10.2.9 Trace Elements
The methods to be followed in the TE (trace elements) analysis are reported in the
EN 13346 (2000) (sludges) and in the ISO 11885 (wastewater) (2007), as in APHA
3120 C (National Environmental Methods Index, 3120 B n.d.). Drying and milling
of the biogas feedstocks is recommended before the analysis.
After drying, the sample is digested using boiling aqua regia (EN 13346 2000).
Filtration is practiced on the sample after digestion. The determination of the trace
elements can be done then by using different instruments:
– AAS (atomic absorption spectroscopy)
– ICP-OES (inductively coupled plasma—optical emission spectroscopy).
– ICP-MS (inductively coupled plasma—mass spectroscopy)
This analysis usually is used to determine the concentrations of many trace
elements. The useful ones in the anaerobic digestion are represented by Co, Ni,
Mn, Fe, Se, Zn, and Mo. These are used to build up enzymes, nucleic acids for the
bacteria, and vitamins. Scarcity of useful trace metals can be encountered if single
substrates are digested (e.g. corn silage), while the problem can be avoided, for
example, with co-digestion.
On the other hand, toxic heavy metals can exert a toxic effect on bacterial growth,
so those concentrations also have to be checked.
10.2.10 Sulfur
According to ISO 11885 (2007), the total sulfur content can be analyzed using
ICPOES. The preparation process for the biogas feedstock sample is almost the same
as for the trace element analysis. However, the sulfur wavelength is very low with
respect to the trace metals which have been previously described. This can make
detection not easy and reduce its accuracy. The effect of high sulfur concentration on
the anaerobic digestion process is mainly negative and responsible for the formation
of H2S, which can inhibit the microbial fauna but also damage the internal combustion engine used to covert biogas in electricity and heat. The damage caused by H2S
can be also increased by the high presence of NH3 so the two gases have a
synergistic negative effect (Chen et al. 2008).
10.2.11 Phosphorus
Phosphorus content can be measured according to the methods reported in the
following norms: ISO 6878 (2004), APHA 4500-P (4500-P PHOSPHORUS
2017), and DIN 38414 (S12) (DIN 38414-8 1985). Methods can be colorimetric
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The methods to be followed in the TE (trace elements) analysis are reported in the
EN 13346 (2000) (sludges) and in the ISO 11885 (wastewater) (2007), as in APHA
3120 C (National Environmental Methods Index, 3120 B n.d.). Drying and milling
of the biogas feedstocks is recommended before the analysis.
After drying, the sample is digested using boiling aqua regia (EN 13346 2000).
Filtration is practiced on the sample after digestion. The determination of the trace
elements can be done then by using different instruments:
– AAS (atomic absorption spectroscopy)
– ICP-OES (inductively coupled plasma—optical emission spectroscopy).
– ICP-MS (inductively coupled plasma—mass spectroscopy)
This analysis usually is used to determine the concentrations of many trace
elements. The useful ones in the anaerobic digestion are represented by Co, Ni,
Mn, Fe, Se, Zn, and Mo. These are used to build up enzymes, nucleic acids for the
bacteria, and vitamins. Scarcity of useful trace metals can be encountered if single
substrates are digested (e.g. corn silage), while the problem can be avoided, for
example, with co-digestion.
On the other hand, toxic heavy metals can exert a toxic effect on bacterial growth,
so those concentrations also have to be checked.
10.2.10 Sulfur
According to ISO 11885 (2007), the total sulfur content can be analyzed using
ICPOES. The preparation process for the biogas feedstock sample is almost the same
as for the trace element analysis. However, the sulfur wavelength is very low with
respect to the trace metals which have been previously described. This can make
detection not easy and reduce its accuracy. The effect of high sulfur concentration on
the anaerobic digestion process is mainly negative and responsible for the formation
of H2S, which can inhibit the microbial fauna but also damage the internal combustion engine used to covert biogas in electricity and heat. The damage caused by H2S
can be also increased by the high presence of NH3 so the two gases have a
synergistic negative effect (Chen et al. 2008).
10.2.11 Phosphorus
Phosphorus content can be measured according to the methods reported in the
following norms: ISO 6878 (2004), APHA 4500-P (4500-P PHOSPHORUS
2017), and DIN 38414 (S12) (DIN 38414-8 1985). Methods can be colorimetric
318
PietroBartocci et al.