Construction History

Spring 2008

The design of the tank was completed during the Spring 2008 semester. The sedimentation tank was designed to be contained in a polyethylene tank of dimensions 24" x 24" x 36" (length × width × height) with a wall thickness of about 5/16". The design goal was to have enough area in the tank to create a floc blanket. With the available water level height, approximately the same height as the water level in the floc tank, we did not have enough room to include plate settlers. Initially we wanted to split the plant flow rate (110 L/min) in half, allowing us the possibility of installing two parallel sedimentation tanks for experimentation purposes, but we found that a flow rate of 55 L/min into the tank would have required a 6 inch pipe to transport water from the floc tank to the sedimentation tank to avoid breaking up flocs. Due to cost restraints (a six inch bulk head fitting would have cost about $300) we limited this pipe to 4 inches. This was done by lowering the flow rate of the sedimentation tank to 24.5 L/min. This constraint on the inlet pipe and flow rate required that we switch to a smaller tank than originally planned so that so our tank would have an upward velocity of 100m/day, the upward velocity of full scale plants in Honduras; keeping this parameter the same made the two designs comparable. This low flow and smaller tank set-up allowed for parallel testing of tanks containing different sedimentation processes.

Fall 2008

Issues

When work began on the pilot plant in the Fall 2008, several leaks were discovered. The plant had to remain shut off until the leaks would be repaired. At first it has seemed that the leaks were in the pipes, so all of the joints in the pipes were caulked. After the caulk had dried, water continued to leak from the system. It was discovered that the leveling tank (a plastic bucket) was leaking.

Solutions and Changes to the Pilot Plant

When caulk did not seal the leveling tank, the outlets to the sed tanks were sealed off (to allow the flocculator team to conduct experiments) and the leveling tank was replaced with a PVC pipe. This is the current set-up as of mid-October 2008.