1. 10
CHAPTER II
LITERATURE REVIEW
2.1 INTRODUCTION
Composting is a controlled process for the rapid decomposition of waste in stack
(Biddlestone& Gray 1988). The stack contains a variety of stages of a food chain
which consists of microflora and macrofauna (Table 2.1). However, microflora such
as bacteria, actinomycetes and fungi play an important role in the real composting
process (Day & Shaw 2001).
Table2.1Microflora and macrofauna in the composting process
Bacteria,
Actinomycetes
Microflora
Fungi, Algae
Protozoa
Macrofauna
Mites, ant,Termites, millipede,
Spider, beetle, earthworm
Source: Biddlestone& Gray 1988
During the process of composting, microorganisms convert organic materials into
carbon dioxide, biomass, heat energy and a final product which resembles humus. The
main component of organic material is carbohydrates (example cellulose), protein,
lipids and lignin. Through the coupling reaction of microorganisms, complex organic
compounds will be decomposed into smaller molecules which can be utilized by

2. 11
microbial cell (Golueke 1991). The metabolism of microbes results in the increase of
temperature in the compost stack because the heat released by metabolism of microbes
is captured faster than that released to the environment (Miller 1991). The increase in
temperature will enhance the degradation process (Biddlestone& Gray 1988).
2.2 THEMICROBIOLOGYOF COMPOSTING
It has long been known that composting is primarily a microbiological process. If one
has the chance to read the work by(Waksman et al.1939), most likely he will get
impressed with the amount of knowledge about the microbiology of the process that
already existed by that time. The understanding that composting is, above all, a
microbiological process is of paramount importance since this is actually the basis for
good process management (Finstein 1980, de Bertoldiet al. 1983,Golueke 1991). This
was one of the strongest basis for the development of the rutgers system of
composting (Finstein 1980), where process rate is controlled by maintenance of an
appropriate process temperature by forced aeration and it has been one of the guiding
principles in most of the composting systems available nowadays. Although small
animals like earthworms or small insects can be found in composting, most of the
organic matter degradation is carried out by microbes. There are three main groups
ofmicrobes involvednamely bacteria, fungi and actinomycetes which may be
facultative or strict aerobic (Huang et al. 2000).They may have individual preferential
substrates andenvironmental conditions for growth.The materials subjectedfor
composting usually contain an indigenous population of microorganisms derived from
the atmosphere, water or soil (Gray &Bidlestone 1973). Once materials are piled for
composting, feeding of this microbiological population on the substrates leadto the
production of heat and is accumulation in the pile, causing process temperature to rise
(Finsteinet al. 1987a.,Rynket al. 1992).Microbial activity and the resulting heat
generation trigger a change in the environmental conditions and substrate composition
along process time, which in turn causes a succession of mixture of
microbialpopulations to occur (Waksman et al. 1939, Gray &Bidlestone 1973,
Silveira1999,Tiquiaet al. 2002,Nakasakiet al. 2005, Klammeret al. 2008,Chroniet al.
2009).Microbial populations can be subdivided by the temperature ranges of their
activity: i)psychrophiles, preferring temperatures below 20ºC; ii) mesophiles, for a

3. 12
temperature range in between 20ºC and 40ºC; and iii) thermophiles, above 40ºC (Gray
&Bidlestone 1973).
2.3 BIOPROCESS COMPOSTING
Microorganisms require carbon material, macronutrient such as nitrogen, phosphorus
and potassium and other few side elements for their growth. Carbon is the main
energy source for microorganisms while small constituents from carbon will be
inserted into the cell. Some of the energy formed will be used for microbial
metabolism and the rest of it will be released as heat. Nitrogen is an important element
for microorganism because it is a component of protein, nucleic acid, amino acid,
enzymes, and co-enzymes which are needed for development and cell function
(Golueke 1991).
During composting, the carbon source which is dissolved and biodegradable
such as monosaccharide, starch and lipid will be used by microorganism in the early
stage of composting. pH value will decrease because the organic acid formed as a
result of microbial decomposition compound during the process of degradation.
Microorganisms will later start the process of protein degradation, resulting in
ammonia being released and rise in pH value. After the biodegradable source of
carbon is used up, the compound which takes more time for biodegradable such as
cellulose, hemicellulose and lignin will undergo biodegradable and part of it will be
converted into humus (Crawford 1983).
Ammonia formed will undergo different process depending on the condition of
compost mixture. For example, if it is possible to be dissolved (example NH4+) will be
later immobilized by microorganisms by using ammonium as nitrogen source and
subsequently changing it back to organic nitrogen. At temperature below 40 0C and
also at a suitable ventilation, ammonia is possible to be converted to nitrate (NO3-) by
nitrating bacteria. During nitration, nitrating bacteria will lower down pH caused by
the released oh hydrogen ion. The process can be simplified as follows:
Nitrosomonasbacteria: 2NH4++ 3O22NO2-+ 4H+ + 2H20

4. 13
Nitrobacterbacteria: 2NO2- + O22NO3-
The lack of oxygen will cause the microorganisms to utilize nitrate as oxygen source
which will cause the occurrence of denitration and halts nitration. At a higher
temperature and pH exceeding 7.5, ammonia can be vaporized and released (Sanchez-
Monederoet al. 2001).
Microorganisms have the tendency to utilize organic molecule which is
dissolved in water. If the moist content falls below the critical level, the microbial
activity will decrease and it will be dormant (not active temporarily). On the contrary,
high moisture content will cause the ventilation of compost to be less efficient,
causing leaching of nutrient and the process to be anaerobic (Golueke 1991).
Humidity is also important is the storage of energy in the stack of compost (Schaub&
Leonard 1996).
Composting process can be either more aerobic or more anaerobic. The
decomposition is faster and lesser foul if the process is more aerobic. This condition
results in a process which is more aerobic to be conducive in order to stabilize the
larger scaled waste. Biochemical equation for an aerobic process in shown as below
(Day & Shaw 2001; Polprasert 1989):
Organic material + O2+ aerobic microbes CO2 + NH3 + H20 + Product + Energy
On the other hand, a more anaerobic process is easier and less costly although
the degradation is time consuming and more have more foul. The biochemical
equation for an anaerobic process is shown below (Day & Shaw 2001; Polprasert
1989):
Organic material + anaerobic microbes CO2 + NH3 + H2S + Product + Energy + CH4
Composting is a microbiological process which relies on the increase and decrease of
temperature.Day and Shaw (2001) stated that microorganisms in a compost stack is
divided into three categories, namely cryophilic or psychrophilic (0-250C),

5. 14
mesophylic (25-45 0C) and thermophylic (>45 0C). Generally, mesophylic and
thermophylic microorganisms are prone to domination in stack compost. The
temperature profile for composting is shown as in Figure 2.1. At optimum condition,
composting will go through three phases namely, mesophylic phase, thermophylic
phase (happens from few days to few months) and cooling and maturation phase (can
happen for few months).
Figure2.1 Profile of Temperature and Microbial Growth in Compost Stack
Source: Polprasert 1989
The period of each phase relies on natural factors or the condition of organic material
which is compost and the effectiveness of the process which is determined by degree
of ventilation and stirring (Golueke 1991). The addition of starting compost can
eliminate long mesophylic phase and hence speeding up the composting process
(Agamuthuet al. 2000). The active composting phase is considered ended when the
mixture temperature is stabilized and reaching atmospheric temperature (Sanchez-
Monederoet al. 2001). The population of microorganisms in the stack also changes
during the composting process as portrayed in Figure 2.2.

6. 15
When composting is not done properly, the breeding and spread of pathogens
can occur. According to Federal Biosolid Technical Regulation, U.S., to reduce the
risk of pathogens, limit system (windrow) is compulsory to have a minimum
temperature of 55 0C at a compost stack for 15 days, whereas the minimum
temperature of 55 0C in the reactor for 3 days (Day & Shaw 2001).
Figure2.2The Change in Overall Population of Microorganisms (total of
bacteria,actinomycetes and fungi) during Sludge-saw dust Composting.
Source: Day & Shaw 2001
2.4 SUITABLE MATERIALS FOR COMPOSTING
Any waste material with high organic matter content is a potential replacement used
for centuries to stabilize human and animal wastes.Recently it has been used for
sewage sludge,industrial wastes (e.g. food, pulp & paper),yard and garden
wastes.Municipal solid wastes (up to 70% organic matter by weight),softprunings,
clippings, leaves, woody prunings (finely shredded),straw based farmyard and horse
manure, pure wool jumpers, paper shredded mixed with grass cuttings are used
sparingly.Kitchen waste includes waste from fruit, peelings, teabags, egg shells and

7. 16
bedding from vegetarian pets such as rabbits.When selecting materials for your
compost, avoidusing coal ash, metal, glass and plastic, nappies,the roots of persistent
weeds like bindweed and couch grass, leaves with persistent disease such asblackspot,
meat or fish and cooked food, especially meat as this attracts vermin (home
composting).
2.5 COMPOSTING SYSTEM
Composting system can be classified into reactor and non-reactor. There are two types
of non-reactor system namely long rows (windrow): stirred system and air static
system. Long rows refer to stirred system which is usually done manually. In an air
static system, sludge is piled on a perforated pipe. Air will be forced by air
compressor into the perforated pipe so that there is direct contact between sludge and
air in order to activate the microbes (Hassounehet al. 1999).In a reactor system,
compost will be circled by container (reactor) and the flow of substance will be
directed according to reactor design. The reactor is usually closed even though there
are researches which uses open reactor system (Papadimitriou et al. 1997). For a
vertical reactor, raw materials are inserted from the top of the reactor while air is
supplied from the bottom so that all substances get sufficient air. In general, reactor is
used for organic material without sludge.
In a horizontal reactor, the reactor is placed in a horizontal or slightly inclined
with small gradient so as to ease the flow of substances in a reactor. The direction of
feed and air feed is opposite in order to maximize the contact time. The final compost
is collected near the air nozzle (Hassounehet al. 1999). Table 2.2 shows the summary
of composting system of commercial scale. A non-reactor system is less costly but
requires a bigger space (Furhacker&Haberl 1995;Haug 1993). Although it is costly
and requires skilled labor, the reactor system has a good control which makes it more
suitable for sludge composting in a larger quantity (Bhamidimarri&Pandey 1996;
Haug 1993). In order to increase process efficiency and to reduce cost, only active
composting is usually carried out on reactor system while maturation process is
carried out on limit system (Furhacker&Haberl 1995; Vourinen&Shaharinen 1997).

