Sketch of a Recirculating Sand Media Filter System - EPA How to Use Peat as a Septic Media Filter

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Peat bed septic system designs:

This document discusses the design and use peat septic media filter systems.

Peat media filter septic systems use a conventional septic tank followed by any of several methods to further filter and treat septic effluent before it is discharged to the soil, soil surface, or waterway. Peat-based septic media filter types are explained here.

We include a list of product sources for various types of septic filters. Our page top photo shows a septic mound installed on a narrow lot bordering on Lake Superior in Minnesota, reported to use peat as a septic media filter.

To protect this system from surface runoff flooding, the installers included intercept drainage to route runoff away from the mound itself and to improve drainage towards the lake. It is instructive to compare the mound shape to the peat system described below.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Design & Use of Septic Media Filters Using Peat

Sketch of a Recirculating Sand Media Filter System - EPAPeat filter septic systems take a conventional septic system design (such as those regulated in MA under Title 5) and adds an effluent filter stage for additional effluent treatment.

Some literature refers to this extra treatment step as tertiary treatment of septic effluent, or as multiple module effluent treatment, or moving bed biological reactor treatment systems.

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Article Contents

Peat bed septic design in northern Minnesota (C) Daniel FriedmanPhoto below: a peat mound septic installed in Two Harbors MN in 2010, at a site upon which a home had not yet been constructed.

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Dr. Joan Brooks [as part of a masters thesis] installed the first sphagnum peat-based onsite wastewater treatment system in Maine in 1978[3] where it supported a septic system supporting a home with nine occupants.

Brooks subsequently designed and installed additional peat filter septic systems in Maine.Shaw [op cit] claims that the system treated septic tank effluent "to drinking water standards" and that the system was still in use after 25 years.

[Note that this does not mean that maintenance and repair have not been required during that period.]

Brooks is credited with development of the "modular peat system" that uses multiple effluent treatment tanks connected to the septic tank to receive its effluent.

In simpler terms, adding a peat media filter to a septic system is an extra step in treatment of septic effluent that removes a higher percentage of fine solids that otherwise would be discharged from a septic tank or an aerobic septic tank.

The result is cleaner wastewater discharged into the environment, and probably a longer drainfield or soakaway bed life.

A peat septic system functions much like a conventional Title 5 septic system with the exception that the wastewater receives treatment by being filtered through 2 to 3 feet of peat before being discharged to the soil for final disposal.

Water from the dwelling first flows to a conventional septic tank where solids settle.

The clarified effluent then flows, either by gravity or by pump, to the peat filter. - Barnstable BOH in Massachusetts [1]

You can infer from this data that a higher level of effluent treatment is achieved with a peat filter septic design. That's surely why the septic treatment system shown at the top of this page used a peat filter: the system is located very close to the shores of Lake Superior in northern Minnesota. The Barnstable BOH continues to describe how and why peat is an effective filter.

The peat acts much like a sponge, absorbing and wicking the effluent in all directions and providing treatment as the wastewater slowly filters through the peat. Eventually the effluent filters to the bottom of the peat where it percolates into the soil for final disposal.

Experimental results show that peat filters are capable of very efficient removal of fecal coliform bacteria, biochemical oxygen demand (BOD) and total suspended solids (TSS).

They also appear to be capable of a producing a significant loss of total nitrogen in finished effluent. - op.cit.

Below: the same Minnesota Peat-bed Septic System that appears earlier in this article is shown six years later and under light snow cover.

This interesting peat filter septic system might serve for technical research as it has been on this site for at least six years now, but as the property remains un-built, the peat bed septic system has never been used.

Peat bed septic system  inspection in Two Harbors MN (C) Daniel Friedman Peat bed septic system  inspection in Two Harbors MN (C) Daniel Friedman

Septic effluent treatment systems using peat as the filter media include an effluent dosing system, peat filter media, and a drainage system. Unlike sand bed filters, peat filtration systems are sold as prepackaged systems which provide modular peat units enclosed in containers or "pods" ready to install.

Peat filter media systems may receive effluent doses by a pump system (similar to sand filter systems) or by a gravity-operated tipping bucket which, when filled with effluent, tips to distribute the effluent into the media distribution pipes.

Watch out: Jantrania/Gross point out that you should not try to build your own septic treatment system using peat from a local landscaper as such material has a short life. Don't run out and buy peat moss for your septic system filter by going to the landscape and gardening supplier.

