Kinetics and degradation pathway of sulfamethazine chlorination in pilot-scale water distribution systems

Abstract

As a new type of environmental micro-organic pollutant, sulfonamides (SAs) have been shown to damage organisms if they are exposed to them over the long term. Moreover, an increasing number of SAs has been detected in natural water and urban water supply systems in recent years because they cannot be completely removed through conventional water treatment processes. Therefore, sulfamethazine (SMZ) in urban water systems was selected as a target to be investigated. The reaction kinetics of sulfamethazine chlorination were studied in a pilot-scale water distribution system (WDS) under the influence of different factors, including pH, temperature, flow rate and pipe materials, to determine the optimal factors for removing SMZ and to provide a reference for water quality in urban drinking water systems.According to the experimental results, the kinetics models of SMZ chlorination fitted a second-order reaction in pure water. The degradation of SMZ was not only affected by the water quality conditions but also the operating temperatures, flow rates and pipe materials. The rate constants of SMZ chlorination under different temperatures were related to the Arrhenius equation. Different flow rates had little effect on SMZ degradation. In different pipes, the degradation rates of SMZ followed the order stainless-steel pipe>polyethylene pipe (PE)>ductile iron pipe. Moreover, eight reaction intermediates during SMZ degradation were observed and identified, and a degradation pathway was proposed. The concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) during the degradation of SMZ in WDS were also determined.