Transcript GENERACION DE BIOGAS A PARTIR DE RESIDUOS

ANAEROBIC DIGESTION
BASIC CONCEPTS
JOAN MATA-ALVAREZ
EPROBIO COURSE
3rd Edition 2012
Dpt. Chemical Engineering
UNIVERSITY of BARCELONA
UNIVERSITAT DE BARCELONA
WAGENINGEN SUMMER SCHOOL AD BIOPROCESS CONCEPTS
ANAEROBIC DIGESTION PROCESS
ANAEROBIC DIGESTION IS A PROCESS WHICH, IN THE
ABSENCE OF OXYGEN, DECOMPOSES ORGANIC
MATTER.
MAIN PRODUCT IS BIOGAS – A MIXTURE OF
APPROXIMATELY 65% METHANE AND 35% CARBON
DIOXIDE –, ALONG WITH A REDUCED AMOUNT OF A
BACTERIAL BIOMASS.
ORGANIC MATTER
BIOGAS + MAT. CEL.
ANAEROBIC DIGESTION PROCESS
APPLICATIONS:
TREATMENT OF
EFLUENTS WITH
ORGANIC MATTER
ALTERNATIVE (OR COMPLEMENTARY) PROCESS
TO THE AEROBIC WITH THE ADVANTAGE OF:
- POSITIVE ENERGY BALANCE
- LESS BIOMASS GENERATION
WAGENINGEN SUMMER SCHOOL
AD BIOPROCESS CONCEPTS
BIOMETHANIZATION
APPLICATIONS
LIQUIDS
SOLIDS
SEMI-SOLIDS
INDUSTRIAL
Food industry,
Paper industry
Food industry
Food markets
URBAN
Domestic wastewaters
Sewage-Sludge
Organic fraction MSW
PROCESS LIMITATIONS
- IN SOME CASES ANAEROBIC DIGESTION WILL BE
JUST A PRE-TREATMENT
- IT CAN BE FOLLOWED BY AN AEROBIC
TREATMENT (FOR INSTANCE, AMMONIUM-N
REMAINS)
- LOW BIOMASS YIELD MAKES START-UP PERIOD
QUITE LONG
WAGENINGEN SUMMER SCHOOL
AD BIOPROCESS CONCEPTS
BIOGAS COMPOSITION
- BIOGAS IS MAINLY FORMED BY CH4 AND CO2
- COMPOSITION DEPENDS ON SUBSTRATE.
USUALLY OSCILLATES BETWEEN 60-65% IN
CH4
- THERE ARE STOICHIOMETRIC RELATIONS THAT
ALLOW TO ESTIMATE BIOGAS COMPOSTION
BIOGAS COMPOSITION
IF
THE ORGANIC
COMPOUND
HAS THE
GREASE
YIELDS HIGH
PERCENTAGES
FORMULA
OF CH4 AND THE CONTRARY HAPPENS
CxHFORMIC
WITH OXALIC OR
ACID.
yOzNt
RATIO CH4/CO2 CAN APPROXIMATELY
BE GIVEN BY:
(4-T)/(4+T)
T= (2z + 3t -y)/x
DIGESTER COD BALANCE
BIOGAS COD
90
INLET COD
100
OUTLET COD
5
DIGESTOR
BIOMASS
COD
5
DIGESTER COD BALANCE
BIOGAS COD
45
INLET COD
100
OUTLET COD
50
DIGESTOR
BIOMASS
COD
5
TWO-STEP REPRESENTATION
ORGANIC MATTER
Fermentation
VOLATILE FATTY
ACIDS
Methanization
BIOGAS
STOICHIOMETRY OF A.D. OF SEWAGE SLUDGE
Carbohydrates
Proteins
21%
40%
H
5%
Aminoacids
Suggars
Ac
20%
46%
Intermediary products
Propionates,butirates,...
