Stephen Galdi, Natalie Mottl
The team’s task is to test, troubleshoot, and complete the scale model of the weir system developed by last semester’s team. By the end of the semester, the team will create as etup and video that accurately portrays the behavior of the water through the full scale weir system. The Fabrication Team aims to create a plant that is easier to operate, troubleshoot, and build.
Vicki Chou, Nick Farino, Chenhao Qi, Rui Zhang
The goal of StaRS Backwash is to determine the sand grain sizes and distribution for the most efficient and effective backwash in the stacked rapid sand filters. The proper fluidization velocity for efficient backwash must first be determined. An expansion ratio of 1.3 is the current standard for the sand bed during fluidization. A sand size ratio below 1.5 is suggested for minimal segregation during backwash. The team ran experiments with sands sized by sieve combinations of 2040 and 3040 at different backwash velocities to test for segregation. Through the experiments, the team found that the 2040 sized grains always segregated at all backwash velocities, but the 3040 sand, which is under the 1.5 sand size ratio, did not segregate below backwash velocities of 15 mm/s. Current AguaClara plants use a backwash velocity of 11 mm/s, so using 3040 sand would be a good option because it should not segregate according to the data collected.
Alberto Arnedo, Ainhoa Arribas Llona, Jorge Guevara
The current slotted pipes being used in the backwash system of the AguaClara filtration plants have been clogging up with sand, thus posing a problem for the backwash system since the slotted pipes’s purpose is not being fulfilled. Given this issue, the Alternative Backwash without Slotted Pipes subteam will work to find an alternative pipe for the backwash system that will not clog up with sand at any point of backwash or filtration and will be easy to manufacture on site in Honduras and India given the resources available in each respective country. The team has successfully built a STaRS scale model to be used to accurately experiment with alternative pipes for both an inlet and an outlet valve. Through experimentation, it was found that the alternative tubes in the shape of a hollow rectangular prism cut in half lengthwise and placed with the interior facing down did not fill up with sand during the processes of filtration or backwash.Once the pump was turned off, however, the sand would settle underneath the outlet pipe. This led the team to two possible courses of action: the first being that the team could leave the pump running the water at a low flow rate and the second being that the team build a second alternative for the outlet pipe. Both actions would solve the issue of the sand clogging up, but the team pursued the second alternative. The new shape for the alternative was a hollow cylinder with wings that extended out tangentially from the top of the cylinder with a hole in the middle of the cylinder’s bottom. In experimentation, the new alternative outlet pipe worked well for the first trial, but filled up with sand in the subsequent trials. Through more experimentation with the current alternatives, or perhaps new alternatives, future subteams will work to find a solution that will consistently work without filling up with sand.
Theresa Chu, Jonathan Harris, Lucinda Li, William Pennock
Dynamic models of stacked rapid sand filtration has proved elusive in accounting for the diminishing pore space and increasing head loss. Empirical data has shown that head loss increases linearly over time despite filter breakthrough. Dirty filter bed head loss shows that minor losses add to head loss over time. A new model for dynamic filtration is proposed, which models captured particles as embedded rings of flocs in the filter bed. Particle removal through filtration is described with an active filtration zone of empty pores filling up with particles. This zone moves throughout the layer of sand until there is no available pore space and surface area for particles to attach.
Theresa Chu, Lucinda Li, Jonathan Harris
A mathematical model describing sand filtration would promote the understanding of stacked rapid sand filter performance. Variables affecting filter performance include coagulant dosage, influent turbidity, and sand filtration depth. The collected data from a model filter informed a mathematical model explaining the effect of coagulant mass on the filter’s effluent turbidity, head loss, and failure time. Experiment runs demonstrated that increasing coagulant dosage led to an increase in head loss and decrease in time until filter failure as well as vary effluent turbidity. Head loss curves for the various PACl dosages had the same trend after filter failure and converged to the same value after a 24 hour run time.
Lucinda Li, Liz Cantlebary, Lingzi Xia, Dylan Vu
Sand filters have historically been used to lower the turbidity of water, and continue to be used in many conventional water filtration systems. Dynamic modeling, as opposed to static modeling, of rapid stand filtration accounts for the buildup of particles over time in the filter, and this un- derstanding is needed for better filter design and operation. Past sub-teams found that head loss increases linearly with time. This research proposes the hypothesis that flocs are captured in rings created by filter grains, which on a larger scale implies an active filtration zone where empty pores become clogged by the flocs. This active zone moves throughout the bed until there is no remaining space for particles to clog. This research will examine major and minor head loss, along with efflu- ent turbidity, to find optimal filter performance based on varying flow rate, coagulant dosage, and influent turbidity in a 1.967m L/s sand filter. Based on this research, it is hypothesized that the sand bed can filter a certain amount of mass before failing.
