Methane Production from the Digestion of Thermally Treated Food Waste at 80°C

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1017-1022

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Methane Production from the Digestion of Thermally

Treated Food Waste at 80°C

Farizah Fadzil , Farihah Fadzil , Siti Mariam Sulaiman , A'isyah Mardhiyyah Shaharoshaha,

Roslinda Seswoya*

Micro Pollutant Research Centre (MPRC), Universiti Tun Hussein Onn Malaysia, 86400, Parit Raja, Johor, Malaysia

Faculty of Civil Engineering and Built Environment, Universiti Tun Hussein Onn Malaysia, 86400, Parit Raja, Johor, Malaysia

Received: 10/05/2020

Accepted: 23/06/2020

Published: 20/09/2020

Abstract

Food waste is the most suitable feedstock for anaerobic digestion. However, methane yield from the digestion of food waste is low.

Therefore thermal pretreatment serves as the best solution. Also, the effect of thermal pretreatment on food waste (Malaysian dietary) before

anaerobic digestion has low documentation. Hence this research aims to analyze the methane production and its kinetics from the digestion

of thermally treated food waste. The result showed that thermal treatment improves the bioavailability of food waste, subsequently improve

the methane production of food waste. The ultimate methane yield for thermally treated food waste at 80°C was 883.08 CH4/gVS higher

than untreated food waste. The kinetic parameters observed from Modified Gompertz modeling were slightly lower from the laboratory data

for both substrates. Thus, thermal pretreatment undoubtedly improved the anaerobic digestion of food waste.

Keywords: Anaerobic, Food waste, Thermal, AMPTS, Gompertz

List of symbols and unit¹

Symbols and Unit

thrown from the residential, commercial and institutional areas,

and it is characterized in ranges of 52 and 66 % in moisture

Description

content. MSW increases proportionally with population growth in

developed and developing countries. The MSW is rising at the

rate of 0.5-0.8 kg/person-day and is expected to exceed 9 Mt/year

in the year 2020 [1]. The disposal of MSW in an open dumping

area is producing environmental impacts on soil, water, and air.

Dumping MSW on soil affecting soil fertility by reducing the crop

yield, the degradation of organic waste in the landfill produced

the leachate. The discharge of untreated leachate into the river

causes groundwater contamination. Also, the landfill area

associated with an unpleasant odor and uncontrolled release of

methane through waste decomposition [2]. The landfill is also

diminishing the nation's land area to 54% from the year 1990-

Anaerobic digestion

Organic Fraction of Municipal

Solid Waste

Municipal Solid Waste

Food Waste

OFMSW

MSW

Thermally treated food waste at

FW80

0°C

BMP

Biomethane Potential

Automated Methane Potential

Test II

Total Solid

Volatile Solid

Chemical Oxygen Demand

Alkalinity

Modified Gompetrz Model

Lag phase

Ultimate methane yield

Methane production rate

AMPTS II

TS (g/L)

VS (g/L)

COD (mg/L)

008 in Malaysia [1]. 30% of MSW is food waste [3]. Food waste

causes alarming problems to its surroundings due to its essence as

material that is easy to decompose [3].

(mgCaCO /L)

흀(day)

Food waste can be segregated into four groups, which are

edible, non-edible, avoidable, and unavoidable. The edible food

waste, also known as avoidable food and is defined as the food

and drinks that are eaten by people. Others choose not to

consume, whereas the non-edible and unavoidable food waste is

the residue food preparation [4]. Food waste consists of complex

(

mlCH

/gVS)

/gVS-day

Introduction

Municipal solid waste (MSW) is defined as unwanted waste

Corresponding author: Roslinda Seswoya, (a) Micro Pollutant Research Centre (MPRC), Universiti Tun Hussein Onn Malaysia, 86400,

Parit Raja, Johor, Malaysia; and (b) Faculty of Civil Engineering and Built Environment, Universiti Tun Hussein Onn Malaysia, 86400, Parit

Raja, Johor, Malaysia. E-mail: roslinda@uthm.edu.my.

017

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 3, Pages: 1017-1022

organic compounds (e.g carbohydrate polymers, lipids, protein,

and some other inorganic components (e.g silica) [3]. About a

quarter of 1.3 billion food was lost along the food chain due to

human consumption, in the way of preparation of food (e.g food

processing factory) [5].

The method for treating MSW includes incineration, landfill,

and anaerobic digestion [1]. Anaerobic digestion was used for

treating the organic fraction of municipal solid waste (OFMSW),

particularly food waste [6]. Anaerobic digestion is a devoted

method to manage food waste due to its high bio-methane

potential [7]. It can develop renewable energy (methane and

hydrogen), volatile fatty acid (VFA), and alcohol. Anaerobic

digestion is the cost-effective treatment in managing waste

because of high energy recovery and low environmental impact

Gomperts Modelling [22]. Modified Gompertz is regarded as the

kinetic model of asigmoid function, which is used for a time series

as a mathematical model [23]. Modified Gompertz is the highest

feature in anticipating the output of biogas, as the model has one

of the highest fits for methane manufacturing information as a

function of time [24]. In this model, the rate of biogas production,

the maximum biogas production, and the lag phase can be

estimated [25]. Gandhi et al., [18] evaluated the kinetics of

anaerobic digestion of food waste using Modified Gompertz

modeling, and it is reported that the ultimate biogas yield was

improved from the digestion of thermally treated food waste at

80°C and the lag phase was reduced significantly. Unfortunately,

there is limited information on the anaerobic digestion of

thermally treated food waste in Malaysia. Therefore this research

aspiration is to study the effect of thermal pretreatment of food

waste towards the methane yield.

