Coupling biological and photocatalytic treatment of atrazine and tebuthiuron in aqueous solution

Abstract

Pollutants, such as pesticides, find their way into wastewater treatment plants (WWTPs). WWTPs have been reported to be unable to fully remove these pesticides from water. Hence, research has been conducted in the development of methods to degrade them in wastewater. This work reports the coupling of biological and photocatalytic processes to particularly treat two model pesticides (atrazine and tebuthiuron) in aqueous solution. Liquid chromatography-mass spectroscopy/mass spectroscopy (LC-MS/MS) was used as an advanced analytical technique for the identification of both atrazine and tebuthiuron, and their degradation by products. The LCMS/MS data showed that atrazine and tebuthiuron were only removed substantially during their first treatment days. Based on LCMS/MS results, biodegradation of atrazine in the biological treatment section was via dealkylation to yield deethylatrazine (m/z 198), (2) dechlorination to yield N-isopropylammelide (m/z 156), and (3) deamination to yield cyanuric acid (m/z 129). There were no identified metabolites of tebuthiuron which suggested its structural stability, but a decrease was observed at the beginning of the treatment of the pollutant probably due to adsorption on the sludge. Photocatalysis further reduced the concentration of atrazine, while there was no significant decrease in tebuthiuron. The atrazine degradation pathways that were identified during photocatalysis studies were (1) degradation of atrazine (CIET, m/z 216) through the formation of hydroxyatrazine (OEIT, m/z 197), desethylhydroxyatrazine (OIAT, m/z 155), ammeline (OAAT, m/z 127) and cyanuric acid (OOOT, m/z 129), and (2) the degradation of atrazine, after the formation hydroxyatrazine (OEIT, m/z 197), could also proceed to form deethylatrazine (CIAA, m/z 198), followed by the formation of N-isopropylammelide (IAT, 156) and finally cyanuric acid (OOOT, m/z 129). The bio-photodegradation treatment process was efficient for the removal of atrazine but not for the removal of tebuthiuron.