Impact of Tire-Derived Microplastics on Microbiological Activity of Aerobic Granular Sludge

In recent years, there has been an increase in the emission of tire wear particle (TWP) microplastics from wastewater treatment plants into the environment. The aim of this study was to determine the effect of TWPs in wastewater flowing into a biological reactor on the transcription of the <i>16S rRNA</i> gene and the key genes responsible for nitrogen metabolism, <i>amoA</i>, <i>nirK</i> and <i>nosZ</i>, in aerobic granular sludge. The laboratory experiment was carried out in sequencing aerobic granular sludge reactors operated in an 8 h cycle into which TWP microplastics were introduced with municipal wastewater at a dose of 50-500 mg TWPs/L. The ammonia removal rate and the production of oxidized forms of nitrogen increased with the TWP dose. Gene transcript abundance analysis showed that the presence of rubber and substances leached from it promoted the activity of ammonium-oxidizing bacteria (160% increase), while the transcription of genes related to denitrification conversions was negatively affected. The activity of nitrite reductase gradually decreased with increasing TWP concentration in wastewater (decreased by 33% at 500 mg TWPs/L), while nitric oxide reductase activity was significantly inhibited even at the lowest TWP dose (decreased by 58% at 500 mg TWPs/L). The data obtained indicate that further studies are needed on the mechanisms of the effects of TWPs on the activities of the most important groups of microorganisms in wastewater treatment to minimize the negative effects of TWPs on biological wastewater treatment.