Acid Neutralizing Capacity, Fall 2010

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

Acid Neutralizing Capacity - Summer 2010

Sang Hoon Song, Anna Lee, Roy Guarecuco, Drew Hart

Abstract:

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.

Acid Neutralizing Capacity - Spring 2010

Created by Chengfeng Wu, last modified by Lorna Ximena Aristizabal Clavijo on May 28, 2010

Abstract:

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.

Acid Neutralizing Capacity, Fall 2010

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