anaerobic co-digestion of dairy cow manure and high concentrated food processing waste
TRANSCRIPT
ORIGINAL ARTICLE
Anaerobic co-digestion of dairy cow manure and highconcentrated food processing waste
Takaki Yamashiro • Suraju A. Lateef • Chun Ying •
Nilmini Beneragama • Milos Lukic • Iwasaki Masahiro •
Ikko Ihara • Takehiro Nishida • Kazutaka Umetsu
Received: 11 September 2012 / Accepted: 2 December 2012 / Published online: 26 April 2013
� Springer Japan 2013
Abstract Anaerobic co-digestion of dairy manure (DM)
and concentrated food processing wastes (FPW) under
thermophilic (55 �C) and mesophilic (35 �C) temperatures,
and fertilizer value of the effluent were investigated in this
study. Two types of influent feedstock were utilized:
100 % DM and a 7:3 mixture (wet weight basis) of DM
and FPW. The contents of the FPW, as feedstock were
3:3:3:1 mixture of cheese whey, animal blood, used
cooking oil and residue of fried potato. Four continuous
digestion experiments were carried out in 10 L digesters.
Co-digestion under thermophilic temperature increased
methane production per digester volume. However,
co-digestion at 35 �C was inhibited. Total Kjeldahl nitro-
gen (N) recovered after digestion ranged from 73.1 to
91.9 %, while recoveries of ammonium nitrogen (NH4-N)
exceeded 100 %. The high recovery of NH4-N was
attributed to mineralization of influent organic N. The
mixture of DM and FPW showed greater recoveries of
NH4-N after digestion compared to DM only, reflecting its
greater organic N degradability. The ratios of extractable to
total calcium, phosphorus and magnesium were slightly
reduced after digestion. These results indicate that
co-digestion of DM and FPW under thermophilic
temperature enhances methane production and offers
additional benefit of organic fertilizer creation.
Keywords Dairy manure � Food processing waste �Anaerobic co-digestion � Methane � Organic fertilizer
Introduction
Large amounts of animal manure and slurries are produced
yearly by animal breeding sectors around the world. For
instance, in fiscal year 2007, 87.5 million tons of animal
excreta were generated in Japan [1]. Over the past few
years, public concern over environmental problems and
public health risks associated with their improper man-
agement has risen considerably. When untreated or poorly
managed, animal manure becomes a potential source of
various hazards to human life and the environment. Dairy
cow manure (DM), for instance, emits significant green-
house gases, causes nutrient leaching and could be a
potential source of antibiotic resistant bacteria and antibi-
otic residue. Anaerobic digestion is an established tech-
nology that has been used for treating various organic
wastes including animal manure. It offers various advan-
tages over aerobic treatment and traditional land applica-
tion such as methane production; a renewable fuel for
heating and co-generation of electricity and heat, reduction
of pathogens and less production of biomass sludge [2, 3].
Feasibility of farm scale anaerobic digestion of DM in the
cold region of Hokkaido, Japan, has been previously
demonstrated [4]. However, the economics of dairy
digesters, based on investment returns from energy pro-
duction, are not usually favorable because of relatively
low biodegradability and biogas yield of dairy manure
when compared with other organic wastes. Therefore,
T. Yamashiro � S. A. Lateef � C. Ying � N. Beneragama �I. Masahiro � T. Nishida � K. Umetsu (&)
Graduate School of Animal and Food Hygiene,
Obihiro University of Agriculture and Veterinary Medicine,
Obihiro 080-8555, Japan
e-mail: [email protected]
M. Lukic
Institute for Animal Husbandry, Belgrade-Zemun, Serbia
I. Ihara
Department of Agricultural Engineering and Socio-Economics,
Kobe University, Kobe 657-8501, Japan
123
J Mater Cycles Waste Manag (2013) 15:539–547
DOI 10.1007/s10163-012-0110-9
co-digestion of DM and more degradable wastes is an
effective method for improving the economics of dairy
digesters by increasing the biogas production rate [5].
