Extraction of photosynthetic electron from mixed photosynthetic consortium of bacteria and algae towards sustainable bioelectrical energy harvesting

Abstract

Extraction of photosynthetic electron for bioelectrical energy harvesting is an efficient approach to utilize solar energy harvested by photosynthetic microorganisms. To explore this approach in natural and artificial photosynthetic system in which alga and photosynthetic bacteria are usually coexisted, the intracellular electron extraction from mixed photosynthetic consortium of Chlorella vulgaris and Rhodopseudomonas palustris was investigated under three-electrode mode by holding working electrode at different potentials. The mixed-culture biofilm grown at 0 V exhibited a maximum Coulomb efficiency of 42.12% while the peak current (12.2 mA) was 8.07, 1.5, 2.97 and 4.65 fold higher than that produced at −0.4 (1.5 mA), −0.2 (8.06 mA), 0.2 (4.08 mA) and 0.4 V (2.6 mA), respectively. The electrode potential can regulate the dominant species within the biofilm. Large enrichment of Rhodopseudomonas palustris in the biofilm was responsible for the high photosynthetic electron extraction efficiency at 0 V since the photosynthetic electrons extracted by the electrode were mainly derived from photoheterotrophic metabolism of Rhodopseudomonas palustris. Extraction of equivalent amounts of intracellular electron from Chlorella vulgaris required higher potential than that from Rhodopseudomonas palustris and was highly dependent on the presence of exogenous electron mediator. As an electron sacrificer, photosynthetic oxygen released by Chlorella vulgaris could complete electron with electrode. Intracellular electrons can also be extracted from dark respiration, but the peak current (6.4 mA) was 47.54% lower than that produced under illumination (12.2 mA) due to low exoelectrogenic activity of biofilm.