Table 1 Physicochemical and microbiological parameters of oily sludge samples

 Site

Guwahati Refinery, IOCL

Guwahati Refinery, IOCL

Digboi Refinery, IOCL

 Geographical location

N 26^° 10.48′ E 091^° 48.00’

N 26^° 10.48′ E 091^° 48.00’

N 27^° 23.410′ E 095^° 36.665’

 Nature of the sample

Oily sludge at waste disposal pit

Oily sludge at waste water lagoon

Oily sludge waste disposal pit

 Temperature (°C)^a

35.2

44.9

35.6

 pH ^a

7.14

6.25

6.84

 Dissolved Oxygen (mg/l) ^a

0.66

0.19

0.01

 ORP (mV) ^a

− 157.7

−30

− 182

 Conductivity (μS /cm) ^a

0.3

1.4

0

 Moisture content (%, w/w)

27.12

27.87

42.24

 TPH (g/ kg)

143.8

400

140.2

 Total Aliphatic Compounds

60

71

75

 Total Aromatics

40

29

25

 Nitrate

18.24

7.87

13.63

 Nitrite

2.97

<  2.0

9.07

 Chloride

704.00

469.85

469.85

 Sulfate

6109

222

6621

 Phosphate

537.6

17

167

 Ammonium

3.24

3.49

3920

 Sodium

3.13

2.23

3.56

 Calcium

49.51

30.50

78.25

 Chromium

45.39

8.07

48.38

 Iron

150.47

302.97

101.13

 Cobalt

1.34

2.39

2.53

 Nickel

34.93

7.11

38.72

 Copper

12.92

2.39

12.89

 Zinc

34.70

131

68.14

 Arsenic

2.24

1.27

2.22

 Cadmium

0.06

0.16

0.05

 Lead

2.68

4.02

2.62

 Total microbial counts using fluorescence microscopy

(cells/g of sample)

(7.01 ± 0.87) × 10⁸

ND

(3.73 ± 0.68) × 10⁸

 MSM

(1.65 ± 0.78) × 10⁶

0.2 × 10⁶

(5 ± 0.14) × 10⁶

 R2A

(8 ± 1.41) × 10⁵

(6.5 ± 1.5) × 10⁶

(7.35 ± 0.21) × 10⁶

 Anaerobic agar

(3 ± 0.14) × 10⁵

(2 ± 0.7) × 10⁶

(1.23 ± 0.14) × 10⁶

Gene of interest

Copy no./g sample

Bacteria (16S rRNA gene)

4.46 × 10⁹

2.35 × 10¹⁰

3.13 × 10⁹

Archaea (16S rRNA gene)

2.54 × 10⁸

1.01 × 10⁸

1.04 × 10⁸

mcrA

1.75 × 10⁶

2.29 × 10⁶

1.66 × 10⁶

dsrB

2.22 × 10⁸

4.02 × 10⁷

3.48 × 10⁸