Some of the basic criteria for selecting co-substrate for
anaerobic co-digestion with dairy manure are the avail-
ability of such waste in the vicinity of dairy farms and
possibility of utilization of the nutrients and salts of the
waste by the farm land [5]. Food processing waste is a
desirable material to co-digest with dairy manure and
locally available in Tokachi, Hokkaido, Japan. Aside from
being a leading and advanced region of upland farming and
dairy farming in Japan, Tokachi area also has medium and
large-scale dairy related food processing companies as well
potato chips companies. Food processing wastes (FPW),
depending on the sources, usually contain significant
quantities of lipids (fats and oils) and proteins. Compared to
other organic wastes of different biochemical composition,
lipids are more interesting feedstock for biogas production
because of their reduced organic materials and higher
methane potential. However, continuous feeding of lipids to
the digester could result in accumulation of long chain fatty
acids and consequent inhibition of digestion process [6, 7].
Therefore, they must be fed to the digester at a controlled
rate. In addition, FPW are generally concentrated and must
be diluted before being fed to the digester for stable
digestion process. Dilution will cause increase in influent
volume and, consequently, increase heating energy required
for its digestion. These can reduce the cost-effectiveness of
anaerobic digestion of FPW alone. Compared to the quan-
tity of FPW generated, DM is generated abundantly in the
Tokachi area and this makes their co-digestion an attractive
option. It could serve as a disposal route for both DM and
FPW. It may also enhance their anaerobic digestion process
by providing better carbon and nutrient balance as previ-
ously observed in other studies [5, 8, 9]. The nutrient in the
digested residue could also be recycled back to agriculture
and horticulture, thus creating resource recycling society.
Limited information is available on the influence of the
co-digestion on fertilizer value of the digested slurry.
Addition of FPW to DM may increase the fertilizer value
of the effluent. A unique attribute of the methane produc-
tion from agricultural wastes is a high recovery of nutri-
ents, an important factor in the utilization of digested slurry
as organic fertilizer. Normally, total Kjeldahl nitrogen is
partially lost by conventional lagoon treatment systems.
However, manure nitrogen is conserved and ammonium
nitrogen (NH4-N) composition of manure is increased
during anaerobic digestion process [4, 10, 11].
The objectives of this study were to determine the
digester performance in term of methane production and
recovery and changes in extractability of N, P, K, Ca, and
Mg following thermophilic and mesophilic digestion of
DM and mixture of DM and FPW. The information from
the study will be useful for implementing anaerobic
co-digestion of cow manure and food processing wastes
that are locally available in Tokachi, Hokkaido, Japan, in a
single biogas plant. It will also help in determining the
suitability of the digested slurry for land application.
Materials and methods
Materials
Two types of influent feedstock were utilized: 100 % dairy
manure (DM) and a 7:3 mixture (wet weight basis) of DM
and food processing waste (FPW). Selection of DM to
FPW ratio of 7:3 was based on the results of preliminary
batch experiments where an FPW ratio of 30 % of feed
mixture was found to be the maximum concentration
required for anaerobic co-digestion with DM without any
inhibition to the digestion process at both mesophilic and
thermophilic temperatures. In addition, the selection was
based on quantities of DM and FPW generated in the target
areas. The study was initiated to investigate feasibility of
biogas production in centralized biogas digesters planned
for towns with many large dairy farms and few food pro-
cessing factories. The manure (feces only) from ration fed
dairy cows was collected from the concrete floor of a free
stall barn at the Obihiro University Farm, Obihiro,
Hokkaido, Japan. The dairy cows were fed a diet of hay,
plus supplement feeds including dent corn silage and beet
pulp. No antibiotics were incorporated into the feed. The
contents of the FPW, as feedstock, were 3:3:3:1 (weight
basis) mixture of cheese whey, animal blood, used cooking
oil and fried potato waste. The mixture represents the waste
streams from the food processing industry in the Tokachi
area. Cheese whey, fried potato residue and used cooking
oil were obtained from food processing plants in Tokachi,
Hokkaido, Japan. Animal blood was obtained from a local
municipal slaughterhouse. The materials were mixed as
stated above and the mixture was stored at -18 �C until
further use. Prior to use, the mixture was slowly thawed at
room temperature for 24 h. Characteristics of experimental
materials as feedstock are summarized in Table 1. Digested
slurries obtained from a mesophilic biogas digester at
Shihoro Mizoguchi Farm, Shihoro Town, Hokkaido and a
thermophilic biogas digester at Obihiro University Farm,
both digesting dairy cow manure, were used as inoculums
for mesophilic and thermophilic experiments, respectively.
