OPTIMASI PEMBENTUKAN ASAM ASETAT DENGAN
MENGGUNAKAN METODE PENAMBAHAN MINERAL (FeCl3 DAN
CoCl2) UNTUK PROSES DAUR ULANG LIMBAH PULP KAKAO
THE OPTIMATIZATION OF ACETIC ACID FORMATION
RESULTING FROM COCOA PULP WASTE RECOVERY PROCESS
WITH MINERALS ADDITION METHOD (FeCl3 AND CoCl2)
_________________________________________________________________________
Bunga Mentari1 Mindriany Syafila2 Marisa Handajani3
Program Studi Teknik Lingkungan ITB
Fakultas Teknik Sipil dan Lingkungan
Institut Teknologi Bandung
Jl. Ganesha 10, Bandung 40132
bungayusuf@gmail.com 1 mindri@ftsl.itb.ac.id 2 marisa.handajani@ftsl.itb.ac.id 3
Abstrak : Pengolahan buah kakao menjadi biji kakao kering akan menghasilkan limbah pulp kakao yang
apabila dibiarkan terus menerus dan tanpa pengolahan lebih lanjut dapat menimbulkan dampak bagi
lingkungan terutama tanah dan perairan yang dijadikan tempat pembuangan limbah tersebut, bau yang
tidak sedap dan juga akan terjadi fermentasi alami dari mikroorganisme yang terdapat dalam limbah
tersebut dimana akan dihasilkan alkohol. Penelitian ini bertujuan untuk memperoleh pembentukan optimal
asam asetat dalam proses pengolahan limbah cair pulp kakao secara anaerob dengan menggunakan variasi
penambahan mineral. Proses pengolahan limbah cair pulp kakao ini menggunakan Circulating Bed Reactor
yang terbuat dari flexyglass berkapasitas 4,5 liter. Seeding dan aklimatisasi dilakukan sampai tercapai
kondisi steady state, kemudian 2 buah reaktor CBR anaerob dioperasikan dalam suhu ruang selama 20 hari.
Masing-masing reaktor diberikan penambahan mineral yang berbeda yaitu reaktor 1 ditambahkan FeCl3
dan reaktor 2 ditambahkan CoCl2. Pengambilan sampel harian dilakukan untuk analisis temperatur, COD,
VSS, asam asetat, pH dan komposisi gas dengan periode waktu tertentu.Pengukuran asam asetat dengan
kosentrasi tertinggi sebesar 27.375,09 mg/L diperlihatkan oleh reaktor 1(dengan penambahan FeCl3),
sedangkan reaktor 2 (dengan penambahan CoCl2) menghasilkan asam asetat dengan kosentrasi sebesar
20.000,06 mg/L. Laju pembentukkan asam asetat untuk reaktor 1 adalah sebesar 1.156,25 mg/L/hari dan
laju pembentukkan asam asetat untuk reaktor 2 adalah sebesar 681,252 mg/L/hari.
Kata kunci : pulp kakao, asidogenesis, asam asetat, mineral
Abstract : The conversion of cocoa fruit to dried cocoa beans generates cocoa pulp waste, which if it lets
continuously and without further process, can generate the impact of environment especially land and
waters as the exile place of waste, unwell aroma and also there will be natural fermentation from the
microorganism ,which there are in the waste, and alcohol will be yielded. The objective of this research is to
know about the optimatization of acetic acid formation resulting from cocoa pulp waste recovery process
with minerals addition method. The process is run on anaerobic Circulating Bed Reactor which is made
from flexyglass that have 4,5 liters capacities. Seeding and acclimatization are conducted until get a steady
state condition, and then two reactors CBR-anaerobic will be operated at room temperature for 20 days.
Both of the reactors are given with different minerals, reactor 1 is added by FeCl3 and reactor 2 is added by
CoCl2. Checking of temperature, COD, VSS, acetic acid, pH are carried during the operation in 24 hoursbases. Gas analysis has performed on certain time period. Result of acetic acid analysis indicates that
reactor 1 (with attendance of FeCl3) produce the highest concentration of acetic acid about 27.375,09 mg/L,
while the reactor which with attendance of CoCl2 (reactor 2) produced acetic acid concentration about
20.000,06 mg/L. The rapid formation of reactor 1 is about 1.156,25 mg/L/days and 681,252 mg/L/days for
reactor 2.
