Temperature response of methane production in liquid manures and co-digestates

Intensification of livestock production makes correct estimation of methanogenesis in liquid manure increasingly important for inventories of CH4 emissions. Such inventories currently rely on fixed methane conversion factors as knowledge gaps remain with respect to detailed temperature responses of CH4 emissions from liquid manure. Here, we describe the temperature response of CH4 production in liquid cattle slurry, pig slurry, and fresh and stored co-digested slurry from a thermophilic biogas plant. Subsamples of slurry were anoxically incubated at 20 temperatures from 5-52 °C in a temperature gradient incubator and CH4 production was measured by gas chromatographic analysis of headspace gas after a 17-h incubation period. Methane production potentials at 5-37 °C were described by the Arrhenius equation (modelling efficiencies, 79.2-98.1%), and the four materials showed a consistent activation energy (Ea) which averaged 81.0 kJ mol− 1 (95% confidence interval, 74.9-87.1 kJ mol− 1) corresponding to a temperature sensitivity (Q10) of 3.4. In contrast, the frequency factor (A) differed among the slurry materials (30.1 < ln A < 33.3; mean, 31.3) reflecting that origin, age and composition of the manure affect this parameter. The Ea estimate, based on individual slurry materials, was intermediate when compared to published values of 63 and 112.7 kJ mol− 1 derived from composite data, but was similar to Ea estimated for CH4 production at microbial community level across aquatic ecosystems, wetlands and rice paddies (89.3 kJ mol− 1). This supports that the derived temperature sensitivity parameters may be applicable to dynamic modelling of CH4 emissions from livestock manure.