[

3]. Besides, anaerobic digestion is the biochemical method that

occurs when there is no oxygen at all [8]. The absence of oxygen

is a significant difference between anaerobic and aerobic

digestion [9]. Anaerobic digestion involves several biochemistry

processes, such as hydrolysis, acidegenosis, acetogenesis, and

methanogenesis [10]. The implementation of anaerobic digestion

can improve the economic feasibility and become an

environmentally sustainable solution in managing waste [11]. For

instance, methane from anaerobic digestion can replace fossil fuel

power used and reduce greenhouse emissions [12].

Material and Methodology

.1 Substrate and inoculum

The food waste was collected from a cafeteria. The collected

food waste consists of cooked food such as meat, rice, bone, and

vegetables [26]. Impurities such as bone, tissue, and plastic were

manually removed and sorted [11]. The fresh food waste was

collected for two days. The collection during this period is due to

the cafeteria operation period. The special treatment such as

sterilization is not conducted on food waste. Then, the fresh food

waste was diluted with tap water at a ratio of 1:1 for food waste

slurry preparation [27]. After that, the food waste was

homogenized with the aid of kitchen blender [22]. The food waste

was filled in a 1 L glass bottle (Schott Duran) and then was

thermally treated in the oven at 80°C for about 1.5 hours [13].

After 1.5 hours, the bottle was left to cool at room temperature

before it was used for biochemical methane potential (BMP) test

The ultimate methane yield from the digestion of food waste

is low [13] because the solubilization of particulate matter to

simple monomer during the hydrolysis stage of the anaerobic

digestion process requires a long time and thus making this step

problematic [14]. Pretreatment was applied to enhance the biogas

production and overcome problems during the hydrolysis stage of

anaerobic digestion of food waste. The pretreatment methods are

mechanical, biological, chemical, and thermal [13]. Thermal

pretreatment was introduced at a mild temperature of 55 to 90 C

[

15]. Thermal pretreatment increased the organic particle

[

13].

Anaerobically digested sludge used as inoculum was collected

solubilization, subsequently making it more assessable by

anaerobic microbes [13].

from an anaerobic digester treating POME. The sludge was stored

in a plastic container and refrigerated at 4°C prior used for BMP

testing [28].

Thermal pretreatment is a proven approach, as it improved the

digestion process [16]. The characteristics of food waste such as

COD, carbohydrate, and protein were also enhanced as well as

methane production after undergoing thermal pretreatment [17].

Gandhi et al., [18] observed an improvement in protein

solubilization after the thermal pretreatment process. According

to Jin et al., [19], the changes in pH after thermal pretreatment are

lesser in low temperature and higher in high temperature

depending on the duration of the pretreatment. Longer period with

the high temperature of pretreatement, increased the release of

organic acid, making the pH of the substrate to reduce [19].

Thermally treated food waste obtained a higher value of total

solids, volatile solids, and chemical oxygen demand (COD) than

the untreated food, indicated that the thermal pretreatment

increased bioavaiability. Bioavailability makes the thermally

treated food waste easily digested subsequently resulted in higher

methane yield [20]. Meanwhile, according to Ariunbaatar et al.,

.2 Biodegradability assay (biochemical methane potential)

BMP is a well known effective technique for evaluating the

rate of methane transformation of organic matter [29]. The batch

test was conducted by practicing Automated Methane Potential

System Test System II (AMPTS II), as shown in Figure 1

[1][26][30]. The system serves swift service of measuring

biomethane flow and ultra-low biogas in determining biogas

potential [30].

The digestibility of food waste was studied through a series of

batch anaerobic digester conducted using a 500ml digester with a

mass of 400g [31]. The value of substrate and inoculums added

into the mixture were calculated based on VS [31]. Substrate and

inoculums were mixed at inoculum to substrate ratio of 2.0 [28].

This ratio is recommended to avoid the inhibitory effect [32]. The

pH of each reactor was recorded between 7.2 to 7.4. This pH is in

the range for anaerobic digestion, which is from 6.5 to 7.5 [33].

The reactor was flushed with nitrogen for two minutes to provide

an anaerobic condition [30]. Mesophilic state (37±0.5°C) was

maintained by a thermostatic water bath incubator [26]. The

reactor was stirred with a mechanical mixing at 90rpm [18].

[

13], the thermal pretreatment at 80°C for 1.5 hours produces

higher methane yields than untreated food waste. The difference

in methane yield between untreated food waste and thermally

treated food waste at 80°C was about 221.5 ml CH /gVS.

Kinetic analysis is implemented to predict and express the

performance of anaerobic digestion systems [21]. The kinetic

analysis of anaerobic digestion can be accomplished using First

Order Kinetic, the Logistic Function Model, and Modified

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