Evaluation of the Influence of pH On Sorption of Ibuprofen and Naproxen in Simulated Domestic Waste Water.

Detectable concentrations of pharmaceuticals have been reported in wastewater treatment plant (WWTP) effluents and natural waters in many countries. Recently in the U.S. low levels (< 10 µg/L) of pharmaceuticals have also been found in effluent from WWTPs, surface water and treated water, and agricultural lands receiving treated waste water. Although the health effect of very low concentration of pharmaceuticals in aquatic environment is not yet clearly understood, it is important to understand their fate in the waste water and the effect of various treatment methods on the levels of these pharmaceuticals in the receiving waters and the sludge resulting from sewage treatment. Varying range of reduction (7- 96 %) of pharmaceuticals in the aqueous phase during their passage through the WWTPs has been reported. Reduction in concentration of pharmaceuticals has been attributed to sorption and biodegradation; however the contribution of these processes has not been fully characterized. Reduction due to sorption may be determined by batch studies in which sorption coefficient (k_d) is determined at multiple concentration which allow for construction of sorption isotherms. Previous studies have reported the pH dependence of these pharmaceuticals on sorption. Ibuprofen and Naproxen are common over the counter drugs in the U.S., which are used in large quantities in the U.S. and hence are more likely to end up in sewage. The objective of this study was to evaluate the effect of pH on sorption of these two drugs in simulated waste water. Batch experiments were conducted to evaluate the effect of pH (3.5, 5.5, 6.5, 7.5 and 8.5) of respective drugs on sorption. In the pH study, waste water spiked with 500 µg/L of Ibuprofen and Naproxen respectively were incubated in an orbital shaker at 115 rpm and 25^oC. Samples were collected at different time interval (0.1, 1, 3, 6, 12, 18 and 24 hrs) and analysis was conducted by the extraction of the drugs studied by solid phase extraction (SPE) followed by derivatization of extracted drugs. The derivatized samples were subjected to gas chromatography with mass spectroscopic (GC-MS) analysis. The percent recover of Ibuprofen and Naproxen from SPE were 78.89 ± 7.22 and 78.39 ± 2.06 respectively. Results of the effect of pH on sorption showed that Ibuprofen and Naproxen has higher sorption at lower pH values.