Key Findings (Floating Island International)
The following bullet points highlight the research results and efforts that surround BioHaven Floating Islands. We are very excited about the myriad of solutions a seemingly simple island can provide.
• Floating Islands reduce nutrient levels in any water system by supporting the growth of microbes and plants. Measuring only the impact of microbes, one square foot of BioHaven floating island is sufficient to reduce nitrate by over 10 grams per day, ammonia by up to 15 grams per day, and phosphate by 0.5 grams per day.
• All three nutrients tested (nitrate, ammonia, and phosphate) are removed simultaneously by a single island in any water system. A few pilot studies that are currently underway include a wastewater treatment facility in Wiconisco, PA, and a public waterway in Toronto, Canada.
• Various studies are investigating the impacts of floating islands on the removal of multiple pollutants. The National Institute of Water and Atmospheric Research (NIWA) have implemented floating islands in storm water retention ponds to mitigate heavy metals (lead, copper, etc.). Early results indicate that the islands are having significant impacts on those contaminants.
• Collaborations are forming to use floating islands as platforms for the removal of selenium. Floating islands are ideally suited to support selenium digesters and a group from Arizona State University is investigating the appropriate design.
• Several groups have approached Floating Island International with interest and projects to investigate the removal of various “exotic” pollutants such as naphthenic acid, PCB, and pharmaceuticals.
• Floating islands effectively dampen wave activity and act as buffers against wind and wave erosion. Several projects are being developed to measure the efficacy of erosion prevention in marine settings and in lakes.
• BioHaven floating islands sequester carbon dioxide from the atmosphere. With growing concerns about greenhouse gases and their impacts on global climate, floating islands represent a unique way to sequester carbon in, on, and under islands. Measurements are currently being taken to identify how much carbon is retained within both natural floating islands and BioHaven floating islands.
• Floating islands provide wildlife habitat. Various organizations including Citizens for Conservation (Illinois) and Delta Waterfowl (North and South Dakota), have implemented islands as a means of restoring wetland habitat.
Summary of MBRCT Grant findings, taken from the 8th Quarterly Report , author Frank Stewart
We established high-concentration levels of phosphate and nitrate (at 20 mg/l and 100 mg/l, respectively), representative of livestock facility effluent, and established low-concentration levels of phosphate and nitrate (at 2 mg/l and 10mg/l, respectively), representative of urban stormwater retention ponds. We have tentatively set target efficacy goals of 75% removal for both high and low starting concentrations, though these goals may be adjusted based on inputs from potential customers.
[Note: During Q3, we learned that the nitrogen component of livestock effluents exists in the ammonia state rather than the nitrate state. We have subsequently modified our high-concentration experiments to include ammonia. Since the ammonia is converted to nitrate in the first step of a multi-step microbial process, we are also continuing to experiment with nitrate removal].
Contaminant removal rates for Kentucky Bluegrass (Poa pratensis) and Engleman Spruce (Picea engelmannii) were evaluated. Removal rates of phosphate and nitrate met our expectations for unaerated tanks in cool weather conditions. As expected, nitrate removal was highest for the Kentucky Bluegrass, which was actively growing under cool, sunlit conditions. Unexpectedly, Engleman Spruce outperformed Kentucky Bluegrass for phosphate removal, although the spruce plants had smaller biomass and were growing more slowly than the bluegrass.
In Run 5, the tanks were exposed to light on their sides and tops. Under these conditions, we observed significant algae growth in tanks with nutrients, with and without added microbes. From this we infer that microbes will be most effective at reducing algae growth when the microbes are used in low-light conditions.
This finding may affect the future design of the islands.
In Q3, we achieved a nitrate removal rate of about 1500 mg*day-1*ft-2 in Run 11 using bacteria without plants. This is approximately three times the removal rates measured in previous U.S. Bureau of Reclamation and private Australian studies using hydroponically grown aquatic plants.
We achieved an ammonia removal rate of about 200 mg*day-1*ft-2 in Run 9 using bacteria without plants. This is approximately 2.7 times the removal rate measured in a conventional wetland at a swine production facility.
We achieved a phosphate removal rate of about 70 mg*day-1*ft-2 in Run 11 using bacteria without plants. This is approximately 1.3 times the removal rate measured for hydroponically grown aquatic plants in an Australian study.
We found that nutrient removal rates are highly dependent on environmental conditions. Ammonia-removing bacteria require aeration and alkalinity additives to replace the oxygen, carbon dioxide and alkalinity that are used up by the bacteria when they convert ammonia to nitrite and nitrate. Conversely, nitrate-removing bacteria prefer low oxygen conditions plus a carbon source for energy. We tested five commercial microbe formulations and two “natural mixes” obtained from non-commercial sources. The natural mixes include livestock effluent from a holding pond and well water from a shallow well. As shown in Run 10, the commercial microbes and natural microbes had similar nitrate removal rates when the optimum conditions of low oxygen and adequate carbon source were provided. We documented in the nitrate test for Run 9 that two commercial microbe mixes removed a portion of the nitrate that was produced by aerobic conversion of ammonia, but the natural microbe mix did not appear to remove a significant portion of the nitrate.
