 mg/L NaCl solution at 793 kPa operating pressure, 25 °C, pH 7.5 and 15% recovery [17]. The characteristics of the membranes were summarized in Table 1.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
3
COD, phosphate-P, nitrate-N, nitrite-N, ammonium-N, color and silica were measured with a colorimeter (Spectroquant Nova 60, Merck Model). Analyses methods of COD, phosphate-P, nitrate-N, nitrite-N, ammonium-N, color and silica are analogous to ISO 15705, ISO 6878, DIN 38405-9, EPA 354.1, EPA 350.1, APHA 2120B and APHA 4500-Si E standard methods, respectively. Feed characteristics were listed in Table 2. 2.4. Methods
Fig. 1. The flow sheet of the membrane filtration test system.
2.3. Water analyses The secondary treated urban wastewater was obtained from Municipal Wastewater Treatment Plant, Izmir, Turkey in which the advanced biological treatment is applied as the wastewater treatment process. Wastewater Treatment Plant, İzmir with its capacity of 603,000 m3/ day consists of grill, sand traps and pre-treatment structures of parshall flume with 12 pieces of primary clarifiers which have a diameter of 40 m, 6 bio-phosphorus tanks with a capacity of 8850 m3 for each tank [18]. The treatment process in the plant focuses on phosphorus and nitrogen removal to get a biologically better quality effluent. The bio-treated wastewater from the plant is discharged to the sea via a 2.5 km open canal of 8 m in width and 2 m in height. On the other hand, the plant produces an average of 600 tons/day of sludge that is stocked in the stock area built at the site of the plant [18]. For the water quality analyses of the feed and the permeate samples, TDS, conductivity and salinity measurements were performed by a portable Mettler Toledo type conductivity meter. The pH was measured by a portable digital pH meter (WTW pH 315i/SET). Bicarbonate was determined by titration method (APHA 2310B method). The analyses of chloride and sulfate ions with a method analogous to APHA 4110 were carried out using ion chromatography equipment (Shimadzu IC 10 Ai Model). The TOC contents were measured by a TOC analyzer (Shimadzu TOC-VCPH Model). The method used for TOC is analogous to APHA 5310B. The concentrations of Na, K, Ca and Mg ions were measured by an Atomic Absorption Spectrophotometer (Varian 10 Plus Model) with respect to APHA 3111B method. The turbidity measurement (with APHA 2130B method) was performed with a portable turbidimeter (Micro TPI Field Portable Turbidimeter). All other parameters such as
Table 1 Characteristics of RO membranes used [17]. Membrane type (designation)
AK-BWRO
AD-SWRO
Manufacturer Material Maximum operating pressure (bar) Maximum temperature (°C) Operating pH range Minimum NaCl rejection (%)b,c MWCO Membrane permeability (L/m2 h bar)d
GE Osmonics PATFCa 28 50 4.0–11.0 98.0 Dense 6.16
GE Osmonics PATFCa 83 50 4.0–11.0 99.2 Dense 0.85
a
Polyamide thin film composite. Average salt rejection after a 24 hour operation. Testing conditions: 500 mg/L NaCl solution at 793 kPa operating pressure, 25 °C, pH 7.5 and 15% recovery. d Tested in our laboratory with (Milli-Q®) pure water after 24 h of conditioning in pure water. b c
Membrane permeability (Lp) is defined as the amount of permeate transported through the membrane unit area per unit time by unit driving force gradient. Membrane water permeability was measured by using laboratory-grade (Milli-Q®) pure water assuming that the osmotic pressure is equal to zero. To get permeability values for each membrane, an average of collected data at different pressures was calculated. To investigate the performances of AK-BWRO and AD-SWRO membranes in treating bio-treated urban effluent, these membranes were tested at 10 bar of applied pressure during 6 h of operation period. However, for AD-SWRO membrane, operation time was set to 8 h as it had a lower flux at 10 bar than AK-BWRO membrane. The operation time was extended to 8 h for AD-SWRO to be able to get sample quantity needed for analysis. AD-SWRO was also tested at 20 and permeate water flux was seen to be four times more than that of at 10 bar. Before set-up of the experiment, membranes were soaked in the ultrapure water for 24 h for conditioning. For AK-BWRO membrane, the permeate samples were collected after each 30 min in the initial 2 hour period and after each 2 h for the last 4 hour period. Sampling for AD-SWRO membrane was made each 2 h. During sampling, the permeate flow rate was also measured. The flow rate of the concentrate stream was maintained constant as 96 L/h during the experiment. Permeate and concentrate streams were circulated back to the feed tank. 2.5. Calculations Rejection (R) performance and permeate flux (Jv) of the different membranes were derived from the following equations:
