Promotion Role of Hydrothermal Pretreatment on Adsorption Ability of Biochar Derived From Sewage Sludge Converted by Pyrolysis

Abstract

Pyrolysis is widely used as a sludge conversion technology, but the poor adsorption capacity on account of less surface functional groups limits its practical application. In this work, hydrothermal carbonation (HTC) technology was used as the pretreatment of pyrolysis to carbonize sewage sludge to prepare the sludge biochar (SDBC) for enhanced adsorption removal. It was certified that pretreatment with HTC promoted Cu²⁺ adsorption. At a HTC temperature of 120°C, the adsorption removal rate of Cu²⁺ was found to be the highest, achieving an maximum adsorption capacity of 22.5 mg/g for Cu²⁺, which was 1.23 times higher than that of SDBC. The adsorption better fitted with the Langmuir model and pseudo-second-order kinetic. Chemical adsorption was the predominant mechanism. The adsorption interactions include ion exchange, electrostatic effect, surface complexation and cation-π interaction. The HTC pretreatment increased surface oxygen-containing groups (−COOH or C=O, −OH), which was adsorption sites to promote Cu²⁺ adsorption.