Viseu, October 2007
HAASE THECHNOLOPGY FOR ANAEROBIC/AEROBIC TREATMENT
OF RMSW IN THE SLURRY PHASE
R. Sieksmeyer
Keywords: mechanical-biological pre-treatment, MBT, waste, anaerobic, aerobic, operation experience
Haase Energietechnik AG has concentrated its long-term knowledge on key
compounds of MBT plants to create a new innovative technology for treatment of
most kinds of waste the so-called 'wet anaerobic digestion' process (wet-AD) in 2004
and developed it to series-production readiness. The mechanical-biological pretreatment of residual waste by using the principle of fermentation with subsequent
aeration step was undertaken for the first time at full-scale in Lübeck with a target
annual residual waste capacity of 125,000 Mg. In consideration of the development
stage of MBT plants in general and the innovation of wet-AD in particular in the early
2000ers further measures to optimise process control are being explored. This
abstract shows a selection of results from the full-scale process. The schematic for
the biological treatment of residual waste as done in Lübeck and possible other ways
are presented in Figure 1. After the mechanical processing of the residual waste and
the separation of the high calorific value fraction (approx. 50% of the input material)
and the heavy fraction (stones, metals, glass etc.), the predominantly organic waste
(approx. 40% of the input) is mixed into a suspension using a screen filter with a
mesh diameter of d<40mm and d<25mm (from March 2007). In the succeeding grit
chamber, the separation of the light and heavy fractions takes place by flotation and
sinking. Here, any remaining interfering materials, e.g. stones, glass, ceramics, as
well as plastics and woody materials, are separated before the biological treatment
stage. The suspension is then led to the digestion stage which consists of a
hydrolyser (V=4000 m³) and digesters (2x V=4800 m³). In this step, the easily
degradable carbon compounds are converted to biogas at a temperature of approx.
T=37°C and a residence time of approx. 21 days. To further stabilise the residual
waste, the suspension (DS= ~ 4% (w)) is fed to the dual-lane aerobic treatment step.
The aerobic treatment stages are operated as forced flow-through reactors, each
separated into 5 chambers. Each individual chamber is mixed by a stirrer and
pressure-aerated. The exhaust air from each chamber is captured and led to the
exhaust air treatment plant. After an approx. 12 day aeration period, a separation of
the suspension takes place to achieve a mixed solid with a DS content of ~ 40% (w).
The process water is returned to the mixer for mashing the residual waste
suspension. The mixed solids are concentrated to a solids content of approx. 70%
(w) using a dryer. This residue is then mixed with the previously-separated light and
heavy materials from the grit chamber, and landfilled.
Based on initial experiences, further research was necessary to optimise the
operation of the MBP-Lübeck. The aerobic treatment process step is currently
operated using a dry solids content of 4% (w). Since the intention is to increase the
DS content in the aeration step, laboratory experiments made by University of
Technology Hamburg-Harburg using different DS contents could give an initial insight
into optimised field operations. In addition, preliminary field results show that in the
aerobic step, temperatures of approx. 40 to 45°C ca n develop. During summer
operation, higher temperatures are to be found so that a technical cooling is needed.
Viseu, October 2007
In order to be able to assess the possible consequences on the carbon and nitrogen
degradation, laboratory investigations should be undertaken at different temperatures
to optimise the degradation process.
Figure 1. Schematic of the biological pre-treatment in the MBP–Lübeck.
The field results showed that approx. 95% of the biological degradation (BOD5)
already takes place during fermentation (see Figure 2). In the subsequent aeration
stage, an additional 3%, based on the hydrolyser input, are converted. In the aeration
stage, biochemical conversion processes for nitrogen reduction take place. The
ammonium concentration decreased from 600mg NH4-N/l in the output of the
digester to 30mg NH4-N/l in the output of the aerobic stage. In parallel, a nitrification
of 340mg N/l took place. In addition, nitrogen as ammonia was stripped out, and N2
was possibly released via denitrification in the first aeration chamber.
Figure 2. Reduction in the COD content and the BOD5/COD ratio during the
biological treatment in the MBT-Lübeck.
Viseu, October 2007
Comparative investigations on BOD5 degradation in the aeration chambers of the
MBT and in the laboratory test system showed that almost identical results can be
achieved. The BOD5 content decreased from approx. 1000mg O2/l in the start phase
to approx. 200mg O2/l after the end of aeration. Approximately 90% of the BOD5
conversion took place in the first two of the 5 aeration chambers.
The found reduction of BOD as well as COD is one of the main factors that Haase
MBT plants observe the limits of the German landfill ordinance. Further investigations
have shown that at Haase MBT plants the RTO, necessary for all other MBT
technologies, can be replaced by bio filter systems. The waste air composition of the
collected air derived from all areas/halls is of a kind and concentration that even bio
filter systems are able to reduce the emissions below the German limit of
50 mg(THC)/m³ for chemical plants and even below the German limit of
20 mg(THC)/m³ for MBT plants. Also the odour emissions can be reduced by bio
filters below 500 OU/m³. But more significant and as a characteristic difference to
other MBT technologies the odour impressions of waste in the surroundings of the
Haase MBT plants (with closed doors) are mostly undetectable.
MBT Output to Landfill
140,00
120,00
TOC in mg/l
(max: 300)
NH4 in mg/l
(max: 200)
100,00
values
GB 21 in L/kgTM
(max: 20)
80,00
60,00
40,00
20,00
22.08.2007
08.08.2007
25.07.2007
11.07.2007
27.06.2007
13.06.2007
30.05.2007
16.05.2007
02.05.2007
18.04.2007
04.04.2007
21.03.2007
07.03.2007
21.02.2007
07.02.2007
24.01.2007
10.01.2007
27.12.2006
13.12.2006
0,00
Date of sampling
Figure 3. long-term monitoring of waste output at MBT-Lübeck.
The above mentioned results are directly considered in our new projects in England,
Malta and will help to optimise ecological and economical aspects of the Haase wetAD technology.