Pathogen and Vector Attraction Reduction

Pathogens are disease-causing organisms such as certain bacteria, fungi, viruses, protozoans and their cysts, and intestinal parasites and their ova. Vector attraction is the characteristic of sewage sludge that attracts rodents, flies, mosquitoes, or other organisms capable of transporting infectious agents. Subpart D of Part 503 covers alternatives for reducing pathogens in sewage sludge and domestic septage, as well as options for reducing the characteristic of sewage sludge that attracts vectors.

The pathogen and vector attraction reduction requirements apply to bio-solids and their application to or placement on the land for beneficial use or disposal. Depending on how biosolids are used or disposed of and which pathogen reduction alternative and vector attraction reduction options are relied on, compliance with pathogen and vector attraction requirements is the responsibility of:

• The generator of biosolids that are either land applied or surface disposed

• The person who derives a material from biosolids that are either land applied or surface disposed

• The person who applies biosolids to land or places biosolids on a surface disposal site

• The owner or operator of a surface disposal site

Pathogen Reduction Alternatives Biosoilds are classified as class A or B based on the level of pathogens present in biosolids that are used or disposed of. Biosolids meet class A designation if pathogens are below detectable levels. All biosolids that are sold or given away in a bag or other container for application to land, lawns, or home gardens must meet class A pathogen requirements. Biosolids are designated class B if pathogens are detectable but have been reduced to levels that do not pose a threat to public health and the environment as long as actions are taken to prevent exposure to the biosolids after their use or disposal. All biosolids that are land applied or placed on surface disposal sites (except sludge placed on a surface disposal site that is covered with soil or other material) must meet class B pathogen requirements. In general, class A corresponds to Part 257, process to further reduce pathogens (PFRP), designation, and class B corresponds roughly to Part 257, process to significantly reduce pathogens (PSRP), designation.

Class A Pathogen Requirements Part 503 lists six alternatives for treating wastewater sludge to meet class A requirements with respect to pathogens. These alternatives are summarized in Table 1.6, and a short description of each alternative follows. All six alternatives must meet one of the two following criteria at the time biosolids are used or disposed of, prepared for sale or

TABLE 1.6 Summary of Alternatives for Meeting Class A Pathogen Requirements

Alternative 1: Thermally Treated Biosolids

Biosolids must be subjected to one of four time-temperature regimes.

Alternative 2: Biosolids Treated in a High-pH/High-Temperature Process

Biosolids must meet specific pH, temperature, and air drying requirements.

Alternative 3: Biosolids Treated in Other Known Processes

It must be shown that the process can reduce enteric viruses and viable helminth ova. Operating conditions used in the demonstration should be maintained after pathogen reduction demonstration has been completed.

Alternative 4: Biosolids Treated in Unknown Processes

Biosolids must be treated for pathogens—Salmonella sp. or fecal coliform bacteria, enteric viruses, and viable helminth ova—at the time the biosolids are used or disposed of, or in ceratain situations, prepared for use or disposal.

Alternative 5: Biosolids Treated in a PFRP

Biosolids must be treated by one of the processes to further reduce pathogens (PFRPs) (see Table 1-8).

Alternative 6: Biosolids Treated in a Process Equivalent to a PFRP

Biosolids must be treated by a process equivalent to one of the PFRPs, as determined by the permitting authority.

giveaway in a bag or other container for land application, or prepared to meet EQ requirements:

• The density of fecal coliform in the biosolids must be less than 1000 MPN (most probable number) per gram of total solids (dry weight basis); or

• The density of Salmonella sp. bacteria in the biosolids must be less than 3 MPN per 4 g of total solids (dry weight basis).

Alternative 1: Thermally Treated Biosolids This alternative applies when specific thermal heating procedures are used to reduce pathogens. The length of heating time at a given temperature needed to obtain class A pathogen reduction is determined by equations for each of the four thermal heating regimes, which are shown in Table 1.7. Any one of the four regimes may be used. Frequency of monitoring for pathogens is same as in Table 1.5.

