Floating islands as an alternative to constructed wetlands for treatment of excess nutrients from agricultural and municipal wastes – results of laboratory-scale tests

Abstract

Constructed wetlands are recognized as effective mechanisms of water treatment and are employed in a variety of applications. Wetlands comprise diverse and complex systems of interacting plants and animals that remove contaminants from the water column by mechanical filtration and biochemical conversion. A major component of the wetland environment is microbial, with bacteria and other microorganisms proliferating upon all available submerged surfaces (i.e. substrate). In these wetland environments, microbial activity is limited by substrate surface area and nutrient flux. Consequently, the microbial contribution to wetland efficacy can be improved by increasing a wetland’s substrate surface area and increasing water circulation rates through that substrate. Various studies have investigated the use of floating wetland platforms to enhance wetland capacity; however, none of those studies has determined the specific contributions of microbes. In our study, we quantified the microbial component of BioHaven® Floating Islands for aerobic removal of ammonium, anoxic removal of nitrate, and simultaneous aerobic/anoxic removal of ammonium, nitrate and phosphate. This study establishes tank-scale standards to which other microbial data can be compared. In doing this, it has been determined that the microbes growing within a unit volume of BioHaven® Floating Island material are capable of removing 10 600 mg of nitrate per day, 273 mg of ammonium per day, and 428 mg of phosphate per day, where the unit island volume is defined as having a top surface area of 1.0 ft2 and a thickness of 0.6 ft