Diclofenac Degradation by New AOP System Zero-Valent Aluminium–Acid (ZVAl/H+) Process and its Modifications

Abstract

Drugs and other pharmaceutical compounds are often used substances around the world. Diclofenac is one of the widely used anti-inflammatory drug for the treatment of acute and chronic pain, rheumatoid and osteoarthritis. In recent years diclofenac was considered as a new emerging environmental contaminant of water and soil ecosystems. In the present work the new AOP system based on the ZVAl/H+ and its modifications was applied to degrade diclofenac water solutions with its initial concentration of 25 mg L−1. The effects of initial pH, dosage of Al0 , addition of hydrogen peroxide, ferrous, ferric and aluminium ions were studied in the dark experiments. In addition, effects of irradiation with sunlight lamp were also investigated. Finally, environmental toxicity studies were conducted according to OECD tests with terrestrial plants. Degradation efficiency was measured by UV-VIS spectroscopy. After all experiments the degree of resulting TOC removal was determined. Concentration of dissolved oxygen in reaction mixture during and after reaction was also monitored. The results showed that all used systems are able efficiently remove diclofenac. The best diclofenac removal reached 98 % efficiency at pH of 3.0 in 4 hours, with Al0 dosage used of 2.0 g L−1 and with addition of 10 mg L−1 of aluminium ions (Al3+). The best TOC removal (83 %) was achieved under experimental condition of ZVAl/H+ with Al0 dosage of 4.0 g L−1 at pH of 3.0 after 4 hours. Negative results with the utilization of radical scavenger for hydroxyl radicals (methanol) led us to conclusion that degradation process in the first steps of reaction proceeds parallel by both two different mechanisms – reductive dehalogenation and hydrogenolysis. Finally, before and after treatment processes toxicity tests according to OECD Guideline 208 were performed. Resulted toxicity values showed that diclofenac solutions in concentration range from 5 to 25 mg L−1 and solutions after treatment processes had only a low toxic effect on terrestrial plants.