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|Cite as Brittney Dawney (2021). "Decreasing turbidity to optimize solar water disinfection lit review". Appropedia. Retrieved 2021-10-19.|
Project Description An effective method to reduce turbidity has the potential to appreciably increase the number of people with access to SODIS treatment. This study is focused on providing a simple, low-cost method of reducing turbidity of source water prior to SODIS treatment. This study will measure the effectiveness of natural coagulants on a variety of soil media in water. Availability of materials will be considered a strong determinant in the viability of treatment. Global soil distribution and solar energy potential will be considered in determining which areas of the world will benefit most from this type of treatment. Details of project: Decreasing turbidity to optimize solar water disinfection
Full article: Brittney Dawney and Joshua M. Pearce, "Optimizing the solar water disinfection (SODIS) method by decreasing turbidity with NaCl", Journal of Water, Sanitation and Hygiene for Development 2(2) pp. 87-94 (2012). DOI Open access
Need for clean water[edit | edit source]
Managing water in the home[edit | edit source]
Sobsey, M. Managing Water in the Home: Accelerated Health Gains from Improved Water Supply. (Department of Protection of the Human Environment, World Health Organization. WHO/SDE/WSH/02.07: 2002)
- Many rural dwellers lack indoor plumbing or nearby outdoor piped water from a safe supply, and often have to travel great distances to reach water source regardless of quality. Many urban dwellers also lack safe water.
- Water typically collected from most convenient source - often fecally contaminated.
- Water often contaminated due to poor handling or unsafe storage.
- "Repeatedly demonstrated and generally accepted that the most important and immediate risks to human health by using contaminated drinking water are those from enteric microbes of fecal origin or other sources."
- 4 billion cases of diarrhea annually and 2.2 million deaths annually, mostly in children under the age of five
Water in a changing world[edit | edit source]
World Water Assessment Programme (United Nations); UN-Water; UNESCO. "Water in a changing world". (UNESCO Publications; Earthscan: Paris; London, 2009).
- Overall economic loss in Africa alone due to inadequate access to safe water and sanitation is estimated at $28.4 billion a year (about 5% of GDP).
- Almost 50% of the Sub-Saharan population lives below the absolute poverty line of $1.25 per day, and 75% of the population lives below $2 per day.
- The world is not on track to meet the UN Millennium Development Goals sanitation target: between 1990 and 2006 the proportion of people without access to improved sanitation declined by only 8 percent. Based on current trends, the total population without access to improved sanitation in 2015 will only have decreased from 2.5 billion to 2.4 billion. Sub-Saharan Africa and Oceania are not on track to meet the MDG drinking water target.
- At the world population growth rate of 80 million people per year, the corresponding freshwater demand is about 64 billion m3 per year.
- An estimated 3 billion people will be added to the world population by 2050 and of these, 90% will be in developing countries - many in regions without access to improved sanitation and safe drinking water.
- In some developing countries, informal and small-scale private water distributors charge full market prices to households, amounting to 3%-11% of household income.
- Every $1 invested in improved water supply and sanitation yields on average gains of $4-$12.
- Almost 10% of the world disease burden could be prevented by improved water supply, sanitation, hygiene and management of water resources.
- In 2000, diarrhea accounted for 17% of the 10.6 million deaths in children under the age of five.
- Some 1.4 million children die each year from preventable diarrheal diseases, which remains the major killer among water-, sanitation- and hygiene-related diseases, amounting to 43% of deaths. Sub-Saharan Africa and South Asia are the hardest hit.
- Almost 2/3 of people lacking access to safe drinking water live on less than $2 a day, and 1/3 on less than $1 a day. More than 660 million people without adequate sanitation live on less than $2 a day and more than 385 million people on less than $1 a day. Households, not public agencies, often make the largest investment in basic sanitation, with the ratio of household to government investment around 10 to 1. This highlights the need for affordable technologies for access to improved drinking water and sanitation.
- 1.4 billion people classified as poor: 44% in South Asia, 24% in sub-Saharan Africa, 24% in East Asia, and 6.5% in the Caribbean and Latin America.
UN-Water global assessment of sanitation and drinking water[edit | edit source]
World Health Organization. UN-water global annual assessment of sanitation and drinking-water GLAAS 2010 : targeting resources for better results. (World Health Organization,: Geneva, Switzerland :, 2010).
