We are IntechOpen,
the world’s leading publisher of
Open Access books
Built by scientists, for scientists
5,700
139,000
175M
Open access books available
International authors and editors
Downloads
Our authors are among the
154
TOP 1%
12.2%
Countries delivered to
most cited scientists
Contributors from top 500 universities
Selection of our books indexed in the Book Citation Index
in Web of Science™ Core Collection (BKCI)
Interested in publishing with us?
Contact book.department@intechopen.com
Numbers displayed above are based on latest data collected.
For more information visit www.intechopen.com
Chapter
Co-Composting of Various
Residual Organic Waste and Olive
Mill Wastewater for Organic Soil
Amendments
Wafa Hassen, Bilel Hassen, Rim Werhani, Yassine Hidri
and Abdennaceur Hassen
Abstract
The valorization of different organic residues like municipal solid wastes,
sewage sludge and olive mill wastewater is becoming more and more worrying in
the different modern communities and is becoming relevant and crucial in terms of
environmental preservation. The choice of the treatment technique should not be
only from the point of view of economic profitability but, above all, must consider
the efficiency of the treatment method. Thus, an attempt to remove polyphenols
from olive mill wastewater would have a double interest: on the one hand, to solve
a major environmental problem and to recover and valorize the olive mill wastewater for advanced applications in food processing and soil amendments. It is also
interesting to think of associating two harmful wastes by co-composting such as
sewage sludge-vegetable gardens, sewage sludge-municipal solid waste, and green
wastes-olive mill wastewater…, to get a mixed compost of good physical–chemical
and biological qualities useful for agricultural soil fertilization. Finally, in order
to be more practical, we will describe specifically in this chapter a new variant of
composting and co-composting technology intended for waste treatment that is
very simple, inexpensive and easy to implement.
Keywords: Valorization, Wastes, Olive mill wastewater, Compost, Soil fertilization
1. Introduction
Compost makes up a stable, hygienized and humus-rich product resulting from
the mixing of various municipal, plant or animal residues, gradually fermented to
ensure the decomposition of organic matter (OM), and used as a fertiliser, amendment or growing medium. Thus, compost is the resulting product of a complex
microbial process of decomposition and transformation of biodegradable organic
residues. This process operated under varied microbial communities that develop
and grow in aerobic conditions [1–3]. Fermentable organic wastes are coming in
many forms and with different proportions and accessibility to microorganisms.
The raw materials used in composting are much diversified, we can cite as examples
raw manure, bedding, feed residues, straw, various crop residues, olive pomace and
varied products from agro-food industries [4].
1
Humic Substances
Composting is a biochemically continuous phenomenon of organic matter mineralisation or oxidation in the presence of oxygen. The mineralisation or oxidation
is achieved by microorganisms that use oxygen from the air and organic carbon for
all their all-metabolite biosynthesis. To make the degradation or the oxidation easy,
two operations may be implemented. These two operations are always considered
as optional. First, the waste can be sorted to separate the fermentable fraction
from the non-recyclable one. Second, the waste may be mechanically shredded to
improve the structure of the waste mass; thus, on the one hand, the waste shredding facilitated the biodegradation, reduced the treatment time and make handling
more pleasant; and the second hand to make homogenisation of the waste mass
easy by allowing a uniform distribution of the different waste components. Once
the residual substrate has been prepared, fermentation that resides at the heart of
the process, is started. This fermentation leads to a rapid decomposition of easily biodegradable organic matter that generates some fewer complex molecules.
Subsequently, the substrate biodegradation leads to slower maturation. These
steps are commonly known as the processes of humification and stabilisation of
the compost [5]. Once the compost has reached maturity, it will undergo screening
and sieving. This operation is allowed to give two products: a commercial product
known as compost and a refusal product to refine and/or to landfill. All these mentioned operations are well conducted in all common composting processes. Despite,
some precise differences could be existed and lie in the location of the screening
phase and the choice of the fermentation system. The originality aim of this book
chapter is to describe, in the composting plant implemented under semi-arid pedoclimatic conditions, a description of new and simple process of composting and
co-composting of municipal solid wastes, olive mill wastewater, waste farm and
garden cutting, straw and sewage sludge. All these residual materials resulting from
the main human activities commonly known at the present state in modern societies, with especially the olive mill wastewater resulting from oleiocultural activities,
will be considered in this a new process of composting description, mainly characterized as simple to implement and to monitor [6, 7].
Indeed, the process is directed in two principal successive steps: step of prefermentation (uncontrolled fermentation) and step of maturation (controlled
fermentation), respectively.
2. General composting process operation
Composting is a complex bio-physical–chemical operation that comprises
biodegradation of organic waste under controlled conditions of temperature,
humidity and aeration. Two important following one another biophysical phenomenon could include the common composting process. The first process brings
the organic residues to the state of fresh compost. An intense aerobic degradation
concern essentially the decomposition of fresh organic matter at a high temperature
of 50–70°C under the action of thermophilic bacteria; while the second process is
done by a less sustained degradation mainly achieved by mesophilic bacteria. These
bacteria transform the fresh compost into a mature compost, rich in humus. This
maturation phenomenon, which takes place at lower temperatures of 35–45°C, leads
to the biosynthesis of humic compounds by fungi.
