Intensified processes for methane production from olive mill wastewaters

Anaerobic digestion is one of the most promising technologies for treating olive mill wastewaters (OMWs). However, low methane productivities are generally achieved with dispersed-growth bioreactors, which are usually employed in OMW digestion. The methanogenic activity seems adversely affected by phenolic compounds, which are typically present in the OMWs and generally only slightly biodegraded in conventional anaerobic processes. In order to enhance the methane productivity, more efficient digester configurations were proposed: UASB and up-flow biofilm reactors resulted to be the most promising technologies applied to such an aim in the OMW anaerobic digestion. In particular, a significant improvement of the performances of the OMW conventional anaerobic digestion was recently documented by performing it in a passively immobilized biomass loop reactor packed with Granular Activated Carbon (GAC). Under continuous conditions, the GAC-reactor exerted COD and phenols removal productivities higher than those averagely displayed by most of the conventional and packed-bed laboratory-scale reactors previously proposed for the OMW digestion. Thus, to investigate the reproducibility and the stability of the GAC-biofilm process, an identically configured reactor was developed and fed with a wide variety of higher organic loads. It appeared to be a reproducible and stable process whose performances were significantly higher than those displayed by most of the bench-scale conventional and fixed-bed bioreactors proposed so far in the literature. Finally, an aerobic post-treatment, constituted by a second up-flow biofilm reactor packed with SB, was developed and integrated to the GAC-anaerobic digester so to implement the GAC-digester decontamination potential.