How would you design a constructed wetland for wastewater treatment?

Design approach: select wetland type - free water surface (FWS) for secondary/tertiary or subsurface flow (SSF) for primary/secondary treatment. SSF design: gravel/sand media bed (0.6-0.8m depth), hydraulic loading 0.05-0.1 m3/m2/day, aspect ratio 3:1 to 5:1, slope 0.5-1%. Plant species: Phragmites, Typha tolerant to wastewater. Size for BOD removal: first-order kinetics with rate constant 0.1-0.2/day. Include pretreatment (septic tank), distribution system, outlet control structure. Winter performance considerations in cold climates. Suitable for small communities, secondary treatment.