The composting process of organic residues takes place in three distinct and
important phases. First, the temperature rises rapidly to around 40°C or 45°C
following the respiration of aerobic mesophilic microorganisms; in parallel, the
most degradable compounds such as sugars and starch are consumed. Second,
the temperature rises progressively to around 60°C or 70°C and the mesophilic
2
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
microorganisms will be replaced by thermophilic ones, anaerobic fermentation by
aeration of the waste mass must be avoided; pathogens, parasites and weed seeds
will be destroyed by the temperature. Third, the degradation is complete when
aeration no longer increases the temperature, the amount of material easily operational by the microflora becomes scarce and the biosynthesis of humic compounds
becomes predominant, and at the end the thermophilic species in favour of more
common species disappears and appearance of new mesophilic species [8].
3. Physical-chemical parameters monitored during the composting
process
The principal physical–chemical parameters of the process monitoring are
summarised in the parameters that condition the good development and progress
of microbiological activities, and their monitoring is essential to test the effective
conduct and behaviour of the composting process [9, 10]. This is achieved by optimising nutrient supply and regulating pH, temperature, water content and aeration
conditions.
3.1 Grain size of wastes
The waste particle size is an important parameter to consider in the composting process since (i) it determines the size and volume of the pores created by the
arrangement of the particles in the waste matrix, (ii) it is involved in increasing
the specific surface area of the raw organic matter, (iii) it facilitates the diffusion
of oxygen inside the compost waste matrix, thus allowing homogenisation of the
waste, and at last (iv) it is the site of main microbiological activities that take place
on the surface of the organic particles.
3.2 Interstices oxygen rate
This parameter shows the real proportion of oxygen in the interstices of the
waste mass. It is critical to the oxidation of the organic matter, and directly related
to the size, humidity and aeration of the waste during composting. Oxygen requirements decrease along composting whether they are proportionate to the organic
matter gradually disappearing over the mineralisation process. However, maintaining and preserving good aeration avoids the start of an anaerobic process that
could induce the generation of malodorous compounds. Moisture in the waste mass
always interacts negatively with the system aeration. The supply of oxygen allows
the drop in humidity. If this humidity is high, a probable temperature rise will take
place leading to a significant improvement in the substrate mass homogeneity. The
minimum threshold of oxygen needed to maintain aerobic conditions is of the order
of 5% as reported by Jammes [9].
3.3 Prevailing humidity in the waste mass
Humidity is both a raw material-related parameter and a monitoring parameter.
It hosts the development of the microbial flora within the compost. The optimal
water content during composting is around 60%. However, high water content
promotes anaerobic fermentation. If the water content exceeds 70%, the water fills
the voids and space, making oxygen exchange very difficult. On the other hand, if
this prevailing humidity drops below 20%, the decomposition of organic matter
will be inhibited.
3
Humic Substances
The quantity of water lost by vaporisation during the release of heat exceeds
those formed during the reaction of oxidation; therefore, to compensate this lessening, it is tolerated and needed watering materials during composting. Although it
is difficult to determine the volume to be added, water can be added as long as no
runoff appears under the pile of waste or the waste mass.
3.4 C/N ratio of the waste mass
The C/N ratio of the waste mass qualifies the biodegradability of organic waste by
ensuring the trophic balance necessary for the flora optimal development. Suitability
of fermentable waste for composting is determined by the C/N ratio of the mixture
of their various constituents (fermentable, paper and cardboard). Putrescible
materials whose C/N are of the order of 15, are substrates easily biodegradable, while
paperboards, with C/N ranging from 60 to 107, are substrates hardly biodegradable.
During aerobic fermentation, microorganisms consume carbon 15 to 30 times
more than nitrogen. The initial C/N ratio is around 30 to 35, while that of the final
product is less than 15. Sometimes the C/N ratio of waste can be so low that it is
unsuitable for composting. This can be remedied by adding a specific substrate
with a high C/N ratio, which brings the initial C/N value back towards the optimum
[9]. If the initial ratio is less than 30, nitrogen losses are accompanied by the odour
nuisance. If the ratio is low, ammonia nitrogen losses may reduce pH. Tables 1 and 2
showed examples of the C/N values of some compostable materials.
3.5 Temperature developed inside the waste mass
The increase in temperature is caused by microbiological activity. During the
degradation of organic matter, there is energy initially contained in the chemical
bonds of the constituent molecules, which are released, part of which is recovered
by the metabolism of microorganisms, and the other part is dissipated into the
atmosphere. Therefore, the minimum temperature is necessary for degradation and
the evolution of the temperature during composting is allowed distinguishing four
successive distinct phases [1].
Categories
Season
Average C/N
Fermentables
Spring
18.3
Paper-Cardboard
Spring
63.4
Fermentables
Summer
13.1
Paper-Cardboard
Summer
59.2
Fermentables
Autumn
15.6
Paper-Cardboard
Autumn
107.5
Fermentables
Winter
15.2
Paper-Cardboard
Winter
79.1
Table 1.
Average C/N ratios of some fermentable components.
C/N
Municipal wastes
Cattle manure
Sewage sludge
Olive pomace
< 20
20
11
49.3
Table 2.
Average C/N ratios of main fermentable components.
4
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
3.5.1 The mesophilic phase
Mesophilic microorganisms (especially bacteria and fungi) invade the raw
material, so their activity causes a rise in temperature (from 10 to 15°C to 30–40°C),
a significant release of CO2 and subsequently a decrease in the C/N ratio and
acidification.
