Disinfection of total coliform bacteria in Falaj water by solar water disinfection (SODIS)

Document Type: Research Paper

Authors

1 Department of Civil and Environmental Engineering, University of Nizwa, Nizwa, Oman

2 Department of Chemical and petrochemical Engineering, University of Nizwa, Nizwa, Oman

Abstract

In this study an attempt has been made to disinfect total coliform bacteria present in falaj water using solar water disinfection (SODIS) technology. SODIS experiments were conducted in different seasons (winter/February-2018 and Summer/May-2018) using PET (less plastic PET, thin plastic PET and thick plastic PET) and the glass bottles of different capacities (0.5L, 1L and 1.5L). The results show that total coliform disinfection rate in May-18 was two folds greater than disinfection rate in Feb-18. Water depth or volume of sample in the bottle has significant effect on the efficiency of SODIS. Highest disinfection rate was found on samples having water depth 6 cm (0.5L) and the lowest disinfection rate was observed on samples having water depth 8 cm (1.5L). No significant difference was observed in disinfecting total coliform between glass and less plastic PET bottle for shorter exposure periods (1 hour).  Results of this research have proved SODIS as anappropriate household water treatment and safe storage (HWTS) for disinfecting falaj water in Oman. This study is a step forward in Oman in making of use solar energy in the treatment of water and wastewater.

Keywords


Disinfection of total coliform bacteria in Falaj water by solar water disinfection (SODIS)

 

Sreedhar Reddy Sajjala1*, Salam Kadhim Al Dawery2, Anwar Ahmed1, Munira Ali Nasser Al jabri1

 

1. Department of Civil and Environmental Engineering, University of Nizwa, Nizwa, Oman

2. Department of Chemical and petrochemical Engineering, University of Nizwa, Nizwa, Oman

 

*Corresponding Author’s Email: sreedharreddy@unizwa.edu.om

ABSTRACT

In this study an attempt has been made to disinfect total coliform bacteria present in falaj water using solar water disinfection (SODIS) technology. SODIS experiments were conducted in different seasons (winter/February-2018 and Summer/May-2018) using PET (less plastic PET, thin plastic PET and thick plastic PET) and the glass bottles of different capacities (0.5L, 1L and 1.5L). The results show that total coliform disinfection rate in May-18 was two folds greater than disinfection rate in Feb-18. Water depth or volume of sample in the bottle has significant effect on the efficiency of SODIS. Highest disinfection rate was found on samples having water depth 6 cm (0.5L) and the lowest disinfection rate was observed on samples having water depth 8 cm (1.5L). No significant difference was observed in disinfecting total coliform between glass and less plastic PET bottle for shorter exposure periods (1 hour).  Results of this research have proved SODIS as anappropriate household water treatment and safe storage (HWTS) for disinfecting falaj water in Oman. This study is a step forward in Oman in making of use solar energy in the treatment of water and wastewater.

 

Keywords: Falaj, Total coliform bacteria, SODIS, PET bottles.

INTRODUCTION

The Sultanate of Oman is located in the south-east of the Arabian Peninsula. Conventional water resources, including surface and underground water, constitute 85 per cent of Oman’s water resources, while desalinated water and treated wastewater make up the rest. Mega desalination facilities located at Barka, Muscat, Sur and Sallalah account for 76 per cent of produced water, while small desalination plants and wells contribute four per cent and 20 per cent respectively. Wells are considered as strategic long-term reserve, mainly used as an alternative resource during peak consumption or plant shutdowns. Aflaj(singular falaj) are surface and/or underground channels fed by groundwater, springs, or streams, built to provide water to communities for domestic and/or agricultural use (Al-Marshudi 2001; Zekri & Al-Marshudi 2008). Aflaj system was existed in Oman area date back to 2500BC.  Oman has over 4,000 falaj systems, of which some 3,000 are still in use, which account for nearly 700 million cubic metres of water annually (Fairouz Megdiche-Kharrat et al. 2017). Falaj channels continue to be the only water supply for many villages even today. Unfortunately, despite efforts by authorities to educate people about proper use of this resource, it is being polluted by some who use aflaj for doing laundry, dishes, washing cars and bathing. This can release grease and other pollutants into the water. Many studies have been conducted on aflajin Oman related to their physical structure, method of construction and governance, irrigation scheduling, water right and market (Abdel Rahmnn & Omezzine 1996; Norman et al. 1998; Al-Marshudi 2007; Zoubeida Tayara 2015). However, very little information is available on quality, suitability for domestic purposes and treatment of falaj water. In Nizwa region, water quality of Falaj Daris is appropriate for drinking. It requires certain methods of disinfection such as chlorination, ozonation or UV sterilization to nullify the effect of BOD values (Yaqoub et al. 2015).

