anaerobic digestion of swine effluent: impact of production stages
TRANSCRIPT
ww.sciencedirect.com
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9
Available online at w
http: / /www.elsevier .com/locate/biombioe
Anaerobic digestion of swine effluent: Impact of productionstages
Preethi Gopalan, Paul D. Jensen, Damien J. Batstone*
Advanced Water Management Centre, University of Queensland, Brisbane, QLD 4072, Australia
a r t i c l e i n f o
Article history:
Received 27 June 2011
Received in revised form
23 November 2012
Accepted 24 November 2012
Available online 23 December 2012
Keywords:
Anaerobic digestion
Methane
Effluent
Swine
Degradability
* Corresponding author. Advanced WaterUniversity of Queensland, 4072 QLD, Austra
E-mail addresses: [email protected],0961-9534/$ e see front matter ª 2012 Elsevhttp://dx.doi.org/10.1016/j.biombioe.2012.11.
a b s t r a c t
Methane capture and use from intensive livestock industries in Australia is relatively new
and there is a lack of reliable kinetic data to design anaerobic systems both in Australia and
internationally. This paper evaluates two parameters, degradability (BO) and apparent first
order hydrolysis rate coefficient (khyd) from 5 different sites (one sampled twice), and six
different pig growth stages. Hydrolysis rate was not significantly influenced by the
production stage and was statistically similar at 0.1 d�1 and ranged from 0.06 d�1 to 0.3 d�1.
However, degradability, as defined by estimated ultimate methane yield (referenced to
standard temperature and pressure) per kg organics loaded varied substantially. Specifi-
cally, we found that the methane yields (per unit organic substrate (volatile solids) added)
from finisher (470 � 170 L kg�1), weaner (450 � 150 L kg�1) and grower (460 � 160 L kg�1)
effluent streams were more compared to yields from dry sow (260 � 120 L kg�1) and far-
rowing streams (380 � 160 L kg�1). A possible indicator of the extent of degradation is the
organic fraction of solids in the effluent. Variability in the degradation kinetics and
chemical properties of the different effluent streams could be traced back to the differ-
ences in various industry management practices such as feed type, feeding techniques and
effluent handling methods.
ª 2012 Elsevier Ltd. All rights reserved.
1. Introduction
As of 2010, it is estimated that globally, annual methane
emissions from livestock waste management contributed to
more than 230 million tonnes of carbon dioxide equivalents
[1]. In Australia, the livestock sector is responsible for 16% of
the total green house gas emissions [2] and the swine industry
is responsible for approximately 10% of the methane emis-
sions caused by intensive livestock manure management
practices [3]. Historically, methane capture and use in Aus-
tralia’s intensive livestock industries has been limited, and
this can be attributed to the poor economics of small distrib-
uted facilities and the relatively low price of energy. However,
Management Centre, Lelia. Tel.: þ61 7 3346 9051;[email protected] Ltd. All rights reserved012
in a carbon constrained economywith rising energy costs, the
viability of anaerobic digestion technology has the potential to
improve substantially.
While methane capture and use from intensive livestock
industries is well established in the European Union (EU) and
North America (USA) [4] it is still in its infancy in Australia.
The intensive livestock industry in Australia is established
with key differences to the industries in the EU and the USA,
where intensive units are much larger and more densely
located [4]. “Multi-site production” and “Contract-growing”
are popular practices unique to the Australian swine industry.
Throughout the growth cycle, individual pigs may be sent to
different sites or farms that facilitate and cater specifically to
vel 4 Gehrmann Building, Research Road, St. Lucia Campus,fax: þ61 7 3365 4726.au (D.J. Batstone)..
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9122
the particular age or type of pigs [5], as illustrated in Fig. 1.
Individual swine farms or production units generally fall into
one of the following categories; Farrow-to-finish, Breeder,
Weaner, Grower/Finisher (grow out).
A farrow-to-finish piggery includes the breeder, weaner
and grower/finisher stages. The pigs born at the site are reared
until sale age. A breeder piggery includes breeding stock, (dry
sow-pregnant sows or sows awaiting confirmation of preg-
nancy and farrowing sows-lactating sows) with the progeny
being removed from the piggery at or after the weaning phase.
A weaner piggery includes only weaner pigs. These are
generally from 3e4 weeks to 8e10 weeks. Most weaner pigs
live in controlled environment (mechanically ventilated)
conventional shed or deep litter housing. A grower/finisher
piggery includes grower (10e16 weeks), finisher (from 16
weeks up to 22e26 weeks) and sometimes weaner pigs. They
are generally housed in conventional sheds, deep litter
housing, or in a combination of these [6].
Themethod of anaerobic digestion used to stabilise animal
effluent is determined by several factors including end use of
digested product, loading rates and volumes, scale of opera-
tion and economic feasibility. Existing effluent treatment
practices in Australia generally consist of anaerobic stabili-
sation in treatment lagoons, followed by application as fer-
tiliser in agriculture. Lagoons are generally designed based on
an empirical approach (based on historical experience), which
normally applies a fixed hydraulic retention time. In contrast,
a kinetic design approachwould allow for variation in effluent
composition, and consideration for the non-mixed nature of
a lagoon. However, use of kinetics for design is limited in the
Australian swine industry and internationally, largely due to
the lack of reliable kinetic parameters [7]. Key parameters
used to indicate degradation kinetics of complex feed are
degradation extent or degradability (BO) and apparent first
order hydrolysis rate coefficient (khyd) [8].
