Carbon distribution and multi-criteria decision analysis of flexible waste biomass smouldering processing technologies.

Waste biomass treatment is a globally urgent matter which highly relates to environmental quality and human health. Here, a flexible suite of smouldering-based waste biomass processing technologies is developed and four processing strategies: (a) full smouldering, (b) partial smouldering, (c) full smouldering with a flame, and (d) partial smouldering with a flame, are proposed. The gaseous, liquid, and solid products of each strategy are quantified under various airflow rates. Then, a multi-criteria analysis in terms of environmental impact, carbon sequestration, waste removal efficiency, and by-product value is performed. The results show that full smouldering achieves the highest removal efficiency but generates significant greenhouse and toxic gases. Partial smouldering effectively generates stable biochar, sequesters over 30% carbon, and therefore reduces the greenhouse gases to the atmosphere. By applying a self-sustained flame, the toxic gases are significantly reduced to clean smouldering emissions. Finally, the process of partial smouldering with a flame is recommended to process the waste biomass that can sequester more carbon as biochar, minimize carbon emissions and mitigate the pollution. And the process of full smouldering with a flame is preferred to maximally reduce the waste volume with minimum environmental impact. This work enriches strategies for carbon sequestration and environmentally friendly waste biomass processing technologies.