Pilot-plant treatment of olive mill wastewaters by Phanerochaete chrysosporium coupled to anaerobic digestion and ultrafiltration

In this work, we investigated an integrated technology for the treatment of the recalcitrant contaminants of olive mill wastewaters (OMW), allowing water recovery and reuse for agricultural purposes. A pilot plant was devised based on fungal pretreatment using Phanerochaete chrysosporium followed by anaerobic digestion. P. chrysosporium DSM 6909 was cultivated on pre-stored OMW as sole carbon and energy sources in a 120 L air lift reactor (ALR) at a hydraulic retention time (HRT) of 3–5 days. The P. chrysosporium DSM 6909 pre-treated OMW was fed in a 300 L anaerobic filter after a decantation step. This anaerobic reactor worked continuously for 6 months at loading rates reaching 7 g L−1 d−1 of COD without any apparent toxicity. The P. chrysosporium DSM 6909 decreased the OMW relative toxicity from 100% to 74%. Furthermore, the P. chrysosporium DSM 6909 pre-treated OMW was well converted into methane by anaerobic digestion which resulted in an effluent with 38% toxicity referred to as untreated OMW. Moreover, the use of ultrafiltration (UF) as post-treatment technology completely detoxified the anaerobic effluent and removed its high molecular mass polyphenols. Results showed that compared to irrigation with water, treated effluent increased the germination index (GI) of Lycopersicon esculentum and enhanced plant growth while diluted untreated OMW decreased the GI and caused a pronounced growth inhibition.