Anaerobic digestion of olive oil mill effluents: Evaluation of wastewater organic load and phytotoxicity reduction

Olive oil mill effluents (OME) are of great concern worldwide due to their role as pollutants. This work studies, on a laboratory scale, the possibility of reducing the polluting load of olive wastewaters (organic, acid and polyphenolic) through chemical-physical processes (sedimentation-filtration) followed by a biological treatment (anaerobic digestion). This is in order to produce biogas and obtain an effluent suitable for application to the soil. The anaerobic process was followed by determining chemical-physical parameters (pH, COD, N-NH3, polyphenols). The extent of anaerobic digestion was evaluated through measurements of biogas and volatile fatty acids and the microbial metabolism was examined through dehydrogenase activity. Finally, tests of plant germination and growth were carried out using digested waters to determine if they could be used in agriculture. The study demonstrated that anaerobic digestion of OME first reduced the organic load by 78-89% and the content of polyphenols by 33-43%, and secondly produced biogas ( mean value of methane 83-85%). Phytotoxicity tests carried out on Lepidium sativum seeds showed that the anaerobic treatment considerably reduced the phyto-toxic character of OME.