The Research on Food Waste Pre-Treatment Technology for Incineration in Malaysia

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

J. Environ. Treat. Tech.

ISSN: 2309-1185

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

https://doi.org/10.47277/JETT/9(1)147

The Research on Food Waste Pre-Treatment

Technology for Incineration in Malaysia

,2*

Ahmad Faizal Zamli

, W.M.F. Wan Mahmood , W.A.W. Ghopa , M.T. Lim

Department of Mechanical and Manufacturing Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia (UKM),

3600 UKM Bangi, Selangor, Malaysia

Centre of Bioenergy & Sustainability, Renewable Energy & Green technology, Generation and Environment, TNB Research Sdn. Bhd., 43000 Kajang,

Selangor, Malaysia

Received: 09/08/2020

Accepted: 21/10/2020

Published: 20/03/2021

Abstract

Food waste and food loss are used to describe materials that are actually produced for consumption, but are discarded, lost, degraded or

contaminated. Food waste (FW) is one of the main parts of municipal solid waste. Landfill is not preferable when compared with other types

of waste handling method. It has been reported that the impact of landfill on climate change can be ten times higher than other waste handling

methods. However, most FW end up in landfills. This paper reviewed the performance of several food waste pre-treatment technologies to

convert FW into feedstock for incinerators/boilers in terms of electrical power generation purposes. The performance of food waste pre-

treatment methods and their products were extensively discussed and compared in this paper in terms of calorific value, energy density, and

compound reduction, which later directly corresponded with the energy, environmental, and economic factors for the sustainability of future

renewable power generation.

Keywords: Alternative fuel; bioenergy; deep drying; fuel pre-treatment; alternative fuel; waste to energy; energy densification;

thermochemical process

method (7–12). Landfills are one of the factors that contribute

towards climate change due to greenhouse gas (GHG) emission.

Introduction

One third of the food produced globally are wasted, which

It is reported that the impact of landfill on climate change can be

ten times higher than other waste handling methods (13). In Asia,

especially in Malaysia, FW is one of the main components of

MSW. Most FW end up in landfills. Landfills cause gas emission

problems of carbon dioxide (CO2) and methane (CH4) (14,15).

Methane gas is produced through aerobic and anaerobic

decomposition of solid waste and is a more potent GHG than

carbon dioxide (7). Currently, FW recovery from MSW is

relatively low. FW is one of the main parts of municipal solid

waste (MSW). With its abundant source, the potential for this

waste to become power generation feedstock in Malaysia is less

explored. Most of the time, FW is not properly sorted and has high

moisture content. These mixed wastes contaminate other MSW

components and recyclable materials in them. Dewatering and

drying are very important for achieving high energy recovery

from FW and thermal drying is still a main method for FW drying

amounts to about 1.3 billion tonnes per year (1). Food waste (FW)

and food loss (FL) are used to describe materials that are actually

produced for consumption, but are discarded, lost, degraded or

contaminated (2). In 1981, according to the Food and Agriculture

Organisation of the United Nations (FAO), the definition of FW

includes the post-harvest period of food when in possession of

final consumers (3). Gustavsson et al. came up with the same

definition, however, they included the food supply chain (FSC)

that contains a five-system boundary. It comprises agriculture

production, post-harvest handling and storage, processing,

distribution, and consumption (1). Malaysia approximately

produces more than 15,000 tonnes of FW daily as reported in

018 (4). In 2006, 93.5% of the municipal solid waste (MSW) in

Malaysia were sent to landfills or open dumpsites and only 5.5%

were recycled and 1% was composted (5). In the Waste

Management Association of Malaysia (WMAM) Conference

(

16). A correct pre-treatment method of FW can convert it into

019 (6), the rate of recycling in Malaysia had drastically risen to

8.06% in 2018. Nevertheless, in the same year, 13,830,014

feedstock for incinerators or boilers. Incinerators are more

reliable in volume and contribute towards mass reduction of waste

in a shorter duration.

tonnes of waste were generated in the country. The waste had

doubled from 19,100 tonnes per day (5) or 6,971,500 tonnes per

year in 2006. Several studies found that landfills are not

preferable when compared with other types of waste handling

Corresponding author: Ahmad Faizal Zamli, Centre of Bioenergy & Sustainability, Renewable Energy & Green technology, Generation and

Environment, TNB Research Sdn. Bhd., 43000 Kajang, Selangor, Malaysia. E-mail: faizal.zamli@tnb.com.my

