Mitigation of the environmental impact of olive mill waste water through sustainable bioprocess with energy recovery

In olive cultivation areas, groundwater is threatened by possible contamination due to the spreading of olive mill wastewaters (OMW) over agricultural soils. Currently, OMW spreading is subject to regulations that restrict discharged volumes on soil areas according to the local soil drainage properties. Nevertheless, such practice is not without risk of contamination for groundwater resources, since the OMW volumes are very large (2 Mm3/year only in Italy, where triphasic extraction plants are used) and produced in a short period of the year. Long term storage of OMW is problematic due to troublesome fermentative processes. OMW cannot be processed in urban wastewater treatment plants because of inhibition of microbial activity in secondary (biological) treatment. Costs bound to the development and realization of specific physicochemical or biological treatments hindered actual application up to now. The project OilWasteRecovery is aimed at the realization of a combined treatment process for the reduction of toxicity and COD of OMW. Detoxification allows reuse of wastewater for soil irrigation, taking further advantage of residual nutrients and minerals for soil fertilization. Alternatively, detoxification allows OMW processing in urban wastewater treatment plant, so reducing the impact on saturated agricultural soils and underlying groundwaters. The other aspect that the project takes into account is the sustainability of the process thanks to energy recovery resulting from the biogas produced by the anaerobic digestion of OMW. The project aims, therefore, to achieve a net zero energy treatment. The combined treatment consists of three steps, each subject to energetic optimisation: 1) detoxification of waste water from olive mill of Campania region to improve the biodegradability in anaerobic digesters, with the use of catalysis and/or adsorption in operative “mild” conditions (room temperature, atmospheric pressure, neutral pH) and with low energy consumption; 2) anaerobic digestion with biogas production, maximized by the detoxification of the effluent and the co-digestion of agricultural and/or food waste; 3) energy recovery from purified biogas, with improved efficiency of production of electricity and heat through the use of fuel cells and cogeneration.