Experimental procedure
The continuous experiments were carried out in four 10 L
digesters constructed from stainless steel. A schematic diagram
of the experimental digester is shown in Fig. 1. The digesters
540 J Mater Cycles Waste Manag (2013) 15:539–547
123
were placed in temperature-controlled water baths. The
digesters were operated at 35 and 55 �C. The four continuous
digestions of DM and mixture of DM and FPW are abbreviated
as 35DM, 55DM, 35DM ? FPW and 55DM ? FPW. The
parameters of operation of all the digesters are summarized in
Table 2. Feedstock was added once daily. Influent sampling
started at the beginning of the experiments. Effluent collection
began after steady biogas yield was achieved. No supplemental
nutrients were added to the digesters.
Analytical methods
The daily volume of produced gas was measured by a wet
gas meter. All gas measurements were expressed at 0 �C
and a pressure of 1 atm. The composition of the produced
gas was determined using a Shimadzu gas chromatograph
(GC-4C) equipped with a thermal conductivity detector. A
stainless steel column (3 m 9 2 m) packed with 80/100
mesh silica gel was used with helium as the carrier gas at a
flow rate of 28 mL/min. The injector and detector tem-
peratures were 80 and 120 �C, respectively. The column
temperature was 80 �C. Total volatile fatty acids (TVFA)
(formic, acetic, propionic and butyric acids) were deter-
mined by a Shimadzu HPLC (LC-10A), using a Shim-pack
SGR-102H. The analytical procedure for TVFA was
described in detail elsewhere [12].
For determination of total solids, the samples were dried
at 105 �C for 24 h, and total solid contents were calculated
from the differences between weights before and after
drying. The dried matters were heated at 550 �C for 4 h,
and organic matter contents were calculated from the losses
on ignition. For total nitrogen, a 5 g sample was weighed
into a Kjeldahl digestion tube; 10 mL of concentrated
H2SO4 and accelerator (Kjeldahl catalyst tablets) were
added. The tube was placed in a Kjeldahl digestion appa-
ratus (Sibata, B-412) and heated for 2 h. The digestion was
then carried out for another 30 min to ensure conversion of
all nitrogen to ammonium sulphate. After cooling, the
digested sample was transferred into 100-mL volumetric
flasks and diluted with distilled water. Then 20 mL of the
digested solution was analyzed for ammonium by using
Kjel-Auto (Mitamura, MRK automatic nitrogen/protein
measurement apparatus 037800 DTP-3). For ammonium
nitrogen measurement, a mixture of a 5 g sample and
50 mL of 1 mol/L KCl solution was placed into a centri-
fugation tube. After shaking for 1 h with a reciprocating
shaker, the suspension was centrifuged at 3000g for 15 min
and the supernatant was passed through a filter paper. Then
5 mL of the filtrate was analyzed for ammonium-N by
using the Bremner steam-distillation apparatus. The dis-
tillate was titrated against 0.01 mol/L H2SO4.
For measurement of total calcium, potassium and mag-
nesium in the sample, 5 g of the sample was weighed into a
tall-beaker (300 mL). Then 20 mL of concentrated HNO3
and 10 mL of HClO4 were added. The beaker was covered
with a watch-glass and digested at 170 �C on a hot-plate.
