Wastewater Calculations - Mathematics and Statistics for the Environment - page 739

Solution:

Cost = 1925 wet tons per year × 0.18 × $28/dry ton = $9702

24.14.5.1.2 Plant Available Nitrogen
One factor considered when land applying biosolids is the amount of nitrogen in the biosolids avail-
able to the plants grown on the site. This includes ammonia nitrogen and organic nitrogen. The
organic nitrogen must be mineralized for plant consumption. Only a portion of the organic nitrogen
is mineralized per year. The mineralization factor ( if 1 ) is assumed to be 0.20. The amount of ammonia
nitrogen available is directly related to the time elapsed between applying the biosolids and incorpo-
rating (plowing) the biosolids into the soil. Volatilization rates are presented in the example below:

( )

× if 1

Organicnitrogen(mg/kg)

PAN(lb/dry ton) = × 0.002 lb/dry ton (24.163)

( )

+ Ammonianitrogen(mg/kg) × V

1

where
PAN = Plant available nitrogen.
if 1 = Mineral rate for organic nitrogen (assume 0.20).
V 1 = Volatilization rate ammonia nitrogen.

= 1.00 if biosolids are injected.

= 0.85 if biosolids are plowed in within 24 hr.

= 0.70 if biosolids are plowed in within 7 days.

■ EXAMPLE 24.131
Problem: Biosolids contain 21,000 mg/kg of organic nitrogen and 10,500 mg/kg of ammonia nitro-
gen. The biosolids is incorporated into the soil within 24 hr after application. What is the plant
available nitrogen (PAN) per dry ton of solids?

Solution:

( ) + ( )

PAN = 21,000 mg/kg × 0.20 10,500 × 0.85 × .002 = 26.3 lb/dry ton 0

24.14.5.1.3 Application Rate Based on Crop Nitrogen Requirement
In most cases, the application rate of domestic biosolids to crop lands will be controlled by the
amount of nitrogen the crop requires. The biosolids application rate based on the nitrogen require-
ment is determined by the following:

1. Use an agriculture handbook to determine the nitrogen requirement of the crop.

2. Determine the amount of biosolids in dry tons required to provide this much nitrogen:

ac)
Plantavailable nitrogen(lb/dry ton)

Plantnitrogenrequirement (lb/

Drytons/ac = (24.164)

■ EXAMPLE 24.132
Problem: The crop to be planted on the land application site requires 150 lb of nitrogen per acre.
What is the required biosolids application rate if the PAN of the biosolids is 30 lb/dry ton?

Solution:

150 lb/ac
30 lb/dry ton

Drytons/ac = = 5dry to ns/ac