Low frequency aeration of pig slurry affects slurry characteristics and emissions of greenhouse

12 Pages·2017·1.52 MB·English

by  Salvador Calvet

biosystems engineering 159 (2017) 121e132
Availableonlineatwww.sciencedirect.com
ScienceDirect
journal homepage: www.elsevier.com/locate/issn/15375110
Research Paper
Low frequency aeration of pig slurry affects slurry
characteristics and emissions of greenhouse gases
and ammonia
Salvador Calvet a,*, John Hunt b, Tom H. Misselbrook b
aUniversitatPolit(cid:1)ecnicadeVal(cid:1)encia,InstituteofAnimalScienceandTechnology,CaminodeVeras.n.,46022
Valencia,Spain
bRothamstedResearch,NorthWyke,Okehampton,DevonEX202SB,UK
a r t i c l e i n f o
Lowfrequencyaerationofslurriesmayreduceammonia(NH )andmethane(CH )emis-
3 4
Articlehistory: sions without increasing nitrous oxide (N2O) emissions. The aim of this study was to
Received7February2017 quantify this potential reduction and to establish the underlying mechanisms. A batch
Receivedinrevisedform experimentwasdesignedwith6tankswith1m3ofpigslurryeach.Afteraninitialphaseof
25April2017 7dayswhennoneofthetankswereaerated,asecondphaseof4weekssubjectedthreeof
Accepted26April2017 thetankstoaeration(2minevery6h,airflow10m3h(cid:1)1),whereastheotherthreetanks
Publishedonline20May2017 remainedasacontrol.Afinalphaseof9dayswasestablishedwithnoaerationinanytank.
EmissionsofNH ,CH ,carbondioxide(CO )andN Oweremeasured.Intheinitialphase
3 4 2 2
Keywords: nodifferencesinemissionsweredetected,butduringthesecondphaseaerationincreased
Gasemissions NH3emissionsby20%withrespecttothecontrols(8.48vs.7.07gm(cid:1)3[slurry]d(cid:1)1,P<0.05).
Slurrymixing A higher pH was found in the aerated tanks at the end of this phase (7.7 vs. 7.0 in the
Ammonia aerated and control tanks, respectively, P < 0.05). CH4 emissions were 40% lower in the
Methane aeratedtanks(2.04vs.3.39gm(cid:1)3[slurry]d(cid:1)1,P<0.05).ThesedifferencesinNH3andCH4
Nitrousoxide emissionsremainedaftertheaerationphasehadfinished.NoeffectwasdetectedforCO2,
Carbondioxide and no relevant N2O emissions were detected during the experiment. Our results
demonstratethatlowfrequencyaerationofstoredpigslurryincreasesslurrypHandin-
creasesNH emissions.
3
©2017TheAuthors.PublishedbyElsevierLtdonbehalfofIAgrE.Thisisanopenaccess
articleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).
thereforeapropermanagementofslurrybecomesessentialto
1. Introduction
avoidenvironmental impactsandto enhancenutrientrecy-
cling (Brockmann, Hanhoun, Ne(cid:3)gri, & He(cid:3)lias, 2014). During
In recent years, the growth in intensive pig production has
their storage, pig slurries emit considerable amounts of
lead the increasing global livestock production (FAOSTAT,
ammonia (NH ) and greenhouse gases to the atmosphere,
3
2016). However, intensive production of pigs tends to be
mainly in the form of methane (CH ). In intensive pig pro-
4
decoupled from other agricultural production systems, and
duction, slurry treatment techniques become essential to
* Correspondingauthor.
E-mailaddress:[email protected](S.Calvet).
http://dx.doi.org/10.1016/j.biosystemseng.2017.04.011
1537-5110/©2017TheAuthors.PublishedbyElsevierLtdonbehalfofIAgrE.ThisisanopenaccessarticleundertheCCBYlicense(http://
creativecommons.org/licenses/by/4.0/).
122 biosystems engineering 159 (2017) 121e132
fulfiltheenvironmentalregulations(e.g.IndustrialEmissions potential effects of short aeration times on pH and NH
3
DirectiveinEurope).Thesetechniquesaredevisedtofacilitate emissionsmustbeevaluatedbyresearch.
slurry management, reduce the environmental impacts or Thepartialoxygenationcausedbylowfrequencyaeration
obtain potential benefits such as high value fertilisers or may have potential effects on CH and N O emissions.
4 2
biogas(Burton&Turner,2003).However,potentialsideeffects Researchonaerobictreatmentofslurriesnormallyconsiders
ofcertaintreatments,suchasnitrousoxide(N O)emissions alongerdurationoftheaerobicphaseincomparisontothe
2
fromaerobictreatments,mustbeaccountedfor. anaerobic phase, and results indicate that nitrification and
Aerationhaslongbeenproposedasatreatmenttechnique denitrification is enhanced, whereas methanogenesis is
to reduce the nitrogen and organic matter loads of slurries, inhibited (Castro-Barros et al., 2015; Cheng & Liu, 2001; Hu
and thus reduce the pollution risk (Bicudo & Svoboda, 1995; etal.,2010;Hu,Zhang,Xie,Li,Wang,etal.,2011;Hu,Zhang,
Bicudo, 1995; Burton, 1992; Cumby, 1987). During the aera- Xie, Li, Zhang, et al., 2011; Lackner et al., 2014; Wang et al.,
tionofanimalslurries,theanoxicandreductiveconditionsin 2016). However, no information is available on how these
whichslurriesarenormallystored(e.g.<1gL(cid:1)1dissolvedO ) emissionsareaffectedbylowaerationfrequency.