M
0%
12%
Acetate
34%
Fatty acids
66%
At 35%
Lipids
39%
23%
34%
11%
8%
11%
70%
Hydrogen
30%
Gujer and Zehnder, 1983
Methane
Process
Organic
polymers
Organic
monomers
Reduced
organics
-
NO3
=
SO4
Hydrolysis of
organic polymers
Fermentation of
organic
monomers
Oxidation of
reduced organics
Acetogenic
respiration of
bicarbonate
Oxidation of
reduced organics
by SRB and NRB
Oxidation of
acetate by SRB
and NRB
Oxidation of
Hydrogen by SRB
and NRB
Aceticlastic
methanogenesis
Hydrogenotrophic
methanogenesis
NH4
H 2S
+
Acetic
acid
Carbon
dioxide
H2
CH4
Microorganisms
Fermentative
bacteria
Obligate hydrogen
producing bacteria
(OHPA)
Homoacetogen
bacteria
Sulfate-reducing
(SRB),
nitrate-reducing
(NRB) bacteria
SRB and NRB
SRB and NRB
Aceticlastic
methanogenic
bacteria
Hydrogenotrophic
methanogenic
bacteria
Organic polymers : Carbohydrates, Lipides, Proteins
Organic monomers : Sugars, organic acids, aminoacids
Reduced organics : Volatile fatty acids (propionic, butiric, valeric)
Pohland, 1992
ENVIRONMENTAL FACTORS
•NUTRIENTS
•TOXIC SUBSTANCES
•TEMPERATURE
•OTHER (Alkalinity, pH)
NUTRIENTS
LOW REQUIREMENTS
•
COD / N / P = 600 / 7 / 1
•
Other micronutrients
(Fe, Ni, Mg, Ca, Na, Ba, Tu, Mo, Se,
Co, vitamins)
TOXIC SUBSTANCES
•
AT LOW CONCENTRATIONS: BENEFIC
EFFECTS, AT HIGH CONCENTRATIONS:
INHIBITERS OR EVEN TOXIC
•
THERE IS A POSSIBILITY OF
ACCLIMATION. SOME DISCREPANCY IN
LITERATURE VALUES (SYNERGIC AND
ANTAGONIC EFFECTS
TOXIC SUBSTANCES
Common substances (specially
undissociated species)
•VFA
•pH
•SH2
•NH3
Xenobiotic compounds
TEMPERATURA
Operation ranges
•
PSICROPHILIC (< 25ºC)
•
MESOPHILIC (around 35ºC)
•
THERMOPHILIC (around 55ºC)
Thermophilic
Mesophilic
Rate of the AD process
Psichrophilic
0
10
20
30
35
40
Temperature
50
55
60
70
80
OTHER PHSYSICO-CHEMICAL
FACTORS
•
pH: Depends on the bacterial group: 6 7,5
•
ALCALINITY: Is a funtcion of pH and
dissolved CO2. Values over 1.5 g/L at pH
6, are recommended
IMPORTANT PARAMETERS
IN AD PROCESSES
S (substrate concentration) kg substrate/m3 reactor
generally expressed in terms of: TS, TVS,
COD
X, (microorganisms concentration)
kg active biomass/m3 reactor, generally
expressed in terms of TVS or in VSS (volatile
suspended solids) although it can be also
referred as COD
IMPORTANT PARAMETERS
IN AD PROCESSES
HRT (Hydraulic retention time)
It is defined as the ratio of the reactor volume
to the of the influent substrate flowrate. Thus,
it is a measure of the time that the substrate
spends inside the digester:
V
HRT =
Q
IMPORTANT PARAMETERS
IN AD PROCESSES
SRT (Solids retention time).
It is a measure of the sludge age and usually
expressed in days.
VX
X
SRT 
 HRT
Q. X e
Xe
IMPORTANT PARAMETERS
IN AD PROCESSES
OLR (Organic loading rate)
It is expressed as kg substrate/m3reactor day, is
the amount of substrate introduced into the
digester volume in a given time:
QS
S
OLR 

V
HRT
SOLR 
S
HRT  X
IMPORTANT PARAMETERS
IN AD PROCESSES
SOLR (Specific organic loading rate). It expresses
the OLR per unit of active biomass,
It Scan explain why attached biomass systems
HRT  X
support
OLR much higher than suspended growth
ones.
SOLR 
S
SOLR 
HRT  X
YIELD PARAMETERS
IN AD PROCESSES
• Specific gas production (SGP),
[m3biogas/kgsubstrate fed]
• Gas production rate (GPR),
[m3biogas /m3reactorday]
• Substrate removal yield, [%].
