Removal of Arsenic from Water under Static-State Conditions. Jordan Finneseth. Internship: January 2014 July 2014

Transcription

1 Removal of Arsenic from Water under Static-State Conditions Jordan Finneseth Internship: January 2014 July 2014 California State University San Bernardino Advisor: Professor Bob Phalen at CSUSB 12/22/14 1

2 Table of Contents Executive Summary.. 3 Introduction... 4 Methods Part 1. 4 Part 2. 5 Results... 6 Discussion. 6 Conclusion 6 Acknowledgements... 7 References. 8 2

3 Executive Summary The purpose of this experiment was to test different filter media to determine a cost effective way to remove arsenic from water in a static state. Potters for Peace developed special clay pots that, when placed in a bucket, serve as a microbial filter for water. Previous tests showed that while the pots are effective at removing many biological contaminants, they do not remove arsenic from the water. Many areas where the pots are potentially being used have ground water which contains high levels of arsenic (up to 40 ppb); about four times the recommended level. Thus, finding a way to inexpensively remove the arsenic from the water was the focus of this project. The media tested were activated charcoal, activated alumina, silica sand, and ferric oxide. The experiment tested the condition where the media would be placed in the bottom of the catch bucket so that when the water filtered through the pot, it would come into contact with the media in the bucket in a static state, under conditions of passive diffusion in water. Starting with a 40 ppb arsenic solution of non-chlorinated water, three test buckets were prepared for each media with similar conditions to that of the clay filter catch bucket. The test buckets were filled with equal amounts of the arsenic solution. Samples were then taken at specific intervals over a 48 hour period to be used for analysis. Analysis of the samples was done on a graphite furnace atomic absorption spectrophotometer. The results showed that the activated alumina and the ferric oxide were effective within the first hour at removing the arsenic to levels below the U.S. EPA safe limit of 10 ppb whereas, the activated charcoal and silica sand resulted in little change after 48 hours. 3

4 Introduction Clean, potable water is one of the most crucial elements needed for the survival of life. There are many areas on this planet that continue to have scarcity when it comes to this important substance. While many of these areas do have a water supply, often this water is unsafe for consumption due to hazardous contaminants of chemical or biological nature. One organization that has set out to help remedy this problem is Potters for Peace. This organization produces a fairly inexpensive filtering unit which consists of a ceramic pot that fits into a catch bucket which has a spigot at the bottom. Dirty, unfiltered water is poured into the ceramic pot and it proceeds to trickle through the pot and fall into the catch bucket as filtered, potable water (Ceramic Water Filter Project). While this device has been shown to remove many of the impurities that exist in the water, it had previously been determined that one thing that the pot did not remove was Arsenic (Tun, 2009) Arsenic is a naturally occurring element found in plants, animals, rocks and soil, air, and as can be seen in this study, water. There are a variety of ways that it is released into the environment, and due to both natural and human activities it often ends up in the natural water sources (Arsenic in Drinking Water). Human exposure to Arsenic can lead to both short and long term health effects. Some of the health problems linked to long term exposure to Arsenic include: cancers of the lungs, kidneys, bladder, skin, liver and prostate; thickening and discoloration of the skin; nausea, vomiting and diarrhea; and numbness of the hands and feet, blindness, and partial paralysis (Arsenic). Due to these health effects, in 2001 the U.S. Environmental Protection Agency (EPA) adopted a new standard for arsenic in drinking water at 10 parts per billion (ppb) for the U.S. public water supplies (EPA, 2014). This law, however, is only regulated in the public water supply, so areas that are not serviced by one of the numerous public water supply utilities remain unprotected. One such area where this occurs exists in the Coachella Valley area of southern California. Some of the inhabited areas in this valley are impoverished and due to varying circumstances including existing on tribal land, these areas are not connected to the municipal water supply and rely on ground wells as their source of water. Previous testing has shown that some of the well water in this area has arsenic levels up to 40 ppb. Due to limited financial resources, large reverse osmosis systems that are expensive to purchase as well as maintain are not feasible for many of the residents, so an inexpensive option is needed. One such option for this area is the pots produced by potters for peace. As previously mentioned, these pots are not capable of removing arsenic from water, so the purpose of this study was to find a filter media that could be used in conjunction with these filter pots to remove the arsenic from the filtered water. Methods Part 1 There were four types of media that were tested: activated alumina, activated charcoal, ferric oxide, and silica sand. The silica sand was HTH Pool Filter Sand: #20 Silica Sand. The ferric oxide used was AQUAMAXX Phosphate-Out Granular Ferric Oxide. The activated charcoal used was Multavita Coconut Shell 4x8 mesh Granular Activated Charcoal. The activated alumina used was Alcan Iron Coated Granular Activated Alumina, Lot number: 06-FS50-907B Generic plastic laboratory 4

