The elimination of pharmaceuticals and their residues presents a tricky problem in wastewater treatment. Increased attention has been focused on pharmaceuticals and their residues in aquatic environments due to the long-term risks to human health posed by bioaccumulation and ecological disturbance. However, wastewater treatment plants (WWTPs), which are the most important facilities for controlling water pollution, have vastly different removal efficiencies for pharmaceuticals and their residues due to a lack of specifically designed treatment methods. Meanwhile, the researchers believe that the targeted treatment of pharmaceuticals from urine can decrease the dispersion of pharmaceutical contamination and the treatment pressure of WWPTs. Therefore, this research proposes an iron-activa...[ Read more ]

The elimination of pharmaceuticals and their residues presents a tricky problem in wastewater treatment. Increased attention has been focused on pharmaceuticals and their residues in aquatic environments due to the long-term risks to human health posed by bioaccumulation and ecological disturbance. However, wastewater treatment plants (WWTPs), which are the most important facilities for controlling water pollution, have vastly different removal efficiencies for pharmaceuticals and their residues due to a lack of specifically designed treatment methods. Meanwhile, the researchers believe that the targeted treatment of pharmaceuticals from urine can decrease the dispersion of pharmaceutical contamination and the treatment pressure of WWPTs. Therefore, this research proposes an iron-activated persulfate (Fe-PS) system that can be used as an effective procedure for removing pharmaceuticals from municipal wastewater or urine. An industrial-grade iron (Fe) powder was applied as a low-cost catalyst for persulfate (PS) activation to generate sulfate radicals (SO₄^.-). The Fe powder was identified as a mesoporous material, which provided it with sufficient specific surface area to activate PS. In the Fe-PS system, both SO₄^.- and hydroxyl radicals (HO^.) were detected. A biodegradation-resistant pharmaceutical metabolite (clofibric acid, CFA), a pharmaceutical residue (bezafibrate, BZF), and a typical antibiotic (sulfamethoxazole, SMX) were chosen because of their ubiquity in WWTPs and resistance to traditional treatment processes. To optimize the Fe-PS system, CFA was selected as the sample pharmaceutical. The Fe-PS system was optimized by testing different PS concentrations, Fe to PS ratios, and initial solution pH values. Among these oxidants, SO₄^.- was identified as the dominant oxidant for CFA degradation, while HO' were identified as the major oxidant for BZF and SMX removal in the Fe-PS system.

To investigate the interferences of typical compounds in municipal wastewater, the degradation of CFA and BZF was attempted in different ammonium or dissolved organic carbon (DOC) concentrations (using glucose as the resource) and in synthetic municipal wastewater. Both CFA and BZF achieved 100% removal with interferences of ammonium or DOC. But less than 3% of the ammonium was removed, due to the formation of aminopropyl radicals. Furthermore, approximately 15% degradation of DOC was achieved, which was mainly attributed to the oxidation of glucose by HO', indicating the excellent selective oxidation ability of the Fe-PS system targeting pharmaceuticals over glucose. Comparing the complete removal in ammonium and DOC combined interference systems, the results in synthetic municipal wastewater showed that the removal efficiency of pharmaceuticals was decreased to 84.7% for CFA and 86.2 for BZF, but substantially greater than that of DOC (< 15%). For verification, CFA degradation in the Fe-PS system with real municipal wastewater was studied. The decreased removal efficiency of CFA in a real municipal wastewater system compared to the ammonium-only, DOC-only, and the combined interference tests revealed that the alkalinity limited the decomposition rate of PS in the system, thereby further hindering the SO₄^.- generation. In general, the feasibility of using the Fe-PS system for selectively degrading resistant pharmaceuticals in municipal wastewater was confirmed.

Another potential approach for pharmaceutical control is to degrade pharmaceuticals in urine. Therefore, the factors limiting the degradation of pharmaceuticals in synthetic human urine were investigated. A kinetic model was established to expose the major inhibitory effects of removing the pharmaceutical residuals from urine. The concentrations of phosphate and (bi)carbonate associated with pH were identified as the three main hindering factors. In the phosphate-containing system, a high concentration of phosphate (> 200 mg phosphate-P/L) increased the concentration of HO^., which enhanced the oxidative capacity of the Fe-PS system. With (bi)carbonate addition ranging from 50 to 2000 mg bicarbonate-C/L, pharmaceutical removal in the Fe-PS system was found to be over 75%. The analysis of the transformation products (TPs) in the pharmaceuticals revealed more incompletely oxidized TPs in the phosphate-and (bi)carbonate-containing Fe-PS systems than in the control system. These results also showed that phosphate radicals mainly degraded pharmaceuticals via a benzene ring-opening reaction, while carbonate radicals preferentially oxidized pharmaceuticals through a hydroxylation reaction.

This research is expected to explore an Fe-PS system for removing pharmaceuticals prior to biological treatment in municipal wastewater or urine by exploring the pharmaceutical degradation mechanisms and the potential limiting factors of pharmaceutical removal.