Insights into Characteristics of Dissolved Organic Matter Fractions in Co-composted Dairy Manure and Chinese Herbal Residues

Abstract

Dissolved organic matter (DOM) is a crucial indicator of compost maturity and stability. Different pools of DOM fractions may function distinctly from one another and show unique properties in the transformation of organic matter and microbial activity. In this work, compost DOM was fractionated and the properties of individual DOM fractions including humic acids (HA), fulvic acids (FA) and hydrophilic compounds (Hi) were analyzed. The pools of HA, FA and Hi were studied via elemental analysis, FTIR and UV–Vis spectroscopy, and colloidal properties like particle size and zeta potential were characterized as well. Compared to HA or FA, Hi pool had a higher content of nitrogenous compound, higher saturated degree and more easily oxidized capacity. As composting proceeded, the aromaticity of HA and FA was higher and higher while Hi exhibited only a very slight change. The colloidal analysis indicated that the particle size of DOM subfractions gradually decreased. Hi compounds from matured compost had a good application potential in cations absorption. Taken together, these results provide valuable insights into the evolution and characteristics of DOM fractions during a composting process of dairy manure and Chinese herbal residues.