Alternative 2: Biosolids Treated in a High-pH/High-Temperature Process This alternative describes conditions of a specific temperature-pH process that is effective (usually by alkaline treatment) in reducing pathogens to below detectable levels. The frequency of monitoring for pathogens is same as in Table 1.5. The process conditions required are:

TABLE 1.7

Thermal Heating Regimes for Class A Pathogen Reduction Under Alternative 1

Time-Temperature

Regime

Applies to:

Requirement

Relationship2

A

Biosolids with 7% solids or

Temperature of biosolids

D = 131700,000/10al4i

greater (except those

must be 50°C or higher for

covered by Regime B)

20 minutes or longer

B

Biosolids with 7% solids or

Temperature of biosolids

D = 131,700,000/10al4i

greater in the form of small

must be 50°C or higher for

particles and heated by

15 seconds or longer

contact with either warmed

gases or an immiscible liquid

C

Biosolids with less than 7% solids

Heated for at least 15 seconds

D = 131,700,000/10al4i

but less than 30 minutes

D

Biosolids with less than 7% solids

Temperature of sludge is 50°C

D = 50,070,000/10°'14i

or higher with at least

30 minutes or longer contact

time

Source-. U.S. EPA, 1994. " D, time in days; t, temperature in °C.

• Elevating the pH of the biosolids to greater than 12 (measured at 25°C) for a minimum of 72 hours

• Maintaining the temperature above 52°C for a minimum of 12 hours during the period when the pH is greater than 12

• Air drying to at least 50% solids after the 72-hour period of elevated pH

Alternative 3: Biosolids Treated in Other Known Processes The purpose of this alternative is to demonstrate that a new treatment process fully meets the class A pathogen requirements. The presence of enteric viruses and viable helminth ova has to be shown in the sludge prior to the treatment (as sludge in some treatment plants may not contain enteric viruses or helminth ova) to document the effectiveness of the treatment process. Subsequent testing for enteric viruses and helminth ova is not required whenever the tested set of operating parameters has been met. The values for enteric viruses and helminth ova that have to be achieved during the demonstration are:

• Enteric viruses: less than 1 plaque-forming unit per 4 g of total solids (dry weight basis)

• Helminth ova: less than 1 viable ovum per 4 g of total solids (dry weight basis)

If no enteric viruses or viable helminth ova are present in the biosolids before treatment, it is class A with respect to enteric viruses or viable helminth ova, or both, until the next sampling episode, at which time another sample of the biosolids has to be tested for those organisms. The frequency of monitoring for both enteric viruses and viable helminth ova is once per year, quarterly, bimonthly, or monthly until it is demonstrated that the limits stated have been achieved for some period of time, as determined by the permitting authority. Monitoring for fecal coliform or Salmonella sp. bacteria is always required at the frequency in Table 1.5.

Alternative 4: Biosolids Treated in Unknown Processes This alternative is used when the wastewater solids have been treated using a newly developed or innovative treatment process. The biosolids must meet the same pathogen test results as in alternative 3. If the biosolids meet those requirements at the time of disposal, the biosolids meet class A requirements. To continue to be class A, the pathogen requirements have to be met in every sample of biosolids that is collected. The frequency of monitoring for the pathogens is once per year, quarterly, bimonthly, or monthly, as determined by the permitting authority.

Alternative 5: Biosolids Treated in a PFRP This alternative states that biosolids are considered class A if they are treated in one of the PFRPs listed in Table 1.8 and the class A fecal coliform or Salmonella sp. requirement is met.

TABLE 1.8 Process to Further Reduce Pathogens

1. Composting

Using either the within-vessel composting method or the static aerated composting method, the temperature of the sludge is maintained at 55°C or higher for 3 days.

Using the windrow composting method, the temperature of the sludge is maintained at 55°C or higher for 15 days or longer. During the period the compost is maintained at 55°C or higher, there shall be a minimum of five turnings of the windrow.

2. Heat Drying

Sludge is dried by direct or indirect contact with hot gases to 90% solids or greater. Either the temperature of the sludge particles exceeds 80°C or the wet bulb temperature of the gas in contact with the sludge as the sludge leaves the dryer exceeds 80°C.

3. Heat Treatment

Liquid sludge heated to a temperature of 180°C or higher for 30 minutes.

4. Thermophilic Aerobic Digestion

Liguid sludge is agitated with air or oxygen to maintain aerobic conditions, and the mean cell residence time of the sludge is 10 days at 55 to 60°C.

5. Beta-Ray Irradiation

Sludge is irradiated with beta rays from an accelecometer at dosages of at least 1.0 Mrad at room temperature (about 20°C).

6. Gamma-Ray Irradiation

Sludge is iradiated with gama rays from certain isotopes, such as cobalt 60 and cesium 137, at room temperature (about 20°C).

7. Pasteurization

The temperature of the sludge is maintained at 70°C or higher for 30 minutes or longer.

Source: Appendix B of 40 CFR Part 503.

To meet these requirements, the treatment process must be operated according to the conditions listed in the table.

Alternative 6: Biosolids Treated in a Process Equivalent to a PFRP Under this alternative, biosolids are considered class A if they are treated by any process determined by the permitting authority to be equivalent to a PFRP. To be equivalent, the treatment process must be able to meet class A status consistently with respect to enteric viruses and viable helminth ova. The EPA's Pathogen Equivalency Committee is available as a resource to provide recommendations to the permitting authority on equivalency determinations.

