Biochar from sewage sludge: Effect of pyrolysis on functional properties and pollutants fate

Pyrolysis is a promising alternative for the removal or immobilization of hazardous elements in sewage sludge (SS) without compromising its biofertilizer features. However, the effects of pyrolysis on SS emerging contaminants have not been fully investigated. Therefore, this study aimed to assess the fate of heavy metals, pesticides, and organic pollutants in SS through pyrolysis, as well as the suitability of SS and its derived biochar (SSB) for soil application. Municipal SS was pyrolyzed at different scales (bench and micro units) and temperatures (400, 500, and 600 degrees C) for comparison. The general properties, surface morphology, and functional groups of SS and SSB were analyzed. Also, a quantitative analysis of heavy metals (Zn, Cu, Cr, Ni, Cd, and Pb) and a qualitative investigation of organic pollutants and pesticides were performed. The results demonstrated that pyrolysis at 400 degrees C increased the stability of SS and strongly affected its surface area, resulting in a high pore structure with a developed surface charge. Simultaneously, the relative content of organic matter and nutrients remained nearly unchanged. All heavy metals analyzed in SS and SSB400 were within limits set by the International Biochar Initiative for soil application. Moreover, organic pollutants and pesticides were detected in the SS but were partially degraded or immobilized after pyrolysis > 400 degrees C. In conclusion, the production of SSB proved to be an effective method for removing toxic elements from SS while enhancing its properties for soil remediation and crop productivity.