|
The Pathogen Equivalency Committee uses the following
four criteria to determine whether or not to recommend a process for equivalency.
The foundation of every equivalency application must consist of these four criteria.
- Identification of Critical Process Parameters. The applicant must provide a well-defined and detailed process description,
including diagrams, and discuss the disinfection stressors (physical, chemical,
and/or biological) that are employed (For example: time, temperature, pH,
solids concentration, ammonia, etc.).
- Verification of
Pathogen Reduction. The applicant must demonstrate the minimum
mandatory requirements listed in the table below with a high degree
of certainty. Both process efficiency and process compliance parameters
must be demonstrated. Applicants are highly encouraged to perform this testing in the laboratory or with a small-scale pilot
unit. This suggestion is made because frequently pathogenic organisms
must be added into the untreated sludge for testing to be possible.
(See Practical Aspects for Process to Significantly
Reduce Pathogens (PFRP) Equivalency.) Analytical methods for the
quantification of any organism listed on this page are discussed on
the Quality Assurance Project Plan page.
Criteria for Demonstrating Pathogen Reduction
Mandatory Minimum Requirements
|
PSRP Equivalency |
PFRP Equivalency |
Process Efficiency Parameters: |
≥ 2 log reduction of fecal coliform bacteria |
- ≥ 3 log reduction of total enteric viruses,
and
- ≥ 2 log reduction of viable helminth (Ascaris) ova,
and
- ≥ 3 log reduction of fecal coliform bacteria
|
Process Compliance Parameters
(The 40CFR503 Requirements): |
< 2,000,000 MPN or
CFU/g total solids (TS)
of fecal coliform in the treated sludge |
Organism densities in the treated sludge of:
- < 1 pfu/4 g TS of total enteric viruses,
and
- < 1 viable helminth (Ascaris) ova/4 g TS,
and
- < 1,000 MPN fecal coliform / g TS or
- < 3 MPN Salmonella spp./4 g TS (applicant's choice)
|
Several optional organisms are listed in a separate table. EPA
is collecting information on the fate of these microorganisms
by different modes of treatment with the intent of gathering enough
data to support their usefulness as surrogates in full-scale testing. Consider including as many of the optional analyses
as feasible. The measurement of all or some of optional
organisms will enhance your demonstration by increasing the level
of confidence associated with the process under investigation
and will be helpful later when the process is tested on a larger
scale. (See Criterion (3) Demonstration
of Successful Scale-up.)
Top of page
Optional Organisms for Process Efficiency¹
|
PSRP Equivalency |
PFRP Equivalency |
Any of the organisms listed can be quantified instead of or in
addition to only the fecal coliform parameter listed in the mandatory table above |
≥ 2 log reduction of E. coli bacteria
and/or
≥ 2 log reduction of Enterococcus spp. bacteria |
≥ 3 log reduction of E. coli bacteria
and/or
≥ 3 log reduction of Enterococcus spp. bacteria
and/or
≥ 3 log reduction of Salmonella spp. bacteria |
¹Note: Should any of the optional organisms be used in place of fecal
coliform, fecal coliform (or Salmonella spp. in the case of PFRP)
analysis on the treated sludge will still be required to meet the
mandatory process compliance parameters. |
- Demonstration of
Successful Scale-Up. Equivalency recommendations are scale specific. The two equivalency application requirements detailed above
can be performed at any scale (laboratory-scale, pilot-scale, or full-scale).
Applicants are encouraged to work at laboratory-scale up to this point
due to ease of and increased control over the experiments. The Pathogen
Equivalency Committee recommends performing the verification of pathogen
reduction studies on pilot or full-scale only if
an adequate number of helminthes and enteric viruses are naturally
present. However, if all experimentation is performed at the lab or
pilot-scale, only a lab or pilot-scale equivalency will be recommended.
The applicant must show that the process is capable of performing
reliably at the full-scale in order to receive a full-scale equivalency.
This not only includes the microbial parameters above, but also the
process and physiochemical parameters (stressors) identified as the
critical control points in the process description. Experimentation
at the full scale is where analysis of additional organisms may be
very beneficial especially for PFRP equivalency recommendations. (See Practical Aspects for PFRP Equivalency.)
As part pf a successful demonstration of scale-up, the applicant
should out some effort into final development of the process.
Details such as what process parameters will be measured, where,
and how, and other operating parameters and additional conditions
will need to be documented in an operation and maintenance manual
should equivalency be recommended. In fact, an equivalency recommendation
will not be finalized until such a document is received. (See
the Equivalency Recommendation Process page for more information on the operation and maintenance manual
requirement.)
- Appropriate Documentation
of Field and Laboratory Procedures. Documentation that all
data collection efforts submitted for equivalency determinations were
conducted in accordance with EPA approved quality assurance/quality
control requirements and all assays were conducted using EPA or EPA
approved methods of analysis. This criteria is best satisfied by the
preparation of a quality assurance project plan (QAPP) prior to the
collection of data. (See Quality Assurance Project
Plan for more information on QAPPs and guidance on how to prepare
one.)
Top of page
Practical Aspects for PFRP Equivalencies
Over the last few decades the concentrations of naturally occurring enteric viruses
and viable helminth ova routinely observed in raw sludge have dropped well
below the levels necessary to demonstrate the required log reductions for
the foundation of a PFRP equivalency as described in the table above.
While this is good news from a public health standpoint, it has been problematic
for entities applying for PFRP equivalency. Remember, PFRP equivalency must demonstrate
removal efficiencies not just compliance with 40CFR503 limits.
