Development of a Sustainable Household Surface Water Treatment Filter

Abstract

Potable drinking water is essential for the sustainable existence of the humanity. According to the Word Health Organization (WHO), one third of the world's populations are without access of clean drinking water. The urban and rural water supply system in the country is mainly dependent on groundwater. Widespread arsenic contamination and presence of elevated level of iron in groundwater are the major water quality problems for the country. Surface water can be used for domestic purposes in the areas where the ground water contains excess salinity, iron and arsenic. Water for drinking purposes must be free from pathogenic micro-organisms, excess concentration of unusable minerals and toxic substances which can produce adverse effects on health. The socio-economic conditions demands lowcost treatment systems that could be implemented in the rural areas at household levels. Although a few household level ground water treatment units have been developed and tested, little attempt has been made in the development of surface water treatment at household level. Considering the above points, a sustainable bio-physicochemical treatment unit has been developed at laboratory scale for bacterial removal from surface water. The treatment unit using activated carbon and sand filtration has combined the bio-physicochemical removal processes in a single system. The combinations of rapid and slow sand flow have been found successful in reducing very high turbidities and coliform counts. The developed household surface water treatment Unit has two columns with down flow —up flow process. The total length of flow path of the Unit is 143 cm. The first column acts as rapid flow filtration while synthesis raw water passes through it. Comparatively larger suspended particles precipitate and settle at the top of the sand column with a small detention time. The removal of bacteria and other fine particles are done in slow flow portion of the second column. This column was constructed on the basis of simple methodological technique of slow sand filtration under submerged condition i.e. stable bio-film slime layer. Partial treated water up-flowed at very slow rates through fine sands to retain suspended solids in the interstices between the sand grains. The pores in the sand grains bring the fine particles and bacteria in contact with sand surfaces, where they adhere because of physical attraction and presence of gelatinous coating. During the filtration process, the coating of micro-organisms formed around the sand grains was responsible for the removal of organic matters and bacteria. The developed surface water treatment filter is a ‘fixed point use’ device because of its heavy weight. The water to be filtered can be collected from the closest water source, whether pond, river or stream, carried physically to the filter and used immediately thereafter. The water intake, water treatment and water use are therefore all within the control of the individual householder. The main mechanisms for microbial removal are mechanical trapping between sand pores, adsorption - onto each other and on to sand grains; micro-organisms consume pathogens and natural death of pathogens. Following the above technique, detail laboratory analysis and tests were carried out to determine some selected water quality parameters. The main findings drawn from this test were that the unit is capable of treating both pond and river water with the same filter media. No sign of Total Coliform or Faecal Coliform were detected in the treated water produced by the unit. It appeared that the unit performed consistently well in complete elimination of bacteria. Some selected water quality parameters of treated water (pH, Turbidity, Color, TDS and TS) were determined at random basis and they were found within the acceptable limit of Bangladesh standard. The operation and maintenance of the developed treatment unit are simpler and more users friendly. It was observed that the clogging of the unit did not occur over eight months of its successful operation. The final finding was observed that the unit produced sparkling clear water with no bacteria for continuous duration of eight months without any maintenance.