Table 1 Characteristics of experimental materials as feedstock
Characteristics DMa DM ? FPWb
TS (%) 8.1 17.9
VS (%) 6.1 16.5
VS/TS (%) 75.3 92.2
pH 6.8 6.4
Total VFA (mg/L) 1189.1 1600.7
Formic acid (mg/L) 18.2 0.0
Acetic acid (mg/L) 885.9 1247.5
Propionic acid (mg/L) 185.1 235.3
Butyric acid (mg/L) 100.0 8.6
a Dairy cow manureb Food processing waste
Gas sampling port
H2S removal
Gas outlet
Effluent
Thermal Insulator
Temperature controller
Wet gas meter
Feed inlet
Water bath Stirrer
Fig. 1 Schematic diagram of the experimental digester
Table 2 Operation of methane digesters
Temperature
(�C)
Material
type
Loading
(L)
Loading rate
(gVS/L/day)
HRT
(day)a
35 DM 0.5 3.05 20
35 DM ? FPW 0.5 8.25 20
55 DM 0.5 3.05 20
55 DM ? FPW 0.5 8.25 20
a Hydraulic retention time
J Mater Cycles Waste Manag (2013) 15:539–547 541
123
The digestion was carried out until the fume completely
changed to white. After cooling, the digested sample was
filtered and diluted in the volumetric flask to 100 mL with
distilled water. The solution was analyzed for Ca, K, and
Mg by using an atomic absorption spectrometer. For
phosphorus determination, the solution was agitated with
activated charcoal for 1 h and filtered to remove the color.
Phosphorus in the solution was analyzed by a molybdate-
blue colorimetric method. For extractable Ca, K, Mg and P
determination, 5 g sample was weighed into a polypro-
pylene vessel. A 20 mL mixture of 0.05 mol/L HCl and
0.0075 mol/L H2SO4 was added. After shaking for 5 min,
the suspension was passed through a filter paper and the
filtrate was diluted in the volumetric flask to 100 mL with
distilled water. Then, Ca, K, Mg, and P in the solution were
analyzed as previously described.
Escherichia coli in the slurry samples before and after
digestion were selectively grown on Desoxycholate agar.
E. coli selective agar plates were incubated at 35 �C for
20 h. Bacterial colonies of E. coli were characterized by
Enterotube Roche identification kit.
Results
Biogas and methane gas yield
Biogas productions, methane concentrations in the pro-
duced biogas and methane gas yields for the duration of the
experiments are presented in Fig. 2. The highest biogas
yields were observed at 55DM ? FPW digester. The yields
were higher than 21 L/Ldigester/day after 5 days of diges-
tion. The digestion system failed at 35DM ? FPW. In the
35DM ? FPW digester, biogas production ceased after
13 days of digestion. The biogas yields at 35DM and
55DM were almost the same after 13 days of digestion.
Methane concentrations in the produced gas rose steadily
from Day 2 in all the digesters and were stably over 50 %
after 12 days, except in 35DM ? FPW digester, where
significant inhibition was observed. The highest average
concentration of 56 % was observed in 55DM ? FPW
digester. Compared with 35DM and 55DM digesters,
methane yields in 55DM ? FPW digester were higher,
with maximum value of 0.207 L/g VS/day. Similarly,
55DM ? FPW gave highest average methane gas yield
(Table 3).
Change in pH, VFA accumulation and VS reduction
The pH increased in all digesters except for the inhibited
35DM ? FPW digester where effluent pH was low
(Table 4). The pH of the 35DM and 55DM digesters
increased by 0.9 and 1.3 pH units, to 7.7 and 8.1,
respectively, and in the 55DM ? FPW digester, it
increased by 0.9 pH units to 7.3. The concentrations of
total VFA decreased in all the digesters except in
35DM ? FPW (Fig. 3). Total VFA in 35DM and 55DM
digesters decreased from initial concentrations of
1189.08 mg/L from day 1 to day 15. The concentrations
increased slightly until day 30, thereafter remained stably
low at about 998.4 and 323.6 mg/L in 35DM and 55DM,
respectively. In 55DM ? FPW digester, there were sharp
increases of total VFA on days 10 and 30, and it remained
low at about 805.1 mg/L for the remaining days. Total
VFA accumulated above 2500 mg/L after day 21 in
35DM ? FPW. The VS reductions from all the digesters
ranged from 15.6 to 45.8 % (Table 4). The VS reduction
0
5
10
15
20
25
30
35
0 10 20 30 40 50 60
Bio
gas
yie
ld (
L/L
/day
)
0
10
20
30
40
50
60
0 10 20 30 40 50 60Met
han
e co
nce
ntr
atio
n(%
)
0
0.05
0.1
0.15
0.2
0.25
0 10 20 30 40 50 60Met
han
e yi
eld
(L
/g.V
S/d
ay)
Time (day)
a
b
c
Fig. 2 Periodical change of biogas production (a), methane concen-
tration (b) and methane yields (c). Filled diamond 35DM, filled
square 55DM, filled triangle 35DM ? FPW and x 55DM ? FPW
Table 3 Methane gas yields
Digester CH4 L/digester L/day CH4 L/g VS/day
35DM 0.53 ± 0.08a 0.15 ± 0.03
35DM ? FPW Ceased Ceased
55DM 0.53 ± 0.08 0.14 ± 0.02
55DM ? FPW 1.48 ± 0.02 0.17 ± 0.03
a Values are averages ± standard deviation (n = 60)
542 J Mater Cycles Waste Manag (2013) 15:539–547
123
rate was higher at thermophilic temperatures than meso-
philic temperatures. The highest VS reduction rate of
45.8 % was observed at 55DM ? FPW.