TABLE 1.9 Summary of Alternatives for Meeting Class B Pathogen Requirements

Alternative 1: Monitoring of Indicator Organisms

Test for fecal coliform density as an indicator for all pathogens. Seven representative samples of the biosolids that is used or disposed shall be collected. The geometric mean of the seven samples shall be less than 2 million MPN per gram of total solids (dry weight basis), or less than 2 million colony-forming units (CFU) per gram of total solids (dry weight basis).

Alternative 2: Biosolids Treated in a PSRP

Sludge must be treated by one of the PSRPs listed in Table 1.10. Unlike the comparable class A requirement, this alternative does not require microbial monitoring for regrowth of fecal coliform or Salmonella sp. bacteria.

Alternative 3: Biosolids Treated in a Process Equivalent to a PSRP

Sludge must be treated in a process equivalent to one of the PSRPs, as determined by the permitting authority. The EPA Pathogen Equivalency Committee is available as a resource to provide recommendations to the permitting authorities on equivalency determinations.

Class B Pathogen Requirements For biosolids to be classified as class B with respect to pathogens, the requirements in one of the three alternatives listed in Table 1.9 must be met. Class B biosolids may contain some pathogens. Therefore, requirements for land application of class B biosolids also include site restrictions that prevent crop harvesting, animal grazing, and public access for a certain time until environmental conditions have further reduced pathogens. Site restrictions for land application of class B biosolids are summarized in the land application subpart of Part 503. The process to significantly reduce pathogens is summarized in Table 1.10.

Vector Attraction Reduction Options Vectors, which include flies, mosquitoes, and rodents, can transmit pathogens to humans physically through contact or biologically by playing a specific role in the life cycle of the pathogens. Reducing the attractiveness of biosolids to vectors or preventing the biosolids from coming into contact with vectors reduces the potential for transmitting diseases from pathogens in biosolids. The 12 options in Part 503 for reducing vector attraction are summarized in Table 1.11, and the applicability of the options is presented in Table 1.12. Option 12 applies only to domestic septage. Options 1 through 8 and 12 are designed to reduce the attractiveness of the material to vectors, and options 9 through 11 are designed to prevent vectors from coming into contact with the material.

TABLE 1.10 Process to Significantly Reduce Pathogens

1. Aerobic Digestion

Sludge is agitated with air or oxygen to maintain aerobic conditions for a specific mean cell residence time at a specific temperature. Values for the mean cell residence time and temperature shall be between 40 days at 20°C and 60 days at 15°C.

2. Air Drying

Sludge is dried on sand beds or on paved or unpaved basins. The sludge dries for a minimum of three months. During two of the three months, the ambient average daily temperature is above 0°C.

3. Anaeobic Digestion

Sludge is treated in the absence of air for a specific mean cell residence time at a specific temperature. Values for the mean cell residence time and temperature shall be between 15 days at 35 to 55°C and 60 days at 20°C.

4. Composting

Using either the within-vessel, static aerated pile, or windrow composting method, the temperature of the sludge is raised to 40°C or higher and remains at 40°C or higher for 5 days. For 4 hours during the 5 days, the temperature in the compost pile exceeds 55°C.

5. Lime Stabilization

Sufficient lime is added to the sludge to raise the pH of the sludge to 12 after 2 hours of contact.

Source: Appendix B of 40 CFR Part 503.

TABLE 1.11 Summary of Options for Meeting Vector Attraction Reduction

Option 1: Meet 38% reduction in volatile solids content. This percentage is the amount of volatile solids reduction attained by anaerobic or aerobic digestion.

Option 2: Demonstrate vector attraction reduction with additional anaerobic digestion in a bench-scale unit. Frequently, sludge that has been recycled through the biological treatment unit of a wastewater treatment plant or that has resided for long periods of time in the wastewater collection system undergoes substantial biological degradation. Under these circumstances, the 38% reduction required by option 1 might not be possible. This option allows the operator to demonstrate vector attraction reduction by testing a portion of the previously digested sludge in a bench-scale unit in the laboratory. Vector attraction reduction is achieved if after anaerobic digestion for an additional 40 days at a temperature of 30 to 37°C, the volatile solids in the sludge are reduced by less than 17% from the beginning to the end of the bench test.

