Environmental and economic analysis of an olive mill wastewater treatment system integrated with microalgae production

Purpose of the article Olive mill wastewater raises environmental concerns due to the presence of pollutants and phytotoxic compounds. This study aims to evaluate the environmental performance of an integrated process that recycles olive mill wastewater while concurrently producing Arthrospira platensis for food applications. Methods The quantification of the environmental impact is conducted using the life cycle assessment methodology. The environmental burden of the proposed integrated system is also compared with that of alternative wastewater treatment solutions and growing medium for microalgae cultivation considering different functional units. Eventually, a simplified economic analysis of the proposed integrated system is carried out, as a complement of the environmental assessment, to evaluate its economic competitiveness considering different market scenarios. Results and discussion LCA characterisation results have been obtained for a set of reference scenarios using EF 3.0. The set of normalisation and weighting factors of the EF 3.0 impact assessment method is used for comparing various scenarios. In terms of aggregated score, the integrated system can reduce the environmental impact by 75.95% compared to the conventional treatment of olive mill wastewater. The use of nutrients from olive mill wastewater for the cultivation of A. platensis can potentially provide a 10.10% impact reduction compared to MF, while it is slightly higher (+ 7.5%) compared to the use of the standard Zarrouk growing medium due to the residual retentate generated in the system. An optimal retentate-free operating scenario showed a 47.38% impact decrease compared to the standard Zarrouk cultivation. The sensitivity analysis shows that transport and energy consumption have an important influence on the performance of the integrated system. The cultivation of A. platensis can be more impacting than wastewater treatment with membrane filtration if the increase of transportation distances exceeds 30 km. The economic analysis reports that the investment can be recovered in about 10 years, with a net present value of 127,000 € at 20 years, and that the cost of wastewater treatment is more influencing than the cost of electricity and the microalgae selling price. Conclusions Based on the conducted analyses, the valorisation of nutrients from olive mill wastewater to produce A. platensis biomass can be a viable option for olive mill owners. Even though there are margins for process optimisation, this treatment solution can still offer environmental benefits and additional revenues due to the combination of avoided wastewater treatment costs and reduced microalgae production costs.