Influence of inorganic additives on wheat straw composting: Characterization and structural composition of organic matter derived from the process. (15th April 2020) - Medina, Jorge
Abstract: Metallic oxides and clay minerals have gained increasing interest as additives of composting due to their influence in greenhouse gas emissions reduction and their effectivity in the stabilization of carbon both in compost and soils, leading to a cleaner compost production and potentially C sequestrant amendments. In this study, wheat straw (WS) was co-composted with iron oxide and allophanic soil and their influence on WS composting and composition of the end-products was evaluated. WS compost and their humic like-substances (HS) fraction were characterized by chemical and spectroscopic analyzes. After 126 days of process, the elemental composition showed slight differences of the N content for compost and HS, where the C/N atomic ratio tended to decrease relative to the initial material (WS; ~130). This trend was more pronounced in the HS from co-composted treatments (<30). The addition of inorganic materials increased the total acidity and phenolic-OH group contents (~15 and 14 mEq g −1 respectively, iron oxide treatment) relative to the treatment without inorganic additives. Nevertheless, the FTIR and solid-state 13 CNMR spectroscopy barely support the wet chemical analysis and revealed a similar final composition between all the studied compost treatments. These results suggest that the incorporation of these materials as compost additives had no major effect on the spectroscopic features of the end-products, however, critical changes of the properties such as the extractability, functionality and composition of HS were revealed by traditional methods. In conclusion, the supply of metal oxides and clays could impact the aerobic composting of WS favorizing the stabilization of certain C pools and adsorptive properties of the end-products, that is of importance in production of amendments suitable for being used in degraded and contaminated soils. Nevertheless, under the experimental conditions of our research C stabilization apparently depends of other mechanisms that still need to be elucidate. Graphical abstract: Image 1 Highlights: The addition of inorganic materials decreased the C/N ratio in compost and HS. Iron oxide and allophanic soil increase the extractability of N and lignin in HS. Iron oxide decreased the final E4 /E6 ratio associated to the stabilization of compost. The inorganic materials enhance total acidity and phenolic group contents. FTIR and solid-state 13 CNMR showed similar composition of final composts.