Chemical conditioning approach to post-treat temperature-phased anaerobic digestate to improve resource recovery, odour reduction and biosolids quality.

Abstract

Biosolids has several challenges, such as its high water content, huge volume, odour, and pathogen presence. Regulations require biosolids to be reused and disposed of safely. Polymer conditioning focuses on volume reduction, leaving pathogen and odour reduction unaddressed. This study evaluates the use of polymer alone and in combination with ferric chloride (FeCl₃) and hydrogen peroxide (H₂O₂) at pH 8.0 to increase the post-treatment efficiency of temperature-phased anaerobic digestate (TPAD). The goal is to reduce volume, recover phosphorus, reduce odour, and eliminate pathogens. This investigation examined various dewatering indices after treating TPAD with cationic polymer alone, polymer and FeCl₃, and with polymer, FeCl₃, and H₂O₂ combined at pH 8.0. A combination of 2.5 g/kg dry solids (DS) polymer, 2.1 g/kg DS FeCl₃ and 600 mg/l H₂O₂ at pH 8.0 produced the shortest capillary suction time (CST) of 11.5 s, lowest turbidity of 11 NTU, and lowest specific resistance to filtration (SRF) of 0.08 Terra m (Tm)/kg. Compared to raw TPAD, the combined chemical dose improves dewatering by 99%, odour reduction by 90%, 100% centrate P removal, and a 40% increase in cake solids with 57 MPN/g DS fecal coliforms in the treated cake. There was a 100% reduction in pathogens compared to raw cake. TPAD must be post-treated to reduce volume and odour while producing P rich 'class A' biosolids with a greater range of reuse.