Project Location: Rehberg Ranch Residential Subdivision, Billings, Montana USA and McLean’s Pit Landfill, Greymouth, New Zealand

This case study compares treatment results from Floating Island International’s patented floating treatment wetland (FTW) technology (“floating islands”) with those from standard constructed wetlands. Constructed of post?consumer polymer fibers and vegetated with native plants, FTWs improve upon the ability of natural wetlands to purify water by bringing a “concentrated wetland effect” to any water body. In this study, results from treating municipal wastewater and landfill leachate with either FTWs or constructed wetlands were compared.

FTW for Municipal Wastewater:

Located on the outskirts of Billings, Montana (pop. 104,000), the Rehberg Ranch residential subdivision (pop. 560) was built beyond the reach of the city’s municipal sewer system. Developers constructed an aerated lagoon wastewater treatment system engineered and designed to meet US EPA secondary standards for Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS).

In November 2009, FII, Headwaters Floating Island (HFI), the City of Billings and the Montana Board of Research and Commercialization Technology installed an experimental FTW design in one of the subdivision’s two aerated lagoons. HFI has implemented a rigorous monitoring regime to measure efficacy of the FTW system.

FTW for Landfill Leachate:

Landfill leachate is a problematic water stream in New Zealand and worldwide. Greymouth is a South Island town of approximately 3,000 people. The town identified a need for improved treatment of its municipal landfill leachate, which is a dilute stream because of the area’s extremely high annual rainfall (3.5 m or 140 inches).

In Stage 1 of the FTW project, FII licensee Kauri Park Nurseries Ltd constructed and installed 288 m2 (3100 ft2) of FTWs to cover approximately 20% of the lagoon surface in half of the lagoons, in November 2009. The wetland plants being utilized are Carex virgata and Cyperus ustulatus.

Constructed Wetlands:

Constructed wetlands with horizontal sub?surface flow have been used for wastewater treatment for more than 30 years. Most wetlands have been designed to treat municipal or domestic wastewater, but are now also used to treat wastewaters such as landfill leachate, industrial waters and agricultural wastewater. In a 2009 review article in the journal “Ecological Engineering,” data from several hundred constructed wetlands for municipal and domestic wastewaters, and from approximately ten landfill leachate installations, were summarized (Vymazal, J., 2009, The Use of Constructed Wetlands with Horizontal SubSurface Flow for Various Types of Wastewater, Ecological Engineering 35, 117, www.sciencedirect.com).

Results:

Table 1 shows the performance of the Rehberg Ranch FTW compared to the average performance of several hundred constructed wetlands for municipal/domestic wastewater as consolidated in the Vymazal study. The percent removals of BOD, total nitrogen and ammonia were much higher for the FTW. Due to its smaller size (Table 1), the load removed was much higher in the FTW for these parameters and TSS.

Table 2 shows performance of the FTW at McLean’s Pit compared to the average performance of approximately ten constructed wetlands for landfill leachate. The percent removals of BOD, total nitrogen and TSS were much higher for the FTW, and the load removed was much higher in the FTW for BOD and total nitrogen.

FTW influent (left) vs. effluent (right) at McLean’s Pit, May 2010

Extensive FTW root system for nutrient uptake – McLean’s Pit

Rehberg Ranch FTW – July 2010

Compared to the small size required for FTWs, the large area typically required for

constructed wetlands is illustrated in the aerial photo below:

Jackson Bottom Wetlands Preserve, Hillsboro, OR

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