Methane emissions in biogas production - The Biogas: Science, Production and Applications - page 247

Table 11.1 Net total methane emissions during storage and after field
application of differently treated manure (in gCH 4 /m 3 manure)

Untreated Separated Digested Straw cover Aerated

Storage 4045.7 1833.0 1242.6 4904.1 1731.7

Field application 1.3 19.7 2.0 22.2 7.6

Total emissions 4047.0 2363.3 1344.6 4926.3 1739.3

Storage (%) 100 99.2 99.9 99.6 99.6

Application (%) 0.0 0.8 0.1 0.4 0.4

digestate, it is important to realize that long-term storage only takes place
with either manure or digestate, never with both. The latter would result in
an overestimation of the emissions. Finally, it is important to realize that
although emissions from long-term storage of manure are discussed briefly,
this aspect is outside the scope of the current chapter.

11.2.1 Storage of manure and substrates
Two articles report on emissions from the storage of manure or substrate. In
the first of these, Amon et al. (2006) sought to quantify methane emissions,
along with ammonia (NH 3 ) and nitrous oxide emissions, from storage and
after application of differently treated dairy cattle slurry (pure manure). The
treatment options were AD, slurry separation, slurry aeration and straw
cover, and their influence on emission levels was investigated. The main
focus was to compare net total emissions from manure storage and after
manure application. The results are presented in Table 11.1.
The net total methane emissions during storage of untreated cattle
manure were found to be 4045.7 gCH 4 /m 3 manure in an open manure
storage. No emission numbers were reported as a percentage of total
methane utilization. Assuming cattle manure with a density of 1 ton/m 3 and
a biogas yield of 21m 3 /ton, the reported emission of 4045.7 gCH 4 /m 3 yields
192.7 gCH 4 /m 3 biogas. With an average methane content of 60% and
methane density of 710 g/m 3 , this corresponds to 45% of the total methane
produced. Note that this result was based on net total emissions from long-
term (80 days) slurry storage under warm conditions with a mean slurry
temperature of 17

￿ ￿ ￿ ￿ ￿ ￿

C.
Overall, methane emissions from stored dairy cattle manure were reduced
by all treatments except when the manure store was covered with a layer of
chopped straw. Greenhouse gas abatement measures for the management of
stored manure were most effective if they reduced methane emissions during
slurry storage. In the context of manure destined for AD, this can best be
achieved by a reduction in slurry dry matter.
In the second study, a report commissioned by the Dutch government
(SenterNovem, now the NL Agency), Zwart et al. (2006) reported methane

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