Polyamide microplastics act as carriers for cephalexin in the anammox process

Emerging pollutants pose high risks to human health, and also put huge pressures on wastewater treatment. Their interactions would also affect the activity of functional microorganisms. This study investigated the response and mechanism of anaerobic ammonium oxidation (anammox) consortia to the long-term stress of common microplastics (polyamide, PA) and a broad-spectrum antibiotic (cephalexin, CFX). Although 0.1 g L−1 PA microplastics (MP) did not significantly inhibit the nitrogen removal performance, adsorption assays revealed that large amounts of cephalexin were adsorbed by PA. Thus, 0.5 mg L−1 CFX and 0.1–0.2 g L−1 PA caused a deterioration of anammox process. Simultaneously, the most dominant genus changed from Candidatus Kuenenia to norank o SBR1031, and expressional levels of functional genes dramatically decreased. In addition, the abundance of gene encoding superoxide dismutase (SOD) increased by 10.7 %, verifying that PA also caused the oxidative stress of anammox bacteria. PA promoted the accumulation of CFX in the anammox system through adsorption and extended its side effects on anammox consortia. This study provides a new direction into the implementation of anammox process in complex wastewater treatment.