Evaluation of olive processing wastes in terms of zero discharge and green energy production

Olive oil production generates large volumes of solid and liquid waste with high organic load, acidity, and toxic phenolic compounds. Conventional disposal methods cause serious environmental problems such as groundwater contamination, greenhouse gas emissions, and inefficient use of resources. This study investigates a sustainable management approach for olive processing waste based on the zero discharge principle, integrating gasification and organic rankine cycle (ORC) systems for green energy production. The system operates with a biomass feed rate of 440 kg/h, produces 60 kg/h of biochar, and is powered by a thermal input of 2000 kWh_th. The ORC unit operates at 15% electrical efficiency, generating 240 kW of electricity and 1360 kW of thermal energy. Mass and energy balance analyses show that nearly 100% of the waste can be converted into valuable outputs. Water recovery from olive mill wastewater was achieved through thermal evaporation. The biochar by-product can be utilized as a soil amendment or fuel additive. Economic feasibility analyses based on cost data demonstrate that profitability depends on electricity sale prices and the conversion of biochar into value-added products. A comparison of different biomass feedstocks reveals variability in cost but no significant difference in energy conversion efficiency. This research presents a viable, circular economy-oriented model for the olive oil industry in terms of sustainable waste valorization, water recovery, and renewable energy production.