Acidification of Residual Manure in Liquid Dairy Manure Storages and Its Effect on Greenhouse Gas Emissions

Abstract

Liquid manure storages are an important source of greenhouse gases (GHG) on dairy farms. Methane (CH 4) and nitrous oxide (N 2 O) are the predominant GHGs, while ammonia (NH 3) is an indirect source of N 2 O. Addition of acid to manure has shown promising emission reductions, however, cost of acidification may be unfeasible for farmers. Fully cleaning storages has also shown to reduce CH 4 , due to removal of inoculating effects of residual manure ("inoculum") on fresh manure (FM). However, complete removal of inoculum is practically impossible on large farms, thus acidifying only the inoculum may reduce GHGs without requiring acidification of all FM. This study aimed to quantify the effect of acidified inoculum on CH 4 , N 2 O, and NH 3 emissions from stored manure and quantify the changes in methanogen abundance and activity. Emissions were measured from six 10.6 m 3 storages filled with 20% inoculum (1-year-old manure) and 80% FM. Inoculum was treated in three ways: untreated (control); previously acidified (1-year prior); and newly acidified with 70% H 2 SO 4 (1.1 L m −3 manure). The CH 4 and N 2 O emissions were continuously measured from June-November using tunable diode trace gas analyzers coupled with venturi air flow systems. The NH 3 emissions were measured at 24-h intervals 3 × weekly using acid traps. The activity and abundance of methanogens were quantified by targeting the Methyl Coenzyme M Reductase A (mcrA) gene and transcript which encodes a subunit of the key enzyme that catalyzes the final step of methanogenesis. Bacterial abundance was quantified by targeting the bacterial 16S rRNA gene. Quantifications were performed using quantitative real-time PCR. CH 4 emissions were reduced by 77% using newly acidified inoculum and 38% using previously acidified inoculum, compared to the control with untreated inoculum (36.1 g CH 4 m −2). Significant treatment reductions in mcrA gene and transcript abundance suggest that CH 4 reductions were caused by disruption of methanogen activity. NH 3 and N 2 O emissions were reduced by 33 and 73% using acidified inoculum and 23 and 50% using previously acidified inoculum, respectively, compared to the control. Results suggest that lower acid rates and acidifying less frequently may still have good treatment effects while minimizing cost.

Perspectief van het aanzuren van mest in Nederland om methaan- en ammoniakemissie te reduceren

“…Er werden laboratoriumexperimenten en grootschaliger proeven gedaan op basis waarvan geconcludeerd werd dat deze methode een reducerend effect heeft op de methaanemissies vergelijkbaar met het aanzuren van de gehele drijfmestmassa. Bij de grootschaligere proeven werden mestopslagen met een inhoud van 10,6 m³ gebruikt waarin inocula (mest van 1 jaar oud) aangevuld werd met verse mest (verhouding 1:4) (Sokolov et al, 2020a). Het inoculum in de ene tank was niet aangezuurd, in een andere was dit 1 jaar geleden aangezuurd en in een derde was het aangezuurd voorafgaand aan het vullen van de tank.…”

“…Na 150 dagen meten was de pH in de controle en de tank met het een jaar daarvoor aangezuurde inoculum 8,2 en in de tank met het voorafgaand voor vullen aangezuurde inoculum circa 7,6. Dit onderzoek (Sokolov et al, 2020a) geeft de verwachting dat deze manier van aanzuren een langduriger effect op methaanemissie heeft. Voor ammoniak was het reducerende effect lager door het aanzuren van het inoculum vergelijken met het aanzuren van de gehele mestmassa.…”

“…Sokolov et al (2020a;2020b) voerden onderzoek uit naar het effect van het aanzuren van het restant aan mest dat na het uitpompen van mest uit de kelders achterblijft. Dit restant wordt het 'inoculum' genoemd, omdat het een startpopulatie bevat van methanogene micro-organismen.…”

Reducing greenhouse gas emissions from pig slurry by acidification with organic and inorganic acids

“…Frequent slurry removal leaves a residual slurry fraction that may function as an inoculum that speeds up the anaerobic processes in newly produced slurry resulting in accelerated CH 4 production [ 19 ]. However, complete removal of residual slurry is impractical at large farms [ 20 ] or in farms with typical designs of pits and slurry channels. Coupling acidification of the residual slurry with frequent slurry removal may enhance the total mitigation potential and reduce acidification expenses as compared to bulk acidification.…”

“…Laboratory tests of residual slurry acidification have shown very promising results a with reduction of CH 4 emission of up to 99% over 116 days [ 21 ]. In pilot-scale storage tanks (10 m 3 ), 2.12 m 3 residual slurry which was acidified before addition of 8.48 m 3 fresh slurry reduced CH 4 emission by 77% over 155 days compared to a control case where the residual slurry was not acidified before the addition of fresh slurry [ 20 ]. Neither of the studies examined residual slurry acidification in a setup with continuous or daily addition of slurry, which could potentially fuel CH 4 emissions.…”