Analyzing the Effect of Combined Chemical Conditioning and pH Adjustment on Improving Dewatering and Phosphorus Recovery from Anaerobic Mesophilic Digestate

High volume and water content makes anaerobic digestate management difficult. Environmental drawbacks and limited resource recovery are associated with traditional polymer conditioning methods. The method of polymer conditioning incurs high operating costs, affects the environment, and pollutes water. Therefore, modifying traditional polymer conditioning of mesophilic digestate (MD) is necessary to address environmental concerns and promote resource recovery. This study explored alternative chemical conditioning agents, including metal coagulant ferric chloride (FeCl3) and oxidant hydrogen peroxide (H2O2), to enhance the dewatering efficiency of MD with pH adjustment while comparing the corresponding results without pH adjustments. The goal was to determine the best chemical dose combination that minimizes polymer consumption while maximizing volume reduction. After adjusting MD's pH [Ca(OH)2] to 8.0 and treating it with 2.1 kg/t dry solids (DS) polymer, 2.1 kg/t DS FeCl3, and 600 mg/L H2O2, significant improvements in MD dewaterability were observed, including a 96% increase in capillary suction time and 40% increase in cake solid. In addition to dewatering, improving phosphorus recovery in the digestate was investigated. The same chemical conditioning resulted in 98% elimination of P from centrate and recovered in the sludge cake. The study emphasizes the necessity of pH adjustment and choosing suitable conditioning chemicals to improve dewatering performance while considering P release implications. By reducing polymer usage and incorporating FeCl3 and H2O2, significant improvements can be achieved in dewatering performance and P removal from MD centrate while better managing digestate.