pH-Regulated Selective Release of Organic Matter from Urban Sewer Sediments: A Strategy for Enhanced Carbon Source Recovery

Urban sewer sediments represent an underexplored reservoir of recoverable organic resources, yet conventional disposal practices, landfilling and incineration perpetuate greenhouse gas emissions and irreversible carbon loss. This study establishes a pH-regulated pretreatment strategy (pH 4, 6, 10, and 12) for selective release of organic matter from sewer sediments under simulated hydraulic conditions (solid-to-liquid ratio of 10 g/L, 1154 rpm). Pronounced non-linear release response across the pH revealed a crucial window at pH 10, where COD release attained 1488.68 mg/L (42.6% enhancement over controls) with a 93.70% organic dissolution rate, while total phosphorus release was simultaneously suppressed by 22.4%. The resulting liquid-phase carbon-to-nitrogen and carbon-to-phosphorus ratios of 62.9 and 320.8, respectively, markedly surpassed control values of 46.0 and 174.5, highlighting the potential for high-quality external carbon source recovery. The mechanistic underpinning integrates mineral surface deprotonation, EPS disintegration, and calcium–phosphorus precipitation. Extrapolated to China’s national sewer network, this strategy could potentially mitigate methane emissions by approximately 1.73 × 107 t/yr and save wastewater treatment plants USD 794.83 million/yr in carbon procurement, while inorganic residues retain potential for construction material reuse. This study offers a feasible pathway toward integrated pollution control and high-value waste valorization, aligning with circular economy objectives in urban water systems.