139

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

This paper reviews the performance of several FW pre-

treatment technologies to convert FW into feedstock for

incinerators/boilers. The performance of FW pre-treatment

method and its products are discussed in this paper in terms of

calorific value, energy density, compounds/elemental reduction

and etc. for sustainable future renewable power generation.

normally comprises high water content with a low heating value

(23). Therefore, a pre-treatment method is needed to enhance the

properties of FW so that it can become a good feedstock for

incinerators. This unrecoverable source such as FW needs to be

treated as soon as possible since most of the time, the food waste

contains organic materials and will undergo the fermentation

process after a short interval of time with exposure to the

surrounding air.

.1 Municipal Solid Waste, Food Waste, And Waste To Energy

Incineration

The MSW generation in Peninsular Malaysia has been

FW can be alternatively recycled into pelletised poultry food

or pet food. Besides, these food wastes can be converted into

biogas; however, they require a low contamination condition and

the process is very delicate. Most of the time, MSW mixed with

FW cannot be recycled anymore due to high impurity, bad odour,

and high cost of waste sorting, among others. The age of FW

usually determines the method of waste to be treated. Sorted fresh

FW can be used as feedstock for biogas reactors. Older versions

of FW are more suitable to be processed into fertilisers. Normal

incinerators can handle all types of FW. However, untreated or

wet FW can become a problem with steam production in terms of

heat and pressure fluctuation. These conditions happen because

there is a big range of gap of calorific value (CV) in the untreated

FW. Proper pre-treatment is needed for FW so that this source can

become a game changer in power generation using MSW.

A study in Singapore found that on average, the local

residents generated 118 g of table FW and 91 g of kitchen FW per

person for each meal. A total of 1,000 tonnes of FW with 16%

impurities are generated daily in Singapore (23). In Malaysia, it

is reported that in 2011 and 2018, 20,000 tonnes (24) and 37,890

tonnes of solid waste were generated each day and almost half of

them were FW. Abundant solid wastes generated every day

require an expensive handling cost. In Malaysia, local authorities

spend up to 60% of their annual budget on waste management.

This costs Malaysia between RM110 to RM130 to collect and

dispose one tonne of garbage [8] and this does not yet include the

land requisition cost. Other research discovered that 70% of the

total cost of waste management in Malaysia are spent on the

collection of waste (25).

increasing since 2001 (8). Kuala Lumpur is the top city in

Malaysia that produces the most MSW and in 2013, it produced

000 tonnes/day of MSW (8). Table 1 below shows the data of

population and generation of MSW for some countries. It is

observed that the amount of MSW generated daily is directly

proportional with the population living in the town/country. MSW

generation also depends on a person’s diet and the waste

management system’s condition in these certain areas.

Table 1: The trends of population and the MSW generation

Town/

Country

MSW

generated

Country

Malaysia

Iran

Population

5,809,953

700,000

Region

Kuala

Lumpur

South

East

Asia

000

tonnes/ day

(8)

.9 – 1.0

Middle

East

Rasht (17)

tonnes/day

South

East

Asia

Indonesia

190,000

tonnes/day

Indonesia

253,000,000

(18)

Table 2: MSW composition for some country

Asian countries such as China and Singapore are operating

waste-to-energy (WTE) incineration plants to convert their waste

into energy. Gasification and anaerobic digestion plants use FW

as feedstock; however, they are still under research and

development. It has been reported that gasification and anaerobic

digestion (AD) can give better performance in terms of larger

environmental benefits (23) than incineration. The problems with

these systems are that these technologies are not ready or robust

for large-scale commercialization. The shutdown of an AD plant

in Singapore in 2011 is an example of the system’s failure (26).

On the other hand, incineration plants have increased rapidly

in the last 50 years for both China and Singapore. The plan to

increase incineration plants in both countries shows that the

demand for this type of WTE is still huge (22,26). However, as

reported in 2015, the waste separation in China was poorly

executed and no pre-treatment was done to the waste prior to

WTE incineration (22). With more wastes being generated each

and every day, waste incineration is the best option to reduce

waste. For example, incineration can reduce up to 70% of volume

and 80% mass (27) of the waste. This technology has vastly

improved over time (9). As mentioned before, it is not suitable to

utilize raw FW as fuel in incinerators because of its high moisture

content. Furthermore, the combustion of fuel with high moisture

content such as FW is not economical. For example, the National

Town/

Country

Malaysia

7 -

14 -

5 - 48

(8)(19)

South Asia

(

20)

OECD

(20)

Latin

America

(

20)

Estonia

21)

16.

