Development of a high-rate anaerobic thermophilic upflow packed bed reactor for efficient bioconversion of diluted three-phase olive mill wastewater into methane

Olive mill wastewater is the main by-product derived from olive mills using the three-phase extraction process, displaying a serious environmental risk due to its notable content in organics and phenolics. This work focused on a high-rate thermophilic anaerobic digester development, able to remove high organic load amounts, by converting it to biogas. The proposed system is an upflow packed bed reactor with recycling stream and biomass carriers appropriate for inoculum colonization. An anaerobic inoculum was acclimatized under thermophilic conditions and subsequently added into the reactor. Its performance examination against twice-centrifuged olive mill wastewater of 40 g COD/L followed, testing several runs of gradually decreased hydraulic retention time, reaching steady-state conditions until the minimum of 4.2 days, while optimum performance was achieved at 5.6 days. The production of 9.51 +/- 0.37 NLCH4 /L-Feed is considered quite promising for the high-rate anaerobic treatment plants development for olive mill wastewater valorization, without the need of co-digestion.