At the Trail Smelter, contaminated seepage water is collected and a portion is diverted for treatment to a large pilot-scale wetland system. The design, construction (in stages from 1997 to 2002) and long term sampling (1998-2007) of the wetland system treating high concentrations of zinc, arsenic and cadmium is presented. The final system configuration has been operating year-round since 2002 treating approximately 15,000 L/d. The system is comprised of two vertical upflow anaerobic (compost) bioreactors followed by three horizontal subsurface flow vegetated wetland cells, a slow sand filter and a final holding cell. Operational sampling was done for water quality (metals and various anions), bacterial communities (MPN, PFLA and DGGE) and vegetation (metals content). After several years of operation one of the anaerobic cells was taken apart and rebuilt in 2002. Extensive solid substrate sampling during deconstruction was analyzed for mineralization (SEM/EDS), metals and carbon content (Rock-Eval pyrolysis) to estimate the potential cell life.
The system treats seepage with zinc up to 3800 mg/L (average ~ 260 mg/L), arsenic to 3600 mg/L (average ~ 150 mg/L) and Cd to 83 mg/L (average ~ 4.7 mg/L) which are reduced to <0.5 mg/L (<0.02 mg/L for Cd). Vegetation sampling showed variable uptake into exposed plants at much higher levels than control plants. Plant toxicity was experienced in the system. Evapotranspiration and rhizofiltration are the preferred use of plants as opposed to metal hyper-accumulating plants. Bacterial sampling indicated the presence of sulphate reducing bacteria and a diverse anaerobic microbial community throughout the system despite the high metals entering the system. The predicted life of the anaerobic cell by Rock Eval 6 was 18 years with a range from 17 to 21 years, while based on biomass calculations could range from 14 to 34 years. Where wetlands systems can be successfully used, their cost and environmental and social sustainability is very favourable when compared to chemical treatment systems (e.g. lime-dosing systems). Based on author‟s experience at the Trail and other sites, the design issues faced by full scale wetland systems are presented and recommendations made to ensure a successful system. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/3322 |
| Date | 30 May 2011 |
| Creators | Duncan, William Fredrick Alexander |
| Contributors | Van der Flier-Keller, Eileen, Goodarzi, F. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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