anaerobic digestion of waste from a slaughterhouse
TRANSCRIPT
Accepted Manuscript
Title: Anaerobic digestion of waste from a slaughterhouse
Authors: Muhammad Imran Ahmad, Orooj Ejaz, Amjad Ali, Muhammad AbdulQadir Jehangir Durrani, Irfan Ahmed Khan
PII: S2213-3437(14)00074-8
DOI: 10.1016/j.jece.2014.04.001
Reference: JECE 320
To appear in: Journal of Environmental Chemical Engineering
Received date: 28 October 2013Revised date: 18 March 2014Accepted date: 1 April 2014
Please cite this article as: Ahmad Muhammad Imran, Ejaz Orooj, Ali Amjad, Qadir Jehangir DurraniMuhammad Abdul, Khan Irfan Ahmed, Anaerobic digestion of waste from a slaughterhouse, Journal ofEnvironmental Chemical Engineering (2014), doi: 10.1016/j.jece.2014.04.001
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Anaerobic digestion of waste from a slaughterhouse
Muhammad Imran Ahmada,*
, Orooj Ejazb, Amjad Ali
b, Muhammad Abdul Qadir
Jehangir Durranic, Irfan Ahmed Khan
d
aDepartment of Chemical Engineering, University of Engineering and Technology,
25000, Peshawar, Pakistan
bDepartment of Civil Engineering, University of Engineering and Technology, 25000,
Peshawar, Pakistan
cIqra National University, Peshawar, Pakistan
dQadir Enterprises, Peshawar, Pakistan
Abstract
This paper investigates the effects of variation in the inoculum to waste ratio on the
anaerobic treatment of slaughterhouse waste, and proposes a low cost anaerobic
treatment system. The work was carried out using a laboratory scale packed anaerobic
digester with a gas collecting chamber. The inoculum used for seeding the reactors
was septic tank sludge. The operating temperature ranged from 28-37˚C. The
experimental results indicated chemical oxygen demand (COD) removal efficiencies
ranged from 60-90% and increased with increasing inoculum to waste ratio beyond
(1:1). The decrease in the temperature (from 37 to 28˚C) reduced the COD removal
efficiency from 90 to 75%. The system did not show any sign of destabilization under
intermittent mode of operation of the reactors.
*Corresponding author. Tel.: +92 91 9218180; fax: +92 91 9218180.
E-mail address: [email protected] (Muhammad Imran Ahmad)
Keywords: Anaerobic treatment; slaughterhouse waste water; waste treatment.
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1. Introduction
Slaughterhouse waste is a biodegradable waste and consists of blood, manure, offal
and paunch contents. These waste materials are produced during the slaughtering
process involving different steps such as killing the animals, removal of the carcass,
cleaning the stomach and intestines [1]. The blood stream produced as a result of the
slaughtering process is more concentrated and has a high BOD and COD level [2] as
compared to the wash water stream produced by washing of the site after slaughtering
of animals.
The typical levels of COD for slaughterhouse waste range from 18,000 mg/l to 43,000
mg/l [3]. However, it has been observed that the COD can reach levels as high as
100,000 mg/l, depending on the composition and dilution of the waste. If the waste
consists of blood and the paunch contents then the COD levels are high. However, if
the waste is collected from the drains leaving from the slaughterhouses then it mostly
consists of blood diluted with the water flowing in the drains. Both these cases are
observed in this study.
There are more than 20,000 slaughterhouses in Pakistan. In addition to these
slaughterhouses, the butcher shops in which the animals are slaughtered on a small
scale and the slaughtering of poultry animals also add to highly contaminating waste
discharged into water bodies without prior treatment.
Anaerobic digestion is known to be a useful method for a variety of wastes including
municipal waste, industrial waste and slaughterhouse waste. Anaerobic digestion may
be defined as the decomposition of the organic and inorganic material by micro-
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organisms in the absence of oxygen forming different end products including carbon
dioxide and methane [4]. Different types of anaerobic reactors have been used for the
treatment of slaughterhouse waste such as the anaerobic contact reactor, upflow
anaerobic sludge blanket (UASB) reactor and anaerobic filter [5].
The major advantage of anaerobic digestion is that it does not require energy input if
the anaerobic digestion process is carried out in mesophilic temperature range (30-
40°C). This temperature range is easily maintained most of the year in countries
having hotter climate such as Pakistan. The amount of the biological sludge produced
during the anaerobic digestion is significantly lesser compared to the aerobic
digestion [6]. As a result there is a significant reduction in the costs associated with
the sludge processing and disposal. Bio-gas produced during the anaerobic digestion
consists of about 60% methane, the remaining 40% being CO2, H2S and some other
trace gases [7]. The sludge remaining at the end of the anaerobic digestion is also a
useful by product as it can be used as a soil conditioner or a fertilizer because it is rich
in nutrients such as the potassium, ammonia and other trace elements [8].
Anaerobic digestion processes are prone to biological upsets and operational
problems. The process may be inhibited due to the accumulation of toxic substances
for the anaerobic micro-organisms such as ammonia and volatile fatty acids (VFAs).
