Microbial fuel cell for simultaneous caffeine removal and bioelectricity generation under various operational conditions in the anodic and cathodic chambers

A series of studies of the effects of operational parameters including organic substrate loading concentration, initial caffeine concentration, circuit connection, external resistance and salinity were carried out to evaluate the optimal performance of a double chambered microbial fuel cell for the treatment of caffeine. The increment of organic substrate loading concentration at anode increased the maximum power density from 7.84 ± 0.59 to 14.18 ± 0.87 mW m−2 but deteriorated the removal efficiency of caffeine in which only half of the removal efficiency of caffeine attained at 72 h at 1.500 g L−1 acetate (46.28 ± 3.66 %) than that of 0.375 g L−1 (96.89 ± 0.48 %). Initial caffeine concentration of 20 mg L−1 (95.31 ± 1.83 %) achieved 2.40-fold higher removal efficiency of caffeine than that of 50 mg L−1 (39.58 ± 2.83 %) at 48 h as saturated caffeine molecules hindered the oxygen reduction reaction and thus, fewer hydroxyl radicals were produced for the decomposition of caffeine. An optimal external resistance of 1000 Ω exhibited the best performance in terms of pollutants removal efficiency and power generation than that of 500 and 5000 Ω. Sodium chloride concentration of 0.580 g L−1 produced the highest maximum power density of 11.78 ± 0.68 but reduced to 8.26 ± 0.41 mW m−2 at 0.696 g L−1 as high concentration of sodium ions caused dehydration of anodophilic cells which decreased the electron transfer ability of electrochemically active bacteria.