Organic Waste Recycling

464 Organic Waste Recycling: Technology and Management

d. In the fourth year:

ON 4 = (0.0108) - (0.05)(0.0108) = 0.0103

NPR4 = (1,000)(f 4 )(ON 4 ) = (1,000)(0.03)(0.0103)

= 0.309 kg/ton of dry sludge

e. The NPR for year 5 and beyond converges on a value of about 0.3 kg/ton of
dry sludge

(2) Repeat the calculations for sludge applied in years 2 through 5 and
tabulate results.

a. For all applications of sludge in each year.

Year after Application NPR kg/ton

2 1.2

3 0.55

4 0.31

5 0.3

b. The total available N for each year in kg/ton will therefore increase yearly
as shown in column 2 of Table 9.15. Since the crop uptake of N is fixed at 180
kg/(ha-year), the amount of sludge applied has to be decreased yearly according
to Equation. 9.4, as shown in column 3 in Table 9.15.

(3) Since Cd application rate to crop should not exceed 0.5 kg/(ha-year), for
this sludge containing 50 ppm Cd, the recommended loading is:

0.5kg 1 ton

ņņņņņņņ. ņņņņņņņ. ņņņņņņņņņ = 10 tons/(ha-year)

ha-year 0.00005 (1000 kg)

This Cd-application is lower than the N-application rate. Thus the sludge
loading of 10 tons / (ha-year) is the LDP to be used in determining the land
requirement of sludge application.