| Bottom drains should go to settlement/prefiltration and then on to aerated bio then back to the pond. Bio-filtration has no dwell time/speed limit so after prefiltration the "dwell time is no longer an issue. Seperation/settlement/prefiltration/static fines filtration are the types of systems that have speed limits.
I normally run midwater and skimmer circuits to static filtration to remove the floating and neutrally bouyant fines that are created and live in the upper levels of the pond.
Normally I wouldn't use any type of pressurized filtration on new construction unless absolutely necessary because of the waste of energy and lack of oxygen usually associated with these systems along with the inability to see inside them when cleaning. In open unpressurized upflow static filtration a good rule of thumb is not to exceed approximately 630 gph/sq ft of tank area.
Dwell time is usually associated with settlement but static trapping is more a function of tank diameter and flow rate and less about depth. That's not to say a deep tank isn't a good thing. When trapping fines the larger the diameter the slower water travels up through the media so the depth isn't as critical as it is in settlement. The faster water travels through a static trapping filter the less it will trap. |