Biochemical changes and GHG emissions during composting of lignocellulosic residues with different N-rich by-products

Nitrogen availability plays a critical role in the biodegradation of organic matter during composting. Although the optimal initial C/N is known to be around 25-30, the chemical form in which N is present influences microbial activity and therefore degradation rate and gaseous losses. This study was conducted to evaluate the influence of N availability on the composting of a mixture of lignocellulosic materials. Three composting piles were made of a mixture of wheat straw and cotton waste, each pile containing different N-rich animal by-products. The evolution of the main physico-chemical parameters was monitored (temperature, pH, electrical conductivity, C/N, NH4+,-, NO3-, water soluble C and N) as well as the enzymatic activity related to the cycle of the main nutrients (beta-glucosidase, protease, alkaline phosphatase and fluorescein diacetate hydrolysis). Additionally, fluxes of CO2, CH4 and N2O emitted from the composting piles were measured by the closed-chamber technique. Cumulative CO2 emissions were fitted to five different kinetic models with biological significance to C mineralization data. The application of the different N-rich residues had a significant effect on the C and N dynamics during composting. However, most enzymatic activities followed similar patterns in the three piles. The major CO2 fluxes were recorded during the thermophilic phase, showing a direct relationship with temperature peaks. No CH4 fluxes were detected for any of the composting piles during the whole trial, whereas low N2O emissions were found at the early beginning and during the maturation stage. (C) 2012 Elsevier Ltd. All rights reserved.