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RESULTS

The arsenic removal system, installed in September , treated approximately 48 mil gal or 46,500 bed volumes (BVs) of water (23,250 BVs per tank) before the arsenic effluent reached 10 µg/L in October . This run length represented about 40% of the vendor-guaranteed media life for the system of 116,000 BVs. The system was shut down until the first regeneration of the media in tank B took place during March , and the media in tank A was replaced with new media.

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Between and , one tank of media was regenerated each year except during (Table 1). Tank B was regenerated three times and tank A twice. In most cases, media regeneration of a tank occurred when the arsenic concentration in the system effluent (blended water) approached 10 µg/L rather than when the effluent arsenic from at least one tank reached 10 µg/L. Therefore, the arsenic removal capacity (BV) of each individual tank of media was less than what could have been achieved had the media been used to an arsenic breakthrough of 10 µg /L. System performance during the five-year period &#; is shown in Figure 1.

Table 1.

Regeneration No. Regeneration Tank New Media Installed Date of Regeneration As Effluent &#; ug/L+
BV Treated Water
x+ Tank A Tank B System
Effluent* Tank A Tank B 1 Tank B - 1st September, March, NA NA 10 45.6 45.6 2 Tank B - 2st September, July, 6.3 7.3 9.8 55.2 55.2 3 Tank A - 1St March, April, 9.3 2.8 8.0 81.8 27.6 4 Tank B - 3rd September, June, 5.4 8.2 8.5 45.3 70,8 5 Tank A - 2nd March, September, 10 5.7 9.1 85.1 42.2

Tank B performance.

To make a reasonable comparison of the performance of the first regeneration process of the exhausted media of tank B to the performance of the new media of tank A, a very small amount of the new media of tank A was added to tank B to provide equal amounts of media in both tanks. Figure 1 compares the performance of the regenerated media (tank B) with the new media of tank A. As shown in the figure, at 55,000 BVs of treated water for each tank of media, the performance (effluent arsenic of 7.3 µg/L) of regenerated media (tank B) was similar to but slightly lower (effluent arsenic of 6.3 µg/L) than the new media (tank A). The slightly lower performance was expected because the amount of arsenic stripped from the exhausted media was in the range of 83&#;86% and not 100%.

At approximately 55,000 BVs (each tank), the arsenic concentration of finished, blended water was near 10 µg/L, indicating a need to regenerate one of the tanks of media. Although the effluent arsenic concentration from tank B was only 7.3 µg/L, the arsenic concentration from tank A (new media) was even lower (6.3 µg/L), which led to the decision to conduct a second regeneration of tank B media rather than the tank A media (Table 1). Even with an effluent arsenic concentration <10 µg/L in both tanks, the performances for both tanks of media were significantly higher than the performance (23,250 BVs each tank) of the original media. The poor performance of the original media was attributed to an oil film found in both tanks at the time of the first regeneration. The oil (which came from the submersible pumps) likely caused some fouling of the media. Following the caustic regeneration solution to clean up the media in tank B and the correction of the oil leak, the performance of the regenerated media improved.

Approximately three years after the second regeneration of the tank B media and around 72,800 BVs of treated water, a third regeneration of the tank B media was conducted. The effluent arsenic concentration of tank B was approximately 8 µg/L. Following this third regeneration, the effluent arsenic was very low at <1 µg/L, and the early stages of the breakthrough curve appeared to be similar to the performance of the media after the first two regenerations (Figure 2). The media performance results for the tank B media indicated that the three regenerations did not appear to have a major detrimental effect on the performance of this media.

Tank A performance.

Because the media in tank A was replaced with new media at the time of the first regeneration of tank B media, the performance of this new media was anticipated to be higher than the regenerated media. As shown in Figure 1, the new media had an effluent arsenic level of <1 µg/L for approximately 20,000 BVs, which was only slightly lower than the performance of the regenerated tank B media. At around 81,800 BVs, the effluent arsenic concentrations were 9.3 µg/L for tank A and 2.8 µg/L for tank B. The 81,800 BVs of treated water was actually higher than the vendor&#;s projected bed life for one tank of new media. The arsenic concentration of the finished blended water (20%) was 8.0 µg/L, and although the system could have continued operating for another few months, a decision was made to regenerate the tank A media for the first time. This regeneration took place in April before the ambient temperature in this desert location became too hot to conduct the field regeneration process.

The performance of the tank A regenerated media was very similar to the virgin media even in the very early stages when the arsenic level was <1 µg/L for the first 20,000 BVs of treated water. As shown in Figure 3, the breakthrough curve for the regenerated media paralleled the virgin media curve through 55,000 BVs, indicating that the initial regeneration process had little or no effect on media performance.