8. 17
2.5.1 RotatingDrumReactorinComposting
Rotating drum reactor has been long used in composting field either by batch or
continuous in a large and small scale. Compared to the batch process, continuous
process has the ability to manage a larger quantity of material and eliminate the
mesophilic phase (Schulze 1962).
Table 2.2 .Commercial-scale composting system
Decomposing system System’s Information
Category
Rotating row Not a Reactor A long narrow piles is rotated regularly
and passively ventilated.
Static and passive stack Not a Reactor Free standing piles is turned occasionally
ventilation or not at all and aerated without the aid of
passive ventilation.
Static pile and long row Not a Reactor Piles and the long row with the help of
with the help of passive passive air like perforated pipe and
air forced-air plenum.
Aerated piles and bins Not a Reactor Short barrels and free standing piles with
forced ventilation and without rotated.
Stack, long row and Not a Reactor Long row or free standing piles or short
barrel with turnaround barrel forced air system. Material will be
and ventilation fixed or sometimes rotated.
Stirred horizontal layers Reactor Material will be composed in long layers
with a turnaround narrow, usually with
forced ventilation and continuous
movement.
Aerated containers Reactor Material will be included in various
containers with forced ventilation.
Aerated-stirred Reactor The commercial container stirred, aerated
containers by force and material is moved
continuously.
Silo or reactor tower Reactor Forced air system that leads to the
movement of material vertically from top
to bottom.
Rotating drum Reactor Drum is rotated slowly to stir the material
permanently or intermittently and move
the material through the system.
Source: Rynk& Richard 2001

9. 18
Rotating drum reactor differs in size, design and process management. Rotating drum
reactor has common basic technique which is to increase decomposition by mixing up
the materials in the reactor (Rynk& Richard 2011).
Rotating drum reactor (RDB) is a complex multiphase reaction system Figure
2.3 which includes substrate layer, head space gas, and drum wall. In general,
substrate layer covers 10%-40% of bioreactor volume (Hardin et al. 2000). Schulze
(1962) filled up 67% of RDB’s volume during composting of sewage sludge. RDB is
usually rotated to 2-3 rpm although there are values as low as 3 revolutions per day
and there were also revolution values as high as 40-50 reported before. Drum may
contain internal blades in order to increase mixing action caused by rotation (Hardin et
al. 2000).
Figure 2.3 Showing the multiple phase and matter and energy flow in a rotating drum
reactor.
Source: Hardin et al. 2000
In a composting process, rotation functions as to expose the materials to fresh air to
increase oxygen and also to release heat and product gases from decomposition.
Forced ventilation is commonly used to supply fresh air and to eliminate gaseous
products. In a few cases, a short drum can obtain sufficient air by exchange of passive
air through the opening at the end. When forced ventilation is carried out, air will be
directed to compost or the opposite side of where the compost is fed to the output.

10. 19
Drum system are needed for composting less homogeneous materials such as
municipal waste.These drums are of diameter 3 m or more and have a length of more
than 50 m. Some drums can be used in parallel.Smaller drum system can be used to
feed a more homogeneous as excrement, dead animals and leftover food. This unit
range is from 1.5 to 3 m in diameter and 3 to 15 m long. Rotating drum reactor has a
shorter retention time of 3 to 5 days. In practice, the drum works on the early stages of
composting. Material removed from the drum is usually cured in the limit, an aerated
pile composting system or second composting system.
Drum starts feed composting quickly and uniformly in a high and controlled
temperature environment. Drum is effective especially to homogenize heterogeneous
mixture such as municipal waste. Lack of ventilation causes the production of an
organic acid and a decrease in pH in the drum. This is why drum is used in early
stages of composting. In few cases, composting time is extended to a few weeks and
this in turns allows aerobic degradation of many acids with the decrease in ventilation
rate. In other cases, compost will reach maturity after 3 to 5 days in the drum. The
materials released from this short retention time may be useful on only certain
applications for example application on soil during winter and autumn.
However,according to compost maturity analysis, the period of several weeks is
necessary in agriculture application (Rynk& Richard 2001).
One of the important features of rotating drum reactor is its ability to produce
granulate products. In industries such as fertilizer, the granulation process is
successfully done in rotating drum reactor (Walker et al. 2003; Hanafiet al. 2000).
Granulate products are important in order to reduce dust and this will minimize the
risk of material loss, inhalation and blast. It also improves the flow, is manageable,
increasedensity and speeds up the mixing of materials (Ivesonet al. 2001).
2.5.1.1 RotatorComposter Design and Description Used in This Study
Rotator composter reactor system as shown in Figure 2.4 consists of 3 main
components. There are rotator drum, air compressor and gas absorber. Rotator drums
functionally facilitated with 3 phase motor. There are 8 inner blades with length of 5

11. 20
cm each in order to enhance the mixing in the reactor. On the other hand, air
compressor functionsas to provide air to the reactor, hence the function of gas
absorber is to absorb gas and air resulting from the process inside the reactor.
Absorber used in this reactor is charcoal. The characteristic of each components of the
reactor is as shown in Table 2.3. Mixing of palm oil mill effluents (POME) and empty
fruit bunches (EFB) is inserted through the feeding part.
Figure 2.4Rotatorcomposter reactor system
Table 2.3 Rotatorcomposter reactor system specifications
Rotator Composter System
Material Stainless steel
Length 3m
Diameter 0.6 m
Initial active volume 0.4 m3
Maximum rotation 2 rpm (rotation per minute)
To be continued…

12. 21
Continued…
Air Compressor
Model SWAN DR 115
Ability 122 liter/min
Speed 1450 rpm (rotation per minute)
Cycle 50 Hz
Motor
Model CHENTA, Taiwan
Volt 400 V
Current 9.1 A
Cycle 3.50 Hz
2.5.2 Bin-composting
This type of composting can be done easily even at home provided that there is
enough space to install the composter. The composter can be installed in the garden or
on a balcony. Composter is a simple box, made of wood or plastic that can also be
home-made. It has a lid to prevent rodent and other animals from eating the compost
feedstock and is in contact with soil to enhance biological activity.In general, yard
trimmings, preferably shredded and food waste can be added to the composter.
Nevertheless, a few restrictions on what kind of organic waste should be put in the
composter must be observed. Meat, fish, dairy products and sanitary material (e.g.
diapers) are to be avoided because they are likely to attract vermin. Besides that, the
temperature in the compost heap is usually too low to kill potential pathogens present
in such waste and contamination must be avoided (USEPAEnviro.com
2006).Composter can be more sophisticated: the composter might have a forced
aeration system or be automatically turned on. It might also have an odor-control
system as well as a leachate collection system. In this study, the composter size is90
cm high and its width is 60. The composter has system of natural ventilation at its
bottom and the plasticcompost bin is made of dark color so as to absorb as much heat

13. 22
from the Sun as seen in Figure 2.5. Through access doors at thebottom, the finished
compost can be moved out. The organic waste was poured from the upper part of
thecomposter and it involves waste collected from wet market with removed non
composting materials(such as plastics, metal etc.) which has been chopped or
shredded into smaller sizes for faster decomposition andhas been well mixed.
Figure 2.5 Bin composter
2.5.2.1 Types of compost bins
There are several types of compost bins available as follows. Description of each bin
is explained in details.
1. Worm Bins
Worm composting is unique because it uses only food scraps and not yard waste. It is
ideal for people with very small yards or with no yard. Plastic storage bins with holes
drilled on the bottom and on the sides are good for starting out. Homemade wood bins
are easy to make. Manufactured bins with layers help in separating worms from
compost work reasonably well and can be kept indoors but they can be expensive
(Compost Bins).
2. Heaps
This is the simplest composting method.However, compost in a heap may take up
more space than a bin. It is not recommended for food scraps as four-legged critters

14. 23
are likely to visit looking for a meal. To keep it from drying out in summer and getting
too wet during the winter, a heap or open pile should be covered (Compost Bins).
3. Hoops
This type of bin is not costly and can be made from lengths of wire fencing or from
woodenpallets. Hoops are enclosed and are tidier than a heap andcan be moved and
covered easily.However, they are generally not animal resistant. Hoops are easy to
take apartand reassemble when turning or removing compost (Compost Bins).
4. Tumbler or Spinner
These self-contained barrels, drums or balls rotate for easy mixing and fast
decomposition. They are more costly than other systems. Although most models are
easy to turn, end-over-end models can be nearly impossible to turn and poorly
balanced when they are full. Tumblers and spinners are suitable for small spaces and
are usually animal resistant. Since they must be loaded in batches, you will either have
to store fresh materials or use two tumblers. The materials in one will be decomposing
while the other is being loaded (Compost Bins).
5. Multi Bin System
This is a great system for a household or community space generating a significant
amount of waste. It is efficient,allowing you to have three working piles at different
stages of decomposition. It is easy to turn and harvest. This style bin can be made
animal resistant (Compost Bins).
6. One Bin System
A one-bin system canbe square, circular or cone shapedand can be commercial or
homemade. Most commercial bins have lids andgood ventilation.They are of animal
resistant.These bins are good for smaller yardswhere there is a small amount
ofmaterial to be composted. Bins aid inmoisture and heat retention. Manyprefer the
neat appearance of enclosed bins.Although some have small doors near the base,
turningthe material and/or removing the compost typicallyrequires lifting the bin up
and over the material and reloading it (Compost Bins).

