Examples of Equivalent Processes: PFRP and PSRP

On this page you may read about existing examples of companies and products that have received equivalency related to processes to significantly reduce pathogens and processes to further reduce pathogens:

PSRP Equivalent Processes Examples

Applicant/ Process Name EquivalencyType /
Date Received
Process Description
East Bay Municipal Utilities District
Low MCRT Treatment Process
Site Specific PSRP Equivalency
November 2010
Single stage completely mixed thermophilic anaerobic digestion process operated at a temperature of 50 ± 3° C and a mean cell residence time of  ≥ 240 hours (10-day simple moving average) for treatment of primary sludge, waste-activated sludge, and high-strength non-hazardous organic materials. Digester feeding is semi-continuous and draw-off is intermittent, both occurring at any time.
Synox Corp.
(Jacksonville, FL)
National PSRP Equivalency
August 1989
Batch process where sludge is acidified to pH 3.0 by sulfuric acid; exposed to 1 lb. Ozone/1000 gallons of treated sludge under 60 psig pressure for 60 minutes; 100 mg/L of sodium nitrite and held for ≥ 2 hours; and stored at ≤ pH 3.5. Limitations imposed were for total solids to be ≤ 4%; temperature must be ≥ 20°C; and total solids must be ≤ 6.2% before nitrite addition.
N-Viro Energy Systems, Ltd.
(Toledo, OH)
Alkaline Addition to achieve Lime Stabilization
National PSRP Equivalency
April 1987
Use of cement kiln dust and lime kiln dust (instead of lime) to treat sludge by raising the pH. Sufficient lime or kiln dust is added to sludge to produce a pH of 12 for at least 12 hours of contact.
Comprehensive Materials Management, Inc.
(Houston, TX)
Cement Kiln Dust to achieve Lime Stabilization
NationalPSRP Equivalency
March 1987
Use of kiln dust (instead of lime) to treat sludge pH to at least 12 after 2 hours of contact.Dewatered sludge is mixed with cement kiln dust in an enclosed system then hauled off for land application.
Ned K. Burleson and Associates, Inc.
(Fort Worth, TX)
Mid-Range Temperature Aerobic Digestion
National PSRP Equivalency
Prior to 1989
Typical aerobic digestion for 20 days at 30°C (86°F) or 15 days at 35°C (95°F). This is above regulation temperatures for PFRP (15 - 20°C), but below regulation temperatures for PFRP (55 - 60°C).

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PFRP Equivalent Processes Examples

