Waste to Wastewater Treatment: Carbonaceous Materials from Biomass and Plastic using Pyrolysis and Hydrothermal Methods

Rising pollution and waste concerns have heightened interest in sustainable carbon materials. Waste biomass and plastic can be utilised as feedstock to produce valuable materials, fostering sustainability and mitigating environmental pollution. These materials offer solutions to the industrial effluent problem, a significant contributor to water pollution. This study investigates the development of sustainable carbonaceous materials for application in wastewater treatment. Carbon materials were successfully produced from waste using both hydrothermal and pyrolysis methods to compare and evaluate these potential production pathways.Response Surface Methodology was employed to study the effects of process conditions on the quality of the carbon materials. The produced materials were characterised by their elemental composition, energy content, thermal stability and surface properties using SEM-EDX, CHN analysis, FTIR and TGA techniques. Scaled-up production, economic viability and environmental impact were assessed using simulation, economic analysis and life-cycle assessment methods.The study found hydrothermal carbonisation at 220°C had a higher yield (~50%) and milder conditions than 450°C pyrolysis (~30% yield). Hydrochar exhibited better ash content (1 wt.%) but lower carbon (78 wt.%) and energy content (27 kJ/g) than biochar (86 wt.%, 33.7 MJ/kg). In terms of pollutant adsorption, both hydrochar and biochar were found to be less effective (~0 mg/g), making them more suitable as solid fuels, soil additives or for carbon sequestration. The co-pyrolysis of biomass and plastic resulted in char with intermediate qualities, balancing a lower yield (23%) with virtually no ash and high carbon content (67.3 wt.%). After scaling-up, pyrolysis was more economically feasible under the assumed conditions (NPV = $3,275,502) but resulted in higher CO2e emissions (1,580 kg per tonne).In terms of adsorption, activated carbon and biosorbents proved highly effective in pollutant adsorption (200 and ~100 mg/g, respectively), with biosorbents being the cheaper and more economically favourable option ($0.6/m3 of water). The findings highlight that while hydrochar and biochar may not be ideal for adsorption, their other applications hold significant promise. The economic analysis suggested that the choice of feedstock and product pricing were critical to the viability of the production process.This study presents hydrothermal and pyrolysis methods and their products as potential solutions for waste and pollution issues and the growing demand for sustainable carbon materials. It outlines process routes, the impact of production factors and the quality of potential products. The shift away from fossil fuels and the need to manage waste will further enhance the economic feasibility of these processes.