Biomethanization and decontamination of olive mill wastewaters through an integrated anaerobic-aerobic biofilm process

Due to their high COD content, olive mill wastewaters (OMWs) have to be treated before being discharged. Anaerobic digestion is one of the most promising remediation solution for OMWs as it is able to mediate both their decontamination and valorization (by the production of a CH4-rich biogas). The possibility of intensifying the performances of this process by performing it in an anaerobic digestor packed with granular active carbon was recently demonstrated. In order to further remove the COD from the effluent of the developed system, an aerobic post-treatment, constituted by a column reactor packed with silica beads, directly fed with the outlet of the anaerobic plant and colonized by the influent native microflora, was integrated to the anaerobic bioreactor. A 2 month-continuous mode experiment was carried out by feeding the integrated anaerobic-aerobic system with an amended OMW. The COD load with which the reactors were fed were 31.9 and 52.2 g/(ld) for the anaerobic and the aerobic plant, respectively. The integrated system was found to remove the 58% of the inlet COD, and the aerobic post-treatment contributed for ¼ of such removal yield. In order to better understand the biological process, the composition of the bacterial communities of both the anaerobic and the aerobic reactors were characterized.