Applicant / Process Name Equivalency Type /
Date Received
Process Description
BCR Environmental (Jacksonville, FL)
Neutralizer Process
Conditional National Equivalency
November 2010
Waste activated sludge total solids concentration of less than or equal to 4% is treated at temperatures greater than or equal to 15° C (59° F) with an oxidizing agent (chlorine dioxide) at an oxidation reduction potential (ORP) of greater than or equal to +100 mV with a contact time at +100 mV ORP ≥ 1 hour.  Such treatment in followed by addition of sodium nitrite at 1500 mg/L and acid to achieve a pH of ≤ to 2.3 s.u. for six hours.  The ORP during this second treatment stage  must be > +100 mV and nitrite contact time at specified pH and ORP is at least six hours.
Columbus Water Works
(Columbus, GA)
Columbus Biosolids Flow-Through Thermophilic Treatment (CBFT³) Process
Conditional Site-Specific PFRP Equivalency [Conditionality: 1) once built the fluid dynamics of the full-scale CFMD must be verified to be consistent with that of the laboratory-scale CFMD; 2) helminth and enteric viruses must continue to be monitored on the full-scale process in addition to and at the same frequency as, the regulatory requirement for fecal coliform or Salmonella spp. monitoring until data statistically supports the required 2 and 3-log reductions, respectively.]
October 2005
The process consists of four stages: 1) sludge preheat tank; 2) continuously fed, mixed digester (CFMD) operated at a minimum temperature of 53°C and a residence time of > 6.0 days; 3) a plug-flow reactor or series of batch tanks that provide a contact time of at least 30 minutes at a temperature of ≥ 60°C; 4)a mesophilic digester. It is further necessary that the limited conditions under which the process was tested are maintained at full-scale operation, namely that: 1) Columbus’s co-thickened mixed primary and waste activated sludge contains 6.0 & ± 1.0 to 2.0% total solids of which ≥ 50% is volatile; 2) the average ammonium-nitrogen content of the digesting sludge in the CFMD is ≥ 920 mg/L; 3) the pH in the digester is ≥ 7.3 and ≤ 8.3; 4) total volatile acid concentrations are between 1,000 and 2,250 mg/L; 5) thorough heating of the sludge is verified throughout process operations by continuous temperature monitoring.
Burch Biowave, Inc.
(Fredericktown, OH)¹
Burch Biowave™ Process
Acknowledgement as a Class A, Alt. 1 process
March 2005
A thin layer of dewatered sludge (> 7% total solids) is conveyed through a system of microwave generators (75-100 kW) which heat sludge to > 80°C for 6-14 minutes. These conditions exceed the time and temperature requirements for Class A, Alternative 1 [D = 131,700,000/100.1400t where D = time required in days; t = temperature in °C (Regime B)]. Heated air and an exhaust blower assist in drying the sludge to 75 – 90% solids.
Schwing Bioset, Inc.
(Houston, TX)
Bioset Process
National PFRP Equivalency
August 2011
Dewatered municipal sludge solids between six to thirty-five percent total solids by weight are mechanically mixed with calcium oxide (quicklime) to achieve a pH of greater than or equal to twelve standard units. Sulphamic acid is added to, and mixed with the sludge/quicklime to promote an exothermic reaction which increases the temperature of the mixture to equal to or greater than 55°C (131°F).  The sludge/quicklime/sulphamic acid mixture is then directed to a pressurized plug flow reactor for a minimum solids retention time of forty minutes at a minimum temperature of 55°C (131°F).
ONDEO Degremont
(Richmond, VA) (formerly held by Lyonnaise des Eaux (Le Pecz-Sur-Seine,France))
Two-Phase Thermo-Meso Feed Sequencing Anaerobic Digestion (2PAD™)
Conditional National PFRP Equivalency
[Conditionality: Helminth and enteric viruses must continue to be monitored on the full-scale process in addition to and at the same frequency as, the regulatory requirement for fecal coliform or Salmonella spp. monitoring until data statistically supports the required 2 and 3-log reductions, respectively.]
September 2002
Sewage sludge is treated in the absence of air in an acidogenic thermophilic reactor and a mesophilic methanogenic reactor connected in series. The mean cell residence time shall be at least 2.1 days (± 0.05 d) in the acidogenic thermophilic reactor followed by 10.5 days (± 0.3 d) in the mesophilic methanogenic reactor. Feeding of each digester shall be intermittent and occurring 4 times per day every 6 hours. The mesophilic methanogenic reactor shall be fed in priority from the acidogenic thermophilic reactor. Between two consecutive feedings temperature inside the acidogenic thermophilic reactor should be between 49°C and 55°C with 55°C maintained during at least 3 hours. Temperature inside the mesophilic methanogenic reactor shall be constant at least 37°C.
Synox Corp.
(Jacksonville, FL)
National PFRP Equivalency
March 1993
Operation occurs in a batch mode under the following conditions: sludge temperature of > 20 °C; sludge solids of < 6% TSS; pH during ozonation of 2.5 – 3.1 and during nitrate contact of 2.6 – 3.5; sludge ORP after ozonation of > 100 mV; nitrite dose of ≥ 670 mg (NO2)/L sludge or 16 g (NO2)/kg sludge solids, whichever is greater, is to be mixed into the ozonated sludge. Ozonation takes place in a pressure vessel operating at 60 psig.
Pori International, Inc.
(Baltimore, MD)
Pori Process
National PFRP Equivalency
May 1992
Sludge is preheated to 82°C (180°F) using recovered steam. Sulfuric acid is added to reduce the pH to 3. The mixture is then pressurized to 100 psig achieving temperatures of ≥ 165°C (330°F) for a treatment time of 1 hour. Lime slurry is used to neutralize pH.
CBI Walker, Inc.
(Aurora, IL)²
ATP™ Two Stage Sludge Stabilization Process
Conditional National PFRP Equivalency
[Conditionality: 1)Time and temperature in the first vessel must be ≥ 30 minutes and ≥ 50°C, and controlled by the equation D = 50,070,000/100.1400t (where D = time required in days; t = temperature in °C) for sludges of ≤ 7% solids; 2) Operations of the reaction vessel during the time-temperature periods must be either plug flow or batch mode.]
