In Honduras, a Calcium Hypochlorite solution is used in the Agua Clara flow controllers to chlorinate the drinking water. Unfortunately, due to the precipitation of calcium carbonate, the system clogs, which leads to large decrease in the flow rate (and thus dosing) of the chlorinating solution. The goal of these experiments were to find the contributing factors to failure (significantly decreased flow rate) by modeling a hypochlorinator in use in Honduras.
To ease plant preparation for use, it may be beneficial to create stock solutions of required chemicals days in advance of actual operation. Because certain chemical solutions equilibrate with air, they may perform better or worse with age. Using this set of experiments, it was to be determined whether an aluminum sulfate solution produces lower levels of effluent turbidity due to its age.
Drew Hart, Roy Guarecuco, Larry Lin
Abstract:
In light of recent successful tests run by the AguaClara Engineers in Honduras with poly-aluminum chloride (PAC), an alternative coagulant to alum which consumes a fraction of the alkalinity, the ANC Control team is preparing to stop research with lime feeders because they will be largely unnecessary when PAC is adopted for all AguaClara designs. In order to bring closure to ANC research the team will write a final paper detailing the insights pertinent to lime feeder technology that AguaClara has gained over five semesters of research. We will also organize the ANC Control wiki page
Sang Hoon Song, Anna Lee, Roy Guarecuco, Drew Hart
AguaClara plants rely on sweep flocculation to achieve high performance requiring a pH between 6.5 and 7.5 even after the dosing of alum. The low alkalinity of Honduran source waters requires the addition of acid neutralizing capacity to buffer against changes in pH from the precipitation of aluminum hydroxide after alum addition. The summer 2010 ANC Control team has continued to investigate the possibility of using a lime feeder with AguaClara plants to deliver saturated calcium hydroxide solution to the plant flow. The team now believes that the inability of the lime feeder to produce saturated effluent for long periods of time is primarily due to the precipitation of calcium carbonate which inhibits Ca(OH)2 dissolution. Experimental runs with distilled water and Honduran lime have produced better results than those seen in past semesters, but only 15% to 20% of the total lime dissolves to give a saturated effluent, too little for the lime feeder to be economically viable compared to sodium carbonate dosing. The team has added effluent recycle to remove carbonates from the reactor influent, which will be tested by future teams. In addition, the team is closer to determining the composition of the lime using the Total Carbon Analyzer.
Created by Chengfeng Wu, last modified by Lorna Ximena Aristizabal Clavijo on May 28, 2010
The Spring 2010 ANC team is continuing research with lime feeders where the Fall 2009 team left off. The original idea was to create lamellar sedimentation by placing a slanted tube on top of a vertical one and running water upwards through the reactor. With appropriate fluid velocities, one can maintain a fluidized bed of lime particles in the lower segment but prevent the vast majority of solid lime particles from leaving with the effluent (see 2009 design). This semester the team modified the reactor design in order to improve its performance and provide an easy way to feed lime while the reactor is running (see new lime feeder design).
Following the set-up described in each experiment found below with both the new apparatus and the old one, the team is conducting a series of experiments in order to determine which mechanisms are important in producing effluent saturated with lime for long periods of time. The tests are based on hypotheses which the team has developed over the course of the semester. Following the recommendation of previous ANC teams, the Spring 2010 team has tried to isolate variables and test them separately. In all of the experiments, the team has tried to vary only one parameter at a time so that comparisons between tests are more meaningful.
Monica Hill, Aditi Naik, Ritu Raman
The Summer 2010 Chemical Dose Controller (CDC) Team has spent the summer exploring the challenges associated with manufacturing precise orifices. The team has run a series of tests measuring flow rate on orifices created from Legris polyamide, flare cap fittings, refrigerator caps, and carburetor jets to determine their precision and accuracy. The orifices manufactured from polyamide were deemed inadequate, which caused the team to consider in- house and off-the-shelf manufactured orifices created from brass, which showed much lower deviations from the expected flow rate. This report describes the results of the team's experiments on four different types of orifices and endeavors to set future goals for next semester's CDC Team.
Abstract
Accurate alum dosing is vital for plant operation as it has a great impact on the effectiveness of flocculation and sedimentation. The nonlinear chemical dose controller (CDC) is designed to handle turbulent flow chemical dosing used in conjunction with the newly designed Rapid Mix Tube. In contrast, the linear CDC requires that the chemical flow in the dosing tube is laminar.
