An anaerobic septic system is generally what most people who have septic system already have installed. It's been the most popular type partly because there has been so little to compete with it. They do not cost that much to install, they are relatively simple to maintain, and it's been accepted that this is the standard for residential systems. While the private sector has certainly embraced the anaerobic system, municipalities do not use these at all.
An anaerobic septic system breaks down waste product at a rather slow and inefficient rate. When considering the residential use of a septic system this could be found to be acceptable. By the consistent standard use and the fact that one household would have to work pretty hard to fill up the system there has been little question as to the efficiency of the system. Municipal use of such systems simply does not exist. These systems can not handle the large volumes of waste that they encounter on a daily basis. Thus, industrial systems are aerobic.
The technical difference between anaerobic and aerobic is based on oxygen use. Both are bacteria. They each have specific duties and are capable of breaking down the waste material that are collected. The anaerobic bacteria do not need oxygen in order to thrive. Aerobic bacteria do.
The difference between the two bacteria in practical applications is vast. Because anaerobic bacteria are so slow at the breakdown process a secondary treatment is required because the waste water is less than 50% clean in most cases. Secondary treatments often use the aerobic bacteria. The secondary treatment requires more space.
The anaerobic bacteria are also known for creating the noxious odors that often come from a septic system. The breakdown process with these specific bacteria can be directly linked to the production of methane gas. There are other odors that are often even more offensive than methane, and these are often the odors that can be smelled inside the home after a deluge of rain or outside where the septic system lives under the ground.
Anaerobic systems also tend to discharge a foul, repugnant sludge that is thick and slimy. It turns into what is known as a bio-mat. Aside from being a hazard to the environment this is also what eventually backs up the system and requires costly repairs. It may only happen once every 20 years, but the system will eventually stop working properly because of the bio-mat. The waste product that these septic system leave behind is considered to be an environmental hazard and is generally unhealthy to live around. The aerobic systems are starting to win favor among residential units because they tend to counteract all of the general negatives that the anaerobic systems offer.