22.

27.

17.8 6.8

23.9 1.3

2.9

4.8

(

Wenzhou,

China (22)

4.7

1.7

Organization for Economic Cooperation and Development (OECD)

The data from Table 2 above show the composition of MSW

in several countries. In South Asia, for example, it is observed

that FW is almost half of the MSW wastes generated. The range

for FW in Malaysia’s MSW is from 40% to 50% (19). FW

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Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

Environment Agency (NEA) in Singapore has a plan to remove

eatery FW from incineration to AD (23). This could be prevented

if FW in the MSW is pre-treated using pellet technology before

the incineration process. Pre-treatment of FW increases calorific

value, making FW a more suitable fuel for incinerators. The pre-

treatment can reduce unwanted chemicals as well as the moisture

content. This would help to increase the incinerator system’s

efficiency in the future.

Table 3: MSW composition for some country

(MJ/kg)

(%)

Fuel type

Pre-treatment

Product

Anglo

Mafube

bitumin

ous coal

Coal (11)

Raw

25.2

26.15 &

This study looks into the application of seven FW pre-

FW (11)

Torrefaction

Biochar

9.76

treatment technologies and its product characteristic based on the

literature study. The pre-treatment data from literature are

analysed from the point of view of economic, environmental and

energy which represented by energy density, unwanted

compounds/ chemical reduction and calorific value. These data

are ranked using the Weighted Factor Rating to select the best FW

pre-treatment practices for the incineration application.

(Raw)

Landfill

FW (28)

17.45 to

28.42

Torrefaction

Biochar

9.5 to

2.25 &

FW(29)

19.52

Raw)

8.44 to

(

FW(starch

y, rice)

30)

Steam

Torrefaction

27.44 &

18.08

(Raw)

Biochar

(

. Food Waste Pre-Treatment Technology for

Air and

Power Generation

2.86 &

9.95

thermally

assisted bio-

drying

FW can become better fuel for the incineration process with

the correct pre-treatment method. Other problems related to FW

incineration is its emission products are derived from chemical

reaction that comes from the elements and compounds inside the

FW. Unwanted elements and compounds from the FW can be

minimized after the pre-treatment is done. The best FW pre-

treatment method is the one that is capable of economically

minimizing harmful emissions, increasing calorific value, and

increasing energy density of the treated FW. This subtopic will

discuss several FW pre-treatment technologies to convert FW into

feedstock for thermochemical oxidizers such as incinerator, boiler

furnace, and gasifier. Table 3 shows the food waste pre-treatment

methods and their product calorific value.

FW (16)

FW (31)

4.3 (Raw

wet)

63.2

Pre-treat with

enzyme &

Hydro

Hydro-

char

17.4 to

26.9

thermal

carbonization

(HTC)

Restaurant

FW (31)

Hydro-

char

HTC

15 to21.7

Hydro-

char

Hydro-

char

17.85 to

31.73

17.85

FW (32)

HTC

Raw

FW (32)

Restaurant

FW (33)

33.57

.1 Torrefaction

RDF (8-10%

bio-waste)

RDF from

household &

industrial

MSW (34)

Loose

6 to15

Literally, torrefaction is a French word that can be directly

translated as roast or grill and it is likely used in the past as a

process for coffee production. Torrefaction is a technology to

convert FW into char by exposing FW to high temperature

without the presence of oxygen. During torrefaction, moisture

content is reduced as unbound moisture is eliminated through the

evaporation process with increased temperature ranging from 200

3 to

MSW(35)

12 to 21

sources.

Autoclave

Fibre

6.5

Vegetables

and leafy

FW (36)

(Raw) &

°C to 300 °C (11). The normal biomass torrefaction temperature

Autoclave

Fibre

Pellet

is around 300 °C; higher thermal pre-treatment temperature is

referred as pyrolysis (29). With an increase in temperature from

11.7 to

15.7

(Treated)

10 °C to 250 °C, light volatiles like CO₂, CO, and H₂O are

emitted (38). These volatile matters are produced due to the

degradation of hemicellulose and light aliphatic compounds from

carbohydrates, which are more sensitive to temperature than other

biomass components (11).

