Fate of Coliform Bacteria in Composted Beef Cattle Feedlot Manure
Fate of Coliform Bacteria in Composted Beef Cattle Feedlot Manure
Francis https://www.wendangku.net/doc/4413038801.html,rney,*L.Jay Yanke,James https://www.wendangku.net/doc/4413038801.html,ler,and Tim A.McAllister
ABSTRACT manure pile that was exposed to environmental con-
ditions.
The link between livestock production,manure management,and
A rapid increase in the number of intensive livestock human health has received much public attention in recent years.
operations in Alberta over the past decade has com-Composting is often promoted as a means of sanitizing manure to
pelled many farmers to seek alternative methods to ensure that pathogenic bacteria are not spread to a wider environment
during land application.In a two-year study(1998and1999)in south-direct land application of raw manure.By2002,the ern Alberta,we examined the fate of coliform bacteria during windrow adoption of manure composting had increased to at least composting of cattle(Bos taurus)manure from feedlot pens bedded12feedlots in Lethbridge County,in southern Alberta. with cereal straw or wood chips.Numbers of total coliforms(TC)Composting allows transportation of nutrients(espe-and Escherichia coli declined as the composting period progressed.cially nitrogen and phosphorus)from high nutrient-In1998,TC levels(mean of both bedding types)were log107.86cells loading areas and also reduces odor complaints at land
g?1dry wt.for raw manure on Day0,log103.38cells g?1by Day7,
application(Rynk,1992).It eliminates the parasitic pro-and log101.69cells g?1by Day14.More than99.9%of TC and E.
tozoa Giardia and Cryptosporidium(McAllister,un-coli was eliminated in the first7d when average windrow temperatures
published data,1999)and reduces weed seed viability ranged from33.5to41.5?C.The type of bedding did not influence
(Larney and Blackshaw,2003).The principal mode of the numbers of TC or E.coli.Dessication probably played a minor
disinfection during composting is based on time–tem-role in coliform elimination,since water loss was low(?0.07kg kg?1)
in the first7d of composting.However,total aerobic heterotroph perature relationships that destroy pathogens,although populations remained high(?7.0log10CFU g?1dry wt.,where CFU antagonistic microorganisms and ammonia may also is colony forming units)throughout the composting period,possibly play a role(Epstein,1997;Himathongkham and Rie-causing an antagonistic https://www.wendangku.net/doc/4413038801.html,nd application of compost,with its mann,1999).For pathogen elimination during windrow nondetectable levels of E.coli compared with raw manure,should composting of biosolids,temperatures should be main-minimize environmental risk in areas of intensive livestock pro-tained at?55?C for15d or longer(USEPA,1992). duction.During this period,the windrow should be turned a
minimum of five times.Similar guidelines exist in Can-
ada,which also state that final composts should contain T here is growing public concern about the link be-?log103cells g?1dry wt.of fecal coliforms(Canadian tween livestock production and water contamina-Council of Ministers of the Environment,1996).
tion by pathogenic bacteria.This is especially true for However,even though the elimination of pathogens land application of raw manure,which potentially by composting has been well documented(De′portes et spreads pathogens to a wider environment(Bach et al.,al.,1998;Krogmann et al.,2002;Tiquia et al.,2002), 2002;Kudva et al.,1998;Pell,1997).Entry and Farmer composting regimes(time,temperature)required to (2001)reported fecal coliform bacteria(which originate achieve elimination of TC,E.coli,or other pathogens from the intestinal tracts of warm-blooded animals)in vary widely.Turner(2002)demonstrated inactivation ground water flowing from an Idaho aquifer.Gagliardi of E.coli in farmyard manure,pig(Sus scrofa)feces, and Karns(2000)demonstrated that if Escherichia coli and cereal straw after only2h at55?C.In contrast, reached soil,via manure spreading or runoff from a Schleiff and Dorn(1997)reported that E.coli could be point source,it could survive,replicate,and move down-cultured from dry poultry(Gallus gallus domesticus) ward for up to two months,threatening nontarget envi-manure after88d of composting.Pathogen reduction ronments.with increasing time was shown by Himathongkham Escherichia coli O157:H7is one of the many strains and Riemann(1999),who reported that while E.coli of the bacterium E.coli.In Canada,E.coli O157:H7–O157:H7was able to grow for2d in fresh chicken
contaminated water caused seven deaths and made manure at20?C,with a resulting1to2log
10unit increase
more than2000people ill in Walkerton,Ontario in May in colony forming units(CFU),increasing storage time
2000.The outbreak was linked to contamination of the to6d decreased populations by3to4log
10units.The
town’s water supply from land application of livestock effect of higher temperatures on reducing the time re-manure on a nearby farm(O’Connor,2002).Even land quired for pathogen reduction was illustrated by Hima-application of stockpiled manure poses a threat,since thongkham et al.(1999),who reported a105–fold reduc-Kudva et al.(1998)reported that E.coli O157:H7sur-tion in E.coli O157:H7after105d at4?C or45d at37?C vived for more than one year in a nonaerated ovine in a laboratory incubation with cattle manure.Also,
Droffner and Brinton(1995)found that E.coli survived
for59d at60?C,compared with only9d at60to70?C Agriculture and Agri-Food Canada,Research Centre,54031st Ave.in an inoculated laboratory food waste compost.
