Green additive to upgrade biochar from spent coffee grounds by torrefaction for pollution mitigation

A green approach using hydrogen peroxide (H2O2) to intensify the fuel properties of spent coffee grounds (SCGs) through torrefaction is developed in this study to minimize environmental pollution. Meanwhile, a neural network (NN) is used to minimize bulk density at different combinations of operating conditions to show the accurate and reliable model of NN (R-2 = 0.9994). The biochar produced from SCGs torrefied at temperatures of 200-300 degrees C, duration of 30-60 min, and H2O2 concentrations of 0-100 wt% is examined. The results reveal that the higher heating value (HHV) of biochar increases with rising temperature, duration, or H2O2 concentration, whereas the bulk density has an opposite trend. The HHV, ignition temperature, and bulk density of biochar from torrefaction at 230 degrees C for 30 min with a 100 wt% H2O2 solution (230-100%-TSCG) are 27.00 MJ.kg(-1), 292 degrees C, and 120 kg.m(-3), respectively. This HHV accounts for a 29% improvement compared to that of untorrefied SCG. The contact angle (126 degrees), water activity (0.51 a(w)), and moisture content (7.69%) of the optimized biochar indicate that it has higher resistance against biodegradation, and thereby can be stored longer. Overall, H2O2 is a green treatment additive for SCGs solid fuel. This study has successfully produced biochar with greater HHV and low bulk density at low temperatures. The green additive development can effectively reduce environmental pollutants and upgrade wastes into resources, and achieve 3E, namely, environmental (non-polluting green additives), energy (biofuel), and circular economy (waste upgrade). In addition, the produced biochar has great potential in the fields of bioadsorbents and soil amendments. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study developed a green approach using hydrogen peroxide to intensify the fuel properties of spent coffee grounds through torrefaction, reducing environmental pollution. Neural network results showed that the higher heating value of biochar increases with rising temperature, duration, or H2O2 concentration, while bulk density has an opposite trend. Overall, the study successfully produced biochar with greater HHV and low bulk density at low temperatures, offering potential applications in bioadsorbents and soil amendments.