ArsenicArsenic RemovalRemoval UsingUsing AgedAged RapidRapid SandSand FilterFilter MediaMedia byby C.C. Menard,Menard, D.D. Burt,Burt, M.R.M.R. CollinsCollins WaterWater TreatmentTreatment TechnologyTechnology AssistanceAssistance CenterCenter DepartmentDepartment ofof CivilCivil EngineeringEngineering UniversityUniversity ofof NewNew HampshireHampshire Summer 2007 OUTLINEOUTLINE BACKGROUND RESEARCH OBJECTIVE Assess coating characteristics of ‘aged’ rapid sand filter media. Quantity Arsenic removal potentials using “aged” rapid sand filter. Evaluate interferences associated with the adsorption capacity of the metal oxide coating. CONCLUSION BACKGROUNDBACKGROUND Reduction/Elimination of Arsenic Ion exchange Coagulation / Filtration Membrane filtration (Reverse Osmosis) Innovative adsorbents, e.g. metal oxides BACKGROUNDBACKGROUND Conventional Water Treatment (Pathogen Removal) – Coagulants Aluminum Sulfate Ferrous Sulfate, Ferric Sulfate, and Ferric Chloride – Slow sand filtration process BACKGROUNDBACKGROUND Natural Aging of Metal Hydroxides to More Stable Metal Oxides Al(OH)3 →→→→→→Al2O3 Fe(OH)3 →→→→→→Fe2O3 REMOVAL ENHANCEMENT POSSIBILITY!!! Make use of metal oxide coatings that form ‘naturally’ over many years on filter media in WTP from carryover of metal hydroxide flocs produced from “sweep-floc” coagulation RESEARCHRESEARCH OBJECTIVESOBJECTIVES Explore the Arsenic removal potential of ‘naturally’ coated, regenerable sand filter media. 1) Assess coating characteristics of ‘aged’ rapid sand filter media. sand filter media. 2) Quantify Arsenic removal potentials using ‘aged’ sand filter media. ‘aged’ sand