YIELD PARAMETERS
IN AD PROCESSES
SGP (Specific gas production)
It is the biogas produced per unit of substrate fed or
in some cases per unit of substrate converted into
biogas.
Qbiogas is the biogas flowrate, (m3/day). It can be set
in terms of the total volatile solids in the feed, as m3
biogas/kg VS fed.
SGP 
Qbiogas
QS
YIELD PARAMETERS
IN AD PROCESSES
GPR (Gas production rate). It is the biogas produced
per unit of reactor volume and time:
GPR 
Qbiogas
V
GPR and SGP are related through the OLR
GPR  SGP  OLR
BIODEGRADABILITY AND
DEGREE OF BIODEGRADATION
Volatile solids (VS) can be converted to a maximum
amount of biogas, provided optimal conditions are
prevalent. This conversion can be measured through
what has been called ‘ultimate biogas yield’ (B0).
B0
Initial VS
Final non biodegradable VS
(After an “infinite time”)
BIODEGRADABILITY AND
DEGREE OF BIODEGRADATION
In a CSTR:
SGP
(At a given HRT)
Inlet VS
Outlet VS (with a fraction of
non biodegradable VS)
SGP
fB 
Bo
BIODEGRADABILITY AND
DEGREE OF BIODEGRADATION
Assuming a First Order kinetic model:
SGP
dS
dt
Inlet VS
 k ·S
Outlet VS (with a fraction of
non biodegradable VS)
SGP = B0 / (1 +1/(k·HRT))
SGP (m3 biogas/kg VS)
B0 = 300 m3 biogas/kg VS
310
k=3
290
k=1
270
k=0.5
250
230
k=0.3
210
k=0.1
190
0
10
20
HRT (days)
30
40
DIGESTER TYPES
•
FLOW-THROUGH DIGESTER (CSTR)
(Both soluble and solid wastes)
•
DIGESTERS WITH BIOMASS
RETENTION
(Soluble wastes/Two-phase systems)
•
PLUG-FLOW DIGESTERS
(Differents approaches. Solid wastes)
CONTINUOUS STIRRED TANK REACTOR
Different
heating
systems
Different
stirring
devices
•Void volume
equipped with
heating and stirring
systems
•Cheap and very
extended
CONTINUOUS STIRRED TANK REACTOR
•For slurried wastes
ex.: piggery, SS,
OFMSW
* SRT = HRT
* HRT 10-30 d
CONTINUOUS STIRRED TANK REACTOR
•Possible
occurrence of shortcircuiting
•It can impair the
proper hygienization
of the wastes
Digesters with large active
biomass concentration
•
Digesters based on keeping
suspended biomass inside the
reactor
–
–
•
Contact Digester
UASB
Attached growth systems
–
–
Anaerobic Filter
Expanded/Fluidised Bed
CONTACT DIGESTER
• High biomass
concentrations (up
to 25,000 g/L
•Problems with
settleability
Degasifier
UASB DIGESTER
BIOGAS
OUTLET
INLET
* First in 1976 in a
sugar factory located
in Breda, in a pilot
plant of 6 m3 (Prof.
Lettinga and col.).
* It is based on the
development of a
highly settleable flocs
called granules
* Diameter up to 5
mm. High density ->
in the bottom of the
reactor.
UASB DIGESTER
BIOGAS
OUTLET
INLET
* Settling velocities of
60 m/h
* Superficial upflow
velocities below 2 m/h.
* SRT over 200 days
HRT of 6 hours
* Biomass concentration
up to 30g/L-> High OLR
UASB DIGESTER
BIOGAS
OUTLET
INLET
* Low loss of solids,
* No mechanical mixing
is necessary (biogas
generation enough to
ensure mixing)
* Good inlet distribution
necessary
* New developments
ANAEROBIC FILTER
(Immobilised biomass)
BIOGAS
OUTLET
INLET
* For liquid wastes
* Up or Downflow
* HRT << SRT
* High OLR (20
kg/m3.d
* HRT between 0.5
and 4 days
EXPANDED / FLUIDISED BED
BIOGAS
* For liquid wastes
OUTLET
* High recirculation
ratio
* HRT<<SRT
INLET
* HRT between 0.5
and 4 days
EXPANDED / FLUIDISED BED
BIOGAS
OUTLET
INLET
Sand and,
especially, granular
activated carbon
(GAC) are the most
popular.
