A modular liquid waste treatment system is disclosed. In accordance with some embodiments, the system includes a central distribution unit and one or more treatment fins in flow communication therewith. The distribution unit may be configured to receive liquid waste from a given source and distribute that waste, at least in part, to one or more treatment fins. In turn, bacteria present in a given treatment fin treat the liquid waste, and the resultant treated liquid may drain from the fin to the surrounding environment. In some embodiments, a given treatment fin may include porous media providing a large surface area on which bacteria may grow to facilitate treatment. The system may be installed in and/or above the ground, and in some cases may be surrounded, at least in part, with treatment sand and/or other treatment media. The system may be used in aerobic and/or anaerobic processing of liquid waste.