Enhanced Abiotic Humification Of Liquid Digestate By MnO₂:Mechanisms And Influencing Factors

Biomass waste accounts for 62.1%of the annual production of solid waste in China,and its effective treatment is of great strategy and practical significance.Humification of biomass can realize the resource recovery and reduction of biomass waste,and has become an important channel for recycling.Humic-like acids?HLAs?is an importent component produced from the humification process,the unique active functional groups and molecular structures,endowing HLAs with unique ecological and environmental functions.Abiotic humification become a hot issiue in the field of humification of biomass waste due to is not susceptible to environmental impacts.The influence factors and humification mechanisms of biomass is unclear,and the related investigation on representatuve biomass is lack of relevant studies.In the study,the liquid digestate with various attributes was choosed as typical biomass waste,the enhancing effects was investigated by MnO₂ under nitrogen atmosphere and air atmosphere.Based on the analysis of chemical properties of liquid digetate humification products,model humic precursors were applied to reveal the transformation of humification products by MnO₂.Additionally,liquid digeatate characterized with high ammonia nitrogen content was studied.The results are as follows:Humification of liquid digestate can be improved by air and MnO₂.Air improved the humification of liquid digestate feasured with high content NH₄⁺-N,and MnO₂enhanced the humification of liquid digestate charactered with high level of Cl^-and low content total nitrgen,MnO₂ and oxygen played synergistic effect in promotion of humification of liquid digestate.The humification effects of various liquid digestate were different,whereas the FITR groups distribution of HLAs produced from various liquid digestate were similar.Oxygen and MnO₂ can promote the formation of FLAs and HLAs,while both play different roles during the humification process:Oxygen is conducive to the formation of nitrogen-containing lipid chain substance,unfavorable for N-containing component cooperated with benzodiazepines to form HLAs.Oxygen promotes MnO₂ recycling through reacted with Mn ion under atmospheric conditions.Oxygen and MnO₂synergistic promote abiotic humification reaction.MnO₂ improved the polymerization of phenols into HLAs with high aromatization,and improved the yield of HLAs.MnO₂ is conducive to the involvement of nitrogenous substances in the formation of HLAs,and increase the unsaturation degree of HLAs.Reduction of MnO₂ acted as reductant in the formation of fulvic-like acids?FLAs?,and the reduction products MnOOH and Mn?II?,catalysted the formation of HLAs.Moreover,CO₂ release was identified during the formation of FLAs,with 0.73-1.87 mg of CO₂ was released with per mg DOC FLAs.MnO₂ and air played synergistic effect in improving the conversion of products and enhance the degree of aromatization of HLAs.Nitrogen-containing substances have important effects on the conversion of the humification products.Organic nitrogen has a positive effect on the formation of darkening humification products,and inorganic ammonium nitrogen can participate the humification,whereas high concentration of ammonium nitrogen promotes the lipidation and mineralization of organic matter.The entire humification reaction can be divided into two steps,FLAs formation from organic matters,and transformation process from FLAs to HLAs,following pseudo-second-order kinetics equation and pseudo-zero-order kinetics equation,respectively.Tryptophan-like and tyrosine-like substances dominated the humification reaction of liquid digestate.Combined with the changes of the characteristics of humification products,UV-Vis 325 nm was identified,indicating an important intermediate product in the formation of HLAs.