Abstract: This invention relates to the design and operation of paired subsurface flow constructed wetlands in which significant improvements in wastewater treatment are possible. These improvements are brought about by coupling paired subsurface flow wetlands and using reciprocation, whereby adjacent cells are sequentially and recurrently drained and filled using either gravity, mechanical pumps, U-tube air-lifts and/or a combination thereof. This fill and drain technique turns the entire wetland area into a biological reactor, complete with anoxic, anaerobic and aerobic environments. The frequency, depth and duration of the fill and drain cycle can be adjusted to control redox conditions for specific biologically mediated reactions including, but not limited to, nitrification, denitrification, sulfate reduction, and methanogenesis. Emissions of noxious gases such as hydrogen sulfide and mentane can be minimized.