Re ECF Project: 2011-09

Project Title: Dosing of Ferric Iron for the Control of Odour Problems in Typhoon shelters

Applicant: Prof. Xiao-yan LI, of The University of Hong Kong.

Total Approved Grant: $1,058,500.00

Duration: 1/10/2012 to 31/3/2015

Project Status/Remarks: Completed

The project aims to-

  1. develop an innovative ferric iron-based technology for the control of odour problems in typhoon shelters in Hong Kong;
  2. evaluate the effectiveness of the iron-dosing method in well-controlled laboratory sediment chambers for odour control by dosing either "reactive" ferric iron or relatively "inert" iron rust or their mixture;
  3. determine an effective iron dosing scheme, including the chemical form, dosing method, dosage and frequency, for the suppression of odour emission from polluted marine sediment;
  4. investigate the effects of various influential factors, such as the organic content in sediment, hydraulic condition and the dissolved oxygen level in the overlying water, on the odour control results; and
  5. demonstrate the effectiveness of the ferric iron-dosing method for odour control in large-scale field applications in specified typhoon shelters.

Summary of the Findings/Outcomes:
A large-scale field trial was conducted in Yau Mai Tei typhoon shelter on the ferric iron dosing for sediment odour control. A vessel (boat) was employed and a special dosing setup was assembled for the chemical application on the sediment surface in a trial area of 30 m×50 m at a corner of the shelter. Ferric chloride and calcium hydroxide were dissolved in seawater to prepare Fe(OH)3 slurry on the vessel for the chemical dosing. Upon the chemical dosing treatment, the sediment and the bottom water over the sediment surface were sampled after different periods up to 45 days for evaluation of the odour control results. According to the olfactometry tests on the bottom water samples, the odour levels for the sites after the Fe(III)-based chemical dosing were all lower than the odour levels for the comparable background sites. The sediment odour reduction could reach about 80% after 10 days of the Fe(III)-based chemical dosing. After 45 day, the odour reduction could still be kept at around 50%, and at least a 2-month period of effective sediment odour suppression can be expected based on the field trial. The H2S concentrations in the bottom water from the dosing area also were much lower than those in the water from the background area. The odour level of the surface sediment from the dosed area was around 550 OU/m3, which was significantly lower than the value of 1600 OU/m3 for the background sediment. Moreover, the AVS content in the sediment from the dosing area was 3-5 times lower than that in the sediment from the background area without chemical dosing. The results of the field trial demonstrate the effectiveness of the Fe(III)-based chemical dosing for the sediment odour control in typhoon shelters.