Enhancement of anaerobic treatability of olive oil mill effluents by addition of Ca(OH)(2) and bentonite without intermediate solid/liquid separation

Previous work on the anaerobic treatment of olive oil mill effluents (OME) have shown: (a) lipids, even if more easily degraded than phenols, were pot entially capable of inhibiting methanogenesis more strongly; (b) a pretreat ment based on addition of Ca(OH), and bentonite removed lipids almost quant itatively; (c) preliminary biotreatability tests performed on the pretreate d OME showed high bloconversion into methane at very low dilutions ratios, especially when the mixture (OME, Ca(OH), and bentonite) was fed to the bio logical treatment without providing an intermediate phase separation. This paper was directed towards two main aims: (a) to optimize pretreatment: the best results in terms of methane production were obtained by addition of C a(OH)(2) UP to pH 6.5 and of 10 g L-1 of bentonite; (b) to evaluate the enh ancement of anaerobic treatability of OME pretreated under optimized condit ions in a lab-scale continuous mathanogenic reactor fed with the substrate without intermediate solid/liquid separation: very satisfactory performance s were obtained (at an organic load of 8.2 kg COD m(-3) d(-1) and at a dilu tion ratio of 1:1.5 total COD removal was 91%, biogas production was 0.80 g CH4 (as COD)/g tot. COD, lipids removal was 98%, phenols removal was 63%). The results confirm the double role played by bentonite (adsorption of the inhibiting substances and release of the adsorbed biodegradable matter in the methanogenic reactor).