Challenges for Fall 2013

Team Organization

The following sections introduce the objectives of each team with some details. If you wish to read in more detail about the teams' challenges, check out the full challenges document.

Small Scale Plant

Your goal is to produce an easily reproduced and updated scale model representation of the plant that makes it easy to explain and show how a full scale water treatment plant works. The production system that you develop must begin with the AutoCAD drawing of a full scale plant and then with minimal processing send that file (or pieces of that file!) to a 3-D printer.

• Abandon the plexiglass assembly approach because it requires too much labor
• Switch to 3D printing
• Explore options for switching colors while printing to emphasize different materials used to fabricate a full scale plant.
• Assess which components must be made using alternative methods or which components should be printed as separate items.
• Determine the minimum practical thickness for 3-D printing.
• If necessary reduce the scale of the model plant so that it can be printed more easily. The goal is that the final unit can be easily passed from person to person in a classroom.
• Determine whether suitable 3-D printing services are available or if AguaClara should purchase a 3-D printer.

We will use this model for teaching at Cornell, for conferences, and for teaching about the AguaClara technologies internationally. The final model must be easy to transport by airplane.

Laminar Tube Floc

The primary goal is to develop a method to improve the performance of hydraulic flocculators. A secondary goal is to provide additional proof (or to disprove!) that the growth limited flocculation hypothesis is on the right path. A classic method of proving a theory is to take a prediction that is based on the hypothesis and test if that prediction is correct. One of the predictions of the growth limited flocculation hypothesis is that large flocs are useless for capturing colloids because the shear on surface of the large flocs is too high for colloids to attach. Thus colloid removal efficiency potentially could be improved if the large flocs were broken into smaller flocs. The goal would be to create flocs that are small enough to capture colloids and large enough so that they can be captured by the tube settlers.

LFSRSF

The SRSF has been a remarkable success for a brand new technology. The very first SRSF built at full scale in Tamara, Honduras continues to operate and to produce water that meets US EPA standards. The SRSF are also being deployed in Jharkhand, Indiathis fall for 2 village water supply schemes.
We still have many things to learn about SRSF operation. The challenge for this team is to develop an improved LFSRSF that is easy to fabricate, easy to operate, and that produces high quality water. This team should be in contact with Maysoon Sharif who is directing the AguaClara project in India to see if there are any immediate research needs for deployment or troubleshooting of the LFSRSF in India.

SRSF Theory

One of the strengths of the AguaClara model for technology development and innovation is that we have gradually developed a fundamental understanding of unit processes. The insights that come from a fundamental understanding can then be used to optimize the performance of the system. The overarching goal for this team is to conduct experiments that lead to a fundamental understanding and parameterization of SRSF performance. The way to create a theoretical understanding of SRSF is to conduct well controlled experiments while varying the input parameters that we expect to be important. The important filter inputs are filtration velocity, coagulant dose and clay concentration. The important parameters to monitor are influent turbidity, effluent turbidity, and head loss.

Anaerobic Wastewater Treatment

The objective of this research is to develop a robust, sustainable, low energy, operator friendly, wastewater treatment system. The expectation is that wastewater treatment technologies have failed to evolve and optimize due to the same influences that have caused drinking water treatment technologies to not evolve. Our goal is to bring the insight of the fundamental mechanisms, the limitations of mass transfer, an understanding of the interactions between reactor geometry and the fluid dynamics of multiphase flow to this task so that we can create a much improved anaerobic digester.