Previous investigations have shown that feeding practices
and effluent storing and handling methods affect the
composition of effluent produced at piggeries [9]. However,
Breeder
Farrow to finish
Grow-out
Type of Piggery Type of Pig
Dry sows
Farrowing
Weaner
Grower
Finisher
Fig. 1 e Types of piggeries based on pig production stages.
there has been no previous attempt to study how this would
affect the degradation kinetics. More specifically there have
been no efforts to understand individually, degradation
kinetics of the effluent streams generated in the different
housing shed arrangements. This work addresses these issues
by defining the characterisation profile of effluent originating
from different production stages of swine. Evaluation of the
methane potentials and prediction of degradability have also
been done.
2. Methods
2.1. Effluent samples
Samples were sourced from effluent streams leaving different
sheds at one breeder unit, one grow out unit and three farrow-
to-finish piggeries. None of the sampled sites used any
bedding material. All sites except the breeder piggery had
flush systems in place that were operated on a daily basis. The
breeder piggery alone had a sluice-gate mechanism, where
the effluent accumulated under the sheds was released once
a week. The effluent slurries were stored (before flushing) in
the under-slat collection tanks at ambient temperatures
(ranging from 20 �C to 30 �C). Table 1 shows the summary of
diets employed at the different piggery sites for each growth
stage sampled (Complete diet rations are provided in the
supplementary material in Tables S1eS5).
Samples were taken from effluent channels exiting
specific, individual sheds.When flushing commenced, a small
sample (approximately 1e2 L) was taken at periodic intervals.
10e12 samples contributed to a larger composite. This
composite was then sub-sampled several times to finally
attain a 1 L sample that was used in experimental procedures.
At piggeries where the pigs were housed in sheds based on the
growth stages, sheds were sampled separately to obtain
distinct samples termed dry sows, farrowing, weaner, grower
and finisher samples. The breeder unit (BR) had dry sow and
farrowing sheds exclusively, while the grow out unit (GO) had
weaner, grower and finisher sheds only. At the first farrow-to-
finish unit (FA), where it was possible to sample all five stages,
samples were collected on two separate occasions (FA1 and
FA2) to check for seasonal variability within the site. At the
second farrow-to-finish piggery (FB), the weaner shed could
not be sampled due to differences in shed flushing and
sampling times. Likewise at the third farrow-to-finish unit
(FC), the grower shed could not be sampled. Composites of the
individual shed samples were prepared on an equal volume
basis only for GO, FB and FC units.
2.2. Biochemical methane production (BMP) tests
BMP tests were conducted in 240 mL serum bottles (200 mL
working volume) based on methods described by Angelidaki
et al. [10]. Inoculum was selected using competitive activity
testing (hydrolytic and methanogenic, data not shown).
Inoculum was collected from a full-scale anaerobic digester
fed with thermally hydrolysed waste activated sludge in
Brisbane, Australia. Based on the solids content of the samples
and inoculum (4 ¼ 5%) by weight, a substrate: inoculum ratio
Table 1 e Summary of diet compositions used at the sampled piggeries for the different production stages.
Pig type Source Diet base Protein (%vol) Fat (%vol) Fibre (%vol) Calcium (%vol) Phosphate (%vol)
Dry sow FA Wheat 15 3 6 0.8 0.7
FB Barleyewheat 13 2 4 1 0.6
FC Sorghum 15 3 5 1 0.7
BR Barley
Farrowing FA Wheat 18 4.5 4 0.8 0.8
FB Wheatebarley 18 2 4 0.9 0.7
FC Sorghum 18 7 4 0.9 0.6
BR Wheatebarley
Weaner FA Wheat 19 3 3 0.9 0.7
FC Wheat 20 3 2 0.8 0.7
GO Wheatebarley 21 6 4 0.7 0.6
Grower FA Wheat 18 2.5 4.5 0.7 0.7
FB Wheatesorghum 21 2 3.5 0.9 0.6
GO Wheatebarley 20 6 4 0.9 0.5
Finisher FA Wheat 16 2.5 6 0.7 0.3
FB Sorghumewheat 18 2 2.5 0.9 0.5
FC Sorghum 18 2.5 4 0.9 0.7
GO Wheatebarley 16 6 4.5 0.9 0.5
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9 123
of 1:1 was used in all the assays. The headspace of each serum
bottle was purged with nitrogen prior to gas tight sealing with
butyl rubber plugs. Tests were maintained at 37 � 1 �C in
a temperature controlled incubator and mixed by inverting
periodically. Gas volume was measured using a precision gas
tight syringe (SGE International Pty Ltd., Ringwood, Australia)
and a water filled manometer. All tests were conducted in
triplicate. Triplicate blanks were used to measure and correct
for background methane produced from the inoculum and
tests using pure cellulose (SigmaeAldrich� a-cellulose) were
used as a positive control.