3.5.2 The thermophilic phase
During this phase, the temperature reaches 60 to 70°C, values to which only
thermo-tolerant microorganisms like actinomycetes and thermophilic bacteria
could remain in operation in this very hostile environment, and the degradation
activity of resistant fungi will be stopped. Along this hostile phase, the nitrogen
mineralized as NH4+ will be lost as NH3. This hostile environment takes place
specifically inside the waste mass centre, hence leading to the need to turn over the
waste mass for ensuring homogeneous and disinfected products.
3.5.3 The cooling phase
This phase is followed by the operation of turning and watering the mass of
waste being composted. Thus, it is mainly characterised by the reappearance of
ambient temperature and mesophilic microorganisms that decompose materials remained intact during the previous phase and nitrogen of some complex
components.
3.5.4 The maturation phase
The microbiological activity regresses considerably during this phase, and the
waste receives new colonisers that are the macrofauna, particularly earthworms.
The organic matter becomes stabilised and humified compared to their initial state.
It should be pointed out that a temperature above 70°C should be avoided, as it leads
to extreme drying, a very significant loss of material and even a halt in the process
by the microflora destruction.
3.6 pH or acidity degree
The hydrogen potential known as pH is a measure of the chemical activity of
protons or hydrogen ions in solution inside each medium. The pH largely influences
the development of the microflora responsible for the waste decomposition. Its
value is determined and imposed by the raw material used, but varies according
to the progress of the composting process. The pH monitoring is mandatory since
it provides information on the different phases of the process. The optimal pH
prevailing in the waste mass during the composting is on average between 6 and 8.
3.7 Undesirable and non-biodegradable waste products
The composition of municipal waste may show undesirable non-biodegradable
elements that could affect the process and the ultimate product quality. These
elements may be notable as packaging and special wastes, rich in metallic elements. Therefore, these undesirable materials should be separated by sorting. The
operation of sorting can be made at the domestic level known as source sorting
prevailing and well distributed in very advanced modern societies and/or in
composting sites.
5
Humic Substances
4. Description and implementation of a new composting process
We are prompted in this paragraph to describe a suite of a new composting
process, traditional, very easy to implement, economical, but it is a time and
space-consuming process on the plant composting platform. The process is simply
summed up in two successive stages, recognized as the pre-fermentation and
maturation stages.
As earlier said several times, the composting process at the microbial level
involves many interrelated factors, mainly metabolic heat generation, temperature,
ventilation as O2 input, moisture content and nutrients. Temperature profiles
registered during the two steps of pre-fermentation and maturation are shown in
Figure 1 in two experimental wastes windrows W1 and W2 the three classical temperature steps of composting, including the mesophilic, thermophilic and cooling
phases, respectively (Figure 1).
The step of maturation with around 60 days appeared to be as less active as
compared to the first step of pre-fermentation with around 90 days since the values
of temperature, registered during the second step of maturation, are less important
than those to be recorded during the first step. Differences in temperature averaged 15°C. This result is mainly related to differences in the availability of easily
decomposable organic matter content as nutrients in the organic fraction. So,
composted materials used during the first step of pre-fermentation seem richer in
these easily decomposable organic elements as compared to those of the second step
of maturation.
Analytical investigation of some key monitoring biological parameters of
composting such as dehydrogenase activity [11], microbial biomasses C (BC) and N
(BN), extracted total DNA content and microbial diversity in waste masses during
composting were examined. So, the dehydrogenase activity is studied during the
composting process for two major reasons: the first concern the follow-up of the
biodegradation level of substrates, and the second because it represents a reliable
indicator of the stability and maturity of the finished product. The dehydrogenase
Figure 1.
Temperature changes in the two windrows W1 and W2 during the two steps of composting. (i) The first
windrow W1 constituted with 100% of municipal solid wastes, (ii) The second windrow W2 composed by
weight of 60% of municipal solid wastes and 40% of dried stabilized sewage sludge, and (iii) The form of
windrows of 12 × 6 × 2.5 m (length x width x height, respectively).
6
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
activity showed a net increase between 2 and 0 and 15–35 days through the prefermentation and maturation steps, respectively. A good positive correlation is
observed between the values of dehydrogenase and of temperature registered
(r = 0.96, P < 0.01). These values of dehydrogenase activity fluctuated between
3.2–5.84 and 1.7–5.66 mg TPF/g of waste dry weight/24 h during the step of
pre-fermentation in the two windrows W1 and W2, respectively (Figure 2). By
the same, these values varied between 3.6–4.9 and 1.96–3.22 mg TPF/g of waste
dry weight/24 h during the step of maturation in the two windrows W1 and W2,
respectively. So variation of the dehydrogenase activity appeared very narrow
(around 1.2 mg TPF/g of waste dry weight/24 h on average for W1 and W2) during
the second step of composting and showed a certain homogeneity and consistency
of the waste materials used in this second step of maturation; and in the opposite,
a high heterogeneity and assortment of the waste used during the first step of
pre-fermentation since variation of dehydrogenase values generally recorded were
relatively large (around 2.64 and 4 mg TPF/g of waste dry weight/24 h for W1 and
W2, respectively).
