These systems are rapidly becoming more and more common, especially in neighborhoods and in areas where drain field space/absorption is a concern. These systems are by far the most expensive systems to own and maintain. Most owners are required to maintain a maintenance contract with a licensed installer, the waste pumps are more expensive to replace, there is an external air pump to maintain, and you must purchase Chlorine tablets on a regular basis to treat the effluent. However, these systems do an excellent job of maintaining good bacteria, and treating the effluent. They are essentially a miniature waste water treatment plant.
This style of system is the least common system in use. This system comes in many different sizes and configurations, but the big difference between it and the above system is that it uses a pump in a separate tank to push the waste out. This means that the drain field can be located above the tank and in configurations that just would not work for conventional systems. The pumps that are used are readily available from local supply stores and the overall system is typically very reliable, with relatively low maintenance costs. We typically recommend these septic systems be pumped every 2-4 years as well, to prevent sludge from spilling over into the pump tank. This can ruin the pump and cause sludge to be pumped into the drain lines.
This is by far the most common septic system and typically has the lowest cost of ownership. However it is heavily effected by rain, and the capacity of its drain field.
Residential systems typically range from 250 Gallons to 1250 gallons, with 1000 gallons being the most common. Many of the 1000+ gallon systems are dual compartment, as shown in the top picture. We typically recommend pumping these septic systems every 2-4 years depending on how many people are in the home. Going beyond this time can cause sludge to build up to the point where it starts going out into the drain field. This causes a bio mat to be formed, which blocks absorption and reduces capacity. In many cases this damage is not repairable, and in any case leads to costly repairs.