2.3. Analytical methods
The composition (H2, CH4, CO2) of biogas produced during
digestion was measured using a PerkineElmer loop injection
GC. The PerkineElmer GC-TCD (AutoSystem GC, Per-
kineElmer, Waltham, MA, USA) was fitted with a 2.44 m
stainless steel column (Haysep at 80/100 mesh) and a GC Plus
Data Station (model 1022, PerkineElmer, Waltham, MA, USA).
The injection port temperature was set at 75 �C, the oven
temperature at 40 �C and the detector at 100 �C [11]. The GC
was calibrated using external gas standards for H2, CH4 and
CO2 from British Oxygen Company (Sydney, NSW, Australia).
Total solids (TS), Volatile solids (VS) and Chemical Oxygen
Demand (COD) were determined according to standard
methods [11]. COD was measured in replicates of five, using
a Thermoreactor TR 300 (Merck, Germany) and an SQ 118
Photometer (Merck, Germany). Prior to analysis of volatile
Fatty Acid (VFA) content and the combined ammonia and
ammoniumenitrogen (NH4þeN and NH3eN), samples were
centrifuged at 2500 g and the supernatant filtered through
a syringe filter (0.22 mm PES membrane). VFA concentrations
were measured by GC (Agilent, FID with polar capillary
column). NH4þeN and NH3eN and Total Kjeldahl Nitrogen
(TKN) were measured using a Lachat Quik-Chem 8000 Flow
Injection Analyser (Lachat Instrument, Milwaukee). pH of
samples (from BR and GO) were measured on-site using a pH
probe in the effluent pipe.
2.4. Data analysis and parameter estimation methods
Estimation of the kinetic parameters was done by fitting the
data obtained from the BMP analysis to a first order model
(implemented in AQUASIM 2.1d [12]), to estimate hydrolysis
rate (speed of degradation, khyd) and the degradability (extent
of degradation, BO) as previously described [13] using non-
linear parameter estimation (Secant method) with residual
sum of squared errors (J ¼ RSS) as objective function.
The analytical solution to the methane evolution curve is
shown in Eq. (1):-
S ¼ BO
�1� e�khydt
�(1)
where S is the cumulative methane evolution per unit of
volatile solids (VS) (L kg�1) (note yield represents litres of
methane only not total biogas), BO is the degradability (L kg�1),
khyd is theapparentfirstorder coefficient (d�1), and t is the time.
A 95% confidence limit, with appropriate F-values and
degreesof freedomwereused to evaluate thefittedparameters.
The uncertainty around these two parameters was expressed
as a two-dimensional space for each effluent stream and
compared for significant overlaps or differences. Regression
analysis was done against a number of major inputs (organic
fraction, organic acids, elements analysed, nitrogen and phos-
phorous) using a standard linear regression model (imple-
mented in SigmaPlot� 11), and a significance level of 95%.
3. Results
3.1. Characterisation
The results from the characterisation analyses are displayed
in Table 2. The concentrations of elements analysed (per
kg TS) in the different effluent streams are listed in the
supplementary materials in Table S6. Chemical properties of
the dry sow and farrowing effluents were different to that of
the weaner, grower and finisher effluents.
Table 2 e Characteristic propertiesa of piggery effluent streams from sheds holding different production stages.
Waste stream Source TS (g L�1) VS (g L�1) VS (%TS) TKN (g L�1) NH4 (g L�1) TKP (g L�1) VFA (g L�1) TCOD (g L�1)
Dry sows FA1 49 � 3 37 � 2 74 3.4 1 0.6 0.5 62 � 25
FA2 20 � 2 13 � 2 66 2.1 1 0.9 1.4 45 � 37
FB 32 � 4 22 � 4 68 1.9 0.9 1.1 0.9 47 � 42
FC 23 � 4 18 � 3 77 1.7 0.5 0.07 1.7 27 � 26
BR 69 � 2 43 � 1 63 3.1 1.8 1.7 0.2 96 � 23
Farrowing FA1 35 � 10 23 � 6 66 2.6 1.5 0.6 0.7 33 � 29
FA2 21 � 1 15 � 1 70 2.5 1.5 0.6 3.1 43 � 3
FB 17 � 2 12 � 2 70 1.7 1.1 0.5 1.4 29 � 48
FC 35 � 6 28 � 6 80 2.6 0.7 0.3 1.4 52 � 34
BR 19 � 1 12 � 1 64 1.5 0.9 0.3 0.2 39 � 5
Weaner FA1 42 � 10 35 � 8 84 3.2 1.2 1 6 49 � 14
FA2 17 � 1 14 � 1 83 2.1 0.5 0.5 3.5 48 � 14
FC 27 � 10 24 � 9 89 1.7 0.5 0.2 4.6 28 � 6
GO 19 � 3 15 � 3 78 0.8 0.2 0.3 1.1 22 � 33
Grower FA1 41 � 5 34 � 5 81 2.6 1.7 0.6 3.1 47 � 60
FA2 20 � 1 15 � 1 75 2.9 1.6 0.5 6.5 56 � 9
FB 51 � 7 43 � 7 84 3.7 1.6 0.5 7.3 72 � 13
GO 37 � 8 29 � 8 79 2.5 0.9 0.6 3.1 37 � 17
Finisher FA1 37 � 3 29 � 2 77 2.6 1.5 0.6 5.7 35 � 55
FA2 17 � 1 12 � 1 71 4.2 1.7 0.7 5.4 41 � 14
FB 37 � 8 30 � 6 81 2.5 0.2 1.2 1.5 48 � 15
FC 60 � 20 50 � 18 83 2.5 0.9 0.5 7.5 30 � 5
GO 30 � 3 23 � 2 78 2 0.9 0.4 3.8 39 � 15
Composite FB 15 � 5 11 � 4 71 2.5 1 0.6 2.9 36 � 9
FC 20 � 3 15 � 2 76 2 0.6 0.3 3.8 46 � 28
GO 29 � 5 23 � 4 80 1.5 0.7 0.4 4.9 52 � 36
aResults presented as value �95% error for TS, VS (replicates of three) and TCOD (replicates of five).
