Investigation of sequencing batch moving-bed biofilm reactor to biodegradation of cefixime as emerging pollutant in percent of easily degradable co-substrate

Abstract

ABSTRACT In the present study, sequencing batch moving-bed biofilm reactor (SBMBBR) was developed as a new treatment system and was used to treat wastewater containing cefixime antibiotic (CFX). The effect of initial concentration of CFX (0–122 mg/L) on common parameters including total nitrogen (TN), nitrite (NO2 −), nitrate (NO3 −), and chemical oxygen demand (COD) was also evaluated. When a small concentration of CFX (45 mg/L) was added to the SBMBBR, good removal efficiencies were obtained for CFX, COD, and TN. Slight changes in mixed liquor-suspended solids (MLSS) and specific oxygen uptake rates (SOUR) in the reactor containing 92 mg/L of CFX showed that microorganisms had high adaptation in the new SBMBBR system. Biological removal of TN, COD, and CFX was decreased from 70.75, 74.81, and 70.9% to 27.38, 23.2, and 34.8%, respectively, when the initial CFX concentration was increased from 45 to 122 mg/L. Also, value of MLSS was decreased at CFX concentrations of 92 and 122 mg L-1, indicating that bacterial growth was inhibited. CFX degradation products were detected by performing the liquid chromatography-mass spectroscopy (LC-MS/MS) and the results obtained from analysis showed that the CFX was first converted into 5-vinyl-3,6-dihydro-2H-1,3-thiazine-4-carboxylic acid and thiazol-2-amine by breaking C-N bond and chain ring. Then, acetic acid and ethyl (methyl) sulphone were formed with further destruction of the chain ring and ring opening. Finally, these by-products can be converted into CO2 and H2O. Accordingly, the results of the present study demonstrated that hybrid process of SBMBBR with minimal reduction in the concentration of MLSS and SOUR can be a good alternative to processes alone in treatment of high concentrations of CFX.