Conversion and recovery of nutritional elements
The concentrations of NH4-N and TKN in the influents and
effluents are presented in Table 5. The results show that
DM contributed the major part of NH4-N in DM ? FPW’s
feedstock while addition of 30 % (wt/wt) FPW increased
TKN to 6015.1 mg/L, an increase of 5594.6 mg/L when
compared with DM’s TKN. These observations are sup-
ported by results in Table 7 where results show that
influent’s NH4-N/TKN was 22.7 % for DM alone but
reduced to 14.2 % when FPW was added. As expected,
NH4-N increased in all digesters after digestion with con-
centrations ranging from 1639.5 mg/L in 55DM to
2369.9 mg/L in 55DM ? FPW. These translate to 275.4
and 278.4 % recoveries of NH4-N at 35DM ? FPW and
55DM ? FPW, respectively, and were higher than 171.0
and 169.6 % obtained at 35DM and 55DM, respectively
(Table 6). These results imply that, compared with 35DM
and 55DM, more mineralization of organic N occurred at
35DM ? FPW and 55DM ? FPW, with 55DM ? FPW
having higher mineralization and this was also evidenced
by the results of concentrations of TKN in effluent,
recoveries of TKN and effluent’s NH4-N/TKN in Tables 5,
6 and 7, respectively. These results also indicate that the
observed inhibition of digestion process at 35DM ? FPW
affected organic N mineralization to a much lesser extent
than it affected methane yield.
The results of concentrations of K in the influent also
show that the feedstocks’ K was mainly from DM
(Table 5). The ratios of extractable to total K reveal that
large parts of the influents’ K were extractable (Table 7).
After digestion, concentrations of extractable and total K
decreased in all digesters with values ranging from 2306.6
to 3328.1 mg/L. These reductions amount to lesser recov-
eries of 74.5–88.5 % compared to recoveries of NH4-N
(Table 6). Similarly, the ratios of extractable to total K
decreased from 93.6 and 95.7 % to values between 82.6
and 87.9 % after digestion, with the highest reduction
observed at 35DM ? FPW. As similarly observed for
NH4-N and K, influents’ P at 35DM ? FPW and 55DM ?
FPW mainly originated from DM (Table 5). Lower values
(71.0 and 75.6 %) of influents’ ratios of extractable to total
P when compared to other nutritional elements indicate that
a large component of manure P was not extractable
(Table 7). Compared to influent concentrations, effluent
extractable P concentrations as well as total P concentra-
tions in all the digesters were reduced except in
35DM ? FPW digester (Table 5). It is possible that the
component of extractable P in the influent changed form
during digestion and was not extractable after digestion.
Consequently, ratios of extractable to total P reduced
slightly after digestion at 55DM, 35DM ? FPW and
55DM ? FPW, with highest reduction at 55DM ? FPW,
while the ratio increased slightly at 35DM (Table 7).
