or based on optical emission spectrometry (OES). In the first step, as previously
seen, the samples of feedstock are dried and milled; then they are digested using a
mixture of nitric acid and sulfuric acid. The aim is to solubilize all the existing
phosphorous. Then using molybdate, which is an acid complexing agent, the blue
complex antimony phosphorous molybdate is produced. This allows the colorimetric
detection of phosphorous. To determine the total phosphorous, another approach is
defined in ISO 11885 (2007) (wastewater) and EN 13346 (2000) (sludges). When
the sample is digested, the phosphorous concentration can be analyzed by AAS,
ICP-MS, or ICP-OES.
10.2.12 Alkalinity
Alkalinity is a typical measurement of water and wastewater quality. It is the
capacity to neutralize acid components. It is defined as the sum of all the bases
which can be titrated. Because the alkalinity of many feedstock is mainly influenced
by the concentration of carbonate, bicarbonate, and hydroxide, it indirectly provides
an information on the concentration of these compounds. The final measured value
may include also the contribution from other compounds, such as borates, phosphates, silicates, and other bases, if contained. Properly operating anaerobic
digesters typically have supernatant alkalinities ranging from 2000 to 4000 mg
calcium carbonate (CaCO3)/L (Pohland and Bloodgood 1963). Alkalinity is measured mainly with the titration method, in which hydroxyl ions, which are present in
the sample, due to the dissociation or hydrolysis of the solutes, react with acid
compounds, which are added. The final alkalinity value depends also on the pH
considered as an end-point (2320 Alkalinity n.d.). Alkalinity can be also determined
with laboratory test kits, such as the ORION total alkalinity test kit (produced by
Thermo Scientific).
10.2.13 Volatile Fatty Acids
The measurement of VFA is typically performed during the anaerobic digestion
process to check how this is evolving. An example of online monitoring system for
VFA is shown in Fig. 10.4.
For this purpose, different online titration processes can be employed, a comparison of which is proposed in (Holten Lützhøft et al. 2014).
10 Substrate Characterization in the Anaerobic Digestion Process
319
seen, the samples of feedstock are dried and milled; then they are digested using a
mixture of nitric acid and sulfuric acid. The aim is to solubilize all the existing
phosphorous. Then using molybdate, which is an acid complexing agent, the blue
complex antimony phosphorous molybdate is produced. This allows the colorimetric
detection of phosphorous. To determine the total phosphorous, another approach is
defined in ISO 11885 (2007) (wastewater) and EN 13346 (2000) (sludges). When
the sample is digested, the phosphorous concentration can be analyzed by AAS,
ICP-MS, or ICP-OES.
10.2.12 Alkalinity
Alkalinity is a typical measurement of water and wastewater quality. It is the
capacity to neutralize acid components. It is defined as the sum of all the bases
which can be titrated. Because the alkalinity of many feedstock is mainly influenced
by the concentration of carbonate, bicarbonate, and hydroxide, it indirectly provides
an information on the concentration of these compounds. The final measured value
may include also the contribution from other compounds, such as borates, phosphates, silicates, and other bases, if contained. Properly operating anaerobic
digesters typically have supernatant alkalinities ranging from 2000 to 4000 mg
calcium carbonate (CaCO3)/L (Pohland and Bloodgood 1963). Alkalinity is measured mainly with the titration method, in which hydroxyl ions, which are present in
the sample, due to the dissociation or hydrolysis of the solutes, react with acid
compounds, which are added. The final alkalinity value depends also on the pH
considered as an end-point (2320 Alkalinity n.d.). Alkalinity can be also determined
with laboratory test kits, such as the ORION total alkalinity test kit (produced by
Thermo Scientific).
10.2.13 Volatile Fatty Acids
The measurement of VFA is typically performed during the anaerobic digestion
process to check how this is evolving. An example of online monitoring system for
VFA is shown in Fig. 10.4.
For this purpose, different online titration processes can be employed, a comparison of which is proposed in (Holten Lützhøft et al. 2014).
10 Substrate Characterization in the Anaerobic Digestion Process
319