Turbulent Tube Floc

We need to do research with a turbulent flow hydraulic flocculator. We need to test our new limited growth flocculation hypothesis under turbulent conditions to see if the model is correct and to be able to revise the model as necessary. We need to learn how much collision potential is really needed in a turbulent flow reactor. We need to learn what the best energy dissipation rate is for a flocculator. Our current design standard of 10 mW/kg is based on "a reasonable number based on conventional designs". We aren't conventional and there is absolutely no expectation that 10 mW/kg is the right number! A higher energy dissipation rate could be useful to reduce the amount of flocs that settle to the bottom of the flocculators. As the energy dissipation rate increases it should be possible to reduce the residence time of the flocculator, but the head loss will increase and that will require the entrance tank to have a higher level.
The turbulent flow hydraulic flocculator will provide us help us understand the performance tradeoffs and hopefully to develop design modifications that substantially improve flocculator performance.
The turbulent tube flocculator must be designed to easily adjust the energy dissipation rate (perhaps by varying the flow rate) and to adjust the residence time by adding or removing flocculator sections. In the turbulent flow flocculator you will be able to vary energy dissipation rates by either varying Q (in which case energy dissipation rate increases with the cube of the velocity) or by changing the dimensions of the constrictions. If you vary Q, then you are holding the collision potential constant (because energy dissipation rate increases with the cube of velocity and the collision potential is proportional to the cube root of energy dissipation rate) and as you increase Q you are decrease the residence time (and collision potential is proportional to the residence time). If you vary the constrictions the energy dissipation rate will vary and the residence time will be almost unchanged.

Foam Filtration

Provision of safe drinking water for communities smaller than 1000 people is particularly challenging because the per capita costs associated with a full AguaClara plant increase as the community size decreases. Thus we are looking for more cost effective surface water treatment systems that could be applied for flow rates that are less than about 1 L/s. In India we are using a combination of the dose controller and SRSF to create a low cost treatment system that can treat low turbidity water. We anticipate that the SRSF is limited to treating water with a turbidity lower than about 5-10 NTU. In Honduras it is common for water sources to be too turbid in the rainy season to be adequately treated by a SRSF. The reticulated foam filtration system invented by the AguaClara team at Cornell could be a solution to the problem of small communities with turbid water.
Reticulated foam filters have a very high porosity and thus they have a high solids loading capacity. The high porosity also makes it possible to use a higher filtration velocity than can be used with sand.

Arsenic

Arsenic contamination of groundwater is a common problem and one of the methods of removing arsenic is based on flocculation and then removal of the flocs.

Review the report from the previous semester for literature review and background on the many hypothesized mechanisms. Our hypothesis is that arsenic removal requires good contact between arsenic and coagulant precipitate (hence a focus on rapid mix) followed by a highly efficient removal of the flocs that are loaded with arsenic. Given the low turbidity of most groundwater and the very low concentrations of arsenic relative to normal coagulant dosages, it is expected that a low coagulant dose should be adequate if there is ample opportunity for mass transport of arsenic to the coagulant precipitate. If a low coagulant dose is sufficient, then a SRSF should be able to capture the precipitate and produce a very low arsenic concentration. Given that arsenic removal efficiency will likely be correlated with coagulant precipitate removal efficiency, it may be beneficial to use 2 SRSF in series to enhance particle removal and provide additional protection against arsenic laden coagulant precipitate making it into the finished water.
 
It is possible that rapid mix flocculation, floc blanket, plate settler sedimentation, and SRSF would provide a better system for arsenic removal. This disadvantage of using this treatment train is that flocculation and sedimentation require much larger (and more expensive) reactors than an SRSF. Thus it would be better if an efficient arsenic removal system could be created that doesn’t require a sedimentation tank. Some flocculation time might be necessary to provide opportunity for more contact between arsenic and the coagulant precipitate.
The removal of arsenic by precipitation is expected to be limited by the transport of arsenic to the solid surface of the coagulating agent (either iron or aluminum salts). The flocculation process for groundwater containing arsenic is expected to be inefficient due to the low floc volume fraction.  To compensate for the low floc volume fraction it may be necessary to use a longer residence time. Loss of coagulant to the walls of the reactor will also likely be a major problem for small scale reactors given the low solid surface area in suspension. It may be advantageous to use a contact chamber for rapid mix and initial precipitation to reduce losses to the reactor walls.
Devise methods to conduct research safely and to ensure safe disposal of arsenic contaminated waste. Determine the best way to prepare and to measure very low concentrations of arsenic. Design and fabricate a reactor system and data collection system that will make it possible for us to begin to optimize treatment processes for efficient and reliable arsenic removal. Determine how to create a raw water for testing. Should the raw water be created from distilled water or from tap water? What should be added to the raw water to set the ionic composition? How should pH be controlled?