The linear CDC uses the linear relationship between laminar flow and major losses in the doser tube to maintain a constant chemical dose with varying plant flow rates. However, when the flow in the dosing tube is turbulent, the linear relationship no longer exists. In this case, a nonlinear CDC, one that uses minor losses to control flow rates, can be used to maintain a constant chemical dose with the varying plant flow rates. By using an orifice to control chemical flow, the CDC will have the same nonlinear response to increasing flow as the plant flow rate, which is controlled by an orifice. A dual scale system on the lever arm will increase accuracy in dosing at smaller doses.
Figure 1 shows a conceptual design of the dosing system. A float in the entrance tank is connected to one end of the lever arm and allows for the arm to move up or down based on varying plant flow rates. As plant flow rates increase, the float rises, and the lever arm connecting the dosing orifice falls increases the elevation difference between the constant head tank and dosing orifice to power chemical flow. As the flow rate decreases the elevation difference decreases and the chemical flow rate slows down.
Figure 1: Nonlinear chemical dose controller schematic
There are two dosing tubes coming out of the constant head tank each with a different size orifice fitting attached to the end. The two different sized orifices allow for the plant operator to dose alum at two different scales, a high and low scale. The operator will choose which orifice will be used based upon the desired alum dose the operator wishes to apply to the water, a parameter that depends on raw water characteristics. The two scales on the lever arm, as seen in Figure 1, correspond to one of the dosing tubes; for instance, the higher scale (20-100 mg/L) will be used when the larger orifice size is needed. The dosing tube which is not in use is merely lifted to a higher elevation than the constant head tank level and is clipped onto a hook to prevent the flow of alum through this unused orifice.
After the alum exits the dosing orifice it flows down through a rigid tube which then injects the alum over a rapid mix conduit which connects the entrance tank and the flocculator. The rapid mix tube has two orifices which create macro and micro eddies to ensure the uniform distribution of coagulant into the raw water.
Abstract
The ANC Control team has conducted laboratory research to investigate the feasibility of using a lime feeder to add alkalinity to the influent water of AguaClara plants. This was necessary in order to maintain the pH within the ideal range for flocculation after the addition the chemical coagulant, alum, which has an acidic effect. Low-alkalinity source waters in Honduras do not provide sufficient buffering capacity naturally to resist the drop in pH. The team has found that proposed lime feeder designs consistently fail to produce saturated effluent for a length of time which would make them economically and practically viable. The failure is believed to be caused by precipitation of calcium carbonate on the calcium hydroxide solid surfaces. The recent availability of poly-aluminum chloride, an alternative coagulant to alum with a much smaller acidic effect, in Honduras has reduced the need for lime feeders with AguaClara plants
Matthew Higgins, Adam Salwen, Christopher Guerrero
Accurate chemical dosing is important in water treatment plants to ensure optimal conditions for flocculation, sedimentation and disinfection of the treated water. The linear chemical dose controller uses laminar flow through a small diameter tube to create a linear relationship between head loss and chemical flow. The linear flow orifice meter then maintains a linear relationship between plant flow and water elevation. The linear relationships simplify chemical dosing for plant operators who may have a limited education. Our team is researching the upper-flow limit of the linear dose controller and developing innovative designs to increase the capacity of this system to function in plants with flow rates approaching and above 100 L/s. Furthermore, we are redesigning and simplifying the linear flow orifice meter algorithm to improve its precision and performance in the field.
Matthew Higgins
Accurate chemical dosing in water treatment plants is imperative to ensure optimal efficiency during flocculation, sedimentation, filtration and disinfection. AguaClara designed the linear chemical dose controller (LCDC) and linear flow controller (LFC) systems to allow plant operators to reliably set and maintain a desired dose of coagulant and disinfectant. A linear relationship between head loss and chemical ow is created by using the major head loss through a small diameter tube to control the flow. To maintain this linear relationship, the systems have been designed to eliminate sources of minor head loss. Our team is actively working to minimize minor head losses through the systems, reduce the systems' maximum percent error and standardize the components and calibration techniques to be used to fabricate the systems in the field.
