Organic Waste Recycling

Land treatment of sludge 465

Table 9.15 Total available N and sludge application rates for Example 9.2

Year Total Available N (kg/dry ton of sludge) Annual sludge
loading (Equation
9.4), SNt, dry ton
sludge/(ha-yr)
1 2 3 4 5 6 7 8 9

10

13 = 13

13+1.2 = 14.2

13+1.2+0.55 = 14.75

13+1.2+0.55+0.3 = 15.05

13+1.2+0.55+0.3+0.3 = 15.35

13+1.2+0.55+0.3+0.3+0.3 = 15.65

13+1.2+0.55+0.3+0.3+0.3+0.3 = 15.95

13+1.2+0.55+0.3+0.3+0.3+0.3+0.3 = 16.25

13+1.2+0.55+0.3+0.3+0.3+0.3+0.3+0.3 = 16.55

3+1.2+0.55+0.3+0.3+0.3+0.3+0.3+0.3+0.3=16.85

13.85
12.68
12.21
11.96
11.73
11.50
11.28
11.08
10.88
10.68
Note: If the Cd loading rate of 1.9 kg/(ha-year) as listed in Table 9.11 is used, the sludge
loading rate would be 38 tons/(ha-year). However, to avoid excessive N loading to corn
crops, the land area requirements should be calculated from the sludge loading rates
given in Table 9.15

(4) In case where Cd is LDP, the land area requirement for the sludge
production rate of 22 tons/day is:

(22 tons/day) (365 days/year)

ņņņņņņņņņņņņņņņņņņņņ

10 tons / (ha-year)

= 800 ha.

(5) At the sludge application rate of 10 tons/(ha-year), Cd content in sludge =
50 ppm, and soil CEC of 10 meq/100 g, the life period of sludge application that
will not allow Cd to exceed the cumulative limit as given in Table 9.10 is:

10 kg/ha ton 1

ņņņņņņņņņņ. ņņņņņņņņņ. ņņņņņņņ = 20 years

10 tons / (ha-year) 1000 kg (0.00005)

The design period of this land application site based on cumulative limit of
Cd loading is 20 years. The design period based on cumulative limits of other
heavy metals will be several times higher than that of Cd for this type of sludge.