Floc Size Measurement

We need a tool that will allow us to quickly measure floc size and floc size distribution in a nondestructive manner in a flow through cell. We are not the first to need this tool and thus a literature search will provide at least one example of a system used to measure floc size.

The floc size tool will be used to learn more about the relationship between floc size and energy dissipation rate. Ideally it will be possible to use the digital floc camera immediately downstream from the floc break-up points in the laminar flow tube flocculator. It will also be applied at the effluent of both the laminar and turbulent tube flocculators.

Sand Source and Test Methods

Now that SRSFs are being constructed in India and in Honduras we need to develop standards for testing potential sand sources. In Honduras APP budgeted for importing the sand again through a company called Aquatec but that shouldn't be necessary. It should be possible to source the sand locally. In India, the water treatment plant for Ranchi apparently obtained their sand from a local river where the sand has a high silica content. We need a set of tests that can easily be conducted in country to assess.
Find the American Water Works Association guidelines for filter sand and find the ASTM tests that are recommended for filter sand.
There are 4 constraints for SRSF sand

1. No sand should be able to slide through the 0.2 mm slots in the PVC pipe
2. The sand should be hard and not prone to dissolution in acid
3. The backwash velocity required to expand the filter bed by 30% should be very close (this needs to be defined) to 11 mm/s
4. The sand bed must not have significant (this needs to be defined) stratification after backwash

The filter bed stratification after backwash may not be very significant if the bed is transitioned quickly from fluidized at 30% to settled. It is possible that the quick transition will not allow much time for smaller diameter sand to migrate to the top of the filter. This could be a lab research project or it is possible that a literature review will reveal that someone has already conducted these tests. In any case, the amount of stratification allowed should be based on a target distribution of flow between the 6 filter layers.
The challenge for this team is to develop a set of quick tests that can be conducted in the field to determine if a sand is suitable. If a sand isn’t suitable because of the wrong sand size, then this team should provide recommendations for sieve sizes to use to select an appropriate size sand. The team could practice preparing a suitable sand from a poorly sieved source by purchasing a river sand and then sieving it to get it within the specifications.

Stock Tank Concentration Measuring

One of the big goals of the AguaClara program is to design plants that are easy to operate and that provide appropriate feedback to the operator so that the operator can make appropriate adjustments. One of the critical activities for the plant operator is to prepare and mix the stock solutions of chlorine and coagulant. Unfortunately the operator can’t see if the solution is well mixed and there is no way to measure the solution concentration. Thus if an operator makes a mistake while dumping the granular sodium hypochlorite or PACl into the stock tank, there isn’t any way for the operator to know that the resulting stock concentration is incorrect. The goal is to provide the operators with the tools so they can check to see if the stock tank is well mixed and if the concentration is correct. The proposal is to use a simple hydrometer that is labeled to read the concentration of PACl or sodium hypochlorite. The other option is to provide a hydrometer and a table that converts the density to concentration.

Ram Pump

AguaClara needs a ram pump to move filtered water up to the chemical stock tanks and also for use in the water treatment plant bathroom. This need is especially important at larger facilities. For example, at San Nicolas the chemical stock tanks will be 750 L and would require the operator to fill and carry approximately 40 buckets of water. The pumping requirement for San Nicolas is 70 mL/s (750 L stock tank in 3 hr). The best efficiency that we obtained during the summer suggests that we might need 1 L/s of drive pipe water to deliver that flow. A goal for this semester is to improve the efficiency of the pump by tuning the waste valve and by using a 1” drive pipe that is the same diameter as we will be using in San Nicolas.

