They can be costly because of the amount of chemicals to be
used and may cause contamination of the manure if used in
excess.
The main focus being bioconversion as mentioned earlier,
aerobic and anaerobic digestion are among the major processes used in the biological conversion of manure effluents
or manure only as solid waste. These two processes are well
known for their effectiveness under specific operating conditions. This can be possible with the use of oxygen or
without oxygen for aerobic and anaerobic digestion respectively. It is very essential to stress on the fact that anaerobic
digestion has a large ground of applications for bioconversion of manure effluents. It is generating by-products such as
biogas and hydrogen to be used in the energy sector.
However, aerobic digestion is also important in the treatment
of manure effluents because it generates clean effluent and
CO 2 . Composting is an aerobic treatment that is used to
process manure or any other organic feedstock at thermophilic temperatures. It is known as an on-site and reputable process for manure treatment. In this process organic
matter present in manure is subjected to a decay which is
taking place in a pile. Composting can effectively reduce
manure odour, remove completely the weed seeds and
pathogens, and it can also improve the retention of moisture
for light soils. Biodrying is also another aerobic process
using forced-air for drying manure or compost mixture. The
merit of the process is such that odour, volume and weight of
the manure are reduced including the availability of handling
equipment for solid particles on many farms; however, the
operating costs may be higher. Pelletization of solids manure
is achieved through an extrusion technique. The manure
being rich in nutrients is converted into high-grade, pasteurized, pelletized organic fertilizers. This process provides
a great option to farmers in order for them to deal effectively
with wastes management and avoid the contamination of
neighbouring freshwater resources from nutrients runoff.
However, the marketability of pellets is limited coupled with
high transport costs. Gasification or pyrolysis is also a sustainable and effective conversion process; undertaken at
around 600 °C with the assistance of biocatalysts/catalysts
for the conversion of manure into clean fuel. It is generally a
two-step endothermic process because after pyrolysis the
char undergoes a gasification with oxygen, hydrogen and
steam, to collect as much gas from the manure. The fraction
of unburned char will produce enough heat for endothermic
gasification reactions. From this process clean fuel, electricity and heat can be produced while complying with
environmental regulations. Furthermore, from gasification or
anaerobic digestion of manure, it is possible to produce
methanol. In this regard syngas is produced first, followed
by its synthesis to generate methanol. The process can be
cost-effective, however, initial capital costs are higher.
Cofiring process is also a conversion process that combines
the combustion of manure and a base fuel to produce heat
that can be useful for power plants or steam plants. Cofiring
manure and base fuel have recorded some success and
show promise for the future. The process can also generate
electricity by using a pressured steam from a boiler into a
turbine. However, the technology is still new and many
studies should be completed before reaching the maturity
level.
There are also applications dealing with microalgae production, aquaculture, use of manure in building industry,
manure bedding or litter and soil reclamation using manure
which are considered as emerging technologies. Their
growth could add up on the list of bioconversion processes
for manure effluents once they reach the commercial stage
with a certain level of maturity.
References
ACFA. (2000a). A strategic alliance in the Netherlands-new technologies and science for high added value products biosynthesized from
animal manure surplus. Alberta Cattle Feeders’ Association. Report.
ACFA. (2000b). Manure Cleans Up Its Act. Report: Alberta Cattle
Feeders’ Association.
Ak, N., & Demirbas, A. (2016). Promising sources of energy in the
near future. Energy Sources, Part A: Recovery, Utilization, and
Environmental Effects, 38(12), 1730–1738. https://doi.org/10.1080/
15567036.2014.966179.
Altieri, M. A. (2002). Agroecology: the science of natural resource
management for poor farmers in marginal environments. Agriculture, Ecosystems & Environment, 93(1–3), 1–24. https://doi.org/10.
1016/S0167-8809(02)00085-3.
Amenu, D. (2014). Characterization of wastewater and evaluation of
the effectiveness of the wastewater treatment systems. World
Journal of Life Sciences Research, 1(1), 1–11.
Antares Group Incorporated, T.R. Miles Technical Consulting, Inc.,
and Foster Wheeler Development Corporation (1999). Economic
and Technical Feasibility of Energy Production from Poultry Litter
and Nutrient Filter Biomass on the Lower Delmarva Peninsula.
http://www.nrbp.org/. Accessed in June 2020. Report.
ARS. (1998). Agricultural uses of municipal, animal, and industrial
by-products. U.S. Department of Agriculture, Agricultural Research
Service. Report.
Belete, E., & Ayza, A. (2015). A review on alternative technologies to
manage manure: Cost effective and environmentally beneficial.
Livestock Research for Rural Development, 27(10).
Belsie, L. (2000). What the three pigs missed: ‘cow-patty’ construction.
The Christian Science Monitor. Report www.csmonitor.com/
durable/2000/05/08/text/p15s2.html. Accessed June 2020.
Bernal, M. P., Sommer, S. G., Chadwick, D., Qing, C., Guoxue, L., &
Michel Jr, F. C. (2017). Current approaches and future trends in
compost quality criteria for agronomic, environmental, and human
health benefits. In advances in agronomy (Vol. 144, pp. 143–233).
Academic Press. https://doi.org/10.1016/bs.agron.2017.03.002.
Bharathiraja, B., Sudharsana, T., Jayamuthunagai, J., Praveenkumar,
R., Chozhavendhan, S., & Iyyappan, J. (2018). Biogas
production-A review on composition, fuel properties, feed stock
and principles of anaerobic digestion. Renewable and Sustainable
Energy Reviews, 90(C), 570–582. https://doi.org/10.1016/j.rser.
2018.03.093.
