Treatment Pond - Design Characteristics

Design Characteristics

Surface flow reedbeds use a horizontal flow of waste water between plant roots. They are no longer much used, as they need considerable space (A person requires 20 m2 to purify the water they use.) They have increased smell and poorer purification in winter.

With subsurface flow reedbeds, the flow of waste water is between plant roots, but not at the water surface. This is more efficient, less smelly and less sensitive to winter conditions. The soil to purify water is 5–10 m2 per person. Intakes, which can clog easily, are a potential problem.

Vertical flow reedbeds are similar to subsurface flow reedbeds (subsurface wastewater flow is present here as well). Therefore they have similar efficiency and winter hardiness. Wastewater flow is somewhat different though, as it is vertical. The water is distributed through a set of perforated distribution pipes in the top layer of gravel. The wastewater then passes a layer of fine sand mixed with iron and chalk and there it is purified by bacteria that live on the sand grains and in higher concentrations near the plant roots. The purified water is then collected in drainage pipes that are embedded in the bottom layer of gravel. Other than the two previous systems, this system almost makes exclusive use of fine sand to increase bacteria counts. Intake of oxygen into the water is better. Pumping is done in pulses to reduce obstructions with the intakes. Only 3 m2 is needed to purify the water for one person.