Synergistic Influence of Inoculum Type and Laterite Powder on Anaerobic Digestion Kinetics of Canola Straw

The presence of low nutrient content in the lignocellulosic biomass, such as canola straw (CS), limits its anaerobic biodegradability. Therefore, the main focus of the study is to enhance the nutrient content during anaerobic digestion (AD) of CS. For this purpose, three different inoculum sources such as anaerobically digested manure (ADM), acclimatized sludge (AS), and mixed inoculum (MI), and different concentrations of laterite powder (2, 4, 6, 8, and 10%) were added to enhance the batch AD of CS. Results of the study revealed that the reactor inoculated with ADM performed better, and 15.23% and 10.31% higher biogas yields were observed from the reactors inoculated with AS and MI. Moreover, the 2% addition of laterite powder and ADM as inoculum produced the highest biogas yield of 602 NmL/gVS with a 76.4% VS reduction due to the synergistic effect. In addition, reactors showed better buffering capacity and stability in terms of volatile fatty acids to alkalinity ratios due to the addition of laterite powder during AD of CS. Furthermore, characterization of laterite revealed the presence of an iron source, which created the favourable environment for methanogenesis due to direct interspecies electron transfer (DIET). Biokinetic parameters revealed that the modified Gompertz model (MGM) reproduced the biogas production data. In conclusion, AD of CS may be enhanced by using good-quality inoculum and the addition of lateritic mineral. The addition of microbially active inoculums and laterite powder as a nutrient source may also enhance the anaerobic digestate quality and may be used as fertilizer.