Environmental Engineering Reference
In-Depth Information
environment (e.g., toxins, pesticides, heavy metals). Treated biosolids
are land applied by either direct injection or application and plowing in
(incorporation).
10.8.1 sampling and Testing Process Control
Land application of biosolids requires precise control to avoid prob-
lems. The quantity and the quality of biosolids applied must be accurately
determined. For this reason, the operator's process control activities
include biosolids sampling and testing functions, such as determination
of percent solids, heavy metals, organic pesticides and herbicides, alkalin-
it y, total organic carbon (TOC), organic nitrogen, and ammonia nitrogen.
10.8.2 Process Control Calculations
Process control calculations include determining disposal cost,
plant available nitrogen (PAN), application rate (dry tons and wet tons
per acre), metals loading rates, maximum allowable applications based
on metals loading, and site life based on metals loading.
10.8.2.1 Disposal Cost
The cost of disposal of biosolids can be determined by:
Cost = Biosolids (wet tons/yr) × % Solids × Cost per dry ton
(10.27)
Example 10.30
Problem: The treatment system produces 1925 wet tons of biosolids for
disposal each year. The biosolids are 18% solids. A contractor disposes
of the biosolids for $28 per dry ton. What is the annual cost for sludge
disposal?
Solution:
Cost = 1925 wet tons/yr × 0.18 × $28/dry ton = $9702
10.8.2.2 Plant Available Nitrogen
One factor considered when land applying biosolids is the amount
of nitrogen in the biosolids available 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
( f 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
incorporating (plowing) the sludge into the soil. We provide volatiliza-
tion rates based on this example below:
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