Apparatus and methods for removing solutes from wastewater are disclosed. An embodiment provides a reactor tank having a manifold located at or near an interface between a lower (upstream) section having a first cross-section and a higher (downstream) section having a second cross-section smaller than the first cross section. An inlet for wastewater to enter the reactor tank is located in or below the first cross-section. A recycling path is provided for removing wastewater from the manifold and recycling at least part of the removed wastewater into the reactor tank. An outlet for water to exit the reactor tank is located downstream from the manifold.