Enhancing Aerobic Granular Sludge Formation in Domestic Wastewater Through Mg2+ Augmentation

This study investigates the optimal Mg²⁺ concentration for enhancing aerobic granular sludge formation in domestic wastewater treatment. Domestic wastewater samples and activated seed sludge were obtained from a local wastewater treatment plant. The research examined three Mg²⁺ concentrations—130 mg/L, 160 mg/L, and 260 mg/L—alongside a control sample without Mg²⁺. Each sample was supplemented with solid magnesium sulfate (MgSO₄) before being fed with activated seed sludge for aerobic granular sludge cultivation in four lab-scale sequential batch reactors, operated at a 50% volume exchange ratio (VER) and a 2.5 L/min aeration rate. Results indicated that a 160 mg/L Mg²⁺ concentration yielded the highest chemical oxygen demand (COD) removal efficiency and stable granule formation within a 20-day cultivation period. In contrast, Mg²⁺ concentrations exceeding 260 mg/L negatively impacted aerobic granular sludge formation due to altered extracellular polymeric substance (EPS) content. This study identified 160 mg/L as the optimum Mg²⁺ concentration for efficient granular sludge formation, showing promising potential to improve existing practices in wastewater management.