 Water quality assessment of the selected aflaj in Al Jabal Al Akhdar area indicated that quality parameters are within the permissible limits of MD 5/86, 1986 (Regulations for wastewater reuse and discharge in Oman). However, most of the aflaj are contaminated with E.coli bacteria; indicating unacceptable for drinking as per the guidelines of Omani and WHO standards (Al-Kalbani, Price, Ahmed, Abahussain & O’Higgins 2016). From the previous studies, we understood that, falaj water can be made fit for drinking by simple disinfection. Being simple, reliable and cost effective (Oates, Shanahan & Polz  2003; Gelover, Gómez, Reyes & Teresa Leal  2006; Sichel, Fernández-Ibáñez, de Cara & Tello  2009; McGuigan et al. 2012), SODIS (a standard water treatment  method based on the principle of solar (water) disinfection) can be an appropriate household water treatment and  safe storage (HWTS) for disinfecting falaj water,  particularly in rural areas. Another advantage of SODIS in Oman is the availability of clear sky, with high temperatures throughout the year.  Since disinfection potential of SODIS varies from place to place, need to be studied under different local environmental conditions, like solar radiation, temperature, precipitation etc. To the best of our knowledge, no studies related SODIS have been conducted in Oman. The main objective of this research is to develop base line data, which may be useful for further research in future.

 

MATERIALS AND METHODS

Falaj water Samples

Falaj water required for this research was collected in a clean sterilized plastic container from the falaj channel located in Birkat al Mouz, in Nizwa wilayat. Collected samples were transported to environmental engineering lab, University of Nizwa, Nizwa for SODIS treatment and microbial analysis.

 

SODIS containers

Batch- process SODIS involves exposing microbially contaminated drinking water to solar radiation in transparent containers such as plastic bags or plastic or glass bottles. In the present investigation transparent conical shaped PET and glass bottles were used. To study the effect bottle wall thickness on SODIS efficiency, less plastic (0.20 mm wall thickness), thin walled (0.24 mm wall thickness) and thick walled (0.30 mm wall thickness) PET bottles were used. In Oman less plastic and thin walled PET bottles are used for supplying bottled drinking water and thick walled are used for supplying juices.

 

SODIS technique

All the SODIS experiments were performed under natural solar radiation in an open space behind engineering labs  at the University of Nizwa, Birkat Al Mouz, Oman (Latitude: 22.8918; Longitude: 57.5554).

As shown in Fig. 1 the falaj water was filled in transparent containers and placed in direct sunlight. The efficiency of SODIS in disinfecting falaj water was tested under different depths/volumes in bottles, type of bottles, atmospheric temperature and UV intensities. The disinfection rate of total coliform (k) of SODIS was calculated from the ratio of the start (C0) and end (C) concentration of total coliform, and the treatment time (t), assuming first order disinfection kinetics.

 

 

 

Fig. 1. SODIS experimentation.

 

Quantification of total coliform

Efficiency of the SODIS in this study was evaluated in terms of level of disinfection of total coliform bacteria present in the falaj water. To quantify total coliform before and after SODIS treatment, U.S. Environmental Protection Agency (EPA) approved Colilert-18 Quanti-Tray Enumeration procedure was used. 

