Eisenia sp. is not a typical soil organism and occurs naturally in accumulations of
organic matter like compost or manure, thus significance of the specie in soil
bioassays remains questionable (Jager et al. 2005). The alternative use of typical
soil invertebrate Aporrectodea caliginosa was proposed by Jager et al. (2005).
Klobučar et al. (2011) also noted that A. caliginosa is specie suitable for in situ
study of soil toxicity and genotoxicity field surveys, e.g., comet assay.
Species recommended within one type of bioassay differ in the degree of sensitivity (Hubálek et al. 2007). Studies published by Hentati et al. (2013) and Natal-daLuz et al. (2008) revealed that species of Eisenia are more sensitive to TPH
contamination in comparison with F. candida. The differences in the reaction for
the contaminant are probably caused by different morphology of both species.
Eisenia possess a thin dermal layer with high exposure surface and springtails are
protected by thick cuticle. The results of bioassay may also differ within tests on the
same organisms depending on selected toxicity endpoints (Hubálek et al. 2007). It is
important to consider these differences in the design of standard methods, as
sensitivity of test specie as well as the toxicity endpoint affects the evaluation of
bioremediation process.
5.5 Conclusions
Digestate is a solid and/or liquid by-product of biogas production generated during
anaerobic digestion, which constitutes valuable organic amendment rich in nutrients
and characterized by elevated biological stability in comparison to raw feedstock.
However, digestate may contain pathogens and organic contaminants, thus a posttreatment is recommended. Composting of TPH-contaminated soils mixed with
organic matter and bulking agent is an effective bioremediation strategy and may
significantly decrease organic contaminants content in the soils and organic amendments. Composting also has a positive impact on pathogen content decrease in the
organic matter. Many pathogens, e.g., Salmonella or E. coli, which may be present in
digestate, are not detected after composting. Sanitation of the composted matter
occurs when the temperature in the thermophilic phase rises above 50
C and due to
predation in the maturation phase. Organic matter provides nutrients for degrading
agents, stabilizes the C:N:P ratio, and improves soil characteristics. Humic-like
substances present in stabilized organic matter additionally may act as buffering
agent decreasing soil toxicity while high contaminant concentrations are present. In
case of weathered pollutants, humic-like substances support desorption of hydrophobic contaminants which increase bioavailability. Addition of bulking agents to
the composting mixture improves diffusion of oxygen and may constitute additional
carbon source. Bulking agents also may act as biocarriers improving the microbial
contact with nutrients and contaminant.
Many microorganisms have been found to degrade TPH. Bacteria enzymes like
monooxygenases and dioxygenases are responsible for oxidation of alkanes and
PAHs, respectively. To evaluate the efficiency of the bioremediation process
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
273
organic matter like compost or manure, thus significance of the specie in soil
bioassays remains questionable (Jager et al. 2005). The alternative use of typical
soil invertebrate Aporrectodea caliginosa was proposed by Jager et al. (2005).
Klobučar et al. (2011) also noted that A. caliginosa is specie suitable for in situ
study of soil toxicity and genotoxicity field surveys, e.g., comet assay.
Species recommended within one type of bioassay differ in the degree of sensitivity (Hubálek et al. 2007). Studies published by Hentati et al. (2013) and Natal-daLuz et al. (2008) revealed that species of Eisenia are more sensitive to TPH
contamination in comparison with F. candida. The differences in the reaction for
the contaminant are probably caused by different morphology of both species.
Eisenia possess a thin dermal layer with high exposure surface and springtails are
protected by thick cuticle. The results of bioassay may also differ within tests on the
same organisms depending on selected toxicity endpoints (Hubálek et al. 2007). It is
important to consider these differences in the design of standard methods, as
sensitivity of test specie as well as the toxicity endpoint affects the evaluation of
bioremediation process.
5.5 Conclusions
Digestate is a solid and/or liquid by-product of biogas production generated during
anaerobic digestion, which constitutes valuable organic amendment rich in nutrients
and characterized by elevated biological stability in comparison to raw feedstock.
However, digestate may contain pathogens and organic contaminants, thus a posttreatment is recommended. Composting of TPH-contaminated soils mixed with
organic matter and bulking agent is an effective bioremediation strategy and may
significantly decrease organic contaminants content in the soils and organic amendments. Composting also has a positive impact on pathogen content decrease in the
organic matter. Many pathogens, e.g., Salmonella or E. coli, which may be present in
digestate, are not detected after composting. Sanitation of the composted matter
occurs when the temperature in the thermophilic phase rises above 50
C and due to
predation in the maturation phase. Organic matter provides nutrients for degrading
agents, stabilizes the C:N:P ratio, and improves soil characteristics. Humic-like
substances present in stabilized organic matter additionally may act as buffering
agent decreasing soil toxicity while high contaminant concentrations are present. In
case of weathered pollutants, humic-like substances support desorption of hydrophobic contaminants which increase bioavailability. Addition of bulking agents to
the composting mixture improves diffusion of oxygen and may constitute additional
carbon source. Bulking agents also may act as biocarriers improving the microbial
contact with nutrients and contaminant.
Many microorganisms have been found to degrade TPH. Bacteria enzymes like
monooxygenases and dioxygenases are responsible for oxidation of alkanes and
PAHs, respectively. To evaluate the efficiency of the bioremediation process
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
273