S.,Lethbridge,Alberta,Canada T1J4B1.Lethbridge Research Centre
Contribution no.38702070.Received10Sept.2002.*Corresponding
author(larney@agr.gc.ca).
Abbreviations:CFU,colony forming units;MDL,minimum detection
level;TAH,total aerobic heterotrophs;TC,total coliforms. Published in J.Environ.Qual.32:1508–1515(2003).
1508
LARNEY ET AL.:COLIFORM BACTERIA IN BEEF CATTLE FEEDLOT MANURE1509
and24.7for wood chip–bedded manure in1998and14.4for The mechanism for removal of pathogens during
straw-and23.6for wood chip–bedded manure in1999. aerobic composting may not simply be a result of the
In1998,the windrows were turned16times(Days3,7,10, thermal environment.Turner(2002)indicated that patho-
14,17,21,24,28,31,38,45,52,66,73,94,and108of compost-gen inactivation was not merely dependent on tempera-
ing)with a tractor-pull EarthSaver windrow turner(Fuel Har-ture but was also affected by water content and nature vesters Equipment,Midland,TX).This turning frequency was
of the substrate.If incomplete inactivation occurred due higher than at most commercial feedlots in southern Alberta
to low temperatures,recovery and regrowth of the dam-(approximately five to seven times over a90-d period).In
aged pathogenic populations may be possible.In a study1999,the windrows were turned seven times(Days7,14,21,
on composted dairy waste solids as recycled bedding,
29,42,56,and70),which was closer to the turning frequency
at commercial feedlots.Turning was more frequent in the Mote et al.(1988)found that even though there was an
early stages of composting to stimulate thermophilic(?40?C) initial decline or even a disappearance of TC due to
microbial activity and became less so as composting pro-composting,the bacteria reestablished in large numbers
gressed and microbial activity diminished.After the active without reinocculation.Droffner et al.(1995)presented composting phase(turning)the material entered a“curing”
evidence for the survival of E.coli in active compost phase(no turning)for a further90to100d until windrow
that indicated that,although classified as a mesophile,temperature approached ambient.
it had a mechanism for survival and perhaps replication
at elevated temperatures(?60?C).Compost Sampling
Although pathogen elimination is a recognized bene-
Compost sampling for bacterial enumeration coincided with fit of composting,the lack of definitive relationships
turning and sampling for chemical and physical properties between elimination and composting duration,sub-
(Larney et al.,2001).In1998,windrows were sampled eight strates,and temperature conditions prompted a study
times:at establishment(Day0)and just before turning on on the fate of coliform bacteria during open-air windrow Days7,14,21,28,45,66,and94.There were nine sampling
composting of beef feedlot manure in southern Alberta.times in1999:at Day0and just before turning on Days7,14,
Since there has been a recent increase in the use of21,28,42,56,and70,as well as Day91(no turning event).
byproducts from Alberta’s forest industry(wood chips,In1998,the sampling protocol involved cutting each of the
shavings,sawdust)as alternative bedding to traditional
compost windrows in three places(east,center,and west of
windrow)with a skid-steer loader to expose six vertical faces. cereal straw for feedlot cattle(McAllister et al.,1998),
Three of the faces(one each from east,center,and west)were we compared manure from feedlot pens bedded with
sampled at three vertical locations(top,middle,bottom).The straw or wood chips.There is some evidence to suggest
vertical location samples from each face were composited to that wood products contain antimicrobial compounds give three subsamples(east,west,center)per windrow.Each
that may inhibit bacterial levels(Allison and Anderson,sampling time had a total of12samples(two bedding types?
