Assessment of UV combined with free chlorine for removal of valsartan acid from water samples

Highlights: • Evaluation of valsartan acid degradability under UV/free chlorine treatment • Reduced half-life values compared to direct photolysis and UV/hydrogen peroxide • Half-lives increased with water pH and concentration of bicarbonate anions. • Identification of three intermediate degradation products • Valsartan removal demonstrated in spiked wastewater and polluted river water. Valsartan acid (VALA) is a persistent and mobile pollutant, ubiquitously distributed in the aquatic environment. Herein, we assessed the efficiency of UV/free chlorine for the removal of this pollutant. Degradation experiments were performed using different water samples, considering several pH values and concentrations of inorganic anions. Time-course of VALA was measured by injection of different reaction time aliquots in a liquid chromatography (LC) triple quadrupole (QqQ) mass spectrometry (MS) system, whilst the study of potential transformation products (TPs) was evaluated by LC combined with a hybrid quadrupole time-of-flight (QTOF) MS system. Formation of volatile disinfection by-products (DBPs) was investigated by gas chromatography (GC) with TOF-MS detection. Compared to free chlorine treatment and UV photolysis, the combination of both parameters significantly enhanced the degradability of VALA. At neutral pH, UV/free chlorine was also more effective than UV/H₂O₂ to remove VALA from spiked water solutions. Three TPs of VALA were tentatively identified by LC-QTOF-MS, although only one was stable in the UV/free chlorine media. As regards volatile DBPs, the formation of chloroform, dichloroacetonitrile, di- and trichloroacetic acid was noticed. The mass yield of DBPs formation from VALA varied from 0.3% (dichloroacetonitrile) to 1.1% (chloroform). The efficiency of UV/free chlorine was first investigated in spiked solutions with increasing complexities: ultrapure, river and treated wastewater. Thereafter, the feasibility of reducing VALA levels in polluted river water was demonstrated.