Optimization of biochar production from microwave co-pyrolysis of food waste and low-density polyethylene

Biochar is a carbonaceous material with great potential to mitigate pollution by adsorption and be utilized as solid fuel. However, the applicability of biochar depends on its physicochemical properties. In the present study, biochar is produced from microwave (MW) co-pyrolysis of food waste (FW) and dustbin bags (made of low-density polyethylene, LDPE). The effects of operating parameters, viz., temperature, residence time, and LDPE percentage in feedstock on biochar yield were determined using response surface methodology based on central composite design. The optimum condition of 500 °C of temperature, 20% of LDPE in feedstock and 5 s of residence time yielded 61.25 wt.% of biochar. A quadratic polynomial model was developed to predict the biochar yield as a function of operating parameters. Under the optimized operating conditions, the addition of LDPE showed improvement in the volatile matter (by 20%), ash content (by 35%), fixed carbon (by 14%), carbon (by 24%), hydrogen (by 4%), and higher heating value (by 17%) of biochar. Additionally, MW co-pyrolysis improved the fuel ratio of biochar up to 2.03 from 0.13. Biochar showed an energy density of 1.78 and an energy yield of 108.58%. Morphological and toxicity analysis indicated biochar applicability as a promising adsorbent (average pore diameter of 44 nm)/carbon source and safe environmental disposability.