1951;Kudva et al.,1998).two replicates?three horizontal locations).In1999,the sam-
This is the first study of its kind in the intensive feedlot pling protocol varied in that the vertical locations were kept
area of southern Alberta,where manure management
separate.Two faces exposed in the center of the windrow
were sampled at three vertical locations(top,middle,bottom). practices are coming under increased public and media
The vertical location samples from each face were then com-scrutiny.It sought to quantify the duration of compost-
posited to give three samples(top,middle,bottom).Each ing and accompanying windrow temperatures required
sampling time had a total of12samples(two bedding types?to achieve coliform population reductions under typical
two replicates?three vertical locations).
field conditions.
Bacterial Enumeration MATERIALS AND METHODS Total coliforms,E.coli,and total aerobic heterotrophs
(TAH)were enumerated in our study.Total coliform bacteria Windrow Establishment and Turning
are excreted in high numbers in animal and human feces,and The study was performed at the Agriculture and Agri-Food are often used as indicators of fecal contamination in water Canada Research Centre,Lethbridge,Alberta during the sum-and food,even though not all TC bacteria are of fecal origin. mers of1998and1999.Manure was removed with a loader We did not use TC data as an indicator of fecal contamination, and truck from feedlot pens,which had been bedded with since clearly,fecal contamination is inapplicable when working barley(Hordeum vulgare L.)straw or wood chips,and depos-with cattle manure.The TC data were used to examine persis-ited into windrows.The wood chips were a mixture of sawdust tence and potential regrowth during the composting process, and bark peelings derived from80%lodgepole pine(Pinus since the behavior of pathogenic groups may be better repre-contorta https://www.wendangku.net/doc/4413038801.html,tifolia Engelm.)and20%white spruce[Picea sented by TC than by more specific E.coli data.We feel that glauca(Moench)Voss].Windrows were established on22following TC populations in a known experimental sample June1998and20July1999on a concrete pad in an open-(manure)as it changes over time(to compost)gives relevant sided roofed composting facility so that they were exposed to data on environmental fate.Escherichia coli is a member of ambient air temperatures but not precipitation.There were the fecal coliform group,a subset of the TC group,and its two replicates of each bedding material for a total of four presence can be used as a surrogate for specific pathogenic windrows,each on an east–west orientation.At establishment E.coli strains.Ogden et al.(2001)reported that since the die-(Day0)windrows were10.6to11.4m long,approximately off rate of E.coli O157was the same as that of the commensal 2.5m wide at the base,and approximately2m high.Carbon E.coli population in a laboratory study,the field behavior of to nitrogen ratios(dry combustion in an automated elemental E.coli O157in a cattle slurry application study could be C:N:S analyzer;Carlo Erba,Milan,Italy)were19.0for straw-
approximated by monitoring the population of E.coli.Total
1510J.ENVIRON.QUAL.,VOL.32,JULY–AUGUST2003
aerobic heterotroph levels indicate the overall magnitude of
indigenous microbial activity in decomposing organic matter.
