2007:04 Hantering av förpackat livsmedelsavfall - Avfall Sverige

DEWASTER ® - Sorting out the problems of mixed waste
Appendix 1: Overview of the history and the objectives of the DEWASTER ® - system
Background
Beginning in the mid-1980s a number of Danish municipalities engaged in projects for the utilisation of
the Organic Fraction of Municipal Solid Waste (OFMSW) based on source sorting, i.e. a separation of
the organic (“green”, bio-degradable) and non-organic (“black”, non-bio-degradable) parts of domestic
Municipal Solid Waste (MSW) at the individual households.
Source sorting was normally accomplished by a two tier system of “green” and “black” garbage bags
combined with particular collection schemes for certain types of waste, such as chemical waste,
batteries, electronic equipment and recyclables).
The aim of source sorting projects was to decrease the amount of (bio-degradable) waste for landfill or
incineration and to utilise the OFMSW for heat and power production and for fertiliser. The utilisation
of OFMSW was frequently accomplished by bringing the OFMSW to bio-gas plants for anaerobic codigestion
with sewage sludge, animal slurry and/or industrial residues, thereby recovering a part of the
energy potential of OFMSW in bio gas production. The waste remaining after co-digestion was utilised
as fertiliser by spreading on farm land or by composting .
The use of remaining organic matter as fertiliser entails stringent requirement that the input material
for bio gas production, including OFMSW, is free of plastic, paper, metals and other items which are
undesirable on farmland and adhere to threshold limits for heavy metals and various other pollutants.
In Denmark, experience with the use of OFMSW in bio-gas production showed that the sorting quality
from ordinary citizens was frequently insufficient, i.e. non-organic matter and organic matter with slow
bio-degradability was put in the “green bags” through mistake or neglect and that , furthermore, the
plastic and paper bags used for garbage collection themselves frequently left large amounts of plastic/paper
which presented a problem both for bio-gas production as such and for the use of remaining
organic matter as fertiliser.
Aalborg 1999 – the first tests
The idea for the DEWASTER system originates from a project at the bio gas plant at Vaarst-Fjellerad
(VFB) in Jutland, Denmark.
VFB is a facility based primarily on the processing of animal slurry. However, in 1998 VFB agreed with
the municipality of Aalborg and number of surrounding municipalities in Jutland that trials should be
carried out with co-digestion of other types of waste, including OFMSW.
When operations started in 1998 it was soon discovered that the contents plastics in the OFMSW (in
particular plastics from collection bags) was a serious, unanticipated obstacle to practical operations.
In response to these problems the idea that plastics and other soft foreign matter could be separated
from the organic part through a pressing process was devised. The idea was favourably received by
advisors to the VFB project, and within a short period of time the first DEWASTER® screw press “prototype”
was produced.
The unit was operated by VFB/Aalborg municipality personnel on both OFMSW and CFW during trials
at VFB in 1999 and 2000. Although the DEWASTER® screw press was at that time still a very untested
product and the project management for the trials did not allow to make significant alterations to
the unit, the results of the trials were considered very promising.
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