Special Report on Soap: Septic Tank Systems and Today’s Household Cleaning Products……………………
A glossary of common terms
Adsorption: the attachment of soluble material to soil.
Biodegradation: the breaking down of organic (carbon-containing) ingredients into carbon dioxide, water and minerals by the action of microorganisms, such as bacteria.
Drain field: a series of distribution pipes placed in trenches filled with gravel.
Effluent: clarified wastewater.
Groundwater: water beneath the ground surface.
Leach field: another name for drain field.
Septic tank system: wastewater treatment system, usually small, utilizing a settling tank and a wastewater distribution system.
Sludge: heavier solids that collect on the bottom of the septic tank.
Tile field: another name for drain field.
Wastewater: used household water from kitchens, bathrooms, laundry rooms, etc.
Common ingredients in household cleaning products
Antimicrobial agents: Kill or inhibit the growth of microorganisms that cause disease and/or odor. They are effective at the concentrations recommended for use in the home.
Bleaches: Help whiten, brighten and remove stains. Some bleaches disinfect.
Builders: Reduce water hardness, provide alkalinity (which helps cleaning) and help keep soil from redepositing on surfaces.
Fabric softening agents: Impart softness and control static electricity in fabrics.
Fluorescent whitening agents: Attach to fabrics to create a whitening or brightening effect.
Surfactants: Enable the cleaner to wet a surface more quickly so soil can be easily loosened and removed. They break up oily soils and keep them suspended in the wash water so they don’t settle back on the surface being cleaned.
According to the U.S. Census Bureau, 25 percent of homes in the United States are connected to onsite wastewater disposal systems. About 95 percent of those are septic tank systems. That means all household wastewater from these homes is treated on the property owner’s site rather than in a municipal wastewater treatment facility.
Studies show it’s safe to use and dispose of household cleaning products in these systems.
A septic tank system is actually a small wastewater treatment system designed to treat wastewater from one home or group of homes, rather than from a whole community. The system is generally located underground in the backyard and consists of a tank usually connected to a series of pipes set into trenches—into what’s called the drain field.
In the tank
Wastewater from the home flows into the tank. The tank separates solids from the wastewater, so the solids are removed before they reach the drain field. Heavier solids, called sludge, collect on the bottom of the tank; lighter solids like hair and grease float to the top and form a scum layer on the water.
To the field and into the soil
Once the solids have been removed, the clarified wastewater, or effluent, is transported to a drain field by a pipeline. The drain field (sometimes called a tile field or leach field) consists of a series of distribution pipes set in trenches filled with gravel. These distribution pipes have holes so that the wastewater from the septic tank flows out into the gravel trenches then trickles through the gravel and into the soil under the drain field. Soil acts as a natural filter in the septic tank system. It filters out many of the bacteria that can cause diseases.
After a cleaning product has been used and goes down the drain, its ingredients become part of your household wastewater and are treated by the same wastewater treatment system that treats the other wastes from your home—before the water reaches groundwater or its receiving streams, lakes, estuaries or oceans.
Today’s cleaning products are designed to be compatible with a wide variety of wastewater treatment systems in use throughout the United States, including septic tank systems. This means that household cleaning products can be safely disposed down the drain into properly designed and maintained septic tank systems.
Down the drain
Among the ingredients that may be found in household cleaning products:
The major components of cleaning products are surfactants. In a septic tank system, the surfactants are adsorbed onto soils and digested by the microorganisms in the drain field. They break down into water, carbon dioxide and minerals. This is known as biodegradation. The Soap and Detergent Association (SDA) undertook a field study where concentrations of major surfactants were measured in the soil beneath a household septic system drain field. The study found that in a properly sited and maintained septic tank system, there will be no surfactant residues in groundwater, indicating that surfactants are completely removed before they reach groundwater.1
The other major ingredients in cleaning products are builders. The most commonly used builders are inorganic compounds, including carbonate and phosphate compounds and zeolites (aluminosilicates). Builders break down in the drain field into minerals common in nature, such as carbonate, phosphate and silicate; they settle out in the septic tank and are disposed with the sludge; or they’re captured by the soils below the drain field and remain in the soil.
Sodium hypochlorite, sodium perborate and hydrogen peroxide are bleaches commonly used in cleaning products. They react in the wash water or during the cleaning of hard surfaces and convert to sodium, chloride and borate salts—minerals commonly found in the environment.