Fresh compost samples(10g wet wt.)were added to90mL
of sodium phosphate buffer(pH6.5,0.05M)and mixed in a
Stomacher blender(Model400;Seward Medical,Mississauga,
ON,Canada)for2min.The suspension was serially diluted
to the appropriate levels in sodium phosphate buffer.The
dilutions were inoculated(1mL)into triplicate Fluorocult
LMX broth tubes(9mL;Merck KGaA,Darmstadt,Germany)
and incubated aerobically at37?C for enumeration of TC and
E.coli by the most probable number(MPN)method.Total
coliforms were enumerated after48h as those tubes with
hydrolysis of5-bromo-4-chloro-3-indolyl-?-D-galactopyrano-
side(X-Gal).Escherichia coli was enumerated after24and
48h as those tubes with hydrolysis of both X-Gal and
4-methylumbelliferyl-?-D-glucuronide(MUG).Selected col-
onies of presumptive TC and E.coli were isolated from posi-
tive tubes on Fluorocult LMX agar plates for identity confir-
mation using membrane fatty acid composition,cellular
morphology,and biochemical characteristics(Smibert and
Krieg,1994;Paisley1996;Garthwright,1998).Samples posi-
tive for coliforms were confirmed positive by isolation in
96.7%of the cases.In a few cases coliform bacteria were not
isolated,while enterococci were.The data were not corrected
for these false positive samples since the TC results would
change only marginally.All samples positive for E.coli were
confirmed positive by pure culture isolation and identification.
The TC and E.coli enumerations are presented as log10
cells g?1dry wt.Water content of compost subsamples(oven-
drying at60?C for48h)was used to express values on a dry
weight basis.For both enumerations,the minimum detection
level(MDL)was log100.56cells g?1wet wt.We assumed an
average compost water content of0.5kg kg?1to maintain a
constant MDL across all sampling dates and present data on
a dry weight basis.The MDL of log100.56cells g?1wet wt.is
equivalent to log100.86cells g?1dry wt.at a compost water
content of0.5kg kg?1.For determining treatment means,
values?MDL were assigned a value of50%of the MDL Fig.1.Effect of bedding type on total coliforms(mean across loca-(after converting to dry weight),which explains the presence
tions?SE,n?6)in(a)1998and(b)1999.Bedding type(1998,
1999)and bedding?location interaction(1999)effects were non-of data points?MDL in the figures presented.
significant on all sampling dates.
The serial dilutions were also spread-plated(100?L)in
triplicate onto tryptic soy agar plates for enumeration of TAH
Although water content was determined on the bacterial (as log10CFU g?1dry wt.)after incubation at39?C for48h.
compost samples(to convert enumeration data to a dry weight
basis),larger compost samples(approximately0.6kg)were Compost Temperature and Water Content taken to track water content(after oven-drying at60?C for
48h)during composting.In1998,the six vertical faces were Thermocouples and a datalogger(Sciemetric,Nepean,ON,
sampled at three(top,middle,and bottom)locations,giving Canada)were installed as soon as the windrows were formed.
18samples per replicate.In1999,samples were taken at the They were removed just before each turning and reinstalled top,middle,and bottom locations of the two exposed vertical immediately after turning.Temperatures were logged every faces giving six samples per replicate.
20min and averaged to give mean daily values.In1998,three
thermocouples(bottom,middle,top)were attached to each
Statistical Analyses
of three stainless steel pipes.The pipes were then placed
vertically in one replicate of each bedding treatment near the In1998and1999,the effect of bedding on TC,E.coli, center of the windrow,and about2m from the east and west and TAH populations was examined using the general linear ends.The bottom location was approximately0.3m,the center models procedure(SAS Institute,1990).Additionally,in1999, location approximately0.6m,and the top location approxi-the vertical location effect(bottom,middle,top)was examined mately0.9m above ground level.Datalogger malfunction as a subtreatment in a split-plot design with bedding as the resulted in missing temperature data for Days13and14,30main treatment.
through33,and50.In1999,temperatures were measured at
three vertical locations(as in1998:bottom,middle,and top)RESULTS
in three windrow positions:the east and west ends of the one
replicate of each manure bedding treatment(approximately Total Coliforms
25%and75%along its length),and the center of the other
In1998,there was a large decline in TC as composting replicate of each treatment.These nine temperatures were
progressed and populations were not affected by bed-averaged to give the bedding treatment means.The bedding?
ding type on any sampling date(Fig.1a).Values aver-vertical location(n?3)means were also calculated to examine
the location effect.aged log107.86cells g?1(dry wt.)on Day0,decreasing
LARNEY ET AL.:COLIFORM BACTERIA IN BEEF CATTLE FEEDLOT MANURE
1511
Fig.2.Effect of vertical windrow location on total coliforms (mean across bedding types ?SE,n ?4)in 1999.Bedding type and bedding ?location interaction effects were nonsignificant on all sampling dates.
