Solar disinfection potentials of aqua lens, photovoltaic and glass bottle subsequent to plant-based coagulant: for low-cost household water treatment systems
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Unaffordable construction cost of conventional water treatment plant and distribution system in most developing countries makes difficult to provide safe and adequate water for all households, especially for the rural setup. Water treatment at the source can be the best alternative. Solar disinfection is one alternative among point of use treatments. In this study, aqua lens, photovoltaic box and glass bottle were used subsequent to plant coagulants to evaluate microbial reduction potentials. Laboratory- and field-based experiments were conducted from May to August 2016. The Escherichia coli, total coliforms and heterotrophic plate counts were used as indicator organisms. The result indicated that aqua lens (AL), photovoltaic box (PV) and glass bottle (GB) have high inactivation rate subsequently almost for all indicator organisms in short solar exposure time. Total coliforms were inactivated in AL (SD = 15.8 °C, R2 = 0.92) followed by PV inactivation temperature association (SD = 11.6 C, R2 = 0.90), and the GB concentrator was inactivated (SD = 10.9 °C, R2 = 0.70) at turbidity level of 3.41 NTU. As the study indicated, aqua lens coupled with Moringa oleifera coagulant can be an effective with minimum cost for household water treatment system. The study also concludes heterotrophic bacteria were more resistant than other types of bacteria in SODIS with similar exposure time.
KeywordsAcrylic glass Aqua lens Moringa oleifera Photovoltaic box Solar disinfection Water treatment
Unsafe drinking water supply, inadequate sanitation and insufficient hygiene practice are the factors causing the major share (88%) of all diarrhea cases. Diarrhea is a leading killer of children, accounting for nine percent of all deaths in 2015 (UNICEF 2016). About 6000 children underage five die every day, and a child dies at every 8 s from water-related disease around the globe. This accounts 19% of total child deaths in developing countries (Gomez-Couso et al. 2009). It also causes malnutrition, with the subsequent consequences on physical development and susceptibility to other infections (Gomez-Couso et al. 2009; Byrne et al. 2011; Fontan-Sainz et al. 2012).
Despite the fact that developing countries have large amount of freshwater resources, treatment plant construction and inappropriate treatment cost limit the distribution of the system at a household level. According to Bekele and Leta (2016), 51% of Ethiopian rural residents depend on surface water without treatment. Although conventional water treatment improves water quality, studies have shown that household water treatment techniques could also be used to treat water (Sobsey et al. 2008). WHO estimated improving access to safe water and sanitation ought to forestall at least 9.1% of the international burden of ailments and 6.3% of all deaths (Byrne et al. 2011). Point of use systems refers to the range of water treatment methods including solar treatment, physical treatment, chemical treatment and combined treatment which treat water at the point of use by avoiding contamination during distribution, collection, transportation and storage (Sobsey 2002).
SODIS is a cheap and easy to use, environmental friendly and effective drinking water disinfection technology (Sobsey et al. 2008). The method treats contaminated water in transparent plastic bottles through exposure to sunlight for a minimum of 6 h (Byrne et al. 2011). Following the exposure time, the water is safe to be consumed as the microbial loads can be significantly reduced. SODIS technology enhances bactericidal effect of UVA electromagnetic region (wavelengths in the range of 320–400 nm) of solar radiation with synergism effect of heat (infrared wave) and in the presence of dissolved oxygen species for inactivation of pathogens in the water. UV radiation showed an adverse effect on microbial skill to achieve cellular respiration and generation of adenosine triphosphate (Bosshard et al. 2010).
Drinking water disinfection by natural and/or artificial sunlight is widely studied using plastic or/and glass materials by the aid of photoconcentrator catalysts for the inactivation of a number of bacteria (Helali et al. 2013). Light intensity of wavelength, solar exposure time, availability of dissolved oxygen, turbidity level and water temperature are major study variables that affect the efficiency of SODIS (Byrne et al. 2011).
The study aimed to compare the disinfection potential of (GB)-, (PV)- and (AL)-based SODIS disinfection using some indicator organisms like E. coli, total coliforms and heterotrophic plate counts by using M. oleifera as pre-treatment for turbidity reduction.
Materials and methods
Laboratory- and field-based experiments were conducted from May 24, 2016, up to August 2, 2016, to investigate the solar disinfection (SODIS) potential of three concentrators (GB, PV and AL).
During laboratory experiment, all activities were performed in line with laboratory quality standards. All sample bottles and glass wares were sterilized keeping standard time, temperature and pressure. Control sample was kept at room preventing from sunlight and high temperature exposure.
