Structural elucidation of magnetic biochar derived from recycled paper waste sludge

Abstract

Partially treated wastewater released into natural water bodies leads to eutrophication which poses a threat to aquatic animals and water supply security. The recovery of nutrients from wastewater, and their subsequent recycling in other agricultural applications contribute to nutrient recycling and utilization. Biochar derived from biomass waste is increasingly seen as a multifunctional material for the adsorption of various pollutants from wastewater. This is due to its low production cost and carbon footprint. Recycled paper waste sludge (RPWS) is another abundant type of woody biomass that yields biochar as a by-product during pyrolysis processes. This material has emerged as a feedstock to produce several liquid fuels such as bio-oils and alcohols. However, there has been little application of the material as an adsorbent for the removal of nutrients and pollutants from wastewater. Two variants of RPWS were available for this work, primary sludge from screening processes and secondary sludge from a clarification plant were used as feedstocks to produce biochar products via slow pyrolysis at 550 °C, and 650 °C. Furthermore, a step to produce magnetic biochar was added through impregnation with Fe3+ and Fe2+ and subsequent co-pyrolysis. The biochar yields are promising for the pyrolysis of RPWS. The structural analysis and morphological characterization of the samples (before and after pyrolysis) were done through thermogravimetric analysis (TGA), Scanning Electron Microscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), and Brunauer-Emmet Teller (BET). The residues after pyrolysis showed good physical and chemical qualities that can be beneficial for the adsorption of nutrients in wastewater treatment.