to log 103.38cells g ?1by Day 7,and log 101.69cells g ?1by Day 14.To put this in perspective,99.997%of TC were eliminated in the first 7d.The TC were detectable on all sampling dates except for the wood chip–bedded compost on Day 45.On Day 94,TC levels averaged exactly the same as Day 14,and about sevenfold higher than Day 45(log 100.86cells g ?1),indicating some re-growth.In 1999,the effect of bedding type on TC was also nonsignificant (Fig.1b).The trend with time was similar to 1998in that TC levels declined significantly in the early stages of composting (approximately 3log 10Fig.3.Effect of bedding type on E.coli (mean across locations ?units from Days 0–7,and a further 3.2log 10units from SE,n ?6)in (a )1998and (b )1999.Bedding type (1998,1999)Days 7–14).The slight resurgence in TC levels,evident and bedding ?location interaction (1999)effects were nonsignifi-toward the end of active composting in 1998,did not cant on all sampling dates.
occur in 1999(Fig.1b),possibly because the population declined to a greater extent.The TC levels were ?MDL in straw-and wood chip–bedded material by Day 21(Fig.3a).In 1999,the E.coli trends were similar with in 1999(Fig.1b),but were detectable until Day 94in a nonsignificant bedding effect (Fig.3b)and a dramatic 1998(Fig.1a).
drop in levels in the early stages of composting.Values Composting guidelines (Canadian Council of Minis-fell from an average log 107.01cells g ?1on Day 0,to ters of the Environment,1996)dictate that finished com-log 103.93cells g ?1on Day 7,and log 100.71cells g ?1on post should contain ?log 103.0cells g ?1dry wt.of fecal Day 14.Additionally,E.coli was ?MDL on both bed-coliforms,which is a subset of TC.Our final average ding types by Day 14,which was earlier than in 1998.TC values of log 101.69cells g ?1in 1998and log 100.64The final E.coli values at the end of active composting cells g ?1in 1999were well below the guidelines.In 1999,were ?MDL and identical in both years (log 100.40cells the top location had a trend of higher levels of TC than g ?1).Unlike TC,there was no resurgence of E.coli the middle and bottom locations (e.g.,Day 7),but the toward the end of active composting in either year.The effect was nonsignificant (Fig.2)on all sampling dates.
vertical location effect on E.coli populations in 1999was nonsignificant on all sampling dates except Day 14(Fig.4),when the bottom location was significantly Escherichia coli
higher (log 100.94cells g ?1)than the middle and top In 1998,E.coli levels were not affected by bedding locations (log 100.57–0.62cells g ?1).Since all these levels type (Fig.3a).The decline of E.coli with composting are low,the practical significance of this finding may followed a similar trend to that for TC.Escherichia coli be marginal.
levels averaged log 107.57cells g ?1(dry wt.)on Day 0,log 103.29cells g ?1on Day 7,and log 101.24cells g ?1on Total Aerobic Heterotrophs
Day 14.This meant that 99.995%of E.coli was elimi-nated in the first 7d.Escherichia coli was still detectable Initial total aerobic heterotroph (TAH)values (aver-age of two bedding types,Day 0)in 1998were log 109.59on Day 45for straw-bedded compost but was nondetect-able after Day 21on wood chip–bedded compost
CFU g ?1(dry wt.),dropping to a low of log 107.61CFU
1512J.ENVIRON.QUAL.,VOL.32,JULY–AUGUST2003
Fig.4.Effect of vertical windrow location on E.coli(mean across
bedding types?SE,n?4)in1999.The symbol*indicates signifi-
cance at the0.05probability level.Bedding?location interaction
effect was nonsignificant on all sampling dates.
