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Despite the polluting potential olive mill wastewater (OMW) can be a useful source of nutrients and organic compounds to improve soil properties. The aim of this paper was to verify if biochar-based treatment of OMW could be an efficient method to contrast the richness in phenolic compounds and phytotoxicity of OMW making it more suitable. for soil amendment. In this study poplar biochar (BP) was more effective than conifer biochar (BC) in terms of adsorbing phenols and reducing phytotoxicity at different biochar rates (5 and 10 %). In soil amendment BP-treated OMW induced an increase of organic carbon by approximately 15 % and notably BP10 treated OMW enhanced available phosphorous by 25 % after 30 days of incubation. In soil amended with 10 % BP-treated OMW microbial biomass and enzymatic activities were significantly enhanced after 30 and 90 days, with no effect on cress seed germination. Therefore, biochar based-treatment could be cost-effective and able to facilitate the long-term management of OMW in terms of storage and disposal.

Industrial symbiosis is being increasingly recognized as a valuable tool for promoting a more sustainable production process in agriculture. However, the primary motivation for implementing industrial symbiosis is economic viability. In the context of industrial symbiosis, by linking agriculture and food together, the study examines the impact of the use of vermicompost, derived from agricultural by-products, on spinach yield as well as on nutritional and biochemical soil aspects. Moreover, the economic feasibility for spinach farmers is also investigated. A field experiment with five treatments i) solarization ii) solarization and vermicompost iii) green manure and solarization iv) green manure, solarization, and vermicompost, and v) vermicompost has been realized in “Piana del Sele”, a rural area in Southern Italy. Collected data have been analysed through a Partial Least Square Structural Equation Modeling approach to assess the overall impact (direct and indirect effects) of vermicompost on both spinach yield and soil characteristics. Lastly, the economic profitability of using vermicompost is pointed out for spinach growers. The study findings show that the highest positive impact on yield occurs when vermicompost is combined with solarization (+15 %). Moreover, with regard to soil characteristics, the combination of vermicompost and solarization has a positive impact on nutrients, fungal biodiversity, and the biochemical quality of the soil. The economic profitability of using vermicompost in conjunction with solarization is guaranteed when the price of vermicompost is below € 0.84/kg. In light of these findings, some policy interventions can be implemented to enable industrial symbiosis as a viable tool for a circular economy in the agri-food sector. These include promoting the diffusion of biogas plants to valorize agricultural by-products and promoting the use of vermicompost in farms, by encouraging its purchase by farmers.

Olive mill wastewater (OMW) is the effluent derived from the oil extraction processes from olives. Despite the polluting potential OMW can be a useful source of nutrients and organic compounds to improve soil properties. OMW could negatively affect soil and water quality as this waste is rich in phenolic compounds and has high COD and BOD5. Biochar-based treatment could be an efficient method to remediate OMW. In this study poplar biochar (BP) was more effective than conifer biochar (BC) in terms of adsorbing phenols and reducing phytotoxicity at different biochar rates (5 and 10 %). BP-treated OMW was used in soil amendment and induced an increase in chemical properties, especially in organic carbon after 30 days of incubation. In soil amended with 10 % BP-treated OMW microbial biomass, enzymatic activities, and cress seed germination were significantly enhanced after 30 and 90 days.