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Abstract\nSTATEMENT OF NOVELTYSoil heavy metal contamination and sludge disposal have become globally environmental issues problems of great concern. Utilizing sludge pyrolysis to produce biochar for remediating heavy metal-contaminated soil is an effective strategy to solve these two environmental problems. In this study, municipal sewage sludge and papermaking sludge were used as feedstock to prepare co-pyrolyzed biochar, which was then applied to reduce the toxicity of Cd in soil. The results indicated that the application of co-pyrolyzed biochar significantly increased soil pH, CEC, and enzyme activity, while decreasing the content of available Cd in the soil. Following the application of 3% co-pyrolyzed biochar, the proportion of acid-soluble Cd in the soil decreased to below 46%, as the biochar facilitated the conversion of leachable acid-soluble Cd to stable oxidizable and residual forms through precipitation and complexation. The DFT computational results indicate that the aromatics in co-pyrolyzed biochar can adsorb Cd ions through cation-π interactions, while carboxyl, hydroxyl, aldehyde, and amide groups can provide more electrons for the adsorption of Cd ions, resulting in stronger adsorption capacities. The study findings provide a feasible solution for the resourceful treatment of sludge and the remediation of heavy metal-contaminated soil.This study is the first to investigate the remediation potential of municipal sludge and papermaking sludge co-pyrolyzed biochar for Cd-contaminated soil. Additionally, density functional theory (DFT) calculations were employed to elucidate the microscopic adsorption mechanisms of Cd ions by the co-pyrolysis biochar. These findings provide a theoretical foundation for the resource utilization of sludge and the development of cost-effective soil remediation agents. [ABSTRACT FROM AUTHOR]

The chemical looping co-gasification of nitrogen-containing algal biomass and coal could effectively realize the high-value utilization of gasification products, but the mechanism of conversion of nitrogen-containing pollutants is not clear. In this work, the effects of the different ratios of microalgae on the co-gasification process were first explored, and the results showed that the 40 % coal + 60 % microalgae blending had the best synergistic effect, with a comprehensive synergistic index (CSI) of 1.35 as the maximum value. The effects of temperature, the ratio of OCs to feed (O/C) and steam flow rate on the evolution of nitrogen-containing species in the co-gasification products were explored based on the optimal mixing ratio, and the results showed that elevating the reaction temperature promotes the generation of nitrogen oxide precursors, and an appropriate amount of steam could inhibit the generation of NOx. The nitrogen in coke mainly came from the Maillard reaction between carbonyl (-CO) compounds and amino (-NH 2 ) compounds and its main forms are pyridine nitrogen (N-5) and pyrrole nitrogen (N-6). Based on the nitrogen accumulation forms in the products of each phase, the mechanism of nitrogen transport and conversion in the chemical looping co-gasification of coal and microalgae (CM-CLCG) process was proposed. This study provides a reference for the synergistic utilization of coal and biomass and the control process of nitrogen-containing pollutants., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)