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Basic Information
Table of Contents
Introduction According to the 40 CFR Part 503 sewage sludge standards, before sewage sludge can be applied to land, it must meet one of six alternatives for Class A or one of three alternatives for Class B pathogen reduction levels. This can be demonstrated in three ways:
Thus, innovative sewage sludge processes can gain regulatory acceptance through Class A, Alternative 6 or Class B, Alternative 3. The process by which such equivalencies this can be obtained is typically managed by the Pathogen Equivalency Committee and overseen by the permitting authority. What is the Pathogen Equivalency Committee?Created by the U.S. Environmental Protection Agency (EPA) in 1985, the Pathogen Equivalency Committee (PEC) is a federally sponsored technical group that provides technical assistance and recommendations on process equivalencies for pathogen reduction in sewage sludge to government and industry. Originally formed to help EPA permit officials make decisions about new technologies, it now also guides and assembles research, and distributes information to the states and the biosolids industry. The committee currently consists of 10 members with a well-rounded expertise and diverse point of view. It is a multi-agency group with representatives from U.S. EPA's Office of Research and Development, Office of Water, and Regional Offices, as well as from the Center for Disease Control and Prevention. Areas of Expertise
The main charge for the pathogen equivalency committee is to uphold the protection of human health. Their mission in reviewing an equivalency application is to ensure that new processes employed for sewage sludge treatment are robust and effective in pathogen reduction. In this light, the pathogen equivalency committee reviews and makes recommendations to relevant federal and/or state permitting authorities on the merits of applications proposing that innovative or alternative sewage sludge pathogen reduction processes are equivalent to the processes currently listed in the 40 CFR Part 503D regulation. For more information on the PEC, see Chapter 11 of Environmental Regulations
and Technology: Control of Pathogens and Vector Attraction in Sewage Sludge
(EPA/625/R-92/013) revised July 2003, Role
of EPA's Pathogen Equivalency Committee in Providing Guidance Under Part
503 (PDF) (13 pp, 652 KB) What are Processes to Further Reduce Pathogens (PFRPs) and Processes to Significantly Reduce Pathogens (PSRPs)?A process to further reduce pathogens (PFRP) (PDF) (7 pp, 642 KB) is a treatment process that is able to consistently reduce sewage sludge pathogens to below detectable levels. A PFRP must reduce enteric viruses to below 1 plaque forming unit (PFU) per 4 grams of total solids (dry weight basis) and reduce the density of viable helminth ova to below 1 per 4 grams of total solids (dry weight basis). PFRP processes and PFRP equivalent processes, when paired with an appropriate vector attraction reduction (PDF) (7 pp, 615 KB) option, meet the requirements for Class A (PDF) (10 pp, 170 KB) sewage sludge. All Class A alternatives require that either the density of fecal coliforms in the sewage sludge be less than 1,000 MPN per gram total solids (dry weight basis) or the density of Salmonella spp. bacteria in the sewage be less than 3 MPN per 4 grams of the total solids (dry weight basis) at the time the treated sludge is used or disposed. A process to significantly reduce pathogens (PSRP) (PDF) (8 pp, 1.05 MB) is a process that consistently reduces the density of pathogenic bacteria, viruses, and/or parasites (number/gram of biosolids on a dry weight basis) in mixed sludge from a conventional plant by equal to or greater than 1 log (base 10). PSRP processes and PSRP equivalent processes, when paired with an appropriate vector attraction reduction option, meet the requirements for Class B (PDF) (7 pp, 678 KB) sewage sludge. Although effective in reducing some strains of microorganisms, it is expected that some pathogenic microorganisms will survive PSRP treatment. Therefore, to minimize impact on the environment and to maintain public health, additional restrictions are required for land application of PSRP treated biosolids. Some of these measures include restricting the public’s access to the land application site and preventing crop harvesting for a certain amount of time so that the pathogens naturally attenuate to below the detection limit. More information on site restrictions can be found in Section 5.5 (PDF) (7 pp, 678 KB) (p 38) of Environmental Regulations and Technology: Control of Pathogens and Vector Attraction in Sewage Sludge (EPA/625/R-92/013) revised July 2003. The table below is a comparison of some of the main differences between PFRPs and PSRPs. Criteria for demonstrating equivalency to a PFRP or PSRP are located on the Equivalency Criteria page.
