Soil Respiration Measurements Reveal High Retention of Organic Carbon from Corn Residue Derived High-Lignin Fermentation Byproduct Enabling Sustainable Lignocellulosic Biofuel Production

While 2G biofuel production can utilize non-edible, lignocellulosic feedstocks such as agricultural residues to produce liquid fuel, harvesting crop residues is unsustainable without careful management of the soil underneath. By harvesting a fraction of the crop residues left in the field after harvest, soil health can diminish and critically, the soil organic carbon (SOC) stored in agricultural fields can decrease. Currently, in the most popular 2G process models published, the issue of soil degradation remains unresolved with residue harvest strategies receiving considerable attention in the literature and other SOC management strategies receiving far less. Specifically, the strategy of returning the high lignin fermentation byproduct (HLFB) from ethanol production to soil has been sparsely modelled and only tested experimentally once. Our study endeavors to expand on this literature by evaluating the SOC storage potential of various HLFBs and anaerobic digestates and comparing them to their unprocessed corn stover feedstocks using soil incubation experiments, isotope analysis, and simple modelling techniques. For both a 267-day and a 135-day incubation experiment, we measured the amount of carbon lost through microbial respiration and the amount of carbon remaining at the end. We found that in all but one case, for the same initial amounts of substrate inputs, the incubated digestate and HLFBs respired away less carbon and persisted longer in the soil than the incubated corn stover. Then, by applying multi-pool exponential decay models to our data, we found that the incubated corn stover respired away to completion substantially quicker than the biologically processed materials in our projected timespan of 100 years. We then approximated the steady-state SOC levels for a scenario in which the same bioprocessed materials were annually re-added to an incubation with our preliminary results indicating that the biologically processed materials formed .95-4.8 more SOC than their unprocessed counterparts. Emboldened by our experimental results and tenuously strengthened by our preliminary modelling results, we believe that our work supports the feasibility of returning HLFB to soil to restore SOC and opens the door to the increased circularity and viability of biofuels in a future low carbon economy