Treatment Wetland Options
Natural Systems Utilities’ experienced engineers and systems operators have unsurpassed knowledge of wetland microbiology, plants, hydrology, soils, aeration, hydraulics, and ecology. This foundation, along with the experience we and our partners have gained from the design and construction of hundreds of systems worldwide, enables NSU to design a wetland treatment system to meet virtually any conditions. Including the two basic types of treatment wetland options — free surface flow and subsurface flow — NSU’s water ecologies may also include components such as reed beds, hyacinth ponds, recirculating and trickling sand filters, and other devices.
Free-surface-flow treatment wetlands contain areas of open water, floating vegetation, and emergent plants. Depending on local regulations and soil conditions, liners, dikes or berms can be used to control flow and infiltration. Because free-surface wetlands closely mimic natural wetlands, they attract a wide variety of wildlife including fish, amphibians, reptiles, birds, and mammals. Such systems are often the choice of treatment for urban, agricultural, and industrial stormwaters because of their ability to deal with changing flows and water levels. They also provide significant ancillary benefits, primarily in the form of human uses and wildlife habitat.
Subsurface-flow treatment wetlands move effluent (including industrial, agricultural, and domestic) through a gravel or sand medium on which plants are rooted. In subsurface-flow systems, the effluent may move either horizontally, parallel to the surface, or vertically, from the planted layer down through the substrate and out. Subsurface-flow systems have the advantage of requiring less land area for water treatment, but are not generally as suitable for wildlife habitat as are surface-flow constructed wetlands.
NSU can engineer subsurface-flow treatment wetlands to greatly advance the capacity of wetland treatment systems and enable a simple, low cost alternative to challenging wastewater and water problems. Unlike earlier generations of passive constructed wetlands, NSU’s engineered wetlands boost treatment performance through the use of aeration or recirculation. In the past, applications requiring nitrification of wastewater could not use treatment wetlands. NSU’s engineered wetlands provide reliable and cost effective nitrogen removal in such circumstances. Where space is at a premium, NSU can design wetlands systems that cut the treatment area by 50 percent or more, opening up many more sites to wetland treatment. Treatment time is faster in engineered wetlands than passive systems, which also reduces the treatment area requirements. In addition, NSU can design wetlands for use in extremely cold-climate conditions or the treatment of a variety of industrial wastewaters, including landfill leachate, petroleum-contaminated waters, and dairy wastes.
Specialized Technologies: Cold-Climate Engineered Wetlands
NSU’s engineering team has more experience in designing engineered wetlands than any other team in the world. They have specialized experience in cold-climate engineered wetland applications, having designed more than 200 cold-climate systems in North America. While the majority of these have been in Minnesota, systems have also been located in Canada from the northern provinces of Alberta to the Northwest Territories as far north as Nunavut in Canada's Arctic, where the mean January temperature is 35°C (-31°F).
The team has more than 15 years of performance data for cold-climate wetlands by monitoring temperatures and calculating energy flows. The team has authored numerous papers on the subject of cold-climate engineered wetlands and this knowledge has been shared in Treatment Wetlands, 2nd Edition, published in 2009, co-authored by NSU's chief technology officer.
Cold-climate design approach involves understanding energy gains and losses with respect to impact of air temperature, influent and effluent temperature, solar impact, evaporation and convection, and impact of insulation (mulch and snowpack).
Monitoring cold-climate systems has shown that with proper design, systems can perform without freezing at temperatures as low as -20°C.
Data collected at Jackson Meadows, a 64-home residential development in Minnesota designed by the NSU team, provides a detailed portrait as to how horizontal subsurface flow constructed wetlands respond to energy gains and losses under both summer and winter conditions in a cool temperate climate. The graphic to the right illustrates influent and effluent temperatures compared to air temperatures over a 22-month period.
During the summer months, effluent temperatures exceed influent temperatures indicating the water is being warmed as it passes through the wetland. During late summer, effluent temperatures exceeded 20°C, and were often 5°C warmer than the influent.
Under winter conditions (November through snow-melt in April in this region of the Northern Hemisphere) both energy gains and losses are minimized and exhibit little change, resulting in stable effluent temperatures.