Compositional and structural changes of organic matter during commercial hall composting assessed by humic substances fractionation and py-GC-MS

Organic matter (OM) plays a key role in multiple organic-geochemical processes. A key role of OM is that of being a reactive surface to which nutrients and contaminants can bind. This binding, and its associated effect on nutrient and contaminant mobility is affected by compositional and structural (trans)formation of OM during humification. To identify OM (trans)formation during humification we studied the solid organic matter (SOM) / dissolved organic matter (DOM) partitioning and related compositional, structural changes of OM, during household green waste maturation after 1, 2, 3, 5 and 9 weeks of commercial hall composting. We determined the carbon and nitrogen content of SOM and DOM humic substances via rapid-batch fractionation. We characterized the lignin content and molecular structure of SOM and DOM humic acids (HA) and fulvic acids (FA) via pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The SOM/DOM partitioning of HA showed a distinctive increase. This increase in SOM/DOM partitioning was not found for other humic fractions (FA, hydrophilics and hydrophobic neutrals). HA has the lowest C/N ratio ( 10) of the determined humic fractions and is affected little by maturation. The N enrichment of HA compared to FA, Hy and HON was also validated by specific N containing pyrolysis products. Distinct differences were found in lignin content and structural components between the SOM and DOM HA and FA. Overall, our data shows compositional and structural transformation of humic substances during household green waste compost maturation, which could affect their contaminant binding affinities.