On September 23&#;24, , tank A was regenerated for the second time when the blended water concentration reached 9.1 µg/L and the media had treated 85,000 BVs (Figure 3). The effluent arsenic concentrations of tanks A and B were 10 and 5.7 µg/L, respectively. After regeneration, when the system was placed back in service (Oct. 20, ), the effluent arsenic of tank A was <2 µg/L for the first 9,000 BVs. These results indicated that the second regeneration had a very minor effect on system performance during the early life of the media. In March the treatment system was shut down because the finished water concentration of CrVI exceeded California&#;s revised MCL of 10 µg/L.

Regeneration process costs.

Between March and September , the TPWD regenerated a tank of media five times: three regenerations of tank B media and two of tank A media (Table 1). The regeneration processing costs included the chemicals (caustic and acid), labor, and wastewater disposal. The processing costs presented in Table 2 do not include the initial capital costs of plumbing modifications, caustic solution and wastewater storage tanks, chemical feed pumps, pH meters and supplies, and a portable arsenic test kit, or any monitoring costs of the research studies. The costs of the system changes amounted to approximately $3,000 and are not included in the regeneration costs discussed in the following sections. The percentage of the $3,000 assigned to each regeneration depended on the total number of regenerations conducted and decreased with each regeneration completed.

Table 2.

Regeneration Process Date of Regeneration Regeneration Process &#; Cost ($) Chemicals Subcontractor Waste Disposal Total Cost Savings* Tank B - 1st March, $158 $4,641 $10,040 $14,839 $5,686 Tank B - 2nd July, $284 -- $4,618 $4,902 $15,623 Tank A &#; 1st April, $368 -- $5,343 $5,711 14,814 Tank B - 3rd June, $250 -- $10,282 $10,532 $9,983

As shown in Table 2, the cost of the first regeneration process (tank B) was $14,839 and consisted of $158 for chemicals, $4,641 for subcontractor help, and $10,040 for transportation and disposal of the wastewater at a chemical waste disposal facility. For this first regenera-tion process (tank B), the quantity of wastewater produced and the cost of its disposal was not a major concern; as a result, the wastewater transportation and disposal cost represented the highest cost component (68%) of the total cost. The cost of replacing a tank of media (69 ft3) was estimated at $20,525 during the study period. Consequently, even with a fairly high wastewater disposal cost and the subcontractor expense, the cost of the regeneration process (not including any costs associated with system modifications) was $5,686 less than the cost of media replacement.

Having determined that the regeneration process was effective in stripping the arsenic from the media during the first regeneration process, TPWD staff turned their attention to refining the regeneration process to reduce the quantity of wastewater during the second regeneration of tank B (Sorg et al. ). By reducing the quantity of the wastewater, processing the wastewater on site, and locating a lower-cost wastewater disposal company, TPWD was able to lower the regeneration cost to slightly less than $5,000, with offsite wastewater disposal again the major cost. Because only TPWD personnel were used to conduct the second regeneration process and all subsequent regenerations, no out-of-pocket cost for subcontractor assistance was required. The $5,000 regeneration cost does not include any costs associated with system modifications or TPDW personnel costs. These changes resulted in a cost savings of $15,623, which was approximately $10,000 less than the cost of the first regeneration process (Table 2).

The third regeneration process (the first regeneration of tank A media) closely followed the procedures of the second regeneration process. The cost of the process was approximately $6,000, or about one-fourth the cost of media changeout. The cost data for the first three regenerations clearly indicate that the cost of the chemicals was insignificant compared with the cost of wastewater disposal, which accounted for around 95% of the total cost.

Wastewater disposal.

As discussed previously, the total regeneration process cost is almost entirely a function of wastewater disposal. Given that TPWD was unable to dispose of the high-arsenic concentration wastewater (considered a hazardous waste) at a district-owned facility, the only option available was offsite disposal at a chemical waste disposal plant. With the results of the first regeneration study clearly demonstrating some cost benefits of regeneration, the second regeneration study that followed a year later focused on lowering the wastewater disposal cost.

Two modifications were made to the second regeneration process to reduce the quantity and the characteristic of the wastewater. First, the total quantity of wastewater produced was reduced by approximately 1,700 gal by eliminating the water rinse step that followed the caustic regeneration step (Sorg et al. ). This change was also carried out during all subsequent regenerations.

