Illinois Administrative Code › Title 35 - ENVIRONMENTAL PROTECTION › Part 391 - DESIGN CRITERIA FOR SLUDGE APPLICATION ON LAND › Subpart E - SAMPLE COLLECTION AND ANALYSIS › Appendix D - Sample Calculations of Sewage Sludge Application Rates

Current through Register Vol. 48, No. 28, July 12, 2024
I. Units and Conversions
Laboratory analyses are reported on either a wet
				  weight ("as-received") basis or on a dry weight basis. The units for a wet
				  weight basis are millgrams per liter (mg/l - weight per volume). The units for
				  a dry weight basis are milligrams per kilogram of solids (mg/kg - weight per
				  weight). Sludge represents a material in which most of the solid matter is
				  undissolved and the dissolved fraction is of minor importance. It is generally
				  simpler to perform sludge calculations by using dry weight units. Furthermore,
				  some calculations must ultimately be expressed in dry weight units to be
				  correct. For these reasons all the sample calculations are worked on a dry
				  weight basis. However, since may laboratories report results on a wet weight
				  basis, conversion relationships are provided below. Be aware that some
				  laboratories report results in mg/kg on an "as-received" basis. You should
				  consult the laboratory to confirm this and then convert the units to a dry
				  weight basis. Finally, note that the specific gravity of liquid and most dry
				  sludges can be assumed to be 1.0 (equal to water) and sufficient accuracy in
				  the calculations will be obtained.
A) The decimal equivalent (DE) of the percent
				  total solids equals the percentage divided by 100.
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B) Wet Weight to Dry Weight Basis
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C) Dry Weight to Wet Weight Basis
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D) Other useful conversions
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2) ppm x 0.002 = lb/ton
3) 10,000 ppm (or mg/l or mg/kg) = 1%
4) 1 acre = 43,560 square feet
5)
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6)
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7) 1 cubic yard of drying bed sludge is
				  approximately equal to 0.45 dry tons.
8) 1 mg/kg = 0.002 lb/ton
II. Assumptions for Sludge Calculations
A) Sludge will be surface applied with
				  incorporation by disking or chisel plowing.
B) Soils are non-sandy at the application
				  sites.
C) The sludge has been well stabilized by heat
				  anaerobic digestion.
D) Laboratory analysis of sludge (dwb):
5% TS
Total Kjeldahl Nitrogen (TKN) = 30,000
				  mg/kg
Ammonia Nitrogen = 10,000 mg/kg
Phosphorus = 8,000 mg/kg
Potassium = 3,500 mg/kg
Cadmium = 30 mg/kg
Copper = 2000 mg/kg
Manganese = 1000 mg/kg
Nickel = 400 mg/kg
Lead = 1000 mg/kg
Zinc = 4000 mg/kg
E) Corn for grain is grown and the average yield
				  is 110 bushels per acre per year.
III. Calculating Agronomic Nitrogen Application Rates of
				  Sludge
A) Determine the availability of nitrogen forms by
				  referring to Section
				  391.411.
1) Ammonia nitrogen plant availability is
				  80%.
2. Organic nitrogen plant availability is 20% for
				  the first year and decreases as shown in Table I.
B) First Year Application Rate
1) Organic nitrogen is not a laboratory test. It
				  is a calculated value as shown below.
Organic N = Total Kjeldahl N - Ammonia N
Organic N = 30,000 - 10,000 = 20,000 mg/kg
2) Calculate the plant available nitrogen (PAN) in
				  the sludge as follows:
Ammonia Nitrogen: 10,000 x 0.8 = 8,000
				  mg/kg
Organic Nitrogen: 20,000 x 0.2 = 4,000
				  mg/kg
PAN = 8,000 + 4,000 = 12,000 mg/kg
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This means that each dry ton of sludge solids will
				  have 24 pounds of nitrogen available for utilization by plants when the sludge
				  has been disked into the soil. Note that if the sludge has been injected into
				  the soil there would have been 28 pounds of plant available nitrogen provided.
