The use of duckweed as a nutrient removal option for municipal wastewaters can only be realized through regular plant harvesting. As a result, the nutrient-rich biomass generated needs to be effectively managed and disposed of. This study looked at three alternative options for biomass management that would make duckweed-based nutrient removal systems sustainable and attractive to small communities like Wellsville City, Utah. The options included: the use of harvested duckweed biomass as an animal feed, anaerobic digestion of duckweed for methane production, and fermentation of biomass for ethanol production. Duckweed feed quality was determined using feed analysis reports and results from digestibility studies (in vitro fermentation). The performance of the anaerobic digestion process was determined by monitoring pH, VS, TS, NH4-N, VFAs, and alkalinity. The ethanol production yields were obtained from starch content values and ethanol concentrations observed from batch fermentation experiments. Duckweed was composed of 21 - 38% crude protein, 94 - 96% water, 78.5% organic matter, < 10% starch and an average of 19% starch after accumulation by nutrient starvation. Relative feed values (RFVs) of 230 - 241, crude protein content of 21-38%, and neutral and acid detergent fiber values of 30.2% and 13.7%, respectively, showed duckweed as a potential feed for ruminants comparable to alfalfa and corn silage (RFVs of 100). Digester performance showed an average methane yield of 6.3 and 5.8 ft3/lb VS destroyed with methane composition values of 67.1% and 62.5% for fresh DW fed reactor (R1) and air dried DW fed reactor (R2), respectively. The ethanol production yield observed was less than 100 mg ethanol/g DW for both fresh and oven dried DW samples. The recommended duckweed biomass management option for a small community like Wellsville is anaerobic digestion because it is a source of energy and at the same time the digestate can be used as a low-quality feed.

A floating treatment wetland (FTW) is an ecological approach which seeks to reduce point and nonpoint source pollution by installing substrate rooted plants grown on floating mats in open waters. While relatively novel, FTW use is increasing. A review of literature identified several research gaps, including: (1) assessments of the treatment performance of FTWs; (2) evaluations of FTWs in the U.S., particularly within wet ponds that receive urban runoff; and (3) plant temporal nutrient distribution, plant growth rate, and the long-term persistence of the FTWs in temperate regions with periodic ice encasement. An assessment model, i-FTW model, was developed, and its parameter s fitted based on data from 14 published FTW studies in the first research topic. The estimated median FTW apparent uptake velocity with 95% confidence interval were 0.048 (0.018 - 0.059) and 0.027 (0.016 - 0.040) m/day for total phosphorus (TP) and total nitrogen (TN), respectively. The i-FTW model provided a more accurate prediction in nutrient removal than two common performance metrics: removal rate (mg/m2/day) and removal efficiency (%). In the second research topic, the results of a mesocosm experiment indicated that FTWs with 61% coverage, planted with pickerelweed (Pontederia cordata L.) or softstem bulrush (Schoenoplectus tabernaemontani), significantly improved TP and TN removal efficiency of the control treatment by 8.2% and 18.2%, respectively. The pickerelweed exhibited significantly higher phosphorus and nitrogen removal than the softstem bulrush when water temperatures were greater than 25 deg C. Field observations in the third research topic found that pickerelweed demonstrated higher phosphorus removal performance (7.58 mg/plant) than softstem bulrush (1.62 mg/plant). Based on the observed seasonal changes in phosphorus distribution, harvest of above-ground vegetation is recommended to be conducted twice a year in June and September. Planted perennial macrophytes successfully adapted to stresses of the low dissolved oxygen (DO) concentrations (minimum: 1.2 mg/L), ice encasement, and relatively low nutrient concentrations in the water (median: 0.15 mg/L TP and 1.15 mg/L TN). Systematic observation of wildlife activities indicated eight classes of organisms inhabiting, foraging, breeding, nursing, or resting in the FTWs. Recommendations for FTW design and suggestions for further research are made based upon these findings. / Ph. D.