Gas emissions during olive mill waste composting under static pile conditions

This study evaluated gas emissions and chemical parameters during olive mill waste and grape stalk composting for three consecutive years. Each year, a static pile was built, and gas emissions were measured by a stationary chamber custom built for this purpose. The instrument indicated a CO2 concentration that was always higher (ranging from 0.33 to 3.33%) in comparison to nearby atmospheric levels the trails, a high rate of NOx at the beginning of each trial (4.4, 5.9 and 3.9 mg Nm3 in the first, second and third year, respectively) and limited emissions of aldehydes, ammonia, aliphatic amine and VOCs from the composting piles. The TOC concentration decreased by approximately 28% because of the oxidative phenomena typical of the aerobic process. The total N concentration increased slightly (by approximately 24%) during the process. The germination index reached 100% in the three piles, demonstrating the efficiency of the process both in terms of stability and maturity. The overall results indicate that composting the by-products from olive oil extraction and grape transformation leads to the production of a high quality soil organic amendment, even if the environmental impact due to gas emissions must be considered.