152 H. N. Sandvold et al.
Soil improvement
Currently, the main utilisation of organic waste from land- based salmon production is soil improvement and fertiliser in agricultural production, either
directly or indirectly.
The most common practice is through collaboration with local farmers,
where the farmers come to the hatchery to pick up the sludge, normally by
tractor and trailer. Since the sludge typically has a water content of 80–90%,
the farmers need to use large tanks during transport. The organic liquid is
applied directly on the soil without any kind of processing. The farmers are
paid between 0.09C/kg and 0.21C/kg for the job. This collaboration is by
far the most common practice to re- use the waste from smolt production.
However, some hatcheries choose to transport their wastewater to local
recycling facilities. Here the sludge is dried, mixed and further processed with
other kinds of organic waste (human sewage, for example). After processing,
the new by- product is further sold as fertiliser as a dried biomass and also here
used as soil improvement.
Replacement of fossil fuel (biogas)
When organic material goes through anaerobic decomposition, bacteria transform the waste into 60% methane and 40% carbon dioxide and other trace
gases. The methane portion of the gas, often called biogas, can be used to
produce new energy such as heat and electric power.
Sludge from smolt production is high in iron, because of the use of ironchloride as a precipitate within the RA technology. This is a positive aspect
of this feedstock for biogas production because it reduces the hydrogensulphide production as well as carbon dioxide, and is more efficiently converted to methane. The whole organic waste is generally high in fat and is
therefore high in energy content; the large amount of fatty acids is nevertheless a challenge when it comes to biogas producers because they tend to
inhibit methanogenic bacteria (Nges, Mbatia & Björnsson, 2012). So far, the
biogas- producers have solved this by mixing in waste from agricultural
farming.
Currently, biogas has two main areas for use: as a motor fuel for transport
and as a heating fuel for greenhouses. In Norway, around 40 biogas plants
currently exist and the sector is not yet as developed as it is in Denmark.
Nevertheless, interest is increasing in Norway because it represents a sustainable energy source and the Norwegian firms see it as an interesting future
possibility if the biogas facilities could be located near the fish farms, and if
the requirements of mixing the waste with other agricultural residues could
be met.
Biogas production has so far been driven by the agricultural sector. Yet
low electricity costs have, to date, slowed down the development of biogas.
At the time of the interview, the biogas production firms in Denmark were
Soil improvement
Currently, the main utilisation of organic waste from land- based salmon production is soil improvement and fertiliser in agricultural production, either
directly or indirectly.
The most common practice is through collaboration with local farmers,
where the farmers come to the hatchery to pick up the sludge, normally by
tractor and trailer. Since the sludge typically has a water content of 80–90%,
the farmers need to use large tanks during transport. The organic liquid is
applied directly on the soil without any kind of processing. The farmers are
paid between 0.09C/kg and 0.21C/kg for the job. This collaboration is by
far the most common practice to re- use the waste from smolt production.
However, some hatcheries choose to transport their wastewater to local
recycling facilities. Here the sludge is dried, mixed and further processed with
other kinds of organic waste (human sewage, for example). After processing,
the new by- product is further sold as fertiliser as a dried biomass and also here
used as soil improvement.
Replacement of fossil fuel (biogas)
When organic material goes through anaerobic decomposition, bacteria transform the waste into 60% methane and 40% carbon dioxide and other trace
gases. The methane portion of the gas, often called biogas, can be used to
produce new energy such as heat and electric power.
Sludge from smolt production is high in iron, because of the use of ironchloride as a precipitate within the RA technology. This is a positive aspect
of this feedstock for biogas production because it reduces the hydrogensulphide production as well as carbon dioxide, and is more efficiently converted to methane. The whole organic waste is generally high in fat and is
therefore high in energy content; the large amount of fatty acids is nevertheless a challenge when it comes to biogas producers because they tend to
inhibit methanogenic bacteria (Nges, Mbatia & Björnsson, 2012). So far, the
biogas- producers have solved this by mixing in waste from agricultural
farming.
Currently, biogas has two main areas for use: as a motor fuel for transport
and as a heating fuel for greenhouses. In Norway, around 40 biogas plants
currently exist and the sector is not yet as developed as it is in Denmark.
Nevertheless, interest is increasing in Norway because it represents a sustainable energy source and the Norwegian firms see it as an interesting future
possibility if the biogas facilities could be located near the fish farms, and if
the requirements of mixing the waste with other agricultural residues could
be met.
Biogas production has so far been driven by the agricultural sector. Yet
low electricity costs have, to date, slowed down the development of biogas.
At the time of the interview, the biogas production firms in Denmark were