Y.R. Chen

Ultimate methane yield from beef cattle manure: Effect of temperature, ration constituents, antibiotics and manure age

The effects of temperature, ration constituents, antibiotics and manure age on the ultimate methane yield B0, litre CH4/g volatile solids fed (VSf)) were investigated using 4-litre batch fermenters. The average B0 for fermenters maintained at 30–60°C (at 5°C intervals) was 0·328 litre CH4/g VSf. The B0 at 65°C averaged 0·118 litre CH4/g VSf, but this low yield was attributed to unstable fermentation rather than decreased substrate availability at that temperature. These results agreed well with B0 values estimated from daily-fed fermenters. Chlortetracycline and monensin did not affect B0; however, monensin did delay the start of active fermentation in batch fermenters. The average B0 of manure from cattle fed 91·5, 40 and 7% corn silage were 0·173, 0·132 and 0·290 litre CH4/g VSf, respectively. The average B0 for 6–8 week old manure from a dirt feedlot was 0·210 litre CH4/g VSf.

Kinetic analysis of anaerobic digestion of pig manure and its design implications

Abstract The kinetic relationships for the design of anaerobic digesters of pig manure were reviewed. Ultimate methane yield and kinetic constanis for the kinetic equatior proposed by Chen & Hashimoto (1978) were estimated from reported data on the anaerobic digestion of pig manure. The effects of loading rate, influent solids concentration and retention time on methane and net thermal energy production were discussed. The model shows that gross and net thermal energy productions from pig manure are maximized at influent Volatile Solids concentrations of 50 and 55 kg m −3 , respectively. Longer retention times produce higher net thermal energy. A digestion temperature of 55°C produces more net thermal energy than one of 35°C only at short retention times. There is no economic advantage in operating a system at 55°C over 35°C at long retention times. The model also shows that the optimal retention times for net thermal energy production per unit cost for a plant processing 1000 kg Total Solids (TS) of pig manure per day occur at 8·2 and 5·0 days for digestion temperatures of 35°C and 55°C, respectively. Few studies on anaerobic digestion of pig manure have been at retention times shorter than 10 days. Future pilot-scale studies at a retention time less than 10 days are needed.

Thermal properties of beef cattle manure

Abstract The thermal conductivity of beef cattle manure was measured by a transient state method, while its specific heat was measured by a classical method of mixtures. The specific heat of beef cattle manure was found to decrease as Total Solids concentration (TS) increased, ranging from 4·13 kJkg−1 °C−1 at 1·42% TS to 1·400 kJkg−1 °C−1 at 99·4% TS. The thermal conductivity of beef cattle manure was found to range from 630mW m−1 °C−1 at 2·8% TS to 60· 4mW m−1 °C−1 at 95% TS. At low TS, the manure slurrys thermal conductivity was directly proportional to slurry density and decreased as TS increased. At a TS greater than 51%, the thermal conductivity was directly related to the manures bulk density and was independent of the manures TS. An equation relating the thermal conductivity of beef cattle manure to the volume fraction of void space in manure with TS greater than 51% is also given. In addition, results concerning the thermal diffusivity of beef cattle manure are presented.

Laminar tube flow of sieved beef-cattle manure slurries

Abstract The rheological properties of beef-cattle manure slurries were studied using a tube viscometer. The previously proposed rheological model (Che, 1986) is used to describe the relationship between the shear stress and shear rate at the tube wall. The results are compared with those obtained with a rotational viscometer. A modified Reynolds number is defined and used to relate to the friction loss of the laminar flow in the tube. The Reynolds numbers where the laminar flow region terminated are also discussed.