Rð%Þ ¼
Cp 2 100Jv L=hm ¼ V=S t 1− Co
Table 2 Feed characteristics. Parameters
Value (min–max)
TDS (mg/L) ECw (dS/m) T (°C) pH Salinity (psu) Turbidity (NTU) Si (mg/L) COD (mg/L) Color (Hazen) TC (mg/L) IC (mg/L) TOC (mg/L) Na+ (mg/L) Ca2+ (mg/L) K+ (mg/L) Mg2+ (mg/L) NH4-N (mg/L) HCO− 3 (mg/L) SO2− 4 (mg/L) Cl−(mg/L) PO4-P (mg/L) NO3-N (mg/L) NO2-N (mg/L)
3110–3448 6.23–6.89 23.3–24.8 8.00–8.34 3.49–3.80 0.19–0.39 12.5–13.8 30.5–34.0 21.9–23.3 89.4–91.7 79.0–80.1 10.2–13.7 1052–1107 219–226 96.8–113 148–156 0.11–0.14 426–443 261–315 1834–2095 2.28–234 8.65–10.7 0.21–0.26
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
4
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Fig. 2. Permeate flux vs. time plots for the RO membranes.
where Cp, Co, V, S, and t are concentration in the permeate, concentration in the feed, volume of the permeate, membrane area, and time, respectively. The membrane water permeability (Lp) which depends directly on the membrane structure and is derived from the following equation: Lp ¼
Jv ΔP−Δπ
where Jv is permeate flux (L/m2h), Δ Pis differential pressure applied across the membrane (bar), Δ πis the osmotic pressure difference between feed and permeate streams (bar). The calculations of SAR, RSC, SSP and ESP were achieved using the following equations: þ Na SAR ¼ shffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi i h iffi 2þ 2þ þ Mg Ca
ESP ¼
2− CO3
i
2
i h i h − 2þ 2þ þ ½HCO3 − Ca þ Mg ! þ Na
SSP ¼ 100 Ca2þ þ Mg 2þ þ ½K þ þ ½Naþ
RSC ¼
h
100ð−0:0126 þ 0:01475 SARÞ : 1 þ ð−0:0126 þ 0:01475 SARÞ
Note that all concentrations of cations and anions used in above equations are expressed in milliequivalent per liter (meq/L).
Fig. 3. Conductivity rejection vs. time plots for the RO membranes.
Fig. 4. Salinity rejection vs. time plots for the RO membranes.
3. Results and discussion Experiments were carried out by using bio-treated urban wastewater at 10 bar for AK-BWRO and the AD-SWRO membranes, and also at 20 bar for only AD-SWRO membrane. For membrane water permeability test, laboratory-grade (Milli-Q®) pure water was used as feed assuming that the osmotic pressure is zero. According toTable 1, pure water permeability was found quite different. This shows that these polyamide RO membranes have different structures. Although AKBWRO membrane is dense membrane, it tends to fall in nanofiltration range. AD-SWRO membrane is, therefore, denser than AK-BWRO membrane. Fig. 2 shows the permeate flux versus time plots for both membranes. The flux of RO product water (RO permeate) from secondary bio-treated urban effluent (RO feed) was measured and average values of 38 L/hm2, 5 L/hm2 and 14.8 L/hm2 were achieved by AK-SWRO and AD-SWRO membranes at 10 bar, and by AD-SWRO at 20 bar, respectively. As expected from their water permeability values, the AK-BWRO membrane with high pure water permeability value (Table 1) showed a high performance in permeate water flux. The effect of pressure on AD-SWRO membrane for permeate flux was also apparent. Conductivity rejections were good enough for both membranes with an average rejection of 94.6%, 98.4% and 99.3% for AK-BWRO, AD-SWRO membranes at 10 bar and for AD-SWRO membrane at 20 bar, respectively (Fig. 3). In spite of a pressure increase, there was no remarkable difference in the conductivity rejection either at 10 or 20 bar for AD-SWRO membrane. These RO membranes showed good conductivity rejections because of their high rejection properties (Table 1). Near neutral pH, thin film composite RO membranes are negatively charged due to the
Fig. 5. COD rejection vs. time plots for the RO membranes.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Fig. 6. Color rejection vs. time plots for the RO membranes.
