III. PHOTODEGRADATION OF OIL RESIDUALS UNDER ADVANCED OXIDATIVE PROCESSES

Interaction of Oil Residues in Patagonian Soil



161



TABLE 9 Experimental Parameters for Eq. (11)

Oil spill

age

Sample (years)

1

2

3

4

5

6

7



Ͼ10

10

6

3

3

2

—



Without catalyst



With catalyst



f



k F (dayϪ1 )



10 3 k s (dayϪ1 )



f



k F (dayϪ1 )



10 3 k s (dayϪ1 )



0.063

0.159

0.156

0.135

0.198

0.051

0.170



0.09

0.043

0.10

0.09

0.13

0.13

0.08



3.9

0.1

0.8

0.4

0.02

0.4

0.9



0.086

0.135

0.086

0.159

0.246

0.136

0.166



0.11

0.06

0.08

0.04

0.07

0.14

0.19



3.2

1.0

1.9

1.4

0.2

0.9

1.6



Ct

ϭ f exp (Ϫk F t) ϩ (1 Ϫ f ) exp (Ϫk S t)

C0



(11)



The experimental parameters ( f, k F , and k S ) are summarized in Table 9 for

the degraded environmental samples (1–6) and for an artificial sample (7), without catalyst and with catalyst. Figure 14 shows the experimental data for oil

residual in soil with 10 years of exposure time. The results indicate that only the

slow kinetics could correspond to a photodegradative process, because only it is

affected by the AOP (TiO 2 /Fenton’s) catalysis. Figure 15 shows that, in the case

of oil residual with two years of exposure time, it is probable that both kinetics

could be affected by AOP (TiO 2 /H 2 O 2 ) catalysis. This is in agreement with our



FIG. 14 C t /C 0 (%), the fraction percentage of oil remaining as a function of sunlight

exposure time (days) for sample 2: without catalyst (circles) and with TiO 2 /Fenton’s catalyst (triangles).



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162



´

Nudelman and Rıos



FIG. 15 C t /C 0 (%), the fraction percentage of oil remaining as a function of sunlight

exposure time (days) for sample 6: without catalyst (circles) and with TiO 2 /H 2 O 2 catalyst

(triangles).



FIG. 16 C t /C 0 (%), the fraction percentage of oil remaining as a function of sunlight

exposure time (days) for the artificial sample: without catalyst (circles) and with TiO 2 /

H 2 O 2 catalyst (triangles).



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Interaction of Oil Residues in Patagonian Soil



163



observation of similar behavior for an artificial sample. Figure 16 shows an important reduction in the concentration (probably by partial evaporation of the

volatile fraction) and similar initial AOP (TiO 2 /H 2 O 2 ) catalytic effects from the

beginning of the curve, as shown previously.

Because light penetration into soils is very limited (i.e., 0.1 to maximal 0.5

mm) and wavelength dependent, the fraction of total compounds actually exposed

to light depends on the type of soil, on the thickness of the soil layer, and on

the light absorption spectrum of the compounds. Thus, the rate of transport of

the compounds from dark to irradiated zones influences the observed overall

elimination rate. Because transport depends on the gas/solid partitioning behavior

of the compounds, and since sorption is strongly influenced by humidity and

other factors [25], the reported rates may have a comparative value. Transportdiffusion problems to the irradiated zone were excluded in the evaluation of the

rates in the slow kinetics, because the slow kinetics is clearly affected by catalytic

effects, Figures 14–16. The possibility of important catalytic surface effects on

crude oil adsorption can be excluded in the present study, since the solid catalysts

were no better than the liquids (i.e., H 2 O 2 ).



IV.



CONCLUSIONS



The determination of physical chemical parameters in natural field samples can

be an important mechanistic tool for understanding the fate of oil residues, its

significance to bioavailability, and the remediation of organic pollutants and a

guide to the right choice of the cleanup technology. Studies with crude oil and

aged oil residues were preferred to artificial, mock mixtures of few known components, since field studies are more realistic and the parameters and empirical

equations determined can be used straightforwardly in the environmental models

designed to evaluate likely remediation techniques.

Because of the exceptionally low organic matter content of Patagonian soils,

an alternative model for sorption of oils in soils was proposed, involving interactions with clays (dipole–dipole, ion–dipole, and van der Waals types of interactions), based on the finding of biparametric relationships between K d and the clay

and water content of the soils. The model was confirmed by other measurements,

which showed that the sorption and desorption of the oil residues depend on the

age of the spill, the clay and water content of the soil, the salinity of the aqueous

phase in contact with the residue, and the salinity of the soil. A characteristic

compositional index could give the degree of oil residual stabilization.

The influence of AOP catalysts on oil residue photodegradation was shown to

be important, especially in the slow kinetic steps, and catalytic photodegradation

should be considered as a possible remediation treatment of the contaminated

soils, together with other technologies. A numerical model was developed capa-



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´

Nudelman and Rıos



164



ble of handling complex and long time-dependence systems, one that could make

sound contributions to the management of oil residues in the petroleum industry.



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