Lin S.D. Water and Wastewater Calculations Manual

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of indicator organisms (fecal coliform) density; (2) biosolids are treated

in one of the processes to significantly reduce pathogens (PSRP); and

(3) use of the processes equivalent to PSRP.

Land application. Biosolids are applied to land, either to condition the

soil or to fertilize crops or other vegetation grown in the soil. Biosolids

can be applied to land in bulk or sold or given away in bags or other con-

tainers. The application sites may be categorized as nonpublic contact

sites (agricultural lands, forests, reclamation sites) and public contact

sites (public parks, roadsides, golf courses, nurseries, lawns, and home

gardens). In the United States, about half of the biosolids produced are

ultimately disposed of through land application.

Approximately one-third of the 5.4 million dry metric tons of waste-

water sludge produced annually in the US at POTWs is used for land

application. Of that, about two-thirds is applied on agricultural lands

(US EPA, 1995). Land application of wastewater sludge has been prac-

ticed for centuries in many countries, because the nutrients (nitrogen

and phosphorus) and organic matter in sludge can be beneficially uti-

lized to grow crops and vegetation. However, microorganisms (bacteria,

viruses, protozoa, and other pathogens), heavy metals, and toxic organic

chemicals are major public health concerns for land application of

biosolids. Proper management of biosolids utilization is required.

The application rate of biosolids applied to agricultural land must be

equal to or less than the “agronomic rate”. The agronomic rate is defined

in the Part 503 as the rate designed to provide the amount of nitrogen

needed by the crop or vegetation while minimizing the nitrogen in the

biosolids passing below the root zone of the crop or vegetation and flow-

ing to the groundwater.

Biosolids may be sprayed or spread on the soil surface and left on the

surface (pasture, range land, lawn, forest), tilled into the soil after being

applied, or injected directly below the surface. Land application of

biosolids must meet risk-based pollutant limits specified in the Part 503.

Operation standards are to control pathogens and to reduce the attrac-

tion of vectors. In addition, the application must meet the general require-

ments, management practices, and the monitoring, record keeping, and

reporting requirements.

All land application of biosolids must meet the ceiling concentration

limits for 10 heavy metals, listed in the second column of Table 6.28. If a

limit for any one of the pollutants is exceeded, the biosolids cannot be

applied to the land until such time that the ceiling concentration limits are

no longer exceeded.

Biosolids applied to the land also must meet either pollutant concen-

tration (PC) limits, cumulative pollutant loading rate (CPLR) limits, or

annual pollutant loading rate limits for these 10 heavy metals. Either

Wastewater Engineering 845

Class A or Class B pathogen requirements and site restrictions must be

met. Finally, one of 10 options for vector attraction reduction must also

be met.

Annual whole sludge application rate. The annual whole sludge applica-

tion rate (AWSAR) for biosolids sold or given away in a bag or other

container for application to land can be determined by dividing

the annual pollutant loading rate by pollutant concentration. It is

expressed as

(6.219)

where AWSAR ⫽ annual whole sludge application rate, metric

ton/(ha ⭈ yr)

APLR ⫽ annual pollutant loading rate, kg/(ha ⭈ yr)

(Table 6.28)

0.001 ⫽ a conversion factor, kg/metric ton or mg/kg

PC ⫽ pollutant concentration, mg/kg, dry weight

AWSAR 5

APLR

0.001 PC

846 Chapter 6

TABLE 6.28 Pollutant Limits for Land Application of Sewage Biosolids

Ceiling Annual pollutant

concentration Pollutant Cumulative loading rate

limits for all concentration pollutant loading limits (APLR),

biosolids applied (PC) limits, rate limits kg/ha over

Pollutant to land,mg/kg

∗

mg/kg

∗†

(CPLR), kg/ha 365-day period

Arsenic 75 41 41 2.0

Cadmium 85 39 39 1.9

Chromium 3000 1200 3000 150

Copper 4300 1500 1500 75

Lead 840 300 300 15

Mercury 57 17 17 0.85

Molybdenum

†

75 ⫺

‡

⫺

‡

⫺

‡

Nickel 420 420 420 21

Selenium 100 36 100 5.0

Zinc 7500 2800 2800 140

Applies to: All biosolids Bulk biosolids Bulk biosolids Bagged

that are land and bagged biosolids

applied biosolids

From Part 503, Table 1 Table 3 Table 2 Table 4

Section 503.13

∗

Dry-weight basis.

