## Abstract

The aim of this study was to evaluate the role of decentralized municipal desalination plants in removal of physical, chemical and microbial parameters from drinking water in Bushehr, Iran and compare the quality of outlet water with guidelines for drinking water. Fifty samples were taken from 10 decentralized municipal desalination plants (five times from every station). The mean values of physical, chemical and microbial parameters in outlet water were electrical conductivity (322.08 μS/cm), turbidity (0.0 NTU), pH (6.84), alkalinity (61.2 mg/L), carbonate (0 mg/L), bicarbonate (61.2 mg/L), total hardness (82.96 mg/L), calcium hardness (73.8 mg/L), magnesium hardness (18.96 mg/L) as CaCO3, calcium (29.52 mg/L), magnesium (4.72 mg/L), residual chlorine (0.37 mg/L), chloride (25.61 mg/L), TDS (161.04 mg/L), iron (0.045), fluoride (0.167 mg/L), nitrate (1.71 mg/L), nitrite (0.0026 mg/L), sulphate (107.17 mg/L), total coliform (0), fecal coliform (0) (MPN/100 mL) and HPC (322.9 CFU/mL). Our results showed that 10% of HPC outlet samples did not comply with the Iranian National Regulation (INR), Environmental Protection Agency (EPA), and World Health Organization (WHO) guidelines. The mean levels of examined parameters in desalination plants' outlets generally complied with the INR, EPA and WHO guidelines. Decentralized municipal desalination plants efficiency in removal of measured parameters were in the range of 18.52 (in the case of nitrite) to 100% (in the case of turbidity).

## INTRODUCTION

Availability of safe and high-quality water has been an objective of human society going back to prehistoric times (Calderon 2000; Mara 2003; Völker et al. 2010; Fard et al. 2015; Raeisi et al. 2017). Water is a fundamental natural resource for the sustainability of life on earth (Binghui et al. 2006; WHO 2011), but when polluted it may become the source of undesirable substances dangerous to human health (Mancini et al. 2005). Access to adequate water and assurance of its safety are the most significant concerns of health authorities (Ozaki & Li 2002; Fahiminia et al. 2014). Throughout the world, especially in the Middle East, the deterioration in quality of available water and water shortages is increasing (Yassin et al. 2006; Almasri 2008). Today, 450 million people in 29 countries suffer from water deficiency (Güler 2007). Physical, chemical and microbial parameters of drinking water may affect its safety and consumers' consent (Ngari et al. 2013). The main requirements for drinking water are that it should be free from pathogenic organisms and contain no compounds that have a harmful effect in the short or long term on human health (WHO 1998). According to the United Nations (UN), about 80% of infant mortality worldwide occurs due to gastrointestinal diseases such as diarrhea (Gasana et al. 2002) and over one-third of deaths in developing countries occur following the drinking of contaminated water (Balbus & Lang 2001; Al-Khatib & Arafat 2009; Nair & Kumar 2013). The most commonly used indicators for microbiological contamination are total coliform (TC) and fecal coliform (FC) (Viessman et al. 2009). Furthermore, the high amounts of some physical and chemical parameters such as hardness, total dissolved solids (TDS), nitrate, nitrite, pH, salinity, chloride and heavy metals in water may introduce some problems for the consumer (Gagliardo et al. 1998; Salehi et al. 2014). Hence, drinking water guidelines have been developed by national and international organizations to define limits for physical, chemical and microbial contents to ensure the required quality (Sobsey & Bartram 2002; Güler & Alpaslan 2009). Therefore, the monitoring of drinking water from source to consumption to meet drinking water guidelines is an important step towards health and safety (Völker et al. 2010). Various factors such as displeasure and concern about drinking water quality owing to the absence of sufficient water treatment facilities, impurity during storage and distribution, and insufficient or incorrect understanding on the part of consumers about the quality of distributed water can influence community attitudes in such a way as to cause them to substitute or change their drinking water sources (Beverage Marketing Corporation of New York 2006). Decentralized municipal desalination plants play an important role in providing healthy drinking water based on qualitative standards. The increasing trend of water consumption and decrease of natural sources of fresh water make this role even more important. Since the control of drinking water is of great importance in terms of health, this research was carried out to determine the role of decentralized municipal desalination plants in the removal of physical, chemical and microbial parameters of drinking water in Bushehr, Iran; it also sought to compare the quality of outlet water from these plants with Iranian National Regulation (INR), US Environmental Protection Agency (EPA) and World Health Organization (WHO) guidelines for drinking water. Finally, we calculated daily intakes of different anions and cations.

## MATERIALS AND METHODS

### Drinking water source and study area

The Kosar dam is located at a distance of 60 km northwest of Dogonbadan, in the city of Gachsaran in Kohgiluyeh and Boyer-Ahmad Province, which was built on the Kheirabad river. The physicochemical parameter values of the Kosar dam are shown in Table 1. The Bushehr regional water authority uses this dam's water as the main source of drinking water in Bushehr city.

Table 1

Values for physicochemical parameters of Kosar dam

ParameterUnitValue
EC μS/cm 1366
pH – 7.8
Turbidity NTU 0.93
Residual-chlorine mg/L
TDS mg/L 1093
Ca2+ mg/L 202
Mg2+ mg/L 21.5
Cl mg/L 154
Fe mg/L 0.02
F mg/L 0.61
NO3 mg/L 3.96
NO2 mg/L 0.003
SO42− mg/L 410
Alkalinity mg/L as CaCO3 124
Bicarbonate mg/L as CaCO3 124
Total hardness mg/L as CaCO3 592
Ca hardness mg/L as CaCO3 468
Mg hardness mg/L as CaCO3 124
ParameterUnitValue
EC μS/cm 1366
pH – 7.8
Turbidity NTU 0.93
Residual-chlorine mg/L
TDS mg/L 1093
Ca2+ mg/L 202
Mg2+ mg/L 21.5
Cl mg/L 154
Fe mg/L 0.02
F mg/L 0.61
NO3 mg/L 3.96
NO2 mg/L 0.003
SO42− mg/L 410
Alkalinity mg/L as CaCO3 124
Bicarbonate mg/L as CaCO3 124
Total hardness mg/L as CaCO3 592
Ca hardness mg/L as CaCO3 468
Mg hardness mg/L as CaCO3 124

Water samples were collected from 10 sampling sites (including Helali (S1), Shekari (S2), Sangi (S3), Sartol (S4), Rishehr (S5), Bahmani (S6), Mir Alamdar (S7), Ashori (S8), Solh Abad (S9), and Bagh Zahra (S10)), which were located in Bushehr city. The locations of the Kosar dam and the sampling points are shown in Figure 1.

