Renewables-driven membrane distillation for drinking water purification: Main Ethiopian Rift Valley case study

University essay from KTH/Energiteknik

Author: Andrea Gabaldon Moreno; [2018]

Keywords: ;

Abstract: Fluoride is present in all type of water sources, but levels beyond the current World Health Organization guideline of 1.5 mg/L can be very harmful for people’s health. Due to the volcanic nature of rocks in the Ethiopian Rift Valley, groundwater is contaminated with fluoride, and studies have even recorded levels up to 26 mg/L. These excessive levels are affecting more than 14 million women and children in Ethiopia. Providing population with safe and clean water could help to achieve the Sustainable Development Goal 6 (i.e. Ensure availability and sustainable management of water and sanitation for all) from the United Nations. Membrane distillation systems have been extensively tested in literature, proving to be effective in removing fluoride, even at higher concentration levels (500 mg/L). Membrane distillation is a heat driven system that works under feed water temperatures below 100 ºC. Renewable energy sources such as geothermal, solar or biomass can be used to provide that heat. This report evaluates techno-economically different technologies using TRNSYS: flat plate solar collectors, evacuated tube solar collectors and biogas from animal dung, as heat source for the membrane distillation unit. The size of the hypothetical installations was optimized to cover the demand of 30 households. Several indicators were calculated to compare the different technologies: specific energy demand, water production, and efficiency of the systems. Investment costs and operation and management costs were considered to calculate total costs and payback period of the different installations. The results show that the best techno-economic option to be installed is a hybrid model that includes a combined heat and power unit powered by biogas and evacuated tube collectors, as can meet the demand with one membrane distillation unit and also supplies electricity and biogas for cooking. However, depending on the specific location, the availability of solar radiation and manure can vary, and consequently the best option will change. In case the existence of livestock is limited, three membrane distillation units coupled with 85 m2 of evacuated tube collectors can cover the demand. If the availability of sun is limited one membrane unit coupled with a standalone biogas unit can be considered. Flat plate collectors are never the best option, as they require the biggest investment cost. Nevertheless, the existence of local manufacturers can decrease the costs. 

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