Wastewater Calculations - Mathematics and Statistics for the Environment - page 740

24.14.5.1.4 Metals Loading
When biosolids are land applied, metals concentrations are closely monitored and the loading on
land application sites is calculated:

Loading(lb/ac) = Metalconc.(mg/kg) × 0.002 l b/dryton × Applicationrate(drytons/ac) (24.165)

■ EXAMPLE 24.133
Problem: Biosolids contain 14 mg/kg of lead and are currently being applied to the site at a rate of
11 dry tons/ac. What is the metals loading rate for lead in pounds per acre?

Solution:

Loadingrate14mg/kg = × 0.002 lb/dry ton11d × ry tons = 0.31 lb/ac

24.14.5.1.5 Maximum Allowable Applications Based on Metals Loading
If metals are present, they may limit the total number of applications a site can receive. Metals load-
ings are normally expressed in terms of the maximum total amount of metal that can be applied to
a site during its use:

Maximumallowable cumulative lo ad (lb/ac)

Application =

Metalloading (lb/ac)

(24.166)

■ EXAMPLE 24.134
Problem: The maximum allowable cumulative lead loading is 48 lb/ac. Based on the current loading
of 0.35 lb/ac, how many applications of biosolids can be made to this site?

Solution:

48.0 lb/ac
0.35 lb/ac

Application = = 137

24.14.5.1.6 Site Life Based on Metals Loading
The maximum number of applications based on metals loading and the number of applications per
year can be used to determine the maximum site life:

Maximumallowableapplicatio ns

Number of applications peryear

Site life (yr) = (24.167)

■ EXAMPLE 24.135
Problem: Biosolids are currently being applied to a site twice annually. Based on the lead content of
the biosolids, the maximum number of applications is determined to be 135 applications. Based on
the lead loading and the applications rate, how many years can this site be used?

Solution:

135 applications
2applications pe

Site life = = 68 yr

rryear