Microbial electrosynthesis of acetate from CO_(2)under hypersaline conditions

Microbial electrosynthesis(MES)enables the bioproduction of multicarbon compounds from CO_(2)using electricity as the driver.Although high salinity can improve the energetic performance of bioelectrochemical systems,acetogenic processes under elevated salinity are poorly known.Here MES under 35e60 g L^(-1)salinity was evaluated.Acetate production in two-chamber MES systems at 35 g L^(-1)salinity(seawater composition)gradually decreased within 60 days,both under-1.2 V cathode potential(vs.Ag/AgCl)and^(-1).56 A m^(-2)reductive current.Carbonate precipitation on cathodes(mostly CaCO3)likely declined the production through inhibiting CO_(2)supply,the direct electrode contact for acetogens and H2 production.Upon decreasing Ca2t and Mg2t levels in three-chamber reactors,acetate was stably produced over 137 days along with a low cathode apparent resistance at 1.9±0.6 mU m^(2)and an average production rate at 3.80±0.21 g m^(-2)d^(-1).Increasing the salinity step-wise from 35 to 60 g L^(-1)gave the most efficient acetate production at 40 g L^(-1)salinity with average rates of acetate production and CO_(2)consumption at 4.56±3.09 and 7.02±4.75 g m^(-2)d^(-1),respectively.The instantaneous coulombic efficiency for VFA averaged 55.1±31.4%.Acetate production dropped at higher salinity likely due to the inhibited CO_(2)dissolution and acetogenic metabolism.Acetobacterium up to 78%was enriched on cathodes as the main acetogen at 35 g L^(-1).Under high-salinity selection,96.5%Acetobacterium dominated on the cathode along with 34.0%Sphaerochaeta in catholyte.This research provides a first proof of concept that MES starting from CO_(2)reduction can be achieved at elevated salinity.