Peat which is intended to be used as a septic media filter is specially selected and perhaps treated and prepared by the manufacturer, and has an 8-20 year life expectancy.

Peat from the local nursery may not last more than a year or two and it is unlikely to achieve the level of effluent treatment that was assumed when the septic system was designed and approved

We list some supplies of peat-based septic systems and peat suppliers below..

Septic effluent which has been processed through the peat biofilter is discharged into a soil absorption system such as a stone bed below the peat pods, or to a dosing tank where it is pumped to a mound or other soil absorption system.

Watch out: Below: the same peat mound or peat bed septic in Two Harbors in 2017: the site remains unoccupied with no construction past the septic system. Now nearly a decade old the question might be asked: will this septic system function if/when it is connected to a home built on this site.

Peat mound septic, Two Harbors MN in 2017 (C) Daniel Friedman

By now deep roots may have invaded the peat bed and other septic components. Further investigation may be needed before this system, located quite close to Lake Superior's edge, can be used.

Why Does a Peat Filter Treat Effluent and Remove Contaminants at a High Level?

The following is adapted and expanded from Barnstable BOH [1] who, speaking in more technical terms describe peat filter material as having a "high cation exchange capacity"[2] and other properties that make it work well as a septic effluent filter and treatment media.

  1. "Peat fibers are polar, have a high surface area, and a highly porous structure (90-95% porosity)." Holding a lot of water means, in the case of peat used as a septic filter, holding lots of septic effluent, and not just holding it, but holding the effluent in contact with the cellulosic fibers that comprise the peat itself.

    The combination of holding volume and contact time gives opportunity for the peat fibers to capture or treat contaminants that are found in septic effluent before the effluent passes out of the filter and into the drainfield and thence into the environment.
  2. Because peat contains lignin-like substances (wood-fiber cells that are negatively charged particles), those particles give peat a great ability to adsorb positively charged molecules such as happens to be the charge on a high portion of ultra-small particles floating in home septic system effluent.
  3. Peat's high cation exchange capacity means the peat can effectively hold positively charged molecules including ammonium, metals, pesticides, some organic molecules, and possibly viruses. That's the secret.
  4. Peat also has the property that the actual interstitial spaces between individual peat fibers are quite small.

    Combining small inter-fiber space with high water holding volume with high surface area with long contact time we can add these features to explain why peat does an effective job as a filter and treatment media for septic effluent.
  5. Peat's ability to hold on to its moisture also means that the microorganisms (fungi and bacteria) that help the peat perform its treatment functions are able to stay healthy even when the septic system is not in active use - read this as one more argument against septic tank additives and chemicals.
  6. Interestingly, the same experts point out that while peat also is good at removing excess nitrogen from septic effluent (very important for that lakefront property), they're not quite sure how it works, possibly it's due to the activity of certain fungi that are found at high levels in peat.

    Why are the fungi in the peat? Fungi, other than certain bacteria, are the only fellows capable of breaking down wood fibers and cellulose in the first place.

    NItrification and de nitrification might in turn also be explained by the action of certain bacteria also found in peat (also discussed by the article we reference at [1] ).

According to the Shaw Peat Manual[3], use of peat for odor absorption and filtering have been known "since ancient times".

A peat filter system for treating wastewater installed in Finland in 1957 and still functioning today, reports that peat filtering successfully removes phosphorous to 82%, nitrogen to 90%, BOD to 90%, and pathogenic bacteria to 99% in the treated effluent.

So Why Doesn't Every Septic System Use a Peat Filter

OPINION-DF: surely the peat system suppliers would love the answer to this one. We speculate that in any system, where an extra component or device is not needed people don't want to pay for its cost, added complexity, and added maintenance.

Requiring and paying for adequate septic system design, installation supervision, and a regular inspection and maintenance by a professional third party is a way around this problem, but folks may simply not want to face that added expense, even though proper design, supervision, and ongoing maintenance protects the environment, extends the life of the septic system, and ultimately saves money by making the need for septic system replacement less frequent.

Heck, as you will read below, people don't even have their septic tank pumped on schedule until they've begun to smell an incipient failure.

Analysis of a Peat Filter Septic System Failure Study - Mistakes to Avoid

Also some sources ([1] once again) point out that some states such as Maine have issued warnings about peat filter media system clogging failures.

A Maine study of 68 peat filter systems [4] confirmed serious system failures [failure to treat effluent or other failures] in four systems, seven other incipient failures [saturated drainfields] and five "stressed" systems that were at their design limit.