Table 4 Characteristics of
effluents from the digesters
a Data in the table are means
(n = 12)
Characteristics 35DM 55DM 35DM ? FPW 55DM ? FPW
TS (%) 7.0a 6.1 14.3 10.4
VS (%) 5.2 4.5 12.8 8.9
pH 7.7 8.1 5.7 7.3
TVFA (mg/L) 998.4 323.6 2822.2 805.1
Formic acid (mg/L) 0.0 0.0 0.3 0.4
Acetic acid (mg/L) 387.3 260.1 1273.9 490.0
Propionic acid (mg/L) 595.9 61.6 1000.4 294.5
Butyric acid (mg/L) 15.2 1.9 547.6 20.2
NH4-N (mg/L) 1653.6 1639.5 2344.9 2369.9
TKN (mg/L) 3906.4 3644.3 4700.0 4396.6
NH4-N/TKN (%) 42.3 45.0 49.9 53.9
TS reduction (%) 13.9 24.3 20.3 42.2
VS reduction (%) 15.6 26.6 23.2 45.8
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 10 20 30 40 50 60To
tal v
ola
tile
fat
ty a
cid
(m
g/L
)
Time (day)
Fig. 3 Periodical changes of total volatile acid (VFA). Filled
diamond 35DM, filled square 55DM, filled triangle 35DM ? FPW
and x 55DM ? FPW
J Mater Cycles Waste Manag (2013) 15:539–547 543
123
The ratios of extractable to total Ca of influent were
greater than 80 %, suggesting that large proportion Ca,
which also mainly originated from manure, was extractable
(Table 7). Recoveries of extractable and total Ca from all
the digesters ranged from 95.6 to 110.8 % (Table 6) while
ratio of extractable to total Ca increased from 81.4 to
88.4 % and 92.2 % at 35DM and 55DM, respectively, and
decreased from 84.4 to 83.4 and 80.3 % at 35DM ? FPW
and 55DM ? FPW, respectively (Table 7). The results of
extractable to total Mg ratios of the influents indicate high
extractability of manure Mg as similarly observed for K
and Ca (Table 7). There were reductions in the ratios after
digestion in all the digesters except at 55DM ? FPW
where marginal increase was observed. Compared with
digestion of DM alone, higher recoveries were observed in
co-digested effluents (Table 6), suggesting that co-diges-
tion improved the recovery of Mg.
Coliform bacteria
The changes in viable counts of the E. coli from the
digesters are given in Table 8. E. coli was not detected in
the slurries from 55DM and 55DM ? FPW digesters after
digestion process. The viable number also declined in
mesophilic digesters during digestion process with least
reduction observed at 35DM ? FPW.
Discussion
The results of this study support the viewpoint that
co-digestion of different waste materials is an interesting
Table 5 Concentrations of
NH4-N, TKN and extractable
and total K, P, Ca, and Mg in
the influent and effluent
Data in the table are means
(n = 12)
Influent Effluent
DM DM ? FPW 35DM 55DM 35DM ? FPW 55DM ? FPW
NH4-N 996.9a 851.3 1653.6 1639.5 2344.9 2369.9
TKN 420.5 6015.1 3906.4 3644.3 4700.1 4396.6
Extr. K 3728.1 3021.1 2926.8 2781.5 2306.6 2250.1
Total K 3982.1 3158.2 3328.1 3242.2 2794.1 2689.2
Extr. P 601.9 472.1 522.1 489.9 498.9 429.2
Total P 847.4 624.5 723.9 696.9 669.1 606.8
Extr. Ca 1105.1 831.1 1170.7 1196.1 921.1 792.7
Total Ca 1356.9 984.9 1324.5 1297.9 1104.8 986.7
Extr. Mg 991.6 764.7 860.6 818.5 824.8 713.5
Total Mg 1032.2 785.7 910.5 918.1 860.5 725.1
Table 6 Recovery of nutritional elements
35DM 55DM 35DM ? FPW 55DM ? FPW
TKN (%) 91.9a 85.7 78.8 73.1
NH4-N (%) 171.0 169.6 275.4 278.4
Total Ca (%) 97.6 95.6 112.2 100.2
Extr. Ca (%) 105.9 108.2 110.8 95.4
Total K (%) 83.6 81.4 88.5 85.2
Extr. K (%) 78.5 74.6 76.4 74.5
Total Mg (%) 88.4 89.1 109.5 92.3
Extr. Mg (%) 86.8 82.5 107.9 93.3
Total P (%) 85.4 82.2 107.1 97.2
Extr. P (%) 86.7 81.4 105.7 90.9
a Data in the table are means (n = 12)
Table 7 NH4-N/TKN, Extractable/Total Ca, K, Mg and P of the
influent and effluent
NH4-N/
TKN
(%)
Extr/
total Ca
(%)
Extr/
total K
(%)
Extr/
total
Mg (%)
Extr/
total P
(%)
Influent
35DM 22.7a 81.4 93.6 96.3 71.0
55DM 22.7 81.4 93.6 96.3 71.0
35DM ? FPW 14.2 84.4 95.7 97.3 75.6
55DM ? FPW 14.2 84.4 95.7 97.3 75.6