15. 24
Figure 2.6 Types of compost bins
2.6 OPTIMUM FACTORS FOR THE COMPOSTING PROCESS
Composting process control is very important in order to achieve a short processing
time at a lower cost, consistent results and free from pathogens and odour (de
Bertoldiet al. 1985). The composting of sludge is controlled by few factors such as
temperature, ratio of C to N (C/N), moisture content, free air space, pH, ventilation,
rotation and material adapter like stools, wood dust, flying ash and etc. These factors
rely on each other (Figure 2.7) (Campbell et al. 1990).
Figure 2.7 Schematic of granulation process
Source: Iveson et al. 2001

16. 25
2.6.1 Temperature
Temperature in the composting material is a function of the rate of heat evolution and
heat loss to the environment (Miller 1992; Liang et al. 2003). The temperature in the
compost pile is very important to be controlled because it affects metabolism and
microbial population (Liang et al. 2003; Campbell et al. 1990). Temperatures between
30 and 50 0C increase microbial activity based on the highest oxygen consumption (de
Bertoldiet al. 1983). Temperature below 20 0C and more than 60 0C is proven to
decrease microbial activity (Liang et al. 2003). However, the normal operating
temperature range used are as follows: >55 0C to maximize sanitation, 45-55 0C to
0
maximizebiodegradation rate and 35-45 C to maximize microbial diversity
(Stentiford1996). For sludge composting, temperature was found to be responsible for
sludge drying (Buchanan et al. 1999; Walker et al. 1999).
Figure 2.8. Major Factors which affect decomposition in composting
Source: Campbell et al. 1990

17. 26
2.6.2 Ratio of C to N
Sewage sludge with a low C/N ratio causes ammonia to become steam and
temperature to not reach thermophilic temperatures (Qiao& Ho 1997). The high
ammonia emissions can also cause toxicity in microbes and reduce the rate of
biodegradation of cellulose (Shin &Jeong 1996). Available carbon source such as
green waste and sucrose is added to sludge to improve the C/N ratio (Qiao& Ho
1997). When C/N ratio exceeds 35, microorganisms must go through a long lifecycle
to oxidize excessive carbon to a suitable C/N ratio for their metabolic process to be
achieved (de Bertoldiet al. 1983). This causes the composting process to become
longer. Additional resources for nitrogen source such as stool or urea will reduce the
composting time and cause the end result to be better as the ground adapter material
(Hackett et al. 1999; Jokelaet al. 1997).
At optimum conditions, thermophilic phase in stack is achieved in a
shortertime and dehydration of material will be more effective (Jokelaet al. 1997;
Walker et al. 1999). Metcalf and Eddy (1991) mentioned that excellent C/N ratio is of
range 25- 35. In a larger scale, C/N ratio of 43 can also be considered since
thermophilic temperature can be achieved within 24 hours and rate of water
elimination is high (Jokelaet al. 1997). Sludge composting and solid waste from farm
using ventilated limits with C/N ratio of about 18 was found not to hinder degradation
of microbes (Tiquia& Tam 2001). Table 2.4 shows the early C/N ratio for a few
composting process.

18. 27
Table2.4 Initial ratio of C/N used in variety composting processes.
Sludge Suitable Ratio Composting References
materials of Time, day
C:N
Pulp and Paper Mill Flying ash 70 245 Hackett et al. 1999
Pig Farms Waste 18 77 Tiquia& Tam 2000
Olive Mill Solid waste 27 60 Papadimitriou et al.
of olive industry 1997
Sewage Waste 25 50 Pera et al. 1991
Cow Dung Peat moss 16 20 Yu et al. 1991
Cow Dung Paper 18 20 Yu et al. 1991
Wood dust 25 18 Liao et al. 1997
Pig faeces Peat moss 16 14 Lau et al. 1992
Grape residue Chicken manure 14 25 Ferrer et al. 2001
Vinasse (sugar industry) Cotton residue 19 70 Diaz et al. 2002
Gelatin-grenetine industry Urea and wood 30 55 Hoyos et al. 2002
dust
Olive Mill Cotton residue 23 182 Paredes et al. 2002
Sewage Sugar, clay, and 13 50 Qiao& Ho 1997
wood dust
Paper Mill Domesticated 64 168 Charest &
poultry waste Beauchamp 2002
Source: Hackett et al. 1999 &Jokelaet al. 1997
2.6.3 Moisture Content and Free Air Space
Sludge differs from organic materials because it does not contain fibre and is not
capable of supporting high moisture content. When the free space in compost is filled
with water, sludge will have a weaker structure and acts like a plastic. This will cause
aerobic composting to stop and oxygen transfer will be prohibited. Aerobic
composting will occur when the spaces are filled with air. There are five methods of
lowering down moisture content of sludge which are recycling of materials that have
been composted, the addition of bulking agents such as wood dust, the fixed use of
agitation for compost aeration,addition of dry adapter and lastly, the drying of sludge
before being composted (Buchanan et al. 1999).

19. 28
Liang et al. (2003) mentioned that moisture content is to be given more
priority for monitoring compared to temperature in order to increase microbial
activity. Optimum moisture content will fasten oxygen transfer hence increasing
microbial activity, fastens decomposition and reduces odour (Goldstein 2002; Liang et
al. 2003; Schaub& Leonard 1996; Tiquiaet al. 1996). An optimum moisture content is
needed to overcome early cooling problems and also to avoid increase in bulk density
(Goldstein 2002). Liang et al. (2003) mentioned that the minimum moisture content
for sludge-saw dust composting is 50% in order to obtain microorganisms exceeding
1.0 mg g-1 hour-1. According to Metcalf and Eddy (1991), moisture content cannot
exceed 60% for non-reactor system and 65% for reactor system. Goldstein (2002)
stated that optimum moisture content for composting mixture of sludge and wood dust
in aerated static pile is 55-65%. Table 2.5 shows the initial moisture content for few
composting processes.
Moisture content (MC) and free air space (FAS) affect the air movement and
oxygen transfer in decomposing materials. Free air space is defined as ratio of gas
volume to total volume. Free air space is closely related to other physical
characteristics such as porosity (the ratio of vacant space volume with total volume),
structure and bulk density. Biddlestone and Gray (1988) reported that the minimal
porosity is 30%. Optimal bulk density for sewage sludge composting using reactor
system and non-reactor system are 400-500 kg/m3 and 475-593 kg/m3respectively
(Goldstein 2002; Schulze 1962). Haug (1993) combined free air space (%), porosity
(P, %) and MC (%) through the following equation:
FAS = P (1 - ) ----- (1)
Whereby,
P = 100 (1 - ) ----- (2)
Where is bulk density (g cm-1) and is the particle density (g cm-1). Combining
equation (1) and (2) results in,

20. 29
FAS = 100 (1 - )( 1 - ) ----- (3)
Rearranging equation (3),
MC = 100 - ( ) ----- (4)
Moisture content (%) can be expressed in terms of FAS (%). Free air space of
compost can be increased by adapter materials such as recyclable compost product
and bulking agents such as saw dust. There are evidences stating that minimum
moisture content for certain materials are related to the percentage of minimum free
air space.Ventilation is difficult to attain in the initial stage of decomposition before
steaming is carried outfordrying the mixture andtoincrease the volume of space.
Addition of adapter materials can speed up the rate of composting process (Buchanan
et al. 1999).
Table2.5 Initial moisture of various composting process
Sludge Adapter Initial Composting Reference
Materials moisture time, day
content, %
Pulp and Fly ash 53 245 Hackett et al.
paper mill 1999
Pig Farms Waste 65 77 Tiquia& Tam
2000
Olive Mill Solid waste of 51 60 Papadimitriou et
olive fruit al. 1997
industry
Sewage Waste 62 50 Pera et al. 1991
Cow Dung Peat moss 64 20 Yu et al. 1991
Cow Dung Paper 69 20 Yu et al 1991
Fish waste Wood dust 60 18 Liao et al. 1997
Sewage Glucose + wood 59 50 Qiao& Ho 1997
dust + clay
Pig Faeces Peat moss 66-69 14 Lau et al. 1997
Gelatine- Urea and Sawdust 71 55 Hoyos et al. 2002
grenetineindu
stry

