The Dryden Wastewater Treatment Plant may be the first in North America to achieve LEED certification for the entire facility and processes.
Dean Walker appreciates the view from his workplace. Numerous windows in the Dryden Wastewater Treatment Plant overlook the Wabigoon River, the plant’s receiving stream.
“You can get a view of the river from several rooms,” says Walker, waterworks manager for the city of Dryden, Ontario. “In summer you can see eagles hunting over the river. In winter you can see otters playing on the ice. It’s a nice place to work.”
It’s also easy on the environment. The plant, commissioned in January 2014, received LEED Silver certification last November from the Canada Green Building Council. LEED-certified buildings must meet high standards in sustainable site selection, water savings, energy efficiency and other factors. LEED stands for Leadership in Energy and Environmental Design.
The certification is a point of pride in Dryden, a city of 7,600 in northwest Ontario. “We are very proud as The Wilderness City to showcase a LEED-certified structure that not only includes the building, but additionally the plant and processes,” says Blake Poole, manager of Public Works. “This plant meets the goals of sustainability and delivers on environmental responsibility, energy efficiency and innovative design and processes.”
The plant was designed by Stantec, a global engineering and architectural company. Although other wastewater treatment plants have LEED-certified buildings, Stantec designers believe the
Dryden plant is the first entire wastewater facility in North America to attain LEED status. Features that earned credit toward LEED include:
- Reusing the final effluent for plant washdown and cleaning
- Reusing heat generated by blowers
- Reusing heat in exhaust air from the ventilation system
- Minimizing light pollution by designing for lowest possible light levels while still meeting safety and security requirements
- Using high-efficiency electrical equipment, such as motors and lighting
- Providing bicycle storage and showers for staff to encourage alternative transportation
- Reducing water use with waterless urinals and low-flow showers, toilets and sinks
- Using nearly 60 percent regionally produced materials in construction
- Using low-VOC paints, coatings and sealants to maintain good indoor air quality
One unique aspect of the plant’s design is the funneling of wastewater through a building during the entire treatment process. Heat pumps capture heat from the process effluent to heat the building and provide some areas with in-floor heating.
Keeping the treatment tanks inside also helps minimize odor in the neighborhood. Odor control begins just as the wastewater enters the building: A fan draws air off the influent and sends it through biofilters and charcoal. As a result, even with wastewater flowing under the floor, the office space is odor-free. “It smells like a normal office,” says Walker. “There’s no smell at all.”
The windows that provide scenic views are also part of the plant’s energy-efficient design. The windows admit natural light, minimizing electricity usage for lighting. Sensors vary the amount of artificial lighting according to need.
As wastewater enters the building, it passes through a 10 mm fine screen and grit cone (both from Xylem). Then the flow is divided into two sequencing batch reactor (SBR) tanks (also Xylem) under the floor. After settling and aeration, the effluent is decanted. Solids are transferred to holding tanks and then dewatered on rotary presses (Fournier) to 13 to 18 percent solids. The plant sends about four 17-cubic-yard bins of dried material to the landfill per week.
SBR effluent is recycled through the plant for heat recovery. Before discharge, the effluent is disinfected in a UV system (Ozonia). Disinfection is required only from May through October.
Walker says the new plant responds relatively quickly to operational changes, such as adjustments in aeration: “It’s very easy to run. Process changes seem to happen fairly quickly.”
The UV disinfection system has four banks of bulbs and a control panel. “It’s very efficient, very easy to use,” says Walker. “We can turn on more bulbs as needed. If the flow increases, more bulbs come on. There is a lot more technology with this plant. There is a lot more monitoring.”
A SCADA system monitors plant processes and connects to the water treatment plant on the other side of the city. Both facilities can be controlled remotely. There is an alarm center at each plant, and one operator is on call 24 hours a day.
Sustainability doesn’t end with the plant’s design. Operators need to be attentive in day-to-day activities to maintain the LEED certification. “It’s ongoing, even down to the cleaning products we use, including the paper towels,” Walker says. “They all have to be green certified.”
As part of the certification process, Walker had to go to the plant at night to take photos to document the absence of light pollution. “There were quite a few hoops that I had to jump through and a lot of paperwork,” he says.
The plant’s design capacity is 2.6 mgd; average flow is about half that. The plant replaced an old facility that was at the end of its life and too often overwhelmed by rain events and snowmelt, leading to bypassing.
That hasn’t happened at the new plant, except on Aug. 12, 2016, when Dryden received nearly 6 inches of rain in about two hours. The deluge left standing water in parking lots and streets, and numerous homes were damaged by flooding and sewage backups. “It was more than the plant could handle,” Walker says. “We had to bypass for about eight hours. That much water in that short a time was more than anything could handle.”
The LEED designation gives Dryden bragging rights, important for a city that emphasizes its connection to the wilderness. Plant workers can appreciate that connection every day when they look out the windows. “There are always deer there and a couple of groundhogs,” says Walker. “There’s all kinds of wildlife.”