Fig. 7. TOC rejection vs. time plots for the RO membranes.
dissociation of acidic functional groups on the membrane surface and adsorption of other ions on the membrane surface. The presence of negative charges on the membrane surface enhances solute rejection by electrostatic repulsion of co-ions according to Donnan exclusion mechanism [19]. Zeta potentials of AK-BWRO and AD-SWRO membranes are negative in solution of pH above 6 [20,21]. However, when pH decreases, the zeta potentials become positive through the protonation of amine groups. During the experiment, both permeate side and feed side of the membrane had a pH above 6 which means that the membrane
5
surface maintains the presence of negative charges. The negative charges repulse the anions resulting in high rejections of anions. At the same time, the rejection of cations is also high due the maintenance of electroneutrality requirement in solution. Consequently, since the conductivity of a solution is directly proportional to the concentrations of cations and anions, a high conductivity rejection is due to high rejections of these ions. The difference in rejection observed between AK-BWRO and ADSWRO membranes is attributed to their difference in properties such us charge density, surface roughness, hydrophilic/hydrophobic characters and contact angles. Contact angle is a measure of hydrophilicity of a surface. The lower the contact angle, the more hydrophilic is the surface. AD-SWRO membrane is more hydrophilic with a contact angle of below 40° [21] whereas AK-BWRO membrane is more hydrophobic with a contact angle value of 64.8° [22]. The salinity rejection was found to be 95.2% for AK-BWRO membrane, 98.3% for AD-SWRO membrane at 10 bar and 99.2% for ADSWRO membrane at 20 bar (Fig. 4). Both RO membranes revealed a high salinity rejection. The salinity can be referred to electrical conductivity. Then, the reasons discussed above favor to high rejection of conductivity stand for high salinity rejection as well. In addition to size exclusion mechanism, such behavior between charged solute and charged membranes resulted in a high rejection of salinity and conductivity in RO membrane applications. The results depicted in Fig. 5 reveal that COD rejections achieved by all membranes were similar with an average rejection of 84%. Kosutic and Kunst [23] characterized the pores of RO membranes with diameters varying between 0.22 and 0.44 nm. They reported that a membrane with the smallest pore size will not always have the highest solute rejection, especially for low molecular weight non-charged organics. The moderate rejection of COD for both RO membranes reflects the presence of these non-charged organics with low molecular weight. Low molecular weight non-charged organics result from the bio-degradation of organic matters during biological activities. Since the feed water for RO filtration used in this study is bio-treated urban wastewater, the presence of such organic compounds in the effluent is normal. According to Fig. 6, the color of the effluent was removed with an average rejection of 91.3% by the AK-BWRO membrane. The respective values were 86.6% and 90.1% for AD-SWRO membrane at 10 and 20 