Difference between revisions of "Anaerobic Digestion"

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== Introduction ==
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'''This system is also called:''' AD, Digestion,
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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
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=Importance=
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<!--Relay any broader impact-->
  
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== Principles of Operation ==
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=Principles of Operation=
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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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<!-- Only briefly state anything that the StemNode Diagrams can cover within subsystems.  This section is often omitted for specific systems (manuals on a specific make, model, or serial number) -->
  
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=== Alkalinity ===
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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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(Needs work)
 
  
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== Versions on Market ==
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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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[[File:Home_Biogas.jpg|right]]
 
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[https://homebiogas.com/ Home Biogas 2.0]is a market ready version marketed for use in digested food waste to produce biogas.
 
  
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== Regulations ==
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==Modes of Operation==
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(Needs work)
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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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== Operating Requirements ==
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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.
  
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=== Site Requirements ===
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==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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=== Temperature ===
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{| class="wikitable sortable"
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Three different temperature ranges are ideal for anaerobic digestion, (but successful operation can be achieved outside these ranges); phsycrophilic (insert temp), 30-38°C (85-100°F) for Mesophilic Digestion, 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.
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|-
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! rowspan="2" |Condition
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! colspan="3" |Optimum
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! rowspan="2" |Operating Range
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! rowspan="2" |Unit
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! rowspan="2" |Notes
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|-
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!Psycrophilic !! Mesophilic !! Thermophilic
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|-
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| Temperature
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| style="text-align:right;" | 15
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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
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| °C
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| NA
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|-
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| pH
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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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|}
  
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== Troubleshooting Common Failures ==
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==Ratios of Inputs to Outputs==
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<!--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. Alternate units can be placed in parentheses -->
  
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=== Lack of Methane Production ===
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==Mathematic Models==
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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. Methanogen 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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<!-- Alternatively "Mathematical Models". Link to code sets, MatLab models ect. hosted on external websites.  Use [http://www.example.com link title], and replace "link title" with the desired text to appear -->
  
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=== Non-flammable Gas ===
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=Maintenance and Repair=
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Non-flammable gas could be due to too much moisture in the gas or not enough methane in the gas. In order to ignite, biogas must be at least X% methane.  This is common for some time during digester startup.  It may indicate too much oxygen is being introduced which drives a higher portion of CO2 in the final gas.
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==Maintenance Schedule==
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<!--This section is for expected maintenance. Repairs of unexpected problems should go under the "Typical Failures and Known Solutions" section. Cost data should be omitted since it will change over time-->
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Times are based on Mesophilic Digestion
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{| class="wikitable sortable"
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|-
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! Frequency
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! Action
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! Who Performs?
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! Time to Complete
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|-
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| Residence Time of 28 days
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| Remove Liquid
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| Operator
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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 Solutions==
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<!--Historical significance of a failure is better suited for Wikipedia or other sites.  You are encouraged to link out to these sites from this section -->
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{| class="wikitable sortable"
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|-
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! Problem
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! Symptom (s)
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! Fundamental Cause
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! Solution
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|-
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| low gas production
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| low pH
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| Neutral volatile fatty acids or lactic acid penetrate the cell walls of methanogens and inactivate the organisms
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| Reduce inputs, especially carbohydrates, until symptoms relieve, or dilute with water, or add buffers like CaCO3
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|-
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| low gas production
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| high ammonia
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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>
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| Reduce inputs until symptoms relieve, dilute with water, or add buffers like CaCO3
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|-
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| non-flammable gas
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| high moisture in gas
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| Moisture is evaporated during burning and can reduce the temperature below the level that a flame can be sustained.
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| Add a cooling trap where moisture can condense in the gas line
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|-
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| non-flammable gas
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| high CO2 in gas
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| Biogas must be above ?% methane for combustion. Inadvertent introduction of oxygen can increase CO2 production.
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| Add a cooling trap where moisture can condense in the gas line
 +
|}
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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.
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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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=Instances of the System=
 +
<!--This only applies to generalized systems (those that do not have a make, model, or serial number).  Delete section for specific systems -->
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'''Household Scale Anaerobic Digesters'''
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{| class="wikitable sortable"
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|-
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! Make
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! Model
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! Start of Production
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! End of Production
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! Number Produced
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|-
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| [https://homebiogas.com/ Home Biogas]
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| 2.0
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| October 2018
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| In Production
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| -
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|}
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=System Variations=
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<!--Discuss Variations on the System.  Typically these are not Manufacturer Sanctioned and therefor they apply only to specific systems (manuals on a specific make or model) -->
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=Visual models=
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<!-- This section is often only useful for specific systems (manuals on a specific make and model). Link to CAD drawings, PDFs ect on external websites that host the files.  Use [http://www.example.com link title], and replace "link title" with the desired text to appear -->
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=Intellectual Property=
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<!-- List any relevant patents, copyrights, or trade secrets on the system -->
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=Regulations=
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<!-- Subsections should be organized in alphabetical order by country, then state, where the regulations apply -->

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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