Nova Scotia Harbor to Reap Benefits of Treatment, Sediment Study

For two-and-a-half centuries, as Halifax grew from a hardscrabble settlement to a thriving seaport, its wastewater has gone straight into the harbor.

The trickle of domestic waste has increased significantly since 1749. In 2003, the year Halifax Regional Municipality's Harbor Solutions Project got under way, more than 180-million liters of raw sewage ended up in Halifax Harbor every day.

Now that the Halifax plant, the biggest of the three new sewage plants, has been up and running for the past four months, the amount of sewage headed for the harbor has been cut by half, and the water is starting to improve. The Dartmouth plant is expected to be operational later this summer, followed by the Herring Cove plant by year end to address 90 million liters of wastewater coursing through dozens of outfalls.

"Halifax Harbor is a large sink for organic matter," says David Scott, professor of Earth Sciences at Dalhousie. "However, the water in the harbor is not the problem—it's the sediment."

Along with his team, Scott, a Killam professor and director of the Centre for Environment and Marine Geology, has recently received $200,000 in funding from Natural Sciences and Engineering Research Council to study the sediments on the harbor floor and match results with water quality data being collected by the municipality. The project is supported by in-kind contributions by the municipality, Bedford Institute of Oceanography, Department of Fisheries and Ocean, and the Cultural and Educational Bureau of Egypt in Canada (in the form of doctoral student Saad Mohamed).

The money allows the researchers to take core samples at various spots throughout the harbor. By examining these samples—both from the surface of the harbor floor and deep below—researchers will be able to reconstruct the history of pollution in the harbor and determine what it was like in its pristine state, circa 1749. They’ll also be able to monitor improvements in sediment after the $333-million Harbor Solutions Project is completed.

Most of the contaminants released in the water are absorbed or eaten by organisms in the water column or become attached to inorganic particles which then settle and accumulate in the sediment. Organisms are recycled by bottom-dwelling creatures such as lobsters, clams, and mussels. When examining core samples, the researchers will be looking for microfossils, called foraminifera, which faithfully record conditions from past environments.

The three Harbor Solutions plants are deemed "advanced primary," explains James Campbell, communications project manager for Harbor Solutions. Sewage will pass through two levels of screens, a coarse screen and a finer screen, to eliminate particulates. The remaining wastewater then goes through a grit removal chamber, eliminating smaller solids like salt and sand. Once all solids are removed, the wastewater is subjected to ultraviolet light, which kills bacteria.

The treated sewage is then pumped through a diffuser pipe on the harbor floor and mixes with seawater. The entire harbor is flushed out twice daily by the tides.

"All that organic matter is what makes it so unpleasant to look at and smell," says Scott. "Aesthetically, the harbor is going to look better, and some of the chemicals should be cleaned up too."

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