2
changetoaerobicandoxidisingconditions(e.g.>4gL(cid:1)1dis- Theobjectivesofthisstudyare:first,todeterminewhether
solved O ) (Cheng & Liu, 2001). Also, aeration normally in- alowfrequencyaeration(2mineach6h)ofpigslurryaffects
2
volvesstirringtheslurries,bothavoidingsedimentationand its composition and the related emissions of NH , CH , N O
3 4 2
crustformation.Thischangesthebiochemicalandmicrobial andCO ;andsecond,toanalyseanddescribethemechanisms
2
reactionsintheslurry,dependingontheaerationset-uppa- underlyingthesechanges.
rameters (for example aeration flow rates, frequency and
duration in case of intermittent aeration, tank size and air
bubblesize,amongothers). 2. Methodology
Theeffectofaerationonthefateofnitrogenhasbeenlong
demonstrated (Be(cid:3)line & Martinez, 2002; Be(cid:3)line, Martinez, 2.1. Experimentaldesign
Chadwick,Guiziou,&Coste,1999;Cheng&Liu,2001).These
studieshaverevealedthatusingappropriateaerationflowsin TheexperimentwasconductedattheRothamstedResearch
the case of continuous reactors or intermittent aeration for North Wyke site from 8th June to 22nd July 2016. A slurry
batch reactors achieves high nitrogen removals as a conse- storagesystemsimilartothatdescribedbyMisselbrook,Hunt,
quenceofnitrificationanddenitrificationprocesses,produc- Perazzolo,andProvolo(2016)wasused,comprisingsix1.25m3
ingnitrogengases.Therefore,researchhasrecentlyfocused tanks(1.20mdiameterand1.12mheight)locatedinacovered
on reducing N O emissions by controlling the process vari- area to exclude rainfall. Slurry was obtained from a local
2
ables including intermittent aeration or aeration flow rates commercialfinishingpigfarm.Slurrystoredforabout8weeks
(Castro-Barros, Daelman, Mampaey, van Loosdrecht, & wascollectedfromthebelowslatstorageandtransportedto
Volcke,2015;Huetal.,2010;Hu,Zhang,Xie,Li,Wang,etal., the experimental site using a 6 m3 slurry tank. Slurry was
2011; Hu, Zhang, Xie, Li, Zhang, et al., 2011; Lackner et al., mixed and then representatively divided among the experi-
2014; Mampaey, De Kreuk, van Dongen, van Loosdrecht, & mentaltanks,andthuseachtankwasfilledwith1m3ofslurry
Volcke, 2016; Pan, Wen, Wu, Zhang, & Zhan, 2014; Wang, (88cmdepth).Threeofthetanksweresubjectedtotheaera-
Guan,Pan, & Wu, 2016). Accordingto theseauthors, chang- tion treatment, whereas the other three tanks were not
ing operation parameters leads to N O emission factors treatedandservedascontroltanks.Slurrycompositionand
2
mostlybetween1%and10%oftheinitialN. gaseousemissionsweremonitoredduringtheexperiment.
Aerobictreatmentsystemsarenotconsideredbestavail- Theexperimentconsistedofthreephases.Thefirstphase
able techniques because they involve a loss of a valuable lastedforthefirst7daysofstorageandalltanksweresub-
nutrient and the side effects on N O emissions are still jectedtothesamemanagement,thatis,noneofthetankswas
2
considerable (European Commission, 2015). However, the aerated.Duringthisphase,potentialdifferencesamongtanks
short time aeration (less than 1% of time) of slurries could wereevaluated.Thesecondphaselastedfor4weeksduring
have the potential to reduce ammonia emissions without which aeration was conducted in the aeration treatment
these side effects, although to the authors' knowledge, very tanks.Theaerationsystemconsistedofalowfrequencyin-
limited research has been conducted in this area. In this jectionofair.Eachslurrytankundertheaerationtreatment
process,twoeffectsareexpectedtooccur:slurrymixingand had170Lmin(cid:1)1ofambientairinjectedover2minevery6h.
partialoxygenation.Themixingeffectisthemainhypothesis Injectionwasprogrammedtooccurat03:00h,09:00h,15:00h
forreducedNH emissions.AsfirstsuggestedbyNi,Hendriks, and21:00h.Anautomaticcontrollerwasdesignedspecifically
3
Vinckier, and Coenegrachts (2000) and reviewed by Hafner, tocontroloperationtimes,andairwasinjectedusingapump
Montes, and Alan Rotz (2013), CO emission from slurry in- (BeckerVT4.10,Wuppertal,Germany).Airwasinjectedatthe
2
creases surface pH, thus enhancing NH emissions. As a bottom of each tank through a 32 mm diameter PVC pipe.
