depends on the type of soil, contaminant, and composition of indigenous bacterial
populations (Liang et al. 2007).
Soil application of organic matter improves total microbial density and diversity
(Wang et al. 2016). Organic matter is characterized by rich and divers native
microflora and often contain strains able to degrade complex organic pollutants
(Liang et al. 2014). In the studies of Liang et al. (2014), sewage sludge addition to
soil contaminated with organic compounds (dichlorodiphenyltrichloroethane (DDT)
and hexachlorocyclohexane (HCH)) has resulted in soil inoculation with degrading
agents including Pseudomonas sp., Bacillus sp., and Sphingomonas sp. and consequently increased biodegradation rate. Moreover, due to horizontal gene transfer
(HGT) genes useful in degradation of hydrocarbons may be transferred in soil
among bacteria (Shahi et al. 2016). Thus, increase in bacterial diversity and density
will positively affect “catabolic memory” of the treated soil (Fig. 5.4).
Besides, many studies have suggested that soil humic matter may decrease the
bioavailability of organic contaminants through bonding of molecules to the soil
matrix (Rivera-Espinoza and Dendooven 2004). Humic acids have a variety of
binding sides such as carboxyl, hydroxyl, and carbonyl groups which allow for the
sorption of diverse trace elements while hydrophobic part is responsible for the
sorption of organic compounds (Tejada et al. 2008).
For highly contaminated soils, binding properties of humic matter may be also
beneficial in bioremediation process, by decreasing TPH concentration and thus the
toxicity level (Tejada et al. 2008). As a result, organic matter addition can have a
stimulating influence on microbial metabolic activity, manifested by increased
microbial biomass carbon, enzyme activity, and respiration rate (Tejada et al.
2008). Masciandaro et al. (2013) concluded that soil sorption capability is positively
correlated with the amount of humic acids in SOM. The final impact of SOM on
contaminant mobility depends on the concentration of the contaminant and dissolved
humic acids in the soil solution, nature of interactions between contaminant, and
other compounds and the ability of soil matrix to release the contaminant into the
aqueous phase (Masciandaro et al. 2013).
5.3.3 Field Application of Stabilized Organic Matter
Organic fertilizers should not constitute a secondary source of contamination of soil
and water. Therefore, organic amendments should not contain elevated concentrations of organic and inorganic contaminants (Masciandaro et al. 2013). Also the
possible presence of pathogen microorganisms in organic amendment should be
considered. Biological or chemical contamination is a common threat of organic
wastes originating from agriculture or municipal treatment plants. Thus appropriate
pretreatment is needed before large-scale application.
Elevated biological stability of digestate (Scaglia et al. 2014) may be beneficial
for bioremediation process in various aspects. In case of wide-scale organic matter
application, the leaching and runoff of nutrients from the treated field is limited in
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
261
populations (Liang et al. 2007).
Soil application of organic matter improves total microbial density and diversity
(Wang et al. 2016). Organic matter is characterized by rich and divers native
microflora and often contain strains able to degrade complex organic pollutants
(Liang et al. 2014). In the studies of Liang et al. (2014), sewage sludge addition to
soil contaminated with organic compounds (dichlorodiphenyltrichloroethane (DDT)
and hexachlorocyclohexane (HCH)) has resulted in soil inoculation with degrading
agents including Pseudomonas sp., Bacillus sp., and Sphingomonas sp. and consequently increased biodegradation rate. Moreover, due to horizontal gene transfer
(HGT) genes useful in degradation of hydrocarbons may be transferred in soil
among bacteria (Shahi et al. 2016). Thus, increase in bacterial diversity and density
will positively affect “catabolic memory” of the treated soil (Fig. 5.4).
Besides, many studies have suggested that soil humic matter may decrease the
bioavailability of organic contaminants through bonding of molecules to the soil
matrix (Rivera-Espinoza and Dendooven 2004). Humic acids have a variety of
binding sides such as carboxyl, hydroxyl, and carbonyl groups which allow for the
sorption of diverse trace elements while hydrophobic part is responsible for the
sorption of organic compounds (Tejada et al. 2008).
For highly contaminated soils, binding properties of humic matter may be also
beneficial in bioremediation process, by decreasing TPH concentration and thus the
toxicity level (Tejada et al. 2008). As a result, organic matter addition can have a
stimulating influence on microbial metabolic activity, manifested by increased
microbial biomass carbon, enzyme activity, and respiration rate (Tejada et al.
2008). Masciandaro et al. (2013) concluded that soil sorption capability is positively
correlated with the amount of humic acids in SOM. The final impact of SOM on
contaminant mobility depends on the concentration of the contaminant and dissolved
humic acids in the soil solution, nature of interactions between contaminant, and
other compounds and the ability of soil matrix to release the contaminant into the
aqueous phase (Masciandaro et al. 2013).
5.3.3 Field Application of Stabilized Organic Matter
Organic fertilizers should not constitute a secondary source of contamination of soil
and water. Therefore, organic amendments should not contain elevated concentrations of organic and inorganic contaminants (Masciandaro et al. 2013). Also the
possible presence of pathogen microorganisms in organic amendment should be
considered. Biological or chemical contamination is a common threat of organic
wastes originating from agriculture or municipal treatment plants. Thus appropriate
pretreatment is needed before large-scale application.
Elevated biological stability of digestate (Scaglia et al. 2014) may be beneficial
for bioremediation process in various aspects. In case of wide-scale organic matter
application, the leaching and runoff of nutrients from the treated field is limited in
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
261