What type of water treatment clarifier is the most mainteance
freindly? Horizontal or Upflow

horizontal flow water clarifiers are inherintly less maintenance
worthy as the moment of momentum required for the sparger/distributer
comes from the head in the water, being stored presuambley in such a
way o have suffient ead.  Even thought there are the maintenance
requirement for the surrinding plant pumping equipment this would be
present irrespective othe the choice of clarifier.

Presumably upflow here would imply thethe upflow of the water/slurry. 
In this case then is there not the reduction in the net downward force
vector acting on the slurry particulates, thus decreaseing the
effectiveness  of the clarifier, far better to allow for initial
settelment under stokes regime then to have the pressure driven
filtering/clarifying on horizonatal basis as the is no condion for
ther addition/removal of poential kinetic energy.

My question was in reference to the horizontal units sludge rake.