Autumn 2017 EN

Biogas Journal | Autumn_2017 English Issue
biomass potential on board a cruise ship and to determine the
amount of energy associated with it in consideration of possibly
producing and using biogas. The material characteristics of the
biomass obtained in this way are outstanding for use in the biogas
process. The total solid contents of up to 15 percent are in a optimum
range for operating mesophilic biogas reactors. Extensive
drying processes are not necessary, i.e. energy costs are saved.
The cruise ship in the AIDA fleet under consideration is a Sphinx
class ship with a capacity of 2,500 passengers. In the context of
the study, the existing ship disposal system was analysed, samples
of various biogenic materials at various stages of treatment
were taken and characterized with respect to material, gas yield
tests were carried out, and options for utilising the gas on board
were demonstrated.
Challenges of on-board disposal
Currently, the wastewater generated on board is purified in high
performance sewage treatment facilities before the permeate is
flushed into the sea, and the wastewater sludge and food leftovers
are collected, dewatered, dried and burned. In protected
areas, such as the Baltic Sea, the operation of the respective incinerators
is now banned. In this case, the dried biosludge must
be stored and disposed of on shore.
The on-board drying process needed to store the sludge requires
a great deal of energy and generates odour emissions. Based on
the waste categorization in Regulation (EC) No. 1069/2009, in
which waste is classified with regard to its risk to the health of
people and animals, kitchen waste in international transport is
considered material in category 1, the most problematic form
with particularly high requirements for disposal.
In general, this waste cannot be used to generate energy on land
and must be burned in an approved facility. Alternative methods
for treatment are incorporated in Implementing Regulation (EC)
No. 142/2011. It also includes a separate biogas process with
upstream pressure sterilisation and hydrolysis, which is, however,
seen in a negative light from an energy efficiency perspective.
Those responsible for disposing of waste with a special waste
classification charge high rates. For this reason, shipping companies
prefer to dispose of food leftovers in the ocean. According to
MARPOL ANNEX V (International Convention on the Prevention of
Pollution by Garbage from Ships), this is still allowed.
Flushing wastewater into the Baltic Sea will be sharply limited in
the future. At the beginning of the year, the Marine Environment
Protection Committee of the International Maritime Organisation
(IMO) approved new resolutions for flushing ship wastewater.
To reduce the nutrient input into the Baltic Sea, for the first
time the new Performance Tests for Sewage Treatment Plants
[MEPC.227(64)] include binding limit values for effluent containing
phosphorous and/or nitrates.
Most of the on-board wastewater treatment facilities are reaching
their limits in terms of complying with these values. As an future
alternative, passenger ships can also dispose of their wastewater
at special reception facilities in harbours. However, due to uncertainty
with regard to the actual amounts of wastewater, many
harbours have not yet established the respective facilities. For
this reason, shipping companies have great interest in alternative
treatment options on board and disposal options on land.
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