Comparative assessment of thermal and alkaline pretreatments for enhanced solubilization of wastewater-derived microalgal biomass

Abstract Microalgae efficiently assimilate carbon dioxide and nutrients from wastewater, positioning them as a viable and sustainable biotechnology for resource recovery and effluent treatment. These approaches align with the circular economy paradigm and contribute to climate change mitigation in the sanitation sector. This study provides a comparative analysis of thermal and alkaline pretreatments applied to microalgal biomass harvested from stabilization ponds treating anaerobic effluents. While previous research has examined these methods separately, comparative assessments under standardized mild conditions for wastewater-derived biomass are limited. To bridge this gap, thermal pretreatments (70, 80, and 90 °C) and alkaline pretreatments (pH 10, 11, and 12) were applied to microalgal biomass, and the solubilization of organic matter, proteins, carbohydrates, and nutrients was analyzed. Both strategies enhanced solubilization, with thermal pretreatment at 90 °C yielding the highest protein solubilization (33.2%), whereas alkaline pretreatment at pH 12 achieved the highest total organic matter solubilization (11.9%). Significant nutrient release was also observed, including ammoniacal nitrogen (39.9%) and total Kjeldahl nitrogen (33.2%) under thermal conditions. These findings support practical implications for selecting the optimal pretreatment to maximize energy recovery and resource utilization in microalgae-based wastewater treatment systems. This comparative analysis of thermal and alkaline approaches offers valuable insights into advancing large-scale implementations and enhancing the sustainability of wastewater treatment technologies.