3
consequence, NH emissions during and immediately after Detailsoftheaeratedandnon-aeratedtankscanbeseenin
3
aerationmaybelowerthanuntreatedslurries.However,ithas Fig. 1. Finally, in a third phase over the last 9 days of the
alsobeenreportedthattheaerobictreatmentofmanurein- experiment,noaerationwasconductedinanyofthetanks,
creasesslurrypHonaverage,asaconsequenceoftheremoval aiming to evaluate potential permanent changes in slurry
of volatile fatty acids (Fangueiro, Hjorth, & Gioelli, 2015; compositionandgaseousemissionsaftertheaerationtreat-
Sørensen & Eriksen, 2009; Zhang & Zhu, 2005). Therefore, ment had finished. From each tank, representative slurry
biosystems engineering 159 (2017) 121e132 123
Fig.1eSlurrytanksusedintheexperiment.Schematicofthecontrolandaeratedtanks(upper)andarrangementinthe
polytunnel(lower).
samples were taken for analysis at the beginning of each 20e22 isotope ratio mass spectrometer (Sercon, Crewe, UK).
phase. Ammonium-N was determined by automated colorimetric
analysisfollowingextractionwith2MKCl.Totaloxidisedni-
2.2. Slurrycharacteristics trogenanalysiswascarriedoutwithanextractionusing2M
KCl and determined by the colorimetric vanadium chloride
Slurrysamplesweretakenatthestartofeachstoragephase method.
andanalysedfortotalsolidsandvolatilesolidscontent,total AspHwashypothesisedtobeakeydriverforNH emis-
3
nitrogen(N),ammonium-N,andpH,followingasimilarpro- sions, it was monitored 3 times per week using a portable
cedure to Misselbrook et al. (2016). Total solids content was meterwithpHprobe(HI9025,HannaInstruments,Leighton
determinedbymeasuringthemasslossafterdryingat85(cid:3)C Buzzard,UK).Measurementswereconductedthroughoutthe
for 24 h. Volatile solids content was determined on a sub- experimental period at the slurry surface and at a depth of
sample of the total solids by measuring the mass loss on 10cm.Duringphases1and3,measurementswereconducted
ignitionat550(cid:3)C.TodeterminetotalNcontent,sampleswere once per measurement day, whereas during the aeration
pipetted and weighed into tin capsules containing liquid phase(phase2)themeasurementswererepeated3times:one
absorbing pads. These were then analysed on an elemental 10 min before aeration, another immediately after aeration,
analyser (Carlo Erba, NA2000, Milan, Italy) connected to a and the final 15 min after aeration. Ambient and slurry
124 biosystems engineering 159 (2017) 121e132
temperatureofeachtank(atadepthof40cm)wasmeasured forthedifferentphasesoftheexperiment.Duringthefirstand
every minute using an automated data logger (Grant Data thirdphases,noaerationwasconductedandeachsampling
Acquisition Series 2040, UK). Changes in slurry temperature position was monitored for 7.5 min. The analyser continu-
duetoaerationwerethereforemonitored. ously cycled around the eight sampling positions, thus
Inaddition,theCH producingpotential(B )oftheslurryat completing a measurement cycle in 1 h. The instrument
4 o
the start of each storage phase was determined using an measuredgasconcentrationsevery10sandequilibrationof
automated laboratory incubation system (AMPTSII, Bio- theconcentrationreadingwhenswitchingbetweensampling
process Control, Lund, Sweden). Slurry samples were incu- points was about 3 min. The mean concentration at each
bated at 37 (cid:3)C with an inoculum obtained from a farm-fed sampling point for a given cycle was derived from the last
mesophilic anaerobic digester. To reduce direct production 3.5minofreadings(20concentrationmeasurements)ateach
ofbiogasfromtheinoculum,itwasincubatedinadvancefor5 samplingpoint,discardingtheinitial4minofreadings.Dur-
days at 37 (cid:3)C to deplete residual biodegradable organic ma- ingthesecondphasewhenaerationtookplaceevery6h,the
terial present. Samples were prepared for incubation in cycle described before was programmed to take place every
500 mL reactor bottles; each bottle contained 400 g of inoc- 2 h, alternating with 1 h of continuous monitoring of an
ulumandslurrysubstrateata2:1ratiobymassofinoculum aerated tank (from 10 min before aeration began to 48 min
VStosubstrateVS.Gasgeneratedfromtheincubationreactor afteraerationfinished).Eachtankwasmonitoredinthisway
bottles passed through a 3 M NaOH solution (with thy- duringtwodaysonceaweek.Thiswasdevisedtodetermine
molphthaleinpHindicator)toremoveCO andH Sgas,leav- theemissionprofileduringandafteraeration.
2 2
ing only CH to pass through the gas volume measuring Ammoniaconcentration measurements made by the Los
4
device,whichoperatesonaprincipalofbuoyancyandliquid Gatosanalyserwerecheckedagainstthosemadebysampling
displacement.Blanksamplesconsistingofjustinoculumwere airthroughacidabsorptionflaskstwiceperweekthroughout
included. The reactor bottles were stirred automatically at theexperiment.Theselattermeasurementsweremadeovera
110 rpm for a period of 60 s every 2 min. The system was 6-hperiodbysubsamplingtheairflowfromthetankoutlet
controlledviaaPC,andthegasflowrateandcumulativegas ducts or from the ambient sampling points and passing
volume produced from each reactor were normalised for throughacidabsorptionflasks(100mLof0.01Morthophos-
temperature and pressure and recorded continuously for 45 phoricacidperflask).Thequantityofammonia-Ntrappedin
days. the absorption flasks was determined by automated color-
imetryandwasdividedbythevolumeofairpassingthrough
2.3. Gaseousemissionmeasurements the flask to derive the concentration in the sampled air. A
linear correspondence was found between the automated
The slurry storage tanks were fitted with specially adapted measurements and acid trapping of NH , and thus all auto-
3
lids, which had a central circularhole of 10 cm diameterto matedmeasurementstakenwiththeLosGatosanalyserwere
whichafanwasfittedtodrawairfromthetankheadspace correctedaccordingly.
