Effect of Pre- And Post-AD-THP on Dewaterability, COD Solubilization, and Formation of Refractory Compounds

Sandsmark, A.H., Bakke, A.L., Botan, A., Holte, H.R., Lillebø, A.H.

Joint Conference: Residuals & Biosolids and Innovations in Treatment Technology, 2025

Abstract

This study investigates the effects of pre- and post-anaerobic digestion (AD) thermal hydrolysis process (THP) on sludge dewaterability, biogas production potential, and refractory compound formation. Raw and anaerobically digested sludges were thermally treated at various temperatures (from 140 °C up to 200 °C) and retention times. Key performance metrics included capillary suction time (CST) as a measure of dewaterability, chemical oxygen demand (COD) solubilization as an indicator of biogas potential, and filtrate color as a proxy for refractory COD formation. In contrast to pre-digestion THP, results show that post-AD-THP at moderate temperatures significantly improved CST and COD solubilization without notably increasing refractory COD levels. Moreover, extending retention times at these moderate temperatures achieved enhancements in dewaterability and COD solubilization comparable to high-temperature treatments, but with minimal refractory COD formation. These findings underscore the potential of post-AD-THP as a sustainable sludge treatment strategy for wastewater treatment plants.

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