†

Monthly average: also include exceptional quality (EQ) biosolids.

‡

EPA is re-examining these limits.

Bagged biosolids are sold or given away in a bag or other container.

SOURCE: US EPA, 1994, 1995

Example: Ten heavy metals listed in Table 6.28 were analyzed in biosolids

to be sold. The chromium concentration is 240 mg/kg of biosolids. Determine

the AWSAR of chromium for the biosolids.

solution:

Step 1. Find APLR for chromium from Table 6.28

APLR ⫽ 150 kg/(ha ⭈ yr)

Step 2. Compute AWSAR for chromium, using Eq. (6.219)

Note: 1 lb/1000 ft

/y ⫽ 48.83 kg/ha/y; 1 ton/1000 ft

/y ⫽ 97.65 metric ton/ha/y

Site evaluation and selection. Details of site evaluation and the selection

process are discussed by Federal Register (1993) and by the US EPA

(1995). The discussion covers Part 503 requirements, preliminary plan-

ning, phases 1 and 2, site evaluation, and site screening.

Calculation of annual biosolids application rate on agricultural land.Sewage

sludge has been applied to agricultural land for a long time. The use

of biosolids in agricultural land can partially replace costly commercial

fertilizers. Generally, the intention is to optimize crop yields with appli-

cation of biosolids and if required, supplemental fertilizers. The annual

application rates of biosolids should not exceed the nutrients (N and P)

requirements of the crop grown on an agricultural soil. In addition, land

application of biosolids must meet the Part 503 requirements stated

above.

Calculation based on nitrogen. In order to prevent groundwater contam-

ination by ammonia nitrogen due to excess land application of biosolids,

Part 503 requires that bulk biosolids be applied to a site at a rate equal

to or less than the agronomic rate for nitrogen at the site.

5 1.28 ton/1000 ft

5 2560 lb/1000 ft

s125 metric ton/sha

yd 3 s2205 lb/metric tond

107,600 ft

/ha

5 125 metric ton/sha

150 kg/sha

0.001 kg/smetric ton

smg/kgdd 3 1200 mg/kg

AWSAR 5

APLR

0.001 PC

PC 5 1200 mg/kg

Wastewater Engineering 847

Nitrogen may be present in biosolids in inorganic forms such as

ammonium (NH

) or nitrate (NO

), or in organic forms. NO

-N is the

most water-soluble form of N, and is of most concern for groundwater

contamination. NH

-N can readily be volatilized as ammonia. Inorganic

N is the plant available nitrogen (PAN). Not all the N in biosolids is

immediately available for crop use, because some N is present as diffi-

culty decomposable (refratory) organic N (Org-N), Org-N ⫽ total N ⫺

(NO

-N) ⫺ (NH

-N) which is in microbial cell tissue and other organic

compounds. Organic N must be decomposed into mineral or inorganic

forms, such as NH

-N and NO

, before it can be used by plants. Thus,

the availability of Org-N for crops depends on the microbial breakdown

of organic materials (biosolids, manure, crop residuals, soil organics, etc.)

in soil.

When calculating the agronomic N rate for biosolids, the residual N

from previously applied biosolids that will be mineralized and released as

PAN must be accounted for as part of the overall budget for the total PAN.

The residual N credit can be estimated for some sites undergoing soil

nitrate tests, but the PAN credit is commonly estimated by multiplying a

mineralization factor (K

min

) by the amount of biosolids Org-N still remain-

ing in the soil 1 or 2 years after biosolids application. Mineralization fac-

tors for different types of biosolids may be found in Table 6.29.

Example 1: An aerobic digested biosolid with 2.8% of organic nitrogen was

applied at a rate of 4.5 dry ton per acre for the 1997 growing season. No other

biosolids were applied to the same land in 1998. Determine the amount of

plant-available nitrogen that will be mineralized from the biosolids Org-N in

1997 for the 1999 growing season.

solution:

Step 1. Calculate the biosolids Org-N applied in 1997

Org-N ⫽ 4.5 ton/acre ⫻ (2.8%/100%) ⫻ 2000 lb/ton

⫽ 252 lb/acre

848 Chapter 6

TABLE 6.29 Estimated Mineralization Rate for Various Type of Sewage Sludge

Unstablized

primary and Aerobically Anaerobically

Year of growing season WAS digested digested Composted

0–1 (year of application) 0.40 0.30 0.20 0.1

1–2 0.20 0.15 0.10 0.05

2–3 0.10 0.08 0.05 –

3–4 0.05 0.04 – –

SOURCE: Sommers et al. (1981)

Step 2. Determine Org-N released as PAN in 1999 growing season

Construct a PAN credit for the application year, 1 year, and 2 years later for

growing seasons as follows:

Answer: Org-N released as PAN in 1999 ⫽ 12 lb/acre (as bold shown above).

