Antibiotics in two municipal sewage treatment plants in Sri Lanka: Occurrence, consumption and removal efficiency

Abstract

Most of the monitoring data on the occurrence of antibiotics in sewage treatment plants (STPs) have been reported from Europe, North America and some countries in Northeast Asia, while very limited data can be found in Southeast Asian countries. As a pioneering research in Sri Lanka, we collected 24 h composite wastewater samples at the influent and effluent of two municipal STPs for consecutive 7 days to investigate occurrence, consumption and removal efficiency of seventeen antibiotics. The STP was located in Colombo and Hikkaduwa, respectively, representing two kinds of communities (i.e. local and tourists) in Sri Lanka. The targeted antibiotics were extracted by solid-phase extraction method and detected on an Agilent HPLCMSMS (1290/6470QQQ). Results illustrated that the majority of the antibiotics can be always detected from both STPs, except for chlorotetracycine (CTC), doxycycline (DOX) and florfenicol (FF). Fluoroquinolones (FQs) were detected at highest concentrations with ciprofloxacin (CIP) being the dominant compound. Concentrations of CIP in the influent samples were in the range of 433–6010 ng/L. The consumption of antibiotics was estimated on the basis of influent mass load and catchment population data. We found difference in consumption patterns between the two served areas. Compared to local people in Colombo, tourists in Hikkaduwa appeared to take more antibiotics during the study period with the estimated daily dose of 0.25 g per 1000 persons. Moreover, macrolides accounted for a larger portion than FQs in Hikkaduwa, with azithromycin (AZM) being the most prevalent antibacterial agent. After comparison with an official report by Medical Supplies Division of Sri Lanka, we conjected that AZM was not commonly used among local people and it was mainly introduced by foreign arrivals. As for the removal efficiency, the activated sludge system of Colombo exhibited better elimination and more stable performance than the constructed wetland process of Hikkaduwa. Keywords: Antibiotics, Sewage treatment plants (STPs), Activated sludge process, Constructed wetland, Consumption, Removal efficiency, Sri Lanka