Microalgae-based bioremediation of olive mill wastewater: Technical and environmental evaluations using orange peel and orange peel-derived biochar

The discharge of olive mill wastewater (OMWW) presents significant environmental challenges due to its high pollutant load, necessitating sustainable management solutions. This study explores a novel approach to treat OMWW through microalgae-based bioremediation using orange peel (OP) and OP-derived biochar as matrices for microalgae immobilization. Aligning with the principle of bioeconomy, this study treats a waste (OMWW) with another waste in its raw form and as a high-value-added product maximizing its potential (OP and OPderived biochar). The technical feasibility and the environmental footprint through Life Cycle Assessment (LCA) are evaluated. LCA includes different impact categories and focuses on climate change to quantify decarbonization, considering as a function unit (FU) 10 g of OP (the amount used in the bioremediation tests). OMWW was explored at 5 % and 10 % v/v (according to literature studies) using Chlorella vulgaris immobilized on OP (scenario 1) and OP-derived biochar (scenario 2) of the chosen size. Scenario 1 (OMWW at 10 % v/v) reached the highest performance by achieving ~70 % phenolic compound degradation, ~ 60 % chemical oxygen demand abatement, and a climate change impact of 0.43 kg CO2 eq/FU. The strengths of Scenario 1 include high bioremediation capacity and energy recovery from pyrolyzing microalgae-immobilized exhausted OP, specifically refining pyrolysis bio-oil as an energy carrier which generates a surplus of energy. These results demonstrate the potential of integrating microalgae with waste substrates for environmental remediation and energy recovery, offering a sustainable approach to mitigate disposal impacts and close the loop in agro-industrial systems.