Inhibition of the partial nitritation by roxithromycin and Cu(II).

To facilitate the application of partial nitritation (PN) - anaerobic ammonium oxidation process in nitrogen removal from livestock wastewater, the inhibition of roxithromycin (ROX) and Cu(II) on the PN sludge was examined using a respirometric method. The results showed that the IC50 of ROX and Cu(II) on PN sludge were 346 and 74.3mgL(-1), respectively. The relative specific respiration rate (SRR) of ammonia-oxidizing bacteria (AOB) decreased from 87.4% to 17.7% with the ROX concentration increased from 0 to 500mgL(-1). When the concentration of Cu(II) increased from 0 to 160mgL(-1), the SRRs of AOB and nitrite-oxidizing bacteria decreased by 85.5% and 11.2%, respectively. According to the isobole plots analysis, combined suppression by ROX and Cu(II) was synergistic. Fourier transform infrared spectroscopy analyses showed that ROX exposure altered the positions of CO bonds, and the intensity of the absorption peak at 2100cm(-1) changed under Cu(II) exposure.