Difference between revisions of "Anaerobic Digestion"

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'''This system is also called:''' AD, Digestion,
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=Importance=
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=Principles of Operation=
 
=Principles of Operation=
 
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Anaerobic digestion is the conversion of organic matter to biogas which is flammable if the methane content of the biogas is high enough.  Digestion. Bacteria and Archea that perform the individual stages of anaerobic digestion are naturally present in the feces and organic matter that enter the digester or can be introduced from an already functioning digester.  The conditions within the digester can select for which organisms will perform best.
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Anaerobic digestion is the conversion of organic matter to biogas which is flammable if the methane content of the biogas is high enough.  Bacteria and Archea that perform the individual stages of anaerobic digestion are naturally present in the feces and organic matter that enter the digester or can be introduced from an already functioning digester.  The conditions within the digester can determine which organisms proliferate.
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The subprocesses of anaerobic digestion are degredation, hydrolysis, acidogenesis, acetogenesis, and methanogenesis.  Of these, hydrolysis is often the rate limiting step followed by methanogenesis. Typically all subprocesses are carried out concurrently in a single vessel, however large scale facilities are increasingly splitting up the processes in order to provide conditions optimal for each sub-process. For example it is advantageous to split up the acid forming phases (called acid-phase digestion) from the methanogenesis phase because it allows for an overall reduction in reactor volume needed although it increases complexity (See [[#Modes of Operation|Modes of Operation]]). 
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==Modes of Operation==
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Three different temperature ranges are ideal for anaerobic digestion.  Each temperature range selects for a different set of organisms that carry out the process. These temperatures represent local optimums, however biogas can be successfully produced outside these ranges and the rates of organic matter degredation and biogas production generally increase with increasing temperature.
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'''Psycrophilic digestion''' 15°C (59°F) <br />
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'''Mesophilic Digestion''' 30-38°C (85-100°F) <br />
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'''Thermophilic digestion''' 50 to 57°C (122-135°F) <br />
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Psyochrophilic and mesophilic digestion are commonly used at the building scale level, while mesophilic and thermophilic is typically operated at large scale facilities.
  
 
==Operating Requirements and Conditions==
 
==Operating Requirements and Conditions==
 
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<!-- Only briefly state anything that the StemNode Diagrams can cover as inputs. Use metric base units (Kg, L, m, A, cd, mol) where practical, with the exception of temperature which should be in Celsius instead of Kelvin. Chemical and biochemical processes should be in molar ratios.-->
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{| class="wikitable sortable"
 
{| class="wikitable sortable"
 
|-
 
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! Condition
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! rowspan="2" |Condition
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! Optimum(s)
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! colspan="3" |Optimum
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! Range
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! rowspan="2" |Operating Range
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! Unit
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! rowspan="2" |Unit
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! Notes
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!Psycrophilic !! Mesophilic !! Thermophilic
 
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| Temperature*
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| Temperature
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| 15, 30-38, 50-57
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| style="text-align:right;" | 15
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| 15-57
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| style="text-align:right;" | 30-38
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| style="text-align:right;" | 50-57
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| style="text-align:right;" | 15-57
 
| °C
 
| °C
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| See [[#Modes of Operation|Modes of Operation]]
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| NA
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|-
 
| pH
 
| pH
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| 7
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| colspan="3" style="text-align:center;" | 7  
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| ??
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| -
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| -
 
| -
 
| -
 
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==Mathematic Models==
 
==Mathematic Models==
 
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==Modes of Operation==
 
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Three different temperature ranges are ideal for anaerobic digestion, (but successful operation can be achieved outside these ranges); 15°C for phsycrophilic , 30-38°C (85-100°F) for Mesophilic Digestion, and 50 to 57°C (122-135°F) for thermophilic digestion. Of these psyochrophilic and mesophilic digestion is more commonly used at the building scale level, while thermophilic is typically only operated at large scale facilities. The rates of  organic matter and biogas production increase with increasing temperature
 
  
 
=Maintenance and Repair=
 
=Maintenance and Repair=
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==Maintenance Schedule==
 
==Maintenance Schedule==
 
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Times are based on Mesophilic Digestion
  
 
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! Time to Complete
 
! Time to Complete
 
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| state the frequency
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| Residence Time of 28 days
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| state the action
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| Remove Liquid
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| User, Professional, Manufacturer, Anyone
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| Operator
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| Number and unit of time
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| N/A
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|-
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| Residence Time of 28 days
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| Remove Solids
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| Operator
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| N/A
 
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|}
  
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==Failures and Known Solutions==
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==Failures and Solutions==
 
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| low gas production
 
| low gas production
 
| high ammonia
 
| high ammonia
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| Ammonia can penetrate the cell walls of methanogens and inactivate the organisms
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| Ammonia can penetrate the cell walls of methanogens and inactivate the organisms<ref>{{Cite journal|last=Chen|first=Ye|last2=Cheng|first2=Jay J.|last3=Creamer|first3=Kurt S.|date=2008-07-01|title=Inhibition of anaerobic digestion process: A review|url=https://www.sciencedirect.com/science/article/pii/S0960852407001563|journal=Bioresource Technology|language=en|volume=99|issue=10|pages=4044–4064|doi=10.1016/j.biortech.2007.01.057|issn=0960-8524}}</ref>
 
| Reduce inputs until symptoms relieve, dilute with water, or add buffers like CaCO3
 
| Reduce inputs until symptoms relieve, dilute with water, or add buffers like CaCO3
 
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Methanogens are typically the most sensitive organisms in the process but are the most crucial because they perform the final step of converting acids to methane.  Methanogens can be sensitive to high amounts of acid or high amounts ammonia.  A low pH indicates high amounts of acid which can occur by putting too much organic matter in the digester.  This is especially the case with carbohydrates (e.g. from food waste) which break down quickly to acids causing acid build up.  A high pH could The quickest indicator of conditions that are hostile to methanogens is pH, which should be near 7.  
 
