Chemical and spectroscopic analysis of organic matter transformations during composting of pig manure

Composting of separated pig manure (SPM) was studied in an attempt to elaborate upon organic matter (OM) transformation during the process and define parameters for product maturity using both chemical and spectroscopical methods. Composting was performed in two piles and the following parameters were measured in 10 samples during 122 days of composting: temperature, ash content, C/N ratio, water-soluble organic C concentration, and humic substance content (humic acid, fulvic acid, and nonhumic fraction—HA, FA, and NHF, respectively). A spectroscopic method (Fourier-transform infrared [FTIR]) was used to study the chemical composition of the OM. The C/N ratio and ash content exhibited a typically high rate of change during the first 49 days and leveled off thereafter. Water-soluble organic C concentration rapidly increased to a maximum at Day 18 and declined thereafter. The increasing level of HA at various stages of composting indicated the progression of humification. The FTIR spectra revealed an increase in aromaticity and a decrease in carbohydrates as decomposition proceeded. Spectrometric measurements using FTIR provide information significantly correlating to conventional chemical parameters of compost maturity.