Importance of using clay materials in the process of drinking water purification

As per the Sustainable Development Goals (SDGs) implied by the United Nations in 2015, “clean water & sanitation” is one of the major goals to be achieved by each nation by 2030. Hence, the policy-making bodies of Sri Lankan government identify the importance of carrying out research in order to upgrade the quality of drinking water as the water supplying sources are being rapidly deteriorating due to improper agricultural, industrial, urban & household solid waste & waste water discharges. Therefore, the reservoir raw water is processed through a water treatment plant prior to the distribution of water through the household. However, the water circulating through tap water may still consist of mud particles, excess chlorine added during the treatment process, unfavorable microorganisms like E.coli & metal contaminants like lead added through the plumbing system etc. Therefore, it is highly recommended to consume boiled & filtered water. The excess chlorine removal & the killing of harmful microorganisms are done by boiling the tap water. The purpose of filtering water is to sediment the mud particles present in raw water, to remove the metal contaminants through ion exchange process & to remove microorganisms by sticking them to the filter material.

Water Filtration Methods

Starting from a preliminary filtration method, which is arranged as chambers consisting of gravel, sand & charcoal, scientists have developed different types of water filters. The larger particles in raw water will sediment when it drains through gravel where a physical filtration occurs & heavy metals present in raw water will bind to charcoal through the process of ‘adsorption’ where a chemical filtration takes place. Ion exchange resins are commonly used in filtering hard water which contains a higher amount of cations like calcium & magnesium. Most of these ion exchange resins are zeolites & they have loosely bound cations like hydrogen, potassium & sodium ions to the polymeric structure. These loosely bound cations will exchange with the calcium & magnesium ions present in hard water by converting it to soft water. Since clay is also a type of zeolites, the clay pots & clay jars are also considered to be having a better water filtration ability. Activated carbon filters are the modern development of water filters where either bamboo charcoal or coconut shell charcoal is used to increase the effectiveness of adsorbing the contaminants present in raw water such as lead, mercury, chlorine & organic pesticides are dissolved in raw water. Activated carbon may be arranged as a carbon block or as granulated carbon in the filters. However, the effectiveness of filtration is increased if it is arranged as a carbon block over granulated carbon as the volume to surface ratio is higher. Solar disinfection & UV lamp treatment are also used in purifying drinking water.

Quality of Drinking Water

The government has implied rules & regulations to regulate the quality of drinking water. Accordingly, SLS 614 drinking water standard should be followed to monitor the quality of potable water in Sri Lanka & each parameter should be laid within the required level. In general, the water parameters are tested according to the APHA methods.

Usage of Clay Pots in Water Filtration

Conforming to the concept of ‘sustainability’, it is important to analyze the effectiveness of clay pots in filtering water as it can be used as both storing & filtering purposes and also clay is highly abundant and cheaper. Therefore, some researchers have synthesized clay pots by mixing clay & saw dust in different ratios to evaluate the filtration efficiency of certain parameters like E.coli, total coliform, total hardness, turbidity, electrical conductivity, cations & anions when the raw water is stored inside those clay pots. As per the results obtained, researchers have found that all those parameters lie within the acceptable levels for drinking water quality. (Varkey A.J & Dlamini M.D 2012 Point-of-use water purification using clay pot water filters and copper mesh)The filtration efficiency increases with higher amount of clay & lower amount of saw dust in the clay pot composition. The filtration rate increases with the increasing grain size of saw dust and height of the pot. (Zereffa E.A., Bekalo T.B. 2017 Clay Ceramic Filter for Water Treatment Material Science and Applied Chemistry vol 34, pp 69-74) The all particles & microorganisms which are larger than the pore size of clay material will be filtered & trapped in the clay. As colloidal silver is an antibacterial agent, an additional improvement to the removal of microorganisms can be achieved by embedding it in clay. It prevents the growth of moulds & algae on the body of the clay pot. From research point of view, copper also has germicidal properties similar to that of silver, & therefore, it can be used as a novel research idea to develop copper embedded clay in making water filters or clay pots to determine the germicidal effect of copper against pathogens like coliform. (Naddafi K., Mahvi A.M., Nasseri S., Zeraati H. 2005 Evaluation of the Efficiency of Clay Pots in Removal of Water Impurities Iranian J Env Health Sci Eng,2005,Vol.2,No.2,pp.12-16) This will be economically beneficial as well since copper is cheaper than silver. Furthermore, embedding silver nanoparticles to clay water filters may upgrade the efficiency of water filtration as well.

Value addition of clay in making water filters

Nanotechnology can be applied in upgrading the filtration efficiency of water filters. The inclusion of nano-materials such as titanium oxide & ferric oxide to clay materials which are used to make filters may enhance the water purification efficiency by decontaminating heavy metals such as arsenic, cadmium and lead. Moreover, an appropriate amount of either iron coated sand or powdered iron can be used to embed in clay material of water filters in order to remove arsenic content in drinking water. (Annan E.,Tuffour B.A.,Bensah Y.W.,Konadu D.S.,Yaya A., Agyeman B.O., Nyankson E. 2018 Application of clay ceramics and nanotechnology in water treatment. Cogent Engineering Vol.5 pp1-35) The filtering efficiency may also be enhanced by altering different ratios of iron coated sand or powdered iron added. Therefore, it will be more advantageous to use red color soil in making clay jars and water storing pots as red color soil consists of more iron and ferric oxide. (Kumar P. 2020 Effect of Different Storage Vessels on Various Types of Water in Kota City International Journal of Engineering Applied Sciences and Technology vol.4 pp485-490) This may lead to natural water filtering processes inside clay pots as discussed earlier. These should be subjected to study through research. Moreover, another research can be designed where iron oxide particles with magnetic properties can be applied in removing heavy metals such as arsenic in drinking water. Carbon nanotubes coated with alumina have shown a higher adsorption & removal efficiency of lead in drinking water compared to uncoated carbon nanotubes as well. Therefore, as a prevailing country of having severe CKDu (Chronic Kidney Disease of unknown aetiology) issue, Sri Lanka should endeavor on such research to outcome the serious issue of consuming heavy metals containing drinking water specially in north central province.

References

1. Varkey A.J & Dlamini M.D 2012 Point-of-use water purification using clay pot water filters and copper mesh
2. Naddafi K., Mahvi A.M., Nasseri S., Zeraati H. 2005 Evaluation of the Efficiency of Clay Pots in Removal of Water Impurities Iranian J Env Health Sci Eng,2005,Vol.2,No.2,pp.12-16
3. Annan E.,Tuffour B.A.,Bensah Y.W.,Konadu D.S.,Yaya A., Agyeman B.O., Nyankson E. 2018 Application of clay ceramics and nanotechnology in water treatment. Cogent Engineering Vol.5 pp1-35
4. Kumar P. 2020 Effect of Different Storage Vessels on Various Types of Water in Kota City International Journal of Engineering Applied Sciences and Technology vol.4 pp485-490
5. Zereffa E.A., Bekalo T.B. 2017 Clay Ceramic Filter for Water Treatment Material Science and Applied Chemistry vol 34, pp 69-74
6. dreamstime,2021, https://www.dreamstime.com/stock-photo-close-up-beautiful-woman-drinking-glass-water-filter-system-water-purifier-kitchen-background-image93717875
7. Open Learn Create,2021, https://www.open.edu/openlearncreate/mod/oucontent/view.php?id=80352&section=4.1