Determination of cytotoxicity following oxidative treatment of pharmaceutical residues in wastewater

Pharmaceutical residues are released in the aquatic environment due to incomplete removal from wastewater. With the presence of multiple chemicals in sewage waters, contaminants may adversely affect the effectiveness of a wastewater treatment plant (WWTP). In certain cases, discharged metabolites are transformed back into their pristine structure and become bioactive again. Other compounds are persistent and can withstand conventional wastewater treatment. When WWTP effluents are released in surface waters, pristine and persistent chemicals can affect the aquatic environment. To complement WWTPs and circumvent incomplete removal of unwanted chemicals or pharmaceuticals, on-site wastewater treatment can contribute to their removal. Advanced oxidation processes (AOPs) are very powerful techniques for the abatement of pharmaceuticals, however, under certain circumstances reactive toxic by-products can be produced. We studied the application of on-site AOPs in a laboratory setting. It is expected that treatment at the contamination source can eliminate the worst polluters. Thermal plasma and UV/H₂O₂ oxidation were applied on simulation matrices, Milli-Q and synthetic sewage water spiked with 10 different pharmaceuticals in a range of 0.1 up to 2400 μg/L. In addition, untreated end-of-pipe hospital effluent was also subjected to oxidative treatment. The matrices were activated for 180 min and added to cultured HeLa cells. The cells were 24 h and 48 h exposed at 37 °C and subsequently markers for oxidative stress and viability were measured. During the UV/H₂O₂ treatment periods no toxicity was observed. After thermal plasma activation of Milli-Q water (150 and 180 min) toxicity was observed. Direct application of thermal plasma treatment in hospital sewage water caused elimination of toxic substances. The low cytotoxicity of treated pharmaceutical residues is likely to become negligible if plasma pre-treated on-site wastewater is further diluted with other sewage water streams, before reaching the WWTP. Our study suggests that AOPs may be promising technologies to remove a substantial portion of pharmaceutical components by degradation at the source. Further studies will have to be performed to verify the feasibility of upscaling this technology from the benchtop to practice.

Thermal plasma activation and UV/H2O2 oxidative degradation of pharmaceutical residues

The aquatic environment becomes increasingly contaminated by anthropogenic pollutants such as pharmaceutical residues. Due to poor biodegradation and continuous discharge of persistent compounds in sewage water samples, pharmaceutical residues might end up in surface waters when not removed. To minimize this pollution, onsite wastewater treatment techniques might complement conventional waste water treatment plants (WWTPs). Advanced oxidation processes are useful techniques, since reactive oxygen species (ROS) are used for the degradation of unwanted medicine residues. In this paper we have studied the advanced oxidation in a controlled laboratory setting using thermal plasma and UV/H₂O₂ treatment. Five different matrices, Milli-Q water, tap water, synthetic urine, diluted urine and synthetic sewage water were spiked with 14 pharmaceuticals with a concentration of 5 μg/L. All compounds were reduced or completely decomposed by both 150 W thermal plasma and UV/H₂O₂ treatment. Additionally, also hospital sewage water was tested. First the concentrations of 10 pharmaceutical residues were determined by liquid chromatography mass spectrometry (LC-MS/MS). The pharmaceutical concentration ranged from 0.08 up to 2400 μg/L. With the application of 150 W thermal plasma or UV/H₂O₂, it was found that overall pharmaceutical degradation in hospital sewage water were nearly equivalent to the results obtained in the synthetic sewage water. However, based on the chemical abatement kinetics it was demonstrated that the degree of degradation decreases with increasing matrix complexity. Since reactive oxygen and nitrogen species (RONS) are continuously produced, thermal plasma treatment has the advantage over UV/H₂O₂ treatment.