25-01-2014
Review of BioChain Study Tour
Agenda:
 Fredericia Spildevand A/S, Jan 23
 Foulum research center ,Jan 23
 Maarbjerg Biogas ,Jan 24
Participants:
WP leaders, MSc student, PhD students & Post docs involved in WP1, WP2, WP3, WP4
1. Fredericia Spildevand A/S
Fredericia is one of the biggest sewage wastewater treatment plants in Denmark. The
plant receives wastewater from local municipalities and industrial organic waste from
diary
processing
industries,
breweries,
food
industries
and
oil
refineries.
Approximately, there are around 131 pumping stations to deliver the sewage waste
water in to the treatment plant site. Besides this, four big industries mostly cheese and
diary industries such as Arla supply organic industrial waste.
Fredericia plant consists of two process operation line, anaerobic digestion and
Chemical process. The waste water will be pretreated via grit removal and screening in
order to remove non degradable materials that will affect the anaerobic digestion
process and also carry outs the separation of oil phase from the waste water. The
separated oil will be sent directly to the anaerobic digestion reactor while the
remaining sludge will be charged to biological treatment process. De-nitrification takes
place in Anoxic tank to remove nitrates from the wastewater and produce aerobic
biomass via facultative bacteria. The aerobic biomass will be charged to settling tank
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and then to Bio-Phosphorus tank to remove phosphorus. Once the phosphorous
removal is completed, the sludge will be sent to diffuse bubble aeration to remove
inorganic components and also for the purpose of de-nitrification. Before retrofitting
thermal hydrolysis process technology in to the wastewater treatment plant, only the
primary sludge from Anoxic (de-nitrification) tank has been used for anaerobic
digestion to produce biogas while the sludge from the secondary treatment is
dewatered without digestion. However, all of the sludge is currently treated through
thermal hydrolysis and feed to the anaerobic digester to recover energy, biogas. The
dewatered digestate will be sold to farmers depending on the nutrient and moisture
content of the biosolids. Integrating thermal hydrolysis has improved the solid
destruction at mesophilic anaerobic digesters which in turn led lower biosolids volume
that incur low cost. The water used in the cambi process is recovered via sand filter,
carbon filter, ultrafiltration & reverse osmosis and then recycled to be used in the
steam plant as well as in-line dilution or process water.
The design capacity of the central Fredericia wastewater treatment plant is 420,000 PE
but the average load in 2013 was 286,000 PE. The anaerobic digesters were 2 in
number with a capacity of 2000 m3. The operational temperature condition is 40 oC
while the hydraulic retention time (HRT) is 35 days. The rate of input material flow to
the anaerobic digester is 5 m3 / hr. The biogas digester runs mostly with input substrate
from diary processing waste, breweries and oil refineries. The treated sewage sludge
will be charged to the anaerobic reactors. The sizes of the anaerobic digesters were
2000 m3. The total amount of biogas produced was around 1.7 million per annum out
of which 700,000 m3 (close to 50 %) will be utilized in the cambi process(140 oC and 5
bar) while the remaining 1 million m3 of biogas will be sold to DONG energy to produce
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electricity and district heating. The biogas will be upgraded by removing CO2 with water
scrubbing and stripping process technology. Economic wise, at the moment the
Fredericia treatment plant is worth of 2.3 billion DKK if sold. One of the most
impressive experiences in Fredericia treatment plant is the application of smart grid
system in order to save energy. The other innovative R & D going on at Fredericia is the
co-digestion of algae in the anaerobic digester to remove sulfur, phosphorus and
nitrogen while using the recovered CO2 for cultivation of algae in on-site wastewater
reservoir. The bio solids from the sewage treatment and digester will be sold to
farmers to apply as a fertilizer in agricultural land. The amount of dewatered sludge is
6900 tons per year, 25 % total solid content. The production of biogas can be increased
quickly during peak times probably due to the secret special bacteria consortium.
Although this might not be applicable in full scale large biogas plants but works quite
well at Fredericia plant.
2. Foulum research center
The Foulum research center is part of Aarhus University. The major research and study
going on in Foulum is regarding greenhouse gas emission from manure and biogas
production. The main inputs of the biogas production processes were animal manure,
straw, maize and grass silage.
The operational condition of the digester is 52 oC (thermophilic) while the hydraulic
retention time is 14 days. The size of anaerobic digester is around 1100 m3.
Pretreatment of straw and deep litter will be carried out using hammer and extruder
respectively to enhance anaerobic degradability and co-digestion of animal manure
with straw.