bar, respectively. The performances in color rejection of two RO membranes are considered to be sufficient. The RO membranes tested in this work were found to be less effective in TOC rejection as shown in Fig. 7. In the first hours of the experiment, the TOC rejection was low for each case, but the rejection increased and reached a steady state. The average TOC rejections after 4 h of operation were 76.4% and 69.7% for AK-BWRO and AD-SWRO membranes, respectively at 10 bar and 84.5% for AD-SWRO membrane at 20 bar. The rejections of TOC and COD were moderate in this study. In the literature, it was reported that the existence of Ca2+ ions in the feed water lowered the removal of organic micro-pollutants by NF/RO
Table 3 Water quality obtained by AK-BWRO membrane at 10 bar using various blending ratios of RO feed and RO permeate. Parameters
AK-BWRO membrane
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.89 0.10 0.11 0.13 2.85 0.01 0.35 0.19 0.34 8.97 0,14 89.6 10.6
7.18 1.22 1.31 0.40 8.15 0.64 1.01 0.24 0.93 6.38 −1.52 71.0 7.46
11.5 2.34 2.51 0.66 13.4 1.27 1.68 0.30 1.52 7.36 −3.18 67.5 8.66
15.7 3.46 3.71 0.93 18.7 1.91 2.34 0.36 2.10 8.31 −4.84 66.0 9.81
20.0 4.58 4.92 1.20 24.1 2.54 3.00 0.42 2.69 9.19 −6.49 65.2 10.8
24.3 5.70 6.12 1.47 29.4 3.17 3.67 0.48 3.28 10.0 −8.15 64.7 11.8
28.6 6.82 7.32 1.74 34.7 3.80 4.33 0.53 3.87 10.8 −9.81 64.1 12.6
32.9 7.94 8.52 2.01 40.0 4.44 4.99 0.59 4.46 11.5 −11.5 64.0 13.4
37.1 9.06 9.73 2.28 45.3 5.07 5.66 0.65 5.05 12.1 −13.1 63.8 14.1
41.4 10.2 10.9 2.55 50.6 5.70 6.32 0.71 5.64 12.8 −14.8 63.7 14.8
45.7 11.3 12.1 2.81 55.9 6.33 6.98 0.76 6.23 13.4 −16.4 63.5 15.4
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3 (meq/L) NO3-N (meq/L) EC (dS/m) SAR RSC SSP ESP
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
6
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
Table 4 Water quality obtained by AD-SWRO membrane at 10 bar using various blending ratios of RO feed and RO permeate. Parameters
AD-SWRO membrane
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.80 0.06 0.09 0.09 0.87 0.01 0.35 0.03 0.34 2.97 0.20 77.6 2.99
7.70 1.72 1.97 0.50 9.59 0.99 1.39 0.13 1.30 5.67 −2.34 64.8 6.56
9.99 2.28 2.59 0.64 12.5 1.32 1.73 0.17 1.62 6.41 −3.19 64.5 7.49
14.6 3.39 3.85 0.91 18.3 1.98 2.43 0.23 2.25 7.67 −4.89 64.2 9.05
19.2 4.50 5.10 1.18 24.1 2.63 3.12 0.30 2.89 8.76 −6.59 64.0 10.3
23.8 5.60 6.35 1.46 29.9 3.29 3.81 0.36 3.53 9.73 −8.29 63.9 11.5
28.4 6.71 7.61 1.74 35.8 3.94 4.50 0.43 4.17 10.6 −9.99 63.9 12.5
33.0 7.82 8.86 2.01 41.6 4.60 5.19 0.49 4.81 11.4 −11.7 63.8 13.4
37.6 8.93 10.1 2.29 47.4 5.25 5.88 0.56 5.45 12.2 −13.4 63.8 14.2
42.2 10.0 11.4 2.56 53.2 5.91 6.57 0.63 6.09 12.9 −15.1 63.8 14.9
46.8 11.2 12.6 2.84 59.0 6.56 7.26 0.69 6.73 13.6 −16.8 63.7 15.6
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3(meq/L) NO3-N(meq/L) EC (dS/m) SAR RSC SSP ESP
membranes [13]. Therefore, the moderate removal of TOC and COD by RO membranes in our study is explained by the presence of Ca2 + in the feed. In addition, non-charged organics with low molecular weight resulting from biological degradation of macro-organics in municipal wastewater could be another reason for getting such result.
