Study on the Feasibility of Solar Distillation as Household Water Supply in Coastal Areas of Bangladesh

Abstract

Scarcity of potable water as the result of rapid climate change and saltwater intrusion in groundwater has been a major problem in the coastal regions over the world. In equinoctial countries like Bangladesh, where sunlight is available for more than 10 hours a day, Solar Distillation provides a promising sustainable way for safe drinking water supply in coastal poor households with negligible major cost. Solar distillation presents a great potential as sea water is vastly available and construction of solar still is easy and can be done by local people with locally available materials. The objective of this research is to supply potable water for a small family of 3-4 members in the coastal poor regions of Bangladesh who need about 15 liters drinking water per day. In this paper, two passive type solar stills- a Conventional Single Slope Solar still (CSS) and a Pyramid Solar Sill (PSS) is used and relationship is established between distill water output corresponding to four different factors- temperature, solar intensity, relative humidity and wind speed for Gazipur, Bangladesh. Brine was used as input water using the same proportion of salt as seawater which contains average 3.5% of salt. Comparison is analyzed between the two different still outputs for eight months’ period (January-August) and efficiency is calculated. Later a thermal mathematical model is developed to calculate the hourly efficiency and hourly yield of distill water which is mainly based on the temperature of water inside the solar still and the inside glass temperature. Model calibration is done by comparing the theoretical data and observed data. The temperature difference between ambient temperature, temperature of water, temperature of outside glass and temperature of inside glass is compared for Gazipur and the difference is added to the ambient temperature of Khulna, Bangladesh for calculating the temperature of water and inside glass temperature for Khulna and the results are put into the mathematical model in order to compute the inside glass temperature of Khulna. Hourly yield distill water for Khulna is calculated and difference between output of the two cities- xii Gazipur and Khulna is demonstrated and finally an economic analysis is prepared. Effect of height of brine water, different glass cover thickness and different thickness of galvanized steel is measured. The Water quality is tested for both input water and yield water by testing the pH, TDS and Electric conductivity. The distillation output has a positive correlation with temperature and solar intensity, inverse relation with relative humidity and wind speed has nugatory consequence. The maximum output of Conventional Solar Still is obtained 3.8 L/m2/day and Pyramid still is 4.3 L/m2/day for Gazipur and almost 10% more efficiency is found for Pyramid Solar still. In conventional solar still, temperature of water is maximum 30º more than ambient temperature and inside glass temperature is maximum 10º more than ambient temperature. In pyramid solar still, temperature of water is maximum 35º more than ambient temperature and inside glass temperature is 25º more than ambient temperature. This data is put on the mathematical model to find the Khulna hourly yield of distill water and efficiency and model calibration is done and theoretical data is found maximum 500 ml more for theoretical data than observed data. Productivity in Khulna is found almost 10% more than Gazipur. Yield is maximum in conventional still for a clearance height of 0.21 meter, glass cover thickness of 6 mm and galvanized steel thickness of 1 mm. All the water quality parameters were inside the standard limit instructed by World Health Organization (WHO). The economic feasibility analysis was done and benefit cost ratio of conventional solar still is 1.49 in second year and 1.85 for pyramid solar still in second year. So, the project is feasible. Finally, for a 3-4-member family, area of 5 m2 is suggested for Conventional Solar Still and 4 m2 for Pyramid Solar Still is suggested. Further research should be conducted on this subject matter with other different types of solar stills as solar distillation posits a great potential for household water supply in coastal areas of Bangladesh.