Stock Tank Centrifugal Pump

The purpose of the centrifugal pump mixing system is to provide an energy efficient means for a plant operator to mix the stock tank solutions.  This task is relatively easy for small plants where the stock tanks are 220 L tanks. However, as plant size increases the stock tanks grow in size as well and mixing them becomes more difficult.
We need to determine if our theoretical predictions for the pumping rate and the amount of lift generated by the centrifugal pump is correct. To do this, fabricate a small scale version of a tank and pump system that is sufficiently transparent that the level of the dense solution in the central rotating pipe of the pump can be recorded with a webcam. Devise a method to spin the pump at a known rpm (perhaps using a peristaltic pump drive) and to record the level of the dense solution in the central rotating pipe using a webcam. Determine whether or not this pumping system is feasible for mixing a 750 L stock tank at San Nicolas. This will require calculating the force required to rotate the centrifugal pump. The horizontal pipe in the pump will be the source of the majority of the fluid drag and that fluid drag will be significant for a large tank. Determine if the operator will be able to spin a large pump fast enough and determine if the drag could be significantly reduced by streamlining the PVC pipe. The PVC pipe could be heated and then deformed into an airfoil shape to reduce the drag.
Collaborate with the team that is selecting a hydrometer for concentration measurements and use the hydrometer to test the length of time required to mix a stratified solution.

CDC

The chemical dose controller is being adopted in India and in Honduras. It is the most critical AguaClara technology because without it none of our other treatment processes would work. It is critical that the chemical dose controller be easy to install, setup, and use. The dose controller with the lever and slider meets those requirements. The entire chemical dosing system is NOT yet easy to setup and use. The goal is to take a systems perspective and evaluate all of the components of the chemical dosing system and develop a set of dosers that can be shipped where needed.

Water Treatment Technology Selection Guide

In a world where billions still lack access to safe drinking water, the information barrier to selecting the appropriate water treatment technology for resource-poor communities has not been effectively lowered. With rapidly evolving technologies it is difficult even for water supply professionals to select the best technology given a context and a water source. The result is that a high fraction of the capital invested in water treatment infrastructure is wasted on inferior technologies or the wrong unit processes for the water quality problem.
Current technology selection guides tend to focus on providing information on treatment technologies based on contaminant removal requirements, while ignoring the realities of resource-constraints and skill-constraints of communities, and without consideration of sustainable engineering practices. An expert guidance tool is needed to empower water supply professions to make better decisions and to learn which constraints determine which technologies are appropriate. The goal of this project is to develop the framework and decision-making methodology for such a decision-support system, and to implement a platform for usage that can easily be integrated into the AguaClara Design Engine. In the Fall of 2011 an AguaClara team made a technology selection guide. Since then the AguaClara technologies have continued to evolve.
The goal is to develop a technology selection guide that clearly indicates what the constraints are that determine which technology is best suited for different levels and types of water contamination. The comparison of AguaClara and Slow Sand Filtrationwould be a useful resource as an example for how to assess technologies. The guide must be designed as a front end for the AguaClara design engine so that at the end of the process the user receives a design for the required water treatment plant if AguaClara has the best solution.

Carbon Credits

Explore options for using the Voluntary Carbon Markets as a way to help finance AguaClara facilities.  Carbon offsets could be worth looking into for income for AguaClara. Some point of use water filters have received credit for offsetting firewood consumption, so there is a precedent for water treatment offsetting carbon creation from boiling water.

Design

The design team challenges are available in a separate google doc. The design team will consist of 4-8 students that will work on these tasks individually or in pairs. Desired (but not necessary) skills: Mathcad, AutoCAD, 4540, fluids, Spanish fluency, and engineering design experience.

Public Relations

Goals: keep alumni and friends of AguaClara updated on developments with AguaClara

• blog posts at least twice per month (with tweet)
  • include video interview of team members
• website maintenance
  • Add new project sites in Honduras and India
  • Contact AguaClara LLC to get coordinates of villages in India
• newsletters twice per semester
  • include links to specific blog posts
• plans and organizes outreach events on campus
  • Develop expertise in running

raise funds for the trip to Honduras using https://cornell.useed.net/. Coordinate this effort with Rebecca McDonald