Behaviour of brominated and chlorinated flame retardants during drinking water treatment

Abstract

Flame retardants are chemicals that are added to plastic materials in order to prevent them from catching fire and to slow down the burning process. Due to the widespread occurrence of flame retardants in the environment, it can be expected that especially the more hydrophilic compounds already contaminate raw water resources of water utilities. In this paper results of laboratory-scale experiments on the behaviour of ten brominated and chlorinated flame retardants during different steps of drinking water treatment will be presented. The target compounds were selected based on their production volumes and physical-chemical properties. The final list includes 1- and 2-bromostyrene, 2,4- and 2,6-dibromophenol, tetrabromophthalic acid, tetrachlorophthalic anhydride, chlorendic acid, tris(1,3-dichloro-2-propyl) phosphate, tris(2-chloroethyl) phosphate (TCEP), and tris(1-chloro-2-propyl) phosphate (TCPP). The results obtained from the laboratory-scale experiments clearly indicate that from the selected flame retardants only 1- and 2-bromostyrene are well biodegradable under aerobic conditions whereas the other flame retardants under investigation turned out to be persistent. Flocculation with either iron or aluminium salts is not an efficient option for removal of the selected flame retardants. For 1- and 2-bromostyrene removal rates of ca. 50% can be achieved whereas for the other compounds removal rates are in the range of 10 to 30% even when dosing 50 mg/L of flocculation agent. Oxidation with either ozone or ozone/hydrogen peroxide proved also to be rather inefficient for removal of the flame retardants under investigation, even at elevated doses of oxidant of 10 mg/L. However, results showed that the selected flame retardants adsorb well onto activated carbon and thus GAC adsorption seems to be a promising option for their removal.