Improved salt removal and power generation in a cascade of two hydraulically connected up-flow microbial desalination cells

Abstract

A novel two chamber up-flow microbial desalination cell (UMDC) was designed for evaluating desalination of real seawater with simultaneous wastewater treatment and energy generation. Two UMDCs were hydraulically connected in continuous flow mode (cascade mode) and operated at ten different hydraulic retention times (HRTs) [120 h to 12 h] and salt retention times (SRTs) [40 h to 4 h] for improved performance of chemical oxygen demand (COD) and salt removal. These UMDCs were operated at different combinations of high power (higher external resistance) and high current (low external resistance) mode to find the most suitable conditions for obtaining higher COD removal, salt removal, power production and current generation. The optimum HRT and SRT were 60 h and 40 h, respectively. The highest salt removal achieved was 72% at SRT of 40, while the highest COD removal was 83% at a HRT of 60 h. A maximum current density of 2.375 A/m² was obtained, while the maximum power density was 5.879 W/m². The obtained results give an overlook for the scale up of UMDCs in the future. In the entire system, membrane fouling is still a major problem. As the operation time increases, this resulted in low power generation and low salt removal efficiency. The UMDCs can function as sustainable and alternative solution for real wastewater treatment and seawater desalination with resource recovery and power production.

Keywords: Microbial desalination cells; bioelectricity generation; cascade process; salt removal.