Figure 1

Locations of sampling stations in the study area.

Figure 1

Locations of sampling stations in the study area.

### Sample collection and physicochemical analysis

In this cross-sectional study, 50 samples were taken from 10 decentralized municipal desalination plants (five times from each plant) working by a process of reverse osmosis (RO) in Bushehr, Iran. Details of the decentralized municipal desalination plants are shown in Table 2. Representation of a typical RO facility is shown in Figure 2. Physicochemical samples were collected in plastic containers. Electric conductivity (EC) and turbidity were measured using a Greisinger-GLM020 electrical conductivity meter and LUTRON-2016 turbidity meter (with an MDL value of 0.01 NTU), respectively. Residual chlorine levels and pH values were measured using a DPD colorimetric kit test and a pH meter, respectively. Hardness and chloride were measured according to the standard method (APHA 2008). Spectrophotometric methods were used for analyses of F (570 nm), Fe2+ (510 nm), NO2 (507 nm), NO3 (400 nm), SO42− (450 nm) and PO42− (890 nm), using a DR/2000 spectrophotometer (HACH Company, USA).

Table 2

Decentralized municipal desalination plant details and comparison of the costs of other water supplies with these devices

StationsFlow rateFilter replacement period (month)Treatment methodsType of RO membranesManufacturer of RO membranes
S1 (Helali) 24 m3/day RO process Cellulose acetate Pooya-tasfiye/Iran
S2 (Shekari) 10 m3/day RO process Cellulose acetate Pooya-tasfiye/Iran
S3 (Sangi) 10 m3/day 12 RO process Cellulose acetate Pooya-tasfiye/Iran
S4 (Sartol) 15 m3/day RO process Cellulose acetate Parsian-farab/Iran
S5 (Rishehr) 10 m3/day RO process Cellulose acetate Parsian-farab/Iran
S6 (Bahmani) 15 m3/day RO process Cellulose acetate Absun/Iran
S7 (Mir Alamdar) 15 m3/day RO process Cellulose acetate Omransazan-mahab/Iran
S8 (Ashori) 4 m3/day RO process Cellulose acetate Omransazan-mahab/Iran
S9 (Solh Abad) 20 m3/day 12 RO process Cellulose acetate Absun/Iran
S10 (Bagh Zahra) 10 m3/day RO process Cellulose acetate Parsian-farab/Iran
Economics of drinking water supplies
Cost of drinking water in distribution systema (cent/m3) 13.5
Cost of water treatment by decentralized municipal desalination plantsb ($/m3) 3.78 Price of water after treatment in decentralized municipal desalination plants ($/m3) 13.51
Price of bottled water (cent/lit)c 18
StationsFlow rateFilter replacement period (month)Treatment methodsType of RO membranesManufacturer of RO membranes
S1 (Helali) 24 m3/day RO process Cellulose acetate Pooya-tasfiye/Iran
S2 (Shekari) 10 m3/day RO process Cellulose acetate Pooya-tasfiye/Iran
S3 (Sangi) 10 m3/day 12 RO process Cellulose acetate Pooya-tasfiye/Iran
S4 (Sartol) 15 m3/day RO process Cellulose acetate Parsian-farab/Iran
S5 (Rishehr) 10 m3/day RO process Cellulose acetate Parsian-farab/Iran
S6 (Bahmani) 15 m3/day RO process Cellulose acetate Absun/Iran
S7 (Mir Alamdar) 15 m3/day RO process Cellulose acetate Omransazan-mahab/Iran
S8 (Ashori) 4 m3/day RO process Cellulose acetate Omransazan-mahab/Iran
S9 (Solh Abad) 20 m3/day 12 RO process Cellulose acetate Absun/Iran
S10 (Bagh Zahra) 10 m3/day RO process Cellulose acetate Parsian-farab/Iran
Economics of drinking water supplies
Cost of drinking water in distribution systema (cent/m3) 13.5
Cost of water treatment by decentralized municipal desalination plantsb ($/m3) 3.78 Price of water after treatment in decentralized municipal desalination plants ($/m3) 13.51
Price of bottled water (cent/lit)c 18

aThe cost of every m3 of drinking water in distribution systems for public consumption is 13.5 cents. Decentralized municipal desalination plants use drinking water in distribution systems as their feeding water and the cost of this water is 37.84 cent/m3.

bBased on all costs including electricity consumption, buying water, filter replacement, system maintenance, etc.

