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The early designs have water entering the sedimentation tank through a series of pipes connecting from the bottom of the inlet channel down to the bottom of the sedimentation tank. The pipes were designed to be of different lengths to allow for water to be even distributed evenly down the length of the tank. This was necessary to ensure an even upflow velocity. This design proved to be very expensive and took up a lot of room in the sed tanks.
Beginning with the Cuatro Comunidadies design, water was even evenly distributed to the bottom of the tank through two triangular manifolds extending the length of the tank. These manifolds are connected to the inlet channel by concrete chimneys with ports exiting into the manifolds. The water flows out of the manifolds through ports cut into the slopes. An even upflow velocity is maintained by the geometry of the ports.
Lamella
Lamella are set to be angled at 60 degrees. This angle was found to optimal for floc fall out. In older designs lamella were set to be about 5cm apart, but lab experimentation has shown that a minimum spacing of 2cm is still acceptable. Beginning with the Gracias plant, designs are now based on the this closer spacing.
In LA34 and Ojojona, lamella were kept in place via nails that were embedded in the concrete. All designs after Ojojona had lamella that were held in place with a pvc frame sitting on a concrete ledge built into the sides of the tank walls. This would enable operators to easy take the lamella out for cleaning.
Sludge Drain
A launder situated at the bottom of the sedimentation tank is used to drain the tanks. All designs prior to the Cuatro Comunidades have a pvc pipe with holes drilled along its length running the length of the tank that acts as the drain launder. The Cuatro Comunidades has a small concrete channel running the length of the channel to act as the drain. This channel is covered by a flat concrete plate with holes formed down its length to create a launder from the channel. The use of concrete instead of pvc is much cheaper.
Entrance Tank Improvements
The entrance tank is where raw water enters the plant, at . At some point in the entrance tank alum has to be dosed and mixed into the water before entering the floc tank.
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Starting with the Tamara plant, the entrance tank is also the place where dissolved air is removed from the water. Raw water was becoming supersaturated prior to entering the plant . The and the dissolved oxygen was coming out of the water in the flocculator and causing flocs to break up and float up with the air bubbles. These "Floating Floc" where causing plant performance to deteriorate. Sand was added to these later designs to encourage the bubbles to rise out before alum is dosed and flocs are formed.
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