Jordanna Kendrot and Frank Owusu-Adarkwa
Continuous and accurate chemical dosing in water treatment plants is required for optimal efficiency during flocculation, sedimentation, filtration and disinfection. AguaClara designed the linear chemical dose controller (LCDC) and the Linear Flow Controller (LFC) systems to allow plant operators in Honduras to easily set and maintain the dose of coagulant and disinfectant through one system. A linear relationship between the head lost and chemical flow is created by using only major head loss, where the flow is controller by a small diameter tube. To continue using this linear relationship, the current experimental system has been designed with the goal of eliminating minor head loss. Our team is actively working towards the continuation of this work, decreasing the minor head losses throughout the systems, reducing the systems maximum percent error under 10% and standardizing the components and calibration techniques that will be used to fabricate this system in the field.
Julie Silva
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.
Zeyu Yao, Saugat Ghimire
The Chemical Dose Controller is an important of component of a AguaClara plant. The CDC delivers the coagulant (Polyaluminum Chloride (PACl) or Aluminum sulfate (Alum)) to the influent water and disinfectant Calcium hypochloride to the effluent filtered water. The Chemical Dose Controller is a simple mechanical response device which maintains a linear relationship between the plant flow and the chemical dose. It consists of a calibrated lever arm which the operator can use to adjust the dose of the chemical based on the turbidity of the influent water. The Fall 2013 team started off by putting together three half size doser units for stacked rapid sand filters constructed in India. All the parts were shipped to India with a detailed instruction manual to aid the assembly. The dosers sent to India contained CPVC ball valves with fluoroelastomer seals that are more resistant to chlorine than the previously used PVC ball valves. The ball valves in all the AguaClara plants will now be replaced with these CPVC ball valves. Similarly, a lock-and lock container will now be used as the Constant Head tank for both chlorine and coagulant suspended with a chain and a turnbuckle for height adjustment. Although the lock-and-lock container degrades when in contact with chlorine, it is locally available and can be easily replaced. In addition to this, the design of a new half-size doser with single arm which only doses chlorine has been completed. A 3D sketchup file has been created and sent to Hancock Precision for fabrication. This new doser will primarily be used in low flow plants in India which only require chlorine delivery.
Philip Akpan, Tigran Mehrabyan, Desiree Sausele, and Victoria Zhang
The Fluoride subteam seeks to develop a sustainable, inexpensive fluoride removal system for implementation in upcoming AguaClara plants located in India. Using the apparatus developed by previous semesters, the team continued running experiments testing how various concentrations of PACl affect fluoride removal. However, complications with the ability to measure fluoride concentrations required the team to shift its goals to designing a lab scale, gravity-powered system. The team finalized a design and completed construction of the new, electricity-free apparatus. The team plans to run experiments to test its fluoride removal capabilities after ensuring that there are no remaining water leaks.
August Longo, Briana Li-Vidal, Michelle Cheng, Victoria Zhang
The Fluoride subteam seeks to develop a sustainable, inexpensive fluoride removal system for implementation in upcoming AguaClara plants located in India. After earning an EPA Phase II grant for the Spring 2016 fluoride removal reactor, the subteam seeks to improve fluoride purification by testing lab-scale systems to compare a single reactor with reactors in series. At the beginning of this semester, the subteam identified potential issues with floc buildup at the bottom of the reactor. Thus, a sloped plane bottom geometry was incorporated into the reactor system to encourage recirculation of the flocs. Additionally, experiments with high concentrations of PACl resulted in clogging of the apparatus due to PACl buildup. Clay was incorporated into the influent stream to abate this PACl buildup. Initial testing of fluoride removal with the updated one and two reactor systems provided results that seem to indicate slightly better fluoride removal efficiency with two reactors, but more data collected by future testing is required to make a concrete conclusion.