On the other hand, it is important to mention that the dehydrogenase activity
values appeared slightly higher in the windrow free of sludge than in the one with
sewage sludge. The microbial biomasses C and N behavior biochemical transformations in waste materials, and BC/BN ratio is closely related to the changes of the
microbial population during composting. BC/BN ratio values usually showed a net
increase during the thermophilic phase, 30–70 and 20–50 days, for the steps of prefermentation and maturation, respectively (Figure 2). The BC/BN ratio values are
on average around 4 or 6 and 3–4 during the first and second steps of composting,
respectively. The concept of the microbial biomass inventory regards the microorganisms as only one and a single entity. The evolution of BC/BN ratio translates a
microbial diversity, with phases where they are the bacteria and the actinobacteria
which are dominant, and others where the fungi prevail; a net increase of this ratio
is synonymous of a good microbial activity [12–15].
Microbial total DNA extracted from composting materials and followed during
all the two steps of the composting process showed a net variation over time, and
Figure 2.
Dehydrogenase activity and BC/BN ratio changes in two windrows W1 and W2 during the two steps of
composting.
7
Humic Substances
revealed a good parallel increase with the temperature progress inside the waste
materials (Figure 3). This increase varied between 13.2 and 26.1 μg of total DNA
per g dry weight. The lowest values of DNA are observed at the start and the end
of each step of the process (around 13.2 μg of total DNA per g dry weight) and the
highest values are always registered during each thermophilic phase (around 26 μg
of total DNA per g dry weight). The ratio of absorbance at 260 and 280 nm is usually used to assess the purity of DNA and RNA. A ratio of ~1.8 is generally accepted
as ‘pure’ for DNA; a ratio of ~2.0 is generally accepted as ‘pure’ for RNA. If the ratio
is appreciably lower in either case, it may indicate the presence of protein, phenol
or other contaminants that absorb strongly at or near 280 nm. The determination of
A260/A230 and A260/A280 ratios usually defined as a coefficient of purity of DNA.
For compost DNA showed a significantly lower value (0.96 and 1.2) than those for
DNA solutions of pure cultures (1.57 and 1.89) showing that compost DNA was
coextracted with humic and protein compounds, respectively.
Therefore, the investigation concerning microbial diversity in the composted
wastes allowed to assess the changes in microbial diversity that could occur during the two steps of the process by DNA extraction and polymerase chain reaction
(PCR). Main investigation and results showed that along the first process step,
there is a net variation in microbial diversity. This diversity appeared very rich
and obvious in case of windrow W2 added with sewage sludge. The principal
characteristic of the first step of pre-composting or pre-fermentation consists
in subjecting directly to fermentation raw wastes, without sorting and crushing.
Figure 3.
Total compost DNA contents and agarose gel electrophoresis of total DNA extracted from composting materials
(W1) during the two steps of composting. First lane: HindIII-cut bacteriophage lambda molecular size markers
(1 mg), step 1 and step 2 lanes: DNA extracted from waste of W1.
8
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
The usual processes suppose the use of a pre-sorted and crushed raw material. In
the case of the present composting technique adopted in this process, raw wastes
not sorted upstream are very heterogeneous, and then the separation of organic
material is practically impossible. Thus, the operation of pre-fermentation supports
accessibility to this organic material. During this first step and earlier evoked, the
rises of temperature appeared important and reach the 60–65°C inside the two
windrow W1 and W2 of waste masses. Also, the degradation of organic material
makes possible the decrease of plastic bags and the release of organic matter that it
is frequently locked up there.
This pre-fermentation is preferred done into two pyramidal windrows forms and
pile of waste should be often covered with a layer of fresh sewage sludge (approximately 30% of total waste weight). In fact, this layer of sludge participates efficaciously to minimize the fire hazard and to avoid the take-off of certain particles of
waste, such as plastic, paper, and many others.
The optimal duration of this phase of pre-fermentation was previously studied,
and evaluated to three months on average. Consequently, a maximum organic material recovery is ensured during a minimum time interval.
The second step of the process of controlled fermentation (step of maturation)
is characterized by a degradation of the organic materials by microorganisms. The
purpose of management of this second step of composting is to ensure favorable
conditions in order to force the microbiological activity. The procedure of microbes
during this second step of composting appeared on average less active than the one
registered during the first step of pre-fermentation. All parameters considered in
the present paragraph are in favor of this conclusion. We could explain this result
by several factors mainly by the decrease or exhaustion and depletion of readily
degradable compounds in the mass of waste materials.
This chapter review confirms amongst others that temperature is the main
parameter to consider in composting. This important factor conditions the functioning of all the other parameters, specifically the microbial activity. As a result,
the level of temperature conditions and depends on the type of microorganisms
operating during composting. So mesophilic microbes dominate at the beginning
and at the end of each step of the composting process; on the other hand, thermophilic microbes control the important step of composting, the thermophilic phase.
Finally, this paragraph reviews a new and simple composting process tested and
used in an industrial plant for compost production under semi-arid pedo-climatic
condition, and some important chemical, physical and biological monitoring
parameters should be investigated in order to understand and to master the general
process of composting of various solid residues. A molecular detection procedure,
using ribosomal intergenic spacer analysis, was tested for microbial community
diversity assessment. At last, analysis of compost microbial communities is one of
the challenging areas of research due to the enormous complexity of biodiversity
caused by the heterogeneity of the physical and chemical structure of compost
environments [16, 17].