(Fig.1).Airwasdrawnintothetankheadspaceviatenholes Nitrousoxideconcentrationswereobtainedbytakinggas
aroundtheouteredgeofthelideachof3cmdiameter.Theair samples manually from the tank outlet ducts and ambient
wasexhaustedfromthetankheadspacebythefanthrougha sampling points, storing in evacuated glass vials and ana-
duct to an area outside the shed. The lids were left in-situ lysingbygaschromatography(GC;Clarus500,PerkinElmer,
throughout the storage period with fans running continu- Buckinghamshire,UK).Samplesweretakenontwooccasions
ously. Air flow rate was nominally 150 m3 h(cid:1)1, but was perweek.ThesamesampleswerealsoanalysedforCH and
4
measured at the duct outlet for each tank three times per CO concentrationbyGC,whichprovideddataforverification
2
week. The tanks with lids therefore acted as large dynamic ofthecontinuousanalyser.Duringthefirstandthirdphase,
chambers for emission measurements. Gas concentration when no aeration was conducted, only one gas sample was
measurementsweremadeviaacross-sectionalsamplingtube collected per tank. During the second phase of the experi-
withintheoutletductofeachtank.Inletconcentrationswere ment, three samples were collected per tank (one 10 min
alsomeasuredandattwoplaceswithintheshed.Estimatesof before,oneduring,andone15minafteraeration).
fluxforeachgas(F,gh(cid:1)1)wasmadeaccordingtothefollowing Hydrogensulphide(H S)wasmeasuredfortwodaysusing
2
equation: detection tubes (Draeger Safety). Spot measurements were
conductedtwotimesduringtheaerationphase,bothinthe
VðC (cid:1)CÞ
F¼ o i aerated and non-aerated tanks, to obtain an approximate
1000
valueofthepotentialemissionofthisgasduetotheaeration
whereV(m3h(cid:1)1)istheairvolumeflowrateandCoandCithe andmixingprocess.
outletandinletgasconcentrations(mgm(cid:1)3),respectively.
Gas concentrations were measured using Los Gatos ana- 2.4. Datatreatmentandstatisticalanalysis
lysers(Model911-0016forNH and915-0011forCH andCO ,
3 4 2
Los Gatos Research, California) based on cavity enhanced Thedatasetofcontinuousemissionfluxeswasintegratedto
absorption spectroscopy, with a multiport inlet unit (Model obtaindailyemissions(gday(cid:1)1)ofeachgas.Dailyaveragesof
908-0003-9002,LosGatosResearch,California).Samplingwas controlandtreatedtankswereobtainedandarepresentedto
on a semi-continuous basis with measurements from each describe the temporal evolution of emissions. A two-way
sampling position (6 tank duct outlets and 2 ambient air analysisofvariancewasconductedconsideringphase,treat-
samplingpositions).Twosamplingprotocolswereestablished mentandtheirinteractionasfactorsexplainingdifferencesin
biosystems engineering 159 (2017) 121e132 125
slurry composition and emissions. Differences were consid- dayofexperiment.Temperaturechangestendedtobehigher
eredstatisticallysignificantatP<0.05.Thestatisticalanalysis during the first aeration days than during the last ones.
wasconductedusingSAS. Figure3 showsthedailyevolutionoftemperature and tem-
Duringthesecondphase,theimmediateeffectofaeration perature changes in the aerated tanks at the aeration
onslurrytemperatureandemissionswasanalysedinquali- moments.
tative terms; measured values were integrated into a 1-min No statistical differences in pH were found between
timeresolutionandcompared tovaluesimmediately before treatments during the initial phase where no aeration was
aeration. conducted in any tank. However, during phase 2 pH was
significantlyhigherfortheaeratedthanforthecontroltanks
(Table1).TheaverageinitialpHofalltanksduringthisphase
3. Results was7.05.However,asshowninFig.2,pHincreasedsteadily
duringthefirsttwoweeksofaerationuntilitreachedvalues
3.1. Evolutionofslurrycharacteristics around 7.7. In contrast, the pH of control tanks remained
stableataround7.1.Inphase3,whenaerationhadfinished,
Theslurrycompositionandcharacteristicsatthestartofeach thepHoftheaeratedtankstendedtodecrease,butafter10
phasearepresentedinTable1.Slurrycomposition(drymat- daysofnoaerationitwasstillabout0.5pHunitshigherthan
ter, volatile solids, nitrogen content, ammonia content and inthecontroltanks,whichremainedconstant.
