Enhancing ozonation using Meretrix lusoria shell waste biomass: sustainable decontamination of azo dye wastewater via decolorization, mineralization, and detoxification

Azo is a synthetic organic dye that has attracted considerable attention because of its recalcitrance to degradation and toxicity. An upgraded ozonation process must be developed that integrates decolorization, mineralization, and toxicity reduction to manage the residual azo dye in the effluent from the dyeing industry and reduce its associated aquatic environmental risks. In this study, an ozonation system using Meretrix lusoria (ML) shell-waste-derived biomass (ML800) that uses simple calcination was developed. The ML800/O3 system almost completely decolorized ( > 99.0%) and highly mineralized (53.6 ± 1.7%) Congo red (CR) during (CR = 100 mg∙L–1, ML800 = 0.5 g ∙ L–1), surpassing the performance of the other tested systems (single ozonation and single ML800). Moreover, the ML800/O3 system reduced the acute toxicity of CR to the bacterium Aliivibrio fischeri, whereas single ozonation showed temporarily increased the toxicity of CR. The FE-SEM/EDS, FTIR, and XRD analyses verified that Ca(OH)2 was the main calcium species in ML800, which catalyzed the decomposition of O3 into highly reactive •OH. The system was successfully applied to various azo dyes and was robust with water matrix constituents. These findings highlight the potential of marine shell waste for use as a sustainable and ecofriendly additive for ozonation, increasing azo dye removal from wastewater in practical applications.