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One of the very fascinating and impressive ideas in Foulum research center is the
Innovative research on ‘’power to gas’’ that explores a way to store energy from
renewable sources such as excess wind and solar energy in the form of natural gas,
methane. The storage of energy in the natural gas network will provide stability to the
grid and also electricity during peak hours. The aim of the research is to demonstrate
electrochae’s biocatalytic methanation technology at pilot scale. The pure culture
microbes produce high quality methane by using H2 and CO2. The biogas produced via
anaerobic digestion is used as a source of CO2. The test is carried out in bioreactor that
has a size of 10 m3. The output of this research particularly the quality of methane is
lower than the expected pipeline natural gas. Hopefully, further improvements might
enhance the quality set by gas network companies. The research outcome at Foulum
research center shows the application of more diluted digestate on agricultural land as
a fertilizer has low N2O emission.
3. Maarbjerg Biogas
Maarbjerg biogas plant facility has had a very long and interesting history throughout
inception phase, design, implementation, research and development. The biogas
facility become of the one of largest biogas plant built in history across the globe from
what was started as a collections and treatment plant of manure to remove
phosphorus and nitrogen. However, this achievement is not the result of walk in the
park rather a long hard fought and committed outcome of the project group in
Maarbjerg against various challenges such as convincing the society who are living in
the neighborhoods and also the big fellows making policies and regulations in local
municipalities. The perception and visualization of biogas plants as a source of bad
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smell and also facility that collects and treats terrible wastes in the country has been a
huge obstacle at the beginning to build the biogas plant. Nevertheless, the problem
was solved with the nearby society living across the biogas plant through open
discussion and by having industrial tour to local sewage waste treatment plants that
belongs to them as well as explaining the benefit of biogas plants to the society.
The various kinds of feedstock biomass used in Maarbjerg biogas plants include animal
manure, organic industrial waste, energy crop such as maize silage and sewage sludge.
Accordingly, the biogas production process has two production lines based on the
feedstock: green line and sludge line. The green line annually receives 550,000 tons of
manure, 2,000 tons of crop, 120,000 tons of biological industrial waste mostly from
diary industries while the sewage sludge line treats 120,000 tons of sewage sludge with
3.5% solids per year from sewage sludge treatment plants. The total sum of feedstock
biomass used as an input to the plant is 629,000 ton annually. Transportation of
biomass to the plant facility is done by sealed trucks to avoid smell with special design
feature similar to that of dairy industry and also via pumping from manure collection
points. Meanwhile, pumping manure to the plant is expensive and has been
problematic particularly due to viscosity of the manure. The experience shows that
pumping pig manure (9% DM) is much easier than cow manure (8 % DM). The plan of
pumping feedstock is to reduce traffic and avoid odor in the local road. The trucks have
a capacity of 32 m3 while the storage tank capacity is 50 m3. Online monitoring system
controls manure collection time and trucks.
The anaerobic digesters operate at 37 oC (mesophilic conditions) with a hydraulic
retention time (HRT) of 23 days to convert the biomass feedstock in to biogas. The sizes
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of anaerobic digesters were 8000 m3.The Maarbjerg biogas plant produces 18 million
m3 of biogas per annum. The produced biogas will be sent to the combined heat and
Power Company (CHP) which in turn converts the biogas in to heat and electricity. Part
of the biogas will be converted at in-situ engine to electricity for internal plant use. The
annual reduction of CO2 emission is 50,000 tons. The digestate discharged from the
anaerobic reactors will be treated to remove nitrogen and phosphorus via
centrifugation to meet the standard regulation for agricultural land application as a
fertilizer in order to minimize greenhouse gases (GHG) emissions. However, 10% of the
digestate will be recycled to recover the remaining biogas.
Maarbjerg biogas plant has 10 full time workers but the plant is controlled with around
4000 sensors to make sure the plant is functioning normal operation. The total
investment cost is around 400 million DKK.
The latest research and development expansion project that is going on at the moment
is Maarbjerg energy concept. The mind boggling investment cost is around 3 billion
DKK to make it happen. This fascinating and innovative biorefinery concept is a cluster
of second generation bioethanol, Maarbjerg Biogas and CHP plant. Once the Maarbjerg
energy concept becomes reality, the biogas production will be 100 million m3 annually
which is five times higher than the current biogas production capacity. The concept
behind the biorefinery idea is to use straw as a feedstock for bioethanol production
through innovative technology developed by Inbicon and then recover the vinasse to
produce biogas and increase the temperature of anaerobic reactors to enhance the
production capacity. The lignin and non-degradable parts will be recovered from the
bioethanol and biogas plant will be used as a fuel input to the CHP plant. The energy
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produced from the biorefinery will be utilized as transport fuel (34%), power and
heating (53%), CNG from biogas (13 %) and bio fertilizer.
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