Heavier volatiles are reduced as gases during the reduction

of cellulose, protein, and carbohydrate compounds as temperature

is increased to 300 °C. Methane, formic acid, acetic acid, and

aromatic are some examples of the gases produced in this stage

MSW

woody

biomass

and agri-

food waste

Pelletization

19.5

(37)

NR – not reported

Overall, torrefaction technology has big potential to pre-treat

FW in the future since FW is generated every day and still

increases. The main issues that need further consideration in the

torrefaction of FW are to reduce the process time, reduce ash

content, and increase the capacity with efficient use of energy. It

is suggested that solar integration to the torrefier system can

further increase the torrefier technology value.

(

38,39). The carbon content and energy density in the biochar

products are enhanced, which is directly linked with the increase

in calorific value of the biochar products (11,28–30). It is

observed that the treated FW’s lifespan increases as compared to

raw FW.

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2021, Volume 9, Issue 1, Pages: 139-147

.2 Autoclaving

2.4 Hydrothermal carbonization

Hydrothermal carbonization

Autoclaving is a process that involves steam processing in a

(HTC)

another

vessel under the action of pressure (40). This process is done to

FW to enhance the quality of the waste in terms of its potential to

produce better gas from biogas or gasification processes or

produce better fuel for combustion or other types of waste

management process. Moreover, this process sterilizes FW that

decontaminates other wastes and neutralizes odor compounds.

Sterilization of FW also enhances the subsequent application of

recovered wastes. Autoclaving of biodegradable and organic

wastes such as FW and paper converts them into a fiber-like

material (36).

An example of autoclaving process is using 2–3 kg of sorted

and dried FW in a 24 L tank filled with water and treated at a

temperature range of 121 °C to 127 °C and 17 psi to 21 psi (1.17

bar to 1.45 bar) in an autoclave reactor for 35 to 60 minutes (40).

This study found that autoclaved FW had lower heavy metal

content and was within the range of compost standard. Another

study used injected steam and 45.9 kg of vegetables and leafy fruit

waste from supermarkets in a 530 L rotary (7rpm) autoclaved

reactor at temperatures of 408 K (134.9°C), 428 K (154.9°C), and

thermochemical pre-treatment method that can be used to convert

FW into fuel. HTC is able to reduce the unwanted high moisture

content from FW. HTC is a pre-treatment process that is applied

to organic waste at certain operating condition setting,

temperature range of 200–350 °C, and process duration within 0.2

to 120 h (41). The hydro-char products from this thermal pre-

treatment method are with high carbon and energy content.

Besides, a study reported the positive energy balances on the

HTC pre-treatment of FW (33). The energy content may be

influenced by the presence of packaging materials that are usually

found together with the recovered solids. This study compared the

HTC energy content of several samples from pure FW and the FW

with packaging materials. The level of energy content of

recovered solids from FW with packaging materials showed a

reduction when compared with the pure FW. This may due to the

low energetic retention, which is associated with the packaging

materials (33).

Previous research found that hydro-char is possibly

generated by two major reaction pathways (42). One of the

methods is the hydro-char formation via direct solid–solid

conversion, which mainly follows the path of de-volatilization,

intramolecular condensation, dehydration, and decarboxylation

reaction. The next possible reaction is the conversion of

intermediate products in the aqueous phase, which experiences

hydrolysis, dehydration, decarboxylation, polymerization, and

aromatization. HTC resulted in the reduction of volatile matters

(43) and it is found that hydro-chars from the HTC process can

increase the FW energy density and calorific value.

38 K (164.9°C) and 3,6,7 kg/cm² or approximately around 3,6

and 7 bar for 15 and 60 minutes (36). This autoclaved food waste

showed reduced calorific value, volume reduction, and increase

in product density.

This study also discovered that the fiber content of

hemicellulose, cellulose, and lignin fluctuated and it is suggested

that the autoclaving process had altered the fiber in the samples.

Further study is needed to increase the knowledge and fine tune

the system to have a better perspective of the real potential in

treating FW using the autoclaving method.

2.5 Leaching technology

Leaching is another type of pre-treatment method that has

.3 Thermally assisted bio-drying

been proven to treat biomass [44]. Leaching, which uses water,

can be used to reduce some of the FW’s unwanted elements or

compounds such as heavy metals, alkali metals, contamination

during handling, for instance. The application of water-based pre-

treatment for waste, especially FW, has high potential to be

explored. The objective of the pre-treatment is to improve the FW

calorific value and to reduce the unwanted compounds inside the

FW in order to prevent the formation of slag, emission of toxic

gases, and smell pollution.

