Canadian Consulting Engineer
New technology cleans up harbour contamination on siteEngineering
Golder Associates, a consulting engineering firm based in Oakville, Ontario, is the commercial licensee of LIST, a...
Golder Associates, a consulting engineering firm based in Oakville, Ontario, is the commercial licensee of LIST, a new process for dealing with large-scale contaminated underwater sediment on site. Organic waste from sewage and pulp and paper mills in combination with chemicals from steel, petroleum and other industries, often produces a foul-smelling and corrosive hydrogen sulphide gas which contaminates harbours and lakes.
Hamilton Harbour has been one of the most notorious sites and it was efforts to find new ways to deal with its contaminated sediment, as well as contamination in Sault Ste. Marie, that prompted the new technology.
Usually underwater sediment contamination is scooped or vacuumed out using a barge-mounted dredger, and then hauled off to be stored or treated elsewhere. The process which Golder is pioneering is one of the first to deal with the material in-situ at a commercial scale. The technology is called the Limnofix In-Situ Sediment Treatment Technology (LIST) and was developed by scientists with Environment Canada’s National Water Research Institute (NWRI) in Burlington.
The LIST technology uses an underwater harrow towed behind a boat to till the contaminated sediment and inject it with a chemical oxidant. The oxidant is usually calcium nitrate, which is injected deep into the sediment to prevent it escaping and boosting the growth of algae. The injected oxidant promotes the aerobic biodegration of the contaminants by providing oxygen to the bacteria and by oxidizing the sulphides that impede this natural process. The complete bioremediation can take several months.
Golder Associates, with the support of the NWRI, has successfully demonstrated the technology in bench and pilot-scale studies in Canada, the U.S., Europe and Asia.
In 1998, a full-scale treatment was carried out near the old airport in Hong Kong where sewage contaminated sediment in the marine environment was causing serious odour problems and corroding nearby buildings and aircraft. Within weeks, the sediment had turned from black to brown, more than 95 per cent of the sulphides were remediated and the odour had lessened.
Dealing with the sludge on site instead of carrying it away removes the need to find toxic storage facilities and avoids the risk of spillage. It also avoids the expense of transporting the evil stuff.
In places like Asia the problem of harbour contamination from the combination of organic waste with industrial chemicals has become so bad it affects fish and shellfish harvesting and the health of people living near the waterways.
Source: Environment Canada, www.nwri/sande/newremediation