Sewage Sludge Valorization via Phytohormones Production: Parameter Regulation and Process Evaluation

Sludge treatment is of great significance for environmental protection and sustainable development. Existing treatment technologies fall short in terms of carbon emissions, process efficiency, and resource recovery. This study focuses on alkaline hydrothermal treatment, proposing a short-cycle, low-energy, high-value management process for sludge valorization. Here, we investigate the impact of treatment duration, temperature, and solid content on the synthesis of high-value products and their effects on both solid and liquid phases. Based on the comprehensive results, 2 h, 160°C, and 14% solid content can be regarded as the optimized treatment condition. The resulting products, including phytohormones, humic substances, and essential nutrients (C, N, P and K), exhibit substantial potential for high-value agricultural utilization. In the unconcentrated solution, a single phytohormone can reach a concentration of 10⁴ μg/L. Heavy metal content is well below standard limits, simultaneously achieving biological stability, and the volume can be reduced to 60%. This process is 42.12 times more energy-efficient than conventional anaerobic digestion. This novel approach promotes waste resource recycling and sustainable urban management.