I have developed or have an idea for a new treatment process and would like to get equivalency. How do I get started?If you have developed or have an idea for a new sludge disinfection process and are interested in receiving an equivalency recommendation from the Pathogen Equivalency Committee, your first step should be to contact your permitting authority. If you are unsure of whom your permitting authority is, consult the State and Regional Coordinator Locator page. If you are not currently working with a specific wastewater treatment plant you may contact the Pathogen Equivalency Committee directly via e-mail. But before you make contact you should have answered a few key questions which will direct your equivalency application process:(1) What type of pathogen reduction equivalency are you seeking, PSRP or PFRP?To answer this question you will likely have first performed some limited proof-of-concept studies to establish the pathogen reduction of your treatment process. Then use the information in the section above to assist you in deciding the type of equivalency you intend to apply for.(2) Does your process resemble or meet the operating conditions of any current alternatives listed in 40 CFR 503D? (3) Are you seeking a site-specific or national equivalency? (flow diagram adapted from Figure 11-1 (PDF) (13 pp, 672 KB) of Environmental Regulations and Technology: Control of Pathogens and Vector Attraction in Sewage Sludge (p 91)) How can a process receive a national vs. site-specific equivalency recommendation?As indicated in the flow diagram above, processes affected by local climatic conditions or that use materials that may vary significantly from one part of the country to another are unlikely to be recommended as equivalent on a national level. These processes may only receive a site-specific equivalency recommendation. For a recommendation of national equivalency, the process must consistently produce the required pathogen reductions under the variety of conditions that may be encountered at different locations across the country. A recommendation of national equivalency is usually preferred because it enables the treatment processes to be marketed, sold, or used at different locations in the United States. What is the difference between proof-of-concept, laboratory, pilot, and full scale?The term proof-of-concept typically is used to describe any initial small scale or incomplete investigations into a new treatment process. The purpose of proof-of-concept studies is to determine the feasibility of a new idea or concept. In most cases, data taken before a quality assurance project plan or similar type of document is written will be identified as proof-of-concept and will not be considered by the Pathogen Equivalency Committee as part of an application package. Laboratory-scale testing is often referred to as bench-scale testing because the scale is such that it can be comfortably carried out on a laboratory bench top. In laboratory-scale testing the equipment employed to carry out the experiments is typically specifically made for laboratory use and is not manufactured in sizes large enough to be included as part of a full-scale process and/or not practical at larger scales. An example of this is the use of a magnetic stirrer to keep sludge samples mixed during treatment. Laboratory-scale testing is simpler and easier to control than the other two scales because of the smaller quantities of sludge used. For this reason it is typically used to develop operating ranges of key process variables before building a pilot or full scale unit. Pilot-scale testing typically handles volumes larger than the laboratory-scale, but smaller than the full-scale. The defining characteristic of pilot-scale testing is that it is carried out using a pilot-scale unit which is a miniature, but exact replica of the full-scale process. Like a model car to its full-sized counterpart, each component of a pilot-scale unit is exactly the same design as it would be in a “real-life” process. For example, if mixing at the full-scale is to carried out using a recirculation pump which is sized to turn over the entire volume of 10,000 gal tank in 4 hours, the pilot-scale unit would also be mixed by a recirculation pump which would be appropriately sized to turn a smaller volume tank at the same rate. Pilot-scale modeling is often used in engineering disciplines to predict the behavior of a prototype or full-scale system. In order for the model and the prototype to behave in a similar fashion the principles of similitude and dimensional analysis must govern the relationships between physical parameters. True pilot-scale units should be constructed