Option 3: Demonstrate vector attraction reduction with additional aerobic digestion in a bench-scale unit. This option is appropriate for aerobically digested sludge that cannot meet the 38% volatile solids reduction required by option 1. This includes sludge from extended aeration plants, where the minimum residence time of waste activated sludge solids generally exceeds 20 days. Under this option, aerobically digested sludge with 2% or less solids has achieved vector attraction reduction if after 30 days of aerobic digestion at 20°C in a bench test, volatile solids are reduced by less than 15%.

40 CFR PART 503 REGULATION TABLE 1.11 Continued

Option 4: Meet a specific oxygen uptake rate (SOUR) for aerobically digested sludge. SOUR is the mass of oxygen consumed per unit time per unit mass of total solids in the sludge on a dry weight basis. Reduction in vector attraction can be demonstrated if the SOUR of the sludge, determined at 20°C, is equal to or less than 1.5 mg of oxygen per hour per gram of total solids. This test is only applicable to liquid sludge withdrawn from an aerobic process.

Option 5: Use an aerobic process at greater than 40°C for 14 days or longer. This option applies primarily to composted biosolids that also contain partially decomposed organic bulking agents.

Option 6: Add alkali under the conditions specified. Vector attraction reduction is achieved by:

• Raising the pH of the sludge to 12 or higher by adding alkali

• Maintaining pH at 12 or higher for at least 2 hours without the addition of more alkali

• Maintaining the pH at 11.5 or higher for another 22 hours without the addition of more alkali

Option 7: Dry sludge with no unstabilized solids to at least 75% solids. Under this option, vector attraction reduction is achieved if the sludge does not contain unstabilized solids and if the solids content of the sludge is at least 75% before it is mixed with other materials. Thus, the reduction must be achieved by removing water, not by adding inert materials.

Option 8: Dry sludge with unstabilized solids to at least 90% solids. If the sludge contains unstabilized solids, increasing the solids content by 90% or greater adequately reduces vector attraction. The solids increase should be achieved by removal of water, not by adding inert solids.

Option 9: Inject biosolids beneath the soil surface. Injection beneath the soil surface places a barrier of earth between the biosolids and the vectors. Under this option, vector attraction reduction is achieved:

• If no significant amount of biosolids remain on the land surface 1 hour after the injection of the biosolids

• If the biosolids is class A with respect to pathogens, they are injected within 8 hours after they are discharged from the pathogen reduction process.

Option 10: Incorporate biosolids into the soil within 6 hours of application to or placement on the land. If the biosolids are class A with respect to pathogens, the time between processing and application to or placement on the land must not exceed 8 hours.

Option 11: Cover biosolids placed on a surface disposal site with soil or other material at the end of each operating day. In addition to creating a physical barrier between the biosolids and the vectors, covering also helps meet pathogen requirements by allowing environmental conditions to reduce pathogens.

Option 12: Treat domestic septage with alkali to pH 12 or above for 30 minutes without adding more alkaline material.

TABLE 1.12 Vector Attraction Reduction Options for Each Use or Disposal Practice

, Vector Attraction Reduction Option

Practice 123456789 10 11 12

Bulk biosolids applied to XXXXXXXXXX

agricultural land, forest, public contact sites, or reclamation sites

Bulk biosolids applied to XXXXXXXX

lawns or home gardens

Biosolids sold or given away XXXXXXXX

in a bag or other container for application to the land.

Surface disposal XXXXXXXXXX X X

1.2.5 Incineration

Incineration of wastewater sludge is the firing of sludge at high temperatures in an enclosed device called an incinerator (furnace). The most commonly used incinerators are multiple-hearth, fluidized-bed, and electric infrared furnaces. An incinerator system consists of an incinerator and one or more air pollution control devices, which are used either to remove small particles and the adhering metals in the exhaust gas from the incinerator or to further decompose organics. Wet scrubbers, dry and wet electrostatic precipitators, and fabric filters are metal-removing air pollution control devices. Afterburners, another type of air pollution control device, are used to burn organics in exhaust gases more completely.

Subpart E of Part 503 covers requirements for wastewater sludge incineration, including pollutant limits for metals, limits for total hydrocarbons, general requirements and management practices, and monitoring, record-keeping, and reporting requirements. Anyone who fires sewage sludge in an incinerator, except as listed below, must meet the requirements in Subpart E:

• Nonhazardous ash generated from the incineration of sewage sludge is not covered by Part 503. Instead, it must be disposed in accordance with the solids waste disposal regulations in 40 CFR Part 258. If the ash is applied to land or placed on land other than a municipal solid waste landfill, the regulations in 40 CFR Part 257 govern.

