Oriol Larriba, a chemical engineer from UAB, has devoted his master thesis bioelectrochemical systems. Biological treatment of high-strength sulphate wastewaters is limited to anaerobic reactors that require an external supply of electron donor, usually H2 or organic matter, to reduce sulphate to sulphide. Bioelectrochemical systems (BES) with an autotrophic biocathode are a promising alternative to conventional biological treatment since H2 can be generated in situ from the electric current applied. In this work two BES were operated with a cathode potential of -0.8 V vs SHE. Microaerophilic conditions were tried to maintain in the cathodic compartments in order to partially oxidize the sulphide produced and allow elemental sulphur recovery. The oxygen to maintain these cathode conditions was produced in the anodic chamber by water electrolysis reaction and was transferred by diffusion through de membrane placed between compartments. Sulphate reduction rate (SRR) and sulphide production rate (SPR) were low during the whole study, with maximum values observed during the start-up batch (9 mg S-SO42- L-1 d-1 and 9 mg S-S2- L-1 d-1). The system was operated in continuous mode for 26 days and the lowest SRB activity was observed during this period. Then, both BESs were switched to batch mode again and the anolyte of one reactor was changed by a ferrocyanide solution (0.1 M), in order to release electrons without producing oxygen. An increase in sulphate-reducing bacteria (SRB) activity was detected in this reactor; SRR increased up to a 33% compared to start-up period. This enhancement demonstrated that an excess of oxygen in the cathodes limited the performance of the systems.
Luckily for GENOCOV, he will continue with us as a predoctoral researcher!