3.1. Product water quality evaluation Tables 3, 4 and 5 show the quality of product waters obtained by RO membranes and the results of blending of secondary treated effluent and RO product water qualities at various ratios. According to Table 4, AD-SWRO membrane gives the best water quality compared to AKBWRO membrane (Table 3) at the same pressure of 10 bar. Increasing applied pressure to 20 bar for AD-SWRO results in increasing of product water quality (Table 5) and quantity. Based on evaluation of salinity, infiltration, toxicity and miscellaneous hazards for the suitability of RO feed (secondary treated effluent) and permeate water (RO product water), neither secondary treated effluent nor permeate water is suitable for agricultural irrigation. Secondary treated effluent is unsuitable because of its high salinity measured as electrical conductivity (ECw) and its specific ion toxicities compared to irrigation water guidelines in Table 6. The RO permeate is also unsuitable because of the infiltration problem caused by unbalanced removal of the Na+, Ca2 + and Mg2 + which impact on the SAR values. The blending of 20–30% of secondary bio-treated effluent with 80–70% of RO permeate water gives a SAR value of 7.36–8.31 with an ECw varying from 1.52 to 2.10 dS/m for AKBWRO membrane (Table 3). In this case, the infiltration hazard is resolved since the guideline for a good water infiltration is ECw N 1.9 dS/m for a SAR range of 6–12. This blending ratio results in a SAR value of
6.41–7.67 with an ECw value of 1.62–2.25 dS/m for AD-SWRO membrane at 10 bar (Table 4). The SAR and ECwvalues are 6.39–7.75 and 1.42–2.10 for AD-SWRO at 20 bar (Table 5). Thus, for both membranes, blending from 20% to 30% of bio-treated effluent (RO feed) with product water (RO permeate) between 80 and70% results in good water quality effluent suitable for agricultural irrigation. The water quality assessment based on SAR, SSP, ESP and Na+ concentration in the above suggested blending ratio results in reduction of sodium hazard and specific ionic toxicity and miscellaneous hazards (Table 3–6). The sodium hazard related to RSC is completely resolved by this blending strategy. RSC values become negative which is required for agricultural irrigation water. The positive values of RSC remove Ca2+ ions from the soil causing increase of SAR values.
4. Conclusions The results from this study show that management of conventionally bio-treated wastewater and its RO effluent could be helpful to produce reliable and significant source of reusable water. The product water quality assessment revealed that it is suitable for agricultural irrigation when blended with secondary treated urban effluent. Management of both effluents consisted in finding in which ratio they can be blend to meet specific water reuse guidelines. The optimum blending ratio regardless of soil properties was found to be 20–30% of secondary treated urban effluent with 80–70% of its RO product water for agriculture irrigation. The new effluent which results from this bending ratio suggested in this work is, however, susceptible to vary since the crop productivity depends on soil and water quality. Then, knowledge of soil properties is required to specify at which ratio blending can be
Table 5 Water quality obtained by AD-SWRO membrane at 20 bar using various blending ratios of RO feed and RO permeate. Parameters
AD-SWRO membrane (20 bar)
Portion of feed
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Portion of permeate
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.33 0.01 0.02 0.01 0.02 0.01 0.23 0.01 0.05 2.44 0.20 82.3 2.26
5.12 1.11 1.31 0.66 1.31 0.66 0.94 0.08 0.73 4.65 −1.48 65.2 5.25
9.89 2.20 2.59 1.32 2.59 1.32 1.64 0.16 1.42 6.39 −3.15 64.7 7.47
14.7 3.29 3.88 1.97 3.88 1.97 2.34 0.23 2.10 7.75 −4.83 64.5 9.14
19.5 4.39 5.16 2.63 5.16 2.63 3.05 0.30 2.79 8.90 −6.50 64.5 10.5