Fecal contamination of drinking water within peri-urban households[edit | edit source]
Oswald, W.E. et al. "Fecal contamination of drinking water within peri-urban households, Lima, Peru". American Journal of Tropical Medicine and Hygiene 77, 699-704 (2007).
We assessed fecal contamination of drinking water in households in 2 peri-urban communities of Lima, Peru. We measured Escherichia coli counts in municipal source water and, within households, water from principal storage containers, stored boiled drinking water, and water in a serving cup. Source water was microbiologically clean, but 26 (28%) of 93 samples of water stored for cooking had fecal contamination. Twenty-seven (30%) of 91 stored boiled drinking water samples grew E. coli. Boiled water was more frequently contaminated when served in a drinking cup than when stored (P < 0.01). Post-source contamination increased successively through the steps of usage from source water to the point of consumption. Boiling failed to ensure safe drinking water at the point of consumption because of easily contaminated containers and poor domestic hygiene. Hygiene education, better point-of-use treatment and storage options, and in-house water connections are urgently needed.
- Underscores need for point-of-use treatment and storage options - SODIS qualifies as this type of technology
Water, sanitation, and hygiene interventions to reduce diarrhea in less developed countries[edit | edit source]
Fewtrell, L. et al. "Water, sanitation, and hygiene interventions to reduce diarrhea in less developed countries: a systematic review and meta-analysis". The Lancet Infectious Diseases 5, 42-52 (2005).
Many studies have reported the results of interventions to reduce illness through improvements in drinking water, sanitation facilities, and hygiene practices in less developed countries. There has, however, been no formal systematic review and meta-analysis comparing the evidence of the relative effectiveness of these interventions. We developed a comprehensive search strategy designed to identify all peer-reviewed articles, in any language, that presented water, sanitation, or hygiene interventions. We examined only those articles with specific measurement of diarrhoea morbidity as a health outcome in non-outbreak conditions. We screened the titles and, where necessary, the abstracts of 2120 publications. 46 studies were judged to contain relevant evidence and were reviewed in detail. Data were extracted from these studies and pooled by meta-analysis to provide summary estimates of the effectiveness of each type of intervention. All of the interventions studied were found to reduce significantly the risks of diarrheal illness. Most of the interventions had a similar degree of impact on diarrheal illness, with the relative risk estimates from the overall meta-analysis ranging between 0·63 and 0·75. The results generally agree with those from previous reviews, but water quality interventions (point-of-use water treatment) were found to be more effective than previously thought, and multiple interventions (consisting of combined water, sanitation, and hygiene measures) were not more effective than interventions with a single focus. There is some evidence of publication bias in the findings from the hygiene and water treatment interventions.
Drinking water in developing countries[edit | edit source]
Gadgil, A. Drinking water in developing countries. Annual review of energy and the environment 23, 253-286 (1998).
Safe drinking water remains inaccessible for about 1.1 billion people in the world, and the hourly toll from biological contamination of drinking water is 400 deaths of children (below age 5). This paper reviews the general guidelines for drinking water quality and the scale of the global problem. It reviews the various water disinfection technologies that may be applicable to achieve the desired quality of drinking water in developing countries. It then summarizes financing problems that deter extending access to safe drinking water to the unserved population and identifies feasible policy positions for enhancing availability of drinking water in these countries.
Solar water disinfection[edit | edit source]
- Solar water pasteurisation literature review - 2000-2014
Overview[edit | edit source]
Meierhofer, R. & Wegelin, M. Solar water disinfection: A guide for the application of SODIS. (2002).at <http://web.archive.org/web/20200223031506/http://www.sodis.ch:80/methode/anwendung/ausbildungsmaterial/index_EN>
- Gives background on the need for clean water
- How it works
- Provides studies
- Where the technology has been introduced
Centers for Disease Control and Prevention. Household water treatment options in developing countries: solar water disinfection. (2008).at <http://www.cdc.gov/safewater/publications_pages/options-sodis.pdf>
Mechanisms[edit | edit source]
Characterizing the bacterial inactivation process[edit | edit source]
McGuigan, K., Joyce, T., Conroy, R., Gillespie, J. & Elmore-Meegan, M. "Solar disinfection of drinking water contained in transparent plastic bottles : characterizing the bacterial inactivation process". Journal of Applied Microbiology 84, 1138-1148 (1998).
