Re ECF Project: 2010-06

Project Title: Investigation on occurrence of triclosan in wastewater and the possibility of its degradation to 2,8-dichlorinated-p-dioxin

Applicant: Prof. Zongwei CAI of Hong Kong Baptist University

Total Approved Grant: $405,680 (ECF & WWGF: 50/50)

Duration: 1/5/2011 to 31/10/2012

Project Status/Remarks: Completed

The objectives of the project are:

  • to investigate the fate of triclosan and its major degradation products during the wastewater treatment through the qualitative and quantitative analysis; and
  • to investigate the possible formation of dioxins or dioxin-related compounds including 2.8-dichlorinated-p- dioxin.

Summary of the Findings/Outcomes:
The project team developed the analytical methods for triclosan and its major degradation product 2,8-DCDD in wastewater. Triclosan was detected in all wastewater samples at 22-698 ng/L. It was found that triclosan levels were significantly reduced after the wastewater treatment, even with the single sedimentation. The reducing rate was different from different wastewater treatments. The biological treatment in Shatin treatment plant appeared to have the highest triclosan reducing rate.

The “seasonal fluctuation” of triclosan levels was quite different in samples from the three wastewater treatment plants, which should be interpreted not only with the rain dilution during storm seasons, but also with the wastewater influent parameters such as the nature and volume etc. While the triclosan levels in Shatin plant were significantly reduced in Summer raining season, the rain dilution was not obvious in wastewater from Stonecutters Plant.

Triclosan reduction even after the singled sedimentation treatment suggested the need of investigation of triclosan in sludge. Because 2,8–DCDD and other dioxins are hydrophobic, their possible occurrence in sludge should also be investigated. The detection of 2,8 DCDD in some of the wastewater samples should bring us significant attention on its impact to aquatic environment that receives the effluent after the wastewater treatment.