The most prevalent way to treat human waste in rural areas where a large amount of land is available is:

Septic systems.

Explanation:

A septic system refers to a highly efficient, self-contained system for handling underground waste. The simple design of the septic system make them economically efficient to install. Since septic systems handle and dispose of on-site household waster, they are often more cost-effective than consolidated sewer systems in rural areas where lot sizes are larger and houses are widely spaced apart.