A series of experiments is reported to identify and characterize the inactivation process in operation when drinking water, heavily contaminated with a Kenyan isolate of Escherichia coli, is stored in transparent plastic bottles that are then exposed to sunlight. The roles of optical and thermal inactivation mechanisms are studied in detail by simulating conditions of optical irradiance, water turbidity and temperature, which were recorded during a series of solar disinfection measurements carried out in the Kenyan Rift Valley. Optical inactivation effects are observed even in highly turbid water (200 ntu) and at low irradiances of only 10 mW cm−2. Thermal inactivation is found to be important only at water temperatures above 45 °C, at which point strong synergy between optical and thermal inactivation processes is observed. The results conﬁrm that, where strong sunshine is available, solar disinfection of drinking water is an effective, low cost method for improving water quality and may be of particular use to refugee camps in disaster areas. Strategies for improving bacterial inactivation are discussed.
- Used bacterial concentrations (E. coli) of 105 cfu ml-1 and turbidity values of 0 to 200 ntu to simulate complete range of field conditions in Kenya.
- Experimental data for three cases: (a) optical inactivation; (b) thermal inactivation; and (c) optical and thermal inactivation.
- Found that optical inactivation is very dependent on turbidity
- Support for combined solar and thermal inactivation, as in the widely-used SODIS method.
- Found that complete bacterial inactivation occurred even in highly turbid (200 ntu) water but only when exposed to strong to medium solar irradiances for periods of at least 7 h. For temperatures greater than 55, thermal inactivation responsible. Samples in intermediate temps (about 45) can still be fully inactivated if water is of low turbidity and exposed to high irradiances (70 mW cm-2 for up to 7 h.
- Turbidity compromises optical inactivation mechanisms (99% inactivation up to only 1 cm into the optical path) but thermal inactivation is increased due to higher emissivity and the relatively lower specific heat capacity of the turbid agent (darker water will absorb more heat).
- Synergistic relationship observed between thermal and optical effects; combined effect is stronger than just the sum of their parts IF temperatures are above 45 oC. Combined heat and irradiance is best.
- States that solar disinfection can be improved considerably by the inclusion of pre-filtration or reduction of turbidity using locally available flocculating agents.
Effect of radiation intensity, water turbidity and exposure time[edit | edit source]
Gomez-Couso, H., Fontan-Sainz, M., McGuigan, K.G. & Ares-Mazas, E. "Effect of radiation intensity, water turbidity and exposure time on the survival of Cryptosporidium during simulated solar disinfection of drinking water". Acta Tropica 112, 43-48 (2009).
The solar disinfection (SODIS) technique is a highly effective process that makes use of solar energy to inactivate pathogenic microorganisms in drinking water in developing countries. The pathogenic protozoan parasite Cryptosporidium parvum is often found in surface waters and is associated with waterborne outbreaks of cryptosporidiosis. In the present study, a complete multi-factorial mathematical model was used to investigate the combined effects of the intensity of solar radiation (200, 600 and 900W/m2 in the 320nm to 10μm range), water turbidity (5, 100 and 300 NTU) and exposure time (4, 8 and 12h) on the viability and infectivity of C. parvum oocysts during simulated SODIS procedures at a constant temperature of 30°C. All three factors had significant effects (p<0.05) on C. parvum survival, as did the interactions of water turbidity with radiation intensity and radiation intensity with exposure time. However, the parameter with the greatest effect was the intensity of radiation; levels ≥600W/m2 and times of exposure between 8 and 12h were required to reduce the oocyst infectivity in water samples with different degrees of turbidity.
- Based on the protozoan parasite Cryptosporidium, which causes the GI disease cryptosporidisis, characterized by watery diarrhea in immunocompromised people. Oocyst form is resistant to chemical agents normally used to disinfect water.
- Results for simulated effects of solar radiation intensity, water turbidity, and exposure time.
- Used clay typical of tropical areas to create turbid water.
- Largest decreases in oocysts observed in water samples with lowest level of turbidity (5 ntu).
