Treating wastewater, not all options (figuratively) stink

 

Gatineau wants its Notre-Dame wastewater plant to turn all the biosolids it treats into granules or pellets destined to the agricultural world.

As the sludge and the water arrive at the plant, which can treat a maximum of 160,000 cubic metres per day and is currently treating roughly 120,000 cubic metres daily, they go through a remarkable process before finding their way back into the environment.

After first basic and initial steps, equipment in the plant works to reduce the water content in the sludge with the goal of eventually dehydrating it. The wastewater incoming from Aylmer, Hull and Gatineau sectors is treated and is ultimately send back to the river. As for the sludge, it is directed to digesters chambers to reduce pathogens and transform organic waste into biogas by cutting oxygen.

Gatineau is one of half a dozen municipalities in Quebec to adopt the solution of anaerobic digestion of biosolids.

 

In short, this process entails converting organic matter or waste into methane and carbon dioxide called biogas which is composed of roughly two-thirds methane and one-third carbon dioxide (with other gases).

This gas is used to heat the plant and used for the thermal drying unit used to granulate of the sludge. Currently the city granulates 60% of the sludge and that amount should increase to 100% in coming years.

After being thickened, the sludge is further dehydrated once it enters one of three high-speed centrifuges. After this process, the sludge’s rate of dryness reaches the mid to high 20%. Afterwards, the sludge is further dried by the thermal drying unit permitting the rate of dryness to reach 60%. Undried sludge is currently being transported to a composting centre in Brownsburg-Chatham (near Lachute), but the city is hoping to avoid this step in the near future. Eliminating this step will allow the city to save $300,000 annually.

Sludge with a rate of dryness of 60% is then granulated (formed into granules or pellets) permitting the sludge to reach the rate of dryness of 97%. This not only helps reduce tonnage, it helps cut transportation costs. The unit used to granulate is able to dry 3,000 tons a year.

Once granulated, the sludge, high in certain soil nutrients, is acquired by the Third High Farm based out of Iroquois, Ontario and transported to Eastern Ontario to be ultimately applied to the soil as manure. The use of treated sludge is limited and cannot be used in every type of farming, such as animal farming or food crops, for example.

Gatineau’s wastewater treatment plant opened in the early 1980s. The city is looking to modernize the plant by 2020, the year the province is prohibiting the burying of sludge.
(LRC)