Methanogens are typically the most sensitive organisms in the process but are the most crucial because they perform the final step of converting acids to methane.  Methanogens can be sensitive to high amounts of acid or high amounts ammonia.  A low pH indicates high amounts of acid which can occur by putting too much organic matter in the digester.  This is especially the case with carbohydrates (e.g. from food waste) which break down quickly to acids causing acid build up.  A high pH could The quickest indicator of conditions that are hostile to methanogens is pH, which should be near 7.  
  
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Non-flammable gas could be due to too much moisture in the gas or not enough methane in the gas. This is common during digester startup.
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Non-flammable gas could be due to too much moisture in the gas or not enough methane in the gas. This is common during digester startup.
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==Warranty==
 
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=Instances of the System=
 
=Instances of the System=
 
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'''Household Scale Anaerobic Digesters'''
 
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| Home Biogas
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| [https://homebiogas.com/ Home Biogas]
 
| 2.0
 
| 2.0
 
| October 2018
 
| October 2018
 
| In Production
 
| In Production
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| ?
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| -
 
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=System Modifications=
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=System Variations=
 
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Latest revision as of 04:24, 28 February 2019

Authors:

This system is also called: AD, Digestion,

Importance

Principles of Operation

Anaerobic digestion is the conversion of organic matter to biogas which is flammable if the methane content of the biogas is high enough. Bacteria and Archea that perform the individual stages of anaerobic digestion are naturally present in the feces and organic matter that enter the digester or can be introduced from an already functioning digester. The conditions within the digester can determine which organisms proliferate.

The subprocesses of anaerobic digestion are degredation, hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Of these, hydrolysis is often the rate limiting step followed by methanogenesis. Typically all subprocesses are carried out concurrently in a single vessel, however large scale facilities are increasingly splitting up the processes in order to provide conditions optimal for each sub-process. For example it is advantageous to split up the acid forming phases (called acid-phase digestion) from the methanogenesis phase because it allows for an overall reduction in reactor volume needed although it increases complexity (See Modes of Operation).

Modes of Operation

Three different temperature ranges are ideal for anaerobic digestion. Each temperature range selects for a different set of organisms that carry out the process. These temperatures represent local optimums, however biogas can be successfully produced outside these ranges and the rates of organic matter degredation and biogas production generally increase with increasing temperature.

Psycrophilic digestion 15°C (59°F)
Mesophilic Digestion 30-38°C (85-100°F)
Thermophilic digestion 50 to 57°C (122-135°F)

Psyochrophilic and mesophilic digestion are commonly used at the building scale level, while mesophilic and thermophilic is typically operated at large scale facilities.

Operating Requirements and Conditions

Condition Optimum Operating Range Unit Notes
Psycrophilic Mesophilic Thermophilic
Temperature 15 30-38 50-57 15-57 °C NA
pH 7 - - -

Ratios of Inputs to Outputs

Mathematic Models

Maintenance and Repair

Maintenance Schedule

Times are based on Mesophilic Digestion

Frequency Action Who Performs? Time to Complete
Residence Time of 28 days Remove Liquid Operator N/A
Residence Time of 28 days Remove Solids Operator N/A

Failures and Solutions

Problem Symptom (s) Fundamental Cause Solution
low gas production low pH Neutral volatile fatty acids or lactic acid penetrate the cell walls of methanogens and inactivate the organisms Reduce inputs, especially carbohydrates, until symptoms relieve, or dilute with water, or add buffers like CaCO3
low gas production high ammonia Ammonia can penetrate the cell walls of methanogens and inactivate the organisms[1] Reduce inputs until symptoms relieve, dilute with water, or add buffers like CaCO3
non-flammable gas high moisture in gas Moisture is evaporated during burning and can reduce the temperature below the level that a flame can be sustained. Add a cooling trap where moisture can condense in the gas line
non-flammable gas high CO2 in gas Biogas must be above ?% methane for combustion. Inadvertent introduction of oxygen can increase CO2 production. Add a cooling trap where moisture can condense in the gas line

Methanogens are typically the most sensitive organisms in the process but are the most crucial because they perform the final step of converting acids to methane. Methanogens can be sensitive to high amounts of acid or high amounts ammonia. A low pH indicates high amounts of acid which can occur by putting too much organic matter in the digester. This is especially the case with carbohydrates (e.g. from food waste) which break down quickly to acids causing acid build up. A high pH could The quickest indicator of conditions that are hostile to methanogens is pH, which should be near 7.

Non-flammable gas could be due to too much moisture in the gas or not enough methane in the gas. This is common during digester startup.

Instances of the System

Household Scale Anaerobic Digesters

Make Model Start of Production End of Production Number Produced
Home Biogas 2.0 October 2018 In Production -

System Variations

Visual models

Intellectual Property

Regulations

  1. ↑ Chen, Ye; Cheng, Jay J.; Creamer, Kurt S. (2008-07-01). "Inhibition of anaerobic digestion process: A review". Bioresource Technology. 99 (10): 4044–4064. doi:10.1016/j.biortech.2007.01.057. ISSN 0960-8524. 
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