Sunlight-cleaned water: Research papers on the advantages, economics and safety issues of treating water through solar disinfection (SODIS)

In this technique, transparent containers are filled with contaminated water and placed in direct sunlight for at least 6 h, after which time it becomes safe to drink. This simple, straightforward disinfection method that utilises the abundant, freely available sunlight is low cost, easy to use and sustainable.

SODIS technique

SODIS - a technique to disinfect water through solar energy (Image Courtesy: blogs.princeton.edu)

A review of SODIS-treated water: From benchtop to rooftop

Most commonly used are plastic bottles (PET) which although cost effective, limit the volume treated – usually less than 2 L per batch. In this regard, noncoloured glass is preferred. However glass is heavy, can be a potential source of injury if it breaks and also places a financial burden on low income groups.

However plastic bottles have the potential to leach compounds into water after exposure to strong sunlight conditions. Researchers have, so far, failed to detect PET plastic photodegradation products or any other harmful or genotoxic substances at concentrations likely to be harmful in solar disinfected water, though concerns about such contaminants remain high.

Some enhancement technologies experimented for SODIS are thermal, heterogeneous photocatalysis, chemical additives, flow reactors and solar mirrors. But these enhancements will only be viable where the benefit in quality, speed and/or treated volume provided by it can offset the additional cost.

On the roof

PET bottles are widely used for SODIS water treatment at low cost (Image courtesythescienceofcreativity.com)

Solar disinfection is at a great disadvantage compared to other household water treatment and storage (HWTS) techniques such as chlorination or filtration, as it does not depend upon a product that needs to be commercially manufactured, hence is not supported by large advertising campaigns by manufacturing giants. This coupled with concerns centring on the possibility that harmful chemicals leach from the plastic after prolonged use, has restricted it’s use by less than 1% of the households using HWTS throughout the developing world.

Consequently SODIS may be most effective as an intervention against water-borne disease for short periods of time such as in the immediate aftermath of natural or humanitarian disasters. It also improves household finances by reducing fuel costs to boil water and illness associated costs. It can be viewed as a “gateway” HWTS intervention facilitating households to access more reliable, but more expensive, point of use household water treatments higher up the waterladder. It has a major advantage as a short term, emergency water treatment in postnatural disaster and humanitarian crisis situations.

To read the complete paper click here.

Assessment of the genotoxicity of SODIS drinking water: Does it damage cellular DNA resulting in mutation or cancer

Though microbially safe, concerns have been raised about the genotoxic/mutagenic quality of solar-disinfected drinking water, which might be compromised as a result of photodegradation of polyethylene terephthalate (PET) bottles used as SODIS reactors. This study assessed genotoxic risk associated with the possible release of genotoxic compounds into water from PET bottles during SODIS, using the Ames fluctuation test.

The biological effects and toxicological relevance of compounds at varied concentrations remains uncertain ; some compounds might be released at high concentrations but not necessarily have a genotoxic effect, while others might be found at low concentrations and have a highly mutagenic effect. Therefore, short-term tests were conducted to determine the genotoxic risk presented by leaching of compounds from PET.

The results indicated that genotoxicity was not observed in any of the daily-refill samples that were exposed to SODIS conditions or their corresponding control samples regardless of storage time and UV-A dose received. Based on this study, if users apply the SODIS technique correctly, they are unlikely to experience any health hazards from genotoxins generated by SODIS if they replace their bottles every 6 months.

To read the complete paper click here.

Bactericidal effect of SODIS drinking water

Five bacterial species were examined in this study, a set of gastrointestinal pathogens which cause diarrhoea and enteritis in humans. SODIS is observed to inactivate these waterborne pathogens under real sunlight conditions and is an appropriate short-term emergency intervention against waterborne disease until more-permanent solutions can be put in place.

To read the complete paper click here.