Foam Filtration, Spring 2012

Katie Edwards, Walker Grimshaw, Bradshaw Irish, Kelly McBride, Nadia Shebaro

Abstract

The Foam Filtration team developed a two-stage emergency water lter. The lter was presented at the 2012 National Sustainable Design Expo in Washington, D.C. as part of the P3 competition for sustainability. While at the expo, rough data was collected on the performance of the pilot scale lter as a proof of concept. The competition also involved submitting a grant proposal highlighting all past research on foam ltration and presenting a plan for future research and eventual implementation.

Low Flow Flocculator, Spring 2012

Ryan Anthony, Elyssa Dixon, Zac Edwards

Abstract

Open ow occulators, like those currently used in AguaClara plants, increase in cost for lower ow rates (less than 5 L s ). AguaClara must be able to meet the need of a wide range of community sizes, so scaling the design for low ow plants is crucial. This report specically analyzes three dierent scenarios that use obstructions within a pipe to remove the geometric constraints that cause the errors found in the current designs. Two scenarios include placing semi-circular baes (similar to those in open ow occulators) within the pipe and maintaining the spacing between and above the baes or maintaining the area between and above the baf- es. The last scenario involves placing balls on a string through the center of a pipe. A table is provided within this report comparing critical values for these occulators for a 3 L/s plant. An initial comparison of the three options shows that the scenario that maintains area above and between baes is the most eective with materials. However, discrepancies with calculations in the approach using balls as obstructions ultimately yields the results inconclusive.

Stock Tank Mixing, Spring 2012

Julie Silva

Abstract:

The Stock Tank Mixing team is required to improve the mixing process for the coagulant and disinfectant in the stock tank. Previous teams have developed the centrifugal pump design, which can mix the following chemicals: aluminum sulfate (alum), polyaluminum chloride (PACl) and calcium hypochlorite (Ca(ClO)3). This team decided to focus on the use of polyaluminum chloride. Due to its chemical properties, it is most likely the future coagulant of most AguaClara plants. The stock tank mixing team plans to design a mixing system that will improve operator ease in use of the mixer, achieve a truly homogeneous mixer, and be scalable to larger plants. The team will also create operator guidelines, and provide the operator with a verification of homogeneity.

Stacked Rapid Sand Filer Pilot Scale, 2012 Spring

Eva Johnson, Jordanna Kendrot, Bill Kuzara

Abstract:

The stacked rapid sand filter has been proven to be an alternative to traditional rapid sand filtration systems, and their efficiency makes them an appropriate component in gravity powered municipal-scale water treatment facilities. In this study, a pilot-scale apparatus has been create as a model of the hydraulic controls throughout a full-scale stacked rapid sand filter system. After installation and field testing at Tamara, it is vital for the backwash segment of filter operation to be controlled for a more efficient use of the system. The purpose of the current experimentation and lab procedures are to determine the optimal backwash cycle time necessary for the filter to remove as much particulate matter as physically possible with a short filter-to-waste cycle, thus reducing the overall rinse cycle time. Further research will be needed in determining how to lessen bubble formation, be it in the inlet box or filter itself, and in measuring the change in flow distribution throughout filtration and backwash. A four-layer rapid sand filter was created to test filter efficiency versus monetary compensation from using less sand in the filter box, but was shown to have less than optimum particulate matter removal when compared to the tested six-layer.