g?1on Day14,and increasing to log108.18CFU g?1on
Day94(Fig.5a).In1999,a similar trend occurred,with
average values being highest on Day0(log108.97CFU
g?1),lower by approximately2log10units on Day14,
and then increasing again on Day91(Fig.5b).Of the
bacterial groups studied(TC,E.coli,and TAH),TAH
was the only one with a significant bedding effect on
populations.In1998,the straw-bedded material had
significantly(P?0.05)higher TAH than wood chip–
bedded material on Day21(Fig.5a).However,on Day
94,the opposite was true.In1999,the wood chip–
bedded material had significantly higher TAH than
Fig.5.Effect of bedding type on total aerobic heterotroph popula-
tions incubated at39?C(mean?SE,n?6)in(a)1998and(b) straw-bedded material on Days0,21,28,and42
1999.The symbols*and**indicate bedding effect significance at (Fig.5b).
the0.05and0.01probability levels,respectively.
Windrow Temperature and Water Content
maining bacteria sampling dates(Table1).By Day21, The straw-bedded treatment temperature peaked at both manures had dried to water contents of0.49kg 68.7?C on Day23in1998(Fig.6a),and60.6?C on Day kg?1and they continued to lose water until the end of 47in1999(Fig.6b).The wood chip–bedded treatment active composting.In1999,water content was signifi-peaked at66.7?C on Day45in1998(Fig.6a)and59.8?C cantly higher on Day0for straw-bedded(0.65kg kg?1) on Day44in1999(Fig.6b).Daily mean temperature than wood chip–bedded manure(0.60kg kg?1)but dif-(DMT)for both bedding treatments was generally ferences were nonsignificant thereafter(Table1).Water warmer in1998than in1999.For straw-bedded compost,content was generally higher at all points in the compost-45of108d had a DMT of?55?C in1998.In contrast,ing process than in1998.
there were only24of99d with a DMT of?55?C in
1999.For wood chip–bedded compost,44d had a DMT DISCUSSION
of?55?C in1998compared with30d in1999.These
values also show that there was little difference in tem-Populations of TC and E.coli were not affected by perature regime due to bedding type.If a DMT of
bedding type on any sampling date in either year,even ?40?C is used as an indicator of the end of thermophilic though wood products contain antimicrobial compounds
such as phenols and tars(Allison and Anderson,1951). composting,then this occurred on Day108for straw-
and Day91for wood chip–bedded compost in1998and Our findings agree with those of Miller et al.(2003), on Day83for straw-and Day87for wood chip–bedded
working at the same feedlot.They found no difference compost in1999.in TC levels in raw manure samples from feedlot pen Water was not added to the windrows during the
floors bedded with straw or wood chips.In contrast, active composting phase.In1998,water content of the Kudva et al.(1998)indicated that small amounts of straw-bedded manure was not significantly different
wood chip bedding(?5%)in bovine manure may have (0.67kg kg?1wet wt.)than that of the wood chip–bedded contributed to shorter survival times for E.coli manure(0.61kg kg?1)on Day0or on any of the re-
O157:H7.Wood chip bedding represented an average
LARNEY ET AL.:COLIFORM BACTERIA IN BEEF CATTLE FEEDLOT MANURE
1513
Table 1.Effect of bedding type (straw,wood chips)on windrow
water content during composting in 1998(n ?36)and 1999(n ?12).
Water content
Day
Straw
Wood Chips
kg kg ?1
199800.665a?0.612a 70.601a 0.572a 140.569a 0.544a 210.488a 0.492a 280.404a 0.427a 450.332a 0.374a 660.276a 0.328a 940.259a
0.314a 199900.651a 0.595b 70.638a 0.596a 140.591a 0.571a 210.570a 0.545a 290.504a 0.512a 420.382a 0.425a 560.359a 0.393a 700.292a 0.354a 98
0.287a
0.318a ?Within years and days,means followed by the same letter are not signifi-cantly different from each other (P ?0.05).
an early rapid rise to thermophilic conditions,slight temperature decreases followed by partial recovery as-sociated with each turning event,and then a gradual cooling of the windrows toward the end of active com-posting.However,there was little benefit of prolonged exposure above the recognized thermal kill limit of 55?C,as most TC and E.coli were eliminated in the first 7d of composting before attaining 55?C.Additionally,the higher residual levels of TC (Fig.1)observed toward Fig.6.Effect of year on windrow temperature (mean ?SE,n ?9)the end of composting in 1998compared with 1999were during composting of (a )straw-bedded and (b )wood chip–not due to cooler conditions,as there were warmer bedded manure.
