Experimental evaluation of proximate, ultimate, heating values, and structural composition of selected crop shells

In recent decades, the rising global population, high food demand, and advanced agricultural activities have led to an increased generation of crop shells. Inappropriate disposal of crop shells exacerbates environmental pollution, but their effective management can provide low-cost resources for sustainable production of bioenergy and other biobased products. This study evaluates the proximate, ultimate, heating values, and the structural composition of walnut shells (WNS), groundnut shells (GNS), and melon seed shells (MSS). Shells from the selected crops were collected, cleaned, dried, pulverized, and experimentally analyzed using appropriate techniques. The outcome of the study indicates that the volatile matter of the samples varies from 64.38% for GNS to 82.26% for WNS, while the fiber content is 58.20%, 68.22%, and 81.80% for MSS, GNS, and WNS, respectively. The carbon content of the WNS, GNS, and MSS is 45.77%, 39.84%, and 71.49%, respectively. The high heating values of WNS, GNS, and MSS are 37.82 MJ/kg, 27.71 MJ/kg, and 18.3 MJ/kg, respectively. The low nitrogen and sulphur content of the crop shells shows that toxic oxides of nitrogen and sulphur will not be formed during combustion, thereby supporting environmental sustainability. The outcome of the statistical analysis shows low variability and a moderate coefficient of variation (%) for most parameters. Based on the laboratory analysis, the high volatile matter, fiber, carbon, and oxygen contents and low sulphur and nitrogen contents of the WNS, GNS, and MSS will dictate their utilization potentials. More studies on innovative characterization techniques and utilization options are recommended to fully explore the resource recovery, circular economy, and environmental sustainability benefits of crop shell recycling.