- Radiation intensity had a greater effect on survival and at low levels of intensity, turbidity and exposure time had a null effect on the potential viability and infectivity of C. parvum oocysts --> therefore, turbidity only significant for low intensity radiation.
Preparation of turbid water
- Used soil collected from Almeria, Spain, as its composition is known to be very similar to that of soil from tropical areas (Patrick, 1980). --> support with other articles/books.
- Masses added to distilled water to obtain desired turbidities of 5, 100 and 300 ntu, then agitated for 30 min, then left to settle for 1 h.
- Supernatant collected and turbidity adjusted again to 5, 100 and 300 ntu by adding distilled water.
- Suspensions then sterilised my autoclaving for 20 min at 120 psi, then stored at 4-8 oC.
Composition of soil: shown in table in article.
Good source of relevant articles - cites Heaselgrave et al., 2006; Joyce et al., 1996; Conroy et al., 2001; Smith et al., 2004; Kehoe et al., 2004; and Lonnen et al., 2005/Heaselgrave et al., 2006 as demonstrated the high effectiveness of SODIS against Poliovirus type II; Escherichia coli; Vibrio cholerae; Salmonella typhimurium; Shigella dysenteria type I; Pseudomonas aeruginoas, Candida albicans, Fusarium solani, and the trophozoite stage of Acanthamoeba polyphaga, respectively. Also, cysts of Giardia muris and oocysts of Cryptosporidium parvum completevly inactivated after batch SODIS exposures of 4 and 10 h, respectively (McGuigan et al., 2006).
Effect of agitation, turbidity, aluminium foil reflectors and container volume[edit | edit source]
Kehoe, S.C. et al. "Effect of agitation, turbidity, aluminium foil reflectors and container volume on the inactivation efficiency of batch-process solar disinfectors". Water Res 35, 1061-1065 (2001).
We report the results of experiments designed to improve the efficacy of the solar disinfection of drinking water, inactivation process. The effects of periodic agitation, covering the rear surface of the container with aluminum foil, container volume and turbidity on the solar inactivation kinetics of Escherichia coli (starting population = 10(6) CFU ml(-1)) were investigated. It was shown that agitation promoted the release of dissolved oxygen from water with subsequent decrease in the inactivation rates of E. coli. In contrast, covering the rear surface of the solar disinfection container with aluminum foil improved the inactivation efficiency of the system. The mean decay constant for bacterial populations in foil-backed bottles was found to be a factor of 1.85 (std. dev. = 0.43) higher than that of non-foil-backed bottles. Inactivation rates decrease as turbidity increases. However, total inactivation was achievable in 300 NTU samples within 8 h exposure to strong sunshine. Inactivation kinetics was not dependent on the volume of the water container for volumes in the range 500-1500 ml.
Synergistic effect of solar radiation and solar heating[edit | edit source]
Rijal, G.K. & Fujioka, R.S. "Synergistic effect of solar radiation and solar heating to disinfect drinking water sources". Water Sci. Technol 43, 155-162 (2001).
Waterborne diseases are still common in developing countries as drinking water sources are contaminated and feasible means to reliably treat and disinfect these waters are not available. Many of these developing countries are in the tropical regions of the world where sunlight is plentiful. The objective of this study was to evaluate the effectiveness of combining solar radiation and solar heating to disinfect contaminated water using a modified Family Sol*Saver System (FSP). The non-UV transmittable cover sheet of the former FSP system was replaced with an UV transmittable plastic cover sheet to enable more wavelengths of sunlight to treat the water. Disinfection efficiency of both systems was evaluated based on reduction of the natural populations of faecal coliform, E. coli, enterococci, C. perfringens, total heterotrophic bacteria, hydrogen sulphide producing bacteria and FRNA virus. The results showed that under sunny and partly sunny conditions, water was heated to critical temperature (60 degrees C) in both the FSP systems inactivating more than 3 log (99.9%) of the concentrations of faecal coliform and E. coli to undetectable levels of < 1 CFU/100 mL within 2-5 h exposure to sunlight. However, under cloudy conditions, the two FSP systems did not reduce the concentrations of faecal indicator bacteria to levels of < 1 CFU/100 mL. Nonetheless, sufficient evidence was obtained to show that UV radiation of sunlight plus heat worked synergistically to enhance the inactivation of faecal indicator bacteria. The relative log removal of indicator microorganism in the FSP treated water was total heterotrophic bacteria < C. perfringens < F RNA virus < enterococci < E. coli < faecal coliform. In summary, time of exposure to heat and radiation effects of sunlight were important in disinfecting water by solar units. The data indicated that direct radiation of sunlight worked synergistically with solar heating of the water to disinfect the water. Thus, effective disinfection was observed even when the water temperature did not reach 60 degrees C. Finally, the hydrogen sulphide test is a simple and reliable test that householders can use to determine whether their water had been sufficiently disinfected.