If we exclude six peat systems that were used only seasonally, this finds 16 out of 61 malfunctioning systems, or about one forth of the in-use peat filter systems were in failure mode. [Septic system age,original design, and maintenance data must also be considered, as we noted in our similar discussion of aerobic septic system failures.]

Another 29 of the peat filter septic systems were also not installed according to state BOH DEP rules, with these variations that are listed in order of severity of impact on the successful functioning of the peat filter system:

The Maine study also traced peat filter system failures to:

Remarkable for its contradiction, suggesting that at least sometimes robust original design can trump poor maintenance, the study reported that:

An extreme example of this last [lack of owner maintenance of the peat filter system] observation is an eight year old system in Windham that serves seven dwellings (four year round and three seasonal), which continues to function well despite use of only one of its two beds due to an out of level distribution box, and despite the presence of numerous medium sized trees and shrubs in the peat medium.

The 1998 peat septic system study also concluded that

Onsite peat sewage treatment systems can work well, if properly designed, installed, and maintained. DHE is persuaded that the systems inspected included a sufficient number of functioning systems to attest to this. However, the design and installation quality appears to be both critical to the success or failure of an individual system, and much more sensitive to errors than conventional systems.

Other studies conducted of the failure of aerobic septic systems [AEROBIC SEPTIC SYSTEMS, ATUs] may offer a model for septic system design versus maintenance requirements: a significant, perhaps even dominant reason for septic system failure in advanced septic system designs such as aerobic and filter-based septic systems and even in older designs such as sand bed septic systems is that normal homeowners don't think much about the septic system nor its maintenance until something fails.

Basic Maintenance for Peat-Filter Septic Systems

Most of the peat filter septic ongoing maintenance advice detailed below has as its object preventing damage to the peat filter system either from overloading (garbage disposers), chemicals and additives (see x), or traffic that may compact or damage the filter system.

Garbage disposals and peat filter systems: Garbage disposals should not be used with peat disposal fields. However, if such units are to be used, additional septic tank capacity (such as a second septic tank installed in series, or filters) shall be included in the system design to prevent suspended solids from entering the peat disposal field.


Chemicals - not into the septic: Chemicals, other than normal household cleaners, shall not be disposed of in the disposal peat field. Examples of prohibited chemicals include paint, paint thinner, commercial grease and oil, darkroom chemicals, etc. In addition, treatments or additives are not needed and not recommended and in some cases may also be actually harmful to the peat filter.


and see CHEMICALS & TREATMENTS for SEPTICS for details.

Non-biodegradable materials: Non-biodegradable materials, such as diapers, sanitary napkins, etc., shall not be disposed of in a peat disposal system. See WHAT CAN GO INTO TOILETS & DRAINS?

Protect the peat filter septic from foot or vehicle traffic: Fencing is required in heavy foot traffic areas such as school playgrounds, commercial establishments, or vehicular-traffic travel areas.

Traffic: In addition to the above, peat disposal fields should be protected from the type of heavy foot traffic found on a school yard, playground, or ball court. Riding mowers, ATV's, snowmobiles, and other vehicles should not be allowed on peat disposal fields


Planting over Peat Filter or Drainfield: If a peat disposal field is planted with lawn grasses it should be mowed on a regular basis during the growing season with a walk-behind power or manual mower.

See PLANTS & TREES OVER SEPTIC SYSTEMS for details about the types of cover that can be planted over drainfields and the recommended separation distances between drainfield and trees or shrubs.

Maintenance instructions for Peat Filter Septics: System owners shall be provided with a copy of the operation & maintenance requirements by the site evaluator.

Specific peat filter maintenance instructions and requirements for repair or replacement of peat used in the system depend on the system's design and will appear in maintenance instructions that should be provided by the installer or by the septic disposal site evaluator who approved the system.

Our references (below) include documents that also provide details about peat filter septic system design, installation, and maintenance.

- Adapted and paraphrased from Maine's Onsite Peat Sewage Treatment Systems Assessment", James Jacobsen [4] published by the State of Maine, Division of Environmental Health.

Q&A on Peat Bed Septic Systems

Question: Where can I buy peat for my septic tank?

I want to purchase peat for my septic tank. Have you got any suggestions? I'm in the Ohio/Pennsylvania area. - M.G.

Reply: Peat is used for a septic media filter. Here are some suggestions for finding a source of peat for septic system use

You may already know this,but we do not sell anything. provides building and environmental diagnostic and repair information. In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.