5. Co-composting process of municipal solid wastes, green cutting waste
straw and olive mill wastewater
As earlier evoked, olive production represents one of the oldest agricultural
activities in the Mediterranean basin. For these countries, the production of olive
oil is an economic fortune transmitted over several generations. However, it has
the disadvantage of generating huge quantities of by-products with a complex
organic fraction and high chemical oxygen demand (COD). Indeed, 100 kg of olives
9
Humic Substances
produce on average 35 kg of pomace and 100 liters of vegetable oil [18]. Thus, these
residues are commonly considered as an important polluting industrial waste.
Currently, with the promotion of the beneficial virtues of olive oil for human
health, its demand continues to increase and consequently production is constantly
growing at the expense of the environment. The discharge of effluents from olive
oil mills has until now been a challenging ecological concern in the Mediterranean
region. Oil plants furnished with modern equipment produce large quantities of
6 to 7 million tons/year that could reach 80–110% of the initial batch of olives,
while with traditional devices, the production of olive oil mills is 50%. Given these
excessive volumes of waste, treatment is essential to reduce the environmental
impact. The problem posed by olive oil mills discharges resides mainly in their high
polyphenol content that could reach 18–125 mg/g according to the variety of olives,
the level of production, the period of olive picking and extraction.
From the preceding, it is clear that an attempt to remove polyphenols from the
olive oil mills also known as olive mill wastewater would have a double interest: on
the one hand, to solve a major environmental problem and, on the other hand, to
recover and valorize the olive mill wastewater for later applications in agro-food.
It is also interesting to think of associating some other kinds of residual wastes
that could be disruptive and sometimes harmful to the natural environment like
gardening and crop residues, straw, green waste and dried sewage sludge for an
attempt at recovery in terms of co-composting in order to evaluate the quality of the
compost produced.
In this paragraph, a variant of the co-composting technique has been presented
and described: olive mill wastewater with municipal solid waste, or olive mill
wastewater with garden and cutting wastes, olive mill wastewater with dried sewage sludge.
5.1 Setting up waste windrows
As mentioned above, the technique adopted for this application is that of
windrow co-composting. The windrows will be set up as the waste arrives at the
composting plant. Care will be taken to ensure that the date of termination of the
windrow placement is recorded. Also, it should be noted that the raw material collected has not been sorted or crushed before. The windrows were deposited on the
controlled fermentation platform in pyramidal form (L x W x H = 12 × 6 × 2.5 m)
(Figure 4). Co-composting processes are commonly carried out with variants of
organic residues such as straw, cutting and garden waste, and sludge stabilized by
drying in a natural sunny bed. The straw was chosen because of its structure that
can absorb a large amount of olive mill wastewater and it is for the same purpose
that the cutting waste was chosen. As for the WWTP sludge, it was chosen with the
aim of looking for an efficient variant of recovery of this type of environmentally
harmful waste. Main parameters of the composting process will be monitored in
situ or laboratory measurements. Daily monitoring of the temperature considered
as a key parameter of the composting process will be carried out using a compost
thermometer (probe). Thus, a total of 9 × 3 measurements will be taken: three at
the mid-height of the windrow (50 cm), three others at 150 cm from the bottom
and lastly three measurements at 230 cm from the top and at three different points
A, B and C of the windrow surface mass. The temperature of the windrow at a
specific point will be taken as the average value of the temperatures at the different
measuring points. Windrow turning made necessary after the temperature elevation within the waste mass allows a heterogeneous waste at the start of the process
to be progressively homogenized; the watering will maintain a suitable humidity for
the development of the different macro and microorganisms.
10
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
Figure 4.
Diagram showing the different levels of temperature measurement and waste sampling in a waste windrow.
The various possible treatment combinations could be conducted as follows: A1:
Windrow composed of green waste without olive mill wastewater; A2: Windrow composed of green waste +15% olive mill wastewater; A3: Windrow composed of green
waste +30% olive mill wastewater. A4: Windrow composed of premature compost
without olive mill wastewater; A5: Windrow composed of premature compost +15%
olive mill wastewater; A6: Windrow composed of premature compost +30% olive mill
wastewater; A7: Windrow composed of straw + waste cuttings; A8: Windrow composed of straw + waste cuttings with 15% olive mill wastewater; A9: Windrow composed of straw + waste +30% olive mill wastewater. A10: WWTP sludge without olive
mill wastewater; A11: WWTP sludge with 15% olive mill wastewater; A12: WWTP
sludge with 30% olive mill wastewater, A13: Straws without olive mill wastewater;
A14: Straws with 15% olive mill wastewater; A15: Straws with 30% olive mill wastewater; A16: Saturated straws. All these treatment combinations will be carried out in
order to choose the right treatment for the different waste that goes with their rate and
nature, and above all the quality of the finished product, i.e. the finished compost.
5.2 Quality of the finished products
It is important to mention that the olive mill wastewater addition to the sledges
results in a less aerated compact waste structure of the windrow. This reduction
of the interstitial space leads to a reduction in aeration at the level of the windrow,
accompanied necessarily by a reduction in temperature at the level of the WWTP
sludge-based windrows. At the level of these windrows, the temperature does not
generally exceed 60°C. Therefore, monitoring of pathogens must be considered in
order to ensure the sanitary quality of the finished product of compost.
