Mechanical Biological Treatment Trends - Backhus

Germany
Mechanical
Biological
Treatment Trends
Fifty MBT facilities with combined capacity of
6 million tons receive approximately 25 percent
of the total MSW collected in Germany.
Karsten Runge and Christoph Hofmann
COMPOSTING mixed municipal
solid waste has a long tradition
in Germany. In 1953, the first
large-scale facilities in Baden-
Baden and Blaubeuren started
operating, followed later by
plants in Heidelberg, Duisburg
and other locations across the
western part of Germany. Facilities
were being opened to provide
alternatives to landfilling
MSW, and to produce compost
for agricultural use. The quality
of the compost made from MSW was
very poor, however, and the product
was never accepted for use in agriculture,
despite a significant amount of research
and optimization of the waste
treatment process.
Composting of source separated organic
waste from households has not
had as long a history in Germany. The
first pilot test in Witzenhausen started
in 1983; two years later, a total of 100,000
tons/year of source separated organics
(SSO) were collected in all of Germany.
The “brown bin,” dedicated to collec-
tion of SSO from households, started being
rolled out across Germany in the
early 1990s. Today, nearly half of all
German households use the brown bin
system for source separation of organics,
capturing about 35 to 50 percent of
all waste generated in these households,
or about 9 million tons of SSO annually.
There are about 800 composting facili-
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ties in Germany, with a total input capacity
of nearly 10 million tons of organic
waste per year. A little more than
half (422) of those facilities take part in
the quality assurance system of the German
Composting Association, producing
5 million tons of high quality compost
annually.
Although the separate collection system
for organic waste is well developed
in Germany, a larger portion of organics
still remains in the mixed solid waste,
collected in the grey bin. This is attributed
to only about half of German households
participating in SSO programs
and sorting behavior in apartment
buildings; local management of waste
collection systems; and households not
taking the extra steps to empty packaged
food that is out of date, or separating
food from containers that are not
completely empty. This organic waste
ends up in the grey bin.
TASi Rule Lays MBT Groundwork
In 1993, the German Bundesrat adopted
the Technical Instructions for MSW
The largest MBT plant in Germany, situated in Cröbern, started out composting in larger
piles in the final treatment area, but could not get a continuously stable material. It switched
to turned windrows with smaller volumes (above left), and is able to meet the TASi
requirements. The Rosenow MBT plant (above right) had a similar experience, and is now
meeting the output limits.
(TASi), which requires pretreatment of
all waste containing biodegradables prior
to landfilling. (The European Union’s
Landfill Directive that phased in limits
for landfilling unprocessed organic waste
was adopted six years later, in 1999.) Few
incinerators were available to accept this
waste, as costs were high in comparison
to landfilling. With the TASi rule becom-
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ing effective in 2005 — prohibiting landfilling
of mixed waste collected in the
grey bin without pretreatment —most
waste management companies started
looking for alternatives.
When TASi was adopted in 1993, mechanical
biological treatment (MBT) was
not recognized as meeting its requirements.
But two new federal regulations
later, MBT became an accepted alternative
to incineration in 2001. An MBT system
combines a sorting facility (like a
materials recovery facility) with a form
of biological treatment such as composting
or anaerobic digestion to degrade the
organic fraction. Between 2001 and 2005,
a large number of MBT facilities and incineration
plants started operating, just
in time to meet the TASi deadline in June
2005. Today 50 MBT facilities with combined
capacity of 6 million tons receive
approximately 25 percent of the total
MSW collected in Germany. The MBT facilities
feature different biological technologies,
e.g., two-step aerobic treatment
or a combination of anaerobic
treatment followed by aerobic treatment.
Reprinted From:
October, 2008
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The TASi limits have to be met before
the end product can be put into landfill.
Typically, the end product of an MBT facility
is not called compost, even if a
composting process and composting
technologies are used at the MBT facilities.
The output product is ultimately
landfilled.
The MBT plants faced a lot of technical
problems right from the start, with low
throughput capacity caused by machine
overload or breakdown and higher operational
costs than expected due to high
demand for maintenance and service.
There also were challenges getting rid of
the high caloric fraction produced during
mechanical separation. Many problems
were solved, and nearly all of the facilities
are running at their expected
capacities. One weak point at some MBT
facilities is the final biological treatment
process, which is often designed like a
composting process.
“We started our facility with a system
of big heaps in the final treatment area,”
explains Roland Greif, operations manager
of the largest MBT plant in Ger-
many, situated in Cröbern near Leipzig.
“Fighting with the brand new machinery
we learned a lot about the biological
process but still could not get a constant
and stable material in our output. We
realized that even over a short period,
the composition of the waste could
change completely.”
Facility operators decided to put the
processed material into windrows with
smaller volumes that can be treated separately.
The plant purchased a BACK-
HUS 6.68 turner. “Changing from heap to
windrow, we can reach our targets
faster,” adds Greif. “We can operate the
turner according to the requirements of
each single windrow.”
Christoph Hofmann, operations manager
of the biological treatment process
at the Rosenow MBT plant in Mecklenburg,
Germany, had a similar experience.
“It is hard to continuously meet the
TASi limits for oxygen consumption (5
mg O2 /g DS), especially for dissolved
organic carbon in eluate (DOCEluat =
300 mg/l),” he says. “We have a total of
nine weeks of biological treatment to
achieve these limits. Our first treatment
step is tunnel composting with fully automatic
filling and emptying as well as
under floor aeration, followed by our
second treatment step — five to six
weeks of composting in heaps.”
During those last five weeks, the facility
was seeing an increase of the DOC.
“We presumed the reason for the increase
is an adaptation of mostly fungi
cultures that are capable of metabolizing
long-chain organic molecules to soluble
ones, while the further metabolism to
produce CO 2 and water runs more slowly,”
explains Hofmann. “In contrast to
the intensive composting process with
active aeration, the post composting process
resulted in instability of the end
product. We were running out of processing
capacity because we were not
reaching the limits in time. We also were
experiencing high wear costs and constant
downtime of our two turning machines.”
The plant decided to switch
from heaps to windrows. Since switching
to windrows, the MBT plant has been
able to meet its output limits. �
Karsten Runge is Product Manager,
Plant Engineering for BACKHUS Eco-
Engineers GmbH and can be reached at
karsten.runge@backhus.de. Christoph
Hofmann is with ABG GmbH and can be
reached at christoph.hofmann@ovvd.de.
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