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Residential dishwashing machines and their possible effects on septic systems are explained in this article. Will the discharge from a home dishwashing machine into a private septic system harm the septic tank or drainfields? What detergents are best to use in a home dishwasher to minimize impact on the septic system and the environment. How can we reduce the impact of a dishwasher on a septic system - should we install a separate drywell? This document explains how to extend the life of the septic system by being careful about what goes into it.
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Does a dishwasher water volume overload and harm the septic system?
The volume of water from home dishwashing machine use should not be a problem with a normal septic system in good working order.
However as we discussed at "Washing Machines", in some conditions you should avoid emptying dishwasher discharge into the septic system:
Does dishwasher detergent or dish soap harm the septic tank or septic system drainfield?
The volume of dishwasher detergent or dish soap used in sinks entering the septic system is so low as to be very dilute when it enters the septic tank, dilute enough that it is not going to harm the septic tank bacteria at normal levels of residential dishwasher use.
However many if not most dishwasher detergents contain phosphates or nonylphenol ethoxylate surfactants. Surfactants are what make detergents effective in lifting soil particles off of a surface (a dish in the dishwasher or a shirt in the washing machine).
Dishwasher detergents do not make a high level of suds inside the dishwashing machine. If you've ever made the mistake of putting normal dish soap into a dishwasher (as did this author) you know what a disaster will ensue - with sudsy soap overflowing out of the dishwasher and across the floor. Dishwashers rely on surfactants, high water temperature, and time spent spraying across the dishwasher contents to clean them.
Even if they don't kill off your septic tank or drainfield bacteria, surfactants and phosphates that run through a dishwasher ultimately enter ground water and surface water may also become contaminated.
Surfactants in dishwasher detergents (and from any source) are toxic to fish, basically suffocating them by interfering with the ability of the fish's gills to absorb oxygen from water.
Phosphates in dishwasher detergents pass through the septic system (or municipal wastewater treatment system) and enter surface water causing very high growth rates of algae. The algae growth, in turn, suffocates fish and other life in rivers, streams, lakes, and ponds. The rapidly growing "dead zones" at the edges of major water bodies around coastal areas of the U.S. and other countries are blamed on surface runoff that contains phosphates, (probably largely from agricultural use).
According to Cliff Davies, a U.S. EPA engineer reported in the New York Timesthe level of phosphates in dishwasher detergent has been significantly reduced since the 1970's.
But Mr. Davies was unable to identify specific dishwasher detergent products or brands that were high in surfactants or phosphates, and the Times article reported that the U.S. EPA "Design for the Environment Program" which he administers does not track products that are problematic.
The EPA does, however, list dishwasher detergent products whose manufacturers report to the EPA that they use the safest chemicals. The EPA does not perform tests to confirm the accuracy of product claims.
In sum, consumers who want to minimize their contribution to environmental pollutants by their choice of dishwasher or washing machine cleaning products may want to purchase products listed by the EPA's "Design for the Environment Program" but the listing designation does not appear to be supported by independent testing nor publicly available data. As of June 2013 it's the best we've got.
Recommendations for Green Non-Toxic Dishwasher Detergents when Collecting Graywater or Connecting to a Septic System
Reader Question: what dishwasher detergent should I use if I'm collecting graywater to irrigate plants or a garden? How do I match "unwanted chemicals" to detergent products' list of ingredients?
I have been thinking a lot about the grey water plans we have going. Our method will be very simple: all the wash water will go to a drum that is fitted with a hose. We plan to move to the hose to tree basins as needed. The attached is a reference I came across. It really doesn't help me very much in a specific way. For example... how do the ingredients in Dawn dish washing soap match up to the chemicals on the chart? Or, how do I select the least offensive laundry soap?
We discuss dishwasher detergents in detail in this article, beginning at DISHWASHERS vs SEPTICS
The citations sections of this and other articles we cite here list some excellent references on graywater including some building codes that can be taken as a design minimum if you want the water discharged from the system to be long term usable on plants or a garden.
Bottom Line on Dishwasher Detergents, Phosphates, Surfactants
At least in the U.S. where in 2010 seventeen states adopted laws that required a big reduction in the level of phosphates in detergents, most laundry and dish detergents you may buy at even standard outlets are likely to be low in phosphorous. Also using liquid detergents and soaps in the sink, laundry, dishwasher, or soap packets or tablets in the dishwasher may avoid additional plumbing system clogging (and soil clogging where connected to a private septic like yours) that occurs from excessive use of powdered products.
DETAILS: For people who like to research specific products online or to buy online, Amazon lists quite a few "green" dish detergents, laundry detergents, and dishwasher detergents. Here are a few:
Alphabetical List of "Green" Dishwasher Detergents
If we look for "green" laundry detergents, dish soaps, and dishwasher soaps, unfortunately that does not mean you'll find these products at your local bodega.
There is a secondary concern that some "green" detergents may not do as good a cleaning job on dishes or clothes
Home Made Dishwasher Detergent Recipes
Some (not peer reviewed) authors may give a recipe for home made dishwasher detergent
Standard recipe for dishwasher soap or detergent might be
or alternatively (not yet researched, may not be authoritative):
Watch out: you probably already know this, but don't use a sudsing detergent like dish soap in a dishwasher nor washing machine - you'll have a suds disaster.
Translating Dishwasher or Laundry Detergent Ingredient Lists
Look for information on the ingredient label that discusses the level of phosphorous, phosphates, and surfactants. Some readers who wish to avoid perfumes and dyes (generally not harmful to the septic tank or drainfield) may find those chemicals hard to recognize except by the smell test.
[more notes are in process on this, contributions welcomed]
More Reading on Dishwasher & Laundry Soap Recommendations for Graywater & Septic Systems
One option is to install a separate graywater system (greywater) or drywell to receive water from the dishwasher. If you are considering this step, consider connecting both dishwasher and clothes washer to a common drywell.
At some properties with very limited septic capacity, a large drywell may be installed to handle additional gray water from other building fixtures such as sinks and showers. See DRYWELL DESIGN & USES for additional information.
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 comments from readers are welcomed. Contributors are listed at the end of each article.
This article is a section of our online book SEPTIC INSPECTION & TEST GUIDE whose chapters are shown at the left of this page. 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 comments from readers are welcomed. Contributors are listed at the end of each article.
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