Turbidity removal test
A turbidity removal test was conducted on natural surface water from Ginjo Gudru by using M. oleifera seed powder. Initially, the raw water turbidity level was 28.6, 30.7 and 45.6 NTU taken at different sampling times. The jar test apparatus was used in a turbidity removal experiment, whereby 10, 30 and 50 mg/L dose of M. oleifera seed powder was added in each 1-L beaker containing the water samples at three turbidity levels, and the change was measured after 2 h with their control (Lea 2010).
UVA irradiation measurement
UVA was measured within every 30-min intervals (Reed 1997) from 12 up to 31/2 pm by calibrated solar taster and clear sky calculator with a central wavelength of 320–400 nm which provides data in terms of incident WUV/m2. QUV was calculated for comparison of solar test results (Helali et al. 2013).
Dissolved oxygen was one of the critical parameters in this study, and the initial dissolved oxygen availability was measured to compare with the final contents at different solar exposure times. All containers were agitated at 30-min intervals, to maintain oxygen equilibration within the water samples. By using dissolved oxygen measuring apparatus, the variable was measured at 30-min interval similarly to another variables (Burgess et al. 2007).
Microbial indicator organisms
E. coli and total coliforms
Membrane filtration technique was used for both total coliforms and E. coli, 3.81 g of membrane lauryl sulfate broth mixed with 100 mL of distilled water and sterilized at standardized time, temperature and pressure (Oxoid, Basingstoke, England) as ISO 9308-3:1999 and ISO 9308-1:2000 (Almeida et al. 2015). All samples were replicated and prepared at required dilution (0.1 and 0.01) since it is the standard dilution for surface water or rivers. One hundred milliliters of diluted sample discharged to vacuum pumper which contains filter paper with pour size of 0.45 μm and 47 mm diameter. Finally, the filter paper transferred to sterilized petri dishes with 50 × 12 mm diameter that contains absorbent pad already pipetted with 2 mL of culture media. After incubating at optimum temperature and time, colonies were counted to compare with initial load (Myers 2003).
Heterotrophic plate counts
The pour plate method or standard plate count method was used to determine heterotrophic plate count bacteria density. 2.35 g of plate count agar was mixed with 100 mL cool water and sterilized as standard; then, melted medium was kept in a water bath between 44 and 46 °C until used. The appropriate amount (2 mL) of diluted sample pipetted into the sterilized petri dishes for each different volume of diluted sample used 12 mL of liquefied media, and each dilution was replicated. The medium poured into the dish by gently lifting the cover just high enough to pour. Melted medium was mixed thoroughly with the sample in the petri dish by rotating the dish in opposite directions or by rotating and tilting the plates placed on a surface level inside the hood and solidify within 10 min. Finally, dishes placed inverted to prevent condensation and seal in a plastic sheet, followed by incubation at 35 °C for 48 h (Stillings and Herzig 1998).
Chick–Watson model of microbial disinfection kinetics
Solar disinfection methods
Glass bottle solar disinfection
Photovoltaic solar disinfection
Figure 1b shows that the bottom surface of the PV box is alone coated with semiconductor photocatalyst TiO2, while the top portion of the box was left; 92–98% transparent acrylic sheet was used to pass UV light through and fall on the TiO2 layer at the bottom surface to determine bacterial inactivation after exposure. Bacterial inactivation was calculated within the interval of 30 min from each turbidity category (Murugan and Ram 2018).
Solar Reactor—Photocatalytic Reactions of TiO2
Aqua lens solar disinfection
Aqua lens is a developing technology, with low design expenditure by locally available materials and ease for operation. As indicated in Fig. 1d, the structure contains four each 2.5-m-long stand woods and 75–100 cm in diameter plastic sheet to hold water which used as solar concentrator or lens, at the bottom four small tires connected for each stand to push or pull easily in the light direction to get focal point.
Data were analyzed using SPSS software for Windows Version 20 and Microsoft Excel tool 2013. The linear regression coefficient of determination and descriptive statistics of standard deviation were used to summarize the data. The log inactivation tests were conducted to compare inactivation rate of concentrators for each indicator organism (Dessie et al. 2014).
Moringa oleifera (MO) turbidity removal efficiency at low turbidity level
UVA irradiation measurement for solar disinfection experiment
All experiments were exposed for 31/2 h. to follow log inactivation of target indicator organisms. In three disinfection setups, all variables were measured within 30-min interval including UVA irradiation. In different weather conditions and solar exposure time, the UVA intensity was measured in the range of 645–1200 WUV/m2.
Microbial inactivation of aqua lens (AL), photovoltaic (PV) and glass bottle (GB) at different turbidity levels
At 2.81 NTU turbidity level
At 3.41 NTU turbidity level
Figure 4c presents that photovoltaic and glass bottle concentrators completely inactivated after log 3 and log 1.63, respectively, but aqua lens inactivated totally before 3 h. with log 2.14.