5 containers with a 2200 ml capacity were used to simulate the existing plastic catch basin for the water filters. In the catch bucket for the ceramic filter pot there is a space below the accessible water spigot that measures approximately 1 inch. When the pot is inside the bucket there is a distance of approximately four inches from the bottom of the bucket to a level where the filtered water would not be touching the bottom of the pot. These measurements were used to simulate the bucket environment inside of the sample containers. Each container was pre-weighted, one inch of media was placed in each container, and then the container was reweighed to ensure equal amounts of media were placed in each replication. Three replications of each media were prepared, as well as three containers without any media for use as a control. A 40 ppb solution of arsenic water was prepared using 1 ml of a 1,000 ppm Arsenic AA standard: Arsenic Trioxide in 3% Nitric Acid made by the RICCA Chemical Company, which was mixed with 25 liters of deionized (DI) water. Once the solution was prepared, each experimental container was filled to the designated level with the 40 ppb arsenic solution and the time was recorded. Samples, 5 ml aliquots, were taken at 1hr, 2hrs, 4hrs, 8hrs, 12hrs, 24hrs, 36hrs, and 48hrs intervals. The EPA has published method Determination of Trace Elements by Stabilized Temperature Graphite Furnace Atomic Absorption. This method gives procedures for determining the amounts of total dissolved and recoverable elements by Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS) from various water sources. One of the elements included on the list of 16 that this method can test for is Arsenic. For this research project analysis of the samples was conducted on a GBC 906 Atomic Absorption Spectrophotometer with a GBC GF3000 Graphite Furnace and GBC PAL 3000 auto sampler. A Nickel AA standard consisting of Ni in 3% HNO 3 making 1000 ppm Ni was used as a matrix modifier to increase sensitivity. The calibration blank solution used throughout the experiment was a 3% Nitric Acid solution. The peak absorbance detected was used in conjunction with calibration levels to determine the concentration of arsenic in the samples at the given time intervals. Part 2 The second stage of this experiment was conducted with the filter media that was determined to be the best choice for use with the Potters for Peace filter system. As discussed in the results section, the optimal filter media was the Alcan Iron Coated Granular Activated Alumina. Due to the fact that the levels of arsenic in the water lowered substantially within the first hour, the second stage was set up to run the experiment for one hour. The same set up procedures were followed as in part one, and once the 40 ppb arsenic water was in the test bucket the 5 ml aliquots were taken every ten minutes for one hour. GFAAS Optimization Before conducting analysis, testing was done using a prepared 40 ppb solution to optimize detection using this GFAAS. The optimized program is found in Table 1. Table 1: Optimized GFAAS program Final Temperature Ramp Time (sec) Hold Time (sec) 80 F F F F

