are variable depending on the type of organic matter treated
and of the technology implemented. The average amount of
biogas obtained varies with the treated waste; for example, a
ton of household organic waste yields 80–150 m
3 of biogas.
In addition, depending on the nature of the starting biomass,
it is possible to obtain a product usable as fertilizer or
organic amendment (e.g., green waste).
Biogas composition depends on the nature of the organic
material used, but the average composition is as follows:
CH 4 (50–90 %), CO 2 (10–40 %), H 2 (1–3 %), N 2
(0, 5–2 %), H 2 S (0.1–0.5 %), CO (0.0–0.1 %) (La Farge
1995). This is an energy form which is as noble as
natural gas. The presence of H 2 S and CO 2 in biogas
makes it corrosive and requires, for installations, the
use of appropriate materials or the implementation of
technologies that ensure the purification of biogas; the
elimination of H 2 S is carried out by physicochemical or
biological treatments (elimination by sulfur-oxidizing bacteria; cf. Sect. 14.4) which transform H 2 S into elemental
sulfur. It should be noted the presence of H 2 S in fossil gas,
for example, the H 2 S content, is 15 % in Lacq gas (France)
and some deposits contain 50 %. This similarity in composition may be explained by the fact that fossil gas and
contemporary gas are obtained from similar fermentation
processes.
Biogas is a renewable and inexhaustible energy source,
and the possibility of using biogas as a renewable energy
source is now proved; facilities exist around the world,
ranging from domestic digesters to industrial units of several
thousand cubic meters. Given the increasing production of
waste, “industrial development potential which is susceptible to be generated by large-scale production of biogas is of
the same order of magnitude as that derived from the exploitation of natural gas” (La Farge 1995).
16.5.5 Discharges
There are different types of waste including the household
waste and similar (HWS) produced by households: for
example, daily, a Frenchman produces about 1 kg of domestic waste. For the protection of the environment, discharges
and installations for elimination of waste become Ultimate
Waste Storage Facilities (UWSF or landfills). In the field of
HWS, the ultimate waste is defined as the “non-recoverable
fraction of waste.” In 2004 in France, over 47 % of the HWS
were sent to landfills. This technique is also widely used in
European countries, such as Germany, Spain, and the United
Kingdom. A UWSF is constituted by a set of bins, hydraulically independent, themselves composed of boxes, in which
the wastes are stored. Each compartment is isolated by an
impervious membrane. The operating time of a site is about
20 years. The operation of these landfills may be considered
as a bio-physicochemical reactor resulting in reactions
and complex changes that lead to chemical, physical,
and biological processing of wastes. Water promotes the
conversion of wastes and therefore the evolution of landfills.
All of these phenomena lead to the generation of two
pollutants flow:
(i) A gaseous effluent, the biogas, produced by natural
fermentation of the organic matter contained in waste.
(ii) An aqueous effluent, the leachate, which results from the
percolation, through the solid waste, of the water
contained in the waste or added. This water promotes
biodegradation of fermentable organic matter and then
produces leachates that concentrate organic substances
and/or minerals from waste or by-products of waste
degradation.
Understanding the genesis of leachates not only requires
knowledge of the nature of buried waste and the operating
mode of the landfills (waste height, operated, compaction,
etc.) but also the study of interactions between water and
waste. The mechanisms of the genesis of leachate are very
complex: they are of biological and physicochemical nature
(Fig. 16.17).
Microbial processes play an important role. Indeed, buried
waste is used as a substrate for heterotrophic organisms
(prokaryotes, yeasts, fungi) responsible for the degradation
of the organic fraction. The effects of this activity may be
multiple, direct, or indirect and trigger secondary physicochemical phenomena. This then results in a change in environmental conditions (pH, temperature, redox potential) that
affect microbial mechanisms. In the presence and/or absence
of oxygen, by the action of extracellular enzymes secreted
by microorganisms, the organic waste content (proteins,
carbohydrates, lipids, hydrocarbons, phenols, etc.) is
degraded in intermediary metabolites (polypeptides, amino
acids, amines, fatty acids, aldehydes, quinones, diacids,
mono- and disaccharides, etc.). The metabolites formed are
then degraded by aerobic and anaerobic microorganisms:
(i) The aerobic degradation is possible as long as the
density of the waste allows the diffusion of oxygen.
It leads, in particular, the formation of the final
metabolites (H 2 O, CO 2 , HCO 3
À , CO 3
2À , NO 3
À ,
PO 4
3À
, SO 4
2À ). The term “aerobic fermentation” is
commonly used in the treatment of discharges; formally, this term is inappropriate, and the processes
involved are occurring in the presence of oxygen.
The early stages of aerobic degradation of discharges
treatment are identical to the early stages of composting, including a rise in temperature that can reach
60
C within the waste mass.