methane potential) did not differ among tanks assigned to SurfacepH(1cmdepth)isalsoshowninFig.2.Somedif-
differenttreatmentsatthestartoftheexperiment,andalsoat ficultieswerefoundwhenmeasuringsurfacepH,sinceacrust
thestartofphase2,beforeaerationwasinitiated.Afterphase formed during phases 2 and 3 in the control tanks. For this
2,drymattercontentofslurryincreasedinthecontroltanks reason,surfacepHvalueswereveryvariableandthusunre-
with respect to the aerated tanks, whereas no differences liable.Despitehavingahighervariability,surfacepHwasal-
werefoundfortherestofslurryproperties.Nitrateandnitrite ways higher at 1 cm depth than when measured at 10 cm
contentoftheslurrywasnegligiblecomparedtototalNcon- depth. Differences in pH between 1 and 10 cm depth were
tent(lowerthan1mgL(cid:1)1)throughouttheexperiment. about0.3unitsinalltreatmentsforthefirstphase,whenno
Daily averageambient temperatures rangedfrom 13.4 (cid:3)C aerationwasconductedonanytank.Duringphase2forthe
on28thJuneto22.5(cid:3)Con19thJuly,andrangedmostlyfrom14 aerationtreatment,thedifferencebetweensurfaceand10cm
to 18 (cid:3)C (Fig. 2). As the shed had no climate control, tank depthsurfacedecreasedwithtimeaspHat10cmincreased,
temperature oscillated with ambient temperature, and and at the end of the experiment this difference was
therefore changed between days and followed a sinusoidal about 0.05 units. In the control tanks this difference also
diurnal pattern with highest temperatures in the afternoon loweredduringphase2,andwasgenerallybetween0.1and0.2
and lowest temperatures early in the morning. Within each units.
phase,averageslurrytemperaturesdidnotdiffersignificantly The loss of slurry volume at the end of the experiment,
betweentreatments,asshowninTable1. comparedtothestart,wassimilaramongalltreatmentsand
Theaerationhadanimmediatebutnon-permanenteffect wasabout10%oftheinitialvolume.
onslurrytemperature.Changesfromanincreaseof0.6(cid:3)Ctoa
decreaseofmorethan1(cid:3)Cweredetectedimmediatelyafter 3.2. Gasemissions
aeration compared to before aeration. However, this effect
was slight and inconsistent, and therefore no clear pattern For NH3 concentrations, the comparison between the auto-
was obtained. The changes in slurry temperature varied mated analyser and the reference acid trapping method
amongtanks,anddependedonthetimeofthedayandonthe showed a linear relationship (R ¼ 0.96, P < 0.05, details not
Table1eSlurrycharacteristicsatthestartofeachphase(totalsolids,volatilesolids,totalN,ammoniumN,nitrateand
nitrite).Methanepotential(B )isalsoprovidedfortheinitialslurry.AveragevaluesofpH,temperatureandgasemissions
0
duringeachphasearealsoprovided.Withineachphase,valueswithdifferentlettersinthesamerowindicatestatistical
differencesbetweentreatments(P<0.05).Standarderrors(S.E.)andP-valuesfortheeffectsofTreatment(T),phase(P)and
theirinteraction(T£P)arealsoindicated.Non-significantdifferences(n.s.)areconsideredforP>0.05.
Phase1 Phase2 Phase3 S.E. P-values
Control Aeration Control Aeration Control Aeration T P T(cid:4)P
Totalsolids(TS,gkg(cid:1)1) 2.49a 2.60a 2.85ab 2.72a 3.14b 2.74a 0.12 n.s. 0.023 n.s.
Volatilesolids(gkg(cid:1)1TS) 675 683 690 678 690 672 8.9 n.s. n.s. n.s.
TotalN(gkg(cid:1)1) 3.97 4.12 4.10 4.26 4.13 4.04 0.09 n.s. n.s. n.s.
AmmoniumN(gkg(cid:1)1) 3.02 3.03 2.93 2.97 3.07 2.93 0.04 n.s. n.s. n.s.
Bo(m3CH4kg(cid:1)1VS) 0.76 0.71 0.64 0.70 0.60 0.69 0.04 n.s. n.s. n.s.
pHat10cmdepth 7.06a 7.03a 7.05a 7.50b 7.09a 7.65c 0.02 <0.001 <0.001 <0.001
Slurrytemperature((cid:3)C) 16.10abc 16.18ab 15.68a 16.03ab 17.68bc 17.88c 0.61 n.s. 0.015 n.s.
NH3emission(gm(cid:1)3day(cid:1)1) 7.14a 6.81a 7.07a 8.48b 9.35b 11.19c 0.38 0.009 <0.001 0.034
CH4emission(gm(cid:1)3day(cid:1)1) 4.33a 4.24ab 3.39b 2.04a 4.99a 1.62a 0.28 <0.001 <0.001 <0.001
CO2emission(gm(cid:1)3day(cid:1)1) 120.5d 107.1cd 90.4b 97.3bc 85.6b 67.9a 4,8 n.s. <0.001 n.s.
126 biosystems engineering 159 (2017) 121e132
22 Aera(cid:415)on
Control
Ambient
20
C)
º
e (
ur
at
er 18
p
m
e
T
16
14
Phase 1 Phase 2 Phase 3
12
08/06 13/06 18/06 23/06 28/06 03/07 08/07 13/07 18/07
Fig.2eEvolutionofdailytemperature(left)foraerationtanks( ),controltanks( )andambienttemperature( ).