The second modification to the second regeneration process involved the addition of ferric chloride (FeCl3) to both the spent caustic solution and the acid neutralization wastewater; this modification reduced the arsenic concentration of both solutions to a level that would allow the liquid fraction of both wastes to be recycled with the system&#;s influent raw water. To reduce the arsenic concentration of the 800 gal of spent caustic regenerant and 3,000 gal of the neutralization wastewater (held in separate holding tanks), an FeCl3 (40%) solution was added to each storage tank, with the quantity based on a target Fe-to-As (iron-to-arsenic) ratio of around 30:1. The pH of each wastewater was also lowered to about 6.5 with sulfuric acid. Results of the wastewater parameters of the onsite processing are provided in Table 3.

Table 3.

Parameter Unit Spent Caustic Neutralization Water Estimated Volume gal 800 3,000 Initial pH (Before FeCl3 Treatment) S.U. 13.0 12.1 Initial Arsenic Concentration - ICP-MS* mg/L 286 30.9 Amount of 40% FeCl3 Addition gal 55 18 Fe:As Ratio 47:1 38:1 Final pH after FeCl3 Addition/pH Adjustment S.U. 6.0&#;6.2 ~6.5 Final Arsenic Concentration &#; Lab ICP-MS µg/L 82.8 29.4

By adding 55 gal of liquid FeCl3 to the 800 gal of spent caustic solution and adjusting the pH to around 6.5, the arsenic concentration of the caustic solution was lowered from 285,250 µg/L to 82.8 µg/L, for a reduction of 99.97% (Table 4). The arsenic concentration of a portion (575 gal) of the liquid fraction was found to be further reduced to 35 µg/L by passing it through a bag filter followed by an approximately 1 ft3 cartridge filter containing an iron-based media2 (Table 4). The media is somewhat similar to the GFO used in this research and was on hand from another Battelle arsenic demonstration project.

Table 4.

Parameter Unit Wastewater Before FeCL3 Treatment Supernatant after FeCl3 Treatment % Removal by FeCl3 Treatment Supernatant Processed by ARM 200 % Removal by ARM 200 Spent Caustic (800 gal) Date - 07/16/10 07/17/10 - 07/23/10 - pH S.U. 13 6.0&#;6.2 - 7.2 - As (total) µg/L 285,250 82.8 99.97% 35.1 57.6% As (soluble) µg/L 286,890 40.7 99.99% 36.9 9.4% Fe (total) µg/L <250 1,155 0.0% 32 97.3% Fe (soluble) µg/L <250 <250 0.0% <25.0 90.0% P (total) µg/L 46,093 253 99.5% 43.8 82.7% P (soluble) µg/L 45,927 <50 99.9% 17.4 30.3% Si (total) µg/L 425,337 11,367 97.3% 746 93.4% Si (soluble) µg/L 439,387 11,242 97.4% 574 94.9% U (total) µg/L 15,074 < 1.0 99.997% 0.3 39.6% U (soluble) µg/L 15,266 < 1.0 99.997% 0.2 50.2% Neutralization/Rinse Wastewater ( gal ) Date - 07/16/10 08/09/10 - 08/30/10 - pH S.U. 12.1 6.5 - 7.5 - As (total) µg/L 30,881 29.4 99.90% 12.6 57.2% As (soluble) µg/L 30,919 14.3 99.95% 9.1 36.1% Fe (total) µg/L <250 423 0.0% 160 62.2% Fe (soluble) µg/L <250 <25 90.0% <25.0 0.0% P (total) µg/L 4,215 <5.0 99.9% 42.3 0.0% P (soluble) µg/L 4,210 <5.0 99.9% 43.0 0.0% Si (total) µg/L 91,850 21,299 76.8% 3,525 83.5% Si (soluble) µg/L 89,254 20,798 76.7% 3,027 85.4% U (total) µg/L 1,458 2.2 99.97% 0.8 65.7% U (soluble) µg/L 1,455 0.7 99.97% 0.4 36.5%

A total of 18 gal of FeCl3 was added to the 3,000-gal neutralization wastewater, and this solution was adjusted to pH 6.5 with concentrated sulfuric acid. The addition of FeCl3 and acid reduced the arsenic concentration from 30,881 µg/L to 29.4 µg/L, for a 99.9% reduction. Approximately 300 gal of liquid fraction was passed through the bag filter and the alumina-based media, resulting in a further reduction of the arsenic concentration to 12.6 µg/L.

