BIOMASS PYROLYSIS: POTENTIAL FOR BAUXITE RESIDUE AMENDMENT AND MITIGATION OF CLIMATE CHANGE

In 2018, Emirates Global Aluminium partnered with the American University of Sharjah to explore options for adding biochar to soil made from neutralized bauxite residue. The objectives were determining which abundantly available organic waste forms in the United Arab Emirates could be converted to biochar. Due to the UAE's natural soil base and neutralized bauxite residue being alkaline, the biochar should be neutral or slightly acidic rather than basic, like most biochar produced and applied to acidic soils. Thus, the specific brief of the project was to form slightly acidic or neutral rather than a basic/alkaline biochar while maximizing cation exchange and water-holding capacities. The thermal decomposition of organic materials produces biochar without oxygen presence; a process commonly referred to as pyrolysis. In addition to the biochar, the process also produces a pyrolysis vapor, which, upon rapid condensation, reduces to bio-oil and syngas. While bio-oil and syngas can be utilized in energy applications, biochar has multiple potential uses, such as soil amendment, energy, and carbon sequestration. Generally, pyrolysis produces alkaline biochar; however, under the right processing conditions, it can be made acidic while sustaining water retention, nutrient availability, and promoting microbial activity when applied in soils. This paper presents case studies of the pyrolysis of various types of biomasses and organic waste matters relevant to arid and semi-arid regions, namely, post-consumption food waste, biosolids (sewage sludges), segregated fruits and vegetable waste, animal manure, date palm waste, and the halophyte Salicornia Bigelovii. The analysis shows an interdependent correlation between the pyrolysis temperature and type of feedstock on one side and the characteristics of the biochar, including acidity, nutrient availability, cation exchange capacity, and water retention capacity, with significantly favourable characteristics for improving soil quality. In terms of energy and emissions, the pyrolysis of food waste is predicted to contribute 1370 GW to global renewable energy annually, and biosolids have the potential to sequester 987 kg of CO2-eq per ton of biochar. This demonstrates that beyond its potential for improving soil quality, biochar can contribute to mitigating climate change.