21. 30
2.6.4 pH
pH values are important since they play a huge role in affecting the soil acidity as well
as composting process. An optimal pH value for sludge composting is in between 6 to
9 (Metcalf & Eddy 1991). If the pH is too alkaline, this will result in extreme rise in
temperature which will lead to death of bacteria and volatilization of ammonia. When
pH values are not in this range, bacterial activity will experience retardation and
degeneration will slow down or stop entirely (Schaub& Leonard 1996). Addition of
materials such as cotton waste and fly ash to the sludge will increase its pH value
(Diaz et al. 2002; Hackett et al. 1999). Table 2.6 shows the pH value for few
composting processes.
Table2.6 Initial pH value for multiple composting process
Sludge Adapter Initial pH Composting Reference
material value time, days
Pulp and Fly ash 8.9 245 Hackett et al.
paper mill 1999
Pig Farms Waste 8.6 77 Tiquia& Tam
2000
Olive Mill Solid waste of 7.2 60 Papadimitriou
olive fruit et al. 1997
industry
Sewage Waste 7.0 50 Pera et al. 1991
Sewage Glucose + 7.0 50 Qiao& Ho
wood dust + 1997
clay
Paper Mill chicken 7.5 168 Charest &
droppings Beauchamp
2002
2.6.5 Aeration
Aeration is required for metabolic heat production from aerobic microbial. However,
excessive air supply rate will increase cost and cause loss of heat from the compost
pile while too little ventilation will cause anaerobic process (Polprasert 1989). In

22. 31
addition, aeration is important to remove the main waste product, carbon dioxide and
water (Haug 1993). Table 2.7 shows the rate of aeration in few composting processes.
Failure in aeration system can cause a slow decomposition, a process with high
odour, a delay in achieving maximum temperature, a lower maximum temperature and
low rate of water removal (Diaz et al 2002; Ferreret al. 2001; Haug 1993). According
to Campbell et al. (1990), aeration rate depends on biodegradation properties of
compost mixture. The harder the biodegradation, the lower the rate of optimum air
required. For sludge composting, the proposed value is between 300-700 m3 air/tones
of volatile compounds (VC)/days (Biddlestone& Gray 1988; Schulze 1962). Daily
aeration with rate exceeding 1 000 m3 air/min tones of (VC)/days will cause cooling
effect in composting (Campbell et al. 1990; Lau et al. 1992).
Aeration is carried out either through natural passive air movement or by
forced air. Passive aeration uses absorbing and natural air movement. Forced air
depends on the fan to move the air through composting materials. There is a
possibility of a third mode which is pure oxygen gas being injected into the reactor
(Rynk& Richard 2001).
Natural aeration or passive occur when there is diffusion and natural air
movement. Natural or passive aeration is driven by at least three mechanisms namely
molecular diffusion, wind and thermal convection. Oxygen is absorbed into the
material because there is more oxygen in the outer than in the compost media. On the
other hand, carbon dioxide will diffuse out. However, this process is slow and might
give an impact to the aerated pile. If the compost pile is exposed, oxygen transfer is
carried out by the wind (Haug 1993).
Thermal convection is the main mechanism in most passive aeration
composting system. Heat generated from the composting process raises the
temperature of the gas causes a reduction in the density of the material.Hot gas moves
out of the composting process, creating space and the cold outside air will enter.
Ventilation rate is determined by the temperature difference between the gas in the
ambient air and the air flow resistance of compost media. Thus, the actual air flow in

23. 32
the compost heap is dependent on the production of heat to drive the heat convection
and the existence of the physical structure of the porous media in compost (Rynket al.
1992).
Forced aeration can be supplied in a positive or negative way. Positive forced
aeration is forcing air into the compost material while negative forced aeration is
sucking the air out of the compost material. Positive forced aeration is good for air
movement while negative aerationis suitable for inhaling the odour (Rynk& Richard
2001).
Forced aeration can be performed continuously or intermittently depending on
the requirements of the process.Continuous aeration can reduce the rate of air flow,
reduce temperature fluctuations and oxygen.However, continuous aeration will cause
the slope of the composting environment, causing extreme drying and cold areas that
remain in the air in (Rynk& Richard 2001). Aeration can also be supplied
intermittently so that the maximum temperature in the process can be achieved for
longer time and final compost will be safer (Lau et al. 1992).
2.6.6 Rotation
Rotation can be conducted using the front loading tractor. Rotation provides
ventilation, reduced particle size, ensuring that the material experiences the highest
temperature, renewing microbial activity, increasing porosity and producing a more
uniform compost heap (Biddlestone& Gray 1991; Diaz et al. 2002; Hackett et al.
1999; Thambirajah&Kuthubutheen 1989). It is also the primary mechanism for
aeration and temperature control systems for composting using bounds (Tiquiaet al.
1997).
Heap of pile which is rotated experiences reduction in volume by 55 to 72%
(Larneyet al. 2000). The loss is found in mass of C, K and Na (Tiquiaet al. 2002).
Maturation process is achieved at a faster rate for composting of faeces by rotation
(Tiquiaet al. 1997).

24. 33
The rate of rotation also contributes to the effectiveness of composting. It is
suggested that inversion of 3-4 days in a week is necessary for composting (Tiquia et
al. 1997; Wong et al. 2001). High frequency of rotation leads to electrical
conductivity and low NH4-N content and also a low rate of thermophilic phase
because of heat loss by evaporation and volatilization of ammonia in the stack (Wong
et al. 2001).
The disadvantages of using front loading are that it takes a longer time and
uses a large space (Biddlestone& Gray 1991; Tiquia& Tam 1998). Rotation can also
be carried out in rotating drum. The main function of rotation in composting is that it
exposes materials to fresh air, increases oxygen and dissipates the heat and gas from
the product of composting (Rynk& Richard 2001).
Rotation in the rotating drum can also reduce air pollution (Tiquia& Tam
1998) and ease the mixing process. However, the rate of rotation has to be minimized
because frequent rotation will produce large lumps. In the composting of sludge-
waste, the rotation of rotating drum was carried out for 5 minutes after the materials
were added and also 5 minutes before the materials were removed (Schulze 1962). In
the research by Smarset al. (2001), the rotation was limited to only 10-20 minutes per
day.
2.6.7 Adapting Materials
Adapting materials such as sawdust, paper, fruit waste and etc. greatly influence the
decomposition process for active composting, maturation and storage
(Eklind&Kirchman 2000). There are two types of adapter namely structural adapter
and energyadapter. Structural adapter acts as a bulk weight reduction and increases air
space thereby improving its aeration. Energy adapter increases the amount of
biodegradable organic matter in the compost mixture (Liao et al. 1997). Adapter
materials are necessary in composting because they influence the pH, C/N ratio,
humid content and air supply to aerobic bacteria (Golueke 1991). Therefore, adapter
materials are significant in improving microbial degradation process and also in
producing good quality compost so as to ensure its compatibility as fertilizer and soil

25. 34
adapter (Liao et al. 1997). The release of ammonia from mass of compost has been
reduced by addition of woody material, peat and vermiculate (Bhamidimarri&Pandey
1996; Liao et al. 1997; Qiao& Ho 1997). Coal fly ash is found to reduce the potential
of the metal reactions (availability) in sewage sludge composting (Wong et al. 1997).
Composting studyofvinasse (sludge sugar industry) mixture and grape residue
was performed in the reactor system. Increase in amount of vinasse (0-40% wet
weight) was studied for 43 days. The increase in quantity of vinasse did not affect the
pH value. Evolution of organic materials show higher loss and higher capability of
biodegradation when vinasse mixture having a lesser volume. Loss of Nitrogen
increased when quantity of vinasseinin the mixture increased. The optimum rate of
vinassewas found to be in between 10-20% (Diaz et al. 2002). Composting of
vinasseand cotton waste was carried out by adding vinasse (0-80% mass) in the
reactor for 23 days. It was found that 20-30% of vinasse is the optimum condition
since the final product was of good quality, higher rate of biodegradation and the
minimum loss of N (Diaz et al. 2003).
Ash was mixed at 0-50% (dry weight) together with sewage sludge and
composted for three months. The emission of carbon dioxide for every amount of ash
was found to be similar except for 50% of ash. However, the emission of carbon
dioxide experienced a reduction as the quantity of ash was increased. This indicated a
decrease in microbial activity. The increment in content of salt and pH was believed to
cause this inhibition. Rise in more than 25% (dry weight) resulted in a decrease in the
growth of thermophilic bacteria and the production of carbon dioxide.Dry ash of
lesser than 25% in amount is compatible for composting of ash-sludge (Fang et al.
1999; Wong et al. 1995; Wong et al. 1997).
Shin and Jeong (1996) have reported studies of food waste composting with
various amounts of paper of 33%, 50% and 67% (wet weight). Mixture which
contained 33% of paper was found to have inhibitory impairment due to excessive
release of ammonia. From this study, it was found that the highest degradation of
cellulose is 61% when the paper content in the mixture is high.

