Anode Chamber Effluent of a Microbial Fuel Cell as a Sustainable Environment for the Cultivation of the Biohydrogen-Producing Microalga Tetraselmis subcordiformis

This study evaluated the feasibility of using effluent from the anodic chamber of a microbial fuel cell (MFC), powered by real fruit and vegetable wastewater, as a cultivation medium for Tetraselmis subcordiformis, a microalga capable of bio-photolytic hydrogen production. In three experimental variants, different organic loading rates were applied in the anodic chamber, resulting in significant differences in effluent quality and its suitability as a culture medium. In contrast to the dominant MFC configurations, in which microalgae act as cathodic biocatalysts, the microbial fuel cell in this study was used as a source of the inevitable anode effluent, which was subsequently valorized as a cultivation medium for the marine microalga T. subcordiformis to support biomass and hydrogen production. In variants with moderate COD concentration and low lipid content, the highest biomass concentrations, ranging from 941 ± 104 mg VS/L to 1020 ± 108 mg VS/L, were obtained, along with the highest nitrogen assimilation efficiency (48.7–49.1%) and phosphorus assimilation efficiency (62.3–63.1%). The variant in which the culture medium contained the highest concentrations of COD, TSS, and lipids showed a substantial limitation of biomass growth to 745 ± 75 mg VS/L and lower nutrient removal efficiency (total nitrogen—42.3 ± 4.7%, total phosphorus—55.0 ± 5.0%). The obtained biomass was then used for H2 production in a mineral photobiolytic medium. The highest total hydrogen production reached 184.7 ± 25.0 mL, while the specific hydrogen yield reached 193.7 ± 32.6 mL/g VS. Increased concentration of organic matter in the medium reduced total hydrogen production to 112.0 ± 14.8 mL, mainly due to lower biomass concentration, although the specific hydrogen yield remained high (153.4 ± 25.8 mL/g VS). The biogas composition was stable (H2 58.0–58.7%, CO2 35.3–35.9%, O2 6.0–6.2%).