Modular plate settler

Current assembly technique

One idea we got from Fred Stottlemeyer is to drill holes in the lamella large enough to put 1/2¨PVC tube through them, but small enough so that the tube fits snugly. We would then put a short nipple through the hole and put a PVC union on each side of the nipple. We´d squeeze the unions together so that the made a tight sandwich around the lamina. The unions are 4.1 cm (about 5 cm) so we´re thinking we could probably just use one union between each floc lamella.
We´re going to try Fred´s method of the union sandwiches out soon. Concerns are that the holes will be hard to drill and that the unions will not be thick enough to securely detain the lamina. The unions might slip through the holes.

We think we have a good solution to the plate settler issue. We tried Fred`s suggestion of using the 1/2" PVC unions as spacers and connecting them with short nipples of 1/2" pipe. It worked very well. Concerns that we had discussed were:

1. That it would be hard to drill a 7/8" (the O.D. of 1/2" PVC) hole in the lamina without destroying it.
   With a hole saw, as Monroe suggested, the holes came out well. We were able to drill 4 lamina at once and think we will be able to drill 6. The only problem we ran into was that the hole saw heats up and starts to melt the lamina if you drill a lot of hole quickly. We are confident that by keeping the drill at a low speed and cooling the bit between holes we can resolve this problem.
2. That the large holes would compromise the strength of the policarbonate.
   We pulled and pushed pretty hard at the hole and shook the module voilently and saw absolutely no damage. The hole did not expand or crack at the edges. We didn´t push it to failure because we didn´t have any small pieces that we wanted to waste. Still, we´re confident that it will hold up.
   Another advantage of this method, on top of cost, is that Antonio says it is much easier to put together than the caps and scews.
   If you folks at Cornell approve, we´d like to move ahead with this idea. On the other hand, if you want to do more testing of it there and think about other possibilities, we could wait a week to decide for sure.

The unions that we want to use as spacers are only 4 cm in length. This would mean smaller gaps between the sed lamella. I think I remember Fred saying that usually lamella spacing is smaller than 4 cm and that this might give improved performance. Of course it would also mean more lamella. Instead of buying 60 12-foot polciarbonate sheets for the plant (floc and sed), it would mean buying 72 sheets. At a cost of 900L a sheet, this is 10,800 L or about $550, but still much less than what we´ll save by not buying CPVC caps. We had another idea to make the spacers 5 cm: cut 1cm rings from unions and put them together with the full unions. This would work but we think it will be difficult to cut the rings uniforly to 1 cm. If the 4cm spacing will work just as well or better we recommend going with that. The two options are drawn in the attached power point.

We`re also discussing how many spacers to put in the sed modules. In the same attached file is a diagram of three different posibilities. We tried the 7 spacer option and it looked alright but we thought it would be worth adding more. The 8 spacer option, with the middle row staggered looks the strongest to us, even better than the 9 spacer option. One possible concern is that the 8 spacer option blocks more of the path through the lamella with spacers, since they are in 5 different horizontal positions. To us this seems insignificant. Are you in agreement?