26. 35
One of the commonly used adapter materials in the composting process is
wood waste such as sawdust and bark.Wood waste takes a longer time to be
biodegradedand is usually burned to be disposed. There are numerous studies on reuse
and recycling of sawdust such as making fuel, liquid absorbent, building additives and
etc. Wood waste is less suitable as a soil adapter since its C/N ratio is high. However,
by adding nitrogen source such as sludge, wood waste can be converted into soil
adapter materials (Siddiqui&Alam 1990).
The use of wood waste as an adapter material in the composting process
appears to increase the porosity, ability to hold nutrients, reducing odour and
enhancing its energy when applied at the appropriate amount (Bhamadimarri&Pandey
1996; Liao et al. 1994; Tiquia& Tam 2000). Wood waste was found to have the
ability to reduce pathogens more effectively compared to other agricultural waste
during composting of sewage sludge (de Sales-Papa 2002). The difference in
composition of different wood tissues from species to species resultsintheinconsistent
rate of decomposition of wood dust on every different species. Liao et al. (1997)
reported that sawdust from hardwood is more readily biodegradable compared to
sawdust from softwood. Sawdust from hardwood is better inholding nitrogen.
However, it produces a higher concentration of phenol during the process of
composting.
In sewage sludge composting, usage of sawdust is more suitable as a bulking
agent compared to hay and grass (Furhacker&Haberl 1995). Waste wood has the
highest reduction of organic matter, dries the sludge and reduces pathogens compared
to other materials (de Sales-Papa 2002). In swine waste composting, wood waste is
partially decomposedin swine waste providing sufficient empty air space and thus
allowing delivery of oxygen to the microorganisms (Tiquia& Tam 1998).
Bhamadimarri&Pandey 1996 reported that wood dust has the ability to absorb
moisture, providing carbon source, withhold nutrients and providing the appropriate
porosity in the compost pile.
Furhacker and Haberl (1995) reported that volume of wood waste must be
more than 33% in sewage sludge composting using rotating drum. If the density of the

27. 36
sludge and wood waste is estimated to be 700 kg/m3and 100 kg/m3 respectively, then
the minimum amount of wood waste needed is 10%.Liao et al. (1994) havecarried out
the composting of fish waste by using 25%, 33% and 50% by weight of sawdust. The
end result had a C/N ratio of less than 20 except for when sawdust of 50% was used.
The pH value of compost with sawdust of 50% is lower than the others because of low
ammonia content.
2.7 COMPOST MATURATION
According to Commision of the European Communities (CEC 1986), compost is the
product of a stable composting process and free from pathogens which is beneficial
for plant growth. It has undergone an early and fast decomposition process and also
the process of humification. Humification is the process of partial conversion of the
original material into humus which is a humicsubstance andis relatively inert
(Tuomelaet al. 2000).
The usage of immature compost will prevent the uptake of nutrientsby the
microbial population which will further cause nitrogen deficiency in plants. Other than
contributing to excess of carbon source, the presence of phytotoxicitymaterials such as
ammonia and organic acid will speed up the decomposition process of immature
compost which in turn will have a negative impact to the soil and plants. Plants
interact with the retarded environment by lowering down metabolic rate, decrease in
root respiration, drop in nutrient absorption and lowers down the synthesis and
transport of gibrelin and cytokinins (Jimenez & Garcia 1989).
According to Jimenez and Garcia (1989), the techniques of observing compost
maturity is divided into five namely,physical tests, microbial activity research,
methods of compost humic fractions, chemical method and biological method. The
physical test includes observation of physical characteristics of compost mixture such
as its temperature, odour and colour. Microbial activity research includes counting of
total microorganisms, respirometric research, biochemistry parameters for microbial
activity and analysis of biodegradable material. On the other hand, method of compost
humic fraction covers chromatography test and photocalorimetric method. Chemical

28. 37
method includes C/N ratio (solid state), pH, cation exchange capacity and the presence
of nitrate and nitrite. Example of biological method is the test of germination of seed
to detectphytotocity.
The maturation process greatly depends on the composting materials and not
on the type of system (reactor or non-reactor) used (de Bertoldiet al. 1983).Faeces-
straw composting in rotary rotating drum requires three months of composting for
compost maturation using the row system (Vourinen&Shaharinen 1997). Furhacker
and Haberl (1995) composted sewage sludge with wood chips for 4 to 5 days and the
maturation process took 6 months. Composting of paper industry sludge with faeces
using row system failed to undergo maturation after 6 months based on C/N ratio and
calometric test (Charest & Beauchamp 2002). Table 2.7 shows the time taken for
composting process in multiple systems.
Table2.7Duration of composting process for combination of systems and materials
System Mixture Range of Usual Maturation
composting composting
time time
Static stack Leaves 2-3 years 2 years -
Livestock manure 6 months – 2 1 year -
years
Aerated static Sludge + wood 3-5 weeks 4 weeks 1-2 months
pile waste
Leaves 6 months-1 9 months 4 months
Bounds, year
irregular Livestock manure 4-8 months 6 months 1-2 months
round
Bounds with Livestock manure 10-12 weeks - 1-2 months
passive Fish waste + peat
ventilation 8-10 weeks - 1-2 months
Stirred layer Sludge+compound 2-4 weeks 3 weeks 1-2 months
waste or
Faeces+wood dust
Rotating Sludge and/or 3-8 days - 2 months
drum solid waste
Source: Carr et al. 1995

29. 38
2.8 COMPOST AS SOIL ADAPTER MATERIAL
The addition of direct waste into the soil will cause a change in the ecosystem of the
growing plant. The waste which is not composted and added to the soil
causesmicroflorato decompose them and produce transition metabolites which will
inhibit the growth. In addition, a tussle between microorganisms and soil nitrogen, a
high carbon to nitrogen ratio and the production of ammonia in the soil will occur (de
Bertoldiet. al 1983). These conditions can be improved by the production of good
compost.
Compost releases nutrients at a slower rate (Keeling et al. 1994; Maeda et al.
2003).Sikora and Enkiri (2000) described the rate of mineralization of sludge compost
to beabout 9.3% to 29% of the total nitrogen.Composting has many uses in the field of
agronomic, horticulture and forestry. It can be used for field crops, tree seedlings,
plants in the greenhouse, nursery plants, flowers and herbs grown on the land. It can
also be used to maintain organic matter, structure and fertility of agricultural land, to
support urban landscape, to reclaim abandoned land such as mining areas, to create a
landscape and to close the landfill space (Rynk 1992).
Function of compost in the soil and in the relationship of the land-plant
interaction is different with conventional fertilizer even though compost has nutrients
like N, P, and K. The main purpose is not to enrich the soil compost with this element
but isto supply humus and improve soil structure (de Bertoldiet. al 1983). Humus is an
organic material that is relatively stable. It is very important in maintaining good soil
structure, especially in fine-textured soils.It increases the cation exchange capacity,
resulting in the loss of elements such as potassium, calcium, and magnesium (Tisdale
& Nelson 1975). Application of sludge-waste composting in city has found to improve
soil-water content, water holding capacity, saturated hydraulic conductivity,
compression, aggregation, total porosity and pore size distribution
(Aggelides&Londra 2000; Yadavet al. 2002). Atiyehet al. (2001) stated the potential
of compost to supress soil-borne plant pathogen. Table 2.8 indicates the various types
of compost quality which is produced from sludge. Compost is easier to be applied to
soil, easily maintained, easily stored and transported as compared to sludge/waste

30. 39
without composted. It is also a soil medium adapter which is not costly (Hackett et al.
1999; Van Heerdenet al. 2002).
Table 2.8 Quality of compost of sludge for soil adapter materials
Type of Adapter Organic N, % P, K, Note Reference
sludge Materials Material ppm ppm
%
Gelatin Wood dust 55-58 2.4- 2000- 4000 No odour Hoyoset
industry 4.3 3000 0- for final al. 2002
4200 compost
0
Paper Livestock 53-58 0.7- 2600- 3000 Achieved Clarest&
industry manure 0.9 3700 - compost of Beaucham
4000 B Standard p 2002
Pulp and Fly ash 58-63 Not 100- 870- Application Hackett et
paper stated 119 970 for 15m3/ha al. 1999
industry to improve
soil nutrient
Sewage Horse Not 1.1- 9600- 8200 Addition of Warman&
droppings stated 1.2 16000 - compost Termeer
9400 and peat 1996
improves
tree growth
Olive Cotton 36-88 1.4 - Not Not Adapter Paredes et
industry waste/corn 1.7 stated state materials al. 2002
stalk d influences
compost
product
Sugar Grape Not 1.8- 32 1700 Suitable Madejon
industry waste/cott stated 2.7 000 0- with et al. 2001
on waste 2000 moderate
0 compost
dose
application
2.8.1 Plant growth and factors affecting it
Growth is interpreted as a progressive development of an organism.Plant growth can
be referred as the development of a specific organ or the whole plant. Growth can be

31. 40
expressed within the definition of dry weight, length, height or diameter. The factors
which affect plant can be divided into two namely genetic and environmental (Tisdale
& Nelson 1975).
Environmental factors which are important in affecting plant growth are
temperature, moisture content, energy radians, atmospheric composition, gas content
in the soil, soil reaction, biotic factors and supply of mineral elements.Temperature
has a direct impact on plant functions such as photosynthesis, respiration, cell wall
permeability, absorption of water and nutrients, transpiration, enzyme activity and
protein coagulation. Water is required for construction of carbohydrates, maintaining
protoplasm hydration and also as a tool for food and mineral elements
translocation.When the temperature or water content is not optimal, then plant growth
will decrease.Plants will generally grow well in low light intensity than in high light
intensity.However, plants vary in their response to light. Air content consisting of
sulphurdioxide, carbon monoxide and hydrofluoric acid can cause toxicity in plants
(Tisdale & Nelson 1973).
Among the mineral elements which are essential in plant growth are nitrogen,
phosphorus and potassium. Nitrogen is an important plant nutrient. It is absorbed by
plants in the form of nitrates although it can also be absorbed in the form of
ammonium ion and urea.When adequate nitrogen is supplied, plant growth occurs
well and are coloured green.However, when the supply of nitrogen is in excess, it can
cause slow plant maturity, causing plant fibers to become softer and more susceptible
to disease and insect attack.Lack of nitrogen causes the plant to be retarded and
yellowish.Initially, the process of plant becoming yellowish will strike the bottom of
the plant, followed by parts of plants. When nitrogen deficiency is more critical, plants
can also die.
Phosphorus is absorbed by plants in the form of ions in the form of
orthophosphate, H2PO4- and dissolved organic phosphate. Phosphorus plays a
significant role in plant root development. It also accelerates the maturation of plants,
increase the quality of product and resistance to disease.Phosphorus deficiency will
also retard the overall growth.Plants absorb potassium in the form of K+. Potassium