c180 $/m3. Figure 2 Schematic of typical RO system in decentralized municipal desalination plants in Bushehr. Figure 2 Schematic of typical RO system in decentralized municipal desalination plants in Bushehr. ### Microbial analaysis All microbial samples were collected in 250 mL sterile containers, placed in an ice box at 4 °C, and immediately transported to the laboratory for analysis. To determine heterotrophic bacteria, a heterotrophic plate culture technique following the standard method was used (APHA 2008). A 0.1 mL sample water was spread on to R2A agar plate and incubated at 35 °C for 48 h and colonies were counted by using a Scan 100 Interscience colony counter with results reported as CFU/mL. For TC and FC analyses, 100 mL of collected sample was subjected to a multiple-tube5 fermentation method. Lactose Broth and Brilliant Green Bile Lactose were used for the determination of total coliform (incubated at 35.5 ± 0.5 °C for 48 h), while Brilliant Green Bile Lactose was used for the determination of fecal coliform (incubated at 44.5 ± 0.2 °C for 24 h) and the results were reported as the most probable number per 100 mL (MPN/100 mL). ### Data analysis Statistical analyses were carried out using Microsoft Excel 2013. The results were expressed as mean ± SD and the mean value of each parameter was compared to drinking water guidelines. ## Results The EPA, WHO and INR guideline values for physicochemical and microbial parameters of drinking water are presented in Table 3. Table 3 EPA, WHO, and INR guidelines for drinking water ParameterUnitDrinking water quality guidelines EPAaWHObINRc EC μS/cm 1500 pH – 6.5–8.5 6.5–9 Turbidity NTU Residual-chlorine mg/L TDS mg/L 500 500 1500 Ca2+ mg/L Mg2+ mg/L 30# Cl mg/L 250 400 Fe mg/L 0.3 0.3 F mg/L 1.5 1.5 NO3 mg/L 45 50 50 NO2 mg/L 0.3 SO42− mg/L 250 Alkalinity mg/L as CaCO3 Bicarbonate mg/L as CaCO3 Total hardness mg/L as CaCO3 500 Ca hardness mg/L as CaCO3 250 Mg hardness mg/L as CaCO3 50 Total coliform MPN/100 mL Fecal coliform MPN/100 mL HPC CFU/mL 500 500 500 ParameterUnitDrinking water quality guidelines EPAaWHObINRc EC μS/cm 1500 pH – 6.5–8.5 6.5–9 Turbidity NTU Residual-chlorine mg/L TDS mg/L 500 500 1500 Ca2+ mg/L Mg2+ mg/L 30# Cl mg/L 250 400 Fe mg/L 0.3 0.3 F mg/L 1.5 1.5 NO3 mg/L 45 50 50 NO2 mg/L 0.3 SO42− mg/L 250 Alkalinity mg/L as CaCO3 Bicarbonate mg/L as CaCO3 Total hardness mg/L as CaCO3 500 Ca hardness mg/L as CaCO3 250 Mg hardness mg/L as CaCO3 50 Total coliform MPN/100 mL Fecal coliform MPN/100 mL HPC CFU/mL 500 500 500 aUS EPA guideline for drinking water (maximum admissible concentration). bWHO guideline for drinking water (maximum admissible concentration). cINR guideline for drinking water (maximum admissible concentration). *Not determined, #Desirable admissible concentration. Tables 46 show the measured physicochemical parameters of decentralized municipal desalination plant outlets, removal percentage (%), while Tables 4 and 5 also show the calculated daily intakes (mg/day) of different anions and cations. The minimum, maximum, and mean concentration levels of Ca2+ in the outlet waters were 12.16, 48.16, and 29.52 mg/L, respectively. Calcium in the outlet waters decreased by 81.11% compared to the inlet waters. As seen in Table 4, the maximum daily intakes of calcium based on 2 L daily drinking water consumption (Valtin 2002) reached 59.04 with a range of 24.32–96.32 mg/day. The mean concentration level of Mg2+ was 4.72 mg/L as CaCO3 with a range of 2.99–6.58 mg/L in the outlet waters. Magnesium in the outlet waters decreased by 72.86% compared to the inlet waters, and outlet water levels were in the standard range. The maximum daily intakes of Mg2+ based on 2 L daily drinking water consumption reached 9.45 with a range of 6.58–13.16 mg/day. The mean concentration levels of calcium and magnesium hardness in the outlet waters ranged from 30.4 to 120.4 (mean: 73.8) and 12–26.4 (18.96) mg/L as CaCO3, respectively. Calcium and magnesium hardness in the outlet waters decreased by 81.12 and 72.12% compared to the inlet waters, respectively. In the outlet sections of all decentralized municipal desalination plants, the calcium and magnesium hardnes values were compatible with drinking water standards. The concentration level of total hardness in this study was found to be between 13.96 and 141.2 mg/L as CaCO3 with a mean concentration level of 82.96 mg/L as CaCO3 in the outlet waters. The maximum daily intakes of total hardness based on 2 L daily drinking water consumption reached 147.6 with a range of 60.8–240.8 mg/day. The mean concentration level of alkalinity was 61.2 mg/L as CaCO3 with a range of 36–88 mg/L as CaCO3 in the outlet waters. Analyses of carbonate and bicarbonate showed that the amount of CO32− in all samples was equal to zero (0 mg/L as CaCO3) and the concentration level of HCO3 was 36–88 (mean: 61.2) mg/L as CaCO3 in the outlet waters. Alkalinity and bicarbonate in the outlet waters decreased by 64.31% compared to the inlet waters. The concentration levels of nitrate and nitrite in the outlet waters ranged from 0.77 to 2.47 (mean: 1.71) and 0.002–0.003 (mean: 0.0026) mg/L, respectively. Nitrate and nitrite in the outlet waters decreased by 44.48 and 18.52%, respectively, compared to the inlet waters. The maximum daily intakes of nitrate and nitrite based on 2 L daily drinking water consumption reached 88.62 and 0.0054 with a range of 38.56–148.58 and 0.004–0.01 mg/day respectively. Analysis of residual chlorine showed that the mean concentration level of this parameter was 0.42 mg/L with a range of 0.24–0.52 mg/L in the outlet waters. The removal percentage of residual chlorine in the outlet waters was 42.72% compared to the inlet waters. The mean concentration level of