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9124
VS mass fraction (VS as %TS) (average � errors) in the dry
sow and farrowing sows was approximately wTS ¼ 70 � 4%
while that in the weaner, grower and finisher streams was
observed to be significantly higher (wTS ¼ 80 � 2.5%). The
fraction of total VS attributed to VFA in weaner, grower and
finisher effluent streams (wVS ¼ 17%, wVS ¼ 20%, wVS ¼ 20%
respectively) were also greater than that found in dry sow and
farrowing sow sheds (wVS ¼ 5%, wVS ¼ 8% respectively). The
fraction of the total nitrogen that is linked to ammonia in dry
sow and farrowing sows (wTKN ¼ 50 � 10%) was also slightly
higher than that in weaner, grower and finisher streams
(wTKN¼ 40� 10%). Concentration (per kg TS) of some elements
like Ca, Mg and P was higher in dry sow (60 � 23 g kg�1,
15 � 7 g kg�1, 40 � 17 g kg�1 respectively) and farrowing
streams (40� 9 g kg�1, 12� 2 g kg�1, 25� 5 g kg�1 respectively)
than in the finisher (30 � 8 g kg�1, 10 � 3 g kg�1, 20 � 8 g kg�1
respectively) and weaner (30 � 22 g kg�1, 7 � 4 g kg�1,
13 � 7 g kg�1 respectively) streams.
Similar variation were also observed between effluent
streams generated at the breeder piggery and the grow out
unit. The effluent streams from the farrow-to-finish piggeries
displayed properties relatively similar to the effluent from the
grow out unit. The VS fraction in streams generated at the
breeder piggery (wTS ¼ 64 � 3%) was much lower than that at
the grow out unit (wTS ¼ 78 � 2%) and the farrow-to-finish
(wTS ¼ 76 � 3%) piggeries. VFA concentrations in the effluent
streams from the grow out unit (3.5� 2.5 g L�1) and the farrow-
to-finish piggeries (4.0 � 3.5 g L�1) were relatively greater than
that in the effluent from the breeder piggery (0.2 g L�1). The
fraction of the total nitrogen that is linked to ammonia in the
effluent streams at the grow out and the farrow-to-finish units
(wTKN ¼ 40 � 10%) was lower than that in the breeder unit
streams (wTKN ¼ 60 � 10%). The concentrations of some
elements including Al, Ca, Fe, Mg, Mn, P and Zn in the breeder
unit streams were much higher than that in the effluent
streams of the grow out and farrow-to-finish units.
3.2. Methane yields
Fig. 2 shows themethane yields (in Lmethane produced per kg
VS loaded and g COD methane produced per g VS loaded) for
each of the effluent streams sampled at the five piggeries.
Methane yield per unit mass organics loaded (average
value � standard deviation (SD)) from the dry sow
(260 � 120 L kg�1) and farrowing streams (380 � 160 L kg�1)
were relatively poor when compared with that of the weaner
(450 � 150 L kg�1), grower (460 � 160 L kg�1) and finisher
streams (470 � 170 L kg�1).
This trend is also reflected when comparing the overall
methane yield from the different types of piggeries. The yield
of methane per unit organics fed (average value � SD) from
the grow out unit (550 � 80 L kg�1) was significantly greater
than that from the breeder unit (180 � 60 L kg�1). Despite the
variability between the farrow-to-finish units (FA1-
280 � 100 L kg�1, FA2-560 � 70 L kg�1, FB-450 � 120 L kg�1, FC-
350 � 140 L kg�1), they were all significantly greater than the
final yield from the breeder unit.
3.3. Degradation kinetics
Table 3 displays the estimated kinetic parameters. All results
are presented with �95% confidence intervals.
