Advanced treatment of urban wastewater by UV radiation: Effect on antibiotics and antibiotic-resistant E. coli strains.

Urban wastewater treatment plant (UWWTP) effluents are among the possible sources of antibiotics and antibiotic-resistant bacteria (ARB) spread into the environment. In this work, the effect of UV radiation on antibiotic-resistant Escherichia coli (E. coli) strains was compared with that of chlorination process. Under the investigated conditions, UV disinfection process resulted in a total inactivation after 60min of irradiation (1.25×10(4)µWscm(-2)) compared to 120min chlorine contact time (initial chlorine dose of 2mgL(-1)). Moreover, no change in E. coli strains' resistance to amoxicillin (AMX) (minimum inhibiting concentration (MIC)>256mgL(-1)) and sulfamethoxazole (SMZ) (MIC>1024mgL(-1)) could be observed after UV treatment, while the treatment affected resistance of the lower resistance strain to ciprofloxacin (CPX) (MIC decreased by 33% and 50% after 60 and 120min, respectively). Contrarily, chlorination process did not affect antibiotic resistance of the investigated E. coli strains. Finally, the effect of UV radiation on the mixture of three antibiotics was also investigated and photodegradation data fit quite well pseudo first order kinetic models with t1/2 values of 14, 20 and 25min for CPX, AMX and SMZ, respectively. According to these results, conventional disinfection processes may not be effective in the inactivation of ARB, and the simultaneous release of ARB and antibiotics at sub-lethal concentrations into UWWTP effluent may promote the development of resistance among bacteria in receiving water.

Microbial and cod removal in a municipal wastewater treatment plant using coagulation flocculation process.

This study was designed to improve the removal efficiency of COD, SS, and microorganism at the S. Giovanni a Teduccio municipal wastewater treatment plant, Naples, Italy. The plant consists of screen, sand grinder, oil removal, coagulation, flocculation and sedimentation units, hypochlorite disinfection, mechanical dewatering, and thermal sludge conditioning. A series of Jar-test was conducted on twelve samples taken after screen using FeSO4 alone or together with Ca(OH)2 at 100 rpm rapid mixing for 1 min, 30 rpm for slow mixing for 20 min and 30 min for settling. 150 mg L(-1) and 450 mg/L doses of FeSO4 were used at a pH interval in between 6 and 9. The removals of COD, TSS, Escherichia coli and total coliforms were measured ranging from 40 to 70%, 70 to 90%, 96 to 99% and 97 to 99%, respectively when FeSO4 was used alone at 150 mg L(-1) and 450 mg L(-1) doses and at pH 6, 7 and 8. Wastewater discharge standards could be safely obtained at 150 mg L(-1) dose of FeSO4 with the use of 220 mg L(-1) Ca(OH)2 at pH 8 in terms of COD and E. coli removals resulted in 65% and 98%, respectively, with less sludge production to be disposed. Additionally, none of influent and supernatant samples tested in this study was found to be acute toxic on 24h-born Daphnia magna at 50% dilution.