At 6.9 NTU turbidity level
Moringa oleifera as pre-treatment for solar disinfection
Moringa oleifera seed powder was used as a primary natural coagulant for low-cost household water treatment (Yahaya et al. 2011), at a range of turbidity levels. The removal efficiency of M. oleifera was increased when the raw water samples were highly turbid. For water sample of relatively high initial turbidity of 45.6 NTU, M. oleifera produced the best results with an average turbidity reduction of 94%. Similar studies have been reported on turbidity removal efficiency and initial turbidity level (Abatneh et al. 2014).
In all three experimental setups, the water samples that contain relatively high turbidity of 6.9 NTU were achieved low inactivation rate of indicator organisms than the others. A different study that has been conducted in this area explains that inactivation rate clearly decreased when turbidity increased. Naturally dissolved organic matter may act as a photosensitizer and hence advance the inactivation process (Burgess et al. 2007). In aqua lens, E. coli inactivation showed negatively strong association (R2 = 0.98), and both PV and GB were associated negatively (R2 = 0.95) at different turbidity levels. High turbidity increased inactivation times and enhanced bacterial re-growth (Kehoe et al. 2001).
Solar irradiance measurement
Under UVA exposure, the biocidal action of UVA has also been attributed to the production of reactive oxygen species which are generated from dissolved oxygen in water.
The photosensitization of molecules in the cell with any naturally occurring dissolved organic matter can absorb photons of wavelengths between 320 and 400 nm, to induce photochemical reactions (Burgess et al. 2007; Byrne et al. 2011).
Water temperature measurement
As laboratory result indicated next to aqua lens, photovoltaic box disinfection showed relatively high inactivation rate than glass bottle, almost for all indicator organisms in short solar exposure time. Total coliforms were inactivated in AL (SD = 15.8 °C, R2 = 0.92) followed by PV inactivation temperature association (SD = 11.6 °C, R2 = 0.90), and the GB concentrator was inactivated (SD = 10.9 °C, R2 = 0.70) at turbidity level of 3.41 NTU. The role of semiconductor TiO2 with natural organic matter to form highly disinfectants reactive oxygen species and the high light transmittance potential of acrylic glass sheet supports to attain high inactivation rate than GB (Mcguigan et al. 2012; Murugan and Ram 2018).
Water temperature was raised through progress when solar exposure time becomes increased. All disinfection setups were measured slightly different from water temperature concentrating potentials. The aqua lens measured highest water temperature (74 °C) followed by photovoltaic (60 °C) and the glass bottle (52.5 °C) which was the lowest water temperature recorded in this study at different turbidity levels. Similar studies have been investigated that glass bottle is able to concentrate 45–50 °C water temperature at different weather conditions with global irradiance of 800 W/m2 (Navntoft et al. 2008; Mcguigan et al. 2012).
Aluminum foil was used at back side of half-blackened GB, PV and AL disinfection setups. High reflective power of aluminum foil to concentrators was elevated water temperature at short exposure time. Experimental studies confirmed that aluminum foil back-coated solar concentrators increased disinfection rate constants by a factor of twofold (Navntoft et al. 2008; Kehoe et al. 2001; Rengifo-herrera et al. 2011; Mcguigan et al. 2012).
In this study, dissolved oxygen in the water container ranged between 6.35 and 8.74 mg/L, and as investigated in laboratory experiment dissolved oxygen was inversely related to water temperature (R2 = 0.78). A similar study explained that the amount of dissolved oxygen quickly utilized in some stages of the reaction due to increment of temperature (Byrne et al. 2011; Giannakis et al. 2014).
All experiments were exposed to both optical (UVA light) and thermal (infrared heat) electromagnetic spectrum inactivation system. The inactivation result which is shown above is direct synergism effect of light and heat. However, bactericidal action was evidenced at temperatures above 40–45 °C with a synergistic SODIS process (Byrne et al. 2011; Mcguigan et al. 2012; Helali et al. 2013; Giannakis et al. 2014). The E. coli, total coliforms and heterotrophic plate counts inactivation experiments were conducted at natural waters source in three separate turbidity levels (2.81, 3.41 and 6.9 NTU). The relation between three indicator organisms like E. coli is assumed to be a subset of total coliforms, which is a subset of heterotrophic plate counts bacteria (Wilson and Andrews 2011).
