BEHAVIOR OF FLUORESCENT WHITENING AGENTS DURING SEWAGE-TREATMENT

Fluorescent whitening agents (FWAs) are contained in most modern laund ry detergents and are thus discharged in substantial quantities with h ousehold wastewater. To determine the mass flows and fate of the predo minant detergent FWAs, a field study was conducted at a full-scale mec hanical-biological sewage treatment plant at Zurich-Glatt, Switzerland . Samples of wastewater (raw sewage, and primary and secondary effluen t) and sludge (raw, activated, and anaerobically-digested sludge) were collected during a 10-day period. The concentration of FWAs in water samples was determined using solid-phase extraction with C-18 disks an d high-performance liquid chromatography (HPLC). The concentration of FWAs in sludge was determined by supercritical fluid extraction and HP LC. The removal of FWAs from wastewater during sewage treatment varied significantly (53-98%) between different FWAs. Removal was due to ads orption to primary and activated sludge and the observed extent of rem oval was consistent with the individual sorption behavior of FWAs. No evidence for biodegradation of FWAs was found during the aerobic biolo gical treatment of municipal wastewater with activated sludge and duri ng anaerobic-mesophilic digestion of sewage sludge. Average annual dis charge of FWAs to Swiss surface water is approximately 20 t (22% of th e consumed FWAs) while FWA disposal to farmland associated with sewage sludge is 11 t/y (12%), estimated based on the extent of removal from sewage and on a previously reported survey of FWA concentrations in s ewage sludge. The discharge of FWAs to surface water leads to a projec ted average FWA concentration in surface waters of 0.5 mu g/l, which i s well below toxic levels for these compounds. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.