In Iran, waste management can be improved through strategies of converting wastes into energy. Their exploitation is still abandoned due to oil economy and lack of environmental motivation. In this study, co-conversion of polystyrene waste (PS) with walnut shell (WS) biochar for solid biofuel production was conducted to develop a new sustainable economic waste-to-bioenergy strategy. The co-pyrolysis of PS and WS provided solid biofuel (WPS) with a yield of 43 % and HHV of 32.10 MJ/kg. To increase the HHV, PS was co-pyrolyzed with WS non-activated biochar (non-AC), resulting in a yield of 78 % and HHV of 33.03 MJ/kg. To enhance the yield, it was co-pyrolyzed with WS activated biochar (AC), leading to a yield of 93 % and HHV of 29.79 MJ/kg. The yield was increased because AC entrapped melted PS into its porous structure to avoid its vaporization. Interestingly, it successfully enhanced the PS conversion from 38 % (in pyrolysis alone) to 77 % (in the co-pyrolysis). Ultimate analysis of all three solid biofuels revealed a sulfur-free fuel as a clean energy source. The economic evaluation indicated that the production of non-ACPS could make it suitable for future commercialization by net profit of 0.085 $/kg and payback time of 1.12 year.

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