Printer-friendlyEmail to friend

This article was originally produced and distributed in parts. All parts, following their distribution, are provided here on this page together in a single article.

Thanks to Candace Balmer, a Water Resource Specialist for RCAP Solutions, the Northeast RCAP, who was the creator of a training presentation from which this article was adapted.

What is wastewater, and why do we treat it?

We all create wastewater multiple times a day – whenever we use the toilet, take a shower, or wash the dishes or our clothes. In general, residential wastewater is defined as any water generated by household fixtures. It’s what we dispose of down the drain at home.

In most cases, this used water needs to be cleaned before it’s put back into the environment or before we use it again. It’s for the benefit of the public’s health and the Earth’s health that we treat wastewater.

Of course, wastewater looks and smells bad. Beyond that, and more importantly, untreated wastewater can cause and spread disease. Untreated wastewater can have harmful effects to the water when it is returned to the environment. Sewage depletes oxygen in the water, is harmful to aquatic life and can result in excess nutrients being discharged into water bodies resulting in the  growth of nuisance vegetation.

What is a septic system, and why is it important?

In many places, especially large cities, wastewater is collected from a large area and treated at a central treatment plant. In other places, including many rural areas, it is treated close to where it is generated – in a septic system.

A septic system is an underground system that treats wastewater from an individual home. If your home is not connected to a public sewer, then it has or ought to have some sort of a septic system. Septic systems are regulated at a minimum by the state or the local health authority. Different states have similar but not identical requirements.

Reasons to understand septic systems:

• They are widely used, especially in rural areas.
• They are the primary alternative to central sewers.
• They treat wastewater and thus protect the public’s health, water resources and the environment.
• It’s the law: Public health and environmental laws require wastewater to be treated.
• Like other types of wastewater treatment systems, they recycle water back into ground, where it can be used again.

Another reason to understand septic systems is that they can cause harm when they don’t function properly:

• Failing systems can cause contamination of the ground and surface water. Poorly treated wastewater can percolate into the groundwater and even be carried through the groundwater to a nearby lake or river.
• Failing systems threaten the public’s health and the environment.
• You may have a functioning system, but what if your neighbor doesn’t? It may affect you – your property and health. Dirty water often doesn’t follow property boundaries.
• Untreated wastewater contains nutrients, which cause aquatic plants to grow, sometimes out of control. Excess nutrients from untreated wastewater can cause rapid growth of algae and other nuisance vegetation. Nitrogen and phosphorus are examples of nutrients that can be emitted from a substandard septic system. Nuisance growth can degrade water quality. It can impact drinking-water quality, recreation and aesthetic enjoyment, as well as commercial uses and environmental interests.

Finally, septic systems are regulated, so it is important to understand the laws you must follow. Your state sets minimum standards, but other  regional or local authorities may set standards at a more stringent level. You may be required to keep records, permits or other documentation to show the system has been inspected and has been functioning properly. In some states, an inspection may be required upon transfer of property. Realtors need to be aware of any requirements involving septic system condition disclosure requirements.

How does a septic system work?

There are three main processes in wastewater treatment, whether in a septic system or at a central sewer system. The liquids and solids that make up wastewater are treated and disposed of separately. 

1. Collection: The wastewater is collected from household fixtures - sinks, showers, toilets, washing machines, etc. - and piped outside and underground to the septic tank.
2. Treatment

• Physical separation takes place in the septic tank, where solids and greases are trapped.
• Biological treatment takes place in the soil-absorption system, where the liquid wastewater is broken down by bacteria in the soil.

3. Disposal:

• Liquids: Treated wastewater is dispersed into the soil for ultimate disposal.
• Solids: Solids and greases that accumulate in the septic tank are periodically pumped out and typically trucked elsewhere for ultimate disposal.

The diagram below shows the components of a typical septic system:

Functions of the major components:

1. Collection pipes collect the wastewater in the home, and a single pipe exits the home underground, carrying the collected wastewater to the septic tank.
2. Inside the septic tank, solids and greases are allowed to naturally separate from the liquid. Removing solids is critical to wastewater treatment and is always the first step. The solids and greases stay in the tank and eventually need to be pumped out.
3. From the septic tank, the liquid flows into the distribution box, which divides the liquid into equal portions.
4. Soil-absorption system, where the liquid wastewater is treated and disposed of. The soil-absorption system is often referred to as a drainfield or leach field. This is where the real work of wastewater treatment takes place. Wastewater trickles out of small holes in the distribution pipes and into the surrounding soil. Microorganisms that live in the soil eat the wastewater and in the process break it down into simpler components. 

If you are installing a septic system on your property, there are many factors to consider for each of these components for proper installation and efficient operation of your system. These factors are not discussed here, but experienced and reputable installers will know how to properly install the system or what factors are causing an existing system to not function properly.

The diagram below shows inside the septic tank.

In this diagram, wastewater enters through the inlet (to the left). It immediately hits an obstruction, called a baffle, which intentionally slows the flow. This causes the solids to drop out more readily, and they settle to the bottom of the tank as sludge. Oils and greases - cooking oils, for example - float to the top of the tank as scum. Another baffle at the outlet blocks any floating solids from exiting the tank along with the settled wastewater. Baffles are important and may be one of the first things to wear out in an aging tank. Replacing them is cheaper than replacing your tank, or worse, the entire absorption system if it becomes irretrievably clogged.