Characterization, hormetic effects and kinetic modeling of corn stalk-derived biochar in biogas production

Abstract

Anaerobic digestion remains a contemporary technology to manage organic matter with the recovery of valuable products including biogas which can be boosted with biochar supplementation. The properties of biochar in turn determines its effect on anaerobic digestion performance and biogas yield. In our study, corn stalk-derived biochar (CSB) was characterized using advanced techniques like CHN analysis, SEM imaging, EDX, FTIR and BET. The CSB was later applied to the anaerobic digestion of the paper waste codigested with chicken manure at four doses (0, 2.5, 5.0 and 7.5 gL-1 on TS basis). CSB properties revealed significant characteristics [CEC (10 meq100g-1), surface area (15.6 m2g-1), pore size (20.1 nm) and pore volume (0.06 cm3g-1)] suitable for anaerobic digestion and sustained biogas production. Generally CSB mediated and significantly improved biogas production (p < 0.05). Moderate CSB concentrations (2.5 g/L and 5 g/L) resulted in more stable and increased biogas yields by 2.34% and 25.76%, respectively than the control or the highest CSB concentration. However compared to control, high CSB concentration (7.5 g/L) boosted biogas production by 5.54 but produced toxic or inhibitory effect that led to lower biogas production relative to 2.5 and 5.0 gL-1. These outcomes signified a dose-dependent (hormetic) relationship between biogas generation and biochar dosage. The biogas data produced significant goodness of fit (0.995-0.998) when predicted with the kinetic model of the modified Gompertz equation. Overall, CSB as a sustainable alternative material has great potential in digestive engineering by anaerobic digestion, but attention must be paid to its dosage.