 

Measurement of UV Radiation, ambient temperature and water temperature

During experimentation period, UV light intensity for a specific wavelength (254 nm/UV-C, 312 nm UVB-1 and 365 nm UVA-1) was measured using VLX-3W radio meter. Ambient temperature was monitored using IKON made digital weather station. BENETECH GM1311 food thermometer was used to measure the water temperature during SODIS treatment.

 

RESULTS AND DISCUSSION

Turbidity and total coliform count of falaj water

To study the effect of atmospheric temperature on SODIS, this research was carried in the month of February and May. Turbidity and total coliform count of falaj water samples collected in February-18 and May-18 are presented in Table 1.

 

Table 1. Turbidity and total coliform count of falaj water.

Parameter

Month

February,2018

May,2018

Turbidity(NTU)

1

1

Total coliform (MPN/100 mL)

201.4

29.2

 

Disinfection effectiveness of solar radiation is reduced by suspended particles in the water, which absorb and scatter radiation in the visible and UV range. At a turbidity level of 26 NTU, the intensity of UV radiation decreases by approx. 50% after 10 cm penetration depth, compared to 25% reduction in clear water (Sommer et al. 1997). Other studies also showed that the pathogen removal rate of SODIS decreases with the increasing turbidity of water (McGuigan, Joyce & Conroy 1999; Kehoe, 2001; Gómez-Couso, Fontán-Saínz, Sichel, Fernández-Ibáñez & Ares-Mazás 2009). A turbidity level of 30 NTU was postulated as a threshold for the upper limit for effective SODIS treatment (Samuel et al. 2016). Water with higher turbidity should be pre-treated. Since turbidity of falaj water was very low, all the SODIS experiments are carried out without any pre-treatment.

WHO (1993)  classified the presence of 1-10 faecal coliforms or E.coli per 100ml in water supplies as low risk, a concentration of 10-100 per 100 ml as intermediate risk, a concentration of 100-1000 per 100 ml as High risk and above 1000 faecal coliforms or E-Coli per 100 ml as very high risk. Falaj water in February and May classified as high risk and intermediate risk water supply respectively. To compliance with WHO guidelines, water supplies should be free from E-coli or faecal coliforms.

 

UV radiation and ambient temperature

The main mechanism of pathogen disinfection in solar disinfection is direct or mediated damage to proteins and the DNA of the organisms, induced by radiation in the UV-B, UV-A, and possibly the lower visible range (Whitlam & Codd 1986; Woodhead 1987). Ultraviolet (UVA, UVB and UVC) irradiance (Iuv) measured during experimentation period (May 2018 and February 2018) is presented in Fig. 2 and Fig. 3.

In February -2018 Ultraviolet (UVA+B) light levels ranged from minimum of 4.85 W/m2 in morning conditions to a maximum of 14.128 W/m2 at afternoons (ie 12:00 Noon). In May- 2018 Ultraviolet (UVA+B) light levels ranged from minimum of 13.66 W/m2 in morning conditions to a maximum of 33.31 W/m2 at afternoon. Similar trends were observed in a SODIS study conducted in sub-Saharan weather conditions by Asiimwe et al. (2013). In February-2018 the average ambient temperature ranged from a low of 180C to a maximum of 280C. In May 2018, average minimum and maximum ambient temperatures were 290C and 400C respectively.

 

 

Fig. 2. UV irradiance in May -2018 at University of Nizwa, Oman.

 

Fig. 3. UV irradiance in February -2018 at University of Nizwa, Oman.

 

Table 2. Total coliform counts and disinfection percentages in February-2018.

Exposure duration

(Hours)

Volume/ depth of Falaj water in PET bottle

Water Temperature °C

Air Temperature °C

MPN

/100 mL

 

Percentage of reduction of Total Coliform

0

1.5 L/7 cm

21

23

201.4

-

3

37.5

23

143.9

28.55

6

36

28

29.5

85.35

 9

36.5

25

2.0

99

 

Results indicate that falaj water needs more exposure time in February to disinfect the total coliform to undetectable level (Fig. 4). This is mainly due to high count of total coliform, low atmospheric temperature and low UV (A+B) irradiance in February month.