iron was 0.045 with a range of 0.04–0.07 mg/L in the outlet waters. Iron in the outlet waters decreased by 63.71% compared to the inlet waters. The maximum daily intakes of Fe based on 2 L daily drinking water consumption reached 0.102 with a range of 0.08–0.24 mg/day. The concentration level of fluoride in this study was found to be between 0.07 and 0.26 mg/L with a mean concentration level of 0.167 mg/L in the outlet waters. The removal percentage of fluoride in the outlet waters was 65.21% compared to the inlet waters. The maximum daily intakes of fluoride based on 2 L daily drinking water consumption reached 0.334 with a range of 0.14–0.52 mg/day. The minimum and maximum concentrations of sulfate ion were 44.54 and 144.99 with a mean concentration level of 107.17 mg/L in the outlet waters. Sulfate in the outlet waters decreased by 85.29% compared to the inlet waters. The maximum daily intakes of sulfate based on 2 L daily drinking water consumption reached 214.34 with a range of 89.08–289.98 mg/day. The minimum and maximum concentration levels of chloride ion were found to be between 12.19 and 38.58 with a mean concentration level of 82.26 mg/L in the outlet waters. Chloride in the outlet waters decreased by 68.87% compared to the inlet waters. The maximum daily intakes of chloride based on 2 L daily drinking water consumption reached 51.22 with a range of 24.38–77.16 mg/day. The minimum and maximum level values of pH were found to be between 6.8 and 6.96 with a mean level value of 6.84 in the outlet waters. pH in the outlet waters decreased by 3.93% compared to the inlet waters. The results showed that decentralized municipal desalination plants could remove up to 100% turbidity from input water. So, the mean level value of turbidity reached zero in the outlet waters. The mean level value of TDS was 161.04 with a range of 64.9–239.3 mg/L in the outlet waters. TDS in the outlet waters decreased by 72.13% compared to the inlet waters. The maximum daily intakes of TDS based on 2 L daily drinking water consumption reached 322.08 with a range of 129.2–478.6 mg/day. In our study, the minimum and maximum EC was 129.2 and 478.6 μS/cm with a mean level of 322.9 μS/cm in the outlet waters. EC in the outlet waters decreased by 72% compared to the inlet waters. Table 4 Mean level values of the measured physicochemical parameters in the outlet waters of decentralized municipal desalination plants, removal percent (%) and daily intake (mg/day) StationCa2+ (mg/L) Mg2+ (mg/L) SO42− (mg/L) OutletRemoval (%)Daily intakeaOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 29.28 ± 2.86 80.30 58.56 3.89 ± 1.19 77.45 7.78 122.83 ± 23.23 82.10 245.66 48.16 ± 4.53 68.08 96.32 5.18 ± 1.67 65.14 10.36 144.99 ± 45.99 77.89 289.98 36.64 ± 3.36 75.56 73.28 5.08 ± 1.29 69.12 10.16 136.48 ± 29.93 79.21 272.96 20.32 ± 2.86 86.19 40.64 4.68 ± 1.85 72.06 9.36 88.58 ± 6.91 86.02 177.16 35.36 ± 2.61 77.33 70.72 6.38 ± 0.73 60.03 12.76 131.82 ± 24.95 80.63 263.64 35.2 ± 1.6 78.49 70.4 6.58 ± 6.1 62.29 13.16 92.02 ± 7.3 89.76 184.04 12.16 ± 2.96 92.39 24.32 2.99 ± 3.66 84.94 5.98 44.54 ± 51.97 94.58 89.08 28.32 ± 1.55 82.66 56.65 3.89 ± 2.06 77.45 7.78 111.28 ± 17.79 86.22 222.56 31.36 ± 1.53 80.32 62.72 5.28 ± 5.17 75.02 10.56 124.68 ± 20.20 84.56 249.36 10 18.4 ± 3.62 88.78 36.8 3.29 ± 1.56 80.59 6.58 74.5 ± 17.9 88.28 149 Mean ± SD 29.52 ±10.43 81.01 59.04 4.72 ±1.22 72.86 9.45 107.17 ±31.68 85.29 214.34 StationF (mg/L) Fe (mg/L) Cl (mg/L) OutletRemoval (%)Daily intakeOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 0.18 ± 0.06 58.14 0.36 0.04 ± 0.004 66.67 0.08 24.79 ± 3.05 69.23 49.58 0.26 ± 0.06 40.91 0.52 0.04 ± 0.008 33.33 0.08 38.58 ± 13.99 51.39 77.16 0.21 ± 0.09 53.33 0.42 0.04 ± 0.001 63.64 0.08 26.99 ± 4.75 66.63 53.98 0.07 ± 0.04 83.33 0.14 0.04 ± 0.038 75.00 0.08 12.69 ± 2.3 84.01 25.38 0.13 ± 0.03 69.77 0.26 0.04 ± 0.008 88.89 0.08 26.69 ± 5.8 63.17 53.38 0.19 ± 0.08 63.46 0.38 0.04 ± 0.004 33.33 0.08 37.08 ± 3.47 57.99 74.16 0.1 ± 0.052 83.05 0.2 0.12 ± 0.14 50.00 0.24 12.19 ± 1.82 85.65 24.38 0.19 ± 0.09 64.81 0.38 0.04 ± 0.005 33.33 0.08 27.69 ± 3.89 67.87 55.38 0.19 ± 0.12 57.78 0.38 0.04 ± 0.005 0.00 0.08 22.89 ± 4.29 73.25 45.78 10 0.15 ± 0.1 70.59 0.3 0.07 ± 0.06 53.33 0.14 26.49 ± 3.85 68.82 52.98 Mean ± SD 0.167 ±0.05 65.21 0.334 0.054 ±0.03 63.71 0.102 25.61 ±8.58 68.87 51.22 StationCa2+ (mg/L) Mg2+ (mg/L) SO42− (mg/L) OutletRemoval (%)Daily intakeaOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 29.28 ± 2.86 80.30 58.56 3.89 ± 1.19 77.45 7.78 122.83 ± 23.23 82.10 245.66 48.16 ± 4.53 68.08 96.32 5.18 ± 1.67 65.14 10.36 144.99 ± 45.99 77.89 289.98 36.64 ± 3.36 75.56 73.28 5.08 ± 1.29 69.12 10.16 136.48 ± 29.93 79.21 272.96 20.32 ± 2.86 86.19 40.64 4.68 ± 1.85 72.06 9.36 88.58 ± 6.91 86.02 177.16 35.36 ± 2.61 77.33 70.72 6.38 ± 0.73 60.03 12.76 131.82 ± 24.95 80.63 263.64 35.2 ± 1.6 78.49 70.4 6.58 ± 6.1 62.29 13.16 92.02 ± 7.3 89.76 184.04 12.16 ± 2.96 92.39 24.32 2.99 ± 3.66 84.94 5.98 44.54 ± 51.97 94.58 89.08 28.32 ± 1.55 82.66 56.65 3.89 ± 2.06 77.45 7.78 111.28 ± 17.79 86.22 222.56 31.36 ± 1.53 80.32 62.72 5.28 ± 5.17 75.02 10.56 124.68 ± 20.20 84.56 249.36 10 18.4 ± 3.62 88.78 36.8 3.29 ± 1.56 80.59 6.58 74.5 ± 17.9 88.28 149 Mean ± SD 29.52 ±10.43 81.01 59.04 4.72 ±1.22 72.86 9.45 107.17 ±31.68 85.29 214.34 StationF (mg/L) Fe (mg/L) Cl (mg/L) OutletRemoval (%)Daily intakeOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 0.18 ± 0.06 58.14 0.36 0.04 ± 0.004 66.67 0.08 24.79 ± 3.05 69.23 49.58 0.26 ± 0.06 40.91 0.52 0.04 ± 0.008 33.33 0.08 38.58 ± 13.99 51.39 77.16 0.21 ± 0.09 53.33 0.42 0.04 ± 0.001 63.64 0.08 26.99 ± 4.75 66.63 53.98 0.07 ± 0.04 83.33 0.14 0.04 ± 0.038 75.00 0.08 12.69 ± 2.3 84.01 25.38 0.13 ± 0.03 69.77 0.26 0.04 ± 0.008 