the MCB and B concentration rose again to 30% and 65% of their initial concentrations while the T concentration was higher than the initial values.
19.3.3.3 Microbial Biomass
Both water and soil samples reached their maxima of the PLFA concentrations
21 days after the injection. The abundance of the bacterial biomass in the soil was
5.5 times higher compared with the initial values while in the water it was 2.5 times
higher. Subsequently, a gradual decrease of the bacterial biomass was observed to
reach more or less similar levels like the initial ones 147 days after the injection.
19.4 Conclusion
Although it is difficult to compare the tested oxygen sources as the conditions
prevailing in the respective injection areas were different, it can be stated that the
injection of all the materials enhanced the in situ biodegradation and led to
significant drops in the concentrations of the contaminants. In all the cases, the
bacterial biomass more substantially increased in soil microcosms compared with
the bacteria present in the aqueous phase. Therefore, in situ biodegradation
without bioaugmentation can be considered a feasible method for the clean-up
of the tested sites.
Some general remarks on the performance of the different materials can be also
drafted. The longevity of the oxygen sources tested on this particular site was as
follows—modified calcium peroxide > calcium peroxide > gelatinous hydrogen
peroxide. While gelatinous hydrogen peroxide was probably mainly consumed on
the Fenton’s ISCO reactions and it released oxygen for only limited amount of time,
modified calcium peroxide was capable of releasing oxygen for more than 87 days.
Standard calcium peroxide provided oxygen release for about 1 month. Quick
consumption of the oxygen sources might be caused by high iron concentrations
in the groundwater. In the case of calcium peroxide, high pH of the material can
inhibit bacterial growth for several days or weeks after an injection. High H 2 O 2
concentrations caused mainly by gelatinous hydrogen peroxide injection can also
inhibit bacteria temporary.
References
ASTM (1998) Standard guide for direct push soil sampling for environmental site characterizations.
ASTM D6282–98. ASTM International, West Conshohocken. https://doi.org/10.1520/
D6282-98
Bombach P, Richnow HH, Kästner M, Fischer A (2010) Current approaches for the assessment of
in situ biodegradation. Appl Microbiol Biotechnol 86(3):839–852. https://doi.org/10.1007/
s00253-010-2461-2
422
O. Lhotský
19.3.3.3 Microbial Biomass
Both water and soil samples reached their maxima of the PLFA concentrations
21 days after the injection. The abundance of the bacterial biomass in the soil was
5.5 times higher compared with the initial values while in the water it was 2.5 times
higher. Subsequently, a gradual decrease of the bacterial biomass was observed to
reach more or less similar levels like the initial ones 147 days after the injection.
19.4 Conclusion
Although it is difficult to compare the tested oxygen sources as the conditions
prevailing in the respective injection areas were different, it can be stated that the
injection of all the materials enhanced the in situ biodegradation and led to
significant drops in the concentrations of the contaminants. In all the cases, the
bacterial biomass more substantially increased in soil microcosms compared with
the bacteria present in the aqueous phase. Therefore, in situ biodegradation
without bioaugmentation can be considered a feasible method for the clean-up
of the tested sites.
Some general remarks on the performance of the different materials can be also
drafted. The longevity of the oxygen sources tested on this particular site was as
follows—modified calcium peroxide > calcium peroxide > gelatinous hydrogen
peroxide. While gelatinous hydrogen peroxide was probably mainly consumed on
the Fenton’s ISCO reactions and it released oxygen for only limited amount of time,
modified calcium peroxide was capable of releasing oxygen for more than 87 days.
Standard calcium peroxide provided oxygen release for about 1 month. Quick
consumption of the oxygen sources might be caused by high iron concentrations
in the groundwater. In the case of calcium peroxide, high pH of the material can
inhibit bacterial growth for several days or weeks after an injection. High H 2 O 2
concentrations caused mainly by gelatinous hydrogen peroxide injection can also
inhibit bacteria temporary.
References
ASTM (1998) Standard guide for direct push soil sampling for environmental site characterizations.
ASTM D6282–98. ASTM International, West Conshohocken. https://doi.org/10.1520/
D6282-98
Bombach P, Richnow HH, Kästner M, Fischer A (2010) Current approaches for the assessment of
in situ biodegradation. Appl Microbiol Biotechnol 86(3):839–852. https://doi.org/10.1007/
s00253-010-2461-2
422
O. Lhotský