Date of Award:

5-2011

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Advisor/Chair:

R. Ryan Dupont

Abstract

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.

Comments

This work made publicly available electronically on April 11, 2011.

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