However, the temperature changes in the straw-based windrows such A14, A15
and A16 showed high temperature values exceedingly largely 60°C, indicating active
degradation. However, the windrow that has not received the olive mill wastewater,
the temperature values to be recorded during the cycle of composting rates remains
relatively low, this may be due to the fact that the straw has low enough moisture
content for microbial growth, and an olive mill wastewater will be needed to correct
the composition of the windrow in terms of moisture and nutrients.
Also, significant temperature increases will result in peaks between 50°C and
65°C. However, these thermophilic phases are interrupted by falls caused by overturning or naturally by precipitation. These waste turning is necessary to ensure
aeration of the windrow and exudation of leachate from the windrows.
11
Humic Substances
A global reading of the different temperature changes in the different variant
of windrows could show that the composting cycle begins with a mesophilic phase
where the temperature progresses rapidly from 40 to 45°C, just after a few days (5
to 6 days) of windrow implementation. Later and during the second thermophilic
phase of composting, the temperature rise, which can last a month and a half,
ensures pasteurization resulting in compost of good microbiological quality.
On the other hand, moisture is an essential factor in controlling the level of
progress of the composting process. Here, humidity could vary between 20% and
85% with losses of water by evaporation and runoff or gains of water returned following rainfall in the absence of a cover. However, excessive humidity can interfere
with the normal progress of the composting process, which may justify the aberrations that can sometimes be noted during temperature evolution.
Green waste and cutting windrows can have relatively higher moisture values of
65–88% than other straw windrows (A13, A14, A15 and A16). This may be attributed to their remarkable volumes that could create vacuums within the windrow.
However, moisture is less important for the sludge windrows. The small grain
size of the sludge causes the windrows to become stacked. For straw windrows,
low moisture values were recorded, suggesting that straw is a good absorbent, but
significant leaching could be occurred throughout the composting cycle.
As mentioned earlier, the C/N ratio measures the relative proportions of carbon
and nitrogen, nutrients essential to the life of microorganisms. Carbon and nitrogen
measurements were taken at the beginning and end of the composting cycle. The
highest ratios were recorded for straw swaths (A13, A14, A15 and A16) and cuttings
(A7, A8, A9). This is because of their high carbon content, which is one molecule
that is difficult to biodegrade. Hence its persistence in large proportion until the end
of the composting cycle.
As for the windrows (A7, A8, A9, A13, A14, A15 and A16), respectively of cuttings and straw waste, relatively low nitrogen values of 0.30; 0.60; 1.00; 0.40; 0.80;
0.90 and 1.20% will be recorded at the end of the composting cycle.
As a result, C/N ratios remain fairly high, fluctuating between 124 and 139. This
fairly high C/N ratio of the cuttings and straw waste windrows suggests that the
resulting compost may be immature. It is well shown and known in the literature on
this specific topic that the C/N ratio is considered an important indicator of maturity of organic matter in aerobic fermentation.
Green waste windrows represent the lowest final carbon values. This type of
result automatically suggests compost stability, in terms of biodegradation speaking. In fact, green waste is essentially composed of cellulose, a component that
is easily biodegradable. This specific composition means that the C/N ratios are
always low. Indeed, a high initial C/N ratio favors nitrogen immobilization and a
low ratio favors mineralization. This previous character is well confirmed by the
general results obtained on this topic. In fact, the more the initial nitrogen content
is increased by the addition of curbs, the more the mineral nitrogen will increase at
the end of the composting cycle.
Thus, the contribution of olive mill wastewater to windrows rich in sludge considerably increases their nitrogen content. This nitrogen elements have the direct
effect of increasing the general microbial activity and boosting the environment of
the windrow.
Also, the application of olive mill wastewater has the effect of necessarily
increasing the nitrogen content of the appropriate windrows. These nitrogenous
elements reduce the C/N ratio and favor the stimulation of the biological activity.
As regards the co-composting of waste cuttings and straw, windrows with a
large amount of straw and olive mill wastewater showed low C/N ratio values as
compared to those obtained for windrows without olive mill wastewater; with
12
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
respective C/N values for the windrows (A7: 0% margins, A8: 15% margins and A9:
30% margins) of 124, 63.5 and 40.3 will be recorded.
But we could notice that at the level of the finished product, a C/N ratio of 40.3
remains a rather high ratio indicating that the finished compost is not mature and
an extension of the composting process is obligatorily essential because a nonmature compost might cause various important disturbances and an imbalance in
the soil [19]. Thus, fertilizing substances and toxic substances such as ammonium
are added to the soil in parallel. A similarity of the results would be observed in
straw-based windrows where the respective values of C/N or windrows having
received (0.15 and 30%) olive mill wastewater were 139; 54.38; 48.44 and 43.67.
Considering the organic components of the original waste, the addition of olive
mill wastewater has increased the organic content in all the waste mass variants and
this increase is proportional with the proportions of waste added for co-composting, 15% and 30%. Also, it is well known that the degradation of organic matter
essentially corresponds to the mineralization of carbon and nitrogen. This result is
confirmed by the fact that the smallest percentage of final residual organic matter
would be recorded for windrows based on green waste. On the other hand, this
percentage of residual final organic matter would be highest for straw and cuttings
waste windrows, which would generally show low biodegradation.
The significant organic matter contents measured at the end of the composting
cycle for sludge-based windrows could be explained by the richness of the sludge
in easily metabolizable organic elements eliminated and rendered available during
wastewater treatment by the complex biological flocculation-decantation-filtration
phenomena.