Problems such as odour production and corrosion of the digester caused by gases
produced during the process also arise during anaerobic digestion [4]. All these
problems may be solved by proper process design and operation. For example, start-
up performance and improvement of process control was investigated for anaerobic
digestion of waste water from a paper mill [9]. In most of previous studies anaerobic
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treatment is selected for the treatment of slaughterhouse waste [1-3, 10]. In this work
anaerobic digestion is employed for the treatment of slaughterhouse waste under
mesophilic conditions, to determine maximum COD reduction possible for a
slaughterhouse in Peshawar, Pakistan.
2. Material and methods
2.1. Materials
The materials which are used in this work consist of septic tank sludge and
slaughterhouse waste which includes blood, slaughterhouse wastewater and paunch
contents. Anaerobic bacteria required for digesting the slaughterhouse waste were
introduced in the reactor in the form of septic tank sludge. This septic tank sludge
served as the inoculum. The slaughterhouse waste was obtained from the Fakirabad
slaughterhouse, Peshawar, Pakistan.
2.2. Testing techniques
The COD of samples was analyzed using the closed reflux method [11] while the pH
was measured using a pH meter.
2.3. Experimental setup
An anaerobic digester of five litres volume including the packing was employed as
shown in Figure 1.
Figure 1 Schematic diagram of anaerobic digester (www.discoverarmfield.co.uk)
A packed section having working volume of 4.3 litres was available in the reactor.
This packing was in the form of corrugated plastic balls and allowed the biomass to
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get attached, thus providing contact of the feed with the biomass. The feed was
manually dumped into the reactor by removing the lid. Effluent was collected
manually from the surface of the mixture in vessel. The gas produced during the
process was collected in gas chamber connected. The mode of operation was
intermittent as reactor was fed after every five days.
2.4. Experimental procedure
In all the five experiments sludge was first added in the reactor and left for warm up
for twenty four hours. On the next day the slaughterhouse waste was added and then it
was left for five days for acclimatization. Sample was collected for analysis. After the
collection of sample more slaughterhouse waste was added. On the tenth day another
sample was collected for analysis, followed by the addition of the slaughterhouse
waste. On the fifteenth day the last sample was collected for analysis. The addition of
sludge (inoculum), slaughterhouse waste, and water in each experimental run is
presented Table 1.
Table 1 Addition of components in various experimental runs
3. Results and discussion
In the first experiment the slaughterhouse waste sample had a COD level of 27,086
mg/l and the sludge sample had a COD level of 42024 mg/l. Digestion continued for
15 days. On every 5th
day the effluent was analyzed for COD. The 1st reading showed
that the COD level was 9360 mg/l which indicated that COD level reduced by 65%.
However, subsequent readings showed that the COD level did not decrease any
further but increased instead. The reason for this upset in anaerobic digestion may be
attributed to sludge floatation phenomena since the feed for this experiment was not
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diluted. Moreover, due to the high protein and lipid content of the blood the
biodegradation of the lipid content resulted in the formation of floating aggregates
[12]. A similar observation has been reported previously for high organic loading rate
(OLR) resulting in sludge floatation and loss of active biomass [1]. The COD level of
the feed (substrate) and the change in COD levels as observed during the experiments
are shown in Table 2.
Table 2 COD levels of the mixed liquor at various stages during experimental
runs
In case of the 2nd
experimental run the temperature conditions were the same as the
first run. The temperature range was mesophilic (35-37°C). The pH in the reactor was
measured during these experiments and it was observed that it varied from 7.6 to 8 so
there was no requirement for pH adjustment as, reported in a previous study [1]. In
the 2nd
experimental run the slaughterhouse waste sample employed had a COD level
of 1,00,972 mg/l, the sludge sample had the same COD level of 42024 mg/l as in the
1st run. Waste sample was sufficiently diluted in order to remove the discrepancy
observed in the 1st run. The first reading, i.e. on 5
th day, indicated a decrease of 67%
in the COD level. The following readings indicated further decrease in COD levels to
73% and 80%. These results indicate that by increasing the amount of the inoculum
the efficiency of the system in COD removal may be increased. The reduction in
COD levels during experimental runs is shown in Figure 2.
Figure 2 Reduction in COD levels as observed during various experimental runs
In the second experiment 210 g of bio-gas was collected on the 30th
day.
The pH levels measured during the third experimental run remained in the range of
7.6 to 8. In the third run, the slaughterhouse waste sample used had the same COD
level of 1,00,972 mg/l as in the second experiment. COD level of the sludge was
42024 mg/l as in the 1st and 2
nd runs. Day 5 reading showed that the COD was 31,458
mg/l which indicated a decrease in COD level of 69%. The following readings
indicated further decrease to 81% and 90%. These results indicate that by increasing
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the amount of the inoculum the inhibition of the process could be prevented and
significant decrease in COD levels could be obtained. The reason is that the inoculum
usually selected would have a lower protein and lipid content. The septic tank sludge
provides dilution to the slaughterhouse waste which has a higher protein and lipid
content. This prevents the inhibition of the process. In the third experimental run the
amount of gas formed was 270 g, collected on 15th
day.