The FW leaching requires additional energy for the drying

process. Leaching improves the FW properties such as lower

moisture content, cleaner, less odor, and ability to be kept longer.

The reduction of unwanted elements/compounds in the fuel may

produce cleaner gas emission. The water-washing technology is

known to assist the reduction of alkali metals in bio materials

Bio-drying is a process to reduce excessive water in FW. FW

consists of high biology waste materials that are suitable for the

bio-drying process. Solid fuel with higher energy content is

obtained at the end of the bio-drying process. Bio-drying method

uses energy produced from microbial degradation in the FW to

heat up water with the assistance of forced aeration (16). This

condition increases water evaporation and stimulates microbial

degradability. It is found that staged heating acclimation can

obtain a superior thermophilic inoculum with high metabolic

activity and microbial consortia. An extremely high metabolic

activity is obtained during the thermally assisted bio-drying

process, which is greatly higher than conventional bio-drying

(

16).

Jiao Ma et al. conducted thermally assisted bio-drying,

which operated at temperatures of 50 °C to 60 °C using 1.2 to 2.2

L containers filled with 500 to 1000 g FW in 5 days’ reaction time

(

44,45). If these alkali metals are not reduced, they will

devolatilize, nucleate, and condense to form hydroxide, chloride,

and sulphate compounds (46–49).

(

16). At the high airflow rate and high temperature condition,

water vapor is taken out of the matrix in a shorter time. The

remaining solid waste can become refuse-derived fuel (RDF),

which is a carbon neutral fuel and a renewable alternative source

to fossil fuel. The time consumption for the whole process to

complete can become a main issue in the thermally assisted bio-

drying process. Further study can be done to reduce the process

time, increase the calorific value content, and increase the

capacity of the process. FW decomposition method that converts

FW into fertilisers adapts an almost similar concept with

thermally assisted bio-drying.

Slag reduction is expected after the FW leaching pre-

treatment method. The washing process during the leaching pre-

treatment will readjust and modify the elemental composition

inside the FW. Alternatively, slag can be controlled by mixing

known fuel composition with other types of fuel or additive to

balance the slag formation element/compound and this method is

called fuel blending. Leaching can be used together with fuel

blending to maximize the pre-treated product potential.

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2021, Volume 9, Issue 1, Pages: 139-147

(

.6 Refuse-Derived Fuel (RDF) and Solid Recovered Fuel

SRF)

Fundamentally, RDF is similar to SRF; however, they differ

suitable moisture content and binder inside the feedstock. During

the palletization process, heat will be generated during the

compaction process resulted from the friction between the metal

roller, metal die, and feedstock. The fiber structure inside the

organic waste such as lignin can act as a natural binder (52) during

the pellet production process. Pellet mechanical durability and its

quality depend on the densification pressure, temperature, lignin,

and starch content (51).

in terms of source, constituents, and pre-processing included

during the process (9). RDF is composed of wastes generated

from domestic and business sectors that primarily involve

biodegradable and plastics, while SRF is a much more

homogenous waste-derived fuel from MSW and commercial

waste that has undergone an additional process to improve its

quality and calorific value and meet the European CEN/TC 343

standards (50). SRF is standardized as a type of fuel that is non-

hazardous and complies with European standard EN15359. This

solid fuel requires the producer to specify and classify SRF by

specific net calorific value, grain size, chlorine, mercury, and

heavy metal content (34) in the fuel. The fuel specification is

mandatory for several other properties, including all heavy metal

content as mentioned in the Industrial Emissions Directive (IED,

UK) and a declaration of conformity has to be issued.

Table 4: Classification of RDF by ASME 828:1981

No RDF

types

Specification

RDF 1 Raw waste or with minimal processing

RDF 2 Waste processed into coarse particles with no

separation metals in a way that 95% by weight

of 6-inch square mesh sieve pass.

Both fuels are suitable to become feedstock in cement

furnaces and boilers for co-combustion (20). RDF and SRF use

sieving and sorting in the beginning of the process to reduce the

moisture content of MSW and to separate recyclable or directly

burnt waste. RDF and SRF are generally a better option than

traditional landfill in terms of environmental sustainability. A

very large CV range is expected since it is the combination of

many wastes and a fluctuation of CV and gas emission is

understandable. It is suggested that organic and inorganic wastes

are separated at the beginning of the process to understand their

composition, gas emissions, and other combustion products.

