Enhancing Biohydrogen Yield and Slaughterhouse Wastewater Treatment Efficiency through Microalgae and Bacterial Synergy

Slaughterhouse wastewater is highly rich in organic content. It carries an extremely high nutrient load when discharged into the environment, demonstrating that conventional treatment practices usually need to be more sustainable and extremely energy intensive. This research study probes various ways to integrate a microalgae-based platform to realize sustainable biohydrogen production, concurrently addressing critical wastewater treatment and renewable energy generation. A new two-stage cultivation method was developed using native wastewater bacteria and carbohydrate-rich microalgae, Chlorella vulgaris ESP 6. This method increased the efficiency of nutrient recovery and COD reduction compared to conventional single-stage systems. The microalgae, a key component in the process, efficiently converted the organic content of the wastewater into a carbohydrate-rich biomass, with a carbohydrate content of 48.8 ± 2.3%. This biomass was then fermented in the dark with Clostridium butyricum CGS5 to make biohydrogen after being treated with thermal acid. A pH control strategy through automatic operation was enforced, resulting in an impressive improvement in hydrogen production to 211 mL H2/g volatile solids and a maximum productivity of 39.11 mL/L/h, both competitive with the current literature. This study points out a promising way of replacing conventional wastewater treatment with integrated nutrient removal and energy recovery and utilizing wastewater biomass rich in carbohydrates as a renewable feedstock for biohydrogen production. Overall, this is the highest hydrogen yield ever reported on slaughterhouse wastewater and may be highly important for further development in waste-to-energy applications.