Usually, particle
sizes are between
0.2 and 1 mm.
EXPANDED / FLUIDISED BED
BIOGAS
OUTLET
INLET
Free movement of
the particles, which
prevents the
digester to clog
Drawbacks:
Complexity of the
system design
Cost of the energy
required
OPTIMISES
BIOLOGICAL
REACTIONS
COMBINATION OF
TWO DIGESTERS
TWO-PHASE
DIGESTERS
LARGER OVERALL
REACTION
RATE
NOT
ALWAYS
AND
IN PRACTICE
BIOGAS YIELD
INCREASED
TECHNICAL
COMPLEXITY
OPTIMISES
BIOLOGICAL
REACTIONS
The main advantage of
two-stage systems is not
its putative higher
reaction
rate, but rather
TWO-PHASE
a greater
biological
DIGESTERS
reliability for wastes
which cause unstable
performance
in one-phase
LARGER OVERALL
RATE
systems REACTION
AND
BIOGAS YIELD
Pre-treated waste OFMSW
PASTEURIZATION
Biogas
STAGE 1
(hydrolysis)
Solid
Liquid
recycle
Waste and
DEWATE-
process
RING
water
Liquid
STAGE 2 (
COMPOSTING
of the solid fraction
Anaerobic Filter
methanization
)
Capital Cost of Manure Management
Technology
Source: AgStar Publication:
US EPA
Digester economics
• Investment: it has been estimated
around $660 to $1,200 per head.
• Good estimate $1,000 per cow
• At this capital assumption AD system
become economical based on sold
energy alone at power sale price of
$0.09/kWh.
(Mehta, 2002)
Plug Flow Digesters
• Little mixing
• Few mechanical parts
• Simple
Mixed Digesters
Mechanical mixing in tank
More gas production
Slightly higher capital cost
DIGESTERS FOR SOLID WASTE
They are also three-phase reactors.
An heterogeneous approach is needed to
adequately model the system
Substrate solubilization, difussion to the
cells (several microorganisms involved),
gas difussion…: It is a complex model.
REQUIREMENTS
Good mass transfer
(contact microorganisms-substrate)
Good heat transfer
(specially in thermophilic systems)
Good yields
(depends very much in substrate)
Absence of mechanical problems
(experience with different types of
substrates)
TECHNOLOGIES FOR AD OF SOLID
WASTES
Classical classification
Dry (TS contents > 15%) Dranco, Valorga,
Linde BRV, Kompogas…
Wet (TS contents < 15%) Linde KCA,
Waasa, RosRoca-Envital,…)
DIAGRAM OF A WET AD PLANT
TRANSPORT
URBAN
COLLECTION
Bag of
organics
Heat
Engine
BIOGAS
CONDITIONING
Electricity
BIOMETHANIZATION
REACTOR
LIQUIDS
Filtration
SOLIDS
COMPOST
WASTEWATER
(Nutrient flow)
TECHNOLOGY DIFFERENCES
(Many elements in a plant)
Continuos vs. Batch
Conditioning
Pretreatment
Stirring system
Recirculation system
Heating system
Basically:
Wet: Perfect mixing
Dry: Plug-flow
DRY
DIGESTION
Linde
Valladolid
Valorga
Coruña
WET
DIGESTION
Ros-Roca Envital
Boden
Waasa
Groningen
DIGESTION CAN BE INSERTED
INTO EXISTING COMPOSTING SITES
Expansion of existing composting sites
• Many composting sites in Europe are 15 to 20 years
old: can afford or need renovation
• Some sites have more waste but sites have no room
for additional composting area
• Insertion of partial stream dry anaerobic digestion
can increase existing capacity by up to 50% with
minimal surface requirement
• Economically very attractive
• Water balance is crucial: no excess wastewater for
dry systems
Partial stream digestion (I)
• Only part of the organics is digested (up to
70%)
• Other 30% or more of organic fraction is
bypassed and is not subjected to digestion
• Digestate is directly mixed with bypassed
organic fraction without dewatering
• Non-digested organics provide exothermic
energy and needed structure for aerobic
posstreatment and drying
Full stream digestion
MSW OR YARD / FOOD WASTE
METALS
RDF
DRY
