Simultaneous removal of ciprofloxacin and disinfection from wastewater by combined photocatalytic reactor (PCR) and membrane bioreactor (MBR) system

Abstract

Integrated photocatalytic-biological wastewater treatments are being explored as an effective alternative for removing emerging contaminants and pathogens. This study investigates ciprofloxacin (CPX) antibiotic removal and inactivation of Escherichia coli in simulated wastewater by using two systems (i) photocatalytic reactor (PCR) with 0.5 g/L of Ag-doped TiO2 nanoparticles (Ag:Ti in 1:1.7 molar ratio) with 180 min of blue LED light exposure and continuous mixing, and (ii) submerged membrane bioreactor (MBR) operated in continuous mode at 2.75 days hydraulic retention time (HRT) and 30 days of solid retention time (SRT) with 0.68 bar transmembrane pressure (TMP). TEM, XRD, and UV-Vis DRS characterization suggested that Ag doping in the lattice of 25 nm-sized nanoparticles lowered the bandgap from 3.10 to 2.41 eV, improving its photocatalytic performance. Studies on individual PCR, MBR, and combined systems were performed for optimum CPX removal and disinfection. MBR followed by PCR (MBR-PCR) was observed to be the best treatment among all four strategies achieving 99% removal of chemical oxygen demand (COD) and nitrogen from the system, and ensuring ∼99% CPX removal with complete disinfection of 106 CFU/mL E. coli. The study also suggested CPX biodegradation with marginal adsorption on bio-sludge in MBR, and predominant role of h+ over •OH radicals in CPX photocatalysis and bacterial cell disruption. The absence of E. coli zone of inhibition indicated the elimination of CPX toxicity in the treated effluent. Thus, integrated MBR-PCR may find application in the removal of such pharmaceutical compounds and disinfection from wastewater.