680
J.-C. Bertrand et al.
and of the technology implemented. The average amount of
biogas obtained varies with the treated waste; for example, a
ton of household organic waste yields 80–150 m
3 of biogas.
In addition, depending on the nature of the starting biomass,
it is possible to obtain a product usable as fertilizer or
organic amendment (e.g., green waste).
Biogas composition depends on the nature of the organic
material used, but the average composition is as follows:
CH 4 (50–90 %), CO 2 (10–40 %), H 2 (1–3 %), N 2
(0, 5–2 %), H 2 S (0.1–0.5 %), CO (0.0–0.1 %) (La Farge
1995). This is an energy form which is as noble as
natural gas. The presence of H 2 S and CO 2 in biogas
makes it corrosive and requires, for installations, the
use of appropriate materials or the implementation of
technologies that ensure the purification of biogas; the
elimination of H 2 S is carried out by physicochemical or
biological treatments (elimination by sulfur-oxidizing bacteria; cf. Sect. 14.4) which transform H 2 S into elemental
sulfur. It should be noted the presence of H 2 S in fossil gas,
for example, the H 2 S content, is 15 % in Lacq gas (France)
and some deposits contain 50 %. This similarity in composition may be explained by the fact that fossil gas and
contemporary gas are obtained from similar fermentation
processes.
Biogas is a renewable and inexhaustible energy source,
and the possibility of using biogas as a renewable energy
source is now proved; facilities exist around the world,
ranging from domestic digesters to industrial units of several
thousand cubic meters. Given the increasing production of
waste, “industrial development potential which is susceptible to be generated by large-scale production of biogas is of
the same order of magnitude as that derived from the exploitation of natural gas” (La Farge 1995).
16.5.5 Discharges
There are different types of waste including the household
waste and similar (HWS) produced by households: for
example, daily, a Frenchman produces about 1 kg of domestic waste. For the protection of the environment, discharges
and installations for elimination of waste become Ultimate
Waste Storage Facilities (UWSF or landfills). In the field of
HWS, the ultimate waste is defined as the “non-recoverable
fraction of waste.” In 2004 in France, over 47 % of the HWS
were sent to landfills. This technique is also widely used in
European countries, such as Germany, Spain, and the United
Kingdom. A UWSF is constituted by a set of bins, hydraulically independent, themselves composed of boxes, in which
the wastes are stored. Each compartment is isolated by an
impervious membrane. The operating time of a site is about
20 years. The operation of these landfills may be considered
as a bio-physicochemical reactor resulting in reactions
and complex changes that lead to chemical, physical,
and biological processing of wastes. Water promotes the
conversion of wastes and therefore the evolution of landfills.
All of these phenomena lead to the generation of two
pollutants flow:
(i) A gaseous effluent, the biogas, produced by natural
fermentation of the organic matter contained in waste.
(ii) An aqueous effluent, the leachate, which results from the
percolation, through the solid waste, of the water
contained in the waste or added. This water promotes
biodegradation of fermentable organic matter and then
produces leachates that concentrate organic substances
and/or minerals from waste or by-products of waste
degradation.
Understanding the genesis of leachates not only requires
knowledge of the nature of buried waste and the operating
mode of the landfills (waste height, operated, compaction,
etc.) but also the study of interactions between water and
waste. The mechanisms of the genesis of leachate are very
complex: they are of biological and physicochemical nature
(Fig. 16.17).
Microbial processes play an important role. Indeed, buried
waste is used as a substrate for heterotrophic organisms
(prokaryotes, yeasts, fungi) responsible for the degradation
of the organic fraction. The effects of this activity may be
multiple, direct, or indirect and trigger secondary physicochemical phenomena. This then results in a change in environmental conditions (pH, temperature, redox potential) that
affect microbial mechanisms. In the presence and/or absence
of oxygen, by the action of extracellular enzymes secreted
by microorganisms, the organic waste content (proteins,
carbohydrates, lipids, hydrocarbons, phenols, etc.) is
degraded in intermediary metabolites (polypeptides, amino
acids, amines, fatty acids, aldehydes, quinones, diacids,
mono- and disaccharides, etc.). The metabolites formed are
then degraded by aerobic and anaerobic microorganisms:
(i) The aerobic degradation is possible as long as the
density of the waste allows the diffusion of oxygen.
It leads, in particular, the formation of the final
metabolites (H 2 O, CO 2 , HCO 3
À , CO 3
2À , NO 3
À ,
PO 4
3À
, SO 4
2À ). The term “aerobic fermentation” is
commonly used in the treatment of discharges; formally, this term is inappropriate, and the processes
involved are occurring in the presence of oxygen.
The early stages of aerobic degradation of discharges
treatment are identical to the early stages of composting, including a rise in temperature that can reach
60
C within the waste mass.
680
J.-C. Bertrand et al.