SORTING
BIOGAS
ANAEROBIC DIGESTION
PROCESS
WATER
WATER
CO2
DEWATERING
AEROBIC COMPOSTING
/ DRYING
COMPOST OR LANDFILL
Partial stream digestion (II)
MSW OR YARD / FOOD WASTE
METALS
RDF
DRY
SORTING
MIXER
CO2
WATER
AEROBIC
COMPOSTING
WATER
DRYING
COMPOST OR LANDFILL
UP TO 70 %
ANAEROBIC
DIGESTION
BIOGAS
State-of-the-art examples
• Mechanical-Biological Treatment (MBT) –
facility: Hille
• Partial stream digestion: Tenneville
• Plugflow digestion: Bamberg
MBT-facility Hille (1)
MBT-facility Hille (2)
• Hille, Germany
• DRANCO-plant: residual waste & dewatered
sludge
• Plant: 100.000t/y - digestion: 38.000 t/y
• Start-up: January 2005
• Fermenter volume: 2.500m³
• High dry matter content: 40% DM
• Biogas use:
– 1 gas engine of 469 Kwel
– production of steam
– regenerative thermal oxidation
DRANCO process
DRANCO process
safety equipment
feeding tubes
gas storage
conical outlet with extraction
feeding pump
dosing unit
Biowaste treatment plant Tenneville (I)
Biowaste treatment plant Tenneville (II)
Biowaste
& pasty waste streams
Biogas
FLARE
GAS STORAGE
SCHREDDER 1
DRANCO
DIGESTER
> 40
MAGNET
ROTATING SIEVE
(40 mm)
GAS ENGINE +
GENERATOR
STEAM
GENERATOR
3.150 m³
< 40
SCHREDDER 2
MAGNET
Residue
MIXING UNIT
DOSING UNIT
FEEDING
PUMP
Rejects
Structural material
Liquid waste
streams
Composting
Electricity
Biowaste treatment plant Tenneville (III)
• Capacity = 37.700 tpa biowaste + 1.300 tpy
liquid organic waste
• Digester volume = 3.150m³
• Start-up: 2009
• Energy production
– 9.750.000 kWh electricity per year
– 10.000.000 kWh heat per year
• Digestate mixed with fresh yard waste before
aerobic composting
Plugflow digester Bamberg (1)
Plugflow digester Bamberg (2)
• Codigestion: 12.000 t biowaste + 4.000t maize
per year
• Dry-matter content in digester: 24%
• 2 fermenters of each 900m³
• Plug-flow digestion
• Biogas use: 2 gas engines of 345 kW
• Heat use in neighbouring greenhouses
Plugflow digestion
•
•
•
•
•
Horizontal fermenter
Slow-turning paddle stirrers
Medium dry matter content: 10–15% DM
Robust and industrial system
For agro-industrial waste, energy crops,
crop residues, biowaste, food waste &
manure
• Horizontal concrete tank:
– Short time of construction
– Modular concept
Energy
balance
Mainstream
technology
FINAL
Nutrients
REMARKS
ON AD
Greenhouse
effect
TECHNOLOGY
Integration
Minimum
sludge
AD
has
its own
place
in biological
treatments
and
AD
is
aconveys
mainstream
technology
with
great
AD
minimises
the
production
of
waste
sludge
AD
AD
AD
presents
does
not
anutrients
positive
increase
to
energy
gases
the
liquid
with
balance,
greenhouse
stream
with
has to bespecially
integrated
in
the
overall
organic waste
potential,
the
solid
waste
the
which
effect
production
can
be an
ofin
advantage
biogas
treatmentfield
systems
treatment
Conclusions regarding AD-SW
• Strong growth:
2 (1990) < 58 (2000) < 195 (2010)
• > 5.900.000t installed in 2010 = about 5%
OFMSW in Europe
• ±20% of biological treatment capacity for
organics derived from household waste
Conclusions
• Factors hampering growth:
– Investment and operating cost
– Hygienization requirements to meet ABPR
– Negative references: the lower the
technology level, the more malfunctioning
plants
Conclusions
• Factors stimulating growth:
– Revamping existing biowaste composting
plants
– Extending treatment capacity of existing
biowaste composting plants => partial
stream digestion
– Treatment of food waste, agro-industrial
organic residues, harvest residues, is
strongly on the rise