Membrane distillation for the removal of fluoride and pesticides in remote areas in India
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The world’s increasing population, economic development and climate change are driving the demand for more drinking water. In India, more than 100 million people live in areas of poor water quality. It has been reported that more than 33% of India’s groundwater resources are unsuitable for consumption. Anthropogenic contaminants, such as microbial contaminants, nitrate, pesticides and industrial discharge, together with geogenic contaminants, such as fluoride, arsenic, iron and saline water, pose a threat to human health. In many rural areas neither a centralized system for drinking water production nor stable electric power supply exists. Decentralized small-scale water treatment systems with independent power supply could be implemented to produce safe drinking water for the communities. Recently, Membrane Distillation (MD) has been identified as a promising technology for drinking water production in situations with off-grid power supply. The objective of this research was to evaluate the application of MD for the production of drinking water in small-scale communities. It was shown in this study that bulk salinity, as well as fluoride, nitrate and non-volatile pesticides were well removed from a synthetic brackish groundwater solution using a bench scale and a pilot scale MD unit. The application of a vacuum at the permeate side enhanced the permeate production up to 40%. An elevated scaling potential was identified in the presence of fluoride together with calcium. However, only minor traces of loosely deposited solids were observed in this study. The membrane was efficiently cleaned with flushing of Milli Q water. Fluoride and nitrate were removed at rejection rates higher than 98-99% and 99% respectively in all experiments. The removal of pesticides was shown to be strongly depending on the vapour pressure and the LogD of the target compounds. A low vapour pressure and a low LogD were found to be favourable for a good rejection in MD. Post-treatment with granulated activated carbon filtration after the MD was tested for removal of any remaining traces of pesticides to safeguard full compliance with drinking water standards. A 2 log unit removal for all selected pesticides was achieved up to 67,600 bed volumes. The study demonstrates that membrane distillation is a promising alternative for small-scale water supply from brackish groundwater.
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