EvolutionofpH(right)at10cmdepthofaeration( )andcontroltanks( ).pHmeasuredat1cmdepthisalsoindicated
foraeration( )andcontroltanks( ).Standarderrorsofmeansareprovidedaserrorbars(n¼3).Thephasesofthe
experimentarealsoindicated:Phase1:noaerationconductedinanytank;Phase2:aerationconductedonlyintheaeration
tanks;Phase3:noaerationconductedinanytank.
shown) within the range of concentrations measured (be- were significantly higher in the aerated than in the control
tween 0 and 6 mg m(cid:1)3). However, the automated system tanks(20%inbothphases,Table1andFig.6).
overestimatedtheresultsfromtheacidtrappingby54%,and Methaneemissionstendedtobestablethroughouttheday,
thisbiaswasthereforecorrectedbeforedataanalysis.ForCH andduringphases2and3werehigherinthecontrolthanin
4
and CO measurements, no significant differences were the aeratedtanks(Fig.6).However,aerationcauseda sharp
2
detected between the automated measurement system and releaseofCH duringtheaerationevent(Fig.4).Theemission
4
theanalysisofsamplegasesbygaschromatograph. duringthisshortperiodwasabout1000timeshigherthanthe
Nostatisticaldifferencesbetweentreatmentswerefound baselineemission.DespitethefactthattheseoutburstsofCH
4
forNH ,CO orCH gaseousemissionsduringthefirstphase, lastedforshorttime,duetothehighmagnitudeoftherelease
3 2 4
whennoaerationwasconductedatanytank(Table1).How- intheaerationevents,theycontributedamajorproportionof
ever, aeration during phase 2 significantly increased NH total CH emissions from the aerated tanks during phase 2.
3 4
emissions by 20% and reduced CH emissions by 40%. This Between70and80%oftotalCH emissionsemittedfromthis
4 4
effectwasnotonlydetectedduringphase2,butalsoduring treatment were produced during or in the few minutes
phase3,afteraerationhadfinished. followingtheaeration(Fig.6).Intheaeratedtanks,bothCH
4
TheshorttermeffectsofaerationonNH andCH emis- emissionsduringaerationandbaselineemissionsdecreased
3 4
sionsareshowninFig.4,wherethedailyevolutionofemis- exponentiallyoverthefirstdaysofthesecondphase(Fig.5),
sions is presented. Ammonia emissions followed a daily whereastheemissionlevelofthecontroltankswasrelatively
sinusoidalpatterninaccordancewithtemperaturevariation. constant(Fig.6).TotalCH emissionsfromaeratedtankswere
4
During the first days of phase 2, NH emission did decrease significantlylowerthaninthecontroltanks,notonlyinphase
3
during and immediately after aeration, but after a few mi- 2,butalsoinphase3(Table1).
nutesitrecoveredtoinitialvalues,orevenhigher(Fig.4).By ThebehaviourofCO emissionsfollowedasimilarpattern
2
the end of phase 2 emissions increased during the aeration to CH emissions, with very high emissions during and
4
andthisincreaseremainedafteraerationceased.Thesevar- immediately after the aeration. Some problems with the
iations, however, accounted for a small share of total emis- analyser related to overnight measurements prevented the
sionsbecauseoftheirlowmagnitudeandduration.Emissions calculationofdailyaveragesforalldays,asobtainedforNH
3
duringthe2-minaerationeventsincreasedslightlywithtime, and CH ,andthereforedetailsarenotshown.However,the
4
asshownin Fig.5, andat theendofphase 2wereapproxi- evolutionofemissionsduringtheaerationeventswasmoni-
mately double with respect to the beginning of that phase. tored (Fig. 5),showinga verysimilartendencyto CH .From
4
Overall, the average NH emissions during phases 2 and 3 theavailabledatawefoundnosignificantdifferences,either
3
biosystems engineering 159 (2017) 121e132 127
Fig.3eDailyvariationinslurrytemperatureacross2dayatthebeginning(18thJune)andattheend(9thJuly)ofthe
aerationphase.Controltanksareshowningreen(Control1insolidline,Control3indashedline).Aerationtanksare
showninblue(Aeration1insolidline,Aeration2indashedline,Aeration3indottedline).Ambienttemperatureisalso
showninred.Thefouraerationeventsduringthedayareindicatedwitharrows.
forphase2orphase3(Table1),whileingeneralCO emissions
2
4. Discussion
decreased with time, being significantly lower in phase 3
comparedwithphase1.
Theaerationofstoredslurryproducedslightchangesinthe
Nitrous oxide concentrations measured at the tank
main chemical properties, significant changes in slurry pH,
exhaustairwerenotsignificantlydifferentfromtheinletairat
increased NH emissions, whereas increased oxygen supply
anytankandatanymomentoftheexperiment,andtherefore 3
reducedCH emissions.Furthermore,theseeffectsshowedan
N O emissions were considered to be negligible and not 4
2
evolutionovertheweeksoftheexperiment.Predominantly,
affectedbytheslurrytreatmentsystem.Fromthespotmea-
the low frequency aeration affected three main parameters
surements of H S, it was found that concentrations were
2
(pH, temperature and crusting), resulting in very different
lowerthanthedetectionlimitofthecolorimetrictubesused
(<0.5ppm)forthecontroltanks,andalsofortheaeratedtanks behaviourofemissionswithrespecttothecontroltanks.
Aeration of slurry had a combined effect of mixing and
when no aeration was being conducted. In contrast, during
oxygenating.Asreportedthroughpreviousresearch(Blanes-
aeration a sharp increase in H S concentration was found
2 Vidal,Guardia,Dai,&Nadimi,2012;Nietal.,2000;Petersen,
(between 60 and 80 ppm), which involved an emission of
roughly4e5mgm(cid:1)3s(cid:1)1. Markfoged, Hafner, & Sommer, 2014), aeration initiated a
128 biosystems engineering 159 (2017) 121e132
Fig.4eExampleoftheeffectofshorttermaerationonNH emissionatthestartofphase2(18thJune,upper)andattheend
3
ofphase2(9thJuly,centre).Ontheleft,thedailyvariationinemissionsinoneoftheaeratedtanks(solidline)andthe
averageemissionforallcontroltanks(dashedline)areplotted.Ontheright,thedetailacrossoneaerationeventisprovided.
