Life Cycle Assessment of Microbial Desalination Cell for low energy drinking water from seawater

To evaluate the environmental performance of the Microbial Desalination Cell (MDC) technology, an attributional Life Cycle Assessment (LCA) was conducted on a multi-cell MDC that is at pre-pilot scale from cradle-to-gate using the ReCiPe mid-point method. System expansion by substitution was applied to solve the problem of multi-functionality of the MDC and compare its performance with conventional Seawater Reverse Osmosis (SWRO). The study included the construction and operation phases of the MDC. The results show that the operation phase contributed the most (>99.9%) to the potential environmental impacts associated with the production of desalinated water using the MDC technology. The biggest contributor to the negative impacts is the consumption of Iron (III) Chloride that is used as the catholyte, contributing almost 91% of the climate change impacts for the production of 1 m3 of water. The climate change impact due to consumption of electricity (8 kg CO2-Eq for complete desalination) for the recirculation pumps in the MDC stack is five times higher than the impacts associated with SWRO electricity consumption (1.5 kg CO2-Eq). The biggest benefit of the MDC technology is provided by the treatment of wastewater (>97% of benefit in climate change and human toxicity categories). The relative environmental performance of the MDC is better (14 - 22% lower impacts) when used to partially desalinate seawater in combination with a Brackish Water Reverse Osmosis (BWRO) as compared to when it was used as a stand-alone technology. The sensitivity analysis shows that at its current stage of development, when the ratio of seawater to wastewater is reduced to 1:5, the desalination rate of MDC has to increase by about four times (from 5 to 20 L/m2.h) along with the regeneration of catholyte (10 - 40 times) for the MDC to be comparable with the environmental performance of SWRO. The findings of this study indicate the current weaknesses of the MDC technology are associated with regeneration of the catholyte, very low desalination rates, and high amount of wastewater required. Solving these weaknesses could make MDC a viable and environmentally sustainable technological solution for integrated water and wastewater treatment