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A new AguaClara drinking water treatment plant has been designed for the town of Támara, Honduras. The plant has a maximum flow rate of 740 liters per minute and features a vertical flocculation tank with one turn, three sedimentation tanks, and a new plant leveling tank.

Keywords: AguaClara, Design, Támara

AguaClara is a team of students from Cornell University who work to design sustainable water treatment plants in Honduras. The goal of the team is to design and disseminate water treatment plants globally that are easy to build and maintain, that are economical to operate, and that can be prepared using locally available materials.

To date, two AguaClara water treatment plants have been built in Honduras. The first was built under the supervision of Fred Stottlemeyer in La 34, Honduras (Figure 1). This plant featured a horizontal hydraulic flocculator. The second AguaClara plant was built in Ojojona and its initial construction was completed in Fall 2006. The Ojojona plant (Figure 2) was designed by the AguaClara team, and Ted Segal completed the structural design. This was an experimental plant with both a vertical and horizontal flocculator.
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Figure 1. La 34 AguaClara Plant.

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Figure 2. Ojojona Plant.

The next AguaClara plant was planned to be built in the town of Moroceli, Honduras. However, due to transmission pipeline problems, design of this plant was delayed so that it would not sit idle as the transmission line is repaired. The next AguaClara plant will be built in Támara, Honduras.

The Támara design team was only responsible for the environmental engineering design consideration for this plant because Agua Para el Pueblo has hired a civil engineer to deal with all structural aspects.

The Támara plant was partially designed using programs created by the AguaClara team during previous semesters. In Fall 2006, Monroe Weber-Shirk's CEE 454 class created algorithms for the unit processes involved in the plant. In Spring 2007, these algorithms were combined into a Main Program that would begin to design a plant. The program is written in MathCAD, and accepts user inputs such as flow rate and tank width to calculate output design parameters such as tank length and baffle spacing. In Fall 2007, the CEE 454 class created new programs to design pipes and flow measurement structures. These programs were used by the Támara design team as well.

The team also made use of the automated drawing capabilities developed by the Fall 2007 automated design team. This allowed the team to produce AutoCAD commands for drawing of the sedimentation tank by inputting design constraints to a MathCAD program.

The Támara plant flow rate was determined using an initial town population of 5,500 people. The flow rate was based on the projected population and associated water demand in 20 years. Population was calculated using a linear growth model with a 3.5% growth rate. Water demand was estimated as 114 Liters per person per day. The minimum plant flow rate was initially estimated as half of the maximum flow rate. However, after discussion with John Erickson and Carol Serna, the AguaClara engineers in Honduras, it became clear that the town did not currently have a population of 5,500. At the time of design, 570 homes were hooked up to the transmission line. With an average of 6 people per house, this population was 3420 people. This would result in a water demand of 463 L/min in 20 years. The potential for 120 new connections in the near future exists.
However, the engineers in Honduras believe that source at Támara can provide at least 740 L/min. It was decided that 740 L/min should remain the maximum plant flow rate because the actual demand for water is uncertain, and the extra size of the plant would not be too costly. Initial baffle spacing in the flocculation tank will be designed in a way to ensure that the current flow rate, possibly as low as 270 L/ min could be handled.

The Támara plant layout has a few major changes from the layout of the previous Ojojona plant. 
 

1. The horizontal flocculator was removed.  Testing in Ojojona confirmed that the vertical flocculator worked well  The vertical flocculator is less costly to build because it does not need to be elevated, so the horizontal flocculator will no longer be used in AguaClara plants. 
2. At the request of plant operators in Ojojona, a "bodega" was added to the plant.  This walled-in, roofed area is to be used for chemical storage, mixing of chemicals, and possibly a cot for night-time operators.   
3. A plant leveling tank was added to replace the pipe elbow level control feature in Ojojona. 
4. Chemical barrels were separated.  The alum and chlorine barrels will be located on different tables to allow for open walkways without tubes stretching across them, and to allow the tables to be at different heights as necessary. 
5. Tanks will be built of brick.  APP is more familiar with brick, they believes it is less porous than concrete, and they can build more cheaply with brick. 
6. The plant will be more protected.  There are two possible scenarios. The first is to have a fence around the plant with a roof over the platform. The second is to have open walls that start at the platform and stretch partway up to a roof. These walls would eliminate the need for a railing around the plant or extra sunlight protection for thetanks. Overall, this decision and design will be left to the plant operators and engineers inHonduras.  
7. A catwalk may be added to span the flocculation and sedimentation tanks.  Because brick walls will be thin, a catwalk would allow for safer access to these tanks.  The AguaClara team envisions a sturdy, metal catwalk that could slide from one end of the tank to the other.  .The tank walls need to have a ledge inside the external walls of the building covering the plant so there is a place for the catwalk to rest.
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   Figure 3. Támara Plant Layout

The new plant layout will be ideal for scaling of future AguaClara plants.  As long as baffle materials remain available to allow for the same width of tanks, the width of the plant should not change.  When a new plant is designed, the only necessary change to the layout will be the length of the tanks.  This will allow for more rapid design, easier automated design, and more uniform future plants. Another important feature of the new layout is that many of the pipes will be under the platform.  While this may be somewhat more difficult to build, it allows for easier access with no obstructions to walkways. The area under the platform should be secured so that all of the valves and pipes are protected
 Although not shown in the above drawing, all four major tanks will have drains that leave from the entrance side of the tanks.  These pipes will go to a waste collection tank under the platform where the operator will be able to see the water that is leaving the plant.  In this way he may know when all the dirty water has been flushed out.  This will be especially useful when cleaning out the sludge from the bottom of the sedimentation tanks.
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Figure 4. Támara Plant Layout, modified from a drawing by APP engineer Ing Serrano. Magenta pipes in sedimentation tank represent sedimentation tank inlet pipes. Green Pipes are for the sludge drainage.

A major part of designing an AguaClara plant is sizing the pipes in the plant. A pipe design program was created so that all pipes could be designed quickly and correctly. The program returns a pipe diameter given a length, allowable headloss, and number of elbows, tees, valves, etc. A table of the K values used and a table of input pipe sizes used can be found in the Appendix as Table 2 and Table 3.

The program uses functions defined in the Fluids Functions program developed in the Fall 2007 CEE 454 class. In order to find the proper diameter the program iteratively solves for the flow that can fit through a pipe of the given diameter with the given headloss until a large enough diameter is found.

Headloss values are calculated using the following set of equations.
Equation 1
Re = Reynolds Number, to determine if flow is turbulent or laminar
Q = Flow Rate
D = Pipe Diameter
¿ = Kinematic viscosity of water
Equation 2
Equation 3
f = Friction factor, equation for either turbulent or laminar flow
¿ = Roughness factor of PVC
Equation 4
Equation 5
hmajor = Major head loss
hminor = Minor head loss

Values for all constants used may be found in the Appendix