6 2350 F F Results The analysis data for the removal of arsenic in the different media can be found in the following table: Table 2: Average arsenic concentration (ppb) at sampled times 1 hour 2 hours 4 hours 8 Hours 12 hours 48 Hours Activated Charcoal Silica Sand Activated Alumina Ferric Oxide The analysis data for the removal of arsenic in activated alumina over a period of one hour can be found in Table 3 Table 3: Average arsenic concentration (ppb) at sampled times 10 min. 20 min. 30 min 60 min Activated Alumina Discussion After analysis each of the filter media fell into one of two groups. One group was media that were highly effective at rapidly removing arsenic in a static condition and one group that was not effective in removing arsenic in a static condition. The media that were not able to remove the arsenic effectively were the activated charcoal and the silica sand. For activated charcoal, when the arsenic water had been exposed to the media for a period of 48 hours, the average concentration of arsenic remaining in the samples collected was ppb. The samples collected from the silica sand test buckets at the 48 hour mark contained an average of ppb arsenic. For the activated alumina, when the arsenic water had been exposed to the media for a period of one hour, the average concentration of arsenic remaining in the samples collected was 2.58 ppb. For the ferric oxide, when the arsenic water had been exposed to the media for a period of one hour, the average concentration of arsenic remaining in the samples collected was 3.92 ppb. In part two the activated alumina was chosen to be tested alone, and samples were taken at 10 minute intervals. Within the first ten minutes the samples were shown to have a concentration of ppb which is already below the EPA standards and is considered safe for human consumption. Conclusion The results of this study show that while there are a couple media options that could be used in conjunction with the Potters for Peace ceramic pot filtration system to remove arsenic from water, the best choice is activated alumina. Since these filters are designed to be used on a continuous basis, the water needs to be purified and safe to ingest quickly, and the activated alumina was shown to be effective in reducing the levels 6

7 of arsenic to a safe amount in a short period of time. Within the first ten minutes the concentration fell below the EPA standard of 10 ppb to a level of ppb, making it safe to ingest. At this point we can recommend to the users of this filter that live in areas that have levels of arsenic in their drinking water up to 40 ppb that adding one inch of this activated alumina product to the bottom of the catch bucket will effectively reduce the concentration of arsenic down to safe levels within the first ten minutes. At this point further testing would need to be conducted to measure how quickly the concentration drops within the first 10 minutes to get a better estimate of exactly how long it takes for the arsenic concentration to reach safe levels. With the results as they currently are, it is recommended that users allow the after to sit in contact with the activated alumina for ten minutes to be sure that the arsenic concentration is at a safe level. There are several limitations and possible sources of error in this study. Only four removal media sources were tested and there are potentially other viable options for a reasonable price. The test was conducted using testing buckets that were different from the catch buckets used with the filters which could potentially affect the results. Human error was introduced in many aspects of the study including measurements of how much water was placed in the sample buckets as well as the amount of water that was removed from the testing buckets for each sample taken. These variables along with other human factors could affect the outcome of the study. Another main source of error is the GFAAS. At different times throughout the study parts had to be switched out and replaced, and each time this occurred a change in the performance of the GFAAS was seen. Triplicates were run on each sample analysis and often there was a high variation in values determined which decreased the reliability of the GFAAS. These factors were taken into consideration and the plus/minus values were determined account for the variation, and with the recommended media type the results remain acceptable according to the EPA standards. The next step in this research would be to expose the activated alumina media to repeated exposures of 40 ppb arsenic water to determine how long it remains viable and reduces the levels to acceptable amounts. When that is discovered it needs to be determined if there is a way to reactivate/recharge it so that it continues to be effective or if it needs to be completely replaced. A study could also be conducted to see how effective the media would be if placed inside the ceramic pot so that the water is able to filter through the filter media before it is filtered by the pot. If the activated alumina was more effective this way, and the amount added by the pot is small enough, the resulting concentration of arsenic in the filtered water could possibly be lower. It would also need to be determined if placing the media inside the pot would have a negative effect on the pot and its ability to effectively do what it is designed to do. Acknowledgements This project was supported by Hispanic-Serving Institution s Education Program Grant no from the USDA National Institute of Food and Agriculture." 7

8 References Arsenic. (n.d.). Retrieved July 1, 2014, from Centers for Disease Control and Prevention: Arsenic in Drinking Water. (n.d.). Retrieved July 1, 2014, from United States Environmental Protection Agency: Ceramic Water Filter Project. (n.d.). Retrieved July 1, 2014, from Potters for Peace: Tun, W. W. (2009). A study of arsenic leaching from colloidal silver ceramic water filters manufactured in Myanmar. UNICEF. UNICEF. United States Environmental Protection Agency (E.P.A.), 09 June Drinking Water Contaminants: National Primary Drinking Water Regulations 8