				  If the sludge had been surface applied without incorporation there would have
				  been only 18 pounds of plant available nitrogen provided.
3) Calculate the agronomic nitrogen requirement
				  for the corn grain crop using the yield and the values from Appendix B - Table
				  IV:
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This means that each acre of corn with the stated
				  yield requires 143 pounds of plant available nitrogen for proper growth.
4) Calculate the sludge application rate needed to
				  provide the required plant available nitrogen.
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5) For convenience during the actual sludge
				  application it is usually helpful to convert the application rate into gallons
				  per acre.
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C) Second Year Application Rate
1) To simplify your calculations, assume that the
				  laboratory analysis remains the same as used for the first year application
				  rate calculations. However, note that nutrients and metal concentrations in
				  sludge will vary, often considerably.
2) Determine the amount of organic nitrogen (O.N.)
				  applied during the first year that is remaining for plant uptake during the
				  second year by using Table I values and the first year application of organic
				  nitrogen.
(20,000 mg/kg O.N.) x (0.20 ) = 4,000 mg/kg O.N.
				  used up first year
20,000-4,000 = 16,000 mg/kg Organic N remains for
				  second year use
(16,000 mg/kg) x (10%) = 1600 mg/kg O.N. available
				  during second year
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This represents:
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Therefore, the second year crop will need:
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3) Calculate the second year sludge application
				  rate.
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D) Third year application rate
1) In the third year some organic nitrogen applied
				  during the first and second years will become available for plant utilization;
				  5% and 10% respectively from Table I.
2) Determine the amount of organic nitrogen
				  applied during previous years that is available to plants during the third
				  year.
a) From the first year application:
(16,000 mg/kg O.N.) x (0.10 ) = 1600 mg/kg O.N.
				  used the second year
16,000-1600 = 14,400 mg/kg O.N. remaining from the
				  first year sludge application.
(14,400 mg/kg O.N.) x (5%) = 720 mg/kg O.N. is
				  available during the third year
This represents:
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b) From the second year application:
(20,000 mg/kg O.N.) x (0.20) = 4,000 mg/kg O.N.
				  used
20,000 - 4,000 = 16,000 mg/kg O.N. remains
(16,000 mg/kg) x (0.10) = 1600 mg/kg O.N.
				  available
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c) Sum the available organic nitrogen from
				  previous years application of sludge and subtract that sum from the crop
				  nitrogen requirements.
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d) Calculate the third year application rate.
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E) Fourth year application rate
1) In the fourth year some organic nitrogen
				  applied during the previous three years will become available for plant
				  utilization; 2.5 %, 5%, and 10% respectively from Table I.
2) Determine the amount of organic nitrogen
				  applied during previous years that is available to plants during the fourth
				  year.
a) From the first year application:
14,400-mg/kg O.N.) x (0.05) = 720 mg/kg used
				  during the third year.
14,400-720 = 13,680 mg/kg O.N. remaining
(13,680 mg/kg) x (2.5%) = 342 mg/kg O.N.
				  available
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b) From the second year application:
(16,000 mg/kg O.N.) x (0.10) = 1600 mg/kg O.N.
				  used
16,000-1600 = 14,400 mg/kg O.N. remains
(14,400 mg/kg) x (0.05) 720 mg/kg O.N.
				  available
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c) From the third year application:
(20,000 mg/kg O.N.) x (0.20) = 4,000 mg/kg O.N.
				  used
20,000-4,000 = 16,000 mg/kg O.N. remains
(16,000 mg/kg) x (0.10) = 1600 mg/kg O.N.
				  available
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d) Sum the available organic nitrogen from
				  previous years application of sludge and subtract that sum from the crop
				  nitrogen requirements.
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e) Calculate the fourth year application rate.