The fourth and fifth experimental runs were performed in the months of September-
October when the temperature ranged from 28°C to 30°C. The initial COD levels of
the waste were 21,360 mg/l. No significant change was observed in pH during the
experiments as the pH variation with temperature is dependent on the components of
the waste digested which were the same as the first three experiments. The mesophilic
temperature conditions in both the experimental runs (Run No. 4 and 5) were not
satisfied which resulted in the lesser reduction in COD in both the experiments. This
is because anaerobic digestion is accelerated by the rise in temperature [13]. The COD
level of the feed (substrate) and the change in COD levels as observed during the
experimental runs are shown in Table 2.
The amount of gas collected in the fourth experimental run was 130 g on 15th
day.
The reduction in COD levels was lesser compared to the first three runs due to lower
temperatures, 28-30°C, as opposed to 35-37°C. However, as compared to the fourth
run the decrease in COD levels was greater because the amount of inoculum used in
the final run was higher. In the fifth run the amount of gas collected was 170 g on the
15th
day. The amount of gas collected in the 5th
run was more than the 4th
run because
the amount of inoculum used in this experiment was greater.
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4. Design of a low cost anaerobic digester
For fabricating a low cost anaerobic digester an empty pesticide drum having a
volume of 300 gallons (1136 litres) was used as an anaerobic digester and an empty
plastic container was employed for the collection of biogas. A series of these digesters
may be employed in a slaughterhouse for the treatment of the waste. The mesophilic
temperature conditions are maintained most of the time, in Pakistan, during a year.
So, there is no need of artificially adjusting the temperature. The number of these
digesters and the total cost for the system was calculated for the Fakirabad
slaughterhouse in Peshawar, Pakistan. The total volume of waste produced daily in
the Fakirabad slaughterhouse is approximately 2041 litres. The Hydraulic retention
time selected was 5 days. So, the total digesters required are 12. Gravel is used as a
medium for biomass attachment. The total volume occupied by the gravel layer is 341
litres in each drum. Each empty second hand pesticide drum cost PKR 6000/- (2012).
The cost of each plastic container used for gas collection was PKR 40/- (2012). So,
the total cost for the system was calculated as PKR 78,480/- in year 2012. A
simplified flow diagram is shown in Figure 3.
Figure 3 Simplified flow diagram for low cost anaerobic digestion system
5. Conclusions
In this paper anaerobic digestion of slaughterhouse waste having high oxygen demand
was carried out in a lab-scale packed anaerobic reactor. The inoculum used in this
work was septic tank sludge. Results indicate that dilution of slaughterhouse waste
and high inoculum to waste ratio increased the reduction in COD levels from 60-90%
during the first fifteen days of anaerobic digestion. The pH level of reacting mixture
was found to vary between 7-8. The amount of bio-gas produced was also measured
on 15th
and 30th
day for various experimental runs. Increase in temperature resulted in
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higher reduction of COD levels. A commercial scale low cost anaerobic digestion
system is proposed for Fakirabad slaughterhouse, Peshawar, Pakistan.
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[9] H.M. Zwain, S.R. Hassan, N.Q. Zaman, H.A. Aziz, I. Dahlan, The start-up
performance of modified anaerobic baffled reactor (MABR) for the treatment of
recycled paper mill wastewater, Journal of Environmental Chemical Engineering 1
(2013) 61-64.
[10] H. Ganoun, H. Bouallagui, A. Okbi, A. Sayadi, M. Hamdi, Mesophilic and
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Figures
Figure 1 Schematic diagram of anaerobic digester (www.discoverarmfield.co.uk)
Figure 2 Reduction in COD levels as observed during various experimental runs
0
20000
40000
60000
80000
100000
120000
0 5 10 15 20
Run No. 1
Run No. 2
Run No. 3
Run No. 4
Run No. 5
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Figure 3 Simplified flow diagram for low cost anaerobic digestion system
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Tables
Table 1 Addition and removal of components in various experimental runs
Run No. 1 Run No. 2 Run No. 3 Run No. 4 Run No. 5
Sludge (L) 0.5 1.5 2.5 0.2 1.0
Water (L) 0.5 1.3 1.3 1.3 1.4
Waste (L) 1.0 0.2 0.2 0.2 0.1
Table 2 COD levels of the mixed liquor at various stages during
experimentation
COD (mg/L) Run No. 1 Run No. 2 Run No. 3 Run No. 4 Run No. 5
Day 1 27086 100972 100972 21360 21360
Day 5 9360 33586 31458 8643 7829
Day 10 16744 27083 18768 6283 5837
Day 15 19266 19973 9696 5268 4509
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Research Highlights
Experimental investigation of anaerobic digestion of a slaughterhouse waste.
Development of a low cost anaerobic system.
Study of effect of process parameters on reduction of COD of waste.