Key words : cocoa sweating, acidogenic, acetic acid, minerals
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PREFACE
Theobroma cacao L. (Sterculiaceae) is an important tropical rain forest species
which occupies as the third of environmental sub sector commodity in Indonesia after oilpalm and rubber. During the time, the result of cacao crop which form as a cacao seed can
be proceed without or with fermentation. Because of the sell prices have no different far
and fermentation process needs much time, the farmer prefers to process the result of
cacao crop to become a dry seed product without fermentation. There are a number of new
products that have potential for increasing returns to cocoa growers. These include seed
pulp and products from pod husk waste which are byproducts from the chocolate
processing industry. These byproducts have not any attention by society and it is also
attend to be assumed as the garbage, so that by the end of this fermentation process, these
byproducts thrown off hand or let empty into the dismissal channel and after that it will be
contamination for territorial water. From 1 kilogram of dry cacao seed can result about 0,1
- 0,19 liters of cocoa sweating. Imaginable if compared it in to the level of cacao seed
production and the growth of cacao seed industrial process amount, it can be more cocoa
sweating total production amount.
During on-farm processing of cocoa seed, the pulp is removed by fermentation and
is hydrolyzed by microorganisms. The natural fermentation process by microorganism will
have an alcohol as the result. Hydrolyzed pulp is known in the industry as "sweating."
During fermentation, the pulp provides the substrate for various microorganisms which are
essential to the development of chocolate flavor precursors during the roasting process.
Fermentation was once thought to be simply an easy way to remove the pulp to facilitate
drying, but its importance to cocoa quality has been well established (Lopez 1986). The
pulp is about 10% from wet weight of seed (Quesnel, 1967) and potential to be exploited.
That cocoa waste pulp can be exploited for making of acetate (acetic acid), which known
as vinegar, by using microorganism which from pure culture or mixture culture
(Prameswari , 2004).
Clostridium thermoaceticum
C6H12O6
glucose
CH3COOH
acetic acid
+ Q
............................................................(1)
(1) = Anaerobic Fermentation Process
The processing of cocoa pulp waste becomes the acetic acid will be carried by the
anaerobic digestion process up to acidogenesis phase. In this phase, metabolism process
from hydrolysis phase product by acidogenic bacteria happened. According to Torien and
Hattingh (1969), anaerobic species which found in this process are from Streptococcaceae
and Enterobacteriaceae family. In general, those bacteria need CO2 and organic acid as
carbon source, ammonia as Nitrogen source or sulfide as sulfur source, Vitamin B, hemin,
menadion, and minerals as a nutrient. The final special product in this acidogenesis
phase are volatile organic acid (propionate, butyrate, acetate, and formic acids), carbon
dioxide CO2, hydrogen H2 ).
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Table 1. Minerals Function in Microorganism Metabolism (Syafila, 1997)
1.
2.
3.
4.
Unsure
Source
Fe
Fe2+,
Fe3+
Cl
Cl-
Co
Co2+
Function in metabolism
in cytochrome, ferredoxin and any
steel-sulfur protein, co-factor
enzyme (dehydrates)
inorganic anion in cell
inside the enzymes which contain
co-enzyme B12 (glutamate mutase,
methylmalonul - CoA mutase)
The factor that influence the acetic acid fermentation are (Rosdyana, 2004) :
Type of microorganism and also amount of cultures
Temperature
pH
Availability of Oxygen
The used of cocoa pulp waste as substrate give two benefit at the same time, first is
to lessening the cocoa pulp waste discard to the ground and territorial water, and secondly
is obtained the acetic acid as vinegar which can give an economically advantages.