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F. Fifth year application rate
1) In the fifth year some of the organic nitrogen
				  applied during the previous four years will become available for plant
				  utilization; 1.25 %, 2.5%, 5%, and 10% respectively from Table I.
2) Determine the amount of organic nitrogen
				  applied during previous years that is available to plants during the fifth
				  year.
a) From the first year application:
(13,680 mg/kg) x (0.025 ) = 342 mg/kg used during
				  the fourth year.
13,680-342 = 13,338 mg/kg O.N. remaining
(13,338 mg/kg) x (0.0125 ) = 167 mg/kg O.N.
				  available
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b) From the second year application:
(14,400 mg/kg) x (0.05) = 720 mg/kg O.N.
				  used
14,400-720 = 13,680 mg/kg O.N. remaining
(13,680 mg/kg) x (0.025) = 342 mg/kg O.N.
				  available
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c) From the third year application:
(16,000 mg/kg) x (0.10) = 1600 mg/kg O.N.
				  used
16,000-1600 = 14,400 mg/kg O.N. remaining
(14,400 mg/kg) x (0.05) = 720 mg/kg O.N.
				  available
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d) From the fourth year application:
(20,000 mg/kg) x (0.20) = 4,000 mg/kg O.N.
				  used
20,000-4,000 = 16,000 mg/kg O.N. remaining
(16,000 mg/kg) x (0.010 ) = 1600 mg/kg O.N.
				  available
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e) Sum the available organic nitrogen from
				  previous years application of sludge and subtract that sum from the crop
				  nitrogen requirements.
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f) Calculate the fifth year application rate.
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G) During and after the sixth year there will not
				  be any significant amount of organic nitrogen available to the crop from sludge
				  applied during the first year. An equilibrium situation was reached in this
				  sample problem during the fourth year since there is practically no difference
				  between the fourth and fifth year application rates. A conservative operating
				  plan would be to apply sludge at approximately 4.8 dry tons per acre per year.
				  Note, however, that this would mean that additional nitrogen would be needed
				  from fertilizers during the first, second, and third years of sludge
				  application to meet the nitrogen requirement for the crop grown.
IV. Metal Loading Rate Calculations
A) It is useful to estimate the lifetime of a site
				  receiving sludge on the basis of metal loadings. The method for performing this
				  estimation is given below assuming the sludge chemical analysis provided the
				  following quantities.
Percent Solids = 5% (0.05 decimal equivalent)
Cadmium
30 mg/kg
Copper
2000 mg/kg
Nickel
400 mg/kg
Lead
1000 mg/kg
Zinc
4000 mg/kg
Manganese
1000 mg/kg
Application rate 4.8 dry tons/acre/year
B) Set up and complete a table as follows:
Metal
Sludge
Analysis
Loading
Factor
Annual Metal Loading
(lb/acre/year)
Maximum
Metal Loading
(lb/acre)
Site Life
(Years)
Cadmium
30 mg/kg
0.0096
0.29
10
34
Nickel
400 mg/kg
0.0096
3.84
100
26
Copper
2000 mg/kg
0.0096
19.2
250
13
Zinc
4000 mg/kg
0.0096
38.4
500
13
Manganese
2000 mg/kg
0.0096
19.2
900
46
Lead
1000 mg/kg
0.0096
9.6
1000
104
C) The loading factor column will be the same for
				  each metal and is calculated as follows:
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D) Multiply the metal analysis value by the
				  loading factor value (0.0096) to obtain the Annual Metal Loading (lb/acre/year)
				  column.
Divide the maximum metal loading for each metal
				  (from Table II, Section
				  391.420 ) by
				  the annual metal loading rate (pounds/acre/year) to obtain the site
				  lifetime.
E) This example indicates that the zinc and copper
				  loading is the most restrictive to the site lifetime. Therefore a site should
				  be used for no more than 13 years, however updated sludge analyses and
				  different application rates may change these site lifetimes. Records should be
				  kept on each site that sludge is applied to for each year's metal
				  loading.