November 1992
Sludge is introduced intermittently into a vessel, amounting to 5 to 20% of its volume, where it is heated by both external heat exchange and by the bio-oxidation which results from vigorously mixing air with the sludge (pasteurized) and has a nominal residence time of 18 to 24 hours. Time between feedings of unprocessed sludge can range from 1.2 (@ ~ 65°C) to 4.5 (@ ~ 60°C) hours. Exiting sludge is heat exchanged with incoming unprocessed sludge. Thus, the sludge is cooled before it enters a mesophilic digester.
Fuchs Gas Und Wassertechnik, Gmbh
(Mayen, Germany)²
Autothermal Thermophilic Aerobic Digestion (ATAD)
Conditional National PFRP Equivalency [Conditionality: 1)Time and temperature in the first vessel must be ≥ 30 minutes and ≥ 50°C, and controlled by the equation D = 50,070,000/100.1400t (where D = time required in days; t = temperature in °C) for sludges of ≤ 7% solids; 2) Operations of the reaction vessel during the time-temperature periods must be either plug flow or batch mode.]
November 1992
ATAD is a two-stage autothermal aerobic digestion process. The stages are of equal volume. Treated sludge amounting to 1/3 the volume of a stage is removed every 24 hours from the second stage as a product. An equal amount then is taken from the first stage and fed to the second stage. Similarly, an equal amount of untreated sludge is then fed to the first stage. In the 24-hour period between feedings, the sludge in both stages is vigorously agitated and contacted with air. Bio-oxidation takes place and the heat produced increase the temperature. Sludge temperature in the reactors averages between 56 and 57°C for ≥ a 16-hour period, while the overall hydraulic residence time is 6 days.
K-F Environmental Technologies, Inc.
(Pompton Plains, NJ)¹
Type of Sludge Drying Process
Acknowledgement of PFRP by meeting current regulations under 40 CFR 257, App. II
November 1992
Sludge is heated to a minimum temperature of 100°C and indirectly dried to below 10% moisture using oil as a heat transfer medium. The final discharge product has exceeded a temperature of 80°C and is a granular, dry pellet that can be land applied, incinerated, or landfilled. In addition the following conditions must be met: Dewatered sludge cake is dried by direct or indirect contact with hot gases, and moisture content is reduced to 10% or lower. Sludge particles reach temperatures well in excess of 80°C or the wet bulb temperature of the gas stream in contact with the sludge at the point where it leaves the dryer is in excess of 80°C.
International Process Systems, Inc.
(Glastonbury, CT)¹
Type of Composting Process
Conditional National PFRP Equivalency [Conditionality: Process operation is to be controlled so that the composting mass passes through a zone in the reactor in which the temperature of the compost is at least 55°C throughout the entire zone, and the time of contact in this zone is at least three days.]
April 1991
IPS developed a unique within-vessel composting reactor using forced-aeration and bed-agitation to create an optimal aerobic environment. Long rectangular vessels are loaded at one end. An agitator/mixer assembly rides across the top of the vessel, mixing & conveying material down the vessel at a rate of approximately 12 ft/day. Finished compost reaches the opposite end of the vessel in 18 days having passed through five zones of treatment with average temperatures > 60°C.
ATW, Inc.
(Santa Barbara, CA)
Alkaline Stabilization / Pasteurization
PFRP Equivalency
Prior to 1989
Manchak process uses quicklime to simultaneously stabilize and pasteurize biosolids. Quicklime, or a combination of quicklime and fly ash, is mixed with dewatered sludge at a predetermined rate in a confined space. An instant exothermic reaction is created in the product wherein the pH is raised in excess of 12 after two hours of contact, in addition, the temperature is raised in excess of 70°C for > 30 minutes
N-Viro Energy Systems, Ltd.
(Toledo, OH)
Advanced Alkaline stabilization with subsequent accelerated drying
National PFRP Equivalency
January 1988
Method 1: Fine alkaline materials (cement kiln dust, lime kiln dust, quicklime fines, pulverized lime, or hydrated lime) are uniformly mixed by mechanical aeration mixing into liquid or dewatered sludge to raise the pH to > 12 for 7 days. If the resulting sludge is liquid, it is dewatered. The stabilized sludge cake is then air dried (while pH remains > 12 for ≥ 7 days) for > 30 days and until the cake is ≥ 65% solids. A solids concentration of ≥ 60% is achieved before the pH drops below 12. The mean temperature of the air surrounding the pile is > 5°C (41°F) for the first 7 days.
Method 2: Now in 40 CFR 503 as Class A, Alternative 2
Scarborough Sanitation District
(Scarborough, ME)¹
Fly ash composting
Site-Specific PFRP Equivalency
March 1987
Traditional static aerated pile composting using fly ash as the bulking agent. Thus, heat (at least in part) is generated through chemical reaction with the fly ash and not through biological reactions as would a typical composting process. Time and temperature requirements for Class A static aerated piles were exceeded with operating conditions of 60 to 70°C reached within 24 hours and maintained for 14 days. Equivalency was recommended on this basis.


¹These processes, although evaluated by the Pathogen Equivalency Committee, meet the requirements of an existing PFRP or other Class A alternative. In an effort to reduce unnecessary work on behalf of the applicant and speed up the application process for legitimate equivalency applications, the PEC discourages submission of equivalency applications that fall into this category. Beginning in 2005, the PEC began issuing letters of acknowledgement that these processes already meet 40 CFR 503 regulatory requirements and will not be considered for equivalency.

²The conditional terms applied to these equivalencies currently fall under Class A, Alternative 1, Regime D; however, these equivalencies were issued prior to the 503 regulations.

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