What Is In Wastewater Anyway?

Nitrate: Beginning in the septic tank, organic nitrogen compounds are broken down (mineralized) and inorganic ammonium (NH4+) is released.

Ammonium is soluble in water but is weakly retained in soil by attraction to negatively charged soil surfaces. Under aerobic conditions inorganic ammonium is rapidly oxidized to nitrate (NO3-) through a microbial process called nitrification.

Nitrate as an ion is very soluble in soil solution, and is often leached into the ground water.

Nitrate poisoning of infants caused the establishment of drinking water standards for this substance. The increased use of breast feeding and liquid infant formula concentrates have almost eliminated reported cases of Methemoglobinemia in the United States. However, nitrate will continue to be an important indicator of subsurface pollution because it is associated with many other harmful substances that can pollute drinking water.

According to a 1995 US Department of the Interior study in central Washington State, 30% of wells have nitrate concentrations exceeding the US Government MCL (maximum contaminant level ) of 10 PPM (parts per million). Central Washington contains both vast areas of dryland wheat farms and one of the largest irrigation systems in the world spread out below the famous Grand Coulee Dam.

One map from this study shows the application of nitrogen in pounds per acre. Average application is around 120 to 150 pounds per acre per year on farmland, or up to 50 tons of nitrogen per year per square mile from agriculture.

A report by the State of Washington is available to assist designers and operators of septic systems and sewage treatment plants in understanding and estimating the mass loading of nitrogen from residential dwellings (Methodology to Predict Nitrogen Loading from Conventional Gravity On-Site Wastewater Treatment Systems 1995). From this report, the nitrogen from people is about 22 grams per person per day entering the septic system with reduced amounts entering the ground water through the waste stream. This amounts to about 16 pounds of nitrogen per year produced by an average household.

The report then documents the nitrogen removal performance of several recently built test facilities in the US including the Anderson facility in Florida. Not theoretical models, these studies document the performance of actual septic systems.

Septic systems are simply not a significant source of nitrogen.

Few municipal systems use any method of nitrogen removal. Municipal sewage treatment unlike on-site septic systems, concentrates nitrate at the treatment plant. Typically nitrate from municipal sewage treatment is discharged underground in huge drainfields or expelled to surface water. Everything goes somewhere.

Phosphate: Although phosphate is not a toxic substance, excess levels in lake waters can promote eutrophication, the excessive growth of aquatic plants and eventual depletion of oxygen.

The major source of phosphate in surface water is from fertilizer. Application practices can cause soil adsorbed particles to run off into surface water.

Over the years, the amount of phosphate used in households is declining. Very few laundry or kitchen products use phosphates anymore. Certain powder dish washing soaps still contain this substance due to its superior spot resistance.

Phosphate is a minor by-product of organic decomposition of sewage, and small amounts of phosphorus are present in sewage. However, Anderson, and Bomblat in their discussions of 1994 do not include phosphorous or phosphate as materials of interest in their detailed analysis. It is almost impossible to link phosphate in the environment with septic systems because the amounts produced are so small when compared with natural sources and surface application of phosphate on farms and lawns. This has not prevented speculation by individuals who continue to point the finger at septic systems as a source of phosphate pollution, again without direct proof.

It is well known that phosphate is absorbed into and strongly attaches to soil particles close to the drainfield. Phosphate travels only a few inches in a hundred years

Organic compounds: Organic matter comprises the bulk of the solids in wastewater. Chemical and biological oxygen demand (COD and BOD), total organic carbon, and suspended solids are water quality analyses commonly used to indicate the amount of organic matter present in wastewater. Nearly all organic matter in household wastes is biodegradable, and it does degrade readily in soil.

Toxic Synthetic Organic Compounds: It is a popular myth that domestic household sewage contains significant levels of synthetic organic compounds referred to as household chemicals.  Priority pollutant scans by the state department of health of municipal wastewater have discovered that these compounds do not enter the waste water from the building sewer.

The only known products of this type used in houses and likely to enter the sewage stream are shampoos used to treat head lice. The compounds are malathion, carbaryl, and phenothrin.

The only other sources for synthetic compounds are found in the garage and the storage shed. These compounds are used around the house not in it. They are used for ornamental plants and to control pests such as termites.

The likely entry point for these substances into the wastewater stream is through the gravity collection lines leading from the home to municipal treatment plants. Apparently, cracked, broken and ill fitting piping is allowing surface water from the yard to flush these products into municipal sewers.

The numerous studies do not show any presence of synthetic organic compounds in septic systems. The evidence that these materials represent a health hazard in septic tank effluent simply does not exist. The few studies that indicated the presence of these substances involved the sampling of municipal waste water which would have included some groundwater infiltration through faulty collection lines. Septic systems normally use less than 20 feet of collection line per house.

Microorganisms in Wastewater: The removal of pathogenic (disease causing) microorganisms is the constitutional task of a septic system. While most microorganisms in wastewater are harmless, pathogenic (disease-causing) organisms may be present. The interactions of these organisms with soil are much more complex and poorly understood than the reactions of nitrogen and phosphate. Pathogenic organisms in wastewater can include bacteria, viruses, protozoa, and helminths (worms).

To minimize the risk of disease transmission, pathogenic organisms are contained within and treated by the septic system. Treatment in the drainfield prevents the organisms from reaching drinking water aquifers. Trapping of the microorganisms such as protozoa and helminths in the soil followed by attacks by aerobic organisms results in final removal. Soil properties, environmental conditions, and the nature of the microorganisms themselves control the rate at which these creatures die.

Viruses are many times smaller than bacteria. They tend to move easily through soil pores and have been detected moving through soil faster than groundwater flows. They are retained primarily by chemical or physical adsorption to clay or oxide surfaces. Retained organisms are not necessarily inactivated, and may even be protected from inactivation. Viruses have been found surviving underground for up to 200 days. Viruses have been located up to 5000 feet from a source. Retention slows the movement of bacteria and viruses through the soil, but may also prolong their survival.

Retention is not necessarily permanent. During periods of heavy rainfall, retained viruses become resuspended in the soil water, and are transported rapidly by saturated flow through large soil pores. When retention protects viruses from destruction, they may reach ground water by alternate cycles of retention and resuspension.

Human viruses can be hardy and mobile in groundwater. They are also very tiny and difficult and expensive to study. Today however, bacterial colonies are still used as indicators of bad water samples. As viruses become easier and cheaper to detect, they may replace bacteria as the main indicator of health risks in groundwater.


The article above was obtained from the website www.eco-nomic.com , the author John Glassco. His article was with help from Craig G. Cogger, Extension Soil Scientist, WSU Puyallup, WA. and College of Agriculture and Home Economics, Pullman, Washington.  (Sincere apologies to John Glassco for a previous misrepresentation of authorship.)