Stacked Rapid Sand Filter Full Scale, Spring 2012

Michelle Wang, Steph Lohberg, Chris Holmes

Introduction:

The purpose of this report is to effectively summarize the progress that has been made to fabrication methods for the stacked rapid sand filtration system over the course of the semester. The stacked rapid sand filtration system is a new technology developed by AguaClara. It has many advantages over traditional sand filtration systems. First, it uses less water to backwash, because the filter layers are stacked. The filtration system also uses the same water for to backwash all the filter layers, producing a concentrated waste stream and reducing backwash time. Furthermore, this technology is much easier to operate than conventional rapid sand filters. It fits all the criteria of AguaClara technology, as the normal filtration and backwash cycles are driven by gravity. Materials are relatively cheap and widely available in Honduras. Finally, this filtration system has been proven to lower the effluent turbidity sufficiently, producing treated water below the EPA standard of 0.3 NTU and often even less than 0.01 NTU. The first field scale design of this filtration system was recently implemented at the AguaClara plant in Tamara. There have been several previously unforeseen issues that have arisen. In Tamara, in order to fit the slotted pipes into the trunk line and end lines, compression slots were cut into the slotted pipes. However, this allowed sand to leak into the inlet and outlet plumbing. Sand leakage is a serious issue because it increases head loss in the filter, reduces the length of the filter cycles, lowers the efficiency of the filter, and makes it harder to backwash. One of our main goals for this semester was to find a way to make a sand-tight connection between the slotted pipes and the trunk line and end lines. Another challenge we are facing is to find a new construction method so that the manifold can be built outside of the filter box. After the manifold is completely assembled, it will be lowered into the filter box as a unit. A key part to our progress this semester is the steady feedback from the team in Honduras at the Tamara site. Changes that we make this semester will aid in the maintenance of the Tamara filter and the design and implementation of the next stacked rapid sand filtration system in San Nicolas.

Stacked Rapid Sand Filter Bench Scale, Spring 2012

Danhong Luo, Weiling Xu, Huifei Wu, Main Editor: Michael Adelman

Abstract:

Stacked rapid sand filltration (SRSF) is a novel technology for AguaClara water treatment plants. Our team goal is to improve the performance of the SRSF by studying fundamental questions such as the self-healing nature of ow distribution among layers and the effect of upstream energy dissipation rate on performance. In the self-healing test, we found that it is hard to let the sand bed itself control what the flow distribution will be, and that surface removal dominated in the filtration process. The depth filter test reveals that surface removal dominated in the self-healing test, and flow distribution improved when surface removal effects were eliminated. For the energy dissipation rate test, we assume the filter performance would be improved with the increasing energy dissipation rate, while current experiments have not show the result. Therefore, further testing should be addressed in the energy dissipation rate study.

Sedimentation Tank Hydraulics, Spring 2012

Jill Freeman, Mahina Wang, Matthew Hurst, Saied Khan, Yiwen Ng

Abstract:

A floc blanket is a dense, fluidized bed of particles that forms in the sedimentation tank. It helps to reduce effluent turbidity by trapping small flocs and reduces clean water waste through less frequent draining of the sedimentation tank. Floc resuspension is necessary for floc blanket formation so that flocs are recirculated through the tank instead of settling on the tank bottom as sludge. Research was conducted to examine the effectiveness of the retrofitted Marcala sedimentation tank. At high influent turbidities, a steady floc blanket was obtained, but performance was slightly compromised when the influent turbidity was lowered to simulate Marcala conditions during the dry season. A floc blanket visibly formed with an influent turbidity of 5 NTU after about 1 week but “seeding” the tank with coagulated flocs will minimize floc blanket formation time. Images were also acquired for hindered sedimentation velocities of 0.6 mm/s, 1.2 mm/s, and 1.6 mm/s and analyzed with a floc-water interface program using a region of interest to better understand hydraulic processes within a floc blanket. Complete settling curves from this data confirmed wall effects significantly affect settling velocity. A floc hopper proved to be effective at controlling the height of the floc blanket when the accumulated flocs were drained at an adequately high flow rate. A lower alum dose of about 39 mg/L for an influent turbidity of 100NTU resulted in a less sticky sludge that could be more easily drained from the hopper.

