particles together can also improve solids removal by filtration. Because of the corrosive and extreme slippery nature, coagulants should be handled with care (OSU 2000).
Increasing pH around 12 for half an hour is generally done
when dealing with chemical treatment. Lime is normally
used to increase the pH of the manure effluent. The use of
lime to increase the pH may also present a limitation. In
most cases there is a direct loss of ammonia in the form of
emissions from the manure. These emissions have negative
impacts on the human health by causing irritation, burning
and lung damage. Therefore, it is not appropriate to add lime
to manure effluents in areas that are not properly ventilated
or confined (OSU 2000). Chemical treatment method eliminates most of the pathogens present in the manure; consequently, odours are eliminated and the spread of disease will
be limited.
4 Bioconversion Processes of Manure
Effluents
4.1 Anaerobic Digestion and Aerobic Digestion
Bioconversion processes for manure effluents are mainly
based on biological treatment; they involve aerobic or
anaerobic digestion by using naturally occurring microorganisms in manure effluents to generate useful products such
as methane, carbon dioxide, treated effluent, biomethanol
and bioethanol. Aerobic digestion allows the decomposition
of manure effluents or any biodegradable wastes in the
presence of oxygen. It can be undertaken in aerobic lagoons
which stabilize the manure by addition of oxygen as mentioned earlier. Aerobic digestion consists of one step containing one process through which microorganisms are
allowed to convert manure effluents to carbon dioxide and
water. They have an advantage of limiting the generation of
odours; they are smaller than anaerobic lagoons; however,
they require regular maintenance and are energy-demanding
(Tallou et al. 2020; Loyon 2017).
Anaerobic digestion is known as one of the most used
technologies for biodegradable wastes, including manure
effluents, because of its effectiveness and the nature of
manure/biodegradable wastes which are well adapted to
anaerobic digestion. Anaerobic digestion is a process dealing
with the biodegradation of manure/wastes by living organisms in the absence of oxygen. It can be achieved in
anaerobic digesters or lagoons (Tallou et al. 2020; Loyon
2017; Yao et al. 2020). Digesters decompose manure effluents or any biodegradable waste into a biogas that can be
used in energy applications (Bharathiraja et al. 2018).
Anaerobic lagoons may be enclosed for gas collection.
Uncovered anaerobic lagoons are generally hundred times
greater than anaerobic digesters (OSU 2000). Biological
treatment of manure effluents deals with microorganisms in
manure to modify its properties under operating conditions.
Anaerobic digestion is made of four main steps described as
follows: hydrolysis, acidogenesis, acetogenesis and
methanogenesis. In the last phase (methanogenesis) the
manure is transformed into biogas by living organisms.
Biogas is a mixture of CH 4 , CO 2 , N 2 , H 2 , CO, O 2 and H 2 S.
Between 60 and 80% of the biogas is made of CH 4 , and the
rest is made mostly of CO 2 . Generally, N 2 , H 2 , CO, O 2 and
H 2 S are detected in trace amounts (Roos 1997). Methane
(CH 4 ) in biogas is comparable to natural gas. After scrubbing it is possible to use it in combustion engines to run
generators for electricity production (Rozdilsky 1997). The
electricity can be used on the farm or it can also be sold to
the close community if there is an available market for it.
Biogas may also be used for other needs on site as source of
energy for boilers, heaters, refrigeration, cooking and lighting. Furthermore, nitrogen (N 2 ) is transformed into ammonia
(NH 3 ) during digestion. NH 3 is one of the key components
needed to produce commercial fertilizers. The anaerobic
digestion of manure effluents generates a uniform and predictable product. Furthermore, anaerobic digestion can also
generate solids by-products with a wide range of applications. These solids by-products can be used as substrates in
compost aiming to provide sources of carbon and nutrients.
Figures 6 presents the advantages and disadvantages for
anaerobic digestions for manure effluents.
There are numerous sorts of digesters. They are designed
with particularities related to types of manure/biodegradable
wastes and operating conditions. Table 1 presents a summary of different types of digesters used for anaerobic
digestion of manure.
4.2 Composting of Manure
This is an aerobic biodegradation of manure/ organic wastes
under thermophilic conditions between 40 and 65 °C (UNL
1998). It is an established on-farm manure technology. In
this process organic matter present in manure is subjected to
biodegradation or decay process which is taking place in a
pile. Due to the fact that oxygen is important in the composting process, the pile must be mixed frequently to integrate oxygen and to be assured about the composting of the
less disintegrated material at the pile’s edge (Purdue 1996).
