Effects of Two Manure Additives on Methane Emissions from Dairy Manure

Abstract

Liquid manure is a significant source of methane (CH₄), a greenhouse gas. Many livestock farms use manure additives for practical and agronomic purposes, but the effect on CH₄ emissions is unknown. To address this gap, two lab studies were conducted, evaluating the CH₄ produced from liquid dairy manure with Penergetic-g^® (12 mg/L, 42 mg/L, and 420 mg/L) or AgrimestMix^® (30.3 mL/L). In the first study, cellulose produced 378 mL CH₄/g volatile solids (VS) at 38 °C and there was no significant difference with Penergetic-g^® at 12 mg/L or 42 mg/L. At the same temperature, dairy manure produced 254 mL CH₄/g VS and was not significantly different from 42 mg/L Penergetic-g^®. In the second lab study, the dairy manure control produced 187 mL CH₄/g VS at 37 °C and 164 mL CH₄/g VS at 20 °C, and there was no significant difference with AgrimestMix (30.3 mL/L) or Penergetic-g^® (420 mg/L) at either temperature. Comparisons of manure composition before and after incubation indicated that the additives had no effect on pH or VS, and small and inconsistent effects on other constituents. Overall, neither additive affected CH₄ production in the lab. The results suggest that farms using these additives are likely to have normal CH₄ emissions from stored manure.

Keywords: Biochemical Methane Potential (BMP); dairy manure; liquid manure storage; manure additives; methane emissions.

Figure 1

Biochemical methane potential (BMP) trial set-up with 18 bioreactors in InnoTech Alberta’s batch culture set-up. Each additive treatment, the positive control (no additive), and the inoculum control were done in triplicate

Figure 2

Biochemical methane potential (BMP) trial set-up with 24 bottles divided between two incubation temperatures, 20 °C and 37 °C. The substrate was liquid dairy manure. Each additive treatment, the manure control (no additive), and the inoculum control were done in triplicate

Figure 3

InnoTech Alberta’s BMP batch culture automated sampling system including the programmable logic controller (PLC). The biogas produced was measured using a Milligas counter and gas composition analyzed by a CP4900 Micro-GC.

Figure 4

Cumulative methane yields over time from cellulose BMP batch cultures containing the Penergetic-g^® additive at 12 mg/L (a), 42 mg/L (b), or without additive (c). Each timeseries shows the mean ± standard deviation (n = 3). The total yield for all treatments are compared in the bar graph, with the error bars showing standard deviation (d). Yields are scaled by volatile solids (VS).

Figure 5

Cumulative methane yields over time from dairy manure BMP batch cultures containing the Penergetic-g^® (P) additive at 42 mg/L (a), or without additive (b). Each timeseries shows the mean ± standard deviation (n = 3). The total yield for all treatments are compared in the bar graph, with the error bars showing standard deviation (c). Yields are scaled by volatile solids (VS).

Figure 6

Cumulative methane produced (mL CH₄) from BMP batch cultures containing liquid dairy manure over a 30-day incubation at 37 °C (a–c) and a 90-day incubation at 20 °C (e–g). The bottles contained AgrimestMix (AM) (a,e), Penergetic-g^® at 420 mg/L (b,f), or a control without additive (c,g). Each timeseries shows the mean ± standard deviation (n = 3), and the grey line is the average production from inoculum. The total methane yields for each treatment are compared in the bar graph, with error bars showing the standard deviation (d,h).