24.2 5.48 6.45 3.28 6.45 3.28 3.75 0.37 3.47 9.92 −8.18 64.4 11.7
29.0 6.58 7.73 3.93 7.73 3.93 4.46 0.45 4.15 10.8 −9.85 64.4 12.7
33.8 7.67 9.02 4.59 9.02 4.59 5.16 0.52 4.84 11.7 −11.5 64.4 13.7
38.6 8.76 10.3 5.24 10.3 5.24 5.86 0.59 5.52 12.5 −13.2 64.3 14.5
43.4 9.86 11.6 5.90 11.6 5.90 6.57 0.66 6.21 13.2 −14.9 64.3 15.3
48.1 11.0 12.9 6.55 12.9 6.55 7.27 0.73 6.89 13.9 −16.6 64.3 16.0
Na (meq/L) Ca (meq/L) Mg (meq/L) K (meq/L) Cl (meq/L) SO4 (meq/L) HCO3 (meq/L) NO3-N (meq/L) EC (dS/m) SAR RSC SSP ESP
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030
S. Bunani et al. / Desalination xxx (2014) xxx–xxx
7
Table 6 Guidelines for interpretations of irrigation water quality [3]. Potential irrigation problem
Units
Salinity(affects crop water availability) ECw TDS
Slight to moderate
Severe
b0.7 b450
0.7–3.0 450–2000
N3.0 N2000
N0.7 N1.2 N1.9 N2.9 N5.0
0.7–0.2 1.2–0.3 1.9–0.5 2.9–1.3 5.0–2.9
b0.2 b0.3 b0.5 b1.3 b2.9
SAR me/L
b3 b3
3–9 N3
N9
me/L me/L
b4 b3
4–10 N3
N10
mg/L me/L
b5 b1.5
5–30 1.5–8.5
N30 mN8.5
dS/m mg/L
Infiltration (affects infiltration rate of water into the soil. Evaluate using ECw and SAR together) SAR =0–3 ECw = =3–6 = =6–12 = =12–20 = =20–40 = Specific ion toxicity (affects sensitive crops) Sodium (Na) Surface irrigation Sprinkler irrigation Chloride (Cl) Surface irrigation Sprinkler irrigation Miscellaneous effects (affects susceptible crops) Nitrogen (NO3-N) Bicarbonate (HCO3) (overhead sprinkling only) Other paramers for sodium toxicity RSC [24] SSP [25] ESP [26] pH
done to give appropriate management for long-term irrigation for a given site. Salinity and reduced water infiltration, toxicity, or the effects related to a group of miscellaneous water constituent hazards were minimized or completely removed by this management strategy for both unsuitable effluents (secondary treated urban effluent and its RO product effluent) in agricultural irrigation. Although both membranes exhibited high performance in pollutant rejection, effluent from AKBWRO membrane is suggested to be more suitable than effluent from AD-SWRO membrane since AK-BWRO membrane gives good water quality with higher water recovery (regarding higher permeate flux) at a low applied pressure. Acknowledgments This work was partly supported by Ege University Scientific Research Project (EU-2011-FEN-089). We acknowledge Izmir Metropolitan Municipality, Directorate of IZSU for giving us a sample of biotreated wastewater from Çiğli Grand Canal Biological Treatment Plant. We thank M. Akçay for AAS analyses and G.Serin for TOC measurements. References [1] T. Asano, F.L. Burton, H.L. Leverenz, R. Tsuchihashi, G. Tchobanoglous, Water Reuse, Issues, Technologies, and Applications, McGraw Hill, New York, 2007. [2] U.S. Environmental Protection Agency, Guidelines for Water Reuse, EPA/625/R-04/ 108, Washington, DC, 2004. [3] R.S. Ayers, D.W. Westcot, Water quality for agriculture, FAO Irrigation and Drainage Paper 29, FAO, Rome, 1985. [4] Jarusutthirak, G. Amy, Membrane filtration of wastewater effluents for reuse: effluent organic matter rejection and fouling, Water Sci. Technol. 43 (2001) 225–232. [5] T. Wintgens, T. Melin, A. Schafter, S. Khan, M. Muston, D. Bixio, C. Thoeye, The role of membrane processes in municipal wastewater reclamation and reuse, Desalination 178 (2005) 1–11. [6] M. Wilf, S. Alt, Application of low fouling RO membrane elements for reclamation of municipal wastewater, Desalination 132 (2000) 11–19 (TA). [7] J. Radjenovic, M. Petrovic, F. Venturac, D. Barcelo, Rejection of pharmaceuticals in nanofiltration and reverse osmosis membrane drinking water treatment, Water Res. 42 (2008) 3601–3610. [8] C. Bellona, J. Drewes, The role of membrane surface charge and solute physicochemical properties in the rejection of organic acids by NF membranes, J. Membr. Sci. 249 (2005) 227–234.