32. 41
deficiency is most easily detected by inhibition of leaf characteristics.In addition,
potassium deficiency causes the plant growth to be reduced, reduced resistance to
disease, degradation of roots and reduction in photosynthesis. The other important
features of potassium are that it maintains an appropriate water-plant relationship and
plant metabolism (Tidale& Nelson 1975).
Soil structure greatly influences the development of roots and the shoot of
plants. The higher the bulk density of the soil, the more compact the soil will be,
causing weakened soil structure and smaller air space. High soil bulk density resultsin
mechanical resistance to root penetration to increase.This condition usually affects the
rate of oxygen absorption into the soil porous space and root respiration is directly
associated with the gas supply is adequate and continuous.Water holding capacity of
compost/soil shows the maximum moisture that can be supported by the dry soil at
standard conditions.The value of water holding capacity is essential to determine the
moisture needed for plant growth. Porous area/porosity is the volume fraction of
soil/compost that is not filled by a solid material. Porous space is important for air and
water movement in the soil (Iswaran 1980).
In addition, the amount of oxygen in the soil is also important for plant growth.
Soil reaction (soil acidity, pH) affect plant growth by influencing the availability of
certain elements needed for plant growth.At acidic pH, the reaction capacity of
phosphate, manganese and molybdenum were found to decrease.When nitrogen in
ammoniacal form is applied on the surface of the soil at a pH above 7, the ammonia
will be lost due to volatilization.In addition, the disease from the soil can also be
caused by neutral-alkaline soil conditions. There are many biotic factors that will limit
plant growth for farming operations and shows the potential threat to reduce the crop,
if not to the destruction of the crops. Imbalance of available nutrients can also increase
the incidence of disease and insect infestation (Tisdale & Nelson 1973).
2.8.2 Effect of various amount of compost on plant growth
Compost affects physical, chemical and biological characteristics of soil by
influencing the permeability, porosity and structure, as well as the redistribution of

33. 42
movement and transportof nutrients.Therefore, the occurrence of some of the activities
and biosynthetic microbial degradation results in improvement of soil fertility,
particularly in terms of the supply of nutrients to plants.Nutrient intake occurs at
rhizosphere (zone encircling the land and influenced by plant roots) and it is
stimulated by microbial metabolites. Microbial metabolites are capable of influencing
or enhancing the influence of the enzymes in plants.Composting improves mineral
nutrition, protein synthesis and carbon assimilation and increases the production of the
entire plant.In addition, the roots will produce more exudates to the soil. Thus,
composting is a new source of energy that stimulates the growth and microbial
processes and subsequently, the metabolism and plant growth (Figure 2.9)(Tomatiet
al. 1996).
Soil reactions to the application of compost depends on a number of factors
including the type of compost and composition, level and application method, soil
properties and weather conditions (Abdel-Sabour& Abo El-Seoud 1996). Pinamontiet
al. (1997) reported that ornament plants were found to grow well with a mix of 50%
sewage sludge compost and bark.Hountinet al. (1995) reported that the application of
compost with peat shrimp waste exceeding 240 tonnes/ha also showed no increase in
the development of barley.However, Klock (1997) reported that trees namely
Impatienand Snapdragoncan grow fertilein 100% composted sewage sludge together
with farm waste.Applications of droppings on sandy soil can improve crop production
of plantation Brassica parachinensis andBrassica chinensiscompared to sandy soils
alone and treatment with synthetic chemical fertilizers (Wong & Wong 1987).
Composting of sewage sludge is also found to increase the yield of corn and
grain(Abdel-Sabour& Abo El-Seoud 1996).

34. 43
Figure 2.9 Influence of compost on plant system
Source: Tomati et al. 1996
2.9 GENERATED SOLID WASTE
Total solid waste that is generated in Peninsular Malaysia is increasing from day to
day. The average of solid waste produced can be divided into 45.0 percent food, 24.0
percent plastic, 7.0 percent paper, 6.0 percent steel, 3.0 percent glasses and etc. (Ninth
Malaysia Plan). Generation rate of these solid waste differ depending on types of area,
total population and occupation or business (Agumuthu 2001).

35. 44
2.10 DOMESTIC WASTE
Solid wastes that are produced everyday are result of thrown waste of domestic and
housing sectors. There are specific categories that have been identified in producing
these solid waste including housing waste, commercial waste, construction waste,
environmental waste and etc. These waste producedare mainly from housing wastes
which includes food waste, papers, plastic which are in the forms of solid, semi-solid,
or liquid.Organic materials are easy to decompose, decay at a faster rate and extract
odd odour that can disrupt public peace (Agumuthu 2001).
2.10.1 Housing Waste
Housing waste produced from activities done by individual in every home are also in
forms of solid, semi-solid and liquid. Most of these housing wastes consist of food
waste, papers, boxes, plastic and aluminum which are easily decomposed and decayed
(Agumuthu 2001).
2.10.2 Business Waste
These types of wastes are a result of business activities, management and trading.
These wastesare usually in forms of solid/semi-solid and are easily disposed through
combustion. Examples of businesswaste are business premises waste and office
utilities such as papers, files, stationeries, plastic and etc. (Agumuthu 2001).
2.10.3 Industrial Waste
Almost half of waste from industrial sectors and factories exist in forms of solid and
liquid. Examples of industrial waste include wood, plastic, scrap metal, sheet metal
and etc. Generally, these industrial wastes are divided into two parts, which are danger
and non-danger wastes. Danger wastes usually contain chemical substances, biology
process waste and also radioactive waste, whereas non-danger waste are of plastics,
steel, fiber, and etc. (Agumuthu 2001).

36. 45
2.10.4 Construction Waste
Constructions waste are mainly produced from constructions of new building,
construction sites, road repairing work, building renovation, demolition of old
building and etc. Most of the wastes are in solid form such as woods, steel, rock,
plaster, concrete and etc.(Agumuthu 2001).
2.10.5 Environmental Waste
Most of the environmental wastes produced are in forms of solid. Examples include
dried leaves, grasses, tree branches, wood and other waste from gardens and landscape
(Agumuthu2001).
2.11 FACTORS INFLUENCING THE REVENUEOF SOLID WASTE
According to studies by (Laimanet al. 2005) entitled ‘Revenue and Composition of
Solid Waste’ in Mukim Melaka Tengah, Melaka, there are various factors influencing
the increasing revenue of solid waste. Amongst them are mainly housing type that
involves way of living and eating styles in every house namely the high-class, middle-
class, and low-class housing.
Besides that, according to Yusof(2007) in Comparative Research between the
Usage of Soil and Wood Powder on Organically Kitchen Waste Composting System,
among the involving factors that influence the generation of solid waste are
geographically, seasonal, attitude of individual and types of residence.
2.11.1 Geographical Factor
Generally, the geographical factor of an area or country does affect its weather. For
example, Malaysia is a country that is situated on the equator line that is always
experiencing moist and hot weather throughout the year. However, the monsoon wind
that hit this country will cause the raining season on certain times of the year. On top

37. 46
of that, the frequent cooking will increase during these seasons and result in rise of
food waste produced than usual.
2.11.2 Seasonal Factor
Seasonal factor includes the fruitsseasons, festive, vacations/school breaks and etc.
Generally, the rate of waste disposal during these seasons will increase and become
the generated factor of solid waste in Malaysia. The solid wastes produced are food
wastes generated in large quantity from food prepared by the house residence and also
from fruit skin waste from the orchards during fruit seasons.
2.11.3 Society Attitude Factor
The attitude of the society and public that underestimates the result of increased solid
waste contributes to the increasing generation of solid waste. Generally, the public are
unaware of their attitude of throwing rubbish which in real fact is affecting the
cleanliness of the environment.
2.11.4 Type of Residence Factor
The quality of the environment can easily be affected by the attitude of residence in
Malaysia. In studies conducted by Laimanet al.(2005), lifestyles and economic factors
can affect the amount of expenses and eating styles whereby it is proven that the
higher the expensesand the bigger the size of a family, the more solid wastes are
generated.
2.12 SOLID WASTE MANAGEMENT
Solid waste management in Malaysia is not systematic and efficient. Generally, the
waste produced will be disposed at the disposal site provided. Five years ago, there
were 230 disposal site set up in this country. However, only 170 disposal sites are
registered to accommodate the rising waste produced. Unfortunately, almost 80% of

38. 47
the disposal sites available now will be closed in a period of two to three years in the
near future.
There are few methods being applied to overcome the increasing amount of
solid waste producedin Malaysia such as recycling, composting system of wet waste,
and the reduction of reusable waste. For recycling process, either all or some parts of
the items are being reused again.
2.12.1 Disposal Sites
Solid waste disposal sites are the easiest and cheapest method used. Generally, the
disposal sites are operated by dumping the wastes into the Earth and thenby burying
them. These disposal sites are usually situated in places of abandon quarry, mining
area and loan holes. According to Syarina(2007) the disposal sites are divided into two
types which are sanitary and non-sanitary disposal sites. However, almost all disposal
sites in Malaysia are non-sanitary disposal sites. This method requires the waste to be
trimmed and compressed inside the ground with heavy-machinery. The surface of the
waste are then sealed with soil to prevent bad odor. However, this method can
contaminate the environment through the diffusion of waste in the ground and then to
undergroundwater. On the other hand, sanitary disposal sites are covered with
geotextile fiber to prevent waste diffusion into the underground water.This diffusion
will then be channeled and treated at a diffusion treatment plant.
2.12.2 Incinerator
Incinerator is a type of solid waste disposal that involves waste combustion. This
method will convert the solid waste into heat, gases, vapour, ashes, and chemicals.
However, there are few places in the world that has stopped this method due to its
destructive effect to the environment and also to health. The ashes from the incinerator
contain poisonous materials including lead, mercury and cadmium.

