Organic Waste Recycling

Land treatment of sludge 455

In general the CEC ranges of less than 5, 5-15, and more than 15 meq/100 g
correspond to sands, sandy loams, and silt loams, respectively.

Table 9.8 Estimated land area for municipal sludge application

Options Application period Reported range
(dry tons/ha)

Typical rate (dry
tons/ha)
Agricultural
Forest

Site reclamation

Annual

One application or at

3-5 year interval

One application

0.4 – 12

1.6 – 40.5

1.2 – 81

2

8

20
From Reed and Crites (1984); reported by permission of Noyes Publications, from
Handbook of Treatment Systems for Industrial and Municipal Wastes.

Table 9.9 Recommended slopes for sludge sites (U.S. EPA 1983)

Slope (%) Comment
0 – 3
3- 6
6 – 12
12- 15

Ideal

Acceptable for surface application of injection

Applicable for injected liquid sludge

Immediate incorporation of all sludge, and effective runoff control are

necessary

Based on scientific risk-assessment evaluation aimed at limiting human and
ecological exposure to sludge contaminants, in relation to the current sewage
sludge and disposal regulations the U.S. EPA has implemented the new land
application limits for the 10 heavy metals, as shown in Table 9.11. These limits
do not mention about soil CEC, but the cumulative limits for Pb and Ni are
lower than those reported in Table 9.10 (at CEC greater than 15 meq/100g) and
Table 9.12 (for Pb), while the cumulative limits for other heavy metals (Cd, Cu,
and Zn) are higher. Table 9.11 classifies sludge quality as “ceiling concentration
limits” and higher quality pollutant concentration limits”. Sludge quality
classifications and application restrictions are defined as follows:

1. If a sludge meets the “high quality” metal concentration limits, it
   can be land applied provided that the application rate does not
   exceed annual pollutant loading rates as shown in Table 9.11.


2. If a sludge does not meet the “high quality” limits but does meet the
   ceiling concentration limits, the sludge can be land applied provided
   that the cumulative pollutant loading rates as defined in Table 9.11
   are not exceeded (in addition to annual pollutant loading rates).


3. If a sludge does not meet ceiling concentration limits, it cannot be
   land applied.