Organic Matter Transformation during Rotary Drum Composting

Organic matter transformation using chemical and spectroscopic methods was studied for composting of four carbon/nitrogen (C/N) ratio waste combinations (C/N 16, C/N 22, C/N 30 and C/N 38) of grass cuttings, mix vegetable waste, cattle manure, food waste and sawdust. Temperature, moisture content, ash content, total organic matter, C/N ratio and water-soluble organic carbon (WSOC) concentrations were observed in a rotary drum composter for 20 days. In addition, a spectroscopic method (Fourier-transform infrared) was used to study the chemical composition of the organic matter. Temperature reached above 50°C in all waste combinations indicating the immense oxidation within the rotary drum composter, resulting in a final higher ash content (62.28%) in C/N 16 compared to about 30-32% for C/N 22, 30 and 38. The C/N ratio decreased rapidly from initial values of 16, 22, 30 and 38 to 5.4, 10.9, 16.6 and 27.2 after 20 days of composting. Total organic carbon (TOC) of the compost displayed a similar trend to WSOC, which decreased to around 34, 31 and 18% in C/N 22, 30 and 38 compared to 58% in C/N 16. The infrared spectra of the all treatments exhibited the same band pattern, indicating unnoticeable qualitative changes during the composting process. The decrease of the 2930/1030, 2850/1030 (aliphatic C/aromatic C) and 2930/1630 (aliphatic C/polysaccharide) ratios monitored in all treatments (higher decrease in C/N 16) and an increase of the 1380/2930 ratio indicated progress of the composting process and consequently a higher degree of decomposition. _____________________________________________________________________________________________________________