 

Table 3. Total coliform counts and disinfection percentages in May-2018.

Exposure duration

(Hours)

 

Volume of Falaj water in PET bottle

Water Temperature °C

Air Temperature °C

MPN

/100 mL

 

Percentage reduction of Total Coliform

0

1.5 L/7 cm

30

35

29.2

-

1

38

37

25.9

11.3

2

42

39

14.6

50

 3

49

40

<1

100

 

 

Fig. 4. Total coliform count before and after SODIS in Feb-18.

 

Due to high temperatures and low total coliform count in May, complete disinfection happened in three hours. Generally, in sunny conditions the lag phase of bacterial growth before start of disinfection was shorter compared to cloudy conditions (Asiimwe, Quilty, Muyanja & McGuigan 2013). According to Fig.5, total coliform disinfection rate in May-2018 and Feb-2018 were 0.826/hr and 0.428/hr respectively.  Disinfection rate in May-18 was two folds greater than disinfection rate in Feb-18.

 

 

Fig. 5. Disinfection kinetics of total coliform in Feb-2018 and May-2018.

 

This higher disinfection rate in May-18 is due to high water temperature and high UV-A radiation compared to Feb-18. For water temperatures exceeding 450C, a synergetic effect of UV-A radiation and water temperature increases the bacterial die of rate significantly (Ayoub & Malaeb 2019). In a SODIS study conducted by Awrajaw Dessie et al.(2014) in Ethiopia reported that, bacterial disinfection was higher by a factor 1.68 in half surfaced black colored PET bottles than in raw water samples exposed on cardboard, concrete and CIS surfaces.

 

Effect of water volume and depth on SODIS

Data in Table 4 and 5 shows the effect of water volume and water depth on disinfection percentages after exposure to natural solar radiation in February-2018 and May-2018 respectively.

 

Table 4. Effect of water volume and depth on disinfection of total coliform in February-2018.

 

Time

 

Volume of water(L)

Water Temperature °C

 

Water depth in the bottle (cm)

MPN

/100 mL

% Reduction

10:00 am

(initial reading)

1.5

21

8

201.4

 

1

7

0.5

6

1:00 pm

(after 3hr)

1.5

34

8

143.9

28.55

1

37

7

133.4

33.76

0.5

36.5

6

125.9

37.48

4:00 pm

(after 6hr)

1.5

34

8

29.5

85.35

1

36

7

7.5

96.27

0.5

35

6

5.2

97.41

 

Table 5. Effect of water volume and depth on disinfection of total coliform in May-2018.

Time

 

Volume of water(L)

Water depth in the bottle (cm)

Water Temperature °C

MPN

/100 mL

% Reduction

10:00 am

(Initial reading)

1.5

8

30

29.2

 

1

7

0.5

6

11:00 am

 

1.5

8

38

25.9

11.3

1

7

39

24.6

15.75

0.5

6

41

17.6

39.72

12:00 pm

1.5

8

42

14.6

50

1

7

43

1.0

96.57

0.5

6

45

1.0

96.57

1:00 pm

1.5

8

47

<1

100

1

7

47

<1

100

0.5

6

49

<1

100

 

Highest disinfection rate was found on samples having water depth 6 cm  and the lowest disinfection rate was observed on samples having water depth 8 cm both in February and May experimentation(Fig.6 and Fig.7). This might be due to the reduction of intensity of UV radiation with increasing water depth.

UV irradiation intensity decreases significantly with penetration depth in the water column, even in clear water. SODIS efficacy is, thus, higher in smaller bottles (Dessie et al. 2014). This effect is more important if the water contains suspended particles or dissolved organic materials that absorb UV radiation. For this reason, it is recommended to use bottles that are not larger than 2 litre in volume, with a maximum penetration depth of 10cm (Samuel et al. 2016).

