Organic Waste Recycling

Land treatment of sludge 463

c) Sludge will be incorporated, so Kv = 1, CEC of 10 meq/100 g for

site soils. Corn is the intended crop, Un = 180 kg/(ha-yr).

d) The design can be based on N fertilization rates or heavy metal

loading rates.

Mineralization rates (Table 9.14) for digested sludge are:

Year f

1 0.20

2 0.10

3 0.05

4-10 0.03

Solution:

(1) Organic nitrogen (ON) = Total N – NH 4

= 2.5 - 1 = 1.5% = 0.015

From Equation 9.2, available nitrogen in the first year:

Np = (1,000)[0 + 1(0.01) + 0.20(0.015)]

= 13 kg/ton of dry sludge

a. From the first-year sludge, the organic N remaining in second year:

ON 2 = (0.015) - (0.20)(0.015)

= 0.012

b. From Equation 9.3, the amount of first-year sludge mineralized in second
year:
NPR2 = (1,000) (f 2 )(ON 2 ) = (1,000)(0.1)(0.012)
= 1.2 kg/ton of dry sludge

c. From the first-year sludge, organic N remaining in third year:

ON 3 = (0.012) - (0.1)(0.012) = 0.0108

Mineralization of the first-year sludge in third year:

NPR3 = (1,000)(f 3 ) (ON 3 ) = (0.05)(0.0108)(1,000)

= 0.54 kg/ton of dry sludge