FA1
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Dry sows
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Farrowing
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Weaner
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Grower
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Finisher
0 40 80 1200
200
400
600
800
0.0
0.5
1.0
1.5
2.0
Composite
To
tal C
H4
p
ro
du
ced
(L
CH
4 k
gV
S-1)
Time (days)
Time (days)
Time (days)
Time (days)
Time (days)
Time (days)
To
tal C
H4
p
ro
du
ced
(g
CO
DC
H4
g
VS
-1)
FA2 FB FC GO BR
Fig. 2 e Methane yields from the waste streams originating at different production stages of six piggeries. Dot points with
95% errors represent experimental data and solid lines represent simulated data.
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9 125
Fig. 3 shows the distribution of the predicted parameters
across the different effluent streamswith confidence region at
the 95% uncertainty level.
The variability between samples taken at the different sites
is clear. However, the estimated parameter’s regions of the
finisher, weaner and grower streams were found to be further
to the right on the degradability scale, indicating greater
degradation in these streams compared to the dry sow and
farrowing streams. The rates of degradation (khyd) of the
different effluent streams varied between 0.06 and 0.3 d�1 and
Table 3 e Kinetic parametersa (degradability and first order hyd
Dry sows Farrowing Weaner
BO (LCH4 kgVSL1)
FA1 190 � 10 230 � 10 420 � 40
FA2 380 � 40 450 � 30 530 � 20
FB 230 � 30 500 � 40 e
FC 300 � 0.30 450 � 30 270 � 20
GO e e 530 � 40
BR 150 � 10 230 � 10 e
khyd (dL1)
FA1 0.06 � 0.005 0.08 � 0.007 0.09 � 0.03
FA2 0.2 � 0.07 0.2 � 0.07 0.2 � 0.05
FB 0.1 � 0.06 0.2 � 0.1 e
FC 0.2 � 0.07 0.1 � 0.03 0.1 � 0.03
GO e e 0.1 � 0.04
BR 0.06 � 0.01 0.1 � 0.05 e
aResults presented as value �95% error for assays performed in replicate
averaged at (0.1� 0.02 d�1). Fig. 4 shows the distribution of the
predicted parameters across the different sampling sites.
This graph indicates the variability of predicted parameters
for effluents streams generating within the same site. It also
highlights the overall variability between different types of
piggeries, like the breeder unit streams that degrades poorly
when compared to the other sites. The effluent streams from the
grow out unit, on the other hand, were relatively more degrad-
able.Theeffluent streamsgeneratedat the farrow-to-finishunits
exhibit substantial variability with respect to degradability.
rolysis rate) estimated for different piggery waste streams.
Grower Finisher Composite
230 � 20 380 � 20 e
570 � 30 530 � 20 e
380 � 20 420 � 40 380 � 40
e 230 � 20 600 � 10
490 � 30 640 � 30 450 � 40
e e e
0.09 � 0.02 0.08 � 0.01 e
0.2 � 0.05 0.2 � 0.08 e
0.07 � 0.01 0.1 � 0.04 0.3 � 0.1
e 0.06 � 0.01 0.1 � 0.03
0.1 � 0.03 0.1 � 0.03 0.1 � 0.07
e e e
s of three.
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
100 200 300 400 500 600 7000.0
0.2
0.4
0.6
5
4
3
Composite
4 5
3
2
1
Finisher
5
3
21
Grower
45
2
1
Weaner
3
2
4
6
1
FarrowingDry sows
43 2
6 1
BO (LCH4 kgVS-1) BO (LCH4 kgVS-1)
BO (LCH4 kgVS-1) BO (LCH4 kgVS-1) BO (LCH4 kgVS-1)
BO (LCH4 kgVS-1)
k hyd
(d-1
)
k hyd
(d-1
)
k hyd
(d-1
)
k hyd
(d-1
)
k hyd
(d-1
)
k hyd
(d-1
)
1-FA1 2-FA2 3-FB 4-FC 5-GO 6-BR
Fig. 3 e Confidence regions for hydrolysis rate and degradability for effluent streams generated at the various production
stages in six piggeries.
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
FA1
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
FA2
12
345
1
5
2
34
k hyd
(d-1
)
k hyd
(d-1
)
k hyd
(d-1
)k h
yd (
d-1)
k hyd
(d-1
)
k hyd
(d-1
)
BO (LCH4 kgVS-1)
BO (LCH4 kgVS-1)BO (LCH4 kgVS-1)
BO (LCH4 kgVS-1)BO (LCH4 kgVS-1)
BO (LCH4 kgVS-1)
1 Dry sows, 2 Farrowing, 3 Weaner, 4 Grower, 5 Finisher, 6 Composite
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
FB
1
6 2
5
4
FC
5
1
32
6
100 200 300 400 500 600 700
0.0
0.2
0.4
0.6
GO
63
4
5
BR
1
2
Fig. 4 e Confidence regions for hydrolysis rate and degradability for effluent streams generated at different types of
piggeries.
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9126
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9 127
3.4. Co-indicators of degradability and rate ofdegradation
Results from regression analysis used to test for correlations
between effluent compositions and degradability parameters
are presented in the supplementary material in Table S7. BOincreased significantly with increasing VS fraction and VFA
concentrations in the substrate but decreased significantly
with increasing COD: VS ratios and Aluminium concentra-
tions in the substrate. The rate of degradation decreased
significantly with increasing TS and VS contents, and with an
increase in concentrations of a number of elements like
Boron, Calcium, Iron, Magnesium, Manganese, Molybdenum,
Phosphorous and Sulphur. Interaction effects could however
not be determined, partly due to issues with auto-correlation
between the different characteristic properties.