METHODOLOGIES
The researches have started from April 2008, where take place in Environmental
Engineering Laboratory of Water Quality, The Faculty of Environment and Civil
Engineering. The researches have done by a few steps work. The first step is cocoa pulp
waste characteristic test. Cocoa pulp waste as a fermentation media are obtained from
peeling phase of cocoa plantation which come from PT. IGE Cipatat, Bandung, West Java.
The characteristic that measured are temperature, pH, Total Suspended Solid (TSS),
Volatile Suspended Solid (VSS), Chemical Oxygen Demand (COD), Biological Oxygen
Demand (BOD) and Dissolved Oxygen (DO).
After we know the characteristic of cocoa pulp waste that need to recovered, we
can start to assemble the Circulating Bed Reactor (CBR). CBR which used is made from
flexyglass and has the volume about 4,5 liter with sampling port. There are things to be
paid attention when compile the reactor are :
- The circle form of flexyglass which has been holed in the half of area and put down
in reactor base to recirculation.
- The aerator with double port is connected to the reactor. First port will breeze the
air and the second one will suck the air, so that the process happened in anaerobic
condition.
- The “goose neck” is used to detect the existence of gas formed.
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Goose neck
Sample Port
Sparger
Aerator
Fig 1. Scheme of the Reactor
Seeding is aim to growing the microorganism which be used in acetate acid
forming process, in order to process the waste in many number. Inokulum/kultur or
biomass seed of bacterium which used is come from cacao pulp waste itself. After the
seeding process, the Acclimatization process can be started. Acclimatization is done for
microorganism adaption purpose, so that the microorganism have ability to processing the
cocoa waste pulp to become acetate acid. The reactors operated with batch system and take
the sample for VSS and COD analyzed, so that it gets the steady state conditions.
Table 2. The compositions of sample on reactor
Mixed Culture
Glucose
Aquadest : cocoa waste pulp
10 % total volume
1 % total volume
50 50
The mainly process in this research is running process. This process use the
Circulating Bed Reactor (CBR) - Anaerobic . The process of cocoa pulp waste is carried in
different reactor for each variations of minerals added. The volume of reactor is 4,5 liters
with the compositions are cocoa waste pulp (1,4 liters), aquadest (1,4 liters), biomass (20%
total volume; 0,7 liters) and minerals which concentration added is 1 – 10 mg/l (in this
research we use 10 mg/l for mineral concentrations added). The minerals are FeCl3 and
CoCl2. The calculations of the reactor compositions are to create the condition of reactor
with COD sample value about 100.000 mg/l.
The reactor operation time is 20 days, where sampling is carried every day in
purpose to analyze some parameters. The parameters are pH, COD, gasses composition,
temperature, VSS and acetic acid concentration.
After we all get the data, alternate analysis of cocoa pulp waste recovery process
with minerals variations added. The sources which have been researched and analyzed
must be compiled in systematic report.
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RESULTS AND ANALYSIS
The first step of researches is cocoa waste pulp characteristic test as a fermentation
media. The cocoa pulp waste characteristic test, which use Standard Methods For The
Examination of Water and Wastewater 20th Edition 1998 ( SMEWW ) as a reference, has
got the result shown on Table 3.
Table 3. Result of Cocoa Pulp Waste Characteristic Test
No
Parameters
Standard of
Measurement
Methods
Result
1
Temperature
°C
27
2
pH
3
TSS
mg/l
SMEWW 2540-D
3196
4
VSS
mg/l
SMEWW 5560
2930
5
COD
mg/l
SMEWW 5220-B
140000
6
BOD
mg/l
SMEWW 5210-B
64000
7
DO
mg/l
SMEWW 4500-O-G
0,3
3,95
According to the result of cocoa pulp waste characteristic test, high organic
concentration in the waste was found, so it is needed a lot of microorganism for the
process. Seeding of mix culture microorganism is aim to growing the microorganism
amounts. Acclimatization is carried for microorganism adaption purpose to the cocoa pulp
waste that will be proceed. Inokulum/kultur or biomass seed of bacterium which used
come from cocoa pulp waste itself, because there is much microorganism that consists in
cocoa pulp waste and the adaptation process of microorganism will be expected.
