Abstract
Anaerobic degradation of organic matter is a multi-step process through the action of various groups of microorganisms whose optimum conditions can differ considerably regarding e.g. nutrients, pH demand, sensitivity for changes and patterns for growth and nutrient uptake. One way of optimizing the anaerobic digestion process, and thereby increase the biogas production and the reduction of organic matter, can be to physically divide the anaerobic digestion process in two steps consisting of an initial hydrolysis and acid production step followed by a methane production step in an anaerobic digester. One problem with the biogas processes of today is that not all organic matter that is added to the process becomes available for conversion into biogas. This is particularly evident in digestion of waste water treatment sludge where almost half of the organic matter added remains after anaerobic digestion. More efficient utilization of substrate in biogas plants is an important element to increase the profitability of biogas production. The possibility to use different pre-treatment methods is being discussed to increase the degree of conversion of organic matter into biogas in the digester. Pre-treatment methods are often energy as well as cost demanding and can require the addition of chemicals. To use
More>>
Citation Formats
None.
Digestion with initial biological hydrolysis step for enhanced methane production in sewage and biogas plants. Exploratory; Roetning med inledande biologiskt hydrolyssteg foer utoekad metanutvinning paa avloppsreningsverk och biogasanlaeggningar. Foerstudie.
Sweden: N. p.,
2010.
Web.
None.
Digestion with initial biological hydrolysis step for enhanced methane production in sewage and biogas plants. Exploratory; Roetning med inledande biologiskt hydrolyssteg foer utoekad metanutvinning paa avloppsreningsverk och biogasanlaeggningar. Foerstudie.
Sweden.
None.
2010.
"Digestion with initial biological hydrolysis step for enhanced methane production in sewage and biogas plants. Exploratory; Roetning med inledande biologiskt hydrolyssteg foer utoekad metanutvinning paa avloppsreningsverk och biogasanlaeggningar. Foerstudie."
Sweden.
@misc{etde_1011588,
title = {Digestion with initial biological hydrolysis step for enhanced methane production in sewage and biogas plants. Exploratory; Roetning med inledande biologiskt hydrolyssteg foer utoekad metanutvinning paa avloppsreningsverk och biogasanlaeggningar. Foerstudie}
author = {None}
abstractNote = {Anaerobic degradation of organic matter is a multi-step process through the action of various groups of microorganisms whose optimum conditions can differ considerably regarding e.g. nutrients, pH demand, sensitivity for changes and patterns for growth and nutrient uptake. One way of optimizing the anaerobic digestion process, and thereby increase the biogas production and the reduction of organic matter, can be to physically divide the anaerobic digestion process in two steps consisting of an initial hydrolysis and acid production step followed by a methane production step in an anaerobic digester. One problem with the biogas processes of today is that not all organic matter that is added to the process becomes available for conversion into biogas. This is particularly evident in digestion of waste water treatment sludge where almost half of the organic matter added remains after anaerobic digestion. More efficient utilization of substrate in biogas plants is an important element to increase the profitability of biogas production. The possibility to use different pre-treatment methods is being discussed to increase the degree of conversion of organic matter into biogas in the digester. Pre-treatment methods are often energy as well as cost demanding and can require the addition of chemicals. To use the microbiological steps in the biogas process more efficiently by adding an initial hydrolysis step is a method that does not require the usage of chemicals or increased energy consumption. This pre-study is based on literature studies related to anaerobic digestion with initial biological hydrolysis and collected knowledge from full-scale plants, universities and suppliers of equipment. Nearly 70 published scientific articles relevant to the subject have been found in the performed literature searches. The articles have been subdivided according to the purpose of each article. A large part of the articles have concerned modelling of anaerobic digestion why a separate section of the report has been devoted to this. The literature study shows that the majority of the experiments with an initial hydrolysis step that have been performed with substrates such as waste water treatment sludge, organic waste or dairy manure have given advantages in the form of for example higher methane yield, increased degree of degradation and/or increased treatment capacity. In addition other advantages have been achieved by the method, for example elimination of foaming in digester, more stable process and pathogen inactivation. It is difficult to draw any general conclusions about optimal pH for hydrolysis. Optimal pH most likely differs, mainly in relation to the composition and characteristics of the substrate. It seems that pH control, in most cases, is not necessary to achieve a satisfactorily process, which is important considering the costs for addition of acid or base in a full scale application. Concerning process temperature an increase up to 55 deg. C have in most studies resulted in a higher hydrolysis rate. Optimal retention time and organic load for optimization of the hydrolysis process depends on the composition and characteristics of the substrate. For each combination of process parameters there is an optimum that changes if any of the process conditions does change. For waste water treatment sludge generally 4-7 days retention time seems to be appropriate and for dairy manure 2-4 days have been used successfully in studied scientific papers. Simulation of hydrolysis can show a clear optimum for which retention time gives the highest hydrolysis rate. This can be used to design a multi-step process so that the hydrolysis rate, and thus the biogas production, can be optimized. Modelling experiments also show that multi-step digestion processes can be simulated with a good correspondence to data. Hydrogen