LARGER SKETCH of a small diameter pressure dosing system - EPA

Using Pressure Dosing as a Component of Alternative Septic Systems for Difficult Sites

This document discusses types of effluent pressure dosing septic systems, including gravity dosing, pressure manifold dosing, rigid pipe pressure dosing, and dripline effluent dosing systems for septic system effluent final treatment and disposal. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at REFERENCES.

Readers interested in septic effluent dosing systems should also see GRAVITY/SIPHON DOSING SYSTEMS.

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Pressure Dosing Septic System Designs

Septic effluent dosing system sketch USDA - DJFHow and When Septic Effluent is Moved Through a Septic System - Methods For Septic Effluent Distribution Using Gravity Systems

Our sketch (left, edited courtesy USDA) shows a generic septic effluent dosing system, combining a septic tank, a dosing tank, a diverter valve,and two septic efflent dispersal loops through a soil absorption field.

Septic effluent is distributed to a system final treatment and disposal using either gravity methods (which depend on terrain slope - see GRAVITY/SIPHON DOSING SYSTEMS) or pressure methods - PRESSURE DOSING SYSTEMS (which use a pump to move effluent to its destination treatment and disposal area). Effluent may be distributed for final soil absorption by several methods listed here:

  • Single Effluent Line: A 4" perforated PVC pipe receives effluent by gravity from the septic tank. The pipe is buried in a gravel trench and may be run in a straight line or a loop.
  • Distibution Box/Network of Lines A distribution box receives effluent by gravity from the septic tank and routes it to a network of perforated pipes. The network is made of multiple independent trenches which maybe on a flat or sloped site.
  • Serial relief line: multiple, serially connected trenches are built on a sloping site and used serially.
  • Drop box: multiple independent trenches are built on a sloping site, connected from drop boxes.

The purpose of septic effluent "dosing" systems is to place septic effluent in the absorption system or drainfield at intervals rather than continuously. In effect, the effluent dosing chamber forms a "buffer" which receives and stores septic effluent flowing (or being pumped) out of the septic tank until a desired dosing quantity is reached. Then the effluent is dispersed to the absorption system in one "dose." By distributing effluent at intervals rather than on a more nearly continuous or irregular basis the absorption system can "rest" between cycles, extending its life and possibly increasing its ultimate effluent treatment and disposal capability. Not only does the rest interval permit the absorption system more time to dispose of its effluent, also the exposure of the system to air between doses can reduce the rate of clogging of the drainfield.

Methods For Controlling Septic Effluent Distribution Using Pressure Dosing Systems

The Pressure Dosing Controls Shown Below include a Pressure Dosing distribution manifold (below left) and a pressure dosing distributing control valve. Images courtesy Washington State DEHS.

Pressure Dosing Mainfild - DEHS Washington State Pressure Dosing Distributing Valve - DEHS Washington State

Each septic effluent dosing system has its particular operating characteristics, so one type may be more suitable than others to a particular site. These types of pressure dosing septic systems are discussed here:

  • Pressure Dosing Methods permit effluent to be dispersed over the entire absorption field more uniformly than with gravity dosing systems, making maximum use of the absorption system capacity and avoiding the problem of local area or point overloading in the absorption field.
    • Pressure manifold: multiple independent trenches on sloped sites or multiple independent trenches receive effluent from a larger manifold pipe which is fed by an effluent pump from a pumping chamber.
    • Rigid Pipe Pressure Network: multiple independent trenches at the same elevation receive effluent from an effluent pump and pumping chamber.
    • Dripline Pressure Dosing Network: multiple independent pressure drip trenches on flat or sloping sites receive effluent from a pump and pumping chamber at low pressure (potentially even by gravity) where effluent is fed through small pipe openings permitting it to drip at a slow, controlled rate, into the trench and soils.

Controlled vs Uncontrolled Effluent Flow Control When Septic Effluent is Moved Through a Septic System

Wastewater effluent is distributed for final treatment over time either by uncontrolled, or controlled methods.

Uncontrolled septic effluent flow: A conventional gravity septic system and drainfield is "uncontrolled". When waste enters the septic tank, it forces the same volume of effluent out of the tank and into the leach field. Some experts call this a continuous or trickling septic system. Conventional septic tank and drainfields use this approach. The timing of effluent movement or "trickle" into the absorption field is based simply on when people are using the building plumbing and thus based simply on when wastewater flows out of the building into the septic tank.

Controlled septic effluent flow: in controlled systems effluent is sent to the final treatment and disposal system such as an absorption field under either mechanical control such as a tipping or siphon system or under pump control, such as by use of a dosing system which makes use of a gravity dosing method or a pressure dosing method such as septic effluent pressure manifold, rigid pipe distribution, or a septic effluent drip network.

In some large wastewater treatment systems with a significant if not uniformly continuous inflow, outflow of the system may be continuous in some designs. But many system use an intermittent effluent dosing method which operates by a pump controlled perhaps by a float in an effluent receiving chamber, or by a siphoning or tipping bucket mechanical system (gravity systems).

Pressure Distribution and Pressure Dosing Septic System Design Specifications

LARGER SKETCH of a septic effluent pressure dosing pumping stataion - EPA Pressure-dosed Drainfield Septic Systems use a separate effluent pumping chamber and an effluent pump such as the system in this sketch. The effluent pumping station is located downstream from the septic tank and is used to move septic effluent into a pressure-fed network of distribution pipes. In some designs the effluent is pumped to move it up to the absorption field where it then moves by gravity. Other systems pressurize the entire piping network.

Pressure dosing is used in a variety of disposal field designs including mounds and sand beds, and have the advantage of being able to distribute effluent uniformly throughout the absorption system, and the disadvantage of added system cost and complexity, along with the requirement for electricity for system operation.