During Q3 in Run 11, we demonstrated that the bacteria had higher phosphorus removal rates when they were growing on island matrix than when suspended in the water.
We demonstrated an increase in water clarity as a result of the islands removing fine suspended soil particles from aquarium water. In one experiment, maximum visibility increased from 14 cm to greater than 120 cm in 26 days. In a second experiment, water clarity increased from 5 cm to 52 cm in 41 days, as measured with a 2-inch Secchi disk.
During Q4, we increased our maximum microbial nitrate removal rate from about 1500 mg*day-1*ft-2 (early Run 11) to about 3000 mg*day-1*ft-2 (late Run 11 with thicker biofilms).
We increased our maximum microbial ammonia removal rate from about 200 mg*day-1*ft-2 (Run 9) to about 338 mg*day-1*ft-2 (Run 16).
We have achieved a maximum macrophyte nitrate removal rate of 55.9 mg*day-1*ft-2 (Carex nebrascensis grown in solid matrix, Run 15).
We have achieved a maximum macrophyte phosphate removal rate of 11.8 mg*day-1*ft-2 (Carex nebrascensis, Run 15, second dosing).
We demonstrated that naturally occurring bacteria and two commercial microbes all had similar removal rates of ammonia and nitrate when adequate alkalinity and carbon source were provided (Run 16). Two potentially important consequences can be derived from these results:
1) Significant microbial removal of ammonia can occur even in the presence of BOD (carbon source). There is some concern than the BOD present in natural ponds might inhibit the removal of ammonia, since the bacteria might preferentially metabolize the BOD rather than the ammonia, but our experiments do not indicate this to be the case in our laboratory environment. 2) When the islands were placed in an aerated environment with a carbon source and high concentrations of ammonia, the nitrate that was produced during ammonia breakdown was also removed. Although the aerated condition of the test tanks was not expected to result in nitrate removal, the removal did occur. This may be a result of local anoxic zones occurring within the island matrix, which provide areas for denitrifying bacteria to thrive.
During Q5, we demonstrated that islands with macrophytes can provide a significant improvement in water clarity during cool weather periods by removing suspended particles and/or suppressing algae growth, when water is actively circulated through the island matrix. In one experiment (Run 20), tanks containing islands planted with dormant sedges had an average water turbidity of 11 NTU (Nephelometric Turbidity Units), while tanks without plants or islands had a water turbidity of 186 NTU.
We also demonstrated that we could provide significant water circulation through island matrix under field conditions using three 45-watt solar panels and an 1100 gph bilge pump. Cost of materials is approximately $300 per unit.
Our cumulative data to date for the various runs indicate that phosphate removal is strongly correlated with microbial biomass production. In Run 20, we determined that emergent wetland plants do not remove significant amounts of ammonia, nitrate or phosphate during the fall season in Montana. We believe that submerged aquatic plants may be superior to emergent plants for nutrient removal during cold weather conditions.
During Q6, in Run 23, we achieved a microbial nitrate removal rate of 10,600 mg*day-1*ft-2. This is approximately 3.5 times greater than our previous best result from Q4.
In Run 24, we achieved a microbial phosphate removal rate of 140 mg*day-1*ft-2. This is approximately two times greater than our previous best result from Q3. During the Q6 experiments, we learned that dissolved oxygen regulation is likely to be a key factor in the efficacy of floating islands for removing phosphate.
During Q7, in Run 25, we obtained preliminary data correlating temperature to nutrient removal rates. In this run, we observed that the removal rates for both nitrate and phosphate approximately doubled for a temperature change from 11° C to 26° C.
In Run 27, we achieved a phosphate removal rate of 428 mg*day-1*ft-2. This is approximately three times better than our previous best result from Run 24. This removal rate was obtained using a relatively high phosphate starting concentration (15.9 mg/l), which is typical of some livestock
effluents. The phosphate removal rate decreased in the tanks during Run 26 as the phosphate concentration was reduced during the experiment.
The starting concentration of molasses (carbon source) was about 831 mg/l TOC. Limited aeration was used, along with water circulation through the island matrix from top down. “Limited aeration” means that the bubble rate was sufficient to promote phosphate removal (by aerobic bacteria), while at the same time promoting nitrate removal by anoxic bacteria. The bubble rate for this experiment was measured at 0.03 CFM, which is equivalent to a unit bubble rate of about 0.015 CFM per square foot of island top surface.
Comparing Run 27 and Run 28, we measured removal rates that were approximately five times higher at 26° C compared to 11° C. The cool weather experiments should be repeated based on the poor removal rates during the latter portion of the experiments.
We demonstrated that islands significantly reduced the quantity of settled sludge that was produced in outdoor test ponds during nutrient removal.
We demonstrated that a custom wind-solar power generation system could produce significant power for aeration and water circulation through
floating islands.
Our peer-reviewed paper entitled “Floating Islands as an Alternative to Constructed Wetlands for Treatment of Excess Nutrients from Agricultural and Municipal Wastes – Results of Laboratory-Scale Tests” was accepted for publication in Land Contamination and Reclamation Journal.