Role Of Solid In Purifying Waste Water Effluent 1g716v

THE ROLE OF SOILS IN PURIFYING WASTEWATER EFFLUENTS ABSTRACT Due to rapid growth in cities, the demand for water has increased tremendously. To meet the demand of water, the groundwater resources are been tapped at such a rate that they are depleting at a very fast rate. Secondly, there has been no adequate recharge of groundwater resources to maintain the continuous supply of groundwater. Thus, we have to see that the water resources already present are maintained and also they can be increased by some other options. Therefore the water resources have to be maintained and managed well. The future of our water resources depends upon the development of water resources. Thus, reuse of water has become the need of the hour. One of the options could be the use of treated wastewater effluents. Towns and cities generate huge quantities of sewage. This, when discharged directly onto open grounds is causing considerable pollution of water, soil and air. The sewage may first have to be treated in sewage treatment plants, which in turn will yield great quantities of effluents. The problem is how to make good use of effluents, which not only go waste, but also cause environmental pollution. Now, the question is, by what means the effluents from sewage treatment plants can be turned into reasonably pure water. Soil has been known as a greater cleanser of water. It has the capacity of acting as a physical, chemical and biological filter. Can such a commonly available and inexpensive agent be used to convert the effluents from sewage into normal water? That is the great task that lies before us in tackling the national problem of water scarcity.

INTRODUCTION

Towns and cities in India generate huge quantities of sewage, which in most cases is discharged into rivers, or into the sea or even on open ground, thus causing environmental pollution. Recycling this waste would not only take care of this pollution but would also yield large quantities of clean water which would help in alleviating, partly at least the problem of water scarcity gripping many parts of India. The city of Mumbai alone, with its population of 12 Million generates 12,96,000 m3 of sewage per day (taking the consumption of water per head as 135 lts./day, and 80% of this consumed water being converted into sewage). If only 70 % of this could be recovered as clean water, the city of Mumbai would yield 9,07,200 m 3 of good water per day. There are various methods of recycling wastewater, but the simplest and the most inexpensive method of treating sewage to obtain clean water from it is making the wastewater filtrate through sufficiently deep layers of suitable soil. This method is used in certain parts of the world, notably in Holland, though it has been hardly used in India.

Now, a study has been conducted to test the performance of three types of soils— commonly found in Peninsular India—in improving/purifying wastewater effluents. The three soils used were: 1) laterite soil collected from Dodamrg, a village on the eastern border of Goa at the foothills of the Sahyadris (Western Ghats), 2) sandy soil collected from Calangute, a coastal villeage of Goa, and 3) clayey or black cotton soil collected from Khannapur, Belgaum District, Karnataka. Two types of wastewater effluents were used to filtrate through the soils: effluent collected from the outlet of a household septic tank, and effluent collected from the sewage treatment plant of a five-star hotel. Raw sewage was not considered suitable for the following reasons: 1) it contains high quantities of the suspended solids on of which it would heavily clog the soil pores and thereby hamper the further movement of wastewater through the soil; 2) it has high organic and inorganic load which might lead to an increase in harmful minerals in the water collected after filtration through the soil; and 3) raw sewage in any device to convert waste into clean water would cause nuisance to the surroundings, due to the foul smelling gases emanating from it.

The two effluents—septic tank effluent and the sewage treatment plant effluent— were tested for the following parameters 1. pH, 2. Specific conductivity 3. Suspended solids

4. Total alkalinity, 5. Hardness, 6. Potassium, 7. Sodium, 8. Sulphates, 9.

Chlorides, 10. Nitrates, 11. BOD3, and 12. COD. Each of the effluents was ed through soil columns of four different heights for each of the soils. The first soil was compacted with the help of a ramrod in four PVC pipes of internal diameter 7.5 cm. The first pipe was filled with the soil to a height of 0.5 m, the second pipe to a height of 1.0 m, the third to a height of 1.5 m, and the fourth to 2.0m. Then, one of the effluents was made to through each of the said soil columns and after it filtrated through the soil columns, the outcoming water samples were collected for testing. The experiments were repeated in the same manner for the other effluent and the other two soils. Each effluent ing through each type of soil yielded 4 samples of soil-treated water. Thus altogether, the two effluents with the three soils yielded 24 samples of soil-treated water. These samples were then tested for the same parameters as the effluents were tested before filtration, to determine the changes the effluents have undergone while ing through soils. The results of each effluent after filtrating through each soil were tabulated for the four different heights (as shown in the tables).

