Coal-assisted flotation for olive mill wastewater: remediation and resource recovery

Abstract

Olive mill wastewater (OMWW) is difficult to manage due to its high organic load and persistent phenolic content. Here, coal-assisted flotation is evaluated as a single-step process integrating OMWW remediation with the upgrading of low-grade Soma lignite by exploiting interfacial interactions between wastewater constituents and coal surfaces. ATR-FTIR characterized coal and OMWW, while XRF, ash analysis, contact angle, and zeta potential measurements further assessed coal composition and surface behavior. Flotation tests conducted with 5–100% OMWW in the process water showed a strong dependence on wastewater fraction: the highest coal recovery together with the lowest-ash froth product was obtained at 5% OMWW, whereas increasing OMWW content beyond 10% progressively reduced recovery, consistent with partial surface hydrophilization under more concentrated wastewater matrices. The results support a dual mechanism in which OMWW organics enhance coal hydrophobicity to promote bubble–particle attachment. At the same time, phenolic compounds are removed from solution through adsorption onto coal surface sites, corroborated by post-flotation spectroscopic signatures. Overall, coal-assisted flotation defines an operational window where OMWW treatment and lignite beneficiation can be integrated, providing a scalable option for resource-oriented wastewater management.