Mineralization and humification pathways in two composting processes applied to cotton wastes

Abstract We compared the end products and the time courses of mineralization and humification during the theermophilic phase of two different composting processes used to transform residues from cotton carding. The two processes were started under different conditions with respect to percentage humidity, aeration system and C/N ratio. Except for pH and the electric conductivity of aqueous extracts, most of the parameters evolved differently in the two processes examined. The following analyses were performed to assess the degree of evolution of the two composts: weight loss of the total compost mass, cellulose, hemicellulose and lignin content and amount of humified and non humified organic C in 0.1 M Na4P2O7 0.1 M NaOH extracts. At the end of the thermopholic phase, mineralization was more intense, to the detriment of humification, in the composting process that involved forced air ventilation and a lower C/N ratio (35). In the process where manual turning was used throughout the experiment, mineralization was somewhat slower notwithstanding the higher C/N ratio (80), but was accompanied by more intense humification, as shown by the electrofocusing profiles of humic substances extracted in 0.5 M NaOH. At the end of the experiment weight loss was about 50% in both processes, however the content of cellulose and hemicellulose was lower in the compost obtained from the process where manual turning was used throughout the experiment. Forced air ventilation and the lowering of the C/N ratio to 35 did not have any positive effect on the time needed for composting nor on the quality of the end product.