The NH

-N and N0

-N added by biosolids is considered to be available

for plant use. Plant-available nitrogen comprises NH

-N and N0

-N pro-

vided by biosolids and by fertilizer salts or other sources of these mineral

forms of N.

When biosolids or animal manure are applied on a soil surface, the

amount of PAN is reduced by the amount of NH

-N lost by volatilization of

ammonia. The volatilization factor, K

vol

is used for estimating the amount

of NH

-N.

The PAN of biosolids for the first year of application may be deter-

mined as

PAN ⫽ (NO

-N) ⫹ K

vol

(NH

-N) ⫹ K

min

(Org-N) (6.220)

where PAN ⫽ plant available N in biosolids, lb/dry ton

-N ⫽ nitrate N content in biosolids, lb/dry ton

vol

⫽ volatilization factor, or fraction of NH

-N not lost as

gas

⫽ 0.5 for liquid and surface applied

⫽ 1.0 for liquid and injection into soil

⫽ 0.5 for dewatered and surface applied

-N ⫽ ammonium N content in biosolids, lb/dry ton

min

⫽ mineralization factor, or fraction of Org-N converted

to PAN, Table 6.29

Org-N ⫽ organic N content in biosolids, lb/dry ton

⫽ Total N – (NO

-N) – (NH

-N)

Org-N, lb/acre

Year of growing season Mineralization rate Starting Mineralized Remaining

(1) (2) (3) (4) (5)

0–1 (1997 application) 0.30 252 76 176

1–2 (1998) 0.15 176 26 150

2–3 (1999) 0.08 150 12 138

Notes: 1. Values of col. 2 are from Table 6.29

2. Col. 4 ⫽ col. 2 ⫻ col. 3

3. Col. 5 ⫽ col. 3 ⫺ col.4

4. 1 lb/acre ⫽ 1.12 kg/ha

Wastewater Engineering 849

Example 2: An anaerobically digested and dewatered biosolid is to be sur-

face applied on an agricultural land. The biosolids analysis of N content is:

⫺ N ⫽ 1500 mg/kg, NH

-N ⫽ 1.2%, and total N ⫽ 3.7%, based on the

dry weight. The solids content of the biosolids is 4.3%. Determine PAN.

solution:

Step 1. Convert N forms into lb/dry ton

-N ⫽ 1500 mg/kg ⫽ 1.500 ⫻ 10

–3

kg/kg

⫽ 1.5 ⫻ 10

–3

lb/lb

⫽ 3 lb/ton

-N ⫽ 2000 lb/ton ⫻ 1.2%/100%

⫽ 24 lb/ton

Total N ⫽ 2000 lb/ton ⫻ 0.037 ⫽ 74 lb/ton

Org-N ⫽ Total N – (NO

-N) ⫺ (NH

-N)

⫽ (74 – 3 – 24) lb/ton

⫽ 47 lb/ton

Step 2. Compute PAN

For dewatered biosolids and surface applied, K

vol

⫽ 0.5.

Referring to Table 6.29, K

min

⫽ 0.20 for the first year.

Using Eq. (6.220),

PAN ⫽ NO

-N ⫹ K

vol

(NH

-N) ⫹ K

min

(Org-N)

⫽ 3 lb/ton ⫹ 0.5 (24 lb/ton) ⫹ 0.2 (47 lb/ton)

⫽ 24.4 lb/ton

Note: 1 lb/ton ⫽ 0.5 kg/metric ton ⫽ 0.5 mg/kg

It is necessary to determine the adjusted fertilizer N rate by subtracting

“total N available from existing, anticipated, and planned sources” from the

total N requirement. The procedures to compute the adjusted fertilizer N

requirement for the crop to be grown may be summarized as follows (US

EPA, 1995).