temperatures in 1998compared with 1999(Fig.5).Since most of the coliform population decline oc-of 22%,and straw an average of 18%of total manure curred in the first 7d of composting,temperature condi-dry weight in our study (unpublished data,1999).How-tions during this period were examined more closely ever,this level of wood chip bedding did not lower levels (Table 2).In 1998,the average temperature was 39.5?C of TC compared with straw bedding.
in the straw-bedded and 41.5?C in the wood chip–The regrowth of TC between Day 45and Day 94in bedded compost during the first 7d.Maximum tempera-1998agrees with the findings of Hassen et al.(2001),who reported a phase of resurgent growth of fecal coli-Table 2.Average temperature and maximum temperature as af-forms after 9wk of MSW composting.They attributed fected by bedding type (1998and 1999)and vertical windrow location (1999)in the initial 7d of composting.
this secondary growth to recontamination or redistribu-tion during windrow turning.Krogmann et al.(2002)Average Maximum Bedding
temperature
temperature
found that after an initial population decrease in fecal streptococci (Enterococcus spp.),a slight increase (ap-?C
proximately 10-fold)was observed in later composting Bedding effect in 1998
stages of horse (Equus caballus )manure.Their explana-Straw
39.5(?3.2)?50.1Wood chips 41.5(?3.7)
53.5tion of this included (i)normal data variability,(ii)pile Bedding effect in 1999?contamination by turning with dirty equipment or by vermin between sampling dates,or (iii)recontamination Straw
35.0(?2.5)40.7Wood chips 33.5(?2.1)
38.5of sanitized compost by unsanitized material from the Vertical location effect in 1999§
outer mesophilic area of the pile during turning.Any,or Top 36.5(?2.4)42.2all,of these reasons may explain regrowth in our study.Middle 36.0(?2.9)43.6The time–temperature profiles in our study were typi-Bottom
30.2(?1.8)
35.8cal for composting of organic materials and similar to ?Standard errors of the means are in parentheses (n ?7).those reported for open-windrow composting of feedlot ?Averaged across locations.
§Averaged across bedding types.
manure in Nebraska (Eghball et al.,1997).There was
1514J.ENVIRON.QUAL.,VOL.32,JULY–AUGUST2003
tures were50.1?C for straw-bedded and53.5?C for wood more sensitive to elimination at pH7than pH8during chip–bedded compost.In1999,average temperatures
aerobic digestion at55?C.Our straw-bedded manure for the first7d were35?C for straw-bedded and33.5?C had a pH8.1,while wood chip–bedded manure had a for wood chip–bedded and the maxima were40.7?C for
pH7.3on Day0in1998(Larney et al.,2001).The pH straw-bedded and38.5?C for wood chip–bedded com-values decreased to7.3on Day14for the straw-bedded post(Table2).The coolest temperature regime in either
manure and pH6.8on Day14for the wood chip–bedded year was at the bottom windrow location in1999,which manure,which may have enhanced the pathogen reduc-had an average temperature of30.2?C and a maximum
tion effect.
temperature of35.8?C during the first7d.This regime
led to a decrease in TC from log107.08to log103.66cells CONCLUSIONS
g?1(dry wt.)and a decrease in E.coli from log106.7to
During open-air windrow composting of beef feedlot log103.41cells g?1.Hassen et al.(2001)reported a de-
manure in southern Alberta,we achieved102–to104–crease from log107.40cells g?1(dry wt.)to log103.90
fold reductions in bacterial levels(TC and E.coli)in cells g?1in municipal solid waste compost at55to60?C
7d and105–to107–fold reductions in14d.Even though over15wk.Our E.coli levels declined a similar magni-
our straw-and wood chip–bedded composts remained tude at much lower temperatures in just7d.Our find-
thermophilic for?80d in both study years,this pro-ings were closer to those of Lung et al.(2001),who
longed exposure was not required for pathogen elimina-found that E.coli O157:H7at levels of log107.0CFU
tion.More than99.9%of TC and E.coli was eliminated g?1in raw cow manure was not detected after72h of
in the first7d when average windrow temperatures composting at45?C.
