A study, “Evaluation of olive processing wastes in terms of zero discharge and green energy production,” published in Scientific Reports by Arzu Teksoy and Mehmet Şen, reveals a sustainable path for the olive oil industry. Olive oil production, particularly in the Mediterranean, creates massive volumes of waste: solid olive pomace and highly toxic, high-organic-load olive mill wastewater (OMW). Conventional disposal methods, such as storing OMW in open lagoons or uncontrolled burning of pomace, lead to serious environmental crises, including groundwater contamination and greenhouse gas emissions. This new research proposes an integrated, circular-economy-oriented solution to completely valorize these waste streams.

The core of the system is the combination of a biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More gasificationGasification is a high-temperature, thermochemical process that converts carbon-based materials into a gaseous fuel called syngas and solid by-products. It takes place in an oxygen-deficient environment at temperatures typically above 750°C. Unlike combustion, which fully burns material to produce heat and carbon dioxide (CO2​), gasification More unit and an Organic Rankine Cycle (ORC). In the gasification unit, the pomace undergoes partial combustion, producing a combustible gas mixture called syngasSyngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen and carbon monoxide. It is produced during gasification and can be used as a fuel source or as a feedstock for producing other chemicals and fuels.   More, and a solid by-product, biochar. The syngas is then combusted to provide thermal energy to the ORC system, which, operating at a 15% electrical efficiency, generates approximately 240 kW of electricity. A major achievement of the system is the recovery of valuable resources, including heat, water, and biochar. The residual thermal energy from the ORC, approximately 1360 kW in the form of 90–95°C hot water, is not wasted. Instead, it’s strategically recovered and used to thermally evaporate the problematic olive mill wastewater. This process achieves water recovery through condensation, with the recovered pure water potentially reusable for agricultural irrigation. This thermal evaporation is key to achieving the goal of zero liquid discharge for the facility, rapidly eliminating the OMW load that traditionally takes years to evaporate in open lagoons..

The economic evaluation reveals a crucial insight: while electricity generation is a major output, the profitability is highly dependent on the biochar by-product. The analysis showed that revenue from the sale of biochar accounts for a substantial 70–90% of the system’s total income across all scenarios. For example, in the baseline 240 kW scenario with external electricity sales, selling the biochar as low-value powder results in a total monthly revenue of only $52,612. However, transforming the biochar into high-value products like briquettes or hookah charcoal dramatically increases the total monthly revenue to $155,126 and $244,269, respectively. Upgrading the biochar is a more effective way to boost total income than even improving the electrical output.

The system’s technical viability was confirmed at a pilot scale, which occupies an intermediate-scale area of approximately 400 m2. Economic feasibility studies estimated a simple payback time of 5.9 years using olive pomace pellets, but this time can be drastically cut to around 2.5 years when the recovered thermal energy is fully sold or utilized. Furthermore, the system is flexible, allowing for the use of other regional biomass like corn cobs or wood chips during the non-harvest season, which helps maintain continuous operation and investment efficiency. Environmentally, the conversion of olive waste into biochar is significant; the recalcitrant carbon in the biochar acts as a stable carbon sink, supporting the vision of a negative-emission technology.

This integrated gasification-ORC model moves olive waste from an environmental problem to an economic asset. It provides a robust, zero-discharge solution that simultaneously generates green energy, recovers clean water, and creates high-value carbon products, setting a strong precedent for sustainability and the circular economy within the agri-food industry.

Source: Teksoy, A., & Şen, M. (2025). Evaluation of olive processing wastes in terms of zero discharge and green energy production . Scientific Reports, 15:39571.