Bacteriological analyses carried out on the various windrows at the beginning of
the composting process often show great faecal bacteria contamination. Whereas an
important abatement of these bacteria would be recorded at the end of the composting process. This result is certainly due to the inactivating effects of the thermophilic phase often known as the hygienization stage and exercising a significant
influence on the composition of the macro and microbial flora, and consequently
on the biological quality of the finished product.
These microbial inactivation effects during the thermophilic phase are very
variable according to the nature of waste to be composted and the contents of the
compost heap during the composting cycle. The addition of olive mill wastewater in
the materials to be composted generally generates a stimulating effect of the organic
biodegradation and an inhibiting and stressful effects concerning the growth of
organisms presenting pathogenic or phytopathogenic characteristics [20].
The results relating to the analysis of polyphenols at the level of the windrows
during the composting process (samples taken at the beginning and at the end
of the composting cycle) show that the biodegradation or transformation of the
polyphenols contained in the olive mill wastewater is possible by composting.
Indeed, the polyphenol contents recorded at the beginning of the composting cycle
are relatively higher than those obtained at the end of the composting cycle.
However, these polyphenol contents rise at the level of the windrows having
received increasing quantity of 15 and 30% of the compost. At the end of the
cycle, the polyphenol contents become very minimal and barely detectable (traces
of the order of 0.3 mEq/g of dry matter of finished compost). The highest value
is recorded at the level of the straw swath saturated with 0.55 mEq/g of finished
compost dry matter.
This important result underlines the fact that the saturation of the waste windrows in the compost heap is not advisable and not recommended.
The application of a growing proportion of olive mill wastewater in the windrows does not affect the content and richness of the finished compost in mineral
13
Humic Substances
elements such as Zn, Cu, Ca and Cr, etc. The only exception is observed in case of
the WWTPs sludge (A10, A11, and A12) with very high values of these last elements
that are often proven conform to the common standards in vigor.
For the co-composting procedure treated with olive mill wastewater, we
necessity assumes the improvement of the potassium and calcium contents of the
finished product by assuming the great richness of the olive mill wastewater in
these elements. A contrary result could be made and suggested that these nutrients
have leaching with the rain in the case of processes conducted without shelter or
during watering, especially in the case of potassium, which is the most soluble and
therefore the most altered by leaching.
In the same manner, it is advisable to use straws (windrows: A16, A15 and A14)
for composting on condition that more water or olive mill wastewater is used for
watering and for avoiding low-slung water content at the start of the process that
slows down the general process of composting.
Finally, industrial technology systems could therefore exploit the olive mill
wastewater, which is considered as a precious raw material, very rich in organic
matter and nutrients, in order to use them instead of water for watering the windrows during overall composting process.
6. Conclusion
Thus, the problem of the valorisation of the various organic residues, principally
of the municipal wastes and olive mill wastewater, is currently worldwide worrying, and it is specially posed in terms of environmental preservation. The choice
of the treatment technique must not be only from the point of view of monetary
profitability, but above all must consider the efficiency of the treatment process.
It is not possible to develop all the techniques currently being tested. Composting
appeared as the main pathways for remediating this high and gigantic tonnage of
wastes daily generated by modern societies. The processes of composting described
above appeared very simple to be implemented, not expensive, and especially gave
a finished product of good quality on average, but very consuming in space and
in time. At last, I could clearly see that this kind of process might go well with an
implantation especially in developing countries with a sunny and warm climate.
The amendment of agricultural soil with organic matter is made very urgent by the
flagrant lack of its substances on the market and the same demand for fertilisers
from the increasingly demanding crops. Soil and the various bio-physico-chemical
and especially biological processes of degradation and humification prevailing in
the soil contribute intensively and could help in the solution of this thorny problem
of accumulation of all organic residues in modern societies.
14
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
Author details
Wafa Hassen1*, Bilel Hassen2, Rim Werhani3, Yassine Hidri4
and Abdennaceur Hassen3
1 Research Unit of Analysis and Process Applied to the Environmental (APAE),
Higher Institute of Applied Sciences and Technology Mahdia, University of
Monastir, Tunisia
2 University of Tunis El Manar, Institute for Veterinary Research of Tunisia, Tunis,
Tunisia
3 Water Research and Technology Center (C.E.R.T. E), Borj-Cédria Technology
Park, Soliman, Tunisia
4 Laboratory of Integrated Olive Production (LR16IO3), Sousse, Tunisia
*Address all correspondence to: hassen.wafa@gmail.com
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.
15
Humic Substances
References
[1] Hassen A., Jedidi N., K. Belguith, M.
Cherif M. & Boudabous A. (2001),
Microbial characterization during
composting of municipal solid waste.
Bioresources Technology, 80, 231-239.
[2] Mokni – Tlili S., Jaoua L., Murano F.,
Jedidi N. & Hassen A. (2009) Study of
urban organic residues effect on
culturable actinobacteria distribution in
Tunisia. Waste Management &
Research, 27 (3): 224-232.
[3] Mokni-Tlili S., Belguith H., Hassen A.
& Gargouri A. (2011) Studies on the
ecology of actinomycetes in an
agricultural soil amended with organic
residues: II. Assessment of enzymatic
activities of Actinomycetales isolates.
