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Event Recycling

Septage Management

Regulations for the land application of domestic septage are similar to those for municipal biosolids. However, there are important differences between septage and municipal biosolids regulations. These include: Both septage and biosolids are covered under the same federal and state regulations and guidelines for:
  • Soil and crop selection,
  • Soil criteria,
  • Site management,
  • Storage.

Types of Septage

There are three classes of domestic septage depending on its source and degree of stabilization.
  • Class I domestic septage comes from devices that are typically pumped at long intervals, such as septic tanks. The septage is largely stabilized from its long residency in the tank. It has been partially broken down and stabilized by the bacteria that live in the septic tank - a process similar to biosolids digestion. Class I septage can contain as much as 25% Class II material, or as much as 25% restaurant grease trap waste.
  • Class II septage comes from devices that are pumped frequently, such as portable toilets, holding tanks, pit or vault toilets, or Type III marine sanitation devices. This material is only partially stabilized. Class II septage usually has had little time to be digested. Stabilization and site requirements are more stringent than for Class I or III septage.
  • Class III septage includes material from septic tanks, cesspools, or similar devices serving businesses, as long as the septage is of domestic quality as defined by Chapter 173-308 WAC, Biosolids Management. This includes septage from businesses producing only domestic quality bathroom and kitchen wastes, or septic tanks receiving only domestic quality wastes. Class III septage does not include other commercial or industrial wastes. Class III septage has been partially broken down and stabilized by bacteria that live in the septic tank - a process similar to biosolids digestion.

Pathogen and Vector Attraction Reduction Requirements

Class I and III Septage
Class I and III septage are considered to be adequately stabilized for land application, when certain management and access restrictions are observed. Vector attraction reduction requirements are met either by alkaline treatment or by injecting or tilling into the soil.

Alkaline treatment reduces the numbers of pathogenic and odor-producing microbes in the septage by raising the pH. Enough lime must be added to maintain the pH at 12 for at least 30 minutes, and the septage must be tested to check that this pH has been maintained. If the septage is being managed as municipal biosolids, follow biosolids treatment rules in Chapter 173-308 WAC, Biosolids Management. Because alkaline treatment destroys only microbes - not organic matter - odors may return after several weeks. Therefore, alkaline treatment may not control odors when septage is stored for more than a short time before land application. Sites receiving alkaline-treated septage must meet all biosolids requirements for waiting periods for food crops as defined by WAC 173-308-210.

If Class I or III septage is not lime-treated, it must be injected into the soil or tilled into the soil within six hours of application, to provide a barrier to vector attraction. These sites must meet all biosolids requirements for waiting periods for crop production and public contact.

Class II Septage
Class II septage is mostly unstabilized material, and is not considered suitable for direct application to the land. Before land application, Class II septage must be treated to meet at least Class B pathogen reduction standards, or be analyzed to demonstrate that it meets Class B standards for fecal coliform density as defined by Chapter 173-308-170 (Pathogen Reduction). Vector attraction reduction is accomplished through alkaline treatment, soil injection, or soil incorporation. When batches of Class I septage contain less than 25% Class II material, treat the entire batch as Class I. The more stringent requirements for Class II apply when a load or batch contains more than 25% Class II material.

Monitoring Requirements

If septage is lime-treated, monitor every batch to make sure that alkaline treatment requirements are met. Septage managers don't have to measure septage nutrients and metals, as long as they base land application rates on the standard calculation described below. If septage is managed as biosolids derived from municipal sewage sludge, then all applicable requirements for monitoring biosolids derived from municipal sewage sludge (including nutrients and trace elements) must be met. This approach will generally not be practical except for relatively sophisticated septage operations.

If you need to estimate septage production in an area, use the U.S. EPA formula based on septage production data:

Estimated volume=(populaton using septic systems) x (60 gal/person/year)

This formula provides a starting estimate for septage volume. More accurate estimates can be made by analyzing actual septage pumpouts. By keeping central records on pumpouts, you can determine local annual septage volume, seasonal trends, and daily peak volumes. By knowing this information, it will be easier to plan septage treatment and handling facilities, and estimate the needed acreage for land application.


The person who is responsible for applying domestic septage to land is also responsible for maintaining application records. Required records include:
  • Septage source and class. These can be basic business records or receipts documenting the source, volume, and class of septage loads.
  • Septage treatment and site management used to meet pathogen reduction and vector attraction reduction requirements. This includes a certification statement as described in (Chapter 173-308-290 Record Keeping).
  • Site description and application records. This includes the location of the site, acreage of the septage application area, the annual (365-day) nitrogen requirement of the crop grown on the site, the date of each septage application, and the amount of septage applied to the site each year.
Preventing Contamination
Domestic septage can become contaminated if it is mixed with commercial or industrial wastes. Septage from commercial or industrial sources can be applied to land only if it is known to come from septic tanks that receive only domestic quality sewage (Class III septage). If you have any doubt about the quality of the septage, do not pump the source or accept a load of septage until the quality can be verified.

Application Rate

Septage applications are more suitable for sites where peak productivity is not a major concern because the equation for calculating application rates is conservative and probably will not provide the full nitrogen requirement of the crop. This is especially the case when pH adjustment is used, resulting in a loss of ammonia. When the septage equation was developed for the federal biosolids rule, both the agronomic rate, and the underlying risk assessment were considered. The rate calculation for septage applications can be used without measuring the nutrient content of the septage.

Use the following equation to calculate the maximum application rate:

AAR = N/0.0026

AAR is the annual application in gallons per acre per 365-days, and N is the amount of nitrogen needed by the crop in pounds per acre per 365 days.

The table below shows the highest annual septage rates calculated from the equation. If you use this table, you do not need to analyze the septage for nutrients or trace elements. Remember that the rates in this table may not supply the full nitrogen requirement of the crop.

Nitrogen Application Requirement Septage Application Rate Septage Application Rate
lb N/year Thousand gal/acre/year Acre inch/year
20 8 0.3
40 15 0.6
80 31 1.1
100 38 1.4
120 46 1.7
140 54 2.0
160 62 2.3

You can also calculate a site-specific agronomic application rate using this application rate worksheet. If you choose this method, you will need to analyze the septage for both nitrogen and trace elements, and meet all other requirements for land application of biosolids. This approach typically works best for relatively sophisticated septage operations. If you store, or further process septage before land application (such as alkaline treatment or lagoons), consider managing the septage to meet all requirements for land application of biosolids as this will often allow you to apply more material per acre than when using the standard septage equation.

Waiting Periods and Restrictions on Public Access

Requirements for posting sites to restrict public access are the same as for Class B biosolids.

The following restrictions apply for all septage application:
  • Crops cannot be harvested for at least 30 days after application of septage to the land.
  • If harvested parts are above the ground and touch the soil (squash, lettuce or strawberries), crops cannot be harvested until 14 months after septage application.
  • If harvested parts are below the ground (carrots and potatoes), crops cannot be harvested for 38 months after septage application. If the septage remains on the surface for 4 or more months before incorporation, the harvest restriction is reduced to 20 months.
Additional restrictions apply when alkaline treatment is not used:
  • Animals cannot graze for 30 days after septage application to forage.
  • Turf cannot be harvested from turf farms for one year after septage application when used for home lawns or any area with a high potential for public exposure.
  • Public access is restricted for one year in areas with a high potential for public exposure, and for 30 days in areas with a low potential for public exposure.


All land application sites must have large enough buffers to protect receiving waters. 100 feet is the minimum buffer distance to surface water for septage applications. All other minimum buffers are the same as for Class B biosolids. For special situations, buffers may need to be larger.