Latest Generation Floating Treatment Wetland Technology: Achieving Significant Nutrient Removal in Aerated Wastewater Lagoons

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Project Location: Rehberg Ranch Residential Subdivision, Billings, Montana USA

The following case study underscores the capabilities of Floating Island International's (FII) patented floating treatment wetland (FTW) technology and its ability to clean water by significantly reducing nutrient levels. Constructed of post-consumer polymer fibers and vegetated with native plants, FTWs mimic the ability of natural wetlands to clean water by bringing a "concentrated wetland effect" to any water body–in this case, an aerated wastewater lagoon.

Overview:

Located on the outskirts of Billings, Montana (pop. 120,000), 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).

Discharge options were limited to land application or surface water discharge, and nutrient levels in treated wastewater needed to be lower than the lagoons alone could deliver. In this case, the treated wastewater is being land-applied to surrounding prairie grasses, rather than discharged into surface or groundwater. Prairie grasses are able to assimilate only low nutrient loads.

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 continues to implement a rigorous monitoring regime to monitor efficacy of the FTW system in comparison to the control lagoon with no FTW. Both lagoons receive the same wastewater.

Results:

Dramatic increase in nutrient removal rates and reduced costs. As of April 2010, FTW nutrient removal, compared with the control lagoon, has been significant. Removal of ammonia has improved by 38%, while the phosphorus removal rate has improved by 27%. Removal rates of TSS and BOD are 9% higher in the FTW lagoon than the control lagoon.

Costs have been reduced because the lower nutrient levels in the water allow treated water to be applied to less land area at higher rates, reducing overall discharge costs by 50%.

Conclusion:

The need to reduce nutrient levels in wastewater is increasingly critical as rivers, lakes and coastal waters become more nutrient loaded worldwide. This is the entry point for cutting-edge, “green” FTW technology.

Although facultative and aerated lagoons can reduce BOD and TSS, their ability to remove nitrogen and phosphorus from municipal wastewater is extremely limited. FTW technology enhances these lagoons with the “concentrated wetland effect”, facilitating compliance with increasingly stringent wastewater nutrient, BOD and TSS criteria.