We looked through the questions and details sent on January 23, 2008. Below is the follow up for the Tamara Treatment Plant.

Sedimentation Tanks

• Lamella
  • We noticed the Tamara design report says the lamella will be 40" and 91 cm long. 91 cm is 36". Is the 40" a typo? 40" lamella would require us to waste polycarbonate when cutting them from a 12 foot sheet.
     40" is a typo, the report attached named Tamara 6 and AutoCADD drawings should show a 36" (91 cm) long and 42" wide lamella.
    nbsp;* Fred said they are using smaller lamella spacing (1.5" instead of 2") in Marcala. Is that something we're interested in trying? We could even just try it in one tank. The spacing on the Tamara 6 report recommends 2 inch spacing. 1.5 inch spaces seem to only mean that there will be more lamella and might increase costs. We talked to Monroe and he agreed to leave the spacing at 2".  * How many lamellae do we want in each module? We think there are 6 or 7 in each module in Ojojona. Since these lamellae are larger we probably don't want to have any more in each module. No more than 6 lamella should be used in each module.  * Table / platform to support lamella.
  • We talked to Antonio and Ing. Serrano about the idea of having a ledge stick out of the sed tank walls to set a PVC grid on that will support the lamella modules. They think it sounds feasible. Included with this e-mail is a drawing of what we are proposing.
  • We propose having 2 or 3 bricks (25 to 40 cm wide) protrude from the wall every meter or so so support a PVC crosspiece
  • We think that 1" PVC will work fine if it is supported every meter.
  • We propose making the PVC grid in two parts so it will be less cumbersome and easier to remove.
  • Do we need a protrusion up ( a TEE sticking up from the PVC pipe that the lamella rest on) to hold the lamella in place every module? Everything seems fine, except we think that 1" PVC pipe will not provide enough support.
    
• Drainage and floor slope: We talked to Ing. Serrano yesterday, and based on comments he heard from Raul and what we discussed at Marcala with Monroe we tentatively made the following decisions:
  • The perforated drain pipe will run down the middle of the tank in a trench that it can be removed from.
  •  From each sidewall, there will be a 15% slope toward the centerline (8 cm rise on each side).
  • The tank floor and drainage pipe will also have a 2% slope (9cm over the length) from end to end.
  • Does this sound alright from the Cornell end?  The slope on each sidewall and the pipe placing sound fine on the Cornell end, if there is a possibility of increasing the slope in the future. About the 2% slope on the tank floor; it might be better if the tank floor and the drainage floor have a 0% slope. When the drainage starts, the amount of head and pressure going through the pipe This week Raul, Chris, and Sarah are going to test the orifice sizing (currently the orifice diameter is 0.9 cm) on the perforated drain pipe to make sure that sledge and water can easily drain and can create a uniform flow. We will send updates on that issue on a later this week.  Passing tubes through walls
• We propose putting PVC unions in all of the walls and floors that pipes pass through and then connecting tubes to them.
  • Unions are thicker and stiffer than normal tube so might hold up better and seal better with the concrete.
  • If a tube breaks it can be removed from the union it is stuck into, even if it is glued.
  • If in the future we decide we would rather a tube sticking out of the wall, we can always insert a nipple into the union.
  • Unions are not completely cheap (5 to 15 USD for a 6" union?), but there are really only about 5 or 6 wall crossings where we think they're optional and we think that the cost of 5 or 6 unions isn't too significant. Pipe Accessories
• Attached is a spreadsheet with a list of the pipe accessories we think we will need. If someone could edit it that would be great. We think this should be handled in Honduras so that there is a complete understanding between you and the engineers in Honduras. Plant Leveling Tank Exit
• A 6" pipe was selected for the weir by the Tamara design group. We suggest putting a 6" union flush with the tank bottom that that weir will fit into. After that union we would have a reducer to 3 or 4" pipe, then the T where we can send water to waste through a pipe. This waste pipe will require a valve. 4" valves are pricey, so if we could use a 3" pipe and 3" valve that would be good. What diameter do we need for sending the water to waste and to the tank? We will do some calculations too, but would like your opinion.   

Flocculation Tank

l        How big will the space in the divider wall be? We're not sure this was ever finalized in the report. We are not quite sure what you are referring too. On the Tamara 6 report, Figure 3 shows that the Floc Tanks divider wall is 0.2 meters wide and the gap at the 90 degree bend is .53 m long (which is equal to the width of the Floc Tanks passage ways).