88.89 0.08 26.69 ± 5.8 63.17 53.38 0.19 ± 0.08 63.46 0.38 0.04 ± 0.004 33.33 0.08 37.08 ± 3.47 57.99 74.16 0.1 ± 0.052 83.05 0.2 0.12 ± 0.14 50.00 0.24 12.19 ± 1.82 85.65 24.38 0.19 ± 0.09 64.81 0.38 0.04 ± 0.005 33.33 0.08 27.69 ± 3.89 67.87 55.38 0.19 ± 0.12 57.78 0.38 0.04 ± 0.005 0.00 0.08 22.89 ± 4.29 73.25 45.78 10 0.15 ± 0.1 70.59 0.3 0.07 ± 0.06 53.33 0.14 26.49 ± 3.85 68.82 52.98 Mean ± SD 0.167 ±0.05 65.21 0.334 0.054 ±0.03 63.71 0.102 25.61 ±8.58 68.87 51.22 aBased on 2 liters daily drinking water consumption and concentration levels of physicochemical parameters in the outlet waters. Table 5 Mean level values of the measured physicochemical parameters in the outlet waters of decentralized municipal desalination plants, removal percentage (%) and daily intake (mg/day) StationTDS (mg/L) Total hardness (mg/L as CaCO3) Ca hardness (mg/L as CaCO3) OutletRemoval (%)Daily intakeaOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 174.4 ± 51.32 69.19 348.8 88.8 ± 10.63 79.85 177.6 73.2 ± 7.15 80.30 146.4 239.3 ± 40.13 57.02 478.6 141.2 ± 17.64 67.67 282.4 120.4 ± 11.34 68.08 240.8 199.1 ± 52.99 64.37 398.2 13.96 ± 13.19 96.83 27.92 91.6 ± 8.41 75.56 183.2 117.7 ± 51.51 78.76 235.4 69.6 ± 8.87 84.10 139.2 50.8 ± 7.15 86.29 101.6 200.2 ± 56.49 65.35 400.4 114 ± 6.63 74.89 228 88.4 ± 6.54 77.33 176.8 180.3 ± 34.97 70.02 360.6 114.4 ± 22.42 76.13 228.8 88 ± 4.25 78.49 176 64.6 ± 35.25 89.03 129.2 42.4 ± 21.23 91.15 84.8 30.4 ± 7.4 92.39 60.8 152.9 ± 43.89 73.68 305.8 86.4 ± 10.99 81.91 172.8 70.8 ± 3.89 82.66 141.6 154.3 ± 24.69 73.57 308.6 99.6 ± 21.51 79.39 199.2 78.4 ± 3.84 80.32 156.8 10 127.6 ± 40.18 79.05 255.2 59.2 ± 14.6 87.14 118.4 46 ± 9.05 88.78 92 Mean ± SD 161.04 ±18.95 72.13 322.08 92.76 ±29.7 81.92 167.7 73.8 ±26.07 81.12 147.6 StationMg hardness (mg/L as CaCO3) NO3 (mg/L) NO2 (mg/L) OutletRemoval (%)Daily intakeOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 15.6 ± 4.77 77.46 31.2 26.94 82.10 53.88 0.002 ± 0.001 0.00 0.004 20.8 ± 6.72 65.10 41.6 19.28 77.89 38.56 0.002 ± 0.0008 0.00 0.004 20.4 ± 5.17 69.09 40.8 21.33 79.21 42.66 0.003 ± 0.001 0.00 0.006 18.8 ± 7.42 72.02 37.6 66.53 86.02 133.06 0.002 ± 0.001 0.00 0.004 25.6 ± 2.96 60.00 51.2 36.84 80.63 73.68 0.005 ± 0.004 60.00 0.01 26.4 ± 24.47 62.29 52.8 36.18 89.76 72.36 0.002 ± 0.0008 0.00 0.004 12 ± 14.69 84.92 24 74.29 94.58 148.58 0.003 ± 0.0008 33.33 0.006 15.6 ± 8.29 77.46 31.2 42.40 86.22 84.8 0.003 ± 0.001 33.33 0.006 21.2 ± 20.76 75.00 42.4 73.81 84.56 147.62 0.003 ± 0.00 0.00 0.006 10 13.2 ± 6.26 73.81 26.4 45.54 88.28 91.08 0.002 ± 0.005 0.00 0.004 Mean ± SD 18.96 ±4.88 72.12 37.92 44.48 85.29 85.29 0.0026 ±0.01 0.0022 ± .0006 0.0054 StationTDS (mg/L) Total hardness (mg/L as CaCO3) Ca hardness (mg/L as CaCO3) OutletRemoval (%)Daily intakeaOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 174.4 ± 51.32 69.19 348.8 88.8 ± 10.63 79.85 177.6 73.2 ± 7.15 80.30 146.4 239.3 ± 40.13 57.02 478.6 141.2 ± 17.64 67.67 282.4 120.4 ± 11.34 68.08 240.8 199.1 ± 52.99 64.37 398.2 13.96 ± 13.19 96.83 27.92 91.6 ± 8.41 75.56 183.2 117.7 ± 51.51 78.76 235.4 69.6 ± 8.87 84.10 139.2 50.8 ± 7.15 86.29 101.6 200.2 ± 56.49 65.35 400.4 114 ± 6.63 74.89 228 88.4 ± 6.54 77.33 176.8 180.3 ± 34.97 70.02 360.6 114.4 ± 22.42 76.13 228.8 88 ± 4.25 78.49 176 64.6 ± 35.25 89.03 129.2 42.4 ± 21.23 91.15 84.8 30.4 ± 7.4 92.39 60.8 152.9 ± 43.89 73.68 305.8 86.4 ± 10.99 81.91 172.8 70.8 ± 3.89 82.66 141.6 154.3 ± 24.69 73.57 308.6 99.6 ± 21.51 79.39 199.2 78.4 ± 3.84 80.32 156.8 10 127.6 ± 40.18 79.05 255.2 59.2 ± 14.6 87.14 118.4 46 ± 9.05 88.78 92 Mean ± SD 161.04 ±18.95 72.13 322.08 92.76 ±29.7 81.92 167.7 73.8 ±26.07 81.12 147.6 StationMg hardness (mg/L as CaCO3) NO3 (mg/L) NO2 (mg/L) OutletRemoval (%)Daily intakeOutletRemoval (%)Daily intakeOutletRemoval (%)Daily intake 15.6 ± 4.77 77.46 31.2 26.94 82.10 53.88 0.002 ± 0.001 0.00 0.004 20.8 ± 6.72 65.10 41.6 19.28 77.89 38.56 0.002 ± 0.0008 0.00 0.004 20.4 ± 5.17 69.09 40.8 21.33 79.21 42.66 0.003 ± 0.001 0.00 0.006 18.8 ± 7.42 72.02 37.6 66.53 86.02 133.06 0.002 ± 0.001 0.00 0.004 25.6 ± 2.96 60.00 51.2 36.84 80.63 73.68 0.005 ± 0.004 60.00 0.01 26.4 ± 24.47 62.29 52.8 36.18 89.76 72.36 0.002 ± 0.0008 0.00 0.004 12 ± 14.69 84.92 24 74.29 94.58 148.58 0.003 ± 0.0008 33.33 0.006 15.6 ± 8.29 77.46 31.2 42.40 86.22 84.8 0.003 ± 0.001 33.33 0.006 21.2 ± 20.76 75.00 42.4 73.81 84.56 147.62 0.003 ± 0.00 0.00 0.006 10 13.2 ± 6.26 73.81 26.4 45.54 88.28 91.08 0.002 ± 0.005 0.00 0.004 Mean ± SD 18.96 ±4.88 72.12 37.92 44.48 85.29 85.29 0.0026 ±0.01 0.0022 ± .0006 0.0054 aBased on 2 L daily drinking water consumption and concentration levels of physicochemical parameters in outlet waters. Table 6 Mean level values of the measured physicochemical parameters in the outlet waters of decentralized municipal desalination plants and removal percentage StationEC (μS/cm) Residual chlorine (mg/L) Turbidity (NTU) OutletRemoval (%)OutletRemoval (%)OutletRemoval (%) 348.8 ± 77.3 69 0.52 ± 0.11 33.33 100 478.6 ± 83.7 57 0.24 ± 0.16 57.14 100 398.2 ± 48.2 64 0.32 ± 0.14 33.33 100 235.4 ± 65.4 79 0.38 ± 0.13 45.71 100 400.4 ± 76.7 65 0.40 ± 0.22 37.50 100 360.6 ± 26.0 70 0.30 ± 0.21 44.44 100 129.2 ± 10.9 89 0.52 ± 0.12 27.78 100 305.8 ± 22.9 74 0.40 ± 0.16 41.18 100 308.6 ± 30.8 74 0.32 ± 0.13 52.94 100 10 255.2 ± 25.8 79 0.34 ± 0.13 51.43 100 Mean ± SD 322.08 ± 99.1 72 0.37 ± 0.062 45.72 100 StationpH HCO3 (mg/L as CaCO3) Alkalinity (mg/l as CaCO3) OutletReduction (%)OutletRemoval (%)OutletRemoval (%) 6.68 ± 0.21 5.9 74 ± 32.09 58.89 74 ± 32.09 58.89 6.96 ± 0.13 1.1 88 ± 36.8 50.00 88 ± 36.8 50.00 6.92 ± 0.22 3.9 67 ± 13.96 61.05 67 ± 13.96 61.05 6.86 ± 0.21 3.4 44 ± 4.18 74.71 44 ± 4.18 74.71 6.8 ± 0.13 3.4 63 ± 8.36 62.94 63 ± 8.36 62.94 6.8 ± 0.21 76 ± 8.94 55.29 76 ± 8.94 55.29 6.8 ± 0.15 4.8 36 ± 8.94 78.57 36 ± 8.94 78.57 6.8 ± 0.16 5.8 61 ± 8.94 64.12 61 ± 8.94 64.12 6.8 ± 0.13 52 ± 8.36 69.59 52 ± 8.36 69.59 10 6.8 ± 0.13 51 ± 5.47 68.90 51 ± 5.47 68.90 Mean ± SD 6.83 ± 0.062 4.23 61.2 ± 15.84 64.31 61.2 ± 15.84 64.31 StationEC (μS/cm) Residual chlorine (mg/L) Turbidity (NTU) OutletRemoval (%)OutletRemoval (%)OutletRemoval (%) 348.8 ± 77.3 69 0.52 ± 0.11 33.33 100 478.6 ± 83.7 57 0.24 ± 0.16 57.14 100 398.2 ± 48.2 64 0.32 ± 0.14 33.33 100 235.4 ± 65.4 79 0.38 ± 0.13 45.71 100 400.4 ± 76.7 65 0.40 ± 0.22 37.50 100 360.6 ± 26.0 70 0.30 ± 0.21 44.44 100 129.2 ± 10.9 89 0.52 ± 0.12 27.78 100 305.8 ± 22.9 74 0.40 ± 0.16 41.18 100 308.6 ± 30.8 74 0.32 ± 0.13 52.94 100 10 255.2 ± 25.8 79 0.34 ± 0.13 51.43 100 Mean ± SD 322.08 ± 99.1 72 0.37 ± 0.062 45.72 100 StationpH HCO3 (mg/L as CaCO3) Alkalinity (mg/l as CaCO3) OutletReduction (%)OutletRemoval (%)OutletRemoval (%) 6.68 ± 0.21 5.9 74 ± 32.09 58.89 74 ± 32.09 58.89 6.96 ± 0.13 1.1 88 ± 36.8 50.00 88 ± 36.8 50.00 6.92 ± 0.22 3.9 67 ± 13.96 61.05 67 ± 13.96 61.05 6.86 ± 0.21 3.4 44 ± 4.18 74.71 44 ± 4.18 74.71 6.8 ± 0.13 3.4 63 ± 8.36 62.94 63 ± 8.36 62.94 6.8 ± 0.21 76 ± 8.94 55.29 76 ± 8.94 55.29 6.8 ± 0.15 4.8 36 ± 8.94 78.57 36 ± 8.94 78.57 6.8 ± 0.16 5.8 61 ± 8.94 64.12 61 ± 8.94 64.12 6.8 ± 0.13 52 ± 8.36 69.59 52 ± 8.36 69.59 10 6.8 ± 0.13 51 ± 5.47 68.90 51 ± 5.47 68.90 Mean ± SD 6.83 ± 0.062 4.23 61.2 ± 15.84 64.31 61.2 ± 15.84 64.31 The results of total coliform, fecal coliform, and HPC measurements of all samples are presented in Table 7. The results of all FC and TC measurements were negative. In other words, all of the outlet drinking water taken from the decentralized municipal desalination plants was found free from coliforms and met the INR, EPA and WHO guidelines (0 MPN/100 mL) (ISIRI 2001; WHO 2011). The minimum and maximum levels of HPC were 186 and 434 CFU/mL with a mean concentration level of 322.9 CFU/mL in outlet water samples. Table 7 Measured microbial parameters (Mean ± SD) for the outlet drinking water collected from the decentralized municipal desalination plants StationsMicrobiological properties for the outlet water Total coliform (MPN/100 mL)Fecal coliform (MPN/100 mL)HPC (CFU/mL) 0 ± 0.0 0 ± 0.0 432 ± 238.15 0 ± 0.0 0 ± 0.0 410 ± 254.26 0 ± 0.0 0 ± 0.0 286 ± 185.55 0 ± 0.0 0 ± 0.0 434 ± 463.17 0 ± 0.0 0 ± 0.0 254 ± 90.71 0 ± 0.0 0 ± 0.0 300 ± 100.99 0 ± 0.0 0 ± 0.0 205 ± 148.74 0 ± 0.0 0 ± 0.0 186 ± 46.15 0 ± 0.0 0 ± 0.0 356 ± 167.72 10 0 ± 0.0 0 ± 0.0 364 ± 322.84 Mean ± SD 0 ± 0.0 0 ± 0.0 322.9 ± 90.89 StationsMicrobiological properties for the outlet water Total coliform (MPN/100 mL)Fecal coliform (MPN/100 mL)HPC (CFU/mL) 0 ± 0.0 0 ± 0.0 432 ± 238.15 0 ± 0.0 0 ± 0.0 410 ± 254.26 0 ± 0.0 0 ± 0.0 286 ± 185.55 0 ± 0.0 0 ± 0.0 434 ± 463.17 0 ± 0.0 0 ± 0.0 254 ± 90.71 0 ± 0.0 0 ± 0.0 300 ± 100.99 0 ± 0.0 0 ± 0.0 205 ± 148.74 0 ± 0.0 0 ± 0.0 186 ± 46.15 0 ± 0.0 0 ± 0.0 356 ± 167.72 10 0 ± 0.0 0 ± 0.0 364 ± 322.84 Mean ± SD 0 ± 0.0 0 ± 0.0 322.9 ± 90.89 Table 8 shows the distribution of HPC in the outlet drinking water taken from the decentralized municipal desalination plants. As shown in Table 8, 90% of all drinking water samples contained HPC within a range of 1–500 CFU/mL and 10% of samples contained a value higher than 500 CFU/mL. So, 90% of samples in this study met the INR, EPA and WHO regulations (ISIRI 2001; WHO 2011). The results of HPC measurements compared with the EPA, WHO and INR guidelines are shown in Figure 3. Table 8 Distribution of HPC bacteria counts for the outlet drinking water taken from the decentralized municipal desalination plants HPC (CFU/mL)Number of positive sample (percentage of positive sample) <1 0 (0.0%) 1–500 45 (90%) >500 5 (10%) Range 30–1,200 Mean ± SD 322.9 ± 90.89 HPC (CFU/mL)Number of positive sample (percentage of positive sample) <1 0 (0.0%) 1–500 45 (90%) >500 5 (10%) Range 30–1,200 Mean ± SD 322.9 ± 90.89 Figure 3 Mean of the HPC results compared with HPC guidelines for drinking water. Figure 3 Mean of the HPC results compared with HPC guidelines for drinking water. ## DISCUSSION Calcium and magnesium cations make water hard. Calcium ions play a vital role in the physiology and biochemistry of organisms, neuromuscular excitability (decreases it), good function of the conducting myocardial system, heart and muscle contractility, intracellular information transmission and blood coagulability. Osteoporosis and osteomalacia are the most common manifestations of calcium deficiency; a less common but proved disorder attributable to Ca deficiency is hypertension. Magnesium plays a main role as a cofactor and activator of more than 300 enzymatic reactions including glycolysis, ATP metabolism, transport of elements such as Na, K and Ca through membranes, synthesis of proteins and nucleic acids, neuromuscular excitability and muscle contraction, etc. (Derry et al. 1990; Sauvant & Pepin 2002; Kožíšek 2003). The recommended calcium and magnesium daily intake for adults ranges between 700–1,000 and 300–400 mg, respectively (Committee on Dietary Reference Intake 1997; Sauvant & Pepin 2002). In the present study, the mean concentration levels of calcium and magnesium hardness in the outlet waters were compatible with drinking water standards. The total hardness of water may range from trace amounts to hundreds of milligrams per liter (Saleh et al. 2001). EPA and WHO have not set a guideline value for total hardness, but the INR has set a guideline value of 500 mg/L as CaCO3 for total hardness in drinking water (ISIRI 1999). High concentration levels of nitrate and nitrite in water or food can affect the health of consumers, especially in the case of children (Fard et al. 2015). In the outlet waters of all decentralized