Troy Runge Biological Systems Engineering UWMadison Anaerobic Digestion A biological process that breaks down organic materials feedstocks in the absence of oxygen anaerobic conditions ID: 914323
Download Presentation The PPT/PDF document "Biogas: Anaerobic digestion overview" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Biogas:Anaerobic digestion overview
Troy RungeBiological Systems EngineeringUW-Madison
Slide2Anaerobic DigestionA biological process that breaks down organic materials (feedstocks) in the absence of oxygen (anaerobic conditions) producing methane (CH4) and carbon dioxide (CO2) mixture, referred to as (biogas
), in addition to the residual sludge (digestate).Naturally-occurring process:Lakes and swampsWaterlogged soils Cattle rumensOrganic matter + Microorganisms Biogas + Digestate
Slide3O2AD process
1. Photosynthesis: 6 CO2 + 6 H2O + E solar C6H12O6 + 6 O2 E solar = 2.804 MJ/kmol
2. Anaerobic
digestion:C
6
H
12
O
6
3 CH
4
+ 3 CO
2
+ E metabolismE metabolism = 0.134 MJ/kmol
3. Biogas oxidation (combustion):3 CH4 + 6 O2 3 CO2 + 6 H2O + E oxidationE oxidation = 2.670 MJ/kmol
Maximum theoretical efficiency [η ] = 2.670/2.804 = 95.2%
CO
2
H
2
O
Glucose
(C
6
H
12
O
6
)
CH
4
O
2
Sludge
Slide4AD process
VOLATILE
FATTY
ACIDS (VFA)
(
Short
-
chain volatile
organic acids
)
COMPLEX POLYMERS
(
Proteins
,
Polysaccharides
,
etc
.)
CH
4
,
CO
2
MONOMERS AND OLIGOMERS
(
Sugars
,
amino acids
,
peptides
)
H
2
+
CO
2
ACETATE
Fermentative
bacteria
Fermentative
bacateria
Fermentative
bacteria
Fermentative
bacteria
Acetogens
(
H2 producing
Acetogens
CO
2
reducing
methanogens
Acetoclastic
methanogens
Phase 1
Hydrolysis
Phase 2
Acidogenesis
Phase 3
Acetogenesis
Phase 4
Methanogenesis
(H
2
consum
ing)
Slide5AD feedstockTypical AD feedstock:Wastewater treatment sludgeLivestock manureFood processing waste Lignocellulosic biomass
Only biodegradable volatile solids, (b)VS, are accessible to AD bacteria.Although water does not directly contribute to AD reactions, it facilitates mobility and contact between bacteria and organic solids.
(b)VS
A
s
h
Water
T
S
MC
Proximate analysis
(n)VS
Slide6AD ProductsBiogas
Yield0.70 – 1.2 m3 /kg VS @STPvaries with feedstock, operation conditionsComposition55-70% methane (CH4)30-45% carbon dioxide (CO2)Traces of other gases (NH3, H2S)Energy content15.0 – 22.0 MJ/m3 (LHV)Fuel equivalent0.4 – 0.6 m3 natural gas/ m3 biogas
Ignition temperature650 – 750°CNormal density
1.1 –1.2 kg/m3Molar mass
22 – 28 kg/
kmol
Slide7AD ProductsBiogas yields from various feedstock:
Source: Weiland, Appl Microbiol Biotechnol (2010) 84: 849-860
Slide8AD ProductsBiogas uses:Electricity generation (genset)CHP generatorsCompression/liquefactionFeeding into natural gas linesFueling vehiclesEach of these uses involves a degree of biogas conditioning (upgrading/cleaning) to:
Adjust the gas mixture ratios (CH4 enrichment)Eliminate contaminants, i.e., H2S, NH3, and H2OMTU’s 4000 Series engine (~1.2 MWe)
Slide9Digestate uses
Soil applicationThe digestate is low in pathogens, and contains plant-accessible nutrientsDrying and pelletization could facilitate transportation Not all digestate is equal (Class A biosolids, agricultural wastes)BeddingDisinfected residual fibersSignificant revenue sourceCompostComposite boards
AD Products
Slide10AD reactor configurationsCovered lagoonsLow construction costEasy operationLarge footprintDifficult to cleanBiogas production is seasonal
Slide11AD reactor configurationsComplete mix tank reactorFlexible to different feedstockConstruction and operation costsCritical operation (mixing)
Complete mix digester Green Valley Dairy (Krakow, WI)
Slide12AD reactor configurationsPlug flow reactorSuitable for agricultural residuesRelatively low cost of construction and operationRequires high solids loading
GHD plug flow digester
Slide13AD reactor configurations
Solid-state digestionLow moisture content: 55 – 70% MCThe first solid state anaerobic digestion facility, BIOFerm™ Energy Systems, based on University of Wisconsin-OshkoshDry-batch digestion has several advantages:High volumetric biogas ratesEasily loaded and removed from digestion Multiple cells (garages) are operated in schedule to ensure consistent biogas yieldsDigester operation is easier to maintain and troubleshoot when operating multiple cells
Slide14What Can and Can’t ADs Do?CanMake biogas (CH4+CO2) for fuel or feedstockReduce some pathogensReduce odor
Generate an income streamCan’tEliminate phosphate and nitrate from manureGreatly reduce manure volumesAD is only one of many manure processing options
Slide15Agricultural Digestion Systems
Slide16Manure Processing OperationsOperationsPressesCentrifugesScreens
Clarifiers/Settling PondsDissolved air flotationMembrane separationCompostingPelletingGranulation
Benefits
Concentrate nutrientsRecycle water/beddingWater discharge
Export/sell manure
Slide17Questions