gas can be produced in an initial hydrolysis step which gives the opportunity to produce bio-hythane but can also be a safety risk if the plant is not designed for this. No safety problems with hydrogen formation have however been observed at identified full scale plants. Anaerobic digestion with an initial biological hydrolysis step should be possible to implement at a digestion plant with relatively simple means by mainly the addition of one stirred and insulated tank. The importance and effect of an initial separate hydrolyse step is however dependent on the characteristics of the substrate and other process parameters of the plant such as organic load and actual retention time. The added value achieved by addition of an extra step in the digestion process has to be revised compared to the costs and the additional work required for process monitoring and maintenance. Six full scale plants in Sweden (3), Germany (1) and USA (2) that are in operation, or have done experiments, with separate biological hydrolysis step have been identified.}
place = {Sweden}
year = {2010}
month = {Mar}
}
title = {Digestion with initial biological hydrolysis step for enhanced methane production in sewage and biogas plants. Exploratory; Roetning med inledande biologiskt hydrolyssteg foer utoekad metanutvinning paa avloppsreningsverk och biogasanlaeggningar. Foerstudie}
author = {None}
abstractNote = {Anaerobic degradation of organic matter is a multi-step process through the action of various groups of microorganisms whose optimum conditions can differ considerably regarding e.g. nutrients, pH demand, sensitivity for changes and patterns for growth and nutrient uptake. One way of optimizing the anaerobic digestion process, and thereby increase the biogas production and the reduction of organic matter, can be to physically divide the anaerobic digestion process in two steps consisting of an initial hydrolysis and acid production step followed by a methane production step in an anaerobic digester. One problem with the biogas processes of today is that not all organic matter that is added to the process becomes available for conversion into biogas. This is particularly evident in digestion of waste water treatment sludge where almost half of the organic matter added remains after anaerobic digestion. More efficient utilization of substrate in biogas plants is an important element to increase the profitability of biogas production. The possibility to use different pre-treatment methods is being discussed to increase the degree of conversion of organic matter into biogas in the digester. Pre-treatment methods are often energy as well as cost demanding and can require the addition of chemicals. To use the microbiological steps in the biogas process more efficiently by adding an initial hydrolysis step is a method that does not require the usage of chemicals or increased energy consumption. This pre-study is based on literature studies related to anaerobic digestion with initial biological hydrolysis and collected knowledge from full-scale plants, universities and suppliers of equipment. Nearly 70 published scientific articles relevant to the subject have been found in the performed literature searches. The articles have been subdivided according to the purpose of each article. A large part of the articles have concerned modelling of anaerobic digestion why a separate section of the report has been devoted to this. The literature study shows that the majority of the experiments with an initial hydrolysis step that have been performed with substrates such as waste water treatment sludge, organic waste or dairy manure have given advantages in the form of for example higher methane yield, increased degree of degradation and/or increased treatment capacity. In addition other advantages have been achieved by the method, for example elimination of foaming in digester, more stable process and pathogen inactivation. It is difficult to draw any general conclusions about optimal pH for hydrolysis. Optimal pH most likely differs, mainly in relation to the composition and characteristics of the substrate. It seems that pH control, in most cases, is not necessary to achieve a satisfactorily process, which is important considering the costs for addition of acid or base in a full scale application. Concerning process temperature an increase up to 55 deg. C have in most studies resulted in a higher hydrolysis rate. Optimal retention time and organic load for optimization of the hydrolysis process depends on the composition and characteristics of the substrate. For each combination of process parameters there is an optimum that changes if any of the process conditions does change. For waste water treatment sludge generally 4-7 days retention time seems to be appropriate and for dairy manure 2-4 days have been used successfully in studied scientific papers. Simulation of hydrolysis can show a clear optimum for which retention time gives the highest hydrolysis rate. This can be used to design a multi-step process so that the hydrolysis rate, and thus the biogas production, can be optimized. Modelling experiments also show that multi-step digestion processes can be simulated with a good correspondence to data. Hydrogen gas can be produced in an initial hydrolysis step which gives the opportunity to produce bio-hythane but can also be a safety risk if the plant is not designed for this. No safety problems with hydrogen formation have however been observed at identified full scale plants. Anaerobic digestion with an initial biological hydrolysis step should be possible to implement at a digestion plant with relatively simple means by mainly the addition of one stirred and insulated tank. The importance and effect of an initial separate hydrolyse step is however dependent on the characteristics of the substrate and other process parameters of the plant such as organic load and actual retention time. The added value achieved by addition of an extra step in the digestion process has to be revised compared to the costs and the additional work required for process monitoring and maintenance. Six full scale plants in Sweden (3), Germany (1) and USA (2) that are in operation, or have done experiments, with separate biological hydrolysis step have been identified.}
place = {Sweden}
year = {2010}
month = {Mar}
}