Elimination of selected pharmaceuticals by biosolids from municipal wastewater treatment plants: importance of modest pH change and degree of mineralization.

Lab-scale batch experiments with biosolids collected from a full-scale activated sludge system (AS) and a pilot-scale membrane bioreactor (MBR) were carried out to investigate the mechanisms of elimination of 5 acidic pharmaceuticals and 2 neutral pharmaceuticals. Batch elimination experiments were conducted under the conditions of pH of 6 and 7, and a great impact of pH on elimination of pharmaceuticals was shown by the significant differences in elimination rates under different pH conditions: elimination of pharmaceuticals was enhanced under the condition of lower pH regardless of the type of biosolid. Degree of mineralization of ibuprofen was also investigated in this study by using (14)C-labeled compounds. Although ibuprofen has been considered to be a readily biodegradable pharmaceutical in previous studies, the results obtained in this study demonstrated that the degree of mineralization of ibuprofen would be limited in biological wastewater treatment including MBRs. The results obtained in this study imply that a large portion of pharmaceuticals that have been considered "biodegradable", such as ibuprofen, entering into wastewater treatment plants will eventually be discharged into natural water bodies as intermediates, although concentrations of them may look reduced on the basis of common analytical methods (i.e. GC/MS or LC/MS/MS).