Characterisation of Contaminated Soil by Crude Oil Associated with Produced Water
Figure 5: Locations of the Contaminated, Uncontaminated and Produced Water Sampling Points at the Case Study Area
Three replicate samples from each oil/soil mixture at each cell were withdrawn every month for enumeration of the total number of HUB (a mixture of Bacillus and Pseudomonas). HUB in the soil
Spt3 Pit of produced water Spt1 Spt4 A1 B1 C1 Ref1 5m 10m
Code
A1–A6 B1–B6 C1–C6
Ref1–Ref2 Spt1–Spt4
Description
First row of the contaminated soil cells Second row of the contaminated soil cells Third row of the contaminated soil cells Uncontaminated soil samples Produced water samples
Figure 6: Distribution of Total Petroleum Hydrocarbons Content in the Contaminated Soil at the Case Study Area at Each Cell of the Sampling Point
10,000 20,000 30,000 40,000 50,000
0 12 3 Cell C B A
Figure 7: Average Monthly Reading of Hydrocarbon-utilising Bacteria in Soil Samples Treated with Crude Oil at Each Cell During the Interval of Experiments (One Year)
0.00E+00 5.00E+06 1.00E+07 1.50E+07 2.00E+07 2.50E+07
Cell A: 0% Cell B: 10% Cell C: 20% Cell D: 30% Cell E: 40%
HUB = hydrocarbon-utilising bacteria; CFU = colony-forming unit.
4 5 6 A2 B2 C2 A3 B3 C3 A4 B4 C4 A5 B5 C5 A6 B6 C6 Ref2 Spt2
samples were enumerated using oil agar (OA) (1.8g K2HPO4, 1.2g K2HPO4, 4g NH4Cl, 0.2g MgSO4·7H2O, 0.1g NaCl, 0.01g FeSO4·7H2O, 20g agar, 2ml crude oil, 1,000ml distilled water, pH 7.4). The OA plates were inoculated with the soil suspensions and
incubated at 30°C for five days before taking the counts. Isolated colonies of HUB were transferred to nutrient agar slants.11
The
Cell of contaminated soil sampling
average count for each cell along the interval of the experiment (52 weeks) is shown in Figure 7. The variation in the account of HUB is due to the difference in the concentrations of the contaminants, where the high concentration of contaminants raises the toxicity in the soil and decreases the HUB count and vice versa; in other words, at low concentrations of the contaminants, the HUB count and the TPH reduction (biodegradation rate) was high, and vice versa. TPH reduction was monitored via the determination of TPH values every two weeks. The results showed that the rate of crude oil hydrocarbon degradation changes as the concentration of oil contaminants changes. In other words, a higher rate of degradation at the lowest concentration of contaminants has been observed, and the reverse is also true (i.e. four rates of biodegradation of crude oil contaminants have been noted).
The overall rates of TPH reduction estimated (parts per million [ppm]/week) were determined for each cell to depict the relationship between the rate of biodegradation of oil contaminants and its concentration in the soil. This relation was modelled to arrive at an important equation – the natural bio-degradation rate (NBDR) – as a function of the crude oil contaminants (THP) at the soil media, under the ambient temperature of the studied field. Equation 1 below represents the NBDR model (TPH = ppm):
NBDR = e (-2.66364 x10-5 xTPH)
x 1520.9 (1)
Through the application of the NBDR equation to the computational fluid dynamics (CFD) modelling programme, the degradation rate at each unit-cell of the network of the CFD will be estimated corresponding to the TPH content at this unit-cell, and this is what will naturally occur at the contaminated media. In other words, the low TPH content zones will be remediated more rapidly than the high THP content zones.
Computational Fluid Dynamics Modelling
The governing equations that describe fluid flow and contaminant transport in the unsaturated zone will be presented in this section. The equation that governs the saturated–unsaturated flow in the soil is:
[C + Se.S]
∂Hp ∂t
+ .[−K.kr . (Hp + D)] = Qs
(2)
where C denotes the specific moisture capacity (m-1), Se is the effective saturation of the soil, S is a storage coefficient (m-1 represents the dependent variable pressure head (m), t is time (d), K
), Hp
equals the hydraulic conductivity function (metres/day [m/d]), kr is the relative permeability of the soil, D is the co-ordinate (for example
x, y, or z) that represents vertical elevation and Qs is a fluid source defined by volumetric flow rate per unit volume of soil (d-1
). The governing equation for solute transport in the reaction model
130
EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 1
Δ
HUB population count (CFU/g of soil)
Total petroleum hydrocarbons (mg/kg)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148