**4. Conclusion**

82 Management of Organic Waste

\*\*FSOM is a share of metabolic СО2 formed by microbial mineralization of SOM; # PE is a priming effect was calculated according to [ Eq. 11]; ##Time after the crude oil addition to soil. Standard errors of

Using the equation [12], we calculate the value of PE(total) by comparing CO2 production during microbial SOM utilization in the experiments and controls. As follows from Table 5, during 67-day exposure of oil hydrocarbons in soil the PE value reached 150 % in experiment 1 with native soil microbiota and 180 % in experiment 2 with mixed microbiota (soil microorganisms and the bacterium strain *P. aureofaciens* BS1393(pBS216)). Thus, addition of crude oil to the soil activates to a large extent the microbial mineralization of

As follows from Table 6, the oil hydrocarbons introduced into soil were mineralized to CO2 to the extent of about 4.59 (0.2) and 4.81 (0.15) mg C-CO2 g-1 DS or 16.7 and 17.5 percents of the initial crude oil quantities in the soil over the course of 67-day exposure in experiments 1

cParts (%) of the initial amount of SOM and crude oil mineralized to CO2 in soil dParts of the initial amount of crude oil (in percents) consumed by microorganisms producing CO2 and organic substances

Table 6. The quantities of SOM mineralization and crude oil consumption by microbiota

Table 5. Average weighted characteristics (13Cave) of carbon isotope composition and fraction of СО2 formed by SOM mineralization and priming effect (PE) in experiments 1 and

100 100 100 100 38.5 (1.7) 38.5 (1.7) 38.2 (1.6) 38.2 (1.6)

\*13Cave is an average weighted of isotope characteristic of СО2 was calculated [Eq. 4]

**3.7 Microbial utilization of oil hydrocarbons and SOM transformation** 

<sup>a</sup>С-SOM mineralized, mg C-СО2 g-1 DS

> 2.87(0.2) c14.6 % 2.98(0.15) 15.2 %

\*The CO2 evaluation from SOM calculated as QCO2(SOM) = vCO2(SOM +SUB)·Δt·FSOM bR= (Q biomass + exometabolites from oil carbon) / (QSOM mineralized of SOM);

(biomass and exometabolites). Standard deviations are given in brackets.

mg С-СО<sup>2</sup>

25.7 (0.6) 36.7 (0.6) 24.03 (0.6) 34.25 (0.6) 64 (3) 92 (3) 67 (3) 96 (3)

#PE, % ##Time, days

Crude oil metabolized

CO2 Biomass cTotal

4.59 (0.2) d16.7 % 4.81 (0.15) 17.5 %

4.59 (0.2) d16.7 % 4.81 (0.15) 17.5 %

Coil, mg C g-1 DS bR

9.18 (0.2) 33.4 % 9.62 (0.15) 35.0 %

1.60

1.61

Experiment \*13Cave, %o \*\*FSOM, % [CO2](SOM)


three parallel calculations are given in brackets.

Initial Сorg, (SOM + Oil) mg C g-1 DS

19.6+ 27.43

19.6+ 27.43

during the 67-day exposure in soil.

Control 1 Control 1 Control 2 Control 2 Experiment 1 Experiment 1 Experiment 2 Experiment 2

2 relative to controls

native soil organic matter.

and 2, respectively.

Variants of analysis

Experiment 1

Experiment 2

With the proviso that crude oil carbon content no more than 1.4-fold higher than the SOM carbon amount, the soil microbiota is able to mineralize up to 17 % of crude oil hydrocarbons and 15 % of SOM during the 67-day experiments. Using mass isotope balance and differences between the 13C values of SOM and oil hydrocarbons, the quantities of CO2 produced during microbial mineralization of SOM and oil hydrocarbons have been determined. According to the highest depletion of 13C in CO2 evolved from soil during the initial time of the exposure with crude oil, it is suggested that at this time the aliphatic oil fraction predominantly participates in mineralization. Microbial consumption of oil hydrocarbons activates the process of SOM mineralization and demonstrates the presence of PE of oil hydrocarbons. During a 67-day period of the crude oil exposure in soil, the average values of PE reached over 150 % in soil with native soil microbiota and over 180 % in soil with the mixture of native microbiota and introduced bacteria *P. aureofaciens*

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BS1393(pBS216) containing the plasmid pBS216 which controls naphthalene and salicylate biodegradation and able to utilize aromatic oil hydrocarbons. It has been found experimentally that in the total emission of carbon dioxide from soil to atmosphere, about 38 % СО2 was produced as a result of SOM mineralization and about 62 % was formed from oil hydrocarbons as anthropogenic pollutant. The soils polluted with oil hydrocarbons undergo the change of SOM by replacement of part native organic substances on the newly synthesized products in the course of oil biodegradation and the increase of the residual oil share in the total pool of organic matter in soil. Within 6-month time, the quantity of the microbial newly synthesized organic products (carbon of cell biomass and exometabolites) nearly 1.6-fold exceeds the carbon quantity of SOM taken up for the CO2 microbial mineralization. After partially microbial consumption of oil hydrocarbons, the substrate characteristics of residual oil are rather different from crude oil and can be considered as *waste oil* in the soil.
