Basin Water, Inc

Large-scale Arsenic Treatment of Drinking Water Sources

Small-Scale Pilot Testing is No Substitute for Large-Scale Demonstration when an Arsenic Removal Strategy is Implemented.

By Gerald Guter and Peter Jensen

The approach of the US Environmental Protection Agency's (USEPA's) January 2006 deadline for implementation of the new arsenic standard has prompted numerous water purveyors to investigate arsenic treatment.

Don Bartz, General Manager of Baldy Mesa Water District (BMWD) in Southern California commented, “The scarcity of water in the high desert leaves us with no choice except to remove arsenic from the drinking water. Our board feels that it is very important to deal with this issue immediately in order to ensure our customers of a safe and reliable supply of drinking water in the future.”

To date, most arsenic treatment investigations have consisted of small pilot studies that use several small test columns operating at 1-4 gpm (0.06309-0.25 L/s). The problem is that owners and operators of future full scale plants are concerned there is little or no information on the operation of plants treating large flow rates and quantities closer to their needs. Recognizing this lack of important information, Basin Water Inc., of Southern California , has initiated a program to install field demonstration units with capacities of 100 to 550 gpm (6.31-34.7 L/s) at various well sites to obtain the needed data.

Benefits of Large-Scale Process Testing

USEPA has identified ion exchange as one of the best available technologies in its fianl arsenic rule (USEPA, 2002). The removal of arsenic by ion exchange has been studied in great detail. There is no doubt that the chemistry between arsenic in a water solution and an ion exchange resin is highly favorable for treatment. Arsenic can be removed to well below the Maximum Contaminant Level (MCL) in a properly designed ion exchange system. There is little need for further research or pilot studies.

However, certain characteristics or properties of the process - disposal of waste residuals in particular - need to be demonstrated in large scale field studies using water obtained from the well to be treated. These characteristics are summarized in the following paragraphs.

Arsenic recovery. Arsenic is usually present in microgram-per-litre quantities in the contaminated water and is removed into a waste brine. However, credible tests for disposal of recovered arsenic from the waste brines should be done with at least a gram or larger quantities of arsenic. Thus, approximately =1 acre-ft (1,233 m³) of water should be treated to test recovery of waste arsenic. Treating this quantity of water with small lab equipment would be impractical.

Trace contaminants. Undetected trace contaminants that interfere in the waste recovery step may be present. Although these undetected trace contaminants will not interfere with the arsenic removal process, they may interfere in arsenic recovery from the waste brine. The contaminants will be concentrated in the brine in quantities sufficient to be detected and may interfere with the recovery of arsenic from the brine or may present brine disposal problems. Again, large quantities of water should be treated to provide waste brine quantities sufficient for analysis and testing.

Long term accumulation of trace contaminants. Several bed volumes of water can be treated before resin regeneration when the sulfate concentration in the feed water is low. In this case, even greater amounts of the undetected contaminants will concentrate in the brine. Furthermore, a sufficient feedwater supply must be available that can best be obtained in a large-scale operation.

Feedwater changes. The variation of feed water composition must be addressed because process adjustments may be required to compensate for such changes. This can best be done in a field location where sufficient volumes of feed water are available. Over a long period of time, feed composition variations will correspond to those experienced in a full-scale treatment plant.

Accurate wastewater determination. The amount of waste brine requiring disposal must be accurately measured. One of the largest cost factors is that of hauling waste brines to a point of disposal. Thus, accurate measures of waste brine volumes must be determined. Generation of waste can easily be ignored in a small scale system because small amounts can be disposed of without a permit. In contrast, operation of a large field-testing plant will generate highly visible quantities of waste and will require temporary permits. This not only characterizes the amount of waste produced but will also initiate the waste discharge permitting process. Operation of large scale field equipment is required to sufficiently determine and define waste quantities.

Carbonate scale formation. Scale formation is best studied in a large field-testing facility. Water compositions, equipment and process designs vary in their ability to produce scale, such as calcium carbonate scale. The test facility should duplicate the full-scale plant in the materials used and the flow rate, flow path and local pressure gradients.

Preliminary permit processing. Enough waste brine and arsenic should be produced to require actual disposal as the required permits. These factors are easily avoided in small test units. The need for permits provides the future owner with an opportunity to consult with the permitting agency engineers with whom they will be associated in the future.

Large-Scale Field-Testing Program

Basin Water Inc. has developed a proprietary ion exchange technology which is currently being used throughout California for the removal of arsenic, nitrate, chrome 6, perchlorate and uranium. As part of their services, Basin Water has constructed several mobile ion exchange systems with capacities ranging from 100-550 gpm (6.31 to 34.7 L/s) that can be used for field demonstration projects.

