The effect of tire microplastics on aerobic granular sludge performance

Abstract

Although tire microplastics (TMPs) constitute a substantial portion of microplastic entering wastewater treatment plants, there is a knowledge gap regarding the influence of TMPs on aerobic granular sludge (AGS) systems, which, being more resilient than activated sludge, are becoming increasingly important in modern wastewater treatment. This study investigated the effect of TMPs in wastewater (50, 100, 250, and 500 mg/L) on AGS performance and microbiome. TMPs did not affect organics and phosphorus removal, however, total nitrogen removal was significantly higher (about 9 %) at 500 mg TMPs/L compared to the control. TMPs improved biomass settling, but this was due to TMP accumulation (TMPs comprised over 50 % of biomass at 500 mg TMP/L) rather than improved granulation. The biomass yield coefficient was five times lower at 500 mg TMP/L than in the control. TMPs elevated dehydrogenase activity (free radical generation) and increased the abundance of microbes involved in polyP synthesis and nitrogen metabolism. TMP presence increased the microbiome potential in terms of antibiotic resistance genes (cmd and marR) and the abundance of hydrolases, which degrade rubber-associated ester bonds, and significantly increased the abundance of MP-degraders belonging to genera Ideonella, Rhodobacter, Xanthobacter, and Hydrogenophaga. This study demonstrates that while TMPs in wastewater do not impair nutrient removal by AGS, their accumulation significantly degrades biomass properties, complicating sludge management and disposal. Furthermore, TMPs alter the AGS microbiome's composition and metabolic potential. These findings highlight the importance of integrating AGS systems into urban wastewater treatment, optimizing sludge management strategies, and developing targeted approaches to address the challenges posed by TMPs.