municipal desalination plants, the values of nitrate and nitrite were compatible with drinking water guidelines. The presence of chlorine residual in drinking water indicates that: (1) a sufficient amount of chlorine is in the water to inactivate the bacteria and some viruses that cause diarrheal disease; and (2) the water is protected from recontamination and biofilm formation during storage and distribution (LeChevallier et al. 1988). Residual chlorine is present in the most disinfected drinking water at a concentration level of 0.2–1 mg/L (White 1975), but Ridgway et al. (1984) found that a residual of 15–20 mg of chlorine per liter was necessary to control biofilm fouling on reverse osmosis membranes. INR, EPA and WHO have not set guideline values for residual chlorine. EPA and INR set a 0.3 mg/L guideline value for iron in drinking water (White 1975; Ridgway et al. 1984; LeChevallier et al. 1988; ISIRI 1999; EPA 2012). Exposure to excess iron levels may be a cause of a wide range of common diseases, and also may cause corrosion of the pipes in the drinking water distribution network (WHO 2011). All results of iron measurements in this study met the INR and EPA guidelines. Fluoride at elevated levels can have adverse effects on human health. In terms of general health, in communities where drinking water and foodstuffs are excessively high in fluoride, skeletal fluorosis and bone fractures are the most relevant adverse effects (Browne et al. 2005). Fluoride is widely distributed in the environment and is therefore of special interest. Excess fluoride intake can cause a wide range of adverse health effects (Shivarajashankara et al. 2001; Dobaradaran et al. 2008a, 2008b; Spittle 2008; Rahmani et al. 2010; Ostovar et al. 2013). In this regard, various studies in Iran have reported the occurrence of high fluoride concentration levels in drinking water (Dobaradaran et al. 2008a, 2008b, 2009a, 2009b; Shams et al. 2012; Nabipour & Dobaradaran 2013; Akhavan et al. 2016; Karbasdehi et al. 2016), air, fish and the sea (Dobaradaran et al. 2009a, 2009b, 2011; Nabipour & Dobaradaran 2010; Soleimani et al. 2017), as well as in connection with its removal from elevated fluoride waters (Boldaji et al. 2009; Shams et al. 2013; Dobaradaran et al. 2014, 2015, 2016; Zazouli et al. 2014; Keshtkar et al. 2016). In this study the fluoride level in the treated water was lower than the guidelines. Chloride and sodium together create common table salt. Chloride in water may be considerably increased by treatment processes in which chlorine or chloride is used. High chloride levels cause corrosion and shorten the life of pipes, pumps, hot water heaters and fixtures. Chloride concentration levels in excess of about 250 mg per liter usually produce a noticeable taste in drinking water (Benham et al. 2011). All results of chloride measurements met the EPA and INR guidelines. WHO has not set a guideline value for pH, but the EPA and INR have set guideline values of 6.5–8.5 and 6.5–9 for pH in drinking water, respectively. All results of pH measurements met EPA and INR guidelines for drinking water. Sulfates occur naturally in numerous minerals, including barite (BaSO4), epsomite (MgSO4.7H2O) and gypsum (CaSO4.2H2O) (Greenwood & Earnshaw 1984). These dissolved minerals contribute to the mineral content of drinking water. Sulfate minerals can cause scale build-up in water pipes similar to other minerals and may be associated with a bitter taste in water that can have a laxative effect on humans. Uncontrolled observations indicate sulfate in drinking water at concentrations exceeding 500–700 mg/L as a cause of diarrhea (Heizer et al. 1997). EPA and WHO have not set a guideline value for EC, but the INR has set a guideline value of 1,500 μS/cm for EC in drinking water, so all results of EC measurements in this study met the INR guidelines. Also, in our study, all results of TDS measurements met EPA, WHO and INR guidelines for drinking water. As seen in Table 2, the costs of treated water in a distribution system, decentralized municipal desalination plants and bottled water are 13.5 cent/m3, 13.51$/m3 and 18 cent/lit (180 \$/m3). Therefore, due to the lower price, many people in different parts of Iran (such as Bushehr) prefer to use treated water from decentralized municipal desalination plants rather than to bottled water. There are different methods for purifying drinking water to provide safe and healthy water for consumers. Today, membrane separation technology has received much attention among consultant engineers, designers of environment pollution control systems, and industrial factory engineers (Ozaki & Li 2002). The membrane processes play an important role in providing high quality, healthy drinking water. Its purpose is to remove minerals, turbidity, synthetic organic materials and disinfection by-products from the water (Hobson et al. 2007). They are highly efficient at preventing bacteria and protozoan cysts such as Cryptosporidium and Giardia lamblia cysts (Wohlsen et al. 2004). Thus, the use of water desalination devices has recently received more attention. RO, microfiltration (MF), nanofiltration (NF), and ultrafiltration (UF) are the main membrane processes for the removal of minerals from water (Ozaki & Li 2002). Reverse osmosis is a technology that is used to remove large groups of contaminants such as dissolved salts (ions), particles, colloids organics, bacteria and other microorganisms from water by pushing the water through a semi-permeable membrane under pressure (Fahiminia et al. 2014). Considering the increasing use of desalination plants using the RO process across Bushehr, it is necessary to qualitatively control the outlet waters of these devices.

