Static procedure for composting olive mill waste

The activity deals with a novel static composting procedure set-up by ISAFOM-CNR at farm scale and carried out in gas-permeable polyethylene bags (1 m3), aiming at bioremediation of olive mill waste (OMW). OMW was thoroughly mixed with hygroscopic additives, such as waste wool and straw, to avoid leaching. The use of bags as planned has not required forced aeration nor watering of OMW mixture for the period of the static storage. During trial, temperature profiles were taken through an experimental tailor-made device with 45 thermistors arranged in a vertical section mesh placed into the bag; data were then automatically collected every 15 minutes with the Arduino-based system. Oxygen was monitored in the exhausted air extracted from the bags periodically. Oxygen and temperature profiles showed patterns similar to those reported for standard composting systems. The process caused drastic degradation of organic matter associated to high humic carbon content, with optimal C:N in the end product for agronomic purposes. The compost also showed drastic reduction in polyphenols and low phytotoxicity. Dynamic and static respirometric tests (DRI, SOUR, OD12) stated high biological stability of compost at the end of storage while data on chemical-physical and microbiological properties satisfied the standard requirements set by regulators for compost.