Effluent
35DM 42.3 88.4 87.9 94.5 72.1
55DM 45.0 92.2 85.8 89.2 70.3
35DM ? FPW 49.9 83.4 82.6 95.9 74.6
55DM ? FPW 53.9 80.3 83.7 98.4 70.7
a Data in the table are means (n = 12)
Table 8 The numbers of coliform bacteria
Digester Influent Effluent
35DM log CFU/mL 7 1
35DM ? FPW log CFU/mL 7 3
55DM log CFU/mL 7 nda
55DM ? FPW log CFU/mL 7 nd
a Not detected
544 J Mater Cycles Waste Manag (2013) 15:539–547
123
option for improving biogas yields of anaerobic digestion
of solid wastes. Co-digestion of DM with FPW improved
biogas production from DM compared with digestion of
DM alone. The highest methane yield (0.207 L/g VS
added) obtained at thermophilic temperature is the range of
values earlier reported for co-digestion of manure and food
waste. El-Mashad and Zhang [5] reported methane yields
of 0.282 and 0.311 L/g VS from batch co-digestion of
unscreened dairy manure and food waste. Alvarez and
Liden [13] obtained methane yields of 0.27–0.35 L/g VS
added from co-digestion of solid cattle and swine manure,
slaughterhouse waste, and fruit and vegetable waste. Cal-
laghan et al. [14] reported methane yields of 0.21–0.33 L/g
VS added from co-digestion of cattle slurry, chicken
manure, and fruit and vegetable waste.
The present study indicates that thermophilic tempera-
ture is the optimal condition for co-digestion of dairy cow
manure and concentrated food processing waste. This is
consistent with results of the previous studies examining
anaerobic digestion of various wastes. Cecchi et al. [15]
reported that thermophilic temperature was optimal for
digesting organic municipal sludge waste in a pilot scale
study. Similarly, Ganoun et al. [16] found that thermophilic
temperature (55 �C) produced higher biogas yield than
mesophilic temperature (37 �C) when olive mill waste
water and abattoir waste water were co-digested at both
mesophilic and thermophilic temperatures. The observed
performance at thermophilic temperature might be expec-
ted given the fact that higher temperature favors diffusion
and solubility of lipid in aqueous media, thereby increasing
its accessibility to microorganisms [17]. This viewpoint is
also supported by work of Kabouris et al. [18], who sug-
gested thermophilic co-digestion of municipal sludge, fat,
oil and grease (FOG) for increased methane production.
The improved performance could also be explained by a
higher carbon content in the mixture compared to manure
alone and supply of additional nutrients by the co-substrate,
which probably established positive synergism in the
digestion liquor [19]. The VS reduction of 45.8 % obtained
at thermophilic temperature for a mixture of dairy cow
manure and food processing waste is within the range that
has been previously reported for co-digestion of manure
and other organic wastes. For instance, with co-digestion of
cattle slurry, fruit and vegetable wastes and chicken man-
ure, the reductions were between 30 and 50 % [14] and a
study of co-digestion of manure and lipids reported a VS
reduction of 51 % [20].
The digestion system was inhibited at 35DM ? FPW.
The inhibition was characterized by gradual reduction in
biogas production, accumulation of total VFA and conse-
quent low pH. Distribution of total VFA in effluent from
35DM ? FPW shows that acetic acid and propionic acid
were the predominant acids accumulated, accounting for
45.1 and 35.4 % of total VFA, respectively. Accumulation
of propionic acid is known to be an indicator of failure of
methanogenesis. This may explain the observed inhibition.
It is also possible that rate of FPW additions combined with
the rate of cell wash out at 20 days HRT may have been too
rapid for maintenance of a stable methanogenic population.
