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R. MolettaResearch director INRA

Polytech’Savoie, Savoy university

Le Bourget du Lac, France

Smallwat 07

11-15 of November 2007

Anaerobic biofilm reactors

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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.

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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

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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

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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

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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 %)

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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.

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•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

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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

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Completelymixte reactor

Output

Biogas

Input

Anaerobiccontact

Biogas

I

Digesters for wastewater treatment

•No biofilm, but floc formation

• Used when there is suspended solids

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Sludge bed Baffled digestor

I

Biogas

I

O

Sludges

Biogas

Digesters for wastewater treatment

Technologies with Floc and granule formations

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I

B

anaerobic lagune

O

Digesters for wastewater treatment

Floc and granule formations

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UASB Upflow Anaerobic Sludge

Blanket

O

OBiogas

I

Granules

Digesters for wastewater treatment

(With biofilm)

Example of design

Granule formation

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Anaerobic granules : 1 to 4 mm

Layers of microorganisms

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Surface of granule from UASB

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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

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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

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Anaerobic filter with oriented support

Cloisonyl®

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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

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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

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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

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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

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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)

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Thank you for your attention