Assessment of microbial pools by an innovative microbiological technique during the co-composting of olive mill by-products

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 coliforms strongly decreased during the com-posting process. The use of IMT allowed to de-tect a higher and more stable growth of micro-organisms if compared to CMT. IMT was dem-onstrated to be an appropriate and reliable method for monitoring the microbial pools dur-ing the co-composting process