Effect of UV-A dose on inactivation efficiency[edit | edit source]
Ubomba-Jaswa, E., Navntoft, C., Polo-López, M.I., Fernandez-Ibáñez, P. & McGuigan, K.G. "Solar disinfection of drinking water (SODIS): an investigation of the effect of UV-A dose on inactivation efficiency". Photochem. Photobiol. Sci 8, 587-595 (2009).
The effect of solar UV-A irradiance and solar UV-A dose on the inactivation of Escherichia coli K-12 using solar disinfection (SODIS) was studied. E. coli K-12 was seeded in natural well-water contained in borosilicate glass tubes and exposed to sunlight at different irradiances and doses of solar UV radiation. In addition, E. coli K-12 was also inoculated into poly(ethylene) terephthalate (PET) bottles and in a continuous flow system (10 L min(-1)) to determine the effect of an interrupted and uninterrupted solar dose on inactivation. Results showed that inactivation from approximately 10(6) CFU mL(-1) to below the detection level (4 CFU/mL) for E. coli K-12, is a function of the total uninterrupted dose delivered to the bacteria and that the minimum dose should be >108 kJ m(-2) for the conditions described (spectral range of 0.295-0.385 microm). For complete inactivation to below the limit of detection, this dose needs to be received regardless of the incident solar UV intensity and needs to be delivered in a continuous and uninterrupted manner. This is illustrated by a continuous flow system in which bacteria were not fully inactivated (residual viable concentration approximately 10(2) CFU/mL) even after 5 h of exposure to strong sunlight and a cumulative dose of >108 kJ m(-2). This has serious implications for attempts to scale-up solar disinfection through the use of re-circulatory continuous flow reactors.
Takeaway: Attempts to scale up SODIS may face serious limitations - implies (?) that SODIS may only be suitable for household. Fine for the purposes of own study.
Effect of pH, inorganic ions, organic matter and H2O2 on E. coli inactivation[edit | edit source]
Rincon, A. "Effect of pH, inorganic ions, organic matter and H2O2 on E. coli K12 photocatalytic inactivation by TiO2 - Implications in solar water disinfection". Applied Catalysis B: Environmental 51, 283-302 (2004).
The effect of different chemical parameters on photocatalytic inactivation of E. coli K12 is discussed. Illumination was produced by a solar lamp and suspended TiO2 P-25 Degussa was used as catalyst. Modiﬁcations of initial pH between 4.0 and 9.0 do not affect the inactivation rate in the absence or presence of the catalyst. Addition of H2 O2 affects positively the E. coli inactivation rate of both photolytic (only light) and photocatalytic (light plus TiO2 ) disinfection processes. Addition of some inorganic ions (0.2 mmol/l) like HCO3 − , HPO4 2− , Cl− , NO3 − and SO4 2− to the suspension affects the sensitivity of bacteria to sunlight in the presence and in absence of TiO2 . Addition of HCO3 − and HPO4 2− resulted in a meaningful decrease in photocatalytic bactericidal effect while it was noted a weak inﬂuence of Cl− , SO4 2− and NO3 − . The effect of counter ion (Na+ and K+ ) is not negligible and can modify the photocatalytic process as the anions. Bacteria inactivation was affected even at low concentrations (0.2 mmol/l) of SO4 2− and HCO3 − , but the same concentration does not affect the resorcinol photodegradation, suggesting that disinfection is more sensitive to the presence of natural anions than photocatalytic degradation of organic compounds. The presence of organic substances naturally present in water like dihydroxybenzenes isomers shows a negative effect on photocatalytic disinfection. The effect of a mixture of chemical substances on photocatalytic disinfection was also studied by adding to the bacterial suspension nutrient broth, phosphate buffer and tap water.