Table 1: Qualitative Analysis of Septic Tank Effluent with Laterite Soil Bed Effluent Characteristics

Parameters

1. pH 2. Specific Conductivity (mS) 3.Suspended Solids (mg/l) 4.Total Alkalinity as CaCO3 (mg/l) 5.Total Hardness as CaCO3 (mg/l) 6. Potassium (mg/l) 7. Sodium (mg/l) 8. Sulphates (mg/l) 9. Chlorides (mg/l) 10. Nitrates (mg/l) 11. BOD3 (mg/l) 12. COD (mg/l)

Initial influent Charact eristics

After ing throug h 0.5m of soil

After ing through 0.5m of soil

After ing through 1.5m of soil

After Overall ing Percent through decrease 2.0m of soil

9.5 3.85 126

9.3 3.12 0

9.0 2.46 0

8.7 1.53 0

8.3 1.22 0

12.63 68.30 100

1720

460

184

172

163

90.50

260

218

178

136

83

68.00

31 58.0 43.7 250 0 26.55 164

28 54 40 227 0 18.95 135

25 46 35 190 1.1 10.01 108

19.3 37.3 28 162 1.6 5.16 76

12.7 29.1 19.6 129 2.1 0.37 46

59.00 49.80 58.10 48.40 98.61 71.90

Table 2: Qualitative Analysis of STP Effluent with Laterite Soil Bed Effluent characteristics P a r a m e t e r s 1. pH 2. Specific Conductivity (mS) 3. Suspended Solids (mg/l) 4.Total Alkalinity as CaCO3 (mg/l) 5. Total Hardness as CaCO3 (mg/l) 6. Potassium (mg/l) 7. Sodium (mg/l) 8. Sulphates (mg/l)

Initial influent Charact eristics

After ing through 0.5m of soil

After ing through 1.0m of soil

After ing through 1.5m of soil

After ing Throug h 2.0m of soil

Overall percent decrease

9.0

9.3

9.1

8.9

8.6

4.44

2.35

2.125

1.785

1.338

0.986

58.04

0

0

0

0

0

-

108

91

78

70

65

39.81

184

160

129

109

76

59.69

16.8 16 42

15.2 15.4 37.8

13.4 14.6 31.9

10.6 13.2 26.3

8.2 11.8 19.3

51.19 20.00 54.05

9. Chlorides (mg/l) 108 103 90 75 62 10. Nitrates (mg/l) 0 0 0 0 1.8 11. BOD3 (mg/l) 30.40 27 20.10 12.41 0.59 12. COD (mg/l) 146 119 84 52 14 Table 3: Qualitative Analysis of Septic Tank Effluent ed Through Sandy

42.59 98.04 90.41 Soil

Bed Pa ra me ter s 1. pH 2. Specific Conductivity (mS) 3.Suspended Solids (mg/l) 4.Total Alkalinity as CaCO3 (mg/l) 5.Total Hardness as CaCO3 (mg/l) 6. Potassium (mg/l) 7. Sodium (mg/l) 8. Sulphates (mg/l) 9. Chlorides (mg/l) 10. Nitrates (mg/l) 11. BOD3 (mg/l) 12. COD (mg/l)

After ing through 2.0m Of soil 8.5

Overall percent decrease

9.4

Effluent Characteristics After After After ing ing ing through through through 0.5m 1.0m 1.5m of soil of soil of soil 9.2 8.9 8.7

