1
R. MolettaResearch director INRA
Polytech’Savoie, Savoy university
Le Bourget du Lac, France
Smallwat 07
11-15 of November 2007
Anaerobic biofilm reactors
2
What is the anaerobic digestion?
• Anaerobic transformation of organic matter into biogas, of methane and carbon dioxide, by a consortium of anaerobic micro-organisms
• Applied to treat municipal, industrial and agronomical solid or liquid wastes, in order to :
• decrease the volume of waste,
• to remove the pollution,
• to produce energy and fertilizer.
3
Methanisation in natural ecosystems:– Lakes– Rumen– Marshes– Human intestines– Storage of organic matter– Landfills
MICRO-ORGANISMSLiquid Phase Gas Phase
Organic matter CH4 + CO2
MICRO-ORGANISMSLiquid Phase Gas Phase
Organic matter CH4 + CO2
The anaerobic digestion
4
Metabolic way of the Anaerobic digestion
Complex polymers
ACETOGENESIS
HYDROLYSISand
ACIDOGENESIS
METHANOGENESIS
Monomers
Acetogenic B.
Volatils fatty acids(VFA), alcohols, ...
Acetate CO2 + H2
CH4 + CO2 CH4+H2O
Homoacetogenic B.
Acetoclastic M. B. Hydrogenophilic
M. B.
Fermentative acidogenic B.
Figure 1 : Metabolic pathway of anaerobic digestion
5
Power equivalences of one cubic meter of methane
1 M3
of METHANE
9,7 kWh of electricity
1,5 l of petrol
1,3 kg of charcoal
1 l of fuel oil
2,1 kg of wood
0,94 m3 of natural gas
1,7 l of methylated
6
Advantages of the anaerobic digestion
•This biological reaction is usual in natural environment
•There is no need of energy (no oxygen transfer)
•Production of energy (biogas)
•Works with high load (from 1 to 40 kg of COD/m3/d)
•Low rate of sludge production
•Works with effluents with a low grade of N and P compared to the COD
•High COD removal yield (up to 80 % to 98 %)
7
Characteristics of methanisation
Mixed culture of anaerobic micro-organisms.pH 6 to 9.Redox potential under -300 mV.Temperature :– Psychrophilic (5° C to 20° C).– Mesophilic (25° C to 45° C).– Thermophilic (45° C to 70° C).High growth rate of acidogenic bacteria.Low growth rate of methanogenic, acetogenic and synthrophic
bacteria. So we need technologies able to keep microorganismsin the digester.
8
•Because the grow rate of micro-organisms is slow in anaerobiosis, we have to keep them into the digester in order to separate the residence time of liquid (waste water) and the residence time of solid (microorganism)
•Two way :
•Settler with recirculation
•Biofilm formation
• on support (packing media)
• without support
The anaerobic technology for waste water treatment use biofilm
9
Floc and Biofilm formation
• Floc formation : free cell are connected together
• Biofilm formation
• in granule
• on support
- Fixed in the digester
- Mobile in the digester
10
Completelymixte reactor
Output
Biogas
Input
Anaerobiccontact
Biogas
I
Digesters for wastewater treatment
•No biofilm, but floc formation
• Used when there is suspended solids
11
Sludge bed Baffled digestor
I
Biogas
I
O
Sludges
Biogas
Digesters for wastewater treatment
Technologies with Floc and granule formations
12
I
B
anaerobic lagune
O
Digesters for wastewater treatment
Floc and granule formations
13
UASB Upflow Anaerobic Sludge
Blanket
O
OBiogas
I
Granules
Digesters for wastewater treatment
(With biofilm)
Example of design
Granule formation
14
Anaerobic granules : 1 to 4 mm
Layers of microorganisms
15
Surface of granule from UASB
16
Up flow fluidised bed
B
O
I
Up flow fluidised bed
B
O
I
Digesters for wastewater treatment(with biofilm)
Support are generally particles (volcanic stones)with high specific area (up to 3000 m2/m3 in the digester)
Example : Perlite from Degremont
17
Down flow anaerobic filter
O
B
I
RFixed support
Digesters for wastewater treatment
(with biofilm)
Upflow anaerobic filter
B
I
R
Fixed support
Upflow anaerobic filter
B
I
R
Fixed support
Supports are oriented or loosed with specific surface area of 100 to 500 m2/m3
18
Anaerobic filter with oriented support
Cloisonyl®
19
Biogas
wastewater heater
output
pHprobe
Anaerobic filter with Cloisonyl® as support
Cloisonyl The support
•Cloisonyl is an orientedsupport : 6m tubes with 14 channel inside
•Already used for trickling filters (aerobic)
• Specific surface : 180 m2/m3
202 m3 anaerobic filter with « Cloisonyl », and support with biofilm
21
Example of loose supports foranaerobic filter
10 mm30 mm
Bioflow 30 - density : 0,9 or 1,1
Specific area close to 320 m2m-3 Flocor
22
10 mm
Bioflow 9 with density 0,85Specific area is about 528 m2 m-3
(before biofilm formation)
10 mm10 mm
BIOFLOW 9
Bioflow 9 with light biofilm
23
O
I
B
Mixte (sludge bed and filter)
Sludge bed
Anaerobic filter
IC reactor (Internal Circulation)
(3)
(4)
(2)(2)
(1)
B
O
Input Granules
Digesters for wastewater treatment
with biofilm
24
Organics loads for anaerobic digesters
Anaerobic lagune 0.1 to 2 kg COD/m3/dAnaerobic contact 1 to 5.5 kg COD/m3/dAnaerobic filter 5 to 15 kg COD/m3/d UASB 5 to 20 kg COD/m3/dFluidized bed 15 to 30 kg COD/m3/dIC reactor 15 to 30 kg COD/m3/d
With biofilm technologies, the biomass concentration in the digester can reach 50 to 60 g/l of microorganisms (Dry weight)
25
Thank you for your attention
Top Related