Also, to be accurate, peat does not go into the septic tank. Peat used with septic systems is installed in a separately constructed mound or container that acts as an additional or "tertiary" treatment step for sewage effluent between the point of leaving the septic tank and the point of entering the disposal field or drainfield. You may also have seen that you don't want to buy ordinary peat moss from a landscape supplier.

Since you already have a peat bed installed, and as we won't know the names of local suppliers, here is how we look for supplies: We figure that one would not usually build a system that required importing materials from a great distance (cost), I'd start by calling the septic system designers/installers in your immediate area to ask what suppliers they've used.

In some states such as ME we read that the local health department had information about peat bed designs and suppliers so don't forget to ask your local BOH or building department for a suggestion.[1]

We list suppliers of peat media filter systems and peat supplies just below.

Suppliers of Peat-Based Septic Filter Systems and Peat Supplies

CONTACT us to add additional peat filter system or peat filter suppliers here - no fees are involved. InspectAPedia has no business nor financial relationship with systems or materials discussed at our website.

List of U.S. States, Canadian Provinces, European locations where Peat Biofilter and Filtration Systems Have Been Approved

CONTACT us to add additional states where peat filter septic designs are code-approved.

Maine Specifications for Peat Septic Wastewater Disposal Systems

The following information is provided as a model and for background about peat septic system design and installation. Source: 03/16/2011, citing the Maine Division of Environmental Health [4]

Notice: because the study referenced above recommended changes to procedure and possibly state code, the text below may have been subsequently updated by the state.

Readers should check with their own local municipal building and health departments for current regulations regarding septic system installation and maintenance and peat filter septics. The current model building code approved by the state of Maine is provided at



2301.1 General: See Chapter 12 for general construction techniques.

2301.2 Suitable sites: Suitable sites for installing peat disposal fields are the same as for other types of disposal fields. See Chapters 4, 6, and 7.

2301.3 Site preparation: Site preparation for peat disposal fields shall be the same as it is for any disposal field authorized under this code. See Chapter 12.


2302.1 Weather: Peat disposal fields shall not be installed when the ground or the peat material is frozen.

2302.2 Low pressure distribution: Low pressure distribution is not allowed in peat disposal fields.

2302.3 Minimum width: The minimum recommended width of a peat disposal field is 5 feet.

2302.4 Maximum width: The maximum recommended width of a peat disposal field is 20 feet.

2302.5 Maximum length: The maximum recommended length of a peat disposal field is 50 feet with end manifold and 100 feet with central manifold.

2302.6 Distribution pipe sizing: Gravity dosed distribution pipes shall consist of 4 inch diameter perforated pipe.

2302.7 Distribution pipe dosing: Dose to a maximum of 1/2 gallon per linear foot of 4 inch diameter pipe.

2302.8 Distribution pipe placement and bedding: The distribution pipes and bedding in peat disposal fields shall meet the following requirements:

2302.8.1 Distance from outer limits: The distribution pipes shall be installed 2.5 feet from the outer limits of the peat disposal field;

2302.8.2 Distances center-to-center: The distribution pipes shall be 2.5 feet on center;

2302.8.3 Connecting the ends of each distribution pipe: The distribution pipes shall be connected at each end with solid piping;

2302.8.4 Distribution box: If a distribution box is used it shall be located out side the limits of the peat and meet the requirements of section 1104.0;

2302.8.5 Stone beneath and on the sides of the distribution piping: The distribution pipes shall be installed over the center line of a 10 inch wide and 4 inch deep layer of 3/8 inch washed crushed rock. Additional 3/8 inch washed stone shall be placed on either side of the pipe to a 3 inch width. All stone shall be washed before its delivery to the site. No stone may be placed above the pipe;

2302.8.6 Stone under the peat: A minimum of 6 inches of 3/8 inch clean crushed rock or clean coarse sand shall be placed at the bottom of the peat disposal field; and

2302.8.7 Depth of peat: There shall be a minimum of 24 inches of peat below the bottom of the distribution lines and a minimum of 8 inches of peat above the top of the distribution lines.

2302.9 Compaction of the peat: The depth of peat layers depends on the moisture content at the time of the installation. At 50% moisture content (on a dry weight basis) install in 8 to 12 inch lifts. At 60% moisture, install in 12 to 16 inch lifts.

The peat lifts should be hand raked and compacted by an adult walking on it with snowshoes until an in-place bulk density of 6.2 to 9.4 pounds/cubic foot (on a dry-weight basis) is reached. No construction equipment or lawn rollers may be used to compact the peat.