 

Effect of type of bottle on efficiency of SODIS

Results of this study (Fig.8) shows that glass and PET bottle with less plastic are more efficient in disinfecting total coli-form compare to thick and thin PET bottles at a shorter exposure period (1 hour). Percentage removal is same in all the cases at an exposure period of 4 hours. These results are in agreement with studies conducted by Sommer et al. (1997) and Asiimwe et al. (2013).

 

 

Fig. 6. Disinfection kinetics of total coliform on falaj water samples having different depth/volumes in February -2018.

 

 

Fig. 7. Disinfection kinetics of total coliform on falaj water samples having different depths/volumes in May -2018.

 

 

Fig. 8. Effect of type of bottle on efficiency of SODIS.

 

Sommer et al. (1997) reported comparable faecal coliforms and viral disinfection between glass and PET bottles under similar experimental conditions.  Asiimwe et al. (2013) too reported similar observations in disinfecting E-Coli in glass and PET bottles under similar weather conditions. Though PET and glass containers have comparable efficiency, it remains the end user’s choice depending on availability and cost of either glass or PET bottles, concern of health risks associated with PET bottles and other factors.

Glass bottles also have certain disadvantages compared to PET bottles which like greater weight and risk of breaking, limited availability in suitable sizes, and the lack of reusable caps (Samuel et al. 2016).

CONCLUSION

Results of this study have proved SODIS as anappropriate household water treatment and safe storage (HWTS) for disinfecting falaj water in Oman. The disinfection of total coliform in falaj water depends on the length of exposure time, solar radiation and climatic condition under which the sample is exposed to sunlight and type of container/bottle. Due to synergetic effect of UV-A radiation and water temperature, disinfection rate in May-18 was two folds greater than disinfection rate in Feb-18. Samples having water depth of 6 cm have better disinfection rate compare to samples having water depth of 8 cm, due to the reduction of intensity of UV radiation with increasing water depth. PET bottle with less plastic are more efficient in disinfecting total coli-form compare to thick and thin PET bottles at a shorter exposure period.

The overall efficiency of the SODIS in this study reduced the concentration of total coliform bacteria in falaj water from high risk concentration to low risk concentration. The base line data that is developed in this study shall be useful in developing continuous flow solar disinfection systems.

 

ACKNOWLEDGEMENT

Authors would like to thank the Dean and Assistant Dean (Research), College of Engineering and Architecture, University of Nizwa, Oman for necessary support.

 

Authors’ contribution

Sreedhar Reddy Sajjala proposed the research idea, performed experimental part and wrote the manuscript draft. Munira assisted during experimentation. Salam kadhim and Anwar Ahmed aided in interpreting the results and worked on the manuscript. All authors discussed the results and commented on the manuscript.

 

Declarations

It is confirmed that work has not been published, not under consideration for publication elsewhere, approved by all authors and if accepted, it will not be published elsewhere in the same form, in English or in any other language.

 

Abdel Rahmnn, H & Omezzine, A 1996, Aflaj Water Resources Management: Tradable Water Rights to Improve Irrigation Productivity in Oman, Water International, 21(2):70-75.

Al-Kalbani, M, Price, M, Ahmed, M, Abahussain, A & O’Higgins, T  2016, Water Quality Assessment of Aflaj in the Mountains of Oman,  Environment and Natural Resources Research, 6(2):99-114.

Al-Marshudi, A 2001, Traditional Irrigated Agriculture in Oman, Water International, 26(2):259-264.

Al-Marshudi, A 2007, The falaj irrigation system and water allocation markets in Northern Oman, Agricultural Water Management, 91(1-3):71-77.

Asiimwe, J, Quilty, B, Muyanja, C & McGuigan, K  2013, Field comparison of solar water disinfection (SODIS) efficacy between glass and polyethylene terephalate (PET) plastic bottles under sub-Saharan weather conditions,  Journal of Water and Health, 11(4):729-737.

Ayoub, G & Malaeb, L 2019, Solar Water Disinfection: UV Radiation Transmittance of Various Solar Reactor Tubes, Energy Procedia, 157:498-511.

