Pilot Plant
Sedimentation Tank
Overview
Two parallel sedimentation tanks are connected in series with the flocculator at the pilot plant. The sedimentation tanks allow us to further examine the efficiency of the process in the AguaClara design. Sedimentation tank design needs to be optimized to acheive our overriding goal of consistent production of water, under 1 NTU. Testing will include not only the traditional lamella design of sedimentation tanks but also the alternative floc blanket based sedimentation tank designs. These two processes are being tested side by side in parallel sedimentation tanks. One tank combines of lamella and sludge blanket technology and is compared to the other which only uses a sludge blanket to treat water.
One concern when implementating a floc blanket into the AguaClara treatment plants is the length of time it takes to develop a fully functional floc blanket. The water that goes through this sedimentation tank probably has a high turbidity during the formation period. It needs to be determined how long this could take, and explore the option of using a combined floc blanket and lamella design to continue sedimentation when the floc blanket is not fully functional. Another issue is the reliability of the floc blanket. If there is a period of time when either the influent water is clean, or for some reason alum is not being added, it is important to know if the floc blanket will be able to sustain itself, or what might happen. If the floc blanket does not sustain itself, and a new floc blanket has to be created, then this could make a substantial period of time when the sedimentation tank is not producing clean water. This is also a reason that a combined floc blanket and lamella tank may be superior.
When and how excess sludge in the floc blanket is drained is an additional issue that will need consideration. It seems unlikely that a continuous drain, like the one we are currently using, will be a good idea, because there is likely to be too much water wasted. An adequately sized hopper will be necessary and hopefully located in an area that will minimize the disruption of uniform upward flow. It will also be important to determine what may happen if the hopper is not emptied in the designated time frame. There should be an adequate safety factor before the floc blanket rises to the point that it affects the output of clean water.
Ojojona is currently using a sludge judge to monitor the sludge level, but even with the use of the "sludge judge" it may still be difficult to see all that is happening with the floc blanket, and because floc blankets seem to be fragile, it will be very important that plant operators adequately understand how to maintain floc blankets.
Sedimentation Sludge Blanket Tank goals and meeting minutes
Design
Methods and Research
Sampling Method
The method used to collect data at the end of sedimentation.
Sludge Judge
The method used to get a better view of the profile of the sedimentation tank.
Tank Draining
How to drain the sedimentation tank in order to maintain correct function and sanitary standards.
Future Research
Possible research topics to explore in the future with the sedimentation tanks at the pilot plant.
Results
Sludge Blankets at Different Upflow Velocities
The results of trying to form a sludge blanket at various upflow velocities in an otherwise empty sedimentation tank.
The Formation of a Sludge Blanket
The observation of how a sludge blanket is formed as well as how well the control sedimentation tank is operating.