Development of an alkali-producing bioelectrochemical system for sewage-polluted seawater: nutrient removal, scalant mitigation, and resource recovery

The bioelectrochemical system (BES) plays a promising role in developing sustainable water treatment technologies that can treat wastewater while simultaneously generating electricity or recovering valuable resources. However, an unbalanced pH gradient between the anode and the cathode is often observed, which is considered a significant limitation that needs to be addressed. Instead of focusing on pH gradient balancing, this study first constructed a two-unit alkali-producing BES (APBES) for treating coastal sewage-polluted seawater. In Unit I, after five optimization scenarios, the system exhibited a nearly 100-fold increase in electric current production and a significant rise in pH from ∼7 to 9. The partial removal of pollutants (95 % reduction in chemical oxygen demand and 49 % reduction in conductivity) and scalants (28 % removal of sulfate and 76 % removal of calcium) was achieved. The anode and cathode effluents of Unit I were then mixed in a secondary unit (Unit II). After integrating Unit II with Unit I, the results demonstrated that APBES can not only remove pollutants and scalants but also simultaneously recover valuable resources. The removal efficiencies of calcium (80 %), sulfate (53 %), orthophosphate (51 %), and ammonium (81 %), supported by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses, collectively reinforced this observation. This study is the first to verify the potential of APBES for the simultaneous nutrient removal and scalant mitigation, as well as the transformation of nutrients and scalants into valuable resources for sewage-polluted seawater. Further efforts are warranted to develop APBES into a versatile platform for sustainable water resource management.