Agalteca Design

Agalteca has a population of 2,160 residents. A distribution tank is already in place, but another distribution tank is expected. Construction of an AguaClara water treatment plant started on September 30th, 2009.

Agalteca is unique in being the first plant to be designed largely using the [Automated Design Tool].

Design Specifics

Entrance Tank

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--> There are a number of constraints which must be met when considering the dimensions and location of the entrance tank.  These items are discussed below.

1. The elevation of the entrance tank is determined by the design of the rapid mix tube.  The current design of the rapid mix pipe has 10cm of headloss.  Therefore, the entrance tank will need to be located 10cm above the flocculator tank. 
2. Entrance tank height is determined by the headloss throughout the plant and physical size of the rapid-mix tube.  These values are added together to determine the minimum depth of entrance tank.
   1. 10 cm of free-board - this is a standard free-board dimension used in Agua Clara plants.
   2. 10 cm head loss rapid mix pipe - this is a calculated value based on the marco-mix and micro-mix orifices in the pipe
   3. 13.5 cm head loss flocculator - this is a calculated value based on the number of baffles and the baffle spacing
   4. 5 cm head loss launders - also a calculated value based on the number and size of the orifices in the outlet manifolds
   5. 5 cm head weir - designed value
   6. .61 m max height needed for macro scale rapid mix pipe - this is a physical dimension of the rapid mix pipe.  It is assumed that the coupling will be embedded in the concrete floor of the entrance tank.  The micro-mix plate will sit in the coupling with the rapid mix pipe and macro-mix plate placed inside this coupling. 
   7. Total height of entrance tank is rounded to 1.00 meters. 
3. Width and length of entrance tank is are 1 meter x 1 meter (inside dimensions.)  This is a critical dimension to accommodate the length of the lever-arm for the chemical doser.
4. Additional concern: Swing of the lever arm is represented by 33 cm of change in the water level.  The arm length is 40 cm on each side of the pivot.  10 cm of this is accounted for in the freeboard of the tank.  The lever arm will be mounted 30 cm above the entrance tank (preventing the arm from dipping into the water).  Additionally, the roof will need to be a minimum of 70 cm above the entrance tank wall.
5. Important points for entrance tank:
   1. Understanding that PVC dimensions are dependent upon the manufacturer, many of the above figures are guidelines as the PVC available in Honduras is undoubtedly of different dimensions than what we used in our design.
   2. The rapid mix pipe coupling is to be embedded in concrete in the floor of the entrance tank.  The micro-mix plate will fit inside the coupling with the macro rapid mix pipe sitting on top (the nipple connecting the elbow will serve to support the orifice plate).  Therefore, the rapid mix pipe needs to sit deep enough into the coupling that it is well supported.  A long coupling would be suitable here.
   3. The pipe above the rapid mix coupling will be a slip joint (not glued) for easy disassembling and cleaning.  Because the pipe above the coupling is to be removable, it may not be embedded in concrete.
   4. If the coupling is not embedded in the floor of the entrance tank, modifications must ensure that the top of the rapid mix pipe matches the elevation of the exit weir and that the water level above the rapid mix pipe is 33.5 cm is and 10 cm above the flocculator water level.   

      Flocculator

This is the first AguaClara design to use untapered baffles in the flocculator. The goal is to create a 6 mW/kg energy dissipation rate throughout the flocculator. There are 29 baffles in each of the first two channels to ensure that the water flows through the ports connecting channels, which are at the bottom, correctly. The last channel has 28 baffles because the inlet port is at the bottom and the inlet channel for the sedimentation tank is at the top. The baffles use polycarbonate sheets instead of cement which are easier to remove. This makes draining the system much easier.

Inlet Channel

The inlet channel was modified to have only one opening leading to the sedimentation tank instead of two. See the explanation for this under Sedimentation Tank. The concrete in the inlet channel will be rounded going into the pipe so that the transition of flow is smoother. The amount of rounding is yet to be determined.

Sedimentation Tank

The sedimentation tank design is significantly different from previous designs. The main problem that brought about the change is that too much sludge was settling out in the inlet manifolds at Cuatro Comunidades. There was originally a similar design for Agalteca, so it needed to be fixed. To see a list of ideas on how to fix this problem until the final design was chosen, click here. To see other potential changes that can be made if needed to correct this problem, click here.

The final design involves an inlet pipe down the center of the tank instead of two inlet manifolds under the slopes. The pipe will be a 6" diameter PVC pipe. The inlet manifolds will be filled in with concrete. The slopes will remain though so that flocs are directed toward the sludge drain.

One issue that has yet to be resolved is how to distribute the flow of water evenly throughout this pipe. This includes potentially tapering the pipe and determining the size and spacing of the orifices and their positioning in relation to the sludge drain orifices.

If possible, a floc blanket should be formed. The postitioning of the floc weir to accomplish this is yet to be determined. In order to more likely achieve a floc blanket, the orifices in the pipe will point downward, to re-elevate settled sludge along the bottom. If the floc blanket fails, the pipe can be rotated 180 degrees.

Sludge Drain

Plant Drawings