according to these principles. This is especially important when using pilot-scale testing to demonstrate successful scale-up of a process for an equivalency application (see Equivalency Criteria page (3) Demonstration of Successful Scale-up). Full-scale refers to the scale appropriate to treat sludge from an entire plant. Full-scale testing is not often used because of the large quantities of sludge involved. Full scale testing is only appropriate when an adequate amount of enteric viruses and helminth ova are naturally present in the raw sludge to permit the demonstration of a disinfection process' effectiveness. What are the benefits of obtaining an equivalency over operating under Alternatives 3 & 4 for Class A, or Alternative 1 for Class B?It is true that an innovative or alternative sludge disinfection process may be marketed, installed, and operated in compliance with the regulations without ever having received PFRP or PSRP equivalency. Alternatives 3 or 4 for Class A and Alternative 1 for Class B offer the flexibility to use processes that do not meet the operating conditions of any of the listed alternatives/processes in 40 CFR 503D by allowing the operators of such processes to show that their sludges meet the appropriate expected pathogen/indicator levels through comprehensive microbiological monitoring. Class B, Alternative 1 (PDF) (7 pp, 678 KB) (EPA/625/R-92/013 Section 5.2 (p 36)), relies on the routine monitoring of only one organism (fecal coliform). Class A, Alternatives 3 and 4 rely on microbiological monitoring of three classes of organisms, bacteria (either fecal coliform or Salmonella spp.), viruses (enteric), and parasites (viable helminth ova). The difference between Alternative 3 and 4 is subtle.Class A, Alternative 3 (PDF) (10 pp, 170 KB) (EPA/625/R-92/013 Section 4.6 (p 31)) is meant to be used in situations where a defined process exists, but its operating conditions do not meet those of any other established process/alternative. Microbial testing must be performed for helminth ova and viruses on the untreated sludge and for bacteria on the treated sludge in Alternative 3. Helminth ova and viruses need only be tested for in the treated sludge when they are detected in the untreated sludge; and only when adequate pathogen reduction is demonstrated can a process be considered Class A. Class A, Alternative 4 (PDF) (10 pp, 170 KB) (EPA/625/R-92/013 Section 4.7 (p 32)) was meant to be used in the rare instance of an orphaned, stockpiled sludge where the method of treatment is unknown. It was intended for one-time testing, not continued use. In such situations, monitoring the untreated sludge is not feasible and all three organisms must be tested for on the treated sludge. Class A, Alternatives 3 and 4 can be costly because helminth ova and enteric viruses, which are very expensive to analyze, must be analyzed at the same frequencies as other pollutants regulated in 40 CFR 503, e.g. once per month for facilities preparing more than 15,000 dry metric tons of sewage sludge per year. In comparison, if an equivalency determination has been established, only fecal coliform and/or Salmonella spp. must be analyzed to demonstrate Class A, unless special requirements for monitoring are imposed by the permitting authority. The use of these monitoring alternatives is discouraged except under certain site-specific conditions. Without a defined treatment, the absence of specific organisms cannot be used to infer the absence of other potentially pathogenic organisms in the biosolids. Nor with respect to Class A, Alternative 3 can the absence of these organisms be guaranteed over time without the barrier a treatment technology provides. Thus, it is the Pathogen Equivalency Committee's opinion that the treatment technology alternatives (i.e., Class A Alternatives 1, 2, 5, and 6, and Class B Alternatives 2 and 3) provide better and more consistent protective value from a human health standpoint than microbial testing in the absence of defined treatment. The following table summarizes some advantages and disadvantages between choosing the microbiological monitoring route and applying for equivalency.
What are fecal coliform, Salmonella spp., enteric viruses, and helminth ova and why were they chosen to demonstrate equivalency?The cast of characters involved in the demonstration of equivalency is taken directly from the 40 CFR 503D regulations for Class A and Class B disinfection processes. Each microorganism has its own unique characteristics.Fecal Coliform
Multiple Tube Fermentation method using A-1
broth. Gas production from fecal coliform lactose fermentation in
the positive tube on left and negative tube on right.
