Polarity and molecular weight of compost-derived humic acid affect Fe(III) oxides reduction.

Whether polarity and molecular weight (MW) of compost-derived organic matters have significant impacts on their redox properties are far unknown. Our results showed that both the FeO and FeO reduction by S. oneidensis MR-1 were effectively facilitated by compost-derived humic acids (HAs) under anoxic condition. Among the 15 kinds of compost-derived components identified by the reverse phase high-performance liquid chromatography (RP-HPLC) and high-performance size exclusion chromatography (HPSEC), the relatively hydrophilic and high MW compost-derived components presented significant associations with FeO reduction, and the hydrophobic components correlated well with FeO reduction. Quinones content and aromaticity of the compost-derived HAs presented positive correlation with Fe(III) oxides reduction. These findings demonstrated the impacts of the polarity and MW of compost-derived HAs on Fe(III) oxides reduction, further suggested that compost-derived HAs could influence the geochemical behaviors of heavy metal, organic pollutants and nutrient elements in natural environment by facilitating the reduction of Fe(III) oxides, which were very useful for the improvement of composting technology and application of compost products.