Anaerobic digestion

1
Anaerobic digestion

• An overview of digestion technologies Dairy
  farm effluent treatment
• Maarten van de Graaf
• Environmentek, CSIR Pretoria

2
Index

• Dairy farm wastes
• Manure components
• Available technology
• Why anaerobic digestion?
• Anaerobic digestion basics
• Operating temperature choice
• Design approach
• Reactor choice
• Lab scale setup

3
Dairy farm wastes

• Manure
• High COD, ammonia phosphates
• Dairy effluent
• High in COD
• Water
• Emission regulations

4
Dairy manure

• Typical dairy manure composition
• Total solids 16.9
• Volatile solids 83.2 of TS
• Total COD 1237.5 mg/g dry matter
• Soluble COD 10 of total COD
• TKN 4.5 mg N/g dry matter
• Total P 3.4 mg P/g dry matter

5
Why anaerobic?

• Advantages
• Low energy input
• Biogas production net energy production
• Minimal sludge production
• Fertilizer quality sludge
• Pathogen destruction
• Odour reduction
• Disadvantages
• High investment
• Ammonia Phosphate production

6
Introduction

• Anaerobic digestion process

Hydrogen Carbondioxide
1
3
2
Bio-polymers
Mono/oligomers
VFA (Cgt2)
Methane Carbondioxide
1
1
2
1
Acetate
4
7
Introduction

• Temperature range
• Psychrophilic
• (10-25 oC) HRT gt40-60 days
• Mesophilic
• (35 oC), HRT 25-35 days
• Thermophilic
• (55 oC), HRT 15-25 days
• pH range 7 - 8

8
Introduction

• Feedstocks
• Organic material like
• Dilute and concentrated wastewaters
• Municipal waste
• Waste activated sludge
• Manure
• Slaughterhouse waste

9
Operating temperature

• Low temperature for dilute wastes
• phsychrophilic mesophilic
• High temperature for high-solid wastes
• thermophilic

10
Manure treatment

• Manure scraping
• Manure flushing

11
Digester choice

• 2 different approaches
• Digestion of both solid and liquid manure
• (co-digestion).
• Digestion of manure liquids only.

12
Digester choice

• Combined solids liquids treatment
• Completely mixed digester
• Contact digester
• AGF
• ADUF
• Temperature phased digestion
• Unmixed digester
• Bag digester
• Tubular reactor

13
Digester choice

• Digestion of liquids only
• Upward Anaerobic Sludge Bed (UASB)
• Sequential Batch Reactor (SBR)
• Anaerobic baffled reactor (ABR)
• Covered lagoon digester

14
Digester choice

• Covered lagoon digester
• Robust
• Low construction cost
• Use of existing lagoons
• Odour reduction
• Very low organic loadings
• High residence time
• Low biogas production

• Source The society for engineering in
  agricultural, food and biological systems,
  California Polytechnic State University,
  BioResource and Agricultural Department, San
  Luis, CA. Paper no 01-6154.

15
Labscale setup

• 5 Litre working volume
• Inoculated with lagoon sludge
• Operating temperature 55 0C
• 1 month inoculation period

16
Labscale setup

• Organic loading rate 1 g COD/litre/day
• 10 day HRT
• pH rising to 8.2
• Organic loading rate 15-20 g COD/litre/day
• 3-4 day HRT
• Required data pH, gas production, effluent COD

17
Aknowledgements

• CSIR Pretoria

18
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19
Contact digester
20
Anoxic gas flotation
21
Plug Flow Reactor
22
Temperature phased AD
23
Anaerobic Baffled Reactor
24
Covered lagoon digester