Reciprocating wetlands

These are sometimes called "tidal flow" wetlands, or "fill and drain" wetlands.  This is an ingenious technology that can achieve a remarkable standard of treatment and can even be made to work by gravity on some sites.  Two or more wetland cells are required. Water fills up the first wetland cell until it is completely saturated. After a measured residence time, this cell is emptied by pumping to the second cell, until the second cell is filled and the first completely drained. This process is repeated several times until the desired level of treatment is reached. This is another very efficient way of oxidizing wastewater while achieving some of the benefits of extended contact time with the treatment medium. A high level of control over discharge standard can also be achieved with this type of system.