Autumn 2017 EN

English Issue
Biogas Journal
| Autumn_2017
Results
During the investigation, the following
material flows were sampled:
ffBlackwater fresh from
the blackwater tank
ffGreywater fresh from
the greywater tank
ffShredded food leftovers from
the vacuum unit
ffDried biosludge (mixture of
wastewater sludge and food
leftovers)
ffDeep fryer grease
ffFlotate sludge from
the grease trap
The gas yield for each group was determined
at the batch scale according to the Association
of German Engineers [VDI] 4630. The
highest gas yields were obtained with the
grease portion, the biosludge and the food
leftovers. The gas yields from the greywater
and blackwater are rather low, but very large
quantities of these substances are generated.
Due to the limited space on board, it
makes no sense to ferment the fresh wastewater
portion because large storage capacities
and digesters would be needed.
The on-board treatment facilities precipitate
the solids in the wastewater with an
increasing degree of purity, so the solid
portion, which contains potential energy,
can be found in wastewater sludge tank.
Wastewater sludge and food leftovers are
dewatered and mixed to form biosludge.
Because the food leftovers were also sampled
separately, a comparison establishes
that about the same amount of energy is
produced from all of the dewatered wastewater
sludge as with food leftovers.
For this reason, wastewater potential
should absolutely be used as well. In comparison
with agricultural biogas plants, the
target capacity is similar to an average plant
capacity. With regard to the energy required
by a cruise ship, this capacity covers only a
very small proportion. Thus, shipping companies
are not particularly interested in energy
production, but instead in alternative
disposal options that comply with the mandatory
environmental requirements and in
increasing the efficiency of the overall system
and saving costs.
About 160,000 euros could be saved per
year on just one ship by eliminating the
required drying and change in disposal
costs. By using the biogas produced, the
capacity side could be increased by another
190,000 euros per year; this would require
substituting biogas for marine diesel oil
(MDO). There is a wide variety of options
for using biogas on board. For example, it
would make sense to use biogas for auxiliary
thermal or electrical energy while in port
in order to reduce gaseous ship emissions
in the harbour.
Likewise, progress in LNG technologies in
the shipping industry offers utilisation options.
However, in order to install as few
technologies as possible on board that require
extensive oversight and maintenance
by specialized personnel, shipping companies
prefer disposing of waste on land. In
this case, the capacity of a facility on land
could even be expanded with the waste of
other ships. Every year there are 350 cruises
on the Baltic Sea alone. The effects on
cost savings, the contribution to renewable
energy production, and the positive ecological
effects would be considerable.
Motiv2017_175x56.5_en_b 09.05.2017 15:48 Seite 1
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