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Septic system basics for homeowners, community leaders, planners and realtors (Part 2)

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.