312
J. K. Bwapwa
used and may cause contamination of the manure if used in
excess.
The main focus being bioconversion as mentioned earlier,
aerobic and anaerobic digestion are among the major processes used in the biological conversion of manure effluents
or manure only as solid waste. These two processes are well
known for their effectiveness under specific operating conditions. This can be possible with the use of oxygen or
without oxygen for aerobic and anaerobic digestion respectively. It is very essential to stress on the fact that anaerobic
digestion has a large ground of applications for bioconversion of manure effluents. It is generating by-products such as
biogas and hydrogen to be used in the energy sector.
However, aerobic digestion is also important in the treatment
of manure effluents because it generates clean effluent and
CO 2 . Composting is an aerobic treatment that is used to
process manure or any other organic feedstock at thermophilic temperatures. It is known as an on-site and reputable process for manure treatment. In this process organic
matter present in manure is subjected to a decay which is
taking place in a pile. Composting can effectively reduce
manure odour, remove completely the weed seeds and
pathogens, and it can also improve the retention of moisture
for light soils. Biodrying is also another aerobic process
using forced-air for drying manure or compost mixture. The
merit of the process is such that odour, volume and weight of
the manure are reduced including the availability of handling
equipment for solid particles on many farms; however, the
operating costs may be higher. Pelletization of solids manure
is achieved through an extrusion technique. The manure
being rich in nutrients is converted into high-grade, pasteurized, pelletized organic fertilizers. This process provides
a great option to farmers in order for them to deal effectively
with wastes management and avoid the contamination of
neighbouring freshwater resources from nutrients runoff.
However, the marketability of pellets is limited coupled with
high transport costs. Gasification or pyrolysis is also a sustainable and effective conversion process; undertaken at
around 600 °C with the assistance of biocatalysts/catalysts
for the conversion of manure into clean fuel. It is generally a
two-step endothermic process because after pyrolysis the
char undergoes a gasification with oxygen, hydrogen and
steam, to collect as much gas from the manure. The fraction
of unburned char will produce enough heat for endothermic
gasification reactions. From this process clean fuel, electricity and heat can be produced while complying with
environmental regulations. Furthermore, from gasification or
anaerobic digestion of manure, it is possible to produce
methanol. In this regard syngas is produced first, followed
by its synthesis to generate methanol. The process can be
cost-effective, however, initial capital costs are higher.
Cofiring process is also a conversion process that combines
the combustion of manure and a base fuel to produce heat
that can be useful for power plants or steam plants. Cofiring
manure and base fuel have recorded some success and
show promise for the future. The process can also generate
electricity by using a pressured steam from a boiler into a
turbine. However, the technology is still new and many
studies should be completed before reaching the maturity
level.
There are also applications dealing with microalgae production, aquaculture, use of manure in building industry,
manure bedding or litter and soil reclamation using manure
which are considered as emerging technologies. Their
growth could add up on the list of bioconversion processes
for manure effluents once they reach the commercial stage
with a certain level of maturity.
References
ACFA. (2000a). A strategic alliance in the Netherlands-new technologies and science for high added value products biosynthesized from
animal manure surplus. Alberta Cattle Feeders’ Association. Report.
ACFA. (2000b). Manure Cleans Up Its Act. Report: Alberta Cattle
Feeders’ Association.
Ak, N., & Demirbas, A. (2016). Promising sources of energy in the
near future. Energy Sources, Part A: Recovery, Utilization, and
Environmental Effects, 38(12), 1730–1738. https://doi.org/10.1080/
15567036.2014.966179.
Altieri, M. A. (2002). Agroecology: the science of natural resource
management for poor farmers in marginal environments. Agriculture, Ecosystems & Environment, 93(1–3), 1–24. https://doi.org/10.
1016/S0167-8809(02)00085-3.
Amenu, D. (2014). Characterization of wastewater and evaluation of
the effectiveness of the wastewater treatment systems. World
Journal of Life Sciences Research, 1(1), 1–11.
Antares Group Incorporated, T.R. Miles Technical Consulting, Inc.,
and Foster Wheeler Development Corporation (1999). Economic
and Technical Feasibility of Energy Production from Poultry Litter
and Nutrient Filter Biomass on the Lower Delmarva Peninsula.
http://www.nrbp.org/. Accessed in June 2020. Report.
ARS. (1998). Agricultural uses of municipal, animal, and industrial
by-products. U.S. Department of Agriculture, Agricultural Research
Service. Report.
Belete, E., & Ayza, A. (2015). A review on alternative technologies to
manage manure: Cost effective and environmentally beneficial.
Livestock Research for Rural Development, 27(10).
Belsie, L. (2000). What the three pigs missed: ‘cow-patty’ construction.
The Christian Science Monitor. Report www.csmonitor.com/
durable/2000/05/08/text/p15s2.html. Accessed June 2020.
Bernal, M. P., Sommer, S. G., Chadwick, D., Qing, C., Guoxue, L., &
Michel Jr, F. C. (2017). Current approaches and future trends in
compost quality criteria for agronomic, environmental, and human
health benefits. In advances in agronomy (Vol. 144, pp. 143–233).
Academic Press. https://doi.org/10.1016/bs.agron.2017.03.002.
Bharathiraja, B., Sudharsana, T., Jayamuthunagai, J., Praveenkumar,
R., Chozhavendhan, S., & Iyyappan, J. (2018). Biogas
production-A review on composition, fuel properties, feed stock
and principles of anaerobic digestion. Renewable and Sustainable
Energy Reviews, 90(C), 570–582. https://doi.org/10.1016/j.rser.
2018.03.093.
312
J. K. Bwapwa