Aerobic Septic Systems Explained

Although the number of miles of sewerage seems to be growing steadily across the country every year as more and more communities turn from individual septic systems to community-based sewage systems (sewage flows through sewerage) and mass processing, there are still areas where septic systems are the norm, whether anaerobic or aerobic septic systems.

Aerobic System

Of the two types of septic systems, the aerobic system is probably the best for a number of reasons:

  1. It handles waste water more quickly and efficiently
  2. It relies on aerobic bacteria which are quicker acting
  3. Quicker acting septic systems tend to keep odors down

Aerobic and anaerobic septic systems have two things in common. They are based on large cement in-ground tanks, and they may require leaching fields for overflow. This is where the similarities stop, and the differences begin. Aerobic systems require electrical outlets or separate services, aerators, motors and proper installation and grounding.

Differences Explained

Standard anaerobic septic systems are not active systems. Let's walk through a standard anaerobic system's operation to see how it works.

Assuming a toilet is flushed, waste water shoots into the cement storage tank where things slow right down. Solids sink to the bottom, while fluids remain on top. Since this is a closed system, the anaerobic bacteria work on cleaning on the fluid effluent first. As the tank fills up, the fluid effluent exits through piping that puts the liquid portion of the effluent into what is called a leaching field. The leaching field is made up of a combination of materials. First sandy and clay-based soil is used through which the effluent must pass. The sand/clay-based soils are overlayed on gravel and rock that form the base of the leaching field. Once the effluent passes through the sand/clay and gravel/rock, the liquid effluent travels into the soil where it is further filtered. Solids are worked on much more slowly by anaerobic bacteria which is why an aerobic system is better because the aerobic bacteria tend to work more quickly than anaerobic bacteria to clean more area through which the fluid must pass and those fluids are eventually leached into the soil.

Active Systems

Aerobic systems are also called active systems. The working of the system is not very complicated. Effluent enters the system; once in the system an aerator constantly injects oxygen into the effluent, while a paddle (it might be more like an eggbeater paddle) constantly churns the effluent. This provides the aerobic bacteria with a constant flow of oxygen. Aerobic bacteria works more quickly than anaerobic bacteria and, because the system is constantly churned, even the solids that normally gather at the bottom of the tank are exposed to the bacteria so the solids are worked on as well.

You will find that installation cost is the key difference between the systems because the aerobic system requires:

  • A separate electrical feed or service
  • A proper insulation bed so that the in-ground tank remains safe
  • An aeration system
  • A paddle or churning system

The cost differential can be a factor of three or four when everything is factored in.