39. 48
2.12.3 Recycle
Recycling is a process ofobtaining or ensuring half of the materials of solid waste can
be reused again. The recycled materials include glasses, plastic, paper product and
aluminum can. There are multi types of recycling barrels that can be seen in public
places to tell the public the importance of recycling. According to Yusof(2007), the
success of recycling can reduce the control cost of handling solid waste and
environmental pollutions. Malaysia has targeted the rate of recycling to increase by
22% in the year 2020.
2.12.4 Composting System
Solid waste in organic form such as plants, food waste and paper products can be
recycled using the method of composting system and biological digestion to
decompose the organic matter. This method can be easily done and managed to
produce fertilize compost product that can be used in agriculture. This method of
composting was practiced before the Second World War. However, it is still not
usedtraditionally intoday’sworld (Day et al. 1998).
2.13 PALM OIL MILL EFFLUENT SLUDGE (POMES)
The market for palm oil industry is continuouslybeing an attractive topic even though
it is now sold at about one half of its highest price recorded. In Malaysia, palm oil
industry is growing quickly becoming a significant agriculture-based industry. A total
of about 80 million tonnes of palm oil and 57.4 tonnes of palm oil mill effluent
(POME) was generated in the year 2009 (MPOB 2009). Malaysian government is also
supporting the treatment process of palm oil mill effluent (POME) in order togenerate
biogas that can be an alternative source of electricity. Moreover, the palm oil industry
provides a source of livelihood to rural families throughthe government land schemes
and private small holders as well as employment opportunities to agriculture workers
in estates (Ma et al., 1993).

40. 49
The production of palm oil may result in the generation of huge quantities of
highly polluting waste water, also called as palm oil mill effluent (POME). The
properties of POME include thick brownish viscous liquid waste but non-toxic as no
chemicalsis added during oil extraction. However, it has an unpleasant odour. POME
is predominantly organic in nature but highly polluting (Ma 2000). Other than that,
POME is a colloidal suspension of 95 – 96 % water, 0.6 – 0.7 % oil and 4 – 5 % total
solids including 2–4% suspended solids originating from mixture of sterilize
condensate, separate sludge and hydrocyclone wastewater (Ahmad et al. 2003).
POME has been identified to be one of the major sources of water pollution due to its
high biochemical oxygen demand (BOD) and chemical oxygen demand (COD)
concentrations. Hence, Malaysian government had enacted the Environmental Quality
Act (EQA) in 1978 and parameter limits were set for the discharge of POME into the
environment. The parameter limits are as shown in Table 2.9.
Due to the mentioned characteristicsof POME, a wide range of approaches for
POME treatment have been developed to alleviate the pollution problems caused by
the palm oil industry. The conventional treatment technology of POME employed in
most of the palm oil mill factories in Malaysia which is the ponding system of
biological treatment have been adapted (Chin et al., 1982). However, with the
increasing production in most palm oil mills, the under-sized biological treatment is
unable to cope with the increased volume of POME (Ismail 2005). Therefore, a proper
POME treatment is needed urgently in order to ensure the sustainable economic
growth of palm oil industry without neglecting the precious environment.
Table 2.9. Characteristic of POME and its respective standard discharge limit
by the Malaysian Department of Environment.
Parameters Concentration (mg/L) Standard Limit (mg/L)
pH 4.7 5-9
Oil and Grease 4000 50
BOD 2500 100
COD 50000 -
Total Solids 40500 -
Suspended Solids 18000 400

41. 50
The global energy demand is growing rapidly and at present time,about 88% of this
demand is met by fossil fuels. Researches have shown that the energy demand will
increase during this century by a factor of two or three (EIA 2006). At the same time,
concentrations of greenhouse gases in the atmosphere is rising rapidly, with CO2
emission derived from fossil fuels being the most significant contributor. Therefore,
environmental pollution due to the use of fossil fuels as well as their gradual depletion
makes it necessary to find alternative energy and chemical sources which are
environmental friendly. For fossil fuel-derived energy, reduced environmental impacts
by providing a clean fuel from renewable feedstock such as energy crops, organic
fractions of municipal solid wastes and agro-industrial wastes is necessary
(Chynoweth et al. 2001). Palm oil mill effluent (POME) from palm oil mill waste
water is one of the obvious wastes in Malaysia. In Malaysia, palm oil is utilized for
the production of biodiesel (palm oil methylester or palm oil diesel) for buses and cars
and is a major expansion of Malaysian diesel production with 5% palm oil is expected
for biodiesel production from the year 2006 (Kalam&Masjuki 2002 ;
Reijnders&Huijbregts 2008).
The production of biogas through anaerobic digestion offers significant
advantages over other forms of bioenergy production. This has been evaluated as one
of the most energy efficient and environmentally beneficial technology for bioenergy
production (Fehrenbachet al., 2008). The proper control of anaerobic digestion of
POME treatment will generate gas and renewable energy. Megatet al.,(1989) and
Borjaet al.,(1996) had investigated the performance of anaerobic digestion of POME,
whereby 62 – 98 % of COD reduction and 34 – 98 % of methane production was
reported depending on feed rate, substrate concentrations and system operation.
2.13.1 Anaerobic Digestion in POME Treatment
Anaerobic treatment is the most suitable method for the treatment of effluents
containing high concentrations of organic carbon (Perez et al., 2001). A wide range of
approaches have been developed for the POME treatment. This is because anaerobic
system offers more potential for POME treatment due its high organic content. On the
other hand, anaerobic treatment does not require high energy for aeration and

42. 51
allowsthe recovery of energy in the form of methane. The conventional way to treat
POME which is widely used in Malaysia is the ponding system. Ma et al., (1993)
reported that more than 85% of the palm oil mills in Malaysia have adopted ponding
system for POME treatment. However, ponding system requires long retentions time
and large treatment facilities because the system usually consist of de-oiling tank,
acidification, anaerobic and facultative pond with hydraulic retention time (HRT) of 1,
4, 45 and 16 days respectively (Ma &Ong 1985). Another disadvantages by using
ponding system as reported by Chin et al., (1996) are the system could not meet the
effluent quality requirement. For instance, COD and BOD5 in the effluent were about
1725 and 610 mg/L respectively.
Sporadic researches have been performed in order to find approachable
solutions for POME treatment. The main aim of the researchers in POME treatment
nowadays are to shorten the treatmenttime, lessen the land required and at the same
time to collect the useful biogas produced.Borjaet al. (1995) in their research reported
on usage of two stages upflow anaerobic sludge blanket (UASB) system in POME
treatment. They observed that the optimum organic loading rate (OLR) in order to
produce a good methane yield and COD reduction of greater than 90% is 30
g/l.d.COD. In addition, 4.1 g/l.d of acetic acid isproduced at OLR of 16.6.g/l.d.COD
at only 0.9 days of hydraulic retention time (HRT).
Furthermore, Zhang et al., (2007) examined the integration of biological
method and membrane technology in treating POME. In their study, 43% organic
matter in POME was converted into biogas and COD reduction efficiency reached
93% in the expended granular sludge blanket (EGSB) system. Najafpouret al., (2005)
demonstrated the use of upflow anaerobic sludge fixed film bioreactor (UASFF) in
treating POME. Their study showed a high COD removal of 89% and 97% at HRT of
1.5 and 3 days respectively. Besides, the highest organic loading rate (OLR) value of
0.346 l.CH4/g. COD removed of methane yield was obtained. The OLR value gradually
increased from 2.63 to 23.15 g COD/l.d in this study.

43. 52
Table 2.10Literature on POME treatment using variable of anaerobic reactor
System Influent COD removal HRT Methane Reference
COD (COD/mg.L) (h or d) Production
(mg/L) (%)
UASB 30600 94 6.5d 63 Borja and
Banks
(1994)
Anaerobic 30000- 97.8 40d 54.4 Yacob et
Pond 40000 al., (2006)
AF 25000 80.7 20d 36 Yacob et
Digester al., (2005)
UASFF 15000– 97 3d 71.9 Najafpour
35000 (2006)
CSTR 20000– 80 18d 62.5 Tong and
35000 Jaafar
(2005)
SBR 11000– 96 20h NM* Chan et
18650 al., (2009)
EGSB 79723 91 2d 70 Zhang et
al., (2007)
UASFF 44300 94 1.5d - 2.2d NM Zinatizade
h et al.,
(2005
Anaerobic 25000 93.3 4.7d 63 Ibrahim et
Contact al., (1984)
Process
Fluidised 15000 78 0.25d NM Borja and
Bed Banks
(1995)
On top of that,Zinatizadehet al., (2005) studied about the kinetic evaluation of POME
digestion in high rate upflow sludge fixed film bioreactor. They reported that with
HRT ranges between 1 and 6 days, the removal efficiency of COD was between
80.6% and 98.6%. The methane production rate was between 0.287 and 0.384
l.CH4/g. COD removed. Their study also demonstrated the apparent rate constant, K
calculated by simplified Monod model which were in the range of 2.9 – 7.41 l.CH4/g.
COD. Other literatures on POME treatment using anaerobic treatment is simplified as
shown in Table 2.10.