2302.10 Surface treatment: No fill material may be placed over the top of the peat. Instead, the peat shall extend to the mineral soil surface of the original ground, or the fill on each side, and shall be crowned at a slope of 3%.

The surface of the peat may be left bare, seeded with lawn grasses, or planted with shallow rooted vegetation so as to blend into the natural surroundings. Deep-rooted vegetation shall not be allowed to grow on the surface of a peat disposal field.

2302.11 Vehicular and pedestrian traffic: No portion of any peat disposal field may be located under a paved area, driveway, or roadway.


2303.1 Type of peat: Ideally, the peat should be air-dried, milled, unscreened, bulk-loaded Sphagnum peat with a pH of 3.5 to 4.5, a von Post degree of decomposition of H4, a moisture content of 50% to 60%, an organic content of 95% or greater, and an ash content of 5% or less. The peat should not have been dried to less than 40% at any time during production.


2304.1 Soil profile vs peat disposal field application rates: The required bottom area of peat disposal fields shall be determined using the following:

2304.1.1 Soil profile 6: Soil profile 6 require a peat disposal field application rate of 1 square foot per gallon per day;

2304.1.2 Soil profiles 4 and 5: Soil profiles 4 and 5 require a peat disposal field application rate of 1.25 square feet per gallon per day;

2304.1.3 Soil profiles 2, 3, and 7: Soil profiles 2, 3, and 7 require a peat disposal field application rate of 1.50 square feet per gallon per day;

2304.1.4 Soil profiles 1 and 8: Soil profiles 1 and 8 require a peat disposal field application rate of 1.75 square feet per gallon per day;

2304.1.5 Soil profile 9: Soil profile 9 requires a peat disposal field application rate of 2.0 square feet per gallon per day;

2304.1.6 Soil profile 11: Soil profile 11 is for alluvial soils that vary in texture. For design purposes, use the peat disposal field application rate from a soil profile listed above which best describes the texture encountered; and

2304.1.7 Site suitability: Site suitability for peat disposal fields is as prescribed in Chapter 7.

2304.2 All other aspects: In all other aspects, construction of a peat disposal field shall comply with Chapter 7, unless otherwise specified.


2305.1 Scope: Under-drained peat filters are designed to pre- treat septic tank effluent prior to its ultimate disposal in any disposal field authorized under this code. See Chapter 1.

2305.2 Polyethylene liner: The under-drained peat filter is placed in an excavation or fill material that is lined with an 18 mil polyethylene sheeting or equivalent.

2305.3 Final disposal in a disposal field: The effluent from the peat filter is conveyed to a separate disposal field for final disposal.

2305.4 Sizing the disposal field: The disposal field used for final disposal is sized according to Chapter 9 and sized at 90% of the minimum hydraulic loading rate required in Table 700.1. Field size may be further reduced based on Subsection 702.6.


2306.1 Garbage disposal: Garbage disposals should not be used with peat disposal fields. However, if such units are to be used, additional septic tank capacity (such as a second septic tank installed in series, or filters) shall be included in the system design to prevent suspended solids from entering the peat disposal field.

2306.2 Chemicals: Chemicals, other than normal household cleaners, shall not be disposed of in the disposal peat field. Examples of prohibited chemicals include paint, paint thinner, commercial grease and oil, darkroom chemicals, etc.

2306.3 Non-biodegradable materials: Non-biodegradable materials, such as diapers, sanitary napkins, etc., shall not be disposed of in a peat disposal system.
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2306.4 Fencing: Fencing is required in heavy foot traffic areas such as school playgrounds, commercial establishments, or vehicular-traffic travel areas.

2306.5 Mowing: If a peat disposal field is planted with lawn grasses it should be mowed on a regular basis during the growing season with a walk-behind power or manual mower.

2306.6 Traffic: In addition to the above, peat disposal fields should be protected from the type of heavy foot traffic found on a school yard, playground, or ball court. Riding mowers, ATV's, snowmobiles, and other vehicles should not be allowed on peat disposal fields.

c6.7 Maintenance instructions: System owners shall be provided with a copy of the operation & maintenance requirements by the site evaluator.


Continue reading at SAND SEPTIC MEDIA FILTERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see PEAT BED SEPTIC SYSTEM FAQs - questions & answers posted originally at this article

Or see SEPTIC DRAINFIELD SIZE for wastewater application rate tables & septic trench design tables


Suggested citation for this web page

PEAT SEPTIC MEDIA FILTERS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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