Assessment of microbial pool by an innovative microbiological technique in olive mill by-products co-composted under natural conditions

Different mixtures of olive pomace (OP), olive mill wastewater (OMWW) and olive pruning residues (OPR) were aerobically co-composted under natural conditions. Compost temperature showed a sharp increase in the first 40-60 days, followed by a stabilization at 60°C and a decline after 150 days, whereas compost water content ranged from 50-55% to 25-30%. Total and selec-tive microbial counts were followed throughout the experiment by means of innovative (IMT) and conventional (CMT) microbiological techniques. Pseudomonas spp., anaerobic bacteria, actino-mycetes, and fungi reached levels of 8, 7, 5 and 6 log CFU g–1 compost, respectively, with a slight depression after 30-80 days. Total and fecal coli- forms strongly decreased during the compost-ing process. The use of IMT allowed to detect a higher and more stable growth of microorgan-isms if compared to CMT. IMT was demonstrated to be an appropriate and reliable method for mo- nitoring the microbial pools during the co-com- posting process.