44. 53
2.14 NITROGEN FIXING BACTERIA
Nitrogen is the most limiting nutrient for increasing crop productivity.Nitrogen is a
critical nutrient for virtually all life forms. Input efficiency of nitrogenous fertilizers is
low (Prasad et al. 1990) and in turn contributes substantially to environmental
pollution. Nitrogen which is present in the atmosphere occupies about 79% of the air.
Plants cannot use nitrogen in its gaseous state (Sing 2005). Many industrial important
compounds such as ammonia, nitric acids, organic nitrates and cyanides contain
nitrogen. However its conversion in utilizable form is very less and requires high
amount of energy due to presence of triple bond between two N atoms(Singh 2005).
Nitrogen fixing microbes (bacteria and blue green algae) has a natural power to bring
about the conversion of N2 into NH3 which is further being incorporated into amino
acids and finally into proteins.Nitrogen must be fixed or combined into either
ammonia, NH3or nitrate, NO3. Specifically, tree legumes (Nitrogen Fixing Trees,
NFTs) are valuable in subtropical and tropical agroforestry. They can be integrated
into the agroforestry system to restore nutrient cycling and self-reliance fertility (Craig
&Wilkinson 1995). There are many species of Nitrogen Fixing Trees (NFTs) that can
provide numerous useful products and functions including food, wind protection,
shade, animal fodder, wood fuel and timber in addition to providing nitrogen to the
system (MacDicken 1994).Biological nitrogen fixation is the process that changes
inert N2into biologically useful NH3. This process is mediated in nature only by
bacteria. In legumes and a few other plants, the bacteria lives in small growths on the
roots called nodules. Within these nodules nitrogen fixation is done by bacteria and
the NH3 produced is absorbed by the plant. Biological nitrogen fixation can take many
forms in nature, including in blue green algae which is a bacterium, in lichens, and in
free-living soil bacteria (Lindemann 2003). An enzyme called nitrogenase performs
this. Nitrogen fixing microorganismsfix nitrogen in five different modes.Through
6
biological nitrogen fixation, 180 x 10 tones nitrogen per year is being added to the
soil but this figure is still insufficient to replace completely the use of chemical
fertilizers. Various Nitrogen fixing systems shares this global fixation and the
estimated contribution of each component is shown in Table 2.11.

45. 54
Table 2.11N-fixing systems share this global fixation and the estimate of contribution
of each component
Nitrogen fixing system Estimated contribution (kg/h/year)
Free living 15
Cyanobacteria 7- 80
Aossciative Bacteria 36
Azolla/Anabaena 4.5-450
Frankia 2.0-362
Rhizobium-legume 24-585
2.14.1 Nitrogen Fixing Bacteria - Frankie
Nitrogen is a critical nutrient for virtually all lifeforms. We get our nitrogen either
directly or indirectly from plants. While nitrogen makes up about 79% of our
atmosphere, plants cannot use nitrogen in its gaseous state. It first must be fixed or
combined into either ammonia, NH3 or Nitrate, NO3-. The natural nitrogen cycle relies
on nitrogen fixing bacteria like those found in the Frankia family of actinobacteria to
supply the fixed nitrogen. Fixed nitrogen is often the limiting factor for growth, both
in your garden and in the general environment.
About 15% of the world's nitrogen fixed naturally is from symbiotic
relationships between various species of the Frankia family of actinobacteria and their
host plants.The plants that form symbiotic relationships with Frankia are called
actinorhizal plants. Scientists have found over 160 plants that host these
actinomycetes including alders, Russian olive, bayberry, sweet fern, bitterbush and
cliffrose. The Frankia is able to provide most or all of the host plant's nitrogen needs.
These nitrogen fixing bacteria and their host plants are often pioneer species on young
nitrogen deficient and disturbed soils such as moraines, volcanic flows and sand
dunes. They help in creating a reservoir of nitrogen rich soil that the next wave of
plants can benefit from.
Scientists believe that much of the new nitrogen in temperate forests, dry
chaparral, sand dunes, moraines, and mine waste tailings is as a result of the
mutualism of Frankia and host plants. They are the main nitrogen fixing relationships

46. 55
in large parts of the world and will only become more important as we adjust the
climate change.
Figure 2.10.Nitrogen fixing bacteria – Frankie
2.14.2 Nitrogen Fixing Trees for Agroforestry
Nitrogen fixation is a pattern of nutrient cycle which has successfully been used in
perennial agriculture for ages. Legumes, which are nitrogen fixers,are of particular
importance in agriculture. The tree legumes (nitrogen fixing trees, hereafter called
NFTs) are especially valuable in subtropical and tropical agroforestry. They can be
integrated into an agroforestry system to restore nutrient cycling and fertility self-
reliance.
The "pioneer" plants (plants which grow and thrive in harsh, low-fertility
conditions) begin the cycling of nutrients by mining and accumulating available
nutrients. As more nutrients enter the biological system and vegetative cover is
established, conditions for other non-pioneering species become favorable. Pioneers
like nitrogen fixing trees tend to benefit other forms of life by boosting fertility and
moderating harsh conditions.
NFTs are often deep rooted, which allows them to gain access to nutrients in
subsoil layers. Their constant leaf drop nourishes soil life, which in turn can support
more plant life. The extensive root system stabilizes soil, while constantly growing

47. 56
and atrophying, adding organic matter to the soil while creating channels for aeration.
There are many species of NFTs that can also provide numerous useful products and
functions, including food, wind protection, shade, animal fodder, fuel wood, living
fence, and timber, in addition to providing nitrogen to the system.
2.14.3 Nitrogen: From the Air to the Plants
Nitrogen is often referred to as a primary limiting nutrient in plant growth. In another
phrase, when nitrogen is not available plants stop growing. Although lack of nitrogen
is often viewed as a problem, nature has an immense reserve of nitrogen everywhere
plants grow, even in the air. Air consists of approximately 80% nitrogen gas (N2),
representing about 6400 kg of N above every hectare of land. However, N2 is a stable
gas, normally unavailable to plants. Nitrogen fixation, a process by which certain
plants "fix" or gather atmospheric N2 and make it biologically available, is an
underlying pattern in nature.
2.14.4 How to Use NFTs in a System
In the tropics, most of the available nutrients (over 75%) are not in the soil but in the
organic matter. In subtropical and tropical forests, nutrients are constantly cycling
through the ecosystem. Aside from enhancing overall fertility by accumulating
nitrogen and other nutrients, NFTs establish readily, grow rapidly, and regrow easily
from pruning. They are perfectly suited to jump-start organic matter production on a
site, creating an abundant source of nutrient-rich mulch for other plants. Many fast-
growing NFTs can be cut back regularly over several years for mulch production. The
NFTs may be integrated into a system in many different ways including clump
plantings, alley cropping, contour hedgerows, shelter belts, or single distribution
plantings. As part of a productive system, they can serve many functions:
microclimate for shade-loving crops like coffee or citrus (cut back seasonally to
encourage fruiting); trellis for vine crops like vanilla, pepper, and yam; mulch banks
for home gardens; and living fence and fodder sources around animal fields.

48. 57
2.14.5 Literature Review on Nitrogen Fixing Bacteria in Composting
Pramanik et al(2006) have studied the effect of organic wastes; cow dung, grass,
aquatic weeds and municipal solid waste with lime and microbial moculants on
chemical and biochemical properties of vermicompost. In this research, it shows that
cow dung was the best substrate of vermicompostcompared to other organic wastes.
Application of lime and inoculation of microorganisms increases the nutrient content
in vermicompost. Besides, Bacillus Polimyxa, the free-living N-fixer, has increased
the N-content of vermicompost significantly. The results show that the C/N ratio for
cow dung was decreased from 18.95 to 12.46 and it was the least C/N ratio reading.
Other than that, cow dung recorded the maximum increase in nutrient content of 275%
in the vermicompost over its initial reading.
Diazotrophs,the potential use of free-living nitrogen fixing bacteria as a source
of nitrogen nutrition for crops has not been realised in most parts of the world, largely
because of the inability of the organism to multiply effectively in temperature of
agriculture soils (Keeling 1998). The population ofDiazotrophicwas enhanced 300%
over the long term and nitrogen uptake by plants increased by over 100% in the first 2
months post 15 gl−1 glucose treatment in compose-grown swards while soluble starch-
treated sward growth was inhibited.
In addition, a typical field soil similarly treated with glucose failed to respond
to the treatment. Contrary, a nitrogen immobilizing effect was observed. It was
concluded that significant nitrogen fixation and plant N availability was stimulated by
the glucose treatment of compose but the mechanisms of these processes require more
extensive research.
Low(2008) studied on the isolation and characterization of nitrogen free fixer
bacteria from empty fruit bunches (EFB) of oil palm. In his study, the ability of the
microorganism to fix nitrogen freely was examined by using the N-free mannitol agar
medium. The microorganisms which were able to grow in N-free mannitol agar
medium were considered as free living nitrogen fixing bacteria (Alexander 1977). The
medium used containing carbon source without the supplement of nitrogen. Based on