Alison Valibuena, Liz Cantlebary, Dylan Vu
Sand filters have historically been used to lower the turbidity of water and are still used in conventional filtration systems. The research in this report is based on the hypothesis that flocs are captured in rings created by filter grains, which implies there is an active filtration zone where empty pores become clogged by the flocs. This active zone moves throughout the bed until there is no remaining space for particles to clog. This research examines the factors that influence the time it takes for the filter to clog. Several key factors affect the failure time including size and density of flocs and were explored through experiments with different coagulant doses and with a constriction placed before the filter.
Wenjie Lu, Claire Kenwood, Kelly Ly
StaRS (Stacked Rapid Sand) Filtration is crucial to the water treatment process. As one of the last steps in AguaClara’s water treatment, StaRS filters are responsible for removing the last of the unwanted particles. In order to operate effectively under EPA standards, the filters must reduce the turbidity to 0.3 NTU or less. In efforts to better refine the AguaClara filters, variables such as grain size, the height of the active zone, coagulant dosage will be tested in order to increase the failure time. At the beginning of experimentation, the Fall 2019 StaRS sub-team will focus specifically on the grain size.
Barbara Oramah, Lainey Reed, Pablo Alonso Alguacil and Ronya Strom
Stacked Rapid Sand (StaRS) Filtration is the last stage in an AguaClara treatment plant. The filters are used to further reduce the turbidity of water to meet EPA standards of 0.3 NTU or less. As a whole, the StaRS sub-team is working to develop a mathematical model to describe sand filtration. This semester, the StaRS Filter Theory team worked towards running experiments with the three newly constructed StaRS filters with varying sand grain sizes. This research will show the extent to which sand grain size has an effect on filter performance.
Isha Chaknalwar, Theresa Chu, Michelle Lee
Modeling the physics of particle capture in stacked rapid sand filters allows for greater understanding and further innovation in filtration. A two-layer sand filter will be built to measure filtration performance parameters of effluent turbidity, head loss, and time until turbidity breakthrough or excessively high head loss. Sand filtration should be effective in removing small flocs, so flocculated influent water with coagulant and clay will enter the filter to simulate filtration and clogging.
Theresa Chu, Nick Coyle, Alexandra Schwab
The Stacked Rapid Sand Filter Theory team designed and built an apparatus to induce clogging and test the head loss across a slotted pipe, which allows the water to flow directly into the filter without sand leaving the filter. Experiments were run with high turbidity and coagulant doses to clog the slotted pipe and determine which influent conditions led to clogging and high head loss. Slotted pipes as an injection system for the stacked rapid sand filters have proven to be problematic due to clogging. Results show that floc build up of coagulant clay increased head loss and clogged the slots.
Barbara Oramah, Lainey Reed, Emily Spiek
Stacked Rapid Sand Filtration is the last stage in an AguaClara treatment plant. The filters are used to further reduce the turbidity of water to meet EPA standards of 0.3 NTU or less. This semester, the Stacked Rapid Sand (StaRS) Filter Theory team constructed 3 StaRS filters with sand of varying sizes. These filters will be used in future experiments to analyze how specific parameters, including sand grain size and coagulant dosage, affect filter performance. The StaRS Filter Theory team has spent the semester compiling a manual so that future teams can run experiments and reconstruct experimental filters if necessary.
Wenjie Lu, Claire Kenwood, Kelly Ly, Valentina Dai
StaRS (Stacked Rapid Sand) Filtration is crucial to the water treatment process. As one of the last steps in AguaClara’s water treatment, StaRS filters are responsible for removing the last of the unwanted particles. In order to operate effectively under EPA standards, the filters must reduce the turbidity to 0.3 NTU or less. In efforts to better refine the AguaClara filters, variables such as grain size, the height of the active zone, coagulant dosage will be tested in order to increase the failure time. At the beginning of experimentation, the Fall 2019 StaRS sub-team will focus specifically on the grain size.