Fig. 2 The Seeding Process of Cocoa Pulp Waste
Chemical Oxygen Demand (COD) and Volatile Suspended Solid (VSS) analysis
will be carried in acclimatization process. The analysis purpose is to know about the
degradation of organic compound from the waste and also the improvement of
microorganism amount in the reactor. The reactors volume is 6,5 liters with the
composition which shown in Table 4.
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Table 4. Compositions of Reactor in Acclimatization Process
Mixed Culture
Glucose
Waste
Aquadest
650 ml
65 gr
2925 ml
2925 ml
Anaerobic condition can be created by giving nitrogen flushing about ±15 minutes
before and after the compositions of reactor entered. The result of COD measurement in
Fig. 3 have shown that there are the degradation of COD values from 109.760 mg/L
become 50.960 mg/L during 14 days.
Fig. 3 Degradation of COD Values in Aclimatization Process
The measurement of VSS parameter cannot be used as a standard rules, caused by
the growth of microorganisms in the reactor which make a flock and bio-film. The flock
and bio-film are patching in the reactor wall, so this conditions assumed that there is no
homogeneous mixing in the reactor. Bio-film is one of microorganism form which growth
and patch at one particular surface and surrounded by some mucus compound. Bio-film
usually growth on the surface that have contact with the water and almost 99 % of bacteria
live in bio-film community (http://www.edstrom.com in Prameswari, 2004). Acetobacter
aceti is one of the bacterium which takes a part of cocoa seed fermentation and consists in
cocoa pulp waste. They also can make the bio-film (Adams, 1997). This flock and bio-film
formed have influence the amount of microorganism (suspended in waste), become more
less. The measurement of VSS parameter based on suspended solid materials in waste, so
that the value are decreased (Fig. 4).
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Fig. 4 VSS Value in Aclimatization Process
Acclimatization process have been carried after achieve the steady-state condition,
where there is no significant degradation of COD value. After the acclimatization process
has done, we have got more microorganisms that have adapted with the waste to be used in
CBR-anaerobic operation step called Running.
The operation of CBR-anaerobic for the cocoa waste pulp recovery process will be
carried in different reactors, with the capacity of each reactor is around 4,5 liter, for each
variation mineral added. Reactor 1 has given by FeCl3 and reactor 2 has given by CoCl2 as
the mineral addition, with each mineral concentration is about 10 mg/L. In the beginning
and after waste-biomass-aquadest-mineral compositions packed into the reactor, nitrogen
flushing must be carried about 15 minutes with the purpose is to create the anaerobic
condition in the reactor. In this operation phase, besides measuring COD and VSS values,
we are also measuring other parameters such as pH, temperature, acetic acid as a daily
parameters and gas composition at selected time of period. After 20 days of operation time
and sampling, the reactors will be stopped.
Temperature as one of the factors that influence acetic acid formation process, has
been measured in purpose to save the optimum temperature for the reactor. Figure. 5
shown that both of the process have ruined in the optimum temperature (23,9 – 29,4 °C).
Fig. 5 Temperature
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The COD measurement results from both reactors (Fig. 6) shown that the more
degradation value has happened in reactor 2 (with CoCl2 as mineral addition). The
degradation is until 35.280 mg/L (on 20th day). In the reactor 1 (with FeCl3 as mineral
addition) the degradation value reaches 50.960 mg/L (on 20th day).
Fig. 6 The Degradation of COD Values
The result of VSS value measurement, visible at Fig. 7, have shown that VSS
values from both of the reactors are tend to increasing by the end of period. It is mentioned
that the microorganism which take a part in this process are decreasing. The fluctuation of
VSS value can be caused by the microorganism from cocoa pulp waste which have
tendency to forming a bio-film at the wall and the surface of the reactor, also forming the
flock in waste dilution, so that the posibility of flock and bio-film from the sample which
measured daily to be brought or not becomes one of the factors that influence the result.