In three and half hour solar disinfection exposure time almost in all experiments, E. coli were inactivated prior than total coliforms and heterotrophic plate counts with complete inactivation range of 2 h (2.81 NTU) in aqua lens and 3 h (6.9 NTU) in glass bottle disinfection system with the association (SD = 10.8 °C, R2 = 0.81). However, E. coli were inactivated in aqua lens concentrator (SD = 14.1 °C, R2 = 0.91), which shows high association between E. coli inactivation and water temperature. Different studies support this complete inactivation rate with indicated exposure time range, keeping other variables similar to this result (Mcguigan et al. 2012).
Mesophilic characteristics of E. coli thrive between 20 and 45 °C, but for the temperature beyond the range there is a thermal tension exerted to the cells, affecting the cell wall in addition to destroying the proteins and nucleic acids, leading to death of bacteria (Giannakis et al. 2014). Total coliforms and HPC completely inactivated at 21/2 and 3 h. in aqua lens solar concentrator with the association of (SD = 15.3 °C, R2 = 0.90) and (SD = 16.0 °C, R2 = 0.77) at 2.81 NTU turbidity level, respectively. Total coliforms were recorded similar inactivation time in PV disinfection system; however, 30 additional minutes were required to inactive heterotrophic plate counts completely, considering at different turbidity levels (Wilson and Andrews 2011).
The disinfection potential of concentrators was increased at 2.81 NTU. Aqua lens solar disinfection was shown to be an effective household water treatment system. Heterotrophic plate counts were more resistant than the other coliforms in SODIS treatment within similar inactivation exposure time.
We are grateful to Jimma University for financial and logistic support.
- Almeida J, Félix A, Figueiredo RAA (2015) Drinking-water microbiological quality survey in the district of Aveiro (Portugal): a nine-year surveillance study (2000–2008). 3(March), pp 38–44Google Scholar
- Bekele T, Leta S (2016) Water supply and health: drinking water and sanitation coverage in Ethiopia 1990–2015 review. Int J Environ Agri Biotec 1(1):11–24Google Scholar
- Burgess L, Gara A, Le B, Letkeman S (2007) The role of reactive oxygen species in the solar disinfection (SODIS) system of water contaminated with Escherichia coli and Salmonella enterica serovar Typhimurium. J Exp Microbiol Immunol 11:35–41Google Scholar
- Fontan-Sainz M, Gomez-Couso H, Fernandez-Ibanez P, Ares-Mazas E (2012) Evaluation of the solar water disinfection process (SODIS) against cryptosporidium parvum using a 25-l static solar reactor fitted with a compound parabolic collector (cpc). Am J Trop Med Hyg 86(2):223–228. https://doi.org/10.4269/ajtmh.2012.11-0325 CrossRefGoogle Scholar
- Helali S, Polo-Lopez, MI, Fernandez-Ibanez P, Ohtani B, Amano F, Malato S, Guillard C (2013) Solar photocatalysis: a green technology for E. Coli contaminated water disinfection. Effect of concentration and different types of suspended catalyst. J Photochem Photobiol A 276:31–40CrossRefGoogle Scholar
- Lea M (2010) Bioremediation of turbid surface water using seed extract from Moringa oleifera Lam. (Drumstick) Tree. (February), pp 1–14Google Scholar
- Myers DN (2003) Fecal indicator bacteria. 7:1–64Google Scholar
- Navntoft C, Conroy RM, Mosler HJ, du Preez M, Ubomba-Jaswa E, Fernandez-Ibanez P (2008) Effectiveness of solar disinfection using batch reactors with non-imaging aluminium reflectors under real conditions: natural well-water and solar light. J Photochem Photobiol B Biol 93:155–161CrossRefGoogle Scholar
- Rengifo-herrera JA, Rengifo-herrera A, We J (2011) Solar disinfection of wild Salmonella Sp. In natural water with a 18L CPC photoreactor: detrimental effect of non-sterile storage of treated water solar disinfection of wild Salmonella Sp. In natural water with a 18 L CPC photoreactor : detrimental effect of non-sterile storage of treated water (2015)Google Scholar
- Sobsey MD (2002) Managing water in the home: accelerated health gains from improved water supply. Department of Protection of the Human Environment, World Health Organization, Geneva pp 1–70Google Scholar
- Stillings D, Herzig BR (1998) Comparative Assessment of the newly developed simplatetm method with the existing EPA-approved pour plate method for the detection of heterotrophic plate count bacteria in ozone-treated drinking water, pp 0–13Google Scholar
- UNICEF (2016) One is too many ending child deaths from pneumonia and diarrhoea. https://www.unicef.org/publications/index93020.html
- Yahaya DS, Enemaduku AM, Eru EO (2011) The use of Moringa seed extract in water purification. Int j Res 2(4):1265–1271Google Scholar
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