Degradation of a mixture of pharmaceuticals in hospital wastewater by a zero-valent scrap iron (ZVSI) combined reduction-oxidation process

Abstract

Zero-valent scrap iron (ZVSI) combined with Fenton-based oxidation reaction (reduction-oxidation process) was studied under natural sunlight conditions to degrade a mixture of six pharmaceuticals. ZVSI is a waste product from metalworking industries, which present excellent reactivity. The morphological and structural properties of ZVSI were evaluated using different techniques. The parent compounds and their transformation products (TPs) were monitored using Liquid Chromatographic coupled with Quadrupole-Time of Flight mass spectrometer (LC-QTOF MS). The in silico (quantitative) structure-activity relationship ((Q)SAR) predictions of toxicity and biodegradability were predicted for each TP by using different freely available models. According the characterization ZVSI consisted mainly of carbon (48.5 %) and iron (43.6 %) with 0.6922 m2/g of surface area. Hematite and magnetite were the main crystalline phases ZVSI. Doehlert design and desirability profile were used to select the experimental conditions. Higher degradation rates were achieved at pH 3.0, 32.5 mg L−1 H2O2 and 2 g L−1 ZVSI. Under the optimal conditions, pharmaceuticals removal was as high as 87 % in all matrixes evaluated, following a pseudo-first order kinetic model behavior. Three reuse cycles were performed using real hospital wastewater (RHWW) achieving degradation percentages >70% and no substantial variation in the crystalline phases of the ZVSI was observed. Twenty-three TPs were detected. According to in silico (Q)SAR predictions, the integrated system decreased the toxicity of TPs. Moreover, most of TPs were predicted as persistent compounds. The results indicated that ZVSI combined with solar Fenton-based oxidation is an interesting alternative for the degradation of pharmaceuticals in RHWW allowing the reuse of catalyst.