Fig. 7 The Fluctuation of VSS Value
The formation of acetic acid from both of reactors visible in Fig. 8. In the
beginning of period, the formation of acetic acid is unvisible or just about 6000 mg/L. The
highest concentration of acetic acid by the end of period is about 27.375,09 mg/L from
reactor 1. The formation rapid from reactor 1 is about 1.156,25 mg/L/day. Reactor 2 is
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yielding about 20.000,06 mg/L for the acetic acid, with the formation rapid about 681,252
mg/L/days.
Fig. 8 The Formation of Acetic Acid from Cocoa Pulp Waste
Acetic acid concentration that formed, inversely with acidity degree that
represented by pH value from each reactor. The concentration of acetic acid that increase
can make the pH value of the reactor decrease (Fig. 9).
Fig. 9 pH Value from Cocoa Pulp Waste Recovery Process
Gasses kromatografi is used to measuring gas composition. The result from the
measurement (Fig. 10) are O2 gasses concentration in reactor 1, about 17,8229 % v/v in the
beginning of period and 18,5128 % v/v in the end of period. In reactor 2 (Fig. 11), O2
gasses concentration has decreased from 20,3259 % v/v become 17,5361 % v/v in the end
of period. Attedance of O2 gasses in the reactor have influence the path of acetate. Reactor
1, which have O2 gasses concentration increased from beginning to the end of period,
cause acetic acid formed faster. The decreased of O2 gasses concentration in reactor 2
causes acetic acid formed slowly.
The concentration of N2 in the beginning of reaction (t0) of reactor 1 is about
81,5837 % v/v and concentration of N2 in reactor 2 about 79,4986 % v/v, but the
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concentration of N2 from reactor 1 and 2 have a relative values is about 81 % v/v in the
end of reaction. CO2 concentration is about 0,5933 % v/v for the reactor 1 and 0,1753 %
v/v for the reactor 2 in the beginning of reaction. At the end of reaction, CO2 concentration
of reactor 1 has been decreased about 0,2662 % v/v, but the CO2 concentration for reactor
2 has been increased about 0,4 % v/v.
Fig. 10 Gasses Composition (Reactor 1; FeCl3 as Mineral Addition)
Fig. 11 Gasses Composition (Reactor 2; CoCl2 as Mineral Addition)
At the reactor 1, there is no H2 gasses concentration from the beginning until the
end of the periode. While, in the reactor 2 the H2 gasses concentration did not founded in
the beginning of periode, but there is H2 gasses concentration founded about 0,0723 % v/v
by the time of periode. The attendance of H2 gasses at the reactor can be happened because
of the H2 producer bacterium existence. According to Grady & Lim (1980), in anaerobic
process there are the H2 producer bacterium which included in to non-metanogenic
bacterium group. Bitton (1994) is also told that there are group of acidogenic fermentatif
bacterium and acetogenic bacterium which produce H2 gasses in anaerobic process.
Attendance of H2 gasses will cause the pressure of hydrogen parcial decreased, the
pressure of hydrogen parcial above 10-4 will cause acetic acid formed process will be
blocked.
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CONCLUSION
Cocoa pulp waste can be exploited and proceed with anaerobicly, produce various
byproduct compound from the acidogenic process. The acetic acid is a special byproduct
compound that produced. The cocoa pulp waste recovery process which use Circulating
Bed Reactor-anaerobicly with minerals added method (FeCl3 dan CoCl2) for about 10
mg/L, has the highest acetic acid concentration from reactor 1 (with FeCl3 as mineral
addition) about 27.375,09 mg/L as a result. The acetic acid concentration from reactor 2
(with CoCl2 as mineral addition) is about 20.000,06 mg/L by the end of period. Oxygen
gasses concentration which founded in the reactor has influence the acetic acid forming
process. The anaerobicly acetic acid forming process will be blocked with the attendance
of H2 gasses in reactor.
The big scale of cocoa pulp waste recovery process better be done by anaerobicly
process, because the path of acetic acid forming process which done aerobicly will require
O2 so that the biggest energy will be needed to take care the reactor condition keep
aerobic. On the other hand, the aerobiclly acetic acid forming process can be done with
technological engineering such as minerals added method which give a nutritions source to
the mixed culture of cocoa pulp waste anaerobic bacterium.
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