The fecal coliform group is largely made up of two genera of bacteria; Escherichia and Klebsiella. Not all fecal coliform are associated with fecal contamination. Some species of Klebsiella, for instance, are commonly found in vegetation (e.g., wood). Within the fecal coliform group there are numerous strains of Escherichia coli, a few of these are known to be pathogenic. However, the fraction of pathogenic strains of E. coli in wastewater typically are so low that it is difficult (and in most cases impossible) to detect them. Fecal coliform are widely used as an indicator of pollution because they are directly proportional to fecal wastes, present in high numbers, and easier to quantify than pathogens. Also, their low pathogenicity makes the fecal coliform group safer to analyze as opposed to measuring pathogens directly. Fecal coliform are used to demonstrate sewage sludge safety and process equivalency for the same reasons. Salmonella spp.
Salmonella spp. growing on MSRV media produce a bright blue halo.
The Salmonella sp. S. enteritidis is currently the single most common cause of food poisoning in the United States. The symptoms of S. enteritidis are non-fatal gastroenteritis. S. enteritidis is generally associated with improper handling or undercooking of poultry and eggs. Salmonella spp. were chosen as an indicator of sewage sludge safety mainly because of interference of non-fecal associated fecal coliform stemming from the use of wood chips and sawdust as bulking materials, especially in composting practices. Since S. enteritidis is so widespread, sufficient numbers of Salmonella spp. typically exist in untreated sewage sludge. Thus, if Salmonella spp. are at or below the detection limit (3 MPN Salmonella / 4 grams total solids (dry weight)) in the treated sludge, one usually can be assured that effective disinfection has occurred. Enteric Viruses
Electron micrograph of poliovirus; often
used as the representative enterovirus when spiking is required.
Enteric viruses include: rotaviruses, astroviruses, caliciviruses, picornaviruses, adenoviruses, parvoviruses, and reoviruses. Most of these viruses cause viral gastroenteritis. For example, rotaviruses are the leading cause of childhood gastroenteritis world-wide. Left untreated it can lead to death, primarily due to severe dehydration. The picornavirus family is particularly significant. It includes more well-known viruses such as the poliovirus, coxsackievirus, and the hepatitis viruses. Most picornavirus are associated with diseases other than gastroenteritis, such as, Polio, viral hepatitis, myalgia, pancreatitis, diabetes, myocarditis, hand-foot-and-mouth disease, and conjunctivitis. Enteric viruses were selected as an indicator of sewage sludge treatment effectiveness for two primary reasons. First, they are shed in large numbers by infected individuals and, therefore, likely to be present in untreated sewage sludge. Second, they are inherently resistant to environmental stresses, including heat and low pH. Thus, if conditions are effective for the disinfection of enteric viruses one can be reasonably assured that they are effective for most other viruses and bacteria. Viable Helminth Ova
Ascaris ova and hatched second stage
larva.
Unfertilized (left) and fertilized (right) Ascaris ova.
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Typically, to receive an equivalency recommendation, laboratory work is
performed to establish the boundary conditions of all key process variables,
and then pilot or full-scale testing is performed to demonstrate successful
scale-up. It should be obvious that for a site-specific equivalency this
work only needs to be performed on one sludge at one location. For a national
equivalency, however, the laboratory work must be repeated with several
sludges. These sludges should include all the different types that the
innovative or alternative process might be used with and the range of
characteristics that the process would be expected to see. In addition,
successful scale-up will need to be demonstrated by pilot or full-scale
studies at a single location. This, of course, is only the typical manner
in which equivalency recommendations are received and there is room for
variation from application to application. For instance, if preferred,
a mobile pilot-unit could be constructed and used for all testing, eliminating
the need for laboratory studies. Note that in cases where pilot testing
is used without any full-scale testing, the applicant must ensure that
the pilot-scale accurately represents the full-scale (see