Kinetic Parameters in Thermophilic Methane Fermentation of Swine Manure

A laboratory study was conducted to investigate the kinetic parameters important in the design and operation of thermophilic digestion of unmedicated swine manure. The experimental design was set up to test the effects of temperature, retention time and feed concentration on these parameters using the modified Contois model. Feed concentrations of 3%, 4%, 5% and 6% VS in influent were tried at 5-, 8- and 13-days RT at 50 C to determine a non-inhibitory concentration. Based on the evidence collected, 3% VS was then chosen for the temperature treatments at 45, 50, 55 and 60 C at RTs of 4, 5, 8, 10 and 13 days. The manure was from 3 to 7 days old, and had an average TS content of about 10%, of which 85% were VS. The ultimate methane yield of the manure (0.508 L CH(,4)/g VS fed) was determined by extrapolation using steady-state data. Inhibition played a significant role in the determination of the ultimate methane yield. A hypothesis was set forth to describe the effects of three types of inhibition on this value. The dimensionless kinetic parameter K, which reflects inhibition in the digesters was shown to be dependent on both temperature and retention time. A statistical relationship between K, temperature and retention time was developed. Together with the modified Contois kinetic equation, the volumetric methane production rates were calculated. Regression analysis of the calculated and the measured methane production rates gave a coefficient of determination of 0.93. At 45 and 50 C, the gas production rates were similar. Gas production rates at 55 C were generally not as high. Digestion at 60 C was unstable as indicated by the low gas production rates and the high volatile acids concentrations. The average methane percentages ranged from about 45 to 65% of the biogas. It was demonstrated that loading rates of up to 6 g VS/L/day (at 3% VS) at temperatures of 45 and 50 C provided from 58% to 80% of the ultimate methane yield at retention times of from 5 to 13 days. Digesters seemed more susceptible to temperature variations in the 55 to 60 C range. Either a much longer time for acclimation than was practiced in this study must be allowed, or some inhibiting agents were involved at these higher tempratures. It was suggested that a temperature range of from 45 to 50 C, a feed concentration of 30 g VS/L and a retention time of 10 days be used in the digestion of swine manure.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Agricultural Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Chen, Ten-Hong

• Engineering, Agricultural

Identifier

(UMI)AAI8409892

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70952