These mobile units have been used primarily in arsenic removal. Over the past two years, they have processed in excess of 20 mil gal (76 ML) of water from a variety of different sources. A summary of the different locations, volumes and water qualities is included in Table I.

The variation of water quality present at each location has provided valuable insight into residual handling, consistency of results and other operational issues.

Case Study

The Victor Valley Water District (VVWD) and the BMWD are located in the high desert of Southern California . Both districts are dependent on groundwater to supply a population of roughly 100,000 people. Currently, 20 out of 27 wells operated by the two districts will exceed the new arsenic level of 10 µg/L set by the USEPA. If California lowers the arsenic MCL to 5 µg/L, all 27 of the wells will require treatment. As a result, the districts have been actively investigating various water treatment technologies to meet the January 2006 implementation deadline.

During October and November of 2002, Basin Water mobilized its 100 gpm (6.31 L/s) mobile ion exchange unit to well 29, operated by the VVWD. The unit was located adjacent to well 29, an area that also included a 3 mil gal (11 ML) storage tank. Figure 1 shows how the unit is tied into the existing system.

The Basin Water mobile unit is a self-contained, multibed, ion exchange system (Figure 2). It has multiple sample ports and is configured for automatic data-logging and residuals-handling. The only two discharges are for product water and nonhazardous brine. An external brine tank holds this nonhazardous brine for subsequent disposal.

The mobile unit ran continuously in 2002 from October 2 to October 29 at a flow rate of 50 gpm (3.15 L/s). In order to run a breakthrough curve, on Oct. 30, 2002 , Basin Water selected a bed and operated it beyond the normal point of regeneration. The breakthrough curve run ended Nov. 6, 2002 . A total of 2.2 mil gal (8.3 ML) of water was processed over the course of the test.

Sampling Procedure

The Basin Water mobile unit is designed for unattended operation. Its onboard computer continuously logs operating data, including pressure, flow, pH, alarms, equipment status, all control actions, and other items.

VVWD operators performed all influent and effluent water quality sampling. Table 2 summarizes data and collection frequency information.

Operational Settings and Sampling Results

Before testing, a computer simulation of the operating system was run based on the water quality of well 29. The simulation indicated that both arsenic and vanadium breakthrough would occur at approximately 2,700 bed volumes. For purposes of the test, the system operated at 2,000 bed volumes which resulted in a waste product of .05%. Thus, 2.2 mil gal (8.3 ML) of processed water produced 1,100 gal (4,163.5 L) of waste brine.

For the duration of the test, arsenic was reduced from 12 µg/L to nondetect (ND) and vanadium was reduced from 70 µg/L to ND.

Total arsenic recovered from the treated water was 0.22 lb (101 g). The total precipitate weight was roughly 6.3 lb (2,800 g). Analysis of the waste residuals indicated that the precipitate would pass the toxicity characteristic leaching procedure (TCLP) test but would not pass the total threshold limit concentration (TTLP) test, a ratio of weight of arsenic to weight of solid residual.

Of particular interest was the high level of chromium 6 in the waste brine, because chromium 6 was not detected in the source water. To address this issue, the precipitation step was modified to include the addition of ferrous sulfate. It was important in this case to have a representative sample of waste brine in order to properly design the metals precipitation step.

Conclusion

Large scale testing allowed the districts to accomplish a number of important objectives:

confidence in ease of scaling up to a production unit was achieved.
data needed for subsequent permitting process were obtained.
waste residuals were characterized, and
field operators were educated on use of the production unit.

As a result of the testing, BMWD has contracted with Basin Water for the installation of a full scale 1000 gpm (63.09 L/s) arsenic removal unit. This unit should be in operation by next month.

“The large scale demonstration test gave our district the confidence to move forward with a full-scale unit,” said Don Bartz. “We are proud to be the first water purveyor in the high desert to supply arsenic-free water to our customers.”

Acknowledgement

The authors thank the team members from Baldy Mesa Water District and Victor Valley Water District for their efforts throughout the testing process.

-Gerald Guter, who holds a PhD in chemistry, is vice-president of technology at Basin Water, Inc., 8731 Prestige Court , Rancho Cucamonga , CA , 91730 . He can be reached at (909) 481-6800; fax (909) 481-6801; or at info@basinwater.com .

Peter Jensen is a professional engineer and chief executive officer and president of Basin Water, Inc., 8731 Prestige Court , Rancho Cucamonga , CA , 91730 . He can be reached at (909) 481-6800; fax (909) 481-6801; or at info@basinwater.com .

References

US Environmental Protection Agency Report, 2002.

