The present invention recognizes that there exists a long felt and unfulfilled need for a photobioreactor for treatment of wastewater (Passive Aerobic Treatment Unit (PATU). As a non-limiting introduction to the breadth of the present invention, the present invention includes several general and useful aspects, including but not limited to: a) a device or system for the passive treatment of a liquid wastewater stream using autotrophic, phototrophic, and heterotrophic microorganisms growing in a photobioreactor; and b) a method of treating wastewater using the devices of the present invention.