3.28

2.96

2.54

2.10

1.63

50.3

126

0

0

0

0

100

1690

634

284

194

174

89.70

240

228

196

158

126

47.50

30 57.6 43.7 243 0 38.48 157

28.5 55.2 41.3 231 0 37.76 146

26 51.0 35.3 210 0 30.0 120

22 44.1 29.7 190 0.6 19.83 96

18 36.8 24.6 163 1.2 7.14 73

40.00 36.11 43.70 32.92 81.4 53.50

Initial influent charact eristics

9.6

Table 4: Qualitative Analysis of STP Effluent with Sandy Soil Bed P ar a m et er s 1. pH 2. Specific Conductivity (mS) 3. Suspended Solids (mg/l) 4.Total Alkalinity as CaCO3 (mg/l) 5. Total Hardness as CaCO3 (mg/l) 6. Potassium (mg/l)

Initial influent charact eristics

Effluent characteristics After After After ing ing ing through through through 0.5m 1.0m 1.5m of soil of soil of soil

After ing through 2.0m of soil

Overall percent decrease

8.9

8.7

8.6

8.4

8.2

7.86

2.32

2.2

2.0

1.66

1.31

43.53

0

0

0

0

0

-

107

104

96

87

76

28.30

186

166

147

118

92

50.53

16.4

15.7

14.4

13.1

11.3

31.10

7. Sodium (mg/l) 16 15.4 14.6 13.2 11.9 8. Sulphates (mg/l) 41.8 40.0 36.6 32.7 28.2 9. Chlorides (mg/l) 109 105 99 89 78 10. Nitrates (mg/l) 0 0 0.8 1.6 2.1 11. BOD3 (mg/l) 31.6 27.2 20.09 14.22 3.59 12. COD (mg/l) 140 123 94 68 46 Table 5.5: Qualitative Analysis of Septic Tank Effluent with Clayey Soil Bed

25.62 32.53 28.44 88.64 67.14

Effluent characteristics After After Overall Initial influent ing ing Percent Parameters characteristics through through decrease 0.5m 1.0m of soil of soil 1. pH 9.5 8.9 8.5 10.50 2. Specific Conductivity (mS) 3.16 2.53 1.29 59.20 3. Suspended Solids (mg/l) 106 0 0 100 3.Total Alkalinity as CaCO3 (mg/l) 1630 391 131 91.9 4. Total Hardness as CaCO3 (mg/l) 242 182 105 56.6 5. Potassium (mg/l) 32 26 19 40.6 6. Sodium (mg/l) 57 51.3 38.5 32.4 7. Sulphates (mg/l) 42.8 34 23.4 45.3 8. Chlorides (mg/l) 245 191 148 39.6 9. Nitrates (mg/l) 0 0.8 1.4 10. BOD3 (mg/l) 32.4 14.4 2.86 91.2 11. COD (mg/l) 162 84 35 78.3 [Experiments with soil columns of 1.5 m and 2.0 m of clayey soil could not be carried out in the case of both the effluents due to the low permeability of clayey soil. The effluents did not filtrate through even 1.5 m column of this soil for 10 days during which the effluent column of 20 cm was maintained above the soil. Thereafter the experiments with these soil columns were discontinued] Table 5.6: Qualitative Analysis of Sewage Treatment Plant Effluent with Clayey Soil Bed Effluent characteristics After After Initial influent through through Para characteristics ing ing meters 0.5m 0.5m of soil of soil 1. pH 8.9 8.5 7.9 2. Specific Conductivity (mS) 2.34 1.89 1.354 3. Suspended Solids (mg/l) 0 0 0 4.Total Alkalinity as CaCO3 (mg/l) 108 86 68 5. Total Hardness as CaCO3 (mg/l) 188 143 95 6. Potassium (mg/l) 16.3 13.3 9.1