Degree of restriction on use None
b0 0–1 b60 60–80 2–10 10–40 Normal range 6.5–8.4
N1 N80 N40
[9] L. Malaeb, M.A. George, Reverse osmosis technology for water treatment: state of the art review, Desalination 267 (2011) 1–8. [10] B. Van der Bruggen, C. Vandecasteele, Modeling of the retention of uncharged molecules with nanofiltration, Water Res. 36 (2002) 1360–1368. [11] M.E. Williams, J.A. Hestekin, C.N. Smothers, D. Bhattacharyya, Separation of organic pollutants by reverse osmosis and nanofiltration membranes: mathematical models and experimental verification, Ind. Eng. Chem. Res. 38 (1999) 3683–3695. [12] Y. Kiso, A. Mizuno, R.A.A. Othman, Y.J. Jung, A. Kumano, A. Ariji, Rejection properties of pesticides with a hollow fiber NF membrane (HNF-1), Desalination 143 (2002) 147–157. [13] K.V. Plakas, A.J. Karabelas, T. Wintgens, T. Melin, A study of selected herbicides retention by nanofiltration membranes — The role of organic fouling, J. Membr. Sci. 284 (2006) 291–300. [14] Y. Yoon, P. Westerhoff, S.A. Snyder, E.C. Wert, Nanofiltration and ultrafiltration of endocrine disrupting compounds, pharmaceuticals and personal care products, J. Membr. Sci. 270 (2006) 88–100. [15] L.D. Nghiem, S. Hawkes, Effects of membrane fouling on the nanofiltration of pharmaceutically active compounds (PhACs): mechanisms and role of membrane pore size, Sep. Purif. Technol. 57 (2007) 176–184. [16] L. Braeken, R. Ramaekers, Y. Zhang, G. Maes, B. Van der Bruggen, C. Vandecasteele, Influence of hydrophobicity on retention in nanofiltration of aqueous solutions containing organic compounds, J. Membr. Sci. 252 (2005) 195–203. [17] GE Water & Process Technologies, GE Osmonis Desal Membranes, http://www. lenntech.com/products/membrane/osmonics/osmonics.htm (date of access: on 12 January 2013). [18] İZSU, http://www.izsu.gov.tr (date of access: on 02 July 2014). [19] A.R.D. Verliefde, Rejection of Organic Micropollutants by High Pressure Membranes (NF/RO), (PhD Thesis) Water Management Academic Press, Netherlands, 2008. [20] T. Hoang, G. Stevens, S. Kentish, The effect of feed pH on the performance of a reverse osmosis membrane, Desalination 261 (2010) 99–103. [21] A. Widjaya, T. Hoang, Geoff W. Stevens, Sandra E. Kentish, A comparison of commercial reverse osmosis membrane characteristics and performance under alginate fouling conditions, Sep. Purif. Technol. 89 (2012) 270–281. [22] O. Akin, F. Temelli, Probing the hydrophobicity of commercial reverse osmosis membranes produced by interfacial polymerization using contact angle, XPS, FTIR, FE-SEM and AFM, Desalination 278 (2011) 387–396. [23] K. Kosutic, B. Kunst, Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities, Desalination 142 (2002) 47–56. [24] K.E. Williams, T.W. Ley, Tree Fruit Irrigation: A Comprehensive Manual of Deciduous Tree Fruit Irrigation Needs, Good Fruit Grower Publishing (Washington State Fruit Commission), Yakima, WA, 1994. [25] D.K. Todd, Groundwater Hydrology, John Wiley & Sons, Inc., 1960 [26] D.W. James, R.J. Hanks, J.H. Jurinak, Modern Irrigated Soils, John Wiley & Sons, NY, 1982.
Please cite this article as: S. Bunani, et al., Application of reverse osmosis for reuse of secondary treated urban wastewater in agricultural irrigation, Desalination (2014), http://dx.doi.org/10.1016/j.desal.2014.07.030