What each system does, what it costs, and when the county makes you buy the expensive one.
Tank, then gravity carries clarified liquid to gravel trenches where soil finishes treatment. No pumps, no electricity, simplest maintenance. Requires good-percolating soil, adequate lot size, and a water table that stays well below the field. If your lot qualifies, this is what you want.
Same idea, but manufactured plastic chambers replace gravel trenches. Less gravel to haul, faster install, easier inspection. Common where gravel is scarce or expensive. Maintenance is the same as conventional.
When the water table is high or soil is too shallow, an engineered sand mound is built above grade and effluent is pumped up into it. Needs a pump chamber, electrical, and engineered design. Pumps and controls add ongoing maintenance and replacement costs.
An aerator actively treats wastewater in the tank before it reaches a (usually smaller) drain field. Fits small lots and marginal soils, and many states require them near waterways. Tradeoffs: continuous electricity, required service contracts (typically 1–2 visits/year), and more parts to fail. Bad sites push engineered ATU projects past $40,000.
Pressurized pump pushes effluent through drip tubing buried shallow across a large area. Good for slow soils and landscaped sites. Complex sites reach $35,000+. Drip lines need flushing and monitoring; not a set-and-forget system.
The site evaluation and your county's rules choose for you. Your real decision is the installer: get three quotes from licensed installers, ask each what system type they're proposing and why, and compare their answers. If two say conventional and one says mound, ask the third what they see that the others don't.