liquid digestate in comparison with solid fraction. According to Kataki et al. (2017)
content of aluminum, chrome, lead, arsenic, cadmium, and selenium was respectively 0.39, 0.91, 0.71, 0.22, 0.08, and 0.03 (mg kg
À1 ) in solid fraction of cow
dung digestate. The values are below the average limits concerning concentration of
trace elements in compost in European countries; however, national regulations
concerning concentration limits differ significantly (Kataki et al. 2017). The final
amount of trace elements accumulated in soil after digestate application highly
depends on applied dose which in turn depends on nitrogen concentration in
digestate and C:N ratio in soil.
5.4 Monitoring of Bioremediation Process: How to Predict
Bioremediation Efficiency and Evaluate the Residual
Toxic Effect?
Monitoring of a bioremediation process is used to estimate the potential duration of
the treatment as well as the expected soil quality parameters. Many approaches may
be adopted to monitor the course of the process, which includes chemical, biochemical, microbiological, genetic, or ecotoxicological assays (Fig. 5.5). Combined
monitoring assays are strongly recommended to evaluate the efficiency and potential
risk generated by the bioremediation of TPH-contaminated soils (Shen et al. 2016).
It was observed that the decrease of TPH concentration in soil is not always
unambiguous with the decrease of soil toxicity (Hubálek et al. 2007). During
ecotoxicological monitoring the obtained data should be interpreted carefully since
not only TPH may be responsible for the occurrence of inhibitory or toxic effects.
Factors that may generate stress are also trace elements content, inappropriate
nutrient ratio, salinity, biodegradation by-products, or changes in physicochemical
properties of the soil, to which microorganisms were already adapted (Lapygina
et al. 2006; Xu and Lu 2010; Shen et al. 2016).
5.4.1 Chemical Analytical Assays
Chemical analytical assays are based on the threshold values estimated for target
contaminants in guidelines and legislation, which differ among countries. The assays
include periodic measurement of the contaminants concentration during the treatment. The decrease in hydrocarbons content may be expressed as concentration of
the total amount of TPH, e.g., C10–C40. Measurement of the amount of particular
TPH fraction, e.g., C10–12, C12–C16, C16–C21, C21–C40 may provide important
information about the production of intermediate metabolites, which are often
characterized by the elevated toxicity in comparison to maternal compounds
(Xu and Lu 2010). Metabolites may be accumulated in the heavy fraction of TPH
266
A. Gielnik et al.
content of aluminum, chrome, lead, arsenic, cadmium, and selenium was respectively 0.39, 0.91, 0.71, 0.22, 0.08, and 0.03 (mg kg
À1 ) in solid fraction of cow
dung digestate. The values are below the average limits concerning concentration of
trace elements in compost in European countries; however, national regulations
concerning concentration limits differ significantly (Kataki et al. 2017). The final
amount of trace elements accumulated in soil after digestate application highly
depends on applied dose which in turn depends on nitrogen concentration in
digestate and C:N ratio in soil.
5.4 Monitoring of Bioremediation Process: How to Predict
Bioremediation Efficiency and Evaluate the Residual
Toxic Effect?
Monitoring of a bioremediation process is used to estimate the potential duration of
the treatment as well as the expected soil quality parameters. Many approaches may
be adopted to monitor the course of the process, which includes chemical, biochemical, microbiological, genetic, or ecotoxicological assays (Fig. 5.5). Combined
monitoring assays are strongly recommended to evaluate the efficiency and potential
risk generated by the bioremediation of TPH-contaminated soils (Shen et al. 2016).
It was observed that the decrease of TPH concentration in soil is not always
unambiguous with the decrease of soil toxicity (Hubálek et al. 2007). During
ecotoxicological monitoring the obtained data should be interpreted carefully since
not only TPH may be responsible for the occurrence of inhibitory or toxic effects.
Factors that may generate stress are also trace elements content, inappropriate
nutrient ratio, salinity, biodegradation by-products, or changes in physicochemical
properties of the soil, to which microorganisms were already adapted (Lapygina
et al. 2006; Xu and Lu 2010; Shen et al. 2016).
5.4.1 Chemical Analytical Assays
Chemical analytical assays are based on the threshold values estimated for target
contaminants in guidelines and legislation, which differ among countries. The assays
include periodic measurement of the contaminants concentration during the treatment. The decrease in hydrocarbons content may be expressed as concentration of
the total amount of TPH, e.g., C10–C40. Measurement of the amount of particular
TPH fraction, e.g., C10–12, C12–C16, C16–C21, C21–C40 may provide important
information about the production of intermediate metabolites, which are often
characterized by the elevated toxicity in comparison to maternal compounds
(Xu and Lu 2010). Metabolites may be accumulated in the heavy fraction of TPH
266
A. Gielnik et al.