Date of Award:

5-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

R. Ryan Dupont

Committee

R. Ryan Dupont

Committee

Bruce G. Bugbee

Committee

William J. Doucette

Abstract

Utah State University students under the direction of Dr. R. Ryan Dupont, Environmental Engineering, have been enthusiastically involved in researching ways to improve wastewater treatment at the nearby Wellsville Municipal Sewage Lagoons. Wellsville City, along with several other Cache Valley communities, has experienced some problems with their current wastewater facility, particularly with phosphorus removal, which will become more difficult to address as the population increases in the future. Excessive phosphorus causes unappealing algae blooms in ponds and reservoirs while also posing a threat to local fish. Brittany Wilkes, Brett Housley, and Naho Orita first looked into reducing phosphorus discharge by improving management practices and harvesting duckweed. First, they recommended installing a basic bar rack and grit chamber at the headworks since it did not have any. Next, they recommended discharging wastewater in the morning before phosphorus levels peaked in the evening— preferably from lagoon 3 for highest quality effluent. Their initial duckweed studies provided a foundation for two more in-depth studies.

Jonathan Farrell’s research found that Lemna turionifera and Wolffia borealis duckweed species completely cover these 23 hectare (56-acre) lagoons for 5 to 6 months of the year in this temperate climate zone. Results showed that a single harvest of these lagoons can produce 0.5 kg-dry duckweed/m2 per 90-day harvesting season while biweekly harvesting can produce 1.5 kg-dry duckweed/m2 which accounts for 30-90% removal of the annual phosphorus loading, respectively. In addition, duckweed achieved pharmaceutical removals comparable to literature reported removals by membrane bioreactors and powder activated carbon.

Maureen Kesaano’s research evaluated options for the management of the harvested biomass; after all, successful systems depend not only on growing and harvesting the duckweed, but also on the safe disposal of the harvested biomass. She discovered that anaerobic digestion of the duckweed biomass yielded 370 liters methane per kg volatile solids destroyed with a 65% methane composition. The duckweed contained less than 10% starch but could be raised to an average of 19% starch after accumulation by nutrient starvation. Fermentation for ethanol production yielded 20 to 80 mg ethanol/g-duckweed for dry and fresh material, respectively. As an animal feed option, the duckweed contained 21-38% crude protein and received relative feed values (RFVs) exceeding that of alfalfa and corn silage.

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This work made publicly available electronically on May 10, 2012.

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