TheeffectofaerationonCH emissionsisalsoplottedfor1dayattheendofphase2(9thJuly,lower,pleasenotethe
4
logarithmicscale).
mixing of the slurry and disturbed the pH gradient, thus duringthelastdaysoftheaerationphaseverylittledifference
reducing the pH at the slurry surface and thus the NH wasdetectedbetweensurfaceandbulkpH,andasbothwere
3
emissions. This effect was clearly detected only during the relatively high (about 7.7), NH was stripped to the atmo-
3
first days of treatment and had a very short duration, since sphereduringtheaerationevents.
emissions returned to similar levels after a few minutes. Crustingcanalsoaffectammoniaemissions.Theaerated
Despite the short duration, aeration increased the bulk pH tanks were mixed during the aeration process four times a
overthemediumterm,presumablybecauseofthedegrada- day, whereas control tanks were not stirred at all. Conse-
tionofvolatilefattyacids,asreportedpreviously(Fangueiro quently,acrustformedinthecontroltanks(visualobserva-
et al., 2015; Sørensen & Eriksen, 2009; Zhang & Zhu, 2005). tion),whichwasnotthecasefortheaeratedtanks.Although
According to our results, the medium term and permanent thecrustwasremovedduringtheslurrysamplinginalltanks
riseinpHhadmoreinfluenceonNH emissionsthantheshort (at the beginning of each experimental phase), it re-
3
term and transitory decrease in surface pH. Furthermore, establishedwithinafewdaysifnoaerationwasconducted.
biosystems engineering 159 (2017) 121e132 129
25 1400
CH4 CO2 NH3
1200
20
1000
-1g h) 15 800 -1g h)-1)mg h
CHemissions (4 10 600 COemissions (2NHemissions (3
400
5
200
0 0
15/06 20/06 25/06 30/06 05/07 10/07 15/07
Date
Fig.5eEvolutionofemissionfluxesofNH (triangles)CH (crosses)andCO (rectangles)duringtheaerationevents,during
3 4 2
phase2.
SincecrustformationhasbeenidentifiedasapotentialNH wasexpectedtobelowcomparedtothemoreevidenteffects
3
mitigation strategy (Misselbrook et al., 2005; Wood, Gordon, ofpHchangesinthemediumterm.
Wagner-Riddle,Dunfield,&Madani,2012),theeffectofcrust As expected, low frequency aeration of slurry decreased
removal could also have contributed to higher emissions in CH . However, high amounts of CH were released during
4 4
theaeratedtanks. aerationevents,leadingtoevenhigheremissionsduringthe
Longer aeration times have been reported to increase firstdaysoftreatment.Asreportedintheliterature(Amon,
slurrytemperatureasaconsequenceoftheaerobicdegrada- Kryvoruchko, Amon, & Zechmeister-Boltenstern, 2006;
tion of organic matter (Burton, 1992; Heinonen-Tanski, Nis- Blanes-Vidal et al., 2012; Dai & Blanes-Vidal, 2013), the sol-
kanen, Salmela, & Lanki, 1998). However, no reports are ubility of CH in water is very low, and therefore the CH
4 4
available on the effect of very short aeration times such as produced in the slurry is kept in small bubbles before
thoseusedinthisstudy.Thetemperaturechangesdetected escaping to the atmosphere. During the first days of aera-
due to the aeration lead to no clear interpretation, because tion,CH isstillproducedbecauseeasilydegradableorganic
4
bothincreasesanddecreasesoftemperatureweredetected. matterisstillavailable,andlowfrequencyaerationprobably
The effect of aeration on temperature tended to be higher did not completely preclude the necessary anaerobic con-
duringthefirstdaysofaeration.Thismayindicatetheeffect ditions. However, following low frequency aeration for
of aerobic degradation processes, as more easily degradable several days, readily available organic matter such as vola-
organicmattermaybeexpectedtobepresentintheslurryat tilefattyacidstendtobeaerobicallydegraded(Burton,1992;
thebeginningoftheaerationphase.Incontrast,temperature Zhang & Zhu, 2006), thus reducing the potential for CH
4
decreaseswerealsodetected,andthiscouldbeaconsequence generation. On the contrary, aeration in this case was not
of enhanced water evaporation and sensible heat transfer relatedwithincreasedN Oemissions.Itseemsthatoxygen
2
duringtheaerationprocess.However,theenergyremovalby supply was not enough to enhance nitrification processes,
water vapour evaporation during the short time of aeration which are required to emit relevant amounts of this gas.
