Aerobic treatment units (ATUs) require a mechanical means to add dissolved oxygen to the tank. This is usually accomplished with an air compressor. One type of air compressor referred to as a linear air compressor that is commonly used is the Hi-Blow HP-80 shown below.
This is a very common air compressor used on many 500 gallon per day (GPD) ATUs. It is a reliable and energy efficient air compressor that can be rebuilt under certain circumstances.