4. Discussion
4.1. Suitability of piggery effluent for use in anaerobicdigestion
Methane yield from the effluent streams generated at
a piggery (average BO across 26 samples tested in this study)
was 380 L kg�1 with a standard deviation of 134 L kg�1 (95%
confidence in mean of �50 L kg�1). The Australian National
Greenhouse Gas Inventory Report value of 450 mL kg�1 [3] is
higher than the average, but overlaps the range meaning we
confirm the Australian value as being a conservative estimate
of piggery emissions. Previous studies investigating anaerobic
digestion of swine effluent have reported that effluent from
grower-finisher pigs degrades up to 93% and that from sows,
up to 73% [14]. Other investigations also report comparable
values for methane yields from different swine wastes [15,16].
Although the yield from piggery effluent was lower than the
yields from slaughterhouse, (525 � 25 L kg�1) [17] and primary
sludge (540 L kg�1) [18], it was higher than that of other wastes
such as dairy cattle waste (85 L kg�1 [19], 148 � 41 L kg�1) and
activated sludge (200 L kg�1 [20]) which have proven to be
viable substrates for anaerobic digestion.
Methane yields from this work are presented as yield per g
VS loaded and some values are relatively high. This could be
associated with some error in the measurement of VS (VS
values used are exclusive of the VFA measured) as document
by Derikx,Willers and TenHave [21] andHayward and Pavlicik
[22]. Though the effluent samples used in the study had a pH
of around 7.2 and VFA is in a less volatile form at this pH, some
portion of the VFA may have been lost during drying. This
would result in underestimation of VS. The variation in the
degradability (degradation extent) from the different streams
suggests that ponds operating with effluent from weaner,
grower and finisher sheds would produce more methane
when compared to those operating with effluent from breeder
sheds. In addition, ponds with weaner, grower and finisher
effluents would operate longer when compared to the ponds
designed for breeder units owing to greater sludge accumu-
lation from the dry sow and farrowing effluents. Because the
degradation rates are similar for almost all the streams, the
size of the ponds would be the same for treating all or any of
these streams. The impact of temperature in particular can
generally be accounted for by a doubling in apparent coeffi-
cient for every 10 �C rise in temperature [23], and this would
indicate a kinetic coefficient on the order of 0.03 d�1 at 20 �C.Total solids across the 26 samples used in this study were
1000 mg L�1e5000 mg L�1, and the volatile solids averaged
wTS ¼ 75%, which is within the expected range for piggery
effluent [5,16]. Ammonia content (approx. 1 � 0.5 g L�1) was
typically wTKN ¼ 50%. Literature reports ammonia concen-
trations of 4.7e5 g L�1 and above to be inhibitory to the
methanogenic population of micro organisms [24] and the
ammonia content of all samples analysed in this study were
below these inhibitory concentrations. VFA concentrations in
the samples ranged from 0.2 to 7.2 g L�1, which again were
below the reported inhibitory concentrations of 30e40 g L�1
[25]. Another investigation reported that the hydrolysis rate
was not influenced by the VFA concentrations and was more
influenced by pH [26]. Results from the regression analysis are
in agreement with this. COD concentrations averaged at
45 � 15 g L�1 and are comparable with the 38.5e96.3 g L�1
range specified in a previous study [27]. CODs were measured
in replicates of five. The heterogeneous nature of samples and
large dilutions necessary to perform the COD test produced
results with high errors. There have been few attempts to
measure the COD of piggery effluent due to the issues asso-
ciated with obtaining exact values and most results in the
agricultural industry are represented on a per VS basis.
Due to the difference in anaerobic inocula, effluent
composition, and experimental methods and conditions,
literature values for the inhibition thresholds of specific
toxicants such as ammonia, sulphide, light metal ions and
heavy metals vary substantially. The concentrations of
elemental ions like Aluminium, Calcium, Sodium and
Magnesiummeasured in the effluent streams sampled for this
study (36 � 14 mg kg�1, 1260 � 500 mg kg�1, 300 � 50 mg kg�1
and 350 � 100 mg kg�1 respectively) were well below the
ranges reported to be inhibitory in literature. (2500 mg kg�1,
7000 mg kg�1, 3500e5500 mg kg�1 and 720 mg kg�1 respec-
tively) [24]. While specific dilution experiments targeting
inhibitory compounds were not performed, the relatively high
methane yields and relatively low concentrations of inhibitory
compounds in the effluent streams are good indicators that
piggery effluent is suitable for treatment using anaerobic
processes. Another good indication is that VFA was not
detected in residues (after BMP) in any of the 15 samples
measured; suggesting that all material that was solubilised
was converted to methane.
4.2. Influence of production stage on effluent streams
Fig. 3 presents the results of the degradability analysis on the
basis of the different production stages and it is clear that the
confidence regions (in reference to the degradability-BO) for
the grower, finisher and weaner streams were higher on the
scale when compared to the dry sow and farrowing streams.
