Effect of different production methods on physicochemical properties and adsorption capacities of biochar from sewage sludge and kitchen waste: Mechanism and correlation analysis.

Different pyrolysis methods, parameters and feedstocks result in biochars with different properties, structures and removal capacities for heavy metals. However, the role of each property on adsorption capacity and corresponding causal relationships remain unclear. Here, we investigated various physicochemical properties of biochar produced via three different methods and two different feedstocks to clarify influences of biomass sources and pyrolysis processes on biochar properties and its heavy metal adsorption performance. Experimental results showed biochars were more aromatic and contained more functional groups after hydrothermal carbonization, while they had developed pores and higher surface areas produced by anaerobic pyrolysis. The inclusion of oxygen resulted in more complete carbonization and higher CEC biochar. Different biochar properties resulted in different adsorption capacities. Biochar produced by aerobic calcination showed higher adsorption efficiency for Cu and Pb. Correlation analysis proved that pH, cation exchange capacity and degree of carbonization positively affected adsorption, while organic matter content and aromaticity were unfavorable for adsorption. Microstructure and components determined biochar macroscopic properties and ultimate adsorption efficiency for metal ions. This study identifies the degree of correlation and pathways of each property on adsorption, which provides guidance for targeted modification of biochar to enhance its performance in heavy metal removal.