Overall Percent decrease 19.38 41.50 100 37.03 48.36 45.24

7. Sodium (mg/l) 8. Sulphates (mg/l) 9. Chlorides (mg/l) 10. Nitrates (mg/l) 11. BOD3 (mg/l) 12. COD (mg/l) Conclusion:

16 42.2 110 0 30.40 143

14.4 33 86 0 9.63 55

12.1 23.0 67 0 2.87 15.0

27.97 45.23 37.96 90.47 89.73

From the results thus obtained from all the experiments, the following conclusions can be drawn: 1. All the three soils—the laterite soil, the sandy soil and the clayey soil are effective in varying degrees in improving/purifying wastewater effluents. 2. The sewage treatment plant effluent is preferable to the septic tank effluent for obtaining clean water from wastewater as the final values of the relevant parameters in the case of the sewage treatment plant effluent have decreased much more in comparison to the final values of the same parameters in the case of the septic tank effluent after it filtrated through each of the soils. Another disadvantage of the septic tank effluent is that it contains high quantities of suspended solids, which gradually clog the pores of the soil restricting the further movement of the effluent through the soil. (It is on of this, that the soak pits of the septic tank get choked up and emit bad odours). 3. As the height of the soil column in the case of any of the soil increased, the purification of both the wastewater effluents was better i.e. there was a maximum decrease in all the parameters of both the wastewater effluents after they were ed through the greatest height of soil column, i.e. 2.0 m in this study. 4. With regard to the comparative performances of the three soils, it is found that the laterite soil is the best among the three soils for the purification of both the wastewater effluents. The next best soil for the purpose is the clayey soil, and the last is the sandy soil. The laterite soil is the best because of the three important virtues it possesses: 1) It has high capacity to reduce the organic and inorganic load of the wastewater effluents, on of which there is reduction in most of the relevant parameters of the effluents.

2) It has a reasonably high coefficient of permeability, on of which it allows for a reasonably fast flow of the effluents through it. 3) It has a sufficient content of organic matter allowing micro-flora and micro-fauna to survive and flourish in it, on of which there is a great reduction in BOD 5 (Bio-chemical Oxygen Demand) of the effluents. Hence, summing up these conclusions, the most purified /improved water from sewage is obtained when sewage treatment plant effluent is ed through the laterite soil column of the maximum possible height i.e. the greater the height of soil column, the greater will be purification of the effluent ed through it. The water obtained after the sewage treatment plant effluent es through the soil column of 2.0 m height, is odourless and crystal clear to look at. The values of the parameters in question after filtration through the soil are well within the permissible limits given by the WHO and IS: Specification for normal freshwater. Hence this water is almost as good as normal freshwater. The encouraging results obtained in this study show that it is possible for towns and cities in India to recover clean water from their sewage by means of this simple method of ing the wastewater through sufficiently deep layers of suitable soil. But this being a only a pilot project, further experiments will be needed to ensure that the water recovered from waste has sufficient purity so that it can be used for all purposes for which the normal water supplied to the towns is used. Hence a town or city that intends to recover clean water from its sewage by means of soil treatment, will, first of all, have to set up sewage treatment plant. Secondly, they will have to take care that the effluents from industrial plants and factories are not conveyed to the sewage treatment plants. Then, they will have to set up suitable devices where this sewage treatment plant effluent can be filtrated through thick layers of soil. The effluent may have to be conveyed from the treatment plant to places in the vicinity of the town where the soil conditions may be suitable; or where they are not suitable these conditions may have to be created by supplementing the original soil with the suitable soil (preferably with the laterite soil) transported from elsewhere. These places will have to be in the form of pools or tanks, lined with thick layers of the necessary soil both at the sides and at the bottom, so that the effluent conveyed to these pools or tanks can filtrate through and get purified. Around these pools and tanks, plants and trees can be planted. These will absorb nutrients like nitrates, calcium, magnesium,

and phosphates from the effluents and thus further help in purifying the effluents. In addition, these plants and trees will prevent soil erosion and bind the soil thus strengthening the embankments of pools and tanks. The water after filtration and consequent purification can be collected at a lower level and pumped again to different places in the town or in its vicinity, where it may be intended for use. To begin with, the water recovered from sewage may not be used for the purposes of drinking, cooking or bathing. But it can be utilized profitably and with perfect safety for many other purposes thus effecting saving in the water supplied to the town from the usual sources. The water thus saved could then be diverted to uses of drinking, cooking and bathing. The soil-treated water could be used for the needs of industries, for recharging of aquifers (after monitoring the quality of the water obtained after filtration), for planting and sustaining parks and gardens, for irrigation, for laundries and dairies, for creating and maintaining recreational facilities like artificial lakes, bird sanctuaries and zoos.