1. Determine the total N requirement (lb/ton) of crop to be grown. This

value can be obtained from the Cooperative Extension Service of agri-

cultural agents or universities, USDA-Natural Resources Conservation

Service, or other agronomy professionals.

2. Determine N provided from other N sources added or mineralized in

the soil

a. N from a previous legume crop (legume credit) or green manure crop

b. N from supplemental fertilizers already added or expected to be added

850 Chapter 6

c. N that will be added by irrigation water

d. Estimate of available N from previous biosolids application (Example 1)

e. Estimate of available N from previous manure application

f. Soil nitrate test of available N present in soil [this quantity can be sub-

stituted in place of (a ⫹ d ⫹ e) if test is conducted properly; do not use

this test value if estimates for a, d, and e are used]

Total N available from existing, expected, and planned sources of N ⫽ a

⫹ b ⫹ c ⫹ d ⫹ e or ⫽ b ⫹ c ⫹ f

3. Determine the loss of available N by denitrification, immobilization, or

fixation

Check with state regulatory agencies for approval before using this site-

specific factor.

4. Compute the adjusted fertilizer N required for the crop to be grown

N required ⫽ step 1 ⫺ step 2 ⫹ step 3

Finally, the agronomic N application rate of biosolids can be calculated

by dividing the adjusted fertilizer N required (step 4 above) by PAN

(using Eq. (6.220)).

Example 3: Determine the agronomic N rate from Example 2, assuming the

adjusted fertilizer N rate is 61 lb/acre (68.3 kg/ha). The solids content of the

biosolids is 4.3%.

solution:

Step 1. Compute agronomic N rate in dry ton/acre

Rate ⫽ (adj. fert. N rate) ⫼ PAN

⫽ (61 lb/acre) ⫼ (24.4 lb/ton)

⫽ 2.5 dry ton/acre

Step 2. Convert agronomic N rate in dry ton/acre to wet gal/acre

Rate ⫽ (2.5 dry ton/acre) ⫼ (4.3 dry ton/100 wet ton)

⫽ 58 wet ton/acre

⫽ (58 wet ton/acre) (2000 lb/wet ton) (1 gal/8.34 lb)

⫽ 13,900 gal/acre

Note: 1 gal/acre ⫽ 9.353 L/ha

Calculation based on phosphorus. The majority of phosphorus (P) in

biosolids is present as inorganic forms, resulting from mineralization of

biosolids organic matter. Generally, the P concentration in biosolids is

considered to be about 50% available for plant uptake, as is the P normally

Wastewater Engineering 851

applied to soils with commercial fertilizers. The P fertilizer required for

the crop to be grown is determined from the soil fertility test for avail-

able P and the crop yield. The agronomic P rate of biosolids for land

application is expressed as (US EPA, 1995)

Agronomic P rate ⫽ P

req

⫼ (available P

/dry ton) (6.221)

where P

req

⫽ P fertilizer recommended for harvested crop, or the

quantity of P removed by the crop

Available P

⫽ 0.5 (total P

/dry ton) (6.222)

Total P

/dry ton ⫽ % of P in biosolids ⫻ 20 ⫻ 2.3 (6.223)

where 20 ⫽ 0.01 (⫽ 1%) ⫻ 2000 lb/ton

2.3 ⫽ MW ratio of P

: P

⫽ 142 : 62⫽2.3 : 1

If biosolids application rates are based on the crop’s P requirement,

supplemental N fertilization is needed to optimize crop yield for nearly

all biosolids applications.

Calculation based on pollutant limitation. Most biosolids are likely to contain

heavy metals concentrations that do not exceed the Part 503 pollutant

concentration limits. Therefore, pollutant loading limits are not a limit-

ing factor for determining annual biosolids application rates on agricul-

tural lands. Biosolids meeting pollutant concentration limits, as well as

certain pathogen and vector attraction reduction requirements, gener-

ally are subject to meet the the CPLRs requirement. A CPLR is the max-

imum amount of a pollutant that can be applied to a site by all bulk

biosolids applications after July 20, 1993. When the maximum CPLR is

reached at the application site for any one of the 10 metals regulated by

Part 503 (molybdenum was deleted with effect from February 25, 1994),

no more additional biosolids are allowed to be applied to the site.

