MacLaren Industries’ kraft pulp mill, located in Thurso, Quebec, was built in 1958 and used only a primary treatment process for its pulp waste until the mid-1990s. At this time, more stringent effluent requirements for BOD5 were defined for discharge into the nearby Ottawa River.
To meet the new requirements and make a commitment to protecting the environment, the company decided to employ a secondary treatment process. MacLaren turned to Aqua-Aerobic Systems for a solution because of its reputation for efficiency and economical operation, as well as recommendations by other pulp mills already employing its equipment.
This involved the installation of 41 75-HP Aqua-Jet® surface aerators in an aeration basin to biologically treat its pulp waste, as well as six 75-HP ThermoFlo® surface spray coolers to cool the pulp wastewater prior to biological treatment.
The Aqua-Jet aerator is a mechanical direct-drive unit designed to provide optimum oxygen transfer in a variety of wastewater applications. The performance of the technology also provides the mixing necessary to uniformly disperse oxygen and organic matter within the microbial population.
Accordingly, basin water is pumped into the intake cone and through the volute and is dispersed through the diffusion head in a spray pattern. Oxygenation then occurs at two critical points: when the water exits the diffusion head and when the spray enters the water surface.
MacLaren typically utilizes 22 to 24 of the 41 Aqua-Jet aerators at any one time for biological treatment of its pulp waste and to reduce BOD5 and TSS to required levels. Because the temperature of the waste is so high, it is necessary to cool it prior to biological treatment during the summer months.
MacLaren chose to employ the six ThermoFlo spray coolers as an alternative to cooling towers and ponds in an effort to efficiently dissipate the heat of the waste. Process water is pumped through a heavy-duty cast manifold and is divided between each of the unit’s spray arms. Discharge of the process water occurs at the end of each arm through a cast anti-clog nozzle.
MacLaren’s kraft pulp mill currently produces 238,000 metric tons of pulp annually. This includes hardwood pulp and four specialty pulps, which are used to produce high-quality papers such as parchment and photographic paper. The company’s new treatment process has enabled the plant to consistently meet effluent requirements and reduce pollution into the Ottawa River.
For more information about Aqua-Aerobic and to learn more about the company’s Aqua-jet and ThermoFlo technologies, visit www.aqua-aerobic.com.