This variation is in correlation with the variation in VS frac-
tion and is supported by the outcome of the regression anal-
ysis. VS fraction thus is a good indicator of the degradability of
the substrate. The variation in the VS fraction between the
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9128
different streams could in turn be an affect of the feeding
techniques applied in the swine industry. Feed wastage in
weaner (w ¼ 15%), grower and finisher sheds (10%) is more
than that in dry sow and farrowing sheds (w ¼ 5%) [28]. This is
because most piggeries practice adlib feeding with weaner,
grower and finisher pigs while the dry sow and farrowing
sheds have a more rationed, monitored feeding design in
place [29,30]. Another possibility for reduced VS content in the
dry sow and farrowing streams and increased VS content in
weaner could be the extent of hind gut fermentation in these
types of pigs. Weaner pigs are known to have poorer hind gut
fermentation causing relatively poor feed conversion. Dry
sows and farrowing sows, on the other hand, have enhanced
hind gut fermentation [31].
Variation in themetal concentrationsbetween thedifferent
streams can be associated to the differences in the feed
ingredients supplied to the different stages of pigs. Dry sow
and farrowing pigs are fed diets rich in vitamins andminerals
while grower and finisher pigs are fed diets that are relatively
protein rich. For instance, diets for dry sowand farrowing sows
have larger concentrations of limestone when compared to
that in the feed prepared for weaners, grower and finisher pigs
[29,30] and this would explain increased concentration of
calcium observed in the dry sow streams in this study.
Results from the characterisation analysis also show that
the dry sow and farrowing streams have a higher fraction of
ammonia associated nitrogen (as % TKN). Because the
nitrogen associated with nitrite and nitrate forms were also
nil, this implies that the balance of the TKN is organically
associated nitrogen. It is reasonable to assume thus that the
weaner, grower and finisher streams have a higher concen-
tration of organic nitrogen, suggesting higher protein content.
This is also supported by the respective COD: VS ratios.
Literature reports COD: VS ratios of 1.5 for proteins and 2.9 for
lipids [31]. The results show that the COD: VS ratios in dry sow
and farrowing streams were closer to the COD: VS ratio of
lipids while that of the weaner, grower and finisher were
closer to that of proteins or carbohydrates. Investigation into
the diets also shows that the dry sow and farrowing sows are
fed diets that are rich in fat and lower protein content
compared to the weaner, grower and finisher pigs [29,30].
4.3. Influence of site on effluent
The breeder sheds produces material that takes longer to
degrade and to a lesser extent than the material produced at
the farrow-to-finish piggery as seen in Fig. 4. As with the
effluent streams, the variation in the methane potentials of
the effluents from the different production units can also be
associated with the respective inherent chemical properties.
Management practices in the piggeries, other than those dis-
cussed in the previous sections, that could be attributed to the
abovementioned variability are the effluent handling systems
employed. The breeder unit employs a static-pit and pull-plug
system, unlike other sites that flush sheds on a daily basis. At
this site, effluent goes into pits below the floor slats holding
recycled water that collects the effluent from the pigs. This
water is replaced only once a week. Samples sourced here
were more aged (up to one week) compared to samples
collected at other sites, and hencemay have lost some organic
fraction to volatilisation and degradation.
5. Conclusions
While all effluent streams degrade at similar rates, effluents
fromthefinisher, growerandweaner shedsdegrade toagreater
extent, and have almost twice the methane potential as that
from dry sow and farrowing sheds. Correlation between VS
fraction and degradability suggests that VS fraction is a good
indicator of effluent degradation potential. The variation in
methane potential of the effluent streams can be linked to the
variation in industry management practices such as feed,
feeding techniques and effluent handling methods.
Acknowledgements
This study was funded by APL and MLA under the methane to
markets scheme, project number 2008/2217. Preethi Gopalan
holds an APL PhD scholarship. We would like to thank Dr. Ian
Wood for his help with statistical analysis of the experimental
data.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.biombioe.2012.11.012.
r e f e r e n c e s
[1] EPA. Global anthropogenic non-CO2 greenhouse gasemissions 1990e2020. Washington, DC: United StatesEnvironmental Protection Agency; 2006 June (revised). p. 274.Report No. 430-R-06e003.
[2] Garnaut R. The Garnaut review 2011: Australia in the globalresponse to climate change. Cambridge: CambridgeUniversity Press; 2011.
[3] Australian national greenhouse accounts. Nationalinventory report 2010. Canberra, Australia: Department ofClimate Change and Energy Efficiency; 2010.
[4] RIRDC. Assessment of methane capture and use from theintensive livestock industry. Barton, ACT, Australia: RuralIndustries Research and Development Corporation,Australian Government; 2008. p.58 Publication No.08/025.
[5] Kruger I, Ferrier M, Taylor G. Effluent at work. Tamworth,N.S.W: NSW Agriculture; 1995.
[6] Tucker RW, McGahan EJ, Galloway JL, O’Keefe MF. Nationalenvironmental guidelines for piggeries. 2nd ed. Deakin, ACT,Australia: Australian Pork Limited; 2010 (revised). p. 206Project No. 2231.
