by Water Research Bhutan, 12 Jan 2022, waterresearchbhutan@gmail.com
The Context - This article is targeted to create general public awareness that the installation of portable filtration systems at home is linked to a better understanding of the quality of incoming raw water. Such information is required to make the best possible outcomes from the expensive purchase of a variety of household filtration options. The group of experts contributing to the article also uses non-technical language with an expectation to provide insights into underlying physical and chemical designs and the operation of disinfection systems in drinking water treatment plants in the Bhutanese context.
According to Bhutan Living Standard Survey 2017, recorded 99.5 percent of households have improved access to the water supply. One of the Key Performance Indicators (KPI17.1) of the 12 Five Year Plan also targets that both urban and rural households will have access to 24 hours supply of “safe/piped” drinking water in the dwelling. Similarly, the Ministry of Health is also working towards the achievement of ‘Access to improved drinking water sources (%) (Piped water)’. In our opinion, the piped water from a source to the dwelling may not always mean access to safe water. For instance, in Thimphu city, every household has to deal with turbid water during rainy seasons which is also common across Bhutan. This is one simple observable water quality indicators at the household level while we are uncertain of safe limits on other quality indicators.
There are no dimensions to ensuring a safe drinking water supply. In the article, the context of the disinfection of water to kill disease-causing microorganisms is discussed. The water supply systems are being built in Bhutan are mostly a storage tank connected to the source and then the distribution line. In some cases, additional structures were added to remove the inflow of debris and sediments. In most cases, disinfection agents such as Chlorine, are added to kill pathogenic organisms while the use of ozone and UV systems are also observed in some cases.
Figure - Water source for Tamshing monastic school in Bumthang
Problem Description - One of the key missing points in our water treatment system is the management of disinfection by-products formed during the disinfection process. The use of disinfection agents like chlorine and chlorine-related chemicals results in by-products such as Trihalomethanes (THM) and Haloacetic acids (HAA), and ozone results in by-products such as bromate. Use of UV doesn't generate abt by-products incoming raw water needs to be free from turbidity while UV lamp should be free from any slime or dirt. The disinfection by-products at a higher level of concentrations are detrimental to human health with the potential to cause cancer and genetic disorders, given their high potential for cytotoxicity, mutagenicity, teratogenicity, and carcinogenicity. However, the actual process of formation of those harmful substances is still an ongoing active research area.
The applied dose of disinfection agents (e.g. Chlorine) must be accurate - it has to be as high as necessary to eliminate pathogens and as low as possible not to overdose. Overdose can be harmful to customers via the formation of those by-products while it is expensive to the water supply managers. On the other hand, underdose can cause the growth of slime and the build-up of contaminants in the distribution line. The efficacy of disinfection is determined by raw water quality parameters such as turbidity, pH, water temperature, nature of pathogens present, and also other factors like disinfection dosage and contact time. How far our water supply managers consider those raw water quality parameters during the ad-hoc chlorination in our water tanks will significantly affect the quality of incoming water into each and every household.
Most of our water sources are from surface runoff or subsurface flow with high content of organic matter as a result of seepage through forest floors from our forested catchments. Even larger streams like Dhur Chu one of the tributaries of Chamkhar Chu in Bumthang valley has dark tea-like colour indicating high organic matter content. The water sources with high organic matter content when treated with Chlorine significantly increased the production of those harmful by-products increasing the risk to public health. In Bhutan’s situation, organic matter content in water sources would get higher in autumn when leave litters fall into water producing more organic matter while water flow is reduced. The example of water colour indicator organic matter content is one such example of the influence of our natural systems on our raw water quality. Thus, the take-home message is our water supply managers should have in-depth long-term raw water quality information on each and every water source which would then determine disinfection processes to ensure supply safe drinking water. There are no default values or reference ‘magic number’ to be used for disinfection of our water sources given the fact that raw water quality is significantly influenced by land use, elevation, and hydrology.
Proposed Solutions - The first and foremost way forward is to characterize raw water quality. Based on these parameters the choice of disinfection agent should be made, and accordingly, the design of storage tanks needs to be built to ensure enough contact time for the disinfection agent to eliminate all possible pathogens as per the standard safe limits advised by the public health authorities. In many water treatment plants, plug-flow systems are built to ensure enough contact time, which is not a common sight in the treatment plants in Bhutan. The main parameters of concern for disinfection should include total organic carbon, bromide, turbidity, pH, and other pathogens such as bacteria and viruses. The quarterly bulletin of the Royal Centre for Disease Control published a chlorination report (from only 6 health centers) and 593 samples for bacteriology tests from all over Bhutan during the period of July to September 2021. The report highlighted that more than 80 percent of chlorination reported were found inadequately chlorinated. This further highlights the need to better document those raw water quality parameters to ensure the effectiveness of our water treatment systems.
Organic matter load in raw water is one of the key concerns when water is sourced from surface runoff. One of the simple and easy measurements like UV absorbance at 254nm and different wavelengths would serve the purpose to indicate the organic matter load. However, quality results can be achieved by measuring SUVA254. Such measurements could also be automated using data loggers where DOCeq and UV absorbance gets measured at higher frequency (eg. at intervals of a few seconds to hours) using an in-situ spectrometer where results can be viewed on personal computers of relevant technical personnel. The equipment comes with high cost but it should still be cost-effective considering high-quality data and reduced cost for sampling and laboratory processing needed in the case of conventional methods. Similar hi-tech IoT-based sensors are also available which measures water pH, temperature, UV absorbance, and then calculate the required dose of disinfection.
In worst-case scenarios, if possible holding the water in the storage tank and applying Chlorine when the water is less turbid could be the last resort. Loads of incoming external or terrestrial organic matter will be reduced due to biological activity producing a different class of organic matter of microbial origin which is known for producing fewer harmful by-products than external incoming organic matter.
In summary, the quality of incoming raw water would determine the effectiveness of any household filtration system. If a UV system is installed the incoming water has to be free of turbidity while the UV lamp has to be slime and dirt free. If ozone disinfection systems are installed make sure there is low bromide in incoming water to eliminate the formation of harmful bromate by-products. The complications of using chlorine and chlorine-related disinfections are discussed above in detail.
The article is published based on personal experiences and observations by a group of freshwater researchers from Bhutan. The group can be contacted via tershong@gmail.com
The article was also published in National Newspaper of Bhutan (Kuensel). The link https://kuenselonline.com/how-safe-is-the-treatment-of-our-drinking-water/
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