Nitrogen Removal

Nitrification/denitrification is the principal mechanism for removal of ammonia and nitrate from the wastewater in SAT systems. Ammonia adsorption also plays

TABLE 8.15

BOD Removal for Soil Aquifer Treatment Systems

TABLE 8.15

BOD Removal for Soil Aquifer Treatment Systems

Location

Applied Wastewater BOD

(mg/L)

Percolate Concentration (mg/L)

Removal

(%)

Boulder, Colorado

48b

131b

10b

92

Brookings, South Dakota

11

23

1.3

94

Calumet, Michigan

95b

228b

58b

75

Ft. Devens, Massachusetts

77

112

12

89

Hollister, California

156

220

8

96

Lake George, New York

47

38

1.2

97

Milton, Wisconsin

138

28

5.2

81

Phoenix, Arizona

40

15

0-1

93-100

Vineland, New Jersey

43

154

6.5

96

a Total lb/ac-yr divided by the number of operating days in the year. b Chemical oxygen demand (COD) basis.

a Total lb/ac-yr divided by the number of operating days in the year. b Chemical oxygen demand (COD) basis.

Source: Crites, R.W. and Tchobanoglous, G., Small and Decentralized Wastewater Management Systems, McGraw-Hill, New York. 1998. With permission.

an important role in retaining ammonia in the soil long enough for biological conversion. Nitrification and denitrification are affected by low temperatures and proceed slowly at temperatures of 36 to 41°F (3.6 to 5°C). In addition, denitrification requires an adequate carbon source and the absence of available oxygen.

The ANAMMOX (anaerobic ammonia oxidation) process of ammonia and nitrate reduction was found to be occurring in SAT systems at Lake Tahoe-Truc-kee, California (Woods et al., 1999) and at Mesa, Arizona (Gable and Fox, 2000). The process appears to be continuing through the saturated soil.

Experience with nitrification has been that rates of up to 60 lb/ac-d (67 kg/ha-d) can be achieved under favorable moisture and temperature conditions. Total nitrogen loadings should be checked to verify that they are not in excess of the 50 to 60 lb/ac-d (56 to 67 kg/ha-d) range. Ammonia will be retained in the upper soil profile when temperatures are too low (below 36°F or 2.2°C) for nitrification.

Nitrogen removal is a function of detention time, BOD-to-nitrogen ratio (adequate carbon source), and anoxic conditions. Detention time is related to the hydraulic loading rate through the soil profile. For effective nitrogen removal (80% or more), the loading rate should not exceed 6 in./d (Lance et al., 1976). The BOD-to-nitrogen ratio must be 3:1 or more to ensure adequate carbon to drive the denitrification reaction. Secondary effluent will have a BOD-to-nitrogen ratio of about 1:1, while primary effluent usually has a BOD-to-nitrogen ratio of 3:1. To overcome the low BOD-to-nitrogen ratio in secondary effluent, a longer application period (7 to 9 d) is necessary (Bouwer et al., 1980). Typical removals of total nitrogen and percolate concentration of nitrate nitrogen and total nitrogen are presented in Table 8.16.

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