Effects of aeration rates on composting of ornamental pruning wastes.

The aim of this work was to study the effects of two aeration rates (0.45 and 0.30 L kg-1dry matter min-1, P1 and P2, respectively) during the bio-oxidation phase on composting process of pruning wastes coming from cultivation of ornamentals. Piles were turned every 15 days during the maturation phase. Temperature, oxygen concentration, carbon-to-nitrogen ratio, N-NH4+, N-NO3-, hemicellulose, cellulose and lignin contents were measured throughout the whole composting process. To evaluate compost stability and maturity, humification and germination indexes were recorded during the maturation phase. The highest aeration rate in P1 reduced the length of bio-oxidation and maturation phases and subsequently the whole process (170 days in P1 vs. 226 days in P2). Oxygen concentration was slightly higher in the more aerated pile compared to the P2 for almost the whole duration of the first phase. On the contrary, during the maturation phase the concentration was lower in P1 than P2. The application of the lowest rate (0.30 L kg-1DM min-1) has promoted the biodegradation process improving the maturity and stability of compost. Nevertheless, the humification parameters and germination indices recorded at the end of the process indicate a good maturation and stability degree for both aeration rates.