Integrated biological approaches for olive mill wastewater treatment and agricultural exploitation

• An integrated biological approach for OMW bioremediation has been investigated.
• Aerobic treatment of OMW with N2-fixing bacteria yielded a bioferment.
• The bioferment was characterized by a reduced antimicrobial activity.
• At the end of composting with added bioferment a good abatement of polyphenols was achieved.
• Mature compost was biologically stable.

In this study, an integrated biological approach, consisting of the aerobic treatment of olive mill wastewater (OMW) for the production of a N2-fixing culture followed by laboratory-scale composting, was investigated for the agricultural exploitation of this agro-industrial waste. In the first stage, presumptive azotobacteria isolated from soils annually treated with OMW and three reference cultures were screened for their capacity to abate water-soluble polyphenols from sterile lime-treated OMW. Two soil isolates, molecularly identified as Azotobacter chroococcum and the reference strain Azotobacter spp. GP1 were selected for the formulation of a bacterial consortium to be exploited for the production of a N2-fixing culture in a 2-L laboratory fermenter by using sterile neutralized OMW. Once assayed for its residual antimicrobial activity, the resulting bioferment was applied to wheat straw piles at the start of the laboratory-scale composting process, and the properties of the final compost were assayed. The effect of regular application of OMW during prolonged composting (136 days) was also evaluated and total abated polyphenols were quantified.The preliminary results of this first study were an aerobic OMW bioferment enriched with N2-fixing bacteria and characterized by a significantly reduced antimicrobial activity, and a significant improvement in the compost stability through the inoculation of straw piles with this N2-fixing bacterial culture.