Chemical Dose Controller, Spring 2012

Frank Owusu-Adarkwa, Julia Mertz, Ruju Mehta

Abstract:

Continuous, accurate chemical dosing is an essential part of AguaClara plant function. Proper dosing ensures effective flocculation, sedimentation, filtration and disinfection. The chemicals that must be added at different points during the water treatment process are coagulant (PACl or Alum may be used) and chlorine. The linear chemical dose controller (LCDC) is a device that the plant operator can use to directly set doses of coagulant and disinfectant based on the flow rate into the plant. Previous LCDC designs have only been configured to add coagulant prior to flocculation. The triple-doser design is capable of adding coagulant before the influent water enters the stacked rapid sand filter and of adding chlorine for disinfection before the treated water enters the distribution tank. The Spring 2012 team is introducing a more sophisticated LCDC device that will allow the operator to set and monitor the two doses of coagulant and the dose of disinfectant, for a total of three chemical doses, on a single dosing apparatus. In order to ensure accurate chemical dosing, we are testing and documenting the calibration of the new LCDC. Ultimately, we will determine a method for the triple-armed dosing mechanism to be built and added to plants on site, putting a focus on simplicity and elegance of design so that the AguaClara LCDC can be constructed with local resources.

Floc Recycle Venturi, Spring 2012

Ryan Anthony, Elyssa Dixon, Zac Edwards

Abstract:

The purpose of a venturi is to create a low pressure zone in the contraction of a pipe that can be used to pull􏰄fluid from another location into the existing 􏰄ow against the force of gravity. AguaClara can use this technology to implement floc recycle and decrease the necessary size of the flocculator. A pipe will transport heavily flocculated and turbid water from the floc hopper in the sedimentation tank to the horizontal section of the rapid mix pipe that leads into the flocculator. A venturi constructed in this horizontal portion of the rapid mix pipe will pull this turbid water from the floc blanket into the incoming plant flow and thereby increase the incoming turbidity. The flow of the turbid water transported from the floc blanket to the rapid mix pipe is dependent upon difference in head at the end of the system compared to the head in the throat of the venturi. By recycling the turbid water, a greater floc volume fraction will be present at the beginning of the flocculator to increase collisions and thereby reduce the amount of time that the water must spend in the flocculator; this, in return, will reduce the size of the flocculator and reduce material and construction costs.

Demo Plant, Spring 2012

Sahana Balaji, Muhammed Abdul-Shakoor, Thalia Aoki, Miree Eun, Diana Kelterborn

Abstract:

The AguaClara water treatment process consists of coagulation, flocculation, sedimentation, and filtration, with flow/chemical dose control using gravity. The Demonstration Plant (Demo Plant) is an important educational tool to explain and publicize AguaClara technologies. Currently, a new Demo Plant has been constructed, tested, and documented. This version of the Demo Plant includes a sedimentation tank and a Stacked Rapid Sand Filter (SRSF) as well as a chemical doser and flocculator. The sedimentation tank design is based on the design from the ENGRI 1131 course and includes the formation of a floc blanket. The SRSF shows the new filtration method recently developed by AguaClara. There has also been emphasis on the systematic documentation of both theoretical calculations behind the design and operation of the Demo Plant.

Ram Pump – Spring 2012

Christine Curtis, Harrison Gill, Teresa Wong

Abstract:

AguaClara plants are driven entirely by gravity. This makes it difficult to provide treated, running water in the plants to fill chemical stock tanks and to provide bathroom service. The Ram Pump sub-team was charged with designing and optimizing a pump to elevate a small amount of water in the plant. The pump works by transferring the momentum from a large amount of water falling a short distance into the potential energy to raise a small amount of water. Initial efforts were focused on designing and building a modular test pump to characterize how ram pumps function and how to optimize performance and ease of construction for specific sites. To accomplish this, we developed a MathCAD document to characterize the testing parameters that we anticipated would most affect the modular pump performance. From these parameters, we were able to collect data regarding cycle time, mass pumped per cycle, and aver- age 􏰃ow of the pump under various configurations. Future teams should explore better data acquisition methods to collect instantaneous velocity data within each cycle. Eventually, decisions regarding the design of the full-scale pump will be made based on experimentation with adjusting these parameters.