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

Abstract

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. The conditioning process consists of a novel chemical combination of cationic polymer, FeCl3, and H2O2 at an adjusted pH that would enhance the post-treatment efficiency of municipal anaerobic digestates with improved dewatering efficiency, reduced odor, improved pathogen elimination, and resource recovery. The research suggested that switching toward a two-staged temperature phased anaerobic digestion process would significantly enhance resource recovery and yield class A biosolids. Complying with class A biosolids regulations allows for broadening its practical application and increasing its market value. Contributing to the economic viability of the wastewater treatment plants (WWTPs). Research findings suggest that WWTPs can reduce polymer consumption by 40%, substantially reducing their operational costs and improving their efficiency. Improved cake solid content and reduced volume result in lowered storage and transportation costs. As a result of nutrient and resource recovery from digestate, biosolids are more economically valuable and align with sustainability goals by minimizing waste and conserving resources. In this research, odor reduction is improved by 91%, improving the quality of WWTP environments. This research provides cost-effective and environmentally friendly wastewater treatment solutions that address nutrient imbalance, pathogen contamination, and odors.