Draft Report for Discussio,n Arsenic Guidance, Appendix B- 3 EPA 40 CFR Parts 9, 141 and 142 [WH- FRL- 6934- 9] RIN 2040- AB75. National Primary Drinking Water Regulations; Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring. http://www.epa.gov/safewater/ars/dimpguidaxb.pdf


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> News Home Large-scale Arsenic Treatment of Drinking Water Sources Click to view PDF Small-Scale Pilot Testing is No Substitute for Large-Scale Demonstration when an Arsenic Removal Strategy is Implemented. Reprinted from Journal AWWA, Vol 95, No.6 (June 2003), by permission. Copyright © 2003, American Water Works Association. By Gerald Guter and Peter Jensen The approach of the US Environmental Protection Agency's (USEPA's) January 2006 deadline for implementation of the new arsenic standard has prompted numerous water purveyors to investigate arsenic treatment. Don Bartz, General Manager of Baldy Mesa Water District (BMWD) in Southern California commented, “The scarcity of water in the high desert leaves us with no choice except to remove arsenic from the drinking water. Our board feels that it is very important to deal with this issue immediately in order to ensure our customers of a safe and reliable supply of drinking water in the future.” To date, most arsenic treatment investigations have consisted of small pilot studies that use several small test columns operating at 1-4 gpm (0.06309-0.25 L/s). The problem is that owners and operators of future full scale plants are concerned there is little or no information on the operation of plants treating large flow rates and quantities closer to their needs. Recognizing this lack of important information, Basin Water Inc., of Southern California , has initiated a program to install field demonstration units with capacities of 100 to 550 gpm (6.31-34.7 L/s) at various well sites to obtain the needed data. Benefits of Large-Scale Process Testing USEPA has identified ion exchange as one of the best available technologies in its fianl arsenic rule (USEPA, 2002). The removal of arsenic by ion exchange has been studied in great detail. There is no doubt that the chemistry between arsenic in a water solution and an ion exchange resin is highly favorable for treatment. Arsenic can be removed to well below the Maximum Contaminant Level (MCL) in a properly designed ion exchange system. There is little need for further research or pilot studies. However, certain characteristics or properties of the process - disposal of waste residuals in particular - need to be demonstrated in large scale field studies using water obtained from the well to be treated. These characteristics are summarized in the following paragraphs. Arsenic recovery. Arsenic is usually present in microgram-per-litre quantities in the contaminated water and is removed into a waste brine. However, credible tests for disposal of recovered arsenic from the waste brines should be done with at least a gram or larger quantities of arsenic. Thus, approximately =1 acre-ft (1,233 m³) of water should be treated to test recovery of waste arsenic. Treating this quantity of water with small lab equipment would be impractical. Trace contaminants. Undetected trace contaminants that interfere in the waste recovery step may be present. Although these undetected trace contaminants will not interfere with the arsenic removal process, they may interfere in arsenic recovery from the waste brine. The contaminants will be concentrated in the brine in quantities sufficient to be detected and may interfere with the recovery of arsenic from the brine or may present brine disposal problems. Again, large quantities of water should be treated to provide waste brine quantities sufficient for analysis and testing. Long term accumulation of trace contaminants. Several bed volumes of water can be treated before resin regeneration when the sulfate concentration in the feed water is low. In this case, even greater amounts of the undetected contaminants will concentrate in the brine. Furthermore, a sufficient feedwater supply must be available that can best be obtained in a large-scale operation. Feedwater changes. The variation of feed water composition must be addressed because process adjustments may be required to compensate for such changes. This can best be done in a field location where sufficient volumes of feed water are available. Over a long period of time, feed composition variations will correspond to those experienced in a full-scale treatment plant. Accurate wastewater determination. The amount of waste brine requiring disposal must be accurately measured. One of the largest cost factors is that of hauling waste brines to a point of disposal. Thus, accurate measures of waste brine volumes must be determined. Generation of waste can easily be ignored in a small scale system because small amounts can be disposed of without a permit. In contrast, operation of a large field-testing plant will generate highly visible quantities of waste and will require temporary permits. This not only characterizes the amount of waste produced but will also initiate the waste discharge permitting process. Operation of large scale field equipment is required to sufficiently determine and define waste quantities. Carbonate scale formation. Scale formation is best studied in a large field-testing facility. Water compositions, equipment and process designs vary in their ability to produce scale, such as calcium carbonate scale. The test facility should duplicate the full-scale plant in the materials used and the flow rate, flow path and local pressure gradients. Preliminary permit processing. Enough waste brine and arsenic should be produced to require actual disposal as the required permits. These factors are easily avoided in small test units. The need for permits provides the future owner with an opportunity to consult with the permitting agency engineers with whom they will be associated in the