Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Civil Engineering

Major Professor

Qiang He

Committee Members

Shawn Hawkins, Randall W. Gentry


The largest waste stream from agricultural livestock activity is manure. Efforts herein focus on the improvement of anaerobic digestion of animal wastes which creates a stable solid residue and recovers energy in the form of methane. Co-digestion of chicken litter (CL) and dairy manure (DM) was studied using stirred reactors at mesophilic temperature (35 °C) to evaluate the feasibility of co-digesting these two substrates by varying the organic loading rate (OLR) using increasing amounts of chicken litter. The results indicate that chicken litter and dairy manure can be successfully co-digested with chicken litter present at up to 33% of Volatile Solids (VS) in the feedstock (OLR 1.5(±0.03) gVS Lreactor-1 day-1). Synergistic and/or antagonistic effects were not observed in terms of methane production. It was also found that reactors reach a dynamic stability 7 days after increasing the organic loading rate. While both total and free ammonia tolerance of the bioreactors solids improved by combining these two substrates, true adaptation was only observed for free ammonia which increased as the proportion of CL was increased. No improvement in pathogen indicator removal was detected. Other co-digestion experiments were performed in batch reactors using filtered dairy manure solids (FDMS), grease trap waste (GTW), and sawdust (S). Manure solids (0.417 and 0.842 mm) was present at up to 70% as VS in feedstock and increased total methane production by 1142 %, but decreased efficiency (methane yield) by 5914 %. Grease trap waste alone was difficult to degrade, but co-digestion improved efficiency and VS removal of dairy manure alone by 1119 % and 764%, respectively, for all additions tested. In contrast, sawdust could not be degraded reducing efficiency in all additions tested. Finally, adaptation to different temperatures was evaluated in batch reactors. Microbial population could adapt to lower temperatures down to 19 °C with an acceptable decrease in methane production, but longer retention times were needed. At a 20 days retention time, methane production decreased by only 10% when the temperature decreased from 35 to 25 °C.

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