Recycling of nutrient medium to improve productivity in large-scale microalgal culture using a hybrid electrochemical water treatment system.

Recycling and reusing of nutrient media in microalgal cultivation are important strategies to reduce water consumption and nutrient costs. However, these approaches have limitations, e.g., a decrease in biomass production, (because as reused media can inhibit biomass growth). To address these limitations, we applied a novel membrane filtration‒electrolysis‒ultraviolet hybrid water treatment method capable of laboratory-to-large-scale operation to increase biomass productivity and enable nutrient medium disinfection and recycling. In laboratory-scale experiments, electrolysis effectively remove the biological contaminants from the spent nutrient medium, resulting in a high on-site removal efficiency of dissolved organic carbon (DOC; 80.3 ± 5 %) and disinfection (99.5 ± 0.2 %). Compared to the results for the recycling of nutrient medium without water treatment, electrolysis resulted in a 1.5-fold increase in biomass production, which was attributable to the removal of biological inhibitors from electrochemically produced oxidants (mainly OCl-). In scaled-up applications, the hybrid system improved the quality of the recycled nutrient medium, with 85 ± 2 % turbidity removal, 75 ± 3 % DOC removal, and 99.5 ± 2 % disinfection efficiency, which was beneficial for biomass growth by removing biological inhibitors. After applying the hybrid water treatment method, we achieved a Spirulina biomass production of 0.47 ± 0.03 g L-1, similar to that obtained using a fresh medium (0.53 ± 0.02 g L-1). The on-site disinfection process described herein is practical and offers a cost-saving and environmental friendly alternative for nutrient medium recycling and reusing water in mass and sustainable cultivation of microalgae.

Induction of Primary Male in Juvenile Red Spotted Grouper Epinephelus akaara by Immersion of 17α-Methyltestosterone.

We investigated the androgenic effects of 17α- methyltestosterone (MT) on gonadal sex reversal in juvenile red spotted grouper Epinephelus akaara. The fish were immersed in 17α-MT at 1 and 5 mg/L. Treatment method of 17α-MT was once weekly for 4 and 8 weeks. Fish were sampled at 12 months after end of the treatment period in order to histological analysis. At the initiation of an experiment (70 day after hatching), juvenile red spotted grouper have the paired primordial gonads with somatic cells bellow kidney in the posterior portion of the body cavity. Formation of ovarian cavity indicates that the ovarian differentiation beginning at 70 DAH in red spotted grouper. At 12 months after end of the treatment period, control group, 17α-MT 1 mg/L treatment group for 4 and 8 weeks, and 17α-MT 5 mg/L treatment group for 4 weeks were all female. However, sex-changed males without ovarian cavity were observed in the 17α-MT 5 mg/L treatment group for 8 weeks. In grouper, we firstly reported that the red spotted grouper be able to induce the primary males by hormone treatment prior to gonadal sex differentiation.