Dessie, A, Alemayehu, E, Mekonen, S, Legesse, W, Kloos, H & Ambelu, A  2014, Solar disinfection: an approach for low-cost household water treatment technology in Southwestern Ethiopia,  Journal of Environmental Health Science and Engineering, 12(25):1-6.

Fairouz Megdiche-Kharrat, Mohamed Moussa & Hichem Rejeb  2017, 'Aflaj’ Water Management in Oman: The Case of Falaj Al-Khatmeen in Birkat Al-Mouz, Wilayat Nizwa', in M. Ouessar et al. (eds.), Water and land

security in dry lands, Springer International Publishing, AG.

Gelover, S, Gómez, L, Reyes, K & Teresa Leal, M  2006, A practical demonstration of water disinfection using TiO2 films and sunlight, Water Research, 40(17):3274-3280.

Gómez-Couso, H, Fontán-Saínz, M, Sichel, C, Fernández-Ibáñez, P & Ares-Mazás, E  2009, Efficacy of the solar water disinfection method in turbid waters experimentally contaminated with Cryptosporidium parvumoocysts under real field conditions, Tropical Medicine and International Health, 14(6):620-627.

Kehoe, S 2001, Effect of agitation, turbidity, aluminium foil reflectors and container volume on the disinfection efficiency of batch-process solar disinfectors, Water Research, 35(4):1061-1065.

McGuigan, K, Conroy, R, Mosler, H, Preez, M, Ubomba-Jaswa, E & Fernandez-Ibañez, P 2012, Solar water disinfection (SODIS): A review from bench-top to roof-top, Journal of Hazardous Materials, 235-236:29-46.

Mcguigan, K, Joyce, T & Conroy, R 1999, Solar disinfection: Use of sunlight to decontaminate drinking water in developing countries,  Journal of Medical Microbiology, 48(9):785-787.

Norman, WR, Shayya, WH, Al-Ghafri, AS & McCann, IR 1998, Aflaj irrigation and on-farm water management in northern Oman, Irrigation and Drainage System., 12(1):35-48.

Oates, P, Shanahan, P & Polz, M 2003, Solar disinfection (SODIS): Simulation of solar radiation for global assessment and application for point-of-use water treatment in Haiti, Water Research, 37(1):47-54.

Samuel Luzi, Monika Tobler, Fabian Suter & Regula Meierhofer 2016, SODIS manual: Guidance on solar water disinfection, Eawag, Switzerland.

Sichel, C, Fernández-Ibáñez, P, de Cara, M & Tello, J  2009, Lethal synergy of solar UV-radiation and H2O2 on wild Fusarium solani spores in distilled and natural well water, Water Research, 43(7):1841-1850.

Sommer, B, Marino, A, Solarte, Y, Salas, M, Dierolf, C, Valiente, C, Mora, D, Rechsteiner, R,   Setter, P & Wirojanagud, W 1997, SODIS- An emerging water treatment process. J Water SRT-Aqua., 46(3):127–137.

Whitlam, GC & Codd, GA 1986, Damage to micro-organisms by light, Special Publication of the Society of General Microbiology., 17:129-69.

Woodhead, A 1987, Understanding UV Solar-UV Actions on Living Cells. Jagger John, BioScience, 37(10):737-737.

World Health Organization (WHO) 1993, Guidelines for Drinking Water Quality, 2nd ed, Vol. 1, Geneva.

Yaqoub Al Harthi, Natiq joodi, Satya Narayana, SV 2015, Water quality analysis of falaj daris at Nizwa area- A case study,International Journal of Multidisciplinary Research and Development, 2(5):302-305.

Zekri, S & Al-Marshudi, A 2008, A millenarian water rights system and water markets in Oman, Water International, 33(3):350-360.

Zoubeida Tayara 2015, Integrated Water Management for Aflaj System in Oman —Different approach,  Journal of Agricultural Science and Technology A, 5:811-823.