456 Organic Waste Recycling: Technology and Management
Table 9.10 Recommended cumulative limits for metals of major concern applied to
agricultural cropland (U.S. EPA 1983)
Metal Soil cation exchange capacity (meq/100 g)a,b
< 5
kg/ha
5 – 15 kg/ha > 15 kg/haPb
Zn
Cu
Ni
Cd
560
280
140
140
51,120
560
280
280
102,240
1,120
560
560
20
a Interpolation should be used to obtain values in the CEC range 5-15
b Soil must be maintained at pH 6.5 or above
Table 9.11 U.S. land application pollutant limits (Walsh 1995)a. Reproduced by
permission of IWA Publishing
Pollutants Ceiling
concentration
limits (mg/kg)
Cumulative
pollutant
loading rates
(kg/ha)‘High quality’
pollutants
concentration
limits (mg/kg)Annual
pollutant
loading rates
(kg/ha-yr)
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Molybdenum
Nickel
Selenium
Zinc
75
85
3,000
4,300
840
57
75
420
100
7,50041
39
3,000
1,500
300
17
18 b
420
100
2,80041
39
1,200
1,500
300
17
18 b
420
36
2,8002.0
1.9
150
75
15
0.85
0.90
21
5.0
140
aAll weight are on a dry weight basis and ceiling concentration limits represent absolute
values. ‘High quality’ pollutants loading rates represent monthly averages.
b In February 1994, the U.S. EPA withdrew the molybdenum value of 18 mg/kg pending
further review of scientific information supporting a higher concentration.
Table 9.13 shows the concentration limits of heavy metals in sewage sludge
used for land application in several Europe countries. These limits put stringent
standards on Cd, Hg, and As similar to those of Table 9.11.
Other guidelines for sludge application for fruits and vegetable production
are given in Table 9.12. It is required that soils at sludge application sites be
maintained at a soil pH of 6.5 or above. Information on fertilizer
recommendations for a particular crop in a specific location can be obtained
from agricultural experiment extension stations located in the province or country
(see Table 8.7). The design is then based on meeting either the N or P needs.