For some biosolids with one or more of the pollutant concentrations

exceeding the Part 503 pollutant concentration limits, the CPLRs as

shown in Table 6.30 must be met. In these cases, the CPLRs could even-

tually be the limiting factor for annual biosolids applications rather

than the agronomic (N or P) rate of application.

For biosolids meeting the Part 503 CPLRs, the maximum total quan-

tity of biosolids allowed to be applied to a site can be calculated on the

basis of the CPLR and the pollutant concentration in the biosolids as

follows:

Maximum allowed in dry ton/acre

⫽ (CPLR in lb/acre) ⫼ [0.002 (mg pollutant/kg dry biosolids)] (6.224)

852 Chapter 6

After computing for each of the eight or nine pollutants regulated by the

Part 503, the lowest total biosolids value will be used as the maximum

quantity of biosolids permitted to be applied to the site. The individual

pollutant loading applied by each biosolids application can be calcu-

lated by

lb of pollutant/acre ⫽ biosolids application rate in dry ton/acre

⫻ (0.002 mg/kg) (6.225)

The pollutant loading for each individual biosolid application must be

calculated and recorded to keep a cumulative summation of the total

quantity of each pollutant that has been applied to each site receiving

the biosolids.

Supplemental K fertilizer. After the agronomic application rate of

biosolids has been determined, the amounts of plant available N, P, and

K added by the biosolids must be computed and compared to the fer-

tilizer recommendation for the crop grown at a specified yield level. If

one or more of these three nutrients provided by the biosolids is less

than the amount recommended, supplemental fertilizers are needed to

achieve crop yield.

Potassium, K, is a soluble nutrient. Most of the concentration of K in

raw wastewater is discharged with the treatment plant effluents.

Generally, biosolids contain low concentrations of potassium, which is

one of the major plant nutrients. Fertilizer potash (K

O) or other sources

Wastewater Engineering 853

TABLE 6.30 Part 503 Cumulative Pollutant Loading Rate Limits

CPLR limits

Pollutant kg/ha lb/acre

Arsenic 41 37

Cadmium 39 35

Chromium

∗

3000 2700

Copper 1500 1300

Lead 300 270

Mercury 17 15

Molybdenum

†

⫺⫺

Nickel 420 380

Selenium 100 90

Zinc 2800 2500

∗

The chromium limit will most likely be deleted from the Part 503

rule.

†

The CRLR for Mo was deleted from Part 503 with effect from

February 25, 1994.

of K usually are needed to supplement the amounts of K

O added by

biosolids application.

Because K is readily soluble, all the K in biosolids is considered to be

available for crop growth. The quantity of K

O provided (credited) by

biosolids application can be calculated as

O added by biosolids ⫽ applied rate in dry ton/acre

⫻ avail. K

O in lb/dry ton (6.226)

where

Available K

O ⫽ % of K in biosolids ⫻ 20 ⫻ 1.2 (6.227)

where 20 ⫽ 2000 lb/dry ton ⭈ %

1.2 ⫽ K

O/K

⫽ 94/78

Example 4: A K fertilizer recommendation for a soybean field is 150 lb

O/acre. The agronomic N rate of biosolid application is 1.5 dry ton/acre. The

biosolid contains 0.5% K. Compute the supplemental (additional) K

required.

solution:

Step 1. Compute the available K

O, using Eq. (6.227)

Available. K

O ⫽ 0.5 ⫻ 20 lb/dry ton ⫻ 1.2

⫽ 12 lb/dry ton

Step 2. Compute K

O added by biosolids, using Eq. (6.226)

Biosolids K

O applied ⫽ biosolids rate ⫻ available K

⫽ 1.5 dry ton/acre ⫻ 12 lb/dry ton

⫽ 18 lb/acre

Step 3. Compute supplemental K

O needed

Additional K

O needed ⫽ recommended – biosolids added

⫽ 150 lb/acre ⫺ 18 lb/acre

⫽ 132 lb/acre

Note: 1 lb/acre ⫽ 1.12 kg/ha

Example 5: (This example combines Examples 1 to 4 and more) Determine

biosolid annual application for the 1999 growing season for an agricultural

site on the basis of the agronomic N rate, P rate, and long-term pollutant

limitations required by Part 503. Also determine the supplemental nutrients

to be added. An anaerobically digested liquid biosolid is designed to be applied

854 Chapter 6