World Journal of Microbiology and
Biotechnology, 17, 1-9.
compost Déchets - Revue Francophone
D’écologie Industrielle -Trimestriel - N°
44 - Parution Décembre 2006 [8] De Bertoldi M., Sequi P., Lemmes B.,
Papi T. (1996) The Science of
Composting Springer; 1996th edition
(February 29, 1996) ISBN-10:
0751403830, ISBN-13: 9780751403831, 1494 p.
[9] Jammes, C. 2007. Co-valorisation of
fatty effluents and lignocellulosic
residues: mechanical dehydration and
composting, PhD thesis, Doctoral School
Sciences-Technology-Health, University
of Limoges, France, 193 pages.
[10] Saidi N., Cherif M., Jedidi N.,
Management of organic matter. F.
Dubusc Eds., Paris, 954p.
Mahrouk M., Murano F., Hassen A. &
Boudabous A. (2008) Evolution of
biochemical parameters during
composting of various waste compost.
American Journal of Environmental
Sciences, 4 (4): 333-341.
[5] Ben Ammar S. (2006). Les enjeux de
[11] Canuto, RA. (2012).
la caractérisation des déchets ménagers
pour le choix de traitements adaptés
dans les pays en développement
Résultats de la caractérisation dans le
grand Tunis: mise au point d’une
méthode adaptée, PhD thèses, École
Nationale Supérieure de Géologie de
Nancy, Institut National Polytechnique
de Lorraine, France, 317 pages.
Dehydrogenases || Dehydrogenase
Activity in the Soil Environment.
IntechOpen, 10.5772/2903(Chapter 8),
DOI:10.5772/48294.
[4] Mustin, M., 1987. Compost,
[12] Jedidi N., Hassen A., Van
Cleemput O. & M’hiri A. (2004)
Microbial biomass in a soil amended
with different organic wastes. Waste
Management & Research, 22. 2:93 – 99.
[6] Fourti O., Hidri Y., Murano F.,
Jedidi N., Hassen A. (2008) New process
assessment of co-composting of
municipal solid wastes and sewage
sludge in semi-arid pedo-climatic
condition. Annals of Microbiology, 58
(3) 403-409.
[7] Ben Ayed L., Hassen A., Gtari M.,
Jedidi N., Saidi N., Jaoua L., Murano F.,
2006. Évaluation de l’efficacité de trois
méthodes d’extraction d’ADN de la
biomasse microbienne totale du
16
[13] Bouzaiane O., Cherif H., Ayari F.,
Jedidi N. & Hassen A. (2007a)
Municipal solid waste compost dose
effects on soil microbial biomass
determined by chloroform fumigationextraction and DNA methods. Annals of
Microbiology. Vol. 57, N° 4
December 2007.
[14] Bouzaiane O., Cherif H., Saidi N.,
Jedidi N. & Hassen A. (2007b). Effect of
municipal solid waste compost
Co-Composting of Various Residual Organic Waste and Olive Mill Wastewater for Organic Soil…
DOI: http://dx.doi.org/10.5772/intechopen.97050
application on the microbial biomass of
cultivated and non-cultivated soil in a
semi-arid zone. Waste Management &
Research. Vol. 25, N° 4, 334-342.
[15] Khan KS., Mack R., Castillo X.,
Kaiser M., Joergensen RG. (2016).
Microbial biomass, fungal and bacterial
residues, and their relationships to the
soil organic matter C/N/P/S ratios.
Geoderma, 271(), 115-123. DOI:
10.1016/j.geoderma.
[16] Cherif H., Ouzari H., Marzorati M.,
Brusetti L., Jedidi N., Hassen A. &
Daffonchio D. (2008). Bacteria
community diversity assessment in
municipal solid waste compost amended
soil using DGGE and ARISA
fingerprinting methods World Journal
of Microbiology and Biotechnology, 24
(7), pp. 1159-1167. DOI 10.1007/
s11274-007-9588-z.
[17] Hidri Y., Bouziri L., Maron P.A.,
Anane M., Jedidi N., Hassen A. &
Ranjard L. (2009). Soil DNA evidence
for altered microbial diversity after
long-term application of municipal
wastewater. Agronomy for Sustainable
Development, 30 (2), 423-432.
[18] Laconi S.; Molle G.; Cabiddu A.;
Pompei R. (2007). Bioremediation of
olive oil mill wastewater and production
of microbial biomass. Biodegradation
(2007) 18:559-566. DOI 10.1007/
s10532-006-9087-1
[19] Fourti O., Jedidi N. & Hassen A.
(2011). Humic substances change
during the co-composting process of
municipal. Comparison of methods for
evaluating stability and maturity of
co-composting of municipal solid
wastes and sewage sludge in semi-arid
pedo-climatic condition. Natural
Science, 3(2), pp. 124-135, DOI:10.4236/
ns.2011.32018.
[20] Hechmi S., Hamdi H., Mokni-Tlili S.,
Ghorbel M., Khelil M. N., Zoghlami I. R.,
17
Benzarti S., Jellali S., Hassen A. &
Jedidi N. (2020) Impact of urban sewage
sludge on soil physico-chemical
properties and phytotoxicity as
influenced by soil texture and reuse
conditions DOI: 10.1002/jeq2.20093
Journal of Environmental Quality ©
2020 American Society of Agronomy,
Crop Science Society of America, and
Soil Science Society of America