SEPA

Onsite Wastewater Treatment Systems

Septic Tank Additives Fact Sheet

EPA Publication 830-F-24-003 (updated 2024)

Overview

Onsite wastewater treatment systems (commonly referred to as septic systems) treat human and domestic waste before returning the
water to the environment. Septic tank additives containing bacteria or chemicals are commonly marketed to improve system
performance. However, use of these additives is not recommended for domestic wastewater treatment because there is already a
significant presence of bacteria, enzymes, yeasts, fungi, and other microorganisms in onsite wastewater treatment systems (U.S. EPA,
2002). Additive products can be ineffective or even harm system operation and the environment. Any operational issues should be
assessed by a septic system professional or local regulator.

Potential Issues Associated with Septic
Tank Additives

The U.S. Environmental Protection Agency does not	SsptiC Tank

recommend the use of septic system additives containing

bacteria or chemicals for the following reasons:	Access

•	Potentially harmful impacts. Some of these products may
interfere with the breakdown of waste, contribute to
system clogging, and contaminate groundwater and
receiving waters (Pradhan et al., 2011; Lee & Coyne, 2012).

•	Unnecessary for operation. Homeowners can save money
by avoiding products that are marketed to improve system
performance. Onsite wastewater treatment systems already
contain the bacteria, enzymes, yeasts, fungi, and
microorganisms needed to function properly (Harwood,

2006).

•	Limited research. Consumer goods sold as septic system
cleaners, decomposers, deodorizers, organic digesters, or
enhancers may have only limited third-party research
demonstrating manufacturer claims (Pradhan et al., 2011).

•	Local limitations. Many individual states and localities have information on the proper operation of septic systems, including lists of
approved additives per their rules and/or regulations. Check with your local and/or state department of health or department of
environmental protection for additional information on allowable septic system additives in your area.



To treatment
or dispersal
system.

Please note: The number of compartments in a septic tank vary by state and region.

(U.S. EPA, 2023)

For more information, visit https://www. epo.gov/septic.

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Groundwater
^ Well

Basics of Septic System Performance

A septic system consisting of a septic tank and drainfield is the most typical
onsite wastewater treatment system in the United States (Yates, 2011). Septic
systems are designed to perform several important functions, including:

•	Removing oils, grease, and solids. The septic tank is designed to allow
solids to sink to the bottom of the tank and allow floatable materials,
such as oils and grease, to rise to the surface (U.S. EPA, 2002).

•	Storing settle able and floatable material. Tanks are sized according to
wastewater flow amounts. Over time, sludge and scum accumulate
naturally in the tank (U.S. EPA, 2002).

•	Digesting/decomposing organic matter. Septic tanks provide an
environment with little oxygen to help bacteria reduce organic molecules
to compounds and gases, including hydrogen sulfide and methane (U.S.

EPA, 2002).

•	Removing remaining compounds. Drainfields filter and break down
remaining compounds in wastewater, such as nutrients, harmful
bacteria, viruses, and some chemicals. The water is treated as it moves
through the soil before returning to the groundwater (Lee & Coyne,

2012).

Conventional
Septic System

Drinking Water	*

To House Wastewater
Gravel From House ™E

Drainfield

Access
^ Risers

Septic
Tank
Distribution

Wastewater

Wastewater
Treatment in Soil

Groundwater

Bedrock

(U.S. EPA, 2023)

Please note: Septic systems vary. Diagram is not to scale.

Tips for Homeowners on Maintaining a Septic System

—~
—~
— ~
— ~

HOW. Septic systems can be maintained through the
following actions:

0 Use water in your home efficiently.

0 Properly dispose of waste in the trash instead of
down the drains.

0 Have the septic system inspected and the tank pumped regularly.

0 Keep the drainfield free of trees or heavy objects such as vehicles. Do
not drain gutters or sump pumps nearby.

0 Always follow the manufacturer's guidelines.

* Maintenance guides can be found on the EPA's website,
https://www.epa.gov/septic/septicsmart-education-materials.

H	h

WHEN. The time between pumping and
inspections is typically three to five years,
depending on household size and sludge
and scum accumulation (Harwood, 2006).

Some advanced systems with electrical float switches,
pumps, or other mechanical parts may require more
frequent inspections. Contact your local permitting
authority to find your inspection requirements.

Contact your local septic system professional to determine
if your system needs to be serviced.

