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During Fall 2010 I have continued working on the Stacked Rapid Sand Filtration Team. In order to wrap up the summer proof-of-concept research we made systematic physical observations of the filter backwashing process in the clear filter column. The We visually observed the backwashing process in the filter was visually observed both to confirm that the bed of a stacked filter could effectively be fluidized, and to develop a procedure for initializing and terminating the process. The backwashing steps were varied and observation was used to determine which method of backwash was most effective. We hope to prepare a paper at some point in the semster explaining We are close to finishing up a proof-of-concept paper explaining the concept of stacked rapid sand filtration, using the summer performance data and this semster's performance data and backwash observations, to show that the technology is viable at the laboratory scale. We have been also running a flow running time-series and steady-state flow distribution tracer dye study studies to determine whether flow in each layer of the filter is in fact uniform. These studies could show how much of the sand bed is effectively being used.
Development of Other things we've been working on include: developing a full-scale filter design tool is underway, as is editing of the proof-of-concept paper from summer research.The team will apply , applying to the EPA P3 sustainable design competition to fund the future development of the stacked filter project, especially at the field scale. This application will be prepared through the semester concurrent with research and design,
An important dimension of the work this semester will be the design of a full-scale version of the stacked rapid sand filter system, which will improve AguaClara plants and allow the field performance of the system to be studied. Stacked filters will be integrated with the AguaClara design tool, and will draw on the resources of the design group.
An future developments, and determining whether an underdrain system may be needed for the bench-scale stacked filter system. This would be intended to eliminate "dead space" in the sand below the lowest inlet, which will never be fluidized during backwashing
In the near future we plan to: build a 20 cm single layer control filter in order to compare upflow from downflow filtration performance, run filter Filter performance studies similar to those that took place during the summer will be carried out, so that the team has a better understanding of the failures observed in the bench-scale system (so as to better understand inconsistencies observed during the summer such as turbidity "spikes"), and the conditions that might lead to these failures. A control filter with one 20-cm sand layer will also be tested to compare to the performance of the stacked system
The size of the sand media will be important to filter sizing, head loss, backwash velocity, and overall performance. Also, sand uniformity will be a special concern in stacked filters. After the filter is fluidized during backwashing, the settling of coarser particles at the bottom of the sand bed may affect both the flow distribution in the filter and the turbidity removal.
The distribution of flow among layers of the stacked filter is important to its overall performance and efficiency. To study this distribution, time-series and steady-state dye tracer studies were carried out using a step increase of a conservative dye. The filter was expected to have uniform flow across inlets and through sand layers, yet experimental results seem to suggest non-uniform flow.
In the near future we aim to have dye studies completed and to have gained a better understanding of flow distribution in the medium. Our dye study conclusions may call for further experiments, but we hope to move on to the performance study. Next week we plan to begin building a 20cm single layer control filter for performance studies of the filter. This filter will help us isolate a single layer and compare up flow from down flow filtration performance.