SOIL CLOGGING IN VERTICAL FLOW REED BEDS - MECHANISMS, PARAMETERS, CONSEQUENCES AND ... SOLUTIONS

The purification efficiency of vertical flow reed beds (VFB) is depend ent on a very efficient soil aeration. In most systems this is achieve d by intermittent pulse loading at the surface providing an oxygenatio n by mass flow and diffusion. These oxygen transportation mechanisms o nly function as long as the upper layers of the bed have a high draina ge capacity. Purification efficiency drops significantly when constant pending occurs. A review of the literature on clogging in sand filter s is given. In our evaluations the following observations are made. Cl ogging occurs only in the upper 0-15 cm of the bed. Clogging is depend ent on the height of organic mass loading. The content of volatile sol ids in the upper layers could not be proven as a significant parameter influencing clogging. The infiltration rate can be restored by giving the beds a recovery period of several weeks. The required length of r est is dependent on weather conditions, winter is the most critical ti me. (C) 1997 IAWQ.