When the untreated sludges used in PFRP equivalency testing are below 1,000 pfu
per gram total solids (dry weight) of enteric viruses and/or 100 viable helminth
ova per gram total solids (dry weight) one of two options is available:
- Spiking. At the laboratory scale, spiking should
not present much of a problem, however, at pilot or full-scale, appropriate
spiking can be costly and difficult to carry out. In some cases, it
may even be outright prohibited due to the potential health risks
of an accidental release of pathogens. For these reasons, the
Pathogen Equivalency Committee does not recommend use of this option
for the purposes of demonstrating successful scale-up unless the spiking
can be completed safely and effectively. If spiking is the
preferred option, several issues must be addressed.
- To determine the necessary number of organisms contained in the spike to ensure that the
desired density of organisms in the untreated sludge is reached; it is recommended that a
preliminary matrix spike be performed ion the sludge to be used.
At a minimum, the spike density must be calculated using a conservative (i.e., highest reasonable)
percent solids concentration expected and a generous safety factor to account for
sludge toxicity and analytical method recovery.
Determining the appropriate spike density and volume is critical to a successful outcome.
If the number of organisms recovered from the untreated sludge after spiking is not
adequate to demonstrate the required log reductions the effort and expense of the test will be wasted.
- The applicant must document the source of the spiking organism, how it was
collected and maintained, and how it was added to the untreated sludge.
- The viability or titer of the spiking solution should be verified just prior to the actual spiking.
- The spiked sludge must be assayed for the organisms of interest just prior to treatment.
Estimates of the density of spiked organisms in the sludge based upon the number
per unit volume of the organisms added to a given mass or volume of sludge is unacceptable.
- Flow-through (typically continuously fed and completely mixed) treatment units present
additional difficulty in ensuring that there is no short circuiting and that the spiked sludge
is what is collected at the outfall. In these situations it is possible that any observed
reduction in numbers can be attributed to, at least partially, dilution of the spiked sludges
with unspiked sludges. Two suggested ways around this problem are adding a tracer to the
spiked sludge and monitoring the tracer for dilution effects or extending the length of
time over which the spike is added to greater than the calculated hydraulic residence time,
then taking the treated samples following one full hydraulic residence time.
Again, all conditions under which such experiments are performed must be specified and verified.
It must be shown that measured log reductions are the result of treatment efficacy, not dilution.
- Surrogates. This option may require some spiking of pathogens,
but only at the laboratory-scale. Appropriate use of surrogates is shown in the table below.
During laboratory-scale testing one or more additional
organisms native to the untreated sludge used would be enumerated alongside of the
spiked enteric viruses and/or helminth ova. In scale-up, the reduction of the surrogate
organisms can be used along with the established relationships to helminth ova and/or
enteric viruses to support successful scale-up and equivalency.
It is currently not possible to identify one
single surrogate organism that will work in all cases as the levels of
naturally-occurring organisms will differ from location to location and
relationships between organisms will differ depending on treatment. However, some
examples of possible surrogates for helminth ova include aerobic endospores and Clostridium perfringens, while some examples of possible surrogates
for enteric viruses include reoviruses and somatic bacteriophages. An appropriate
surrogate must be identified on a case-by-case basis. Applicants are welcome to
suggest other organisms as surrogates as long as data supporting the choice of
surrogate is obtained for the sludge and treatment process under evaluation.
Appropriate Use of Surrogate Organisms
|
Enteric Virus Density in Feed Sludge |
Helminth Ova Density in Feed Sludge |
|
>1,000 pfu/4g TS |
≤1,000 pfu/4g TS |
>100 ova/4g TS |
≤100 ova/4g TS |
Laboratory-Scale Analysis |
enteric viruses |
seeded enteric viruses
and
somatic bacteriophages
or
reoviruses |
helminth ova |
seeded helminth ova
and
aerobic endospores
or
Clostridium perfringens |
Full-Scale Analysis |
enteric viruses |
somatic bacteriophages
or
reoviruses |
helminth ova |
aerobic endospores
or
Clostridium perfringens |
Top of page
Conditions and Restrictions
The Pathogen Equivalency Committee may require additional terms,
conditions, or restrictions to an equivalency recommendation when
the mandatory supporting data in an equivalency application is
substantial, but not sufficient to support a full equivalency or
when uncertainty in the data is at an unacceptable level.
Additional terms and conditions are usually requirements for additional microbial monitoring
at the full-scale above that which is required for routine reporting as required by 40CFR503.
This additional monitoring is typically for a defined period of time and, following the collection
of additional supporting data, the conditional term may be dropped from the equivalency.
A restriction on an equivalency recommendation would place limitations
on access to and use of the land receiving the biosolids. These site restrictions
would be similar to those associated with Class B sludge, such as crop
harvesting, animal grazing, turf harvesting, and public access periods.
(See Chapter
5, Section 5.5, page 38 (PDF) (7 pp, 678 KB) of EPA/625/R-92/013 for
more details on Class B site restrictions.)
As mentioned above, measurement of some or all of the alternative organisms
can be used to bolster the level of confidence associated with the process
under investigation. This additional data could be used in these cases
to make the determination of conditional terms and/or restrictions. Positive
additional supporting data will lessen (or in some cases even eliminate
the need for) terms, conditions, and/or restrictions when the evidence
of the mandatory minimum disinfection verification requirements is weak.
Top of
page
You will need Adobe Reader to view some of the files on this page.
See EPA's PDF page to learn more. |