In the collected samples from the outlet waters of these facilities, all parameters were in the range of safe drinking water but 10% of HPC measurment were not in the favorable standard range. In a study by Khodadadi et al. (2016) on the chemical, physical and biological quality of exiting water from desalination water facilities in Birjand, Iran, it was found that in all the collected samples from these facilities, TDS, calcium, magnesium, chromium, manganese, and nitrite parameters were in the range of safe drinking water but the total hardness was not in the desirable standard range in 2.7% of samples, which is likely due to the high hardness level of entering water from groundwater resources. In another study by Miranzadeh & Rabbani (2010) on the chemical quality evaluation of inlet and outlet waters taken from desalination plants utilized in Kashan, Iran, it was found that the average concentrations of chemical parameters in treated water were: TDS = 245 mg/L, total hardness = 118 mg/L as CaCO3, nitrate = 2.5 mg/L, fluoride = 0.2 mg/L, sulfate = 24 mg/L, chloride = 63 mg/L and pH range = 6.8–7. In their study, based on the findings on desalinated water, all parameters were in accordance with the optimum concentration levels for drinking water. Their results on pH values were consistent with our results. In contrast to our study, the results of research by Yari et al. (2007) on the quality of water extracted from desalination facilities in the cities and villages of Qum, Iran, showed that pH values of exiting water of all facilities were less than the favorable value and reached less than 6, demonstrating that the pH of exiting water of these facilities tended toward acidity and corrosion. In the study by Deghani et al. (2013) on the physical, chemical and microbial quality of raw and treated water from desalination plants by reverse osmosis in Qeshm, Iran, it was shown that the total hardness and fluoride in the treated water from this process were lower than desirable limits and chloride concentration was higher than the permitted limit. The rest of the chemical, physical and microbiological parameters in the mentioned study were in acceptable ranges. In the study by Belkacem et al. (2007) on the treatment of groundwaters by reverse osmosis in Algeria, it was shown that treatment by the reverse osmosis unit effectively decreased the conductivity and TDS of the groundwater by more than 95% for the totality of constituent ions, and microorganisms were also eliminated. In another study by Shams et al. (2012) on the physicochemical qualities of raw and treated water of a decentralized municipal desalination plant water in Gonabad, Iran, the results showed that the TDS value was 868.7 mg/L in the inlet waters, reaching 182.1 mg/L in the outlet waters. The pH values in the inlet and outlet waters were 8.23 and 7.97, respectively. The choloride and sulphate oncentrations were 196.8 and 122.46 mg/L in the inlet waters, and reached 55.09 and 53.04 mg/L in the outlet waters, respectively. Also, total hardness and total alkalinity were 129.5 and 235.2 mg/L as CaCO3 in the inlet waters, and reached 42.01 and 63.91 mg/L as CaCO3 in the outlet waters, respectively. The results of the present study on microbial measurements showed that none of the samples had coliforms contamination, which is in agreement with those of Khodadadi et al. (2016); while in similar research on desalination facilities in Qum, 15 samples (6%) had coliform contamination by Eschershia coli (Yari et al. 2007). Also, in our study, 10% of the HPC bacteria values were outside the accepted range and the mean amount of these bacteria in some samples increased in the outlet waters compared to inlet waters. This can be due to the formation of microbial film on the membranes. In a study by Schwartz et al. (2003) on biofilm formation on membranes, it was found that HPC bacteria were resistant to antibiotics and resistant genes were separated. In Payment et al.’s (1991) research, it was shown that domestic reverse osmosis filtration units were contaminated with HPC bacteria at a higher value than 500 CFU/mL.

## CONCLUSIONS

In the present study, the role of decentralized municipal desalination plants in the removal of physical, chemical and microbial parameters from drinking water in Bushehr, Iran, were evaluated and compared with national and international guidelines for drinking water. The results demonstrated that mean concentration levels of all parameters examined in the outlet drinking water taken from the decentralized municipal desalination plants in Bushehr generally complied with the current drinking water guidelines based on their bacterial and physiochemical properties. However, 10% of HPC samples did not comply with the INR, EPA and WHO drinking water guidelines. The results showed that decentralized municipal desalination plants by RO process could remove most parameters from inlet waters and these devices have high efficiency for providing healthy drinking water based on qualitative guidelines.

## ACKNOWLEDGEMENTS

The authors are grateful to the Bushehr University of Medical Sciences for their financial support and the laboratory staff of the Environmental Health Engineering Department for their cooperation.

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