EVALUATION, IMPLEMENTATION, AND OPTIMIZATION OF LOW-LEVEL ARSENIC REMOVAL TECHNOLOGIES FOR A GROUNDWATER REMEDIATION SYSTEM

摘要

This paper documents laboratory testing, field scale pilot testing, and full scalernimplementation activities for removal of low level arsenic in a groundwater remediationrnapplication. Groundwater contamination, primarily xylenes, existed as a result ofrnprevious operations at the facility. In order to minimize seepage of contaminatedrngroundwater into an adjacent drainage canal, a groundwater recovery and treatmentrnsystem (GRTS) was installed in early 1996. The GRTS consisted of three extractionrnwells with dedicated submersible pumps, an air stripper, carbon polishing, and on-siterndisposal of the treated groundwater. An Air Sparging/ Soil Vapor Extraction Systemrn(AS/SVE) was subsequently installed to efficiently address source removal upgradientrnof the GRTS extraction system.rnThe GRTS satisfactorily treated the ground water to Florida Department ofrnEnvironmental Protection (FDEP) standards for volatiles. However, during the initialrnmonths of operation, the extracted groundwater consistently contained arsenic atrnlevels exceeding the primary drinking water standard (50 ug/L). Arsenic levels in thernextracted groundwater ranged from 61 to 137 ug/L with an average of 101 ug/L. Thernsource of arsenic appears to be isolated in a small area near the wells and wasrnunexpected, considering that arsenic was not historically used in quantities at thernplant. Due to the consistency and level of detection, FDEP required that arsenic bernremoved to below 50 ug/l prior to on-site discharge.rnAlthough precipitation is commonly used to remove arsenic from aqueous wasternstreams, concerns over the effectiveness of achieving removal to ppb levels andrnsludge handling issues resulted in the evaluation of other technologies. In order tornscreen alternative technologies, bench scale treatability studies were conducted usingrnthe following treatment approaches: 1) Lignite Granular Activated Carbon (LGAC); 2)rnTreated Granular Activated Carbon (TGAC); 3) Activated Alumina (AA); 4) IonrnExchange (IX); and 5) Ozone.rnBased upon the results of the bench scale testing , the following were determined tornbe potentially feasible: activated alumina, iron impregnated carbon, and ion exchange.rnEach of these three technologies were then subjected to a screening level analysisrnbased upon effectiveness, and costs for both long and short term operation. Basedrnupon this screening level evaluation, it was determined that ion exchange offered arnfeasible technology with the greatest flexibility for implementation..rnIt was also decided that a flow through rather than batch test of an ozone assistedrnfiltration technology should be further tested. This test can be easily accomplishedrnand has the potential to offer substantial benefit.rnUpon completion of the two field scale pilot tests, ion exchange was selected forrnarsenic removal. The key factors influencing this decision were low capital cost andrnreliability of the resin. The full scale system was installed consisting of two canistersrnoperating in series in March 1998.rnThe full scale resin system has now been operational for over 6 months with the fullrnscale system demonstrating arsenic removal to ppb levels thus achieving designrngoals.. During this time, however resin bed life at full scale operation was variable.rnThis was identified by observance of normal resin life in the first canister followed byrnrapid exhaustion of a second canister when moved to the lead position. Additional pHrnand arsenic monitoring were implemented to characterize system behavior. The resultsrnsupport the probable cause of apparent anion fouling. A key finding in the systemrnoperations review was that the capacity of the second canister to remove arsenic wasrnbeing exhausted at nearly the same rate of the first canister . It is suspected that thernarsenic removal front (break through point) is lagging the "fouling anion" front therebyrnresulting in the reduction of arsenic capacity during the latter stages of canisterrnoperation. Samples are currently being analyzed to confirm carbonate and otherrnanion fouling of these resins. However, operational adjustments have been made inrnthe interim to counteract the affects of this fouling and maintain successful operationrnof the resin system.rnThis abstract summarizes the testing and evaluation (technical and cost effectiveness)rnthat was completed for this project. The paper will present the specific detail of therntechnical data that was collected and its impact on cost analysis decisions that werernmade. The paper is also important in documenting the real-world process of testing,rnevaluation and full scale implementation from identification of the problem throughrnbench scale testing, field pilot testing, full scale implementation, and operationalrnadjustments necessary to assure continued satisfactory performance.