Spent Wash Effluents

In India, about 15,000 million liters of spent wash are produced annually from 246 distilleries. This situation has created an acute spent wash disposal problem with the expansion of distilleries in sugarcane-growing countries. This spent wash, whether treated or not, is used to both irrigate and fertilize sugarcane, as it contains essential plant nutrients (Table 16.9) required for growth (Samuels 1980). However, it also contains heavy metals (Table 16.10). As a result, large-scale applications of spent wash can have deleterious effects on sugarcane growth if it leads to the presence of heavy metals in the soil at levels exceeding their toxicity limits (Table 16.11). Spent wash also contaminates human and animal drinking water and irrigation water.

Industrial effluents containing heavy metals also pollute cultivated fields (Table 16.12) and underground water through seepage or by allowing them into fields nearby. The levels of Pb can range from 2 to 200 ppm in such agricultural lands.

When industrial effluents are diverted into streams, they pollute the water with heavy metals, resulting in Pb levels of 0.07-0.61 ppm, cadmium levels of 0.011-0.043 ppm, Ni levels of 0.22-0.83 ppm, and cobalt levels of 0.16-2.81 ppm (Anon 1992-1993). Likewise, waters from open and bore wells are also polluted with heavy metals such as Cd, Pb, Ni, and Co due to pollution from industrial effluents nearby (Table 16.13).

Table 16.9 Contents (mg l ') of essential plant nutrients in spent wash (from Jain et al. 2001)

Essential plant

Treated spent

Untreated spent

nutrients

wash (pH 9.0)

wash (pH 4.0)

P

35.1

77.6

S

765.0

1609.0

Fe

9.52

68.5

Mn

0.72

3.0

Zn

0.72

4.01

Cu

0.38

2.66

Table 16.10 Concentrations of heavy metals in spent wash (from Jain et al. 2001)

Spent wash

Heavy metals (mg l 1 spent wash)

Cd

Cr

Ni

Pb

Treated

0.004

0.95

0.88

0.54

Untreated

0.025

0.17

0.86

1.24

Table 16.11 Toxicity limits for heavy metals (mg l ') (from SASA 2002)

Solution / water

Cu

Zn

Pb

Cd

Fe

Mn

Al

Solution for plants

0.02

1.3

1.7

2.1

9.3

0.06

0.93

Drinking water for humans

1.5

15.0

0.1

0.01

1.0

0.5

-

Drinking water for farm animals

0.5

25.0

0.1

0.05

-

-

5.01

Irrigation water

0.2

2.0

5.0

0.01

5.0

0.20

5.02

Table 16.12 Results of an analysis of soil samples collected from a commercial farm polluted with effluents (from Anon 1992-1993) S.no. Description Available (DTPA extractable)

heavy metals (ppm)

Table 16.12 Results of an analysis of soil samples collected from a commercial farm polluted with effluents (from Anon 1992-1993) S.no. Description Available (DTPA extractable)

heavy metals (ppm)

Cd

Ni

Pb

Co

1

Marshy soil near well no. 7

0.04

1.40

58.3

1.73

2

Plot no. 39

0.04

0.46

22.4

0.68

3

Plot no. 41

0.02

1.26

16.9

0.26

4

Plot no. 44

0.02

0.40

23.6

0.32

5

Noor Mohd. tank

0.05

0.60

1.76

0.39

6

Stagnant water near plot no. 27

0.05

0.49

2.65

0.66

7

Well no. 7

0.05

0.20

0.46

0.27

8

Shiva Rampally tank

0.12

0.71

1.26

1.63

9

Canal water near well no. 7

0.03

0.26

0.42

0.35

10

Water sample from well no. 7

0.03

0.88

0.37

0.73

11

Oil seed foundation bore well

0.02

0.22

0.70

0.001

Table 16.13 Heavy metal contents (ppm) in waters of open and bore wells near Naddavagu (Patancheru), India, polluted with industrial effluents (from Anon 1992-1993)

S.no.

Open well

Bore well

Cd

Pb

Ni

Co

Cd

Pb

Ni

Co

1

0.013

0.41

0.42

0.62

0.02

0.28

0.63

1.49

2

0.015

0.32

0.22

1.76

0.01

0.12

0.44

0.24

3

0.026

0.16

0.83

1.79

0.03

0.12

0.39

0.57

4

0.019

0.61

0.38

0.47

0.04

0.12

0.59

0.39

5

0.015

0.32

0.75

0.16

0.03

0.02

0.27

2.06

6

0.011

0.24

0.43

0.80

0.02

0.10

0.27

2.06

7

0.022

0.25

0.86

1.10

0.02

0.12

0.53

2.08

8

0.024

0.10

0.28

0.41

0.03

0.16

0.47

2.30

9

0.024

0.36

0.26

0.86

0.02

0.13

0.42

0.48

10

0.020

0.40

0.29

0.45

0.04

0.12

0.80

2.81

11

0.008

0.07

0.28

2.30

0.02

0.10

0.37

2.12

12

0.016

0.28

0.63

0.99

0.03

0.12

0.38

1.58

13

0.021

0.16

0.52

1.85

0.04

0.11

0.42

1.48

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