Assessing plastic and biomass-based biochar's potential for carbon sequestration: an energy-water-environment approach

Biochar from waste has emerged as a vital solution for multiple contemporary issues. While the organic content and porous structure of biochar have granted it multiple benefits. Where the use of biochar is proven to be beneficial for enhancing the soil structure and water and nutrients retention ability, therefore, saving water and boosting yields in arid regions. Moreover, biochar is capable to sequester carbon from the atmosphere and permanently store it within the soil. As such, this study evaluates the potential for carbon sequestration through biochar obtained from the pyrolysis of feedstock mixtures including camel manure, date pits, high-density polyethylene (HDPE) and low-density polyethylene (LDPE), and how it can enhance water and food security. Multiple energy and water supplying sources have been considered for different project scenarios to provide a broader understanding of biochar potentials. The lifecycle analysis (LCA) approach is utilized for the assessment of net emissions, while an economic study is conducted in Aspen Process Economic Analyser (APEA) to evaluate the feasibility of the different scenarios. Finally, single-objective optimization and multi-objective optimizations were carried out using excel and MATLAB genetic algorithm respectively to select optimal biomass blending and utilities options to fulfill the low cost and negative emissions targets. The assessment conducted for a Qatar case study indicates that the best waste blending scenario for maximum carbon sequestration potential was obtained at a mixing ratio of 20.4% Camel manure: 27% date pits: 26.3% LDPE: 26.4% HDPE. Furthermore, the optimum char blend for maximum carbon sequestration corresponding to the minimum cost of char mix was computed. The optimal biochar mixing percentage for highest net emission was obtained at a feedstock mixing ratio of 96.8% of date pits, 1.5% of LDPE, and 1.7% of HDPE with 0% of camel manure with an optimal cost of 313.55 $/kg biochar. Solar PV was selected as the best energy source in this pyrolysis study due to its reduced carbon emissions in comparison to other sources studied such as natural gas, coal and diesel. However, natural gas is selected to fulfill the economic objective. Moreover, the optimal water source was investigated including wastewater treatment, multi-stage flash and reverse osmosis desalination, where treated wastewater is selected as the optimal supply to fulfill both, economic and environmental objectives.