Better environmental impact can be achieved when the power

production plant uses waste from RDF and SRF. The reduction of

chemical pollutants inside the MSW by sorting or other processes

can be integrated to produce better fuel for a cleaner environment.

This would give more public acceptance of the realization of

MSW as a reliable source for incineration power plants.

RDF 3 Processed fuel derived from waste by

separating the metals, glass, and other

inorganic materials. The material in a way that

a 2 inch square mesh sieve passes.

RDF 4 Combustible waste components in powder

form and 95% by weight of 0.035 inch square

mesh sieve pass.

RDF 5 Flammable

waste

extruded

sections

(compressed) in the form of pellets, cubes,

briquettes, or similar forms. Due to the

numerous advantages of portability and

storage, and the ability to coordinate with a

variety of combustion systems in developing

RDF and SRF fuel are generally products of processing waste

derived from MSW and FW. Processing of FW using SRF or RDF

can improve the FW capability to become better fuel in the future.

Table 4 below shows the classification of RDF by the American

Society of Mechanical Engineers (ASME).

RDF 6 The combustible waste in liquid form is

processed

RDF 7 The combustible waste gas is processed to

form.

.7 Palletization technology

Palletization technology can be used to assist the

improvement of FW calorific value. This technology can enhance

the properties of FW and increase its value by removing unwanted

moisture, reducing the porosity inside the FW, and significantly

increasing the FW density. Palletization technology is known to

assist the densification of biomass, which will also enhance

mechanical durability (51). The moisture content reduction less

than 10% is better because Malaysia has high FW moisture

content. Uniform moisture content from FW pellet is needed so

that the incinerator temperature and pressure do not fluctuate

during steam production. Incineration normally requires low

moisture content and high calorific value feedstock. The higher

the energy density, the better with lesser maintenance needed

inside the incinerator. Higher energy density from pelletized FW

can contribute towards higher thermal heating for steam

production. Pelletizing can become one part of several

combinations of FW pre-treatment system. The pellet formed

during high pressure compaction of FW into the metal die is

applied inside the pellet machine. Good pellet formation requires

Detailed Review of the Pre-Treatment

Technologies

This section will review, compare, and discuss all the pre-

treatment methods stated in the earlier section. Table 5 below

indicates the classification of food waste technology and energy

density as well as their assumptions. Table 6 below shows the FW

pre-treatment product characteristics and its rank in terms of

calorific value, energy density and unwanted chemical reduction.

Table 7 below shows the comparison of FW pretreatment method

performance for incineration. From Table 7 above, all FW pre-

treatment methods are rated in terms of their respective

performance in the aspects of energy, economy, and environment.

A scale from 1 to 5 is used to rate the pre-treatment methods. The

setting for the score is as follows: scale 1 - poor performer, scale

2 - below average, scale 3 - average, scale 4 - above average, and

scale 5 - top performer. Three factors had been chosen to compare

each pre-treatment method were calorific value, FW energy

143

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

densification, and compound/ chemical reduction. These

characteristics are used to determine each pre-treatment

performance and its quality to produce better fuel from FW.

Table 6: The score matrix of treated FW

Acidity, alkali

metal, moisture,

volatile, and

heavy metal

compounds

reduction

Calorific

Value

Score Rank

(GJ/m³)

(MJ/kg)

Table 5: Energy Density Performance of FW Pre-Treatment

Technologies

<10

0 to 3.09

No change

Reduction of 1

item

Technol

ogies

Density

(GJ/m )

10 to 14.99

3.1 to 7.09

Waste

(MJ/k

Assumption

(kg/m )

Reduction of 2

items

Reduction of 3

items

Reduction of 4

or more items

15 to 19.99

20 to 24.99

>25

7.1 to 11.09

11.1 to 15.09

> 15.1

Wet –

4.30

(16)

Wet –

2.15 to

3.05

00 (53)

to 709

54)

Average

energy

density.

Raw

(

Organic

waste

Dry -

00.00

(55)

Dry -

25.90

(56)

Pellet

Table 7 :Comparison of FW Pre-Treatment Method Performance

accounts for

over 80% of

the total

MSW.

