Solar photo-Fenton with Fe3+-EDDS and Fe3+-NTA at neutral pH for removal of ibuprofen, diclofenac and their main transformation products in wastewater
Marina Aliste, Lixy Olinda León-Morán, Carmen María Martínez-Escudero, Isabel Garrido, Fulgencio Contreras, Pilar Hellín, Pilar Flores, José Fenoll
Abstract
In recent years, solar photo-Fenton (SPF) processes have gained interest owing to the use of a cost-free and sustainable radiation source and their effectiveness in removing pharmaceuticals, among other Emerging Pollutants (EPs), from wastewater. Especially, when iron complexes are used to work at neutral pH. The stability and biodegradability characteristics make ethylenediamine-N,N-disuccinic acid (EDDS), and nitrilotriacetic acid (NTA) suitable iron complexing agents. In this work, the removal of diclofenac (DCF) and ibuprofen (IBU), two of the most widely used Non-steroidal Anti-Inflammatory Drug (NSAID) for the treatment of pain, at 200 µg L −1 was studied in wastewater using SPF at natural pH, comparing EDDS and NTA as chelating agents for the first time. The main transformation products (TPs) were also monitored. For this purpose, a suitable analytical method using liquid chromatography coupled to triple quadrupole tandem mass spectrometry (LC-QqQ-MS/MS) with Electro Spray Ionization negative mode (ESI - ) was applied to determine the pharmaceutical EPs and their main TPs in wastewater. Next, they were confirmed by LC-QTOF-HRMS. DCF was degraded 44 % faster with NTA (t 1/2 53 min) than with EDDS (t 1/2 77 min), although the final removal percentages, including photolysis, were similar (90–93 %). In contrast, IBU removal with EDDS (t 1/2 116 min) was twice as fast as with NTA (t 1/2 231 min), whereas photolysis was ineffective. Twenty TPs were monitored, of which only three were detected because of the low concentration used in this study: DCF-2C ( m/z 258.0326), DCF-6B ( m/z 310.0040), and IBU-4 ( m/z 221.1181). Their behaviour followed a formation-elimination profile, but only the complete oxidation of DCF-6 was achieved. This work focuses on the kinetic aspects and TPs formed, which are useful for improving knowledge for the development of efficient processes to abate organic pollutants in real aqueous matrices. Therefore, more EPs should be thoroughly studied to determine the efficiency of EDDS and NTA as iron-chelating agents and the necessity of implementing the SPF process in WWTPs. • Ibuprofen removal by direct photolysis was negligible. • Diclofenac (DCF) was degraded 44 % faster with Fe 3+ -NTA than with Fe 3+ -EDDS. • QqQ and QTOF analysers were employed for identification and confirmation. • Twenty TPs were monitored, of which only three were detected. • TPs followed a formation-elimination profile, but only hydroxy-DCF was fully oxidised.