(only2min)wasroughlyestimatedfrommeasuredvaluesof This is evidenced by the low content in oxidised species
temperature and relativehumidity. Thesecalculations(data (nitrites and nitrates) in both control and aerated
notshown)indicatethattheheatremovedfromwaterdueto treatments.
evaporation would decrease the slurry temperature by no Itmustbeconsideredthatthiswaspilotstudyconducted
more than 0.05 (cid:3)C. The decrease in slurry temperature was underspecificconditions.Extrapolationoftheseresultstoreal
double-checked with different temperature probes, so in- farmconditionsmusttakeintoaccountdifferencesinslurry
strumentmalfunctionwasnotconsideredtobeareason,and volume (and surface area to volume ratio), slurry manage-
theremayhavebeenotherinfluencingfactorsnotconsidered mentstrategiesandambientconditions.Changesinthescale,
inthisanalysis.Inanycase,temperaturechangeswereoflow frompilottofarmslurrytanks,havebeendescribedforaer-
magnitude(typicallylessthan0.5(cid:3)C),andthereforethiseffect obictreatments(Sneath,Burton,&Williams,1992)andthese
130 biosystems engineering 159 (2017) 121e132
wouldbeofrelevancetoourstudybecauseofdifferencesin reduced gradually after aeration finishes. Specific research
the volume and homogeneity of aeration and their derived would confirm the effects of aeration at longer times, but a
effects(oxygenationandmixing).Althoughsimilareffectson veryrelevantdecreaseinNH emissionswouldbeneededto
3
slurry pH and emissions may be expected from tanks counteracttheinitialincreasedemissions.Finally,changesin
managed in a similar way as in this study, this could be theambientconditions(particularlythetemperature)would
confirmed with on-farm slurry tank measurements. On the probably affect these results. According to the literature,
contrary, differences may be expected for different slurry temperature affects directly the emissions of CH
4
managementstrategies.Thisstudymimicsanexternalslurry (Haeussermann, Hartung, Gallmann, & Jungbluth, 2006) and
store without addition of fresh slurry. This study is almost NH (Misselbrooketal.,2016).Therefore,itmaybeexpected
3
certainly not representative of under-slat slurry storage, thattheeffectsoflowfrequencyaerationwouldincreasewith
where fresh urine and faeces are continuously added from temperature.However,thismustbeconfirmedwithspecific
animalexcretions. research.
The behaviour of external slurry storages with frequent Inconclusion,shortfrequencyaerationofstoredslurryas
additionoffreshslurrymayalsobedifferentbecauseofthe testedinthisstudycannotbe consideredan optiontomiti-
continuousincorporationofuntreatedslurry,forexamplein gateNH emissions.SlurrymixingreducedthepHgradientin
3
continuous reactors (Loyon, Guiziou, Beline, & Peu, 2007). theslurrysurfacebutthiseffectdidnotcompensatethepH
Also, longer slurry storage times than in this study occur increase in the slurry, and therefore NH emissions
3
underfarmconditions.OurresultssuggestthatpHdifferences increased.CH emissionsdecreasedbyapproximately40%in
4
remainaslongastheaerationphasecontinues,butpHmaybe spite of the short duration of aeration. No N O emissions
2
were detected and therefore, this treatment reduced green-
house gas emissions. The applicability of these results at
differentconditionstothoseinthisstudymustbeevaluated
inpractice.
Acknowledgements
NorthWykeFarmandtechnicalsupportstaff.Mr.R.Knox,Tor
Pigs,Devon,UKforprovidingslurry.SpanishMinistryofEd-
ucation, Culture and Sports, in the framework of the State
ProgrammetoPromoteTalentandEmployabilityinRþDþI,
Sub-programonMobilityofthePlanonScientificandTech-
nical Research and on Innovation 2013e2016, and Spanish
Ministry of Economy, Industry and Competitiveness (Project
AGL2014-56653-C3-2-R).RothamstedResearchissupportedby
the UK Biotechnology and Biological Sciences Research
Council.
references
Amon,B.,Kryvoruchko,V.,Amon,T.,&Zechmeister-
Boltenstern,S.(2006).Methane,nitrousoxideandammonia
emissionsduringstorageandafterapplicationofdairycattle
slurryandinfluenceofslurrytreatment.Agriculture,
Ecosystems&Environment,112(2e3),153e162.http://doi.org/10.
1016/j.agee.2005.08.030.
Be(cid:3)line,F.,&Martinez,J.(2002).Nitrogentransformationsduring
biologicalaerobictreatmentofpigslurry:Effectof
intermittentaerationonnitrousoxideemissions.Bioresource
Technology,83(3),225e228.http://doi.org/10.1016/S0960-
Fig.6eDailyaverageemissionsofNH (upper)andCH 8524(01)00219-X.
3 4 Be(cid:3)line,F.,Martinez,J.,Chadwick,D.,Guiziou,F.,&Coste,C.-M.
(lower)duringtheexperiment.Emissionsfromcontrol
(1999).Factorsaffectingnitrogentransformationsandrelated
tanksarerepresentedwithsolidlinesandfromaeration
nitrousoxideemissionsfromaerobicallytreatedpiggery
tankswithdashedlines.ForCH4emissionsfromaeration slurry.JournalofAgriculturalEngineeringResearch,73(3),
tanks,duringphase2twovaluesareprovided.Firstly,the 235e243.http://doi.org/10.1006/jaer.1999.0412.
emissionaccumulatedduringthewholedayexceptfor Bicudo,J.(1995).Intermittentaerationofpigslurryefarmscale
16minduringandafteraerationperiods(dottedline);and experimentsforcarbonandnitrogenremoval.WaterScience
andTechnology,32(12),83e90.http://doi.org/10.1016/0273-
secondly,totalemissionswhenaddingthereleaseduring
1223(96)00141-2.
andafteraeration(dashedline).