|Klasson, K Thomas|
Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2007
Publication Date: 2/7/2007
Citation: Karim, K., Klasson, K.T., Drescher, S.R., Ridenour, W., Borole, A.P., Al-Dahhan, M.H. 2007. Mesophilic Digestion Kinetics of Manure Slurry. Applied Biochemistry and Biotechnology. 142(3):231-242. Interpretive Summary: Digestion (in absence of oxygen) of manure from grain-fed and pasture-fed dairy cows was studied in small-experiments. These experiments were carried out in 1-gallon containers and different amount of manure was added to each container every other day. The biogas produced from the containers contained methane and the productivity was different from each container. Those having the most waste, produced the most methane. The methane production with different equations, which were dependent on the time the manure spent in the container and the feed manure content. The collected data corresponded well with literature values; however, it was found that the some of the components in the equation had to be changed to fit the data well.
Technical Abstract: Anaerobic digestion kinetics study of cow manure was performed at 35ºC in bench-scale gas-lift digesters (3.78 L working volume) at eight different volatile solids (VS) loading rates in the range of 1.11-5.87 g/L-d. The digesters produced methane at the rates of 0.44-1.18 L/L-d, and the methane content of the biogas was found to increase with longer hydraulic retention time (HRT). Based on the experimental observations the ultimate methane yield and the specific methane productivity were estimated to be 0.42 L CH4/g VS loaded and 0.45 L CH4/g VS consumed, respectively. Total and dissolved COD consumptions were calculated to be 59-17% and 78-43% at 24.4-4.6 days HRTs, respectively. Maximum concentration of volatile fatty acids in the effluent was observed as 0.7 g/L at 4.6 days HRT, while it was below detection limit at HRTs longer than 11 days. The observed methane production rate did not compare well with the predictions of Chen and Hashimoto's and Hill's models using their recommended kinetic parameters. However, under the studied experimental conditions, the predictions of Chen and Hashimoto's model fitted better to the observed data than that of Hill's model. The nonlinear regression analysis of the experimental data was performed using a derived methane production rate model, for a completely mixed anaerobic digester, involving Contois kinetics with endogenous decay. The best fit values for the maximum specific growth rate (µm) and dimensionless kinetic parameter (K) were estimated as 0.43 per day and 0.89, respectively. The experimental data were found to be within 95% confidence interval of the prediction of the derived methane production rate model with the sum of residual squared error as 0.02.