were33.5to41.5?C,which is within the mesophilic range The optimum water content for windrow manure
and14to22?lower than the thermal kill limit of55?C composting is0.4to0.65kg kg?1(Rynk,1992),since
in composting guidelines(USEPA,1992;Canadian dehydration results in inactivation of beneficial as well
Council of Ministers of the Environment,1996).These as pathogenic microbes.Himathongkham and Riemann
guidelines also specify maintenance of55?C for at least (1999)reported that the destruction of E.coli was
15d.While this target was easily exceeded in our study greatly increased by the drying of chicken manure to a
(24–45d?55?C),it was not essential to achieve the water content of0.10kg kg?1.Although overall water
observed levels of pathogen reduction.
losses during summer windrow composting of feedlot
Total coliforms and E.coli were not significantly af-manure in southern Alberta can be substantial(approxi-
fected by bedding type(straw vs.wood chips)at any mately75%),due to turning combined with high evapo-
time.Total coliforms were detectable until Day94in ration rates(Larney et al.,2000),the water contents of
1998(log101.69cells g?1dry wt.).Although this level is our composts showed little change in the first7d,when
well below established guidelines(?log103.0cells g?1 most of the decline in coliform levels occurred.In1998,
dry wt.of fecal coliforms[Canadian Council of Ministers water content fell from0.67kg kg?1on Day0to0.60
of the Environment,1996]),it shows that there may be kg kg?1on Day7for straw-bedded compost and from
some potential for regrowth of coliforms at the later 0.61to0.57kg kg?1for wood chip–bedded compost.In
stages of composting.Escherichia coli was?MDL after 1999,water contents were generally stable in the first
Day45in1998and after Day7in1999.Dessication 7d declining only slightly(0.65to0.64kg kg?1)on the
probably played a minor role in coliform elimination, straw-bedded compost(Table1).
since water loss was low(?0.07kg kg?1)in the first7d Lack of nutrients caused by high populations of indig-
of composting when most of the elimination occurred. enous microorganisms in manure or the production of
Total aerobic heterotroph populations remained high compounds detrimental to coliforms may also play a
(?7.0log10CFU g?1dry wt.)throughout the composting role in the decline of pathogens during composting(Hi-
period and their competition for nutrients may have mathongkham et al.,1999).Pietronave et al.(2002)dem-
caused an antagonistic effect on pathogens. onstrated that indigenous microflora suppressed seeded
In reducing coliform populations by?99.9%,land E.coli growth in a nonsterilized finished compost while
application of compost instead of raw manure should E.coli grew rapidly in sterilized compost.Sidhu et al.
significantly reduce the risk of water quality degradation (2001)reported an antagonistic effect of indigenous mi-
in areas of intensive livestock production,like southern croorganisms on Salmonella in composted biosolids.
Alberta.Although pathogen reduction is a recognized However,the antagonistic effect declined with duration
benefit of composting,our quantification of its magni-of storage and hence long-term storage was not recom-
tude,as well as the duration and temperature regimes mended.In our study,the maintenance of microbial
required for typical feedlot manures under southern activity and competition for nutrients by TAH through-
Alberta conditions,adds to our knowledge base on com-out the composting period may have played a role in
posting as a manure management alternative in the suppressing TC and E.coli.However,since the signifi-
region.
cant bedding effects on TAH populations did not trans-
late into significant effects on TC or E.coli levels,the
ACKNOWLEDGMENTS
role of this inactivation mechanism may have been
small.This study was supported in part by the Canada-Alberta Another mechanism of pathogen reduction is pH Beef Industry Development Fund.We thank Andrew Olson change.Ugwuanyi et al.(1999)found that E.coli was
and Paul DeMaere for compost windrow management,Bruce
LARNEY ET AL.:COLIFORM BACTERIA IN BEEF CATTLE FEEDLOT MANURE1515
posted beef cattle feedlot manure.J.Environ.Qual.32:1105–Beasley and Brian Handerek for compost sampling,and Troy
1113.
Bech for bacterial enumeration.
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