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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Christopher Schmit


The methane production of municipal anaerobic digesters can be increased with the addition of high strength organic wastes, which can help offset energy costs through heating and electricity generation. The Sioux Falls, South Dakota Water Reclamation Facility (WRF) initiated this study to investigate the effects of adding grease waste (GW) to municipal anaerobic digesters. Grease waste is considered to be a good candidate for co-digestion because it is readily available, has little or no market value, and is a high strength organic waste. A sample was collected from a restaurant’s grease interceptor in Sioux Falls and the sample’s top floatable layer of fats, oils, and grease (FOG) was characterized in terms of pH, density, total solids (TS), volatile solids (VS), and chemical oxygen demand (COD). An anaerobic respirometer was used to determine the FOG’s potential methane yield and inhibitory concentration. The methanogenic activity of the biomass before and after the addition of FOG was also determined using the anaerobic respirometer. The anaerobic digester biomass used for all respirometer testing was obtained from the Sioux Falls WRF anaerobic digesters. The pH, density, TS, VS, and COD of the FOG was determined to be 4.32, 0.912 g/mL, 971,000 mg/L, 970,000 mg/L, and 2.26 x 106 mg/L, respectively, indicating that the FOG sample collected was a high strength organic waste. When added to the mesophilic anaerobic biomass, the FOG was determined to have a biochemical methane potential (BMP) of 338 mL/g COD added, which is equivalent to 760 mL/mL FOG xiii added and 860 mL/g VS added. The BMP test results had a standard deviation of 9.2%. During the anaerobic toxicity assay (ATA), the FOG was found to become inhibitory at some concentration greater than 1.13 g COD/L, which is equivalent to 0.44 kg VS/m³. An exact inhibitory concentration could not be determined. Inhibition was observed by a decrease in methane production expressed per gram of COD added with increasing concentrations of FOG. Due to inconclusive specific methane production (SMP) results, the change in methanogenic activity of the anaerobic biomass due to FOG addition could not be substantiated. SMP tests were conducted before and after a 30-day period of daily FOG addition, and individual SMP results after the 30-day period were mixed as compared to their initial values. The averages of the SMP results before and after the 30- day period did not change significantly.

Library of Congress Subject Headings

Sewage--Purification--Anaerobic treatment
Oils and fats


Includes bibliographical references



Number of Pages



South Dakota State University



Rights Statement

In Copyright