References

Bulson, P. C., Johnstone, D. L., Gibbons, H. L., & Funk, W. H. (1984). Removal and inactivation of bacteria during alum treatment of a lake. Applied

and Environmental Microbiology, 48(2):425-430. https://doi.ore/10.1128/aem.48.2.425-430.1984
Harwood, E. (2006). Don't let your dollars go down the drain! Septic tank additives. Washington State University, Clark County Extension.

https://extension.wsu.edu/clark/naturalresources/smallacreageproeram/septic-tank-additives/

Lee, B. D., & Coyne, M. (2012). Impacts of additives on septic system performance. University of Kentucky College of Agriculture (HENV-505).

https://publications.ca.ukv.edu/sites/publications.ca.ukv.edu/files/HENV505.pdf
Pradhan, S., Hoover, M. T., Clark, G. H., Gumpertz, M., Cobb, C., & Strock, J. (2011). Impacts of biological additives, part 2: Septic tank effluent

quality and overall additive efficacy. Journal of Environmental Health, 74(5), 22-29. https://www.istor.org/stable/26329323
U.S. Environmental Protection Agency. (2002). Onsite wastewater treatment systems manual. Office of Water and Office of Research and

Development (EPA/625/R-00/008). https://cfpub.epa.gov/si/si public record Report.cfm?Lab=NRMRL&dirEntrvlD=55133
U.S. Environmental Protection Agency. (2023). Types of septic systems, https://www.epa.gov/septic/types-septic-svstems
Yates, M. V. (2011). On-site wastewater treatment. Encyclopedia of Environmental Health, 256-263. https://doi.org/10.1016/B978-Q-444-52272-
6.00046-5

For more information, visit https://www. epa.gov/septic.

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Common Types of Additives

The following table provides an overview of common septic system additives and challenges associated with each.

Additive Description

Associated Challenges

Septic System Line/Drainfield Cleaners

These products usually contain strong acids or alkalis and are
promoted for their ability to open clogged drains. Product
ingredients (e.g., sulfuric acid, lye) are similar to those used in
popular commercial drain cleaners.

These products can negatively affect how bacteria break down
waste and damage pipes, septic tanks, and other system
components (U.S. EPA, 2002). Hydrogen peroxide was once
promoted as a drainfield reconditioner, but it was found to
break down soil structure and compromise the life of the septic
system (Harwood, 2006).

Degreasers

These products often contain ingredients such as chlorinated
hydrocarbons (e.g., methylene chloride, trichloroethylene), which
are commonly used as degreasers. They are marketed for their
ability to break down oils and grease.

Organic solvents represent significant risks to groundwater and
onsite wastewater treatment. These products can destroy
decomposers and other helpful microorganisms in the
treatment system. Use of products containing organic solvents
in onsite wastewater treatment systems is banned in many
states (U.S. EPA, 2002).

Biological Additives

Many biological additives contain bacteria and enzymes mixed
with other chemicals or nutrient solutions, and are often
identified as biobased, bioactive, or 100% natural. These products
may contain live or active cultures of billions of colony-forming
units of bacteria, but the specific bacteria strains included in the
product are often not identified on the label. Enzymes are non-
living proteins such as cellulase and protease that are marketed
for their ability to break down organic matter.

Some biological additives can reduce septic tank scum and
sludge. However, the impact of long-term use of these
products on the ability of soils to treat wastewater is unknown.
Some studies suggest that material degraded by additives may
cause changes in treated wastewater effluent quality (Pradhan
etal., 2011).

Odor Control Products

This category of additives is advertised to control septic odors by
killing bacteria, which are important to wastewater treatment.
They often contain formaldehyde, paraformaldehyde, quaternary
ammonia, or zinc sulfate.

Bacteria and other microorganisms are necessary for onsite
wastewater systems to function properly (U.S. EPA, 2002). If
odor is a problem, the source should be investigated by a
septic professional.

Phosphorus Removal Products

Phosphorus occurs naturally in wastewater; it is also an essential
nutrient for aquatic plant growth. Phosphorus removal products
are targeted at septic system owners experiencing nuisance algae
blooms in nearby lakes and streams because reducing phosphorus
in freshwater environments can help reduce algae growth.
Chemicals commonly found in these products include aluminum,
ferric iron, ferrous iron, and calcium.

Ingredients such as aluminum (as alum, sodium aluminate,
aluminum chloride, and activated alumna), ferric iron (as ferric
chloride and ferric sulfate), ferrous iron (as ferrous sulfate and
ferrous chloride), and calcium (as lime) have proven to be
effective in stripping phosphorus from effluent and settling it
to the bottom of the tank. A side effect of this form of
treatment can be the unintended removal of beneficial
bacteria in the septic tank (Bulson et al., 1984). Because of the
potential for sludge buildup, a septic professional should be
consulted before using these products.

Flocculants

Flocculants, such as baking soda, are products that cause particles
to stick together. These additives are marketed to lower the
concentration of suspended solids in septic tank effluent,
producing clearer and cleaner wastewater.

Research has not demonstrated successful performance of this
class of additives. A properly designed and constructed onsite
wastewater system allows settling to naturally occur in the
septic tank (Lee & Coyne, 2012).

For more information, visit https://www. epa.gov/septic.

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