Usually during the anaerobic digestion process, about 60–80% of the TKN is
transformed to ammonia. Too much ammonia production can exert also an inhibiting
effect, so this also has to be avoided. This problem is more important when substrates rich in proteins are digested, such as wastes of slaughterhouses, rape seed
cake, stillage, and residues obtained from the meat processing industry. The TKN
essay does not measure obviously all the nitrogen contained in the feedstock because
nitrates and nitrites are not detected.
10.2.8 Total Organic Carbon
In a sample, the total carbon is composed by the following:
– The total inorganic carbon (TIC) which is basically represented by the dissolved
carbonate, carbon dioxide, and bicarbonate
– The total organic carbon (TOC) which represents the organic carbon, which can
be both dissolved or present in form of particulate matter
Therefore, TOC can be either directly analyzed and measured or determined by
subtraction of TIC from the total organic carbon.
The standard procedures to determine TOC content are reported in EN 1484
(1997) or APHA 5310 (5310 TOTAL ORGANIC CARBON (TOC) 2017). Sample
preparation is very important for biogas feedstocks. We can have different cases:
– Solid feedstock can be usually dried
– Liquid samples, such as polluted watery samples (without particulate matter), can
be inserted directly into a TOC analyzer
– In the case of liquid samples with particulates (which is the most frequent in case
of anaerobic digestion), a solid–liquid separation step is necessary, then followed
by a separate analysis of the two obtained phases.
The first step in the TOC analysis is the total inorganic carbon (TIC) removal. For
this sake, a sample is acidified with CO2-free gas. The second step is oxidation of the
total organic carbon. This can be done in two ways:
1. Combustion in case of solid sample
2. Using UV ray photo-oxidation or chemical oxidation in case of a liquid sample
Once the sample has been oxidized, the produced CO2 is measured using infrared
sensors or thermal conductivity sensors.
The final information given by the TOC analysis is the total organic carbon; the
researcher has to take into consideration that this total organic carbon can be
composed also by non-digestible carbon, such as the one contained in lignin.
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transformed to ammonia. Too much ammonia production can exert also an inhibiting
effect, so this also has to be avoided. This problem is more important when substrates rich in proteins are digested, such as wastes of slaughterhouses, rape seed
cake, stillage, and residues obtained from the meat processing industry. The TKN
essay does not measure obviously all the nitrogen contained in the feedstock because
nitrates and nitrites are not detected.
10.2.8 Total Organic Carbon
In a sample, the total carbon is composed by the following:
– The total inorganic carbon (TIC) which is basically represented by the dissolved
carbonate, carbon dioxide, and bicarbonate
– The total organic carbon (TOC) which represents the organic carbon, which can
be both dissolved or present in form of particulate matter
Therefore, TOC can be either directly analyzed and measured or determined by
subtraction of TIC from the total organic carbon.
The standard procedures to determine TOC content are reported in EN 1484
(1997) or APHA 5310 (5310 TOTAL ORGANIC CARBON (TOC) 2017). Sample
preparation is very important for biogas feedstocks. We can have different cases:
– Solid feedstock can be usually dried
– Liquid samples, such as polluted watery samples (without particulate matter), can
be inserted directly into a TOC analyzer
– In the case of liquid samples with particulates (which is the most frequent in case
of anaerobic digestion), a solid–liquid separation step is necessary, then followed
by a separate analysis of the two obtained phases.
The first step in the TOC analysis is the total inorganic carbon (TIC) removal. For
this sake, a sample is acidified with CO2-free gas. The second step is oxidation of the
total organic carbon. This can be done in two ways:
1. Combustion in case of solid sample
2. Using UV ray photo-oxidation or chemical oxidation in case of a liquid sample
Once the sample has been oxidized, the produced CO2 is measured using infrared
sensors or thermal conductivity sensors.
The final information given by the TOC analysis is the total organic carbon; the
researcher has to take into consideration that this total organic carbon can be
composed also by non-digestible carbon, such as the one contained in lignin.
10 Substrate Characterization in the Anaerobic Digestion Process
317