It should be done when there is no reheating of the pile after
its mixing (Purdue 1994). The energy released during the
biodegradation process increases the compost temperature in
order to speed up the decomposition of organic matter and
allow the evaporation of water. This will result in a dried and
stabilized compost within 3 to 6 months. The main limitation on composting is the condition for a dry bulking
amendment required to generate a suitable porosity in
304
J. K. Bwapwa
Increasing pH around 12 for half an hour is generally done
when dealing with chemical treatment. Lime is normally
used to increase the pH of the manure effluent. The use of
lime to increase the pH may also present a limitation. In
most cases there is a direct loss of ammonia in the form of
emissions from the manure. These emissions have negative
impacts on the human health by causing irritation, burning
and lung damage. Therefore, it is not appropriate to add lime
to manure effluents in areas that are not properly ventilated
or confined (OSU 2000). Chemical treatment method eliminates most of the pathogens present in the manure; consequently, odours are eliminated and the spread of disease will
be limited.
4 Bioconversion Processes of Manure
Effluents
4.1 Anaerobic Digestion and Aerobic Digestion
Bioconversion processes for manure effluents are mainly
based on biological treatment; they involve aerobic or
anaerobic digestion by using naturally occurring microorganisms in manure effluents to generate useful products such
as methane, carbon dioxide, treated effluent, biomethanol
and bioethanol. Aerobic digestion allows the decomposition
of manure effluents or any biodegradable wastes in the
presence of oxygen. It can be undertaken in aerobic lagoons
which stabilize the manure by addition of oxygen as mentioned earlier. Aerobic digestion consists of one step containing one process through which microorganisms are
allowed to convert manure effluents to carbon dioxide and
water. They have an advantage of limiting the generation of
odours; they are smaller than anaerobic lagoons; however,
they require regular maintenance and are energy-demanding
(Tallou et al. 2020; Loyon 2017).
Anaerobic digestion is known as one of the most used
technologies for biodegradable wastes, including manure
effluents, because of its effectiveness and the nature of
manure/biodegradable wastes which are well adapted to
anaerobic digestion. Anaerobic digestion is a process dealing
with the biodegradation of manure/wastes by living organisms in the absence of oxygen. It can be achieved in
anaerobic digesters or lagoons (Tallou et al. 2020; Loyon
2017; Yao et al. 2020). Digesters decompose manure effluents or any biodegradable waste into a biogas that can be
used in energy applications (Bharathiraja et al. 2018).
Anaerobic lagoons may be enclosed for gas collection.
Uncovered anaerobic lagoons are generally hundred times
greater than anaerobic digesters (OSU 2000). Biological
treatment of manure effluents deals with microorganisms in
manure to modify its properties under operating conditions.
Anaerobic digestion is made of four main steps described as
follows: hydrolysis, acidogenesis, acetogenesis and
methanogenesis. In the last phase (methanogenesis) the
manure is transformed into biogas by living organisms.
Biogas is a mixture of CH 4 , CO 2 , N 2 , H 2 , CO, O 2 and H 2 S.
Between 60 and 80% of the biogas is made of CH 4 , and the
rest is made mostly of CO 2 . Generally, N 2 , H 2 , CO, O 2 and
H 2 S are detected in trace amounts (Roos 1997). Methane
(CH 4 ) in biogas is comparable to natural gas. After scrubbing it is possible to use it in combustion engines to run
generators for electricity production (Rozdilsky 1997). The
electricity can be used on the farm or it can also be sold to
the close community if there is an available market for it.
Biogas may also be used for other needs on site as source of
energy for boilers, heaters, refrigeration, cooking and lighting. Furthermore, nitrogen (N 2 ) is transformed into ammonia
(NH 3 ) during digestion. NH 3 is one of the key components
needed to produce commercial fertilizers. The anaerobic
digestion of manure effluents generates a uniform and predictable product. Furthermore, anaerobic digestion can also
generate solids by-products with a wide range of applications. These solids by-products can be used as substrates in
compost aiming to provide sources of carbon and nutrients.
Figures 6 presents the advantages and disadvantages for
anaerobic digestions for manure effluents.
There are numerous sorts of digesters. They are designed
with particularities related to types of manure/biodegradable
wastes and operating conditions. Table 1 presents a summary of different types of digesters used for anaerobic
digestion of manure.
4.2 Composting of Manure
This is an aerobic biodegradation of manure/ organic wastes
under thermophilic conditions between 40 and 65 °C (UNL
1998). It is an established on-farm manure technology. In
this process organic matter present in manure is subjected to
biodegradation or decay process which is taking place in a
pile. Due to the fact that oxygen is important in the composting process, the pile must be mixed frequently to integrate oxygen and to be assured about the composting of the
less disintegrated material at the pile’s edge (Purdue 1996).
It should be done when there is no reheating of the pile after
its mixing (Purdue 1994). The energy released during the
biodegradation process increases the compost temperature in
order to speed up the decomposition of organic matter and
allow the evaporation of water. This will result in a dried and
stabilized compost within 3 to 6 months. The main limitation on composting is the condition for a dry bulking
amendment required to generate a suitable porosity in
304
J. K. Bwapwa