Ozone Injection System Based on NETmix Technology for Quaternary Treatment of Urban Wastewater

An innovative high-intensity static mixer technology, known as NETmix, was applied as an ozone (O3) gas injection system to promote the quaternary treatment of urban wastewater (UWW), focusing on the elimination of contaminants of emerging concern (CECs). The NETmix network with an exclusive geometry boosts mass transfer rates and rapidly develops an O3-rich stream to react with CECs. The mixer operated in continuous mode promotes a rapid gas (O3)–liquid (water) dissolution. The ozonation process’ performance was evaluated for the abatement of 19 CECs spiked (10 μg dm−3each) in demineralized water and two tertiary-treated UWW matrices, coming from (i) a secondary settler tank after a conventional activated sludge and (ii) the outlet of a membrane biological reactor (MBR). In addition, the ozonation system was tested for removing a broad range of CECs at natural trace levels from the UWW matrix coming from the MBR. In the realistic wastewater contamination scenario, a maximum transferred O3dose of 1.28 gO3gDOC−1and 0.76 gO3gDOC−1resulted in removal values ≥80% for 12 out of the 19 spiked CECs from the secondary settler tank, and 9 out of the 19 spiked CECs from the post-MBR treatment, respectively, at a very short hydraulic residence time (55 s). Moreover, removals ≥80% were attained for 22 out of 25 CECs detected in the effluent from the MBR, applying a specific O3dose of 0.6 gO3gDOC−1. The enhanced ozone-water mass transfer provided by the NETmix technology enabled high removal efficiencies for CECs.