Fluoride Auto — August Longo, Briana Li-Vidal, Michelle Cheng, Victoria Zhang
The Fluoride subteam seeks to develop a sustainable, inexpensive fluoride removal system for implementation in upcoming AguaClara plants located in India. After earning an EPA Phase II grant for the Spring 2016 fluoride removal reactor, the subteam seeks to improve fluoride purification by testing lab-scale systems to compare a single reactor with reactors in series. At the beginning of this semester, the subteam identified potential issues with floc buildup at the bottom of the reactor. Thus, a sloped plane bottom geometry was incorporated into the reactor system to encourage recirculation of the flocs. Additionally, experiments with high concentrations of PACl resulted in clogging of the apparatus due to PACl buildup. Clay was incorporated into the influent stream to abate this PACl buildup. Initial testing of fluoride removal with the updated one and two reactor systems provided results that seem to indicate slightly better fluoride removal efficiency with two reactors, but more data collected by future testing is required to make a concrete conclusion
Serena Takada
This semester, the Chemical Dose Controller (CDC) Team improved the AguaClara Automated Design Algorithm by updating the CDC drawing file to reflect recent updates in the CDC system design. Updating the CDC drawing code will allow clients and team members to obtain an accurate design of the current AguaClara plant designs using the AguaClara Design Tool. When 1 the existing CDC drawing code was implemented with the most uptodate drawing at the beginning of the semester, AutoCAD outputted the design illustrated in Figure 2. As shown in Figure 2, with the existing code, the CDC system is located inside of the Flocculator even though it should be mounted on the outside wall of the Flocculator. This was the starting point of the challenge. By the end of the semester, the CDC dosing system and lever arm were mounted against the Entrance Tank and Flocculator wall.
Tanapong Jiarathanakul, Imtiaz Karim, Michelle Wagner
The AguaClara Arsenic team for the Fall 2013 semester is the first to begin testing different methods of removing arsenic from drinking water. The initial goal was to develop a reliable method for testing water treatment alternatives and be able to detect small concentrations of arsenic. The work this semester follows the literature review performed in Spring 2013 which evaluated alternative arsenic testing methods and water treatment options for arsenic removal. A key issue is the need to measure low levels of arsenic (below ten parts per billion). Over the summer a graphite furnace atomic absorption spectrophotometer (GFAAS) was repaired for use in arsenic analysis. The lamp and power source of GFAAS have been replaced to improve the arsenic detection limit and the team is learning to operate the instrument. We will be using different coagulants to see which provides the best adsorption of arsenic to remove it from water, and dierent sample processing methods to simulate larger scale treatment processes. The team has a designated area for handling the solutions and samples as arsenic is toxic and we would like to minimize the contact it has with any person or object in the lab. The issue of arsenic waste is also a concern and this is why we are performing experiments using small sample volumes in order to reduce the amount of toxic waste produced.
David Buck and Andrea Castro
The municipality of Las Vegas, Honduras is currently experiencing a decrease in the capacity of their water distribution network due to the accumulation of scale in pipes. Our hypothesis is that this is caused by the karst topography of the region. The water source for Las Vegas is a groundwater spring. Groundwater, initially at a low temperature, flows across sediments containing calcium carbonate, CaCO3(s) . The water heats up when it reaches the surface and as it flows through shallow pipes to the end of the distribution system. As the water warms and reaches equilibrium at a new temperature, calcium carbonate precipitates, coating the pipes in a hard scale. An AguaClara plant could solve this problem by dosing acid, which would drop the pH and prevent the formation of scale by keeping calcium in aqueous form. The purpose of the present analysis is to determine how much acid in the form of aluminum sulfate, Al2 (SO4) 3 , should be added and provide further analysis giving evidence for the present solution.
Zeyu Yao, Saugat Ghimire
The Chemical Dose Controller is an important of component of a AguaClara plant. The CDC delivers the coagulant (Polyaluminum Chloride (PACl) or Aluminum sulfate (Alum)) to the influnt water and disinfectant Calcium hypochloride to the effluent filtered water. The Chemical Dose Controller is a simple mechanical response device which maintains a linear relationship between the plant flow and the chemical dose. It consists of a calibrated lever arm which the operator can use to adjust the dose of the chemical based on the turbidity of the influent water. The Fall 2013 team started off by putting together three half size doser units for stacked rapid sand filters constructed in India. All the parts were shipped to India with a detailed instruction manual to aid the assembly. The dosers sent to India contained CPVC ball valves with flouroelastomer seals that are more resistant to cholrine than the previously used PVC ball valves. The ball valves in all the AguaClara plants will now be replaced with these CPVC ball valves. Similarly, a lock-and lock container will now be used as the Constant Head tank for both chlorine and coagulant suspended with a chain and a turnbuckle for height adjustment. Although the lock-and-lock container degrades when in contact with chlorine, it is locally available and can be easily replaced. In addition to this, the design of a new half-size doser with single arm which only doses chlorine has been completed. A 3D sketchup file has been created and sent to Hancock Precision for fabrication. This new doser will primarily be used in low flow plants in India which only require chlorine delivery
