Energy production, use and saving in a bioelectrochemical desalination system

This study experimentally and quantitatively investigated the energy benefit of a bioelectrochemical desalination system consisting of microbial desalination cells as pre-desalination units before electrodialysis (ED). The pre-desalination in an upflow microbial desalination cell (UMDC) could reduce ED energy consumption and desalination time by 45.3% and 25.0%, respectively. Both serial and parallel connections of three UMDCs achieved comparable performance in desalination and energy production. Direct charging in a serial connection transferred 86.6% of the energy from the UMDC system to a rechargeable battery, and 41.8% of the energy to an ultracapacitor, suggesting that ultracapacitors that are designed for quick charging may not be suitable for energy extraction from bioelectrochemical systems. About half of the stored energy in the rechargeable battery or ultracapacitor was lost during discharging to power the ED unit. The parallel connection aided by a DC-DC converter did not successfully charge either the rechargeable battery or the ultracapacitor.