Grit Removal Flocculator Team
Introduction
The current design of the AguaClara entrance tank was created after difficulties with grit clogging the flocculator at Agalteca. The solution to the grit problem was to make a large entrance tank that is effectively a horizontal flow sedimentation tank, which would settle out larger "grit" particles. The entrance tank could be made smaller by making a more effective grit removal system that uses plate settlers that double as flocculator baffles. This section of entrance tank could be integrated into the first channel of the flocculator. By reducing the size of the entrance tank or integrating it into the flocculator, the plan view size of the overall plant will decrease. This means a decrease in plant construction costs.Current Research
A sketch of a preliminary design of the baffles and grit removal hoppers is shown below. The entrance box at the top left corner of the diagram would serve the same purpose as the current entrance tank, while the sloped alternating baffles would act as plate settlers. The pipe stubs lead to drainage pipes, and would be removable for when settled grit and other large particles need to be cleaned out.
We have strong evidence that flocculators can operate effectively at much higher energy dissipation rates (EDR) than our current design of EDRMax=10 mW/kg. Relaxing the constraint on EDR means that we need to identify the new design constraint that will set the best design for flocculators. One possibility is that cost becomes the new driving factor for the optimal EDR. Low EDR means low head loss and large residence time. Thus low EDR results in a larger plan view area and that has associated costs. High EDR has high head loss and that results in a taller building and taller reactor walls and that increases cost. Preliminary cost analysis suggests that the optimal head loss give a collision potential Ψ=70 m2/3 increases with plant flow. Our current flocculator head loss for a 20 L/s plant is approximately 7 cm. Thus this cost optimization suggests a significant increase in head loss would be beneficial.
The economic analysis assumes that we design the flocculators to be efficient and thus add flow expansions as needed to obtain an H/S ratio of less than 5. The dramatic increase in head loss and EDR makes it possible to decrease the hydraulic residence time. At a head loss of 50 cm the residence time would be only 5.2 minutes.
Over the course of the semester, the team plans to determine the best design characteristics for the proposed entrance tank or flocculator design. At the end of the semester, the team plans to have a set of recommendations as to whether the grit removal flocculator will be a feasible and efficient way to solve the grit problem in future AguaClara plants.
| Challenges | Tasks | Symposium | Final Presentation | Final Report |
| Spring '15 |