Enhanced photolytic and photooxidative treatments for removal of selected pharmaceutical ingredients and their degradation products in water matrices

UV and (V)UV irradiation of sitagliptin in ultrapure water and WWTP effluent: Kinetics, transformation products and degradation pathway

Sitagliptin (SITA) is an antidiabetic drug consumed worldwide in high quantities. Because of the low removal rate of this compound in conventional wastewater treatment plants (WWTPs), it enters receiving surface waters with the discharged WWTP effluents. SITA can be detected up to μg/L concentration in rivers. In this study, UV (254 nm) and (V)UV (185 nm + 254 nm) irradiation was applied in laboratory scale to degrade SITA. The effect of three parameters was evaluated on the degradation rate, namely i) the efficiency in UV and (V)UV irradiation, ii) the presence or absence of dissolved oxygen, iii) the matrix effect of WWTP effluent. Degradation rate of SITA was largely increased by (V)UV irradiation, and decreased in WWTP effluent as expected. The presence of dissolved oxygen increased the degradation rate only in UV experiments and did not have a considerable effect in (V)UV experiments. In total, 14 transformation products (TPs) were identified (twelve new); their structures were proposed based on high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy analyses. The most characteristic reaction steps of the degradation of SITA involved nucleophilic aromatic photosubstitution whereas hydroxide ions acted as attacking nucleophiles and replaced F atoms of the phenyl moiety by hydroxide groups, in agreement with the increase in photolysis rate with increasing pH. The photochemical degradation pathway of SITA was also interpreted. Kinetic profiles revealed TP 421, TP 208 and TP 192 to be the most recalcitrant TPs.

Application of (V)UV/O3 technology for post-treatment of biologically treated wastewater: A pilot-scale study

For the first time, high energy VUV photons and generation of O₃ by (V)UV lamps were applied together for removal of active pharmaceutical ingredients (APIs) from biologically treated wastewater (BTWW) in pilot-scale. The core of the pilot container unit was a photoreactor assembly consisting of six photoreactors, each containing a low-pressure Hg lamp (UV dose of 1.2 J/cm² and 6.6 J/cm² at 185 nm and 254 nm, respectively). BTWW was irradiated (4.75 min residence time) by (V)UV light in presence of in situ photochemically generated O₃ from coolant air of the lamps. Experiments were conducted at the site of two wastewater treatment plants. Out of seven target APIs (namely carbamazepine, ciprofloxacin, clarithromycin, diclofenac, metoprolol, sitagliptin, and sulfamethoxazole), 80-100% removal was accomplished for five and 40-80% for two compounds. Two degradation products of carbamazepine were detected. Degradation products of other target compounds were not found. The applied O₃ dose was 30-45 μg O₃/mg dissolved organic carbon. Inactivation of up to log-4.8, log-4.5 and log-3.8 could be achieved for total coliform, Escherichia coli and Enterococcus faecalis, respectively. SOS Chromotest indicated no genotoxicity nor acute toxicity. Generation of neither NH₄⁺, NO₂^- nor NO₃^- was observed during post-treatment. Electric energy per order values were calculated for the first time for (V)UV/O₃ treatment in BTWW with a median value of 1.5 kWh/m³. This technology can be proposed for post-treatment of BTWWs of small settlements or livestock farms to degrade micropollutants before water discharge or for production of irrigation water. Further studies are essential in pilot-scale for other applications.

Exploring the phototransformation and assessing the in vitro and in silico toxicity of a mixture of pharmaceuticals susceptible to photolysis

The present study comprehensively investigates the phototransformation and ecotoxicity of a mixture of twelve pharmaceutically active compounds (PhACs) susceptible to photolysis. Namely, three antibiotics (ciprofloxacin, levofloxacin, moxifloxacin), three antidepressants (bupropion, duloxetine, olanzapine), three anti-inflammatory drugs (diclofenac, ketoprofen, nimesulide), two beta-blockers (propranolol, timolol) and the antihistamine ranitidine were treated under simulated solar irradiation in ultra-pure and river water. A total of 166 different transformation products (TPs) were identified by ultra-high performance liquid chromatography coupled with Orbitrap high resolution mass spectrometry (UHPLC-Orbitrap HRMS), revealing the formation of twelve novel TPs and forty-nine not previously described in photolytic studies. The kinetic profiles of the major TPs resulting from a series of chemical reactions involving hydroxylation, cleavage and oxidation, dehalogenation, decarboxylation, dealkylation and photo substitution have been investigated and the transformation pathways have been suggested. Additionally, an in vitro approach to the toxicity assessment of daphnids was contrasted with ecotoxicity data based on the Ecological Structure Activity Relationships (ECOSAR) software comprising the in silico tool to determine the adverse effects of the whole mixture of photolabile parent compounds and TPs. The results demonstrated that photolysis of the target mixture leads to a decrease of the observed toxicity.