Effluent from 35DM ? FPW contained high concentration
of NH4-N, which probably resulted from higher protein
content compared to dairy cow manure alone. High con-
centration of proteins could lead to ammonia inhibition [21].
However, we cannot conclude that the inhibition observed at
35DM ? FPW was due to NH4-N production since
55DM ? FPW digester equally produced high quantity of
NH4-N.
Aside from methane production, anaerobic digestion
produces effluent that is rich in nutrient and could be a ready
source of organic fertilizer. Our results indicate that a large
portion of the nutritional elements originated from manure.
This might be expected as elements originally from feed
accumulate in the manure. Most of the elements may
eventually end up in biogas digestate. The fertilizing effect
of digestate is mostly determined by concentrations of
essential nutrients (N, P, K) in the digestate. Higher con-
centration of NH4-N was observed in effluent from mixture
of manure and food processing waste than effluent from
digestion of manure alone. This could be attributed to higher
readily degradable protein in mixture than manure alone as
NH4? is a product of protein deamination. Our results, thus,
indicate that co-digestion of dairy cow manure and food
processing waste will increase the fertilizing potential of the
effluent as a nitrogen fertilizer. Concentrations of P and K in
co-digested effluent reduced slightly after digestion. Similar
observations were reported by Lansing et al., [22]. They
reported increase in effluent NH4-N and reduction of total P
when swine manure was co-digested with used cooking
grease in low-cost digesters. Although the concentrations of
P and K in co-digested effluent reduced slightly after
digestion, application of co-digested manure and food pro-
cessing waste at thermophilic temperature is recommended
for crop cultivation since the concentrations are still
adequate for crop fertilization as specified in Hokkaido
Fertilizer Recommendation Guide [23].
Another important aspect of digested slurry quality is
hygiene. Livestock manure may contain pathogenic bac-
teria, which may originate from the tissue of diseased
animals and healthy carriers who excrete bacteria in feces,
urine, and exudate. Their release to aquatic environments
without proper treatment could pose a risk to public health
[24]. A previous study [22] reported reductions of indicator
organisms of microbial pollution when swine manure was
co-digested with used cooking grease. Moreover, the effi-
ciency of reduction largely depends on various factors such
as temperature, treatment time and mode of digestion,
J Mater Cycles Waste Manag (2013) 15:539–547 545
123
batch or continuous [24]. E. coli was not detected in
effluents from 55DM and 55DM ? FPW. This implies
100 % reductions at thermophilic temperature and the
values were larger than 97.1 % reduction reported by
Lansing et al., [22] for anaerobic digestion of swine man-
ure and used cooking grease at 25 �C. This might be
expected given the fact that thermophilic temperatures
decimate bacterial population faster than mesophilic tem-
peratures [24, 25]. Sahlstrom [24] opined that recycling of
unsafe digested residues as organic fertilizer could present
a new route of transmission of pathogens between man and
animals. Complete organism die-off at thermophilic tem-
perature implies that land application of co-digested
effluent at thermophilic temperature may not present new
route of transmission of pathogens. Considerable reduc-
tions were also observed at mesophilic temperature
([1 log CFU/mL, more than 90 % reduction). This was
probably due to long HRT (20 days) as bacteria decimation
is both temperature and time dependent [24].
Conclusions
Co-digestion of cow manure and food processing waste at
thermophilic temperature was shown to be more efficient
than digestion of manure alone in this study. Co-digestion
of cow manure and food processing waste showed more
than twofold increase in methane production per digester
volume compared to digestion of cow manure alone.
However, the effect of co-digestion at mesophilic temper-
ature on methane production was unclear due to inhibition
that was observed at mesophilic temperature. Based on our
results thermophilic co-digestion of cow manure and food
processing waste (7:3 wt/wt, wet basis) is recommended
for practical application. Co-digesting with food processing
waste increased NH4-N recovering after digestion. The
ratios of extractable to total K, P and Mg were reduced
slightly after digestion. Co-digested effluent can be used as
organic fertilizer. Our results also suggest that land appli-
cation of co-digested effluent from thermophilic treatment
may not present new route of transmission of pathogens.
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