Average dry

biomass

Dry –

20.72

Pellet -

29.85

for Incineration

Torrefac

tion

MSW

Acidity, alkali

metal,

Pellet -

092.70

moisture,

(56)

27.32

Pre-

treatment

method

Energy)

(Economy)

volatile, and

heavy metal

compound

reduction

Total

score

density

(

Average CV

and density

autoclaved

Autocla

ving

97.17

(36)

13.7

(36)

.33

(Environment)

Based on

calculation of

Torrefaction

HTC

12.77 to 709

kg/m ,

Thermal

assisted

bio-

(

62.55

57) to

79.00

54)

60.62% (57)

reduction on

bulk density.

More than

Palletisation

technology

12.86

(16)

2.09 to

3.59

MSW

Leaching

drying

5% are FW

technology

and only

considering

bio-drying

China MSW

which having

high food

composition

dry basis

Based on

data of pure

FW bulk

RDF and

SRF

Autoclaving

00.00

24.90

(58)

HTC

17.43

(58)

Thermally

assisted bio-

drying

Leachin

technolo

182.79

(57)

16.47

(58)

MSW

RDF

3.09

3.75

Baseline

Raw FW

density

reduction by

(Wet)

0.62% (57).

RDF

and SRF

250.00

(34)

15.00

(34)

Average data

for RDF

The average

density and

CV of

palletisation

of woody

4 Results and discussion

Table 7 shows the final result obtained for this study. Overall,

torrefaction and HTC pre-treatment product result are the best in

terms of their products performance. Both pre-treatment got 13

total score. These pre-treatment methods are the best in terms of

calorific value enhancement (> 25 MJ/kg) and FW energy

densification (refer Tables 3, 5, 6, and 7). These pre-treatment

methods undergo deep drying and thermochemical processes that

reduce the volatile matters and moisture content inside the FW

during the char formation, which also enhances the energy

densification of FW. FW energy densification is a very important

factor for economical transportation and storage costs because

these fuel type will not biodegrade over time. Both methods

Palletiza

tion

technolo

(37)

9.50

1027.50

(59)

MSW

20.04

biomass and

agri-FW

144

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

scored lower in terms of compound reduction. This was due to the

process that involved the reduction of only two compounds

public awareness of the FW valorization and its impact on the

environment if FW is not properly managed. The other FW pre-

treatment technologies can still challenge this study’s results with

better upgrade and more development and optimize real potential

of these technologies.

(

volatile matter and moisture content). Volatiles released in

biomass or organic waste commonly includes light hydrocarbons,

carbon monoxide (CO), carbon dioxide (CO₂), hydrogen (H₂),

moisture, and tar (60). Alkali metal-based compounds, such as

from potassium (K) and sodium (Na), play a very important role

during the slag formation (61) and should be reduced. A study

reported that the total amount of potassium and sodium appear to

be constant during the torrefaction of wood and this may due to

the very small release of alkali metal during the process (62).

Palletization scored the third highest in this study.

Palletization of FW could only enhance the energy densification

of FW to the maximum and was on par with HTC and torrefaction

technology based on Tables 5, 6, and 7. The data also showed the

effect of torrefied FW palletization and it was able to increase the

energy density to 29.85 GJ/m³. This indicated the combination of

these technologies is able to produce better fuel. Normal

palletization process only focused on the moisture content

reduction from FW; therefore, only one item was reduced using

this method. Palletization calorific value was in the middle rank

and was not so high as compared to HTC and torrefaction.

5 Conclusions and suggestion

Various pre-treatment methods can be used to enhance the

properties of FW by significantly reducing smell pollutants and

toxic gas emission, reducing slag formation, reducing FW acidity,

converting FW into high energy density fuel, enhancing FW

heating value, and decreasing its moisture content. Better

understanding of the FW pre-treatment methods with the

respective type of FW, FW source, and its composition is required

to select the best pre-treatment method accordingly. Normally,

heating value is one of the most important factors to consider for

the selection of the most suitable pre-treatment method. However,

the emission of fuel gas, slag formation, and energy density are

also important for a sustainable and better future. Autoclaving and

leaching scored higher for the reduction in chemicals/ items from

FW, which is good for the environment. Nevertheless, leaching is

much cheaper and easier than autoclave method.