future. Large-Scale Field-Testing Program Basin Water Inc. has developed a proprietary ion exchange technology which is currently being used throughout California for the removal of arsenic, nitrate, chrome 6, perchlorate and uranium. As part of their services, Basin Water has constructed several mobile ion exchange systems with capacities ranging from 100-550 gpm (6.31 to 34.7 L/s) that can be used for field demonstration projects. These mobile units have been used primarily in arsenic removal. Over the past two years, they have processed in excess of 20 mil gal (76 ML) of water from a variety of different sources. A summary of the different locations, volumes and water qualities is included in Table I. The variation of water quality present at each location has provided valuable insight into residual handling, consistency of results and other operational issues. Case Study The Victor Valley Water District (VVWD) and the BMWD are located in the high desert of Southern California . Both districts are dependent on groundwater to supply a population of roughly 100,000 people. Currently, 20 out of 27 wells operated by the two districts will exceed the new arsenic level of 10 µg/L set by the USEPA. If California lowers the arsenic MCL to 5 µg/L, all 27 of the wells will require treatment. As a result, the districts have been actively investigating various water treatment technologies to meet the January 2006 implementation deadline. During October and November of 2002, Basin Water mobilized its 100 gpm (6.31 L/s) mobile ion exchange unit to well 29, operated by the VVWD. The unit was located adjacent to well 29, an area that also included a 3 mil gal (11 ML) storage tank. Figure 1 shows how the unit is tied into the existing system. The Basin Water mobile unit is a self-contained, multibed, ion exchange system (Figure 2). It has multiple sample ports and is configured for automatic data-logging and residuals-handling. The only two discharges are for product water and nonhazardous brine. An external brine tank holds this nonhazardous brine for subsequent disposal. The mobile unit ran continuously in 2002 from October 2 to October 29 at a flow rate of 50 gpm (3.15 L/s). In order to run a breakthrough curve, on Oct. 30, 2002 , Basin Water selected a bed and operated it beyond the normal point of regeneration. The breakthrough curve run ended Nov. 6, 2002 . A total of 2.2 mil gal (8.3 ML) of water was processed over the course of the test. Sampling Procedure The Basin Water mobile unit is designed for unattended operation. Its onboard computer continuously logs operating data, including pressure, flow, pH, alarms, equipment status, all control actions, and other items. VVWD operators performed all influent and effluent water quality sampling. Table 2 summarizes data and collection frequency information. Operational Settings and Sampling Results Before testing, a computer simulation of the operating system was run based on the water quality of well 29. The simulation indicated that both arsenic and vanadium breakthrough would occur at approximately 2,700 bed volumes. For purposes of the test, the system operated at 2,000 bed volumes which resulted in a waste product of .05%. Thus, 2.2 mil gal (8.3 ML) of processed water produced 1,100 gal (4,163.5 L) of waste brine. For the duration of the test, arsenic was reduced from 12 µg/L to nondetect (ND) and vanadium was reduced from 70 µg/L to ND. Total arsenic recovered from the treated water was 0.22 lb (101 g). The total precipitate weight was roughly 6.3 lb (2,800 g). Analysis of the waste residuals indicated that the precipitate would pass the toxicity characteristic leaching procedure (TCLP) test but would not pass the total threshold limit concentration (TTLP) test, a ratio of weight of arsenic to weight of solid residual. Of particular interest was the high level of chromium 6 in the waste brine, because chromium 6 was not detected in the source water. To address this issue, the precipitation step was modified to include the addition of ferrous sulfate. It was important in this case to have a representative sample of waste brine in order to properly design the metals precipitation step. Conclusion Large scale testing allowed the districts to accomplish a number of important objectives: confidence in ease of scaling up to a production unit was achieved. data needed for subsequent permitting process were obtained. waste residuals were characterized, and field operators were educated on use of the production unit. As a result of the testing, BMWD has contracted with Basin Water for the installation of a full scale 1000 gpm (63.09 L/s) arsenic removal unit. This unit should be in operation by next month. “The large scale demonstration test gave our district the confidence to move forward with a full-scale unit,” said Don Bartz. “We are proud to be the first water purveyor in the high desert to supply arsenic-free water to our customers.” Acknowledgement The authors thank the team members from Baldy Mesa Water District and Victor Valley Water District for their efforts throughout the testing process. -Gerald Guter, who holds a PhD in chemistry, is vice-president of technology at Basin Water, Inc., 8731 Prestige Court , Rancho Cucamonga , CA , 91730 . He can be reached at (909) 481-6800; fax (909) 481-6801; or at info@basinwater.com . Peter Jensen is a professional engineer and chief executive officer and president of Basin Water, Inc., 8731 Prestige Court , Rancho Cucamonga , CA , 91730 . He can be reached at (909) 481-6800; fax (909) 481-6801; or at info@basinwater.com . References US Environmental Protection Agency Report, 2002. Draft Report for Discussio,n Arsenic Guidance, Appendix B- 3 EPA 40 CFR Parts 9, 141 and 142 [WH- FRL- 6934- 9] RIN 2040- AB75. National Primary Drinking Water Regulations; Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring. http://www.epa.gov/safewater/ars/dimpguidaxb.pdf
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