An alternative but possibly less long-term reliable version of a drainfield dosing system that does not require electricity is the siphon system. The sketch shows a generic pumping station of the type used with many pressure dosing systems, source US EPA and Purdue University.

Source for the following is New York State regulations on wastewater treatment and design for individual household septic systems (Note b below) and from the U.S. EPA Wastewater Manual.

(1) These methods permit the rapid distribution of effluent throughout the absorption system followed by a rest period during which no effluent enters the system. The maximum length of absorption lines used in conjunction with these methods shall be 100 feet.

(i) Pressure distribution utilizes a sewage effluent pump to move the effluent through the pipe network and into the soil. The volume discharged in each cycle will exceed the volume available in the pipe network and will be discharged from the pipe under pressure.

(ii) Dosing involves the use of a pump or siphon for pressure dosing septic systems to move the effluent into the pipe network. Discharge from the pipe is by gravity. The volume of effluent in each dose should be 75% to 85% of the volume available in the pipe network.

(2) Dosing or pressure distribution is recommended for all septic systems as it promotes better treatment of wastewater and system longevity.

(3) In absorption fields, single pressure dosing units are required when the total trench length exceeds 500 feet. Alternate dosing units are required when the length exceeds 1,000 feet.

(4) The use of manually operated siphons or pumps for pressure dosing septic systems is not acceptable.

(5) Pipe used in pressure dosing septic systems distribution shall have a minimum diameter of 1.5 inches and a maximum diameter of three inches. Pipe for siphon dosing is sized to conform with the volume of the dose and can range from three to six inches in diameter based upon the volume of each dose. The ends of all pipes shall be capped.

(6) Only pumps for pressure dosing septic systems designated by the manufacturer for use as sewage effluent pumps shall be used.

(7) Pump chambers for pressure dosing septic systems shall be equipped with an alarm to indicate malfunction. Siphon dosing systems normally include an overflow to the distribution laterals. Pressure distribution systems shall not be equipped with an overflow.

(8) Pump chambers for pressure dosing septic systems shall be sized to provide a minimum of one day's design flow storage above the alarm level. Siphon chambers shall have a minimum total storage of one day's design flow below the overflow pipe.

Footnote (b): The preceding example septic pressure dosing system design and descriptive data for septic effluent pressure distribution and pressure dosing systems is from Appendix 75-A to Public Health Law, 201(1)(1) New York State Wastewater Treatment Standards - Individual Household Septic Systems, Wastewater Treatment Design and Regulation Section, specifically chapter 75-A.7 Distribution lines, distribution boxes, gravity flow, pressure distribution, dosing, siphons

Manifold Pressure Dosing Effluent Dispersal Systems

LARGER SKETCH of a rigid pipe pressure dosing effluent dispersal system, details
of design for the distribution manifold - EPAThis sketch shows a closeup of the effluent distribution manifold. The effluent pump moves effluent from the dosing chamber to this manifold under pressure. Pressurized septic effluent leaves the manifold through the small diameter black tubes or "distribution laterals".

Notice that each lateral has an individual control valve permitting the user to balance flow or even to manually alternate which distribution laterals are to be in use and which are to be left at rest.

The enlargers shown at the end of each distribution lateral permit connection of the lateral to a 4" PVC perforated pipe buried in the absorption system.

We'd infer that the effluent dispersal within the 4" pipe is by gravity not by pressure as with the next system discussed below. [Photo, U.S. EPA. Click the sketch to see a larger image of this rigid pipe pressure dosing septic effluent system example.]

Rigid Pipe Pressure Dosing Effluent Dispersal Systems

LARGER SKETCH of a rigid pipe pressure dosing effluent dispersal system - EPA This sketch shows a septic tank, the pumping chamber, also called a "dosing chamber" which contains the effluent pump, and the network of rigid pipe used to distribute effluent into the soil absorption system.

This design might be used with sand bed systems or mound systems as we discuss in this document. Note that the designer specified that a distribution line cleanout was to be provided at the end of each line.

This rigid pipe pressure dosing sketch appears also at the top of this page and in the EPA's Wastewater Manual. [Photo, U.S. EPA. Click the sketch to see a larger image of this rigid pipe pressure dosing septic effluent system example.]

Pressure Drip Dosing Effluent Dispersal Systems - Drip Line Septic Systems

Photograph of a pressure drip effluent dispersal system - EPA This EPA sketch shown a basic effluent drip line system layout. Effluent flows from the septic treatment tank to a pumping chamber where an effluent pump moves the effluent to a control chamber. The control chamber feeds effluent to the drip lines.

A field flush or back-flush line is connected from the control chamber back to the tank to return any settled sludge or debris to the system.

The air/vacuum release valve is installed at the very end of the drip line to assure that effluent can flow through the line to its end. [Sketch, U.S. EPA adapted from American Manufacturing - a supplier of this equipment.

See our link to our listing of product sources below. Click the image to see a larger version of this drip line septic effluent dispersal system example.]

Photograph of a pressure drip effluent dispersal system - EPA

This photo shows the pressure manifold (white pipe) and flexible low pressure drip dispersal system lines (black tubing) to be used for septic effluent treatment and disposal.

As the photo caption indicates, the trench has not been filled. These components will be covered, not left exposed.

The smaller diameter black lines are the drip lines which you'll notice are buried close to the ground surface. Probably a warm climate design. [Photo, U.S. EPA, who obtained it from Ayres Associates.

Click the photo to see a larger image of this drip dispersal system example.]

Pressure Dosing Septic System Products and Suppliers

Please see SEPTIC SYSTEM SUPPLIERS and also review the suppliers listed at ATU Suppliers


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