Leaching, autoclaving, and RDF and SRF pre-treatment

technologies continued the list and shared 8 points. These

technologies scored lower in calorific value assessment, which

was in the range of 10 to 20 MJ/kg based on Table 3. On average,

autoclaving’s CV was the lowest as compared to leaching and

RDF and SRF. The autoclaving pre-treatment method reduced the

CV significantly during the process. The densification rating for

all these pre-treatment was also low because most of the time,

these processes only involved the drying process of FW without

further chemical processing or palletization. RDF and SRF

sorting processes removed high moisture content of MSW from

the fuel and limited the heavy metal inside the fuel (2 items

reduction). Leaching pre-treatment was very effective for

organic-based waste in removing alkali metal, such as K and Na,

which were presented as water soluble salt in biomass and organic

wastes (62) and also able to reduce FW acidity (63) (the effect of

alkali properties of water). Moisture content was also reduced at

the end of this process. Autoclaving pre-treatment scored the

maximum point for the reduction of four items in the FW. These

four items included alkali metal, volatile matter (during

thermochemical dehydration), moisture content, and heavy metal.

It is known that some heavy metal such as Cadmium (Cd), Copper

By comparing all these technologies, the leaching pre-

treatment technology is a less explored method for FW pre-

treatment process. The chemical reaction of water with FW can

impact the changes in the chemical composition of FW. The

changes in chemical composition of FW can produce cleaner flue

gas emission and reduce slag tendencies. Pre-treatment of FW can

also assist WTE to reduce its erosion problem and increase the

energy production. It is recommended that leaching technology

can be coupled with any other chemicals such as acid and other

pre-treatment technologies to enhance its potential for better FW

fuel production. The combination of FW pre-treatments, which

includes torrefaction, leaching, and palletization, can easily

obtain maximum scores for this study assessment as per Table 7.

Furthermore, more pre-treatment methods can be integrated

and combined into one system to solve the FW problems and

management issues, therefore increasing the pre-treatment

product value. Energy, Environment, and Economic (3E)

assessment and Life Cycle Assessment (LCA) method can also

be used to compare the best FW pre-treatment integration method

to ensure the valorization of energy from FW is optimized and

becomes impactful in the future.

Currently, most of the incinerators do not have any FW pre-

treatment system. This is due to the additional cost, which is

required in the value enhancement process. The increasing cost of

FW pre-treatment can be compensated by the increase in

efficiency and its energy density enhancement. Pre-treatment of

FW can become a future technology for sustainable waste

management, especially for WTE incineration. Since the

generation of FW increases every year with the increasing global

population and many other factors, now is the best time to

consider the benefits of treated FW and its value improvement.

(

Cu), Nickel (Ni), and Zinc (Zn) are contained inside FW and

reduced after the autoclaving process (40). This is due to the

autoclaving process that uses high pressure and temperature to

sterile the FW and converts it into a fiber-like material (40).

Thermally assisted bio-drying was the lowest rated

technology in this study. This is due to the focus of this method

that is only to reduce the moisture content of fuel. The CV for this

method was only a bit higher than the raw FW. For energy

densification criteria, bio-drying performed slightly higher than

raw FW and did not really have a significant impact. The process

time for this method was also longer than other FW pre-

treatments.

Overall, the result shows that there is no pre-treatment

achieve full total score in this study. The comparison of FW pre-

treatment methods suggests for torrefaction and HTC to become

the main pre-treatment processes for FW. However the initial cost

and other research gap need to be filled to understand and increase

Acknowledgments

The author would like to acknowledge TNB Research Sdn

Bhd (TNBR) and Universiti Kebangsaan Malaysia (UKM) for

research funding.

145

Journal of Environmental Treatment Techniques

2021, Volume 9, Issue 1, Pages: 139-147

the Technologies for Food Waste Treatment. Energy Procedia

Ethical issue

[Internet].

2017;105:3915–21.

Available

from:

Authors are aware of, and comply with, best practice in

publication ethics specifically with regard to authorship

http://dx.doi.org/10.1016/j.egypro.2017.03.811

4. Ayodele TR, Ogunjuyigbe ASO, Alao MA. Life cycle assessment of

waste-to-energy (WtE) technologies for electricity generation using

municipal solid waste in Nigeria. Appl Energy [Internet].

(

avoidance of guest authorship), dual submission, manipulation

of figures, competing interests and compliance with policies on

research ethics. Authors adhere to publication requirements that

submitted work is original and has not been published elsewhere

in any language.

2017;201:200–18.

Available

from:

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would prejudice the impartiality of this scientific work.

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Derived Fuel (RDF) from Urban Waste as an Alternative Fuel for

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