• Auxiliary fuel is often used to enhance the burning of sewage sludge. Auxiliary fuels include natural gas, fuel oil, grit, screening, scum, coal, and municipal solid waste. If municipal solid waste account for more than 30% on a dry weight basis of the mixture of sludge and auxiliary fuel, the municipal solid waste is not considered an auxiliary fuel under Part 503. Instead, 40 CFR Parts 60 and 61 would regulate the process.

• Hazardous wastes are not considered auxiliary fuels. Such a process is covered by 40 CFR Parts 261 through 268.

Pollutant Limits Subpart E regulates five metals in sewage sludge before incineration: lead, arsenic, cadmium, chromium, and nickel. Subpart E contains equations for calculating pollutant limits for these five metals based on site-specific conditions. These conditions include dispersion factor, incinerator control efficiency, and sludge feed rate. In addition to the five metals noted above, emission of beryllium and mercury are regulated by the National Emission Standards for Hazardous Air Pollutants (NESHAP) per 40 CFR Part 61. The NESHAP limit for the emission of beryllium is 10 g during any 24-hour period from each incinerator. The limit for mercury emitted into the atmosphere from all incinerators at a given site is 3200 g during any 24-hour period.

Organic compounds that are emitted as a result of incomplete combustion or the generation of combustion by-products such as benzene, phenol, and vinyl chloride can be present in incinerator emissions. Part 503 regulates the emission of organic pollutants through an operational standard that limits the amount of total hydrocarbons (THCs) allowed in the incinerator stack gas. The stack gas must meet a monthly average limit of 100 ppm of THCs. The monthly average concentration is the arithmetic mean of the hourly averages. The hourly averages must be calculated based on at least two readings taken each hour that the incinerator operates. The THC concentration must also be corrected for 0% moisture and 7% oxygen.

Management Practices The management practices for sludge incineration are as follows:

• Instruments must be used that continuously measure and record:

• THC concentration

• Oxygen levels

• Information needed to calculate moisture content in the stack exit gas

• Combustion temperature in the furnace

• Instruments must be installed, calibrated, operated, and maintained according to the guidance provided by the permitting authority. The instrument used for THC measurement must:

• Use a flame ionization detector

• Have a sampling line heated to 150°C or higher at all times

• Be calibrated at least once every 24-hour operating period using propane

• The incinerator must not be operated above the maximum combustion temperature set by the permitting authority based on performance test conditions.

• Conditions for operating the air pollution control devices, which are also set by the permitting authority based on performance test conditions, must be followed.

• Sludge may not be incinerated if it is likely to affect a threatened species or its critical habitat negatively, as listed in the Endangered Species Act.

Frequency of Monitoring Table 1.13 shows the monitoring frequency for sludge incinerators. Monitoring frequencies for arsenic, cadmium, chromium, lead, and nickel are the same as those for land application.

Record Keeping and Reporting Operators of sludge incinerators must develop and keep certain records for a minimum of five years. Records should include those related to pollution limits for metals; THC limit; and manage-

TABLE 1.13 Monitoring Frequency for Sewage Sludge Incinerators

Pollutant/Parameter

Amount of Sludge Fired"

Must Monitor at Least:

Arsenic, cadmium, chromium, lead, and nickel in sludge

Beryllium and mercury in sludge or stack exit gas

THC concentration in stack exit gas Oxygen concentration in stack exit gas Information needed to determine moisture content in stack exit gas

Combustion temperature in furnace Air pollution control device condition

0 to <290 290 to <1500 1500 to <15,000 15,000 or greater NA

NA NA NA

NA NA

Once per year

Once per quarter (4 times/year) Once per 60 days (6 times/year) Once per month (12 times/year) As often as permitting authority requires

Continuously

Continuously

Continuously

Continuously

As often as permitting authority requires

a Metric tons per 365-day period, dry weight basis.

ment practices and monitoring requirements, such as THC levels, oxygen levels, and moisture content in stack exit gas, and combustion temperature in furnace. Treatment works serving a population of 10,000 or more, and treatment works with a design flow of 4000 m3/day (1 mgd) must report these records to the permitting authority by every February 19.

REFERENCES

Federal Register (1993), FR 58 No. 32, February 19, pp. 9248-9415. U.S. EPA (1992), Control of Pathogen and Vector Attraction in Sewage Sludge, EPA 625/R-92/013.

- (1994), A Plain English Guide to the EPA Part 503 Biosolids Rule, EPA

-(1995a), Part 503 Implementation, EPA 833/R-95/001.

- (1995b), Process Design Manual: Land Application of Sewage Sludge and

Domestic Septage, EPA 625/R-95/001.

- (1999), Biosolids Generation, Use, and Disposal in the United States, EPA

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  • betty
    How are pathogens reduced in sludge?
    8 months ago

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