[7] Shilton AN. Pond treatment technology. London; Seattle:IWA Pub; 2005.
[8] Pavlostathis SG, Giraldo-Gomez E. Kinetics of anaerobictreatment: a critical review. Crit Rev Environ Con 1991;21(5e6):411e90.
[9] RigolotC, EspagnolS,RobinP,HassounaM,BaclineF, Paillat JM,et al. Modelling of manure production by pigs and NH3, N2O
b i om a s s a n d b i o e n e r g y 4 8 ( 2 0 1 3 ) 1 2 1e1 2 9 129
and CH4 emissions. Part II: effect of animal housing, manurestorage and treatment practices. Animal 2010;4(8):1413e24.
[10] Angelidaki I, Alves M, Bolzonella D, Borzacconi L, Campos JL,Guwy AJ, et al. Defining the biomethane potential (BMP) ofsolid organic wastes and energy crops: a proposed protocolfor batch assays. Water Sci Technol 2009;59(5):927e34.
[11] APHA. Standard methods of examination of water andwastewater. 20th ed. Washington DC: American WaterWorks Association, Water Pollution Control Federation,American Public Health Association; 1998.
[12] Reichert P. Aquasim e a tool for simulation and data analysisof aquatic systems. Water Sci Technol 1994;30(2):21e30.
[13] Batstone DJ, Tait S, Starrenburg D. Estimation of hydrolysisparameters in full-scale anerobic digesters. BiotechnolBioeng 2009;102(5):1513e20.
[14] Møller HB, Sommer SG, Ahring BK. Methane productivity ofmanure, straw and solid fractions of manure. BiomassBioenerg 2004;26(5):485e95.
[15] Vedrenne F, Beline F, Dabert P, Bernet N. The effect ofincubation conditions on the laboratory measurement of themethane producing capacity of livestock wastes. BioresourTechnol 2008;99(1):146e55.
[16] Hill DT. Methane productivity of major animal waste types.Trans ASAE 1984;27(2):530e4.
[17] Salminen E, Rintala J. Anaerobic digestion of organic solidpoultry slaughterhouse waste e a review. Bioresour Technol2002;83(1):13e26.
[18] Skiadas IV, Gavala HN, Lu J, Ahring BK. Thermal pre-treatment of primary and secondary sludge at 70 �C prior toanaerobic digestion. Water Sci Technol 2005;52(1e2):161e6.
[19] Buendıa IM, Fernandez FJ, Villasenor J, Rodrıguez L.Biodegradability of meat industry wastes under anaerobicand aerobic conditions. Water Res 2008;42(14):3767e74.
[20] Hasegawa S, Shiota N, Katsura K, Akashi A. Solubilization oforganic sludge by thermophilic aerobic bacteria asa pretreatment for anaerobic digestion. Water Sci Technol2000;41(3):163e9.
[21] Derikx PJL, Willers HC, Ten Have PJW. Effect of pH on thebehaviour of volatile compounds in organic manures duringdry-matter determination. Bioresour Technol 1994;49(1):41e5.
[22] Hayward G, Pavlicik V. A corrected method for dry matterdetermination for use in anaerobic digester control. BiolWastes 1990;34(2):101e11.
[23] Chen Y, Cheng JJ, Creamer KS. Inhibition of anaerobicdigestion: a review. Bioresour Technol 2008;99(10):4044e64.
[24] Veeken AHM, Hamelers BVM. Effect of substrate-seed mixingand leachate recirculation on solid state digestion ofbiowaste. Water Sci Technol 2000;41(3):255e62.
[25] Veeken AHM, Kalyuzhnyi S, Scharff H, Hamelers BVM. Effectof pH and VFA on hydrolysis of organic solid waste. J EnvironEng 2000;126(12):1076e81.
[26] Hashimoto AG. Methane from swine manure: effect oftemperature and influent substrate concentration on kineticparameter (K). Agri Wastes 1984;9(4):299e308.
[27] RIRDC. Estimates of manure production from animals formethane generation. Barton, ACT, Australia: Rural IndustriesResearch and Development Corporation, AustralianGovernment; 2010. p. 63 Publication No.10/151.
[28] Brewster C. Feeding pigs. In: Fearon P, editor. PigTech notes:breeding, feeding and management. Brisbane, QueenslandAustralia: Queensland Department of Primary Industries, PigResearch and Development Corporation; 2000. p. 120e4.
[29] Singh D, Fearon P. Feeding pig breeding stock. In: Fearon P,editor. PigTech notes: breeding, feeding and management.Brisbane, Queensland Australia: Queensland Department ofPrimary Industries, Pig Research and DevelopmentCorporation; 2000. p. 117e9.
[30] Shi XS, Noblet J. Contribution of the hindgut to digestion ofdiets in growing pigs and adult sows: effect of dietcomposition. Livestock Prod Sci 1993;34(3e4):237e52.
[31] Zeeman G, Gerbens S. Good practice guidance anduncertainty management. In: National greenhouse gasinventories. CH4 emissions from animal manure. Kyoto,Japan: IPCC Press; 2002.