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Facilitator
Anaerobic Digestion, Biogas and the Circular
Economy
Barbara E. Waelkens, M. Sc.
September 24th 2019, Sacramento, CA
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 2
Facilitator
Outline
• Anaerobic Digestion process in digital detail
• Technologies and Developments for Biogas Production
• Biogas from Manure on Dairy Farms
• Biogas from organic municipal solid waste (oMSW)
• Challenges and Opportunities – the circular economy approach
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 3
Facilitator
Anaerobic Digestion, Biogas and the Circular Economy
Substrate is fed to a reactor, processed
and produces biogas and digestate
Biogas is treated and processed to heat,
electricity or upgraded to biomethane
Digestate is dewatered, dried and incinerated, landfilled or used in
agriculture
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 4
Facilitator
Large Particles:
Slow Degradation Anaerobic Digestion
Fundamentals
(Particulate) organic matter
breaks down by action of
enzymes and micro-
organisms, under the
absence of oxygen, to:
Intermediate Products
Amino Acids, Monosacch.
LCFAs, VFAs, H2
Final Products
CO2, CH4, H2S and NH3
Biologic imbalance:
Acidification
Biologic selection:
Loss in CH4 potential
Biogas composition:
Reflex of bio-process Data: Rosenwinkel et al. 2015
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 5
Facilitator
Anaerobic Digestion
Digital Detail
Project MOST: Model based process automation of biogas plants
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 6
Facilitator
Anaerobic Digestion
Fundamentals
Symbiotic dependence of acetogens and
methanogens
Methanogenic growth velocity vs temperature
van Lier et al. 1997
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 7
Facilitator
Biogas Production
Anaerobic Digestion Process Design
Goals:
• Produce as much CH4 as
possible
• Degrade most (or all) organic
material
• CAPEX and OPEX as low as
possible
• Not contaminate the
environment?
• Produce no waste?
• Have predictable performance?
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 8
Facilitator
Biogas Production
Useful Benchmark Values: Control Substrate
• Initial control
• Biogas potential
estimate through
Buswell eq.
• Byproducts
Substrate Composition Biogas Potential
l/kgrem
Methane content
%v
Biogas Potential
l/kgrem
Carbohydrates CcHhOo 700-830 50-55 350-450
Proteins CcHhOoNnSs 700-900 70-75 490-680
Fatty Acids CcHhOo 1000-1400 68-73 680-1020
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 9
Facilitator
Biogas Production
Substrates of Interest
Substrate Organic Municipal Solid
Waste (example) Manure Energy Crops
TS/TVS 450 g/kg / 75% >50 g/kg / 75% >300 g/kg / 90%
Nutrients Variable, may present NH3
toxicity
Nutrient rich, may result in
NH3 toxicity
Variable, may require N and
micronutrient addition
Contaminants Particles, glass, plastic, metal,
sand, ash Sand, stones Large particles, seeds, stones
Biogas Potential [l/kgTVSin] 350-500 500-700 500-700
Methane content [%v] 55-68 50-62 50-62
Biodegradability TVS [%] 40-60 % 40-60 % 90 %
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 10
Facilitator
Biogas Production
Useful Benchmark Values: Reactor Design
Parameter Unit Value
Hydraulic Retention Time d > 20?
Organic Loading Rate kg/(m3*d)
[lb/(ft3*d)]
1.1 – 9.9
0.009 – 0.082
Volatile Solids Removal % 59-89%
Local Power Input W/m3
[W/ft3]
100
0.38
Energy Demand %total 10%
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80 100
Org
anic
Loadin
g R
ate
[kg/(
m3*d
)]
Hydraulic Retention Time [d]
WWTP 1 WWTP 2 Biomass Digester
20 g/l 40 g/l 200 g/l
400 g/l
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 11
Facilitator
Biogas Production
Reactor Design – Wet Digestion (< 10 % TS)
• Covered Lagoon
• Low CAPEX
• Limited Temperature control
• Limited mixing control
• High HRTs
• CSTR
• Higher CAPEX
• Temperature control
• Mixing control
• Lower HRT (smaller footprint)
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 12
Facilitator
Biogas Production
Reactor Design – CSTR Mixing (< 10 % TS)
• Rotors • Gas loop
Krieg & Fischer (2001)
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 13
Facilitator
Biogas Production
Reactor Design – Dry Digestion (> 20 % TS)
• 2 Stage Garage Fermenter
• no pre-treatment
• Work intensive feeding strategy
• Plug Flow Fermenter (requires pre-treatment)
• Requires pre-treatment
• Automated feeding strategy
FNR, 2010
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 14
Facilitator
Digestate Management
Challenges
• Digestate has historically been used as fertilizer
• Global supply chains significantly affect the balance
• 60 % of drinking water in Germany comes from
groundwater (UBA, 2013)
• Upper limit for NO3 in the groundwater is 50 mg/l
(98/83/EU)
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 15
Facilitator
Digestate Management
Current technologies
• Dewatering up to 35 % TS
• Drying up to 90 % TS
• Incineration
• Nutrient recovery from the
ashes
• Direct disposal in
agriculture
• Nutrient recovery +
precision agriculture
https://www.bioecosim.eu/index.html
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 16
Facilitator
• Understanding of nature‘s processes
• Measuring and controlling its limits
• To design functional systems
• Considering all mass streams
• And its consequences
…and the Circular Economy
2nd Germany California Bioenergy Symposium | Sept. 24th 2019 | Seite 17
Facilitator
Digestate
Biogas
Anaerobic Digestion
…and the Circular Economy