Anaerobic Digestion, Biogas and the Circular Economy

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


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


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


Facilitator

Anaerobic Digestion

Digital Detail

Project MOST: Model based process automation of biogas plants


Facilitator

Anaerobic Digestion

Fundamentals

Symbiotic dependence of acetogens and

methanogens

Methanogenic growth velocity vs temperature

van Lier et al. 1997


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?


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


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 %


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


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)


Facilitator

Biogas Production

Reactor Design – CSTR Mixing (< 10 % TS)

• Rotors • Gas loop

Krieg & Fischer (2001)


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


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)


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


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


Facilitator

Digestate

Biogas

Anaerobic Digestion

…and the Circular Economy

Facilitator

Thank you! Danke!

[email protected]

September 24th, Sacramento, CA

Anaerobic Digestion, Biogas and the Circular Economy

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