Micronutrient dynamics after thermal pretreatment of olive mill solid waste

•Thermal pretreated OMSW has a higher methane production rate than unpretreated OMSW.•Metal deficiency limits methane production.•Metal dynamics in pretreated OMSW was studied using metal extraction scheme.•Increase of available Co was coupled to the increase of methane production rate.•Increase of bioavailable cobalt might be a good strategy to optimize biogas production. This study investigated metal dynamics, and their bioavailability, before and after thermal pretreatment of olive mill solid waste (OMSW), using a sequential metal extraction scheme. The 11.5% increase of cobalt in the most available fraction after the pretreatment coupled to the increase of methane production rate have been a good indicator that the OMSW anaerobic digestion might be metal limited due to the lack of cobalt.