Other ingredients, such as fabric softening agents, antimicrobial agents and fluorescent whitening agents, biodegrade and adsorb to solids in the tank and soil.
Products designed to kill microorganisms have become increasingly common in today’s homes. But how do these products affect septic tank systems, where microorganisms are needed to treat wastewater?
An SDA evaluation of this subject1 concluded disposal of household quantities of cleaning products, such as bleaches and disinfectants, does not interfere with the function of a properly sited and maintained septic tank.
A typical septic tank holds 500-to-1,000 gallons of wastewater. Dilution of antimicrobial cleaning products in such large volumes of wastewater allows for effective operation of biological waste treatment following the disposal of cleaning products. This appears to be true even under the worst case scenario, where whole packages of products are disposed into relatively small septic tanks.1
It’s also worth noting the same evaluation concluded that disposal of household quantities of alkali-based drain openers do not interfere with the function of a properly sited and maintained septic tank.
As with any equipment, a septic tank system must be correctly installed and maintained in order to work properly. These six tips will help ensure that you’re properly managing your wastewater system:2
- Have your septic tank system installed by a licensed contractor following local guidelines and regulations.
- Have your system inspected and pumped out regularly, following local guidelines and regulations. Pumping out every three to five years is recommended for a three bedroom house with a 1,000 gallon tank; smaller tanks should be pumped more often.
- Follow basic water conservation practices to avoid overloading the system. For example, fill the sink to do dishes rather than washing them under running water; repair any leaky faucets or toilets; and don’t leave water running continually while brushing teeth.
- Do not use septic system additives. There is no scientific evidence that biological or chemical additives aid or accelerate decomposition in septic tanks; some additives may in fact be detrimental to the system or contaminate groundwater.
- Divert other sources of water, like roof drains, house footing drains and sump pumps, away from the septic tank system. Excessive water keeps the soil in the drain field from naturally cleansing the wastewater.
- Be careful of what you put down the drain. For example, products not normally used with water, such as gasoline, motor oil, etc., should not be disposed into septic tank systems. Avoid or reduce use of your garbage disposal, which contributes unnecessary solids to the system and increases the frequency the system needs to be pumped. Additionally, don’t use toilets as trash cans. If in doubt about disposal of a product, contact the manufacturer.
- Edwards, D.E., and A.J. DeCarvalho, “Assessing the Impact of Disposing Household Cleaning Products to Wastewater Treatment Systems,” The Small Flows Journal, 4(1), pp. 15-27, 1998.
- “Septic System Maintnanence,” EPA Journal, Nov./Dec. 1991, EPA-22k-1005.
This article is a modified version of one written by The Soap and Detergent Association, which is in the process of moving its offices from New York to Washington, D.C. You can find it in its original form on the organization’s website, www. cleaning101.com . For more information, contact Al DeCarvalho via email: firstname.lastname@example.org. Images are courtesy of the National Small Flow Clearinghouse: www.estd.wvu.adu/nsfc
Chemical Fate and Transport in a Domestic Septic System: A Case Study. Cherry, John A. and Rappaport, Robert A., Environ. Toxicol. Chem., 13 (2), pp. 181-182, 1994.
Chemical Fate and Transport in a Domestic Septic System: Site Description and Attenuation of Dichlorobenzene. Robertson, W. D., Environ. Toxicol. Chem., 13 (2), pp. 183-191, 1994.
Chemical Fate and Transport in a Domestic Septic System: Saturated and Unsaturated Zone Geochemistry. Wilhelm, Sheryl R. et al., Environ. Toxicol. Chem., 13 (2), pp. 193-203, 1994.
Chemical Fate and Transport in a Domestic Septic System: Biodegradation of Linear Alkylbenzene Sulfonate (LAS) and Nitrilotriacetic Acid (NTA). Shimp, R. J. et al., Environ. Toxicol. Chem., 13 (2), pp. 205-212, 1994.
Chemical Fate and Transport in a Domestic Septic System: Sorption and Transport of Anionic and Cationic Surfactants. McAvoy, D.C. et al., Environ. Toxicol. Chem., 13 (2), pp. 213-221, 1994.
Environmental Risk Assessment of Cleaning Product Ingredients. Chemosphere, 32(4), pp. 703-715, 1996.