In addition to removing a very high percentage of the arsenic, the FeCl3 and the iron-based media also achieved high removal of phosphorus, silicon, and uranium (Table 4). The results of these tests were provided to the CDPH along with a request that the TPWD be allowed to recycle the liquid fraction of the processed wastewater to the head of the treatment plant using either a 20 or 5 gpm pump. Because the treatment system operates at 296 gpm and has a bypass flow as high as 105 gpm, use of the 20 gpm pump would result in a 16× dilution of the recycled streams, and use of the 5 gpm pump would result in a 60× dilution of the recycled streams. For future operations, the TPWD proposed to combine the two solutions before FeCl3 addition and pH adjustment.

After a review of the process wastewater test results and TPWD&#;s request for approval of the recycle process, CDPH raised several questions about the characteristics of the recycled stream and requested additional information beyond that provided by TPWD. The state also raised concerns about the effect of the recycled regenerant on the GFO media and would consider approval only if extensive water quality tests were conducted on the recycled stream each time the process was carried out. Because of the effort required and subsequent cost to respond to these issues, TPWD chose not to pursue the use of this recycling process and continued to haul the wastewater off site for disposal.

The changes in the characteristics of the wastes to a liquid and iron solids did provide some cost benefit with regard to the total disposal cost. Because the arsenic concentration of the liquid fractions was significantly lower, the waste-disposal-company cost quote was based on the quantity of liquid waste and solids (as shown in Table 5). These cost data indicated that additional cost savings could be achieved if the liquid fraction of the processed regenerant wastewater could be recycled to the front of the treatment system, leaving only the iron solids for disposal. Moreover, drying the solids would also reduce the quantity of solids, and these dried solids would likely pass the toxicity characteristic leaching procedure test, allowing the solids to be disposed at a sanitary landfill at an even lower cost. Although TPWD did not pursue these steps, these waste reduction actions could be considered by systems that may be interested in onsite regeneration of exhausted media.

Table 5.

Item Cost* Liquid/As $0.45/gal Solids 0./gal (solids at 9&#;14%) Transportation $85/hr Truck Washout $125/Truck Fuel Charge $178

The Code of Federal Regulations (CFR) is the official legal print publication containing the codification of the general and permanent rules published in the Federal Register by the departments and agencies of the Federal Government. The Electronic Code of Federal Regulations (eCFR) is a continuously updated online version of the CFR. It is not an official legal edition of the CFR.

Learn more about the eCFR, its status, and the editorial process.

(b) The owner or operator shall submit a description of an inspection, maintenance, and housekeeping plan for control of inorganic arsenic emissions from the potential sources identified under paragraph (a) of this section. This plan shall be submitted within 90 days after the effective date of this subpart, unless a waiver of compliance is granted under § 61.11. If a waiver of compliance is granted, the plan shall be submitted on a date set by the Administrator. Approval of the plan will be granted by the Administrator provided he finds that:

(1) It achieves the following objectives in a manner that does not cause adverse impacts in other environmental media:

(i) Clean-up and proper disposal, wet-down, or chemical stabilization to the extent practicable (considering access and safety) of any dry, dusty material having an inorganic arsenic content greater than 2 percent that accumulates on any surface within the plant boundaries outside of a dust-tight enclosure.

(ii) Immediate clean-up and proper disposal, wet-down, or chemical stabilization of spills of all dry, dusty material having an inorganic arsenic content greater than 2 percent.

(iii) Minimization of emissions of inorganic arsenic to the atmosphere during removal of inorganic arsenic from the arsenic kitchen and from flue pulling operations by properly handling, wetting down, or chemically stabilizing all dusts and materials handled in these operations.

(2) It includes an inspection program that requires all process, conveying, and air pollution control equipment to be inspected at least once per shift to ensure that the equipment is being properly operated and maintained. The program will specify the evaluation criteria and will use a standardized checklist, which will be included as part of the plan required in paragraph (b) of this section, to document the inspection, maintenance, and housekeeping status of the equipment and that the objectives of paragraph (b)(1) of this section are being achieved.

(3) It includes a systematic procedure for identifying malfunctions and for reporting them immediately to supervisory personnel.

(4) It specifies the procedures that will be followed to ensure that equipment or process malfunctions due entirely or in part to poor maintenance or other preventable conditions do not occur.

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(5) It includes a program for curtailing all operations necessary to minimize any increase in emissions of inorganic arsenic to the atmosphere resulting from a malfunction. The program will describe:

(i) The specific steps that will be taken to curtail each operation as soon as technically feasible after the malfunction is discovered.

(ii) The minimum time required to curtail each operation.

(iii) The procedures that will be used to ensure that the curtailment continues until after the malfunction is corrected.

(d) At all times, including periods of startup, shutdown, and malfunction, the owner or operator of each source to which this subpart applies shall operate and maintain the source including associated air pollution control equipment in a manner consistent with good air pollution control practice for minimizing emissions of inorganic arsenic to the atmosphere to the maximum extent practicable. Determination of whether acceptable operating and maintenance procedures are being used will be based on information available to the Administrator, which may include, but is not limited to, monitoring results, review of operating and maintenance procedures, inspection of the source, and review of other records.

(b) The owner or operator shall install, operate, and maintain each continuous monitoring system for the measurement of opacity required in paragraph (a) of this section according to the following procedures:

(1) Ensure that each system is installed and operational no later than 90 days after the effective date of this subpart for an existing source or a new source that has an initial startup date preceding the effective date. For a new source whose initial startup occurs after the effective date of this subpart, ensure that the system is installed and operational no later than 90 days after startup. Verification of the operational status shall, as a minimum, consist of an evaluation of the monitoring system in accordance with the requirements and procedures contained in Performance Specification 1 of appendix B of 40 CFR part 60.

(2) Comply with the provisions of § 60.13(d) of 40 CFR part 60.

(3) Except for system breakdowns, repairs, calibration checks, and zero and span adjustments required under § 60.13(d), ensure that each continuous monitoring system is in continuous operation and meets frequency of operation requirements by completing a minimum of one cycle of sampling and analysis for each successive 10-second period and one cycle of data recording for each successive 6-minute period. Each data point shall represent the opacity measured for one cycle of sampling and analysis and shall be expressed as percent opacity.

(d) No later than 60 days after each continuous opacity monitoring system required in paragraph (a) of this section becomes operational, the owner or operator shall establish a reference opacity level for each monitored emission stream according to the following procedures:

(1) Conduct continuous opacity monitoring over a preplanned period of not less than 36 hours during which the processes and emission control equipment upstream of the monitoring system are operating in a manner that will minimize opacity under representative operating conditions subject to the Administrator's approval.

(2) Calculate 6-minute averages of the opacity readings using 36 or more consecutive data points equally spaced over each 6-minute period.

(3) Establish the reference opacity level by determining the highest 6-minute average opacity calculated under paragraph (d)(2) of this section.

(a) Each owner or operator of a source subject to the provisions of this subpart shall maintain at the source for a period of at least 2 years the following records: All measurements, including continuous monitoring for measurement of opacity; all continuous monitoring system performance evaluations, including calibration checks and adjustments; all periods during which the continuous monitoring system or monitoring device is inoperative; and all maintenance and repairs made to the continuous monitoring system or monitoring device.

(b) Each owner or operator shall maintain at the source for a period of at least 2 years a log for each plant department in which the operating status of process, conveying, and emission control equipment is described for each shift. For malfunctions and upsets, the following information shall be recorded in the log:

(1) The time of discovery.

(2) A description of the malfunction or upset.

(3) The time corrective action was initiated.

(4) A description of corrective action taken.

(5) The time corrective action was completed.

(6) A description of steps taken to reduce emissions of inorganic arsenic to the atmosphere between the time of discovery and the time corrective action was taken.

(b) Each owner or operator subject to the provisions of § 61.183(a) shall submit to the Administrator:

(1) Within 60 days of conducting the evaluation required in § 61.183(b)(1), a written report of the continuous monitoring system evaluation;

(2) Within 30 days of establishing the reference opacity level required in § 61.183(d), a written report of the reference opacity level. The report shall also include the opacity data used and the calculations performed to determine the reference opacity level, and sufficient documentation to show that process and emission control equipment were operating normally during the reference opacity level determination; and

(3) A written report each quarter of each occurrence of excess opacity during the quarter. For the purposes of this paragraph, an occurrence of excess opacity is any 6-minute period during which the average opacity, as measured by the continuous monitoring system, exceeds the reference opacity level established under § 61.183(d).

(c) All quarterly reports of excess opacity shall be postmarked by the 30th day following the end of each quarter and shall include the following information:

(1) The magnitude of excess opacity, any conversion factor(s) used, and the dates and times of commencement and completion of each occurrence of excess opacity, the cause of each exceedance of the reference opacity level, and the measures taken to minimize emissions.

(2) Specific identification of each period of excess opacity that occurred during startups, shutdowns, and malfunctions of the source.

(3) The date and time identifying each period during which the continuous monitoring system or monitoring device was inoperative, except for zero and span checks, and the nature of the system repairs or adjustments.

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