Environ. Sci. Technol. 2007, 41, 3708-3714
Elimination of Selected Acidic Pharmaceuticals from Municipal Wastewater by an Activated Sludge System and Membrane Bioreactors KATSUKI KIMURA,* HIROE HARA, AND YOSHIMASA WATANABE Department of Environmental Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo 060-8628, Japan
The elimination of six acidic pharmaceuticals (clofibric acid, diclofenac, ibuprofen, ketoprofen, mefenamic acid, and naproxen) in a real wastewater treatment plant (WWTP) using an activated sludge system and membrane bioreactors (MBRs) was investigated by using a gas chromatography/mass spectrometry (GC/MS) system for measurement of the compounds. Limited information is available for some of the tested pharmaceuticals at present. Solid retention times (SRTs) of the WWTP and the two MBRs were 7, 15, and 65 days, respectively. The elimination rates varied from compound to compound. The MBRs exhibited greater elimination rates for the examined pharmaceuticals than did the real plant. Dependency of the elimination rates of the pharmaceuticals on SRTs was obvious; the MBR operated with a longer SRT of 65 days clearly showed better performance than did the MBR with a shorter SRT of 15 days. The difference between the two MBRs was particularly significant in terms of elimination of ketoprofen and diclofenac. Measurements of the amounts of adsorbed pharmaceuticals on the sludge and aerobic batch elimination experiments were carried out to investigate the elimination pathways of the pharmaceuticals. Results of the batch elimination tests revealed that the sludges in the MBRs had large specific sorption capacities mainly due to their large specific surface areas. Despite the sorption capacities of sludges, the main mechanism of elimination of the pharmaceuticals in the investigated processes was found to be biodegradation. Biodegradation of diclofenac, which has been believed to be refractory to biodegradation, seemed to occur very slowly.
Introduction Pollution of the environment by organic micropollutants is a great concern. Among these emerging pollutants, the occurrence of pharmaceuticals in the aquatic environment has drawn significant attention during the past decade. Detectable concentrations of pharmaceuticals have been reported in wastewater treatment plant (WWTP) effluents and natural waters (1-6). Most of the pharmaceuticals are excreted in feces and urine after use and eventually enter sewage systems. As a result, WWTPs receive wastewater containing various pharmaceuticals at low concentrations * Corresponding author phone: +81-11-706-6271; fax: 81-11-7066267; e-mail:
[email protected]. 3708
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(from nanograms to micrograms per liter range). Current WWTPs are not designed to deal with these emerging constituents, and their capability for treating pharmaceuticals is therefore not necessarily high (1, 6). Actually, effluents from WWTPs are relevant point sources for pharmaceuticals in the aquatic environment. Since good sources of drinking water are becoming scarcer, unintentional indirect potable reuse, a process resulting in the inclusion of some wastewater effluent in drinking water sources, is being carried out in many places. Depending on the local conditions, pollution of drinking water sources with pharmaceuticals can be possible. Drinking water produced might therefore contain some pharmaceuticals. Pharmaceuticals have been detected in drinking water in nanogram per liter ranges in a few studies (7, 8). Although adverse health effects caused by the consumption of pharmaceuticals at very low concentrations are not clear at present, residues of diclofenac, a widely used antiphlogistic, have recently been reported to be the cause of vulture population decline in Pakistan (9). Therefore, on the basis of precautionary principles, drinking water should be free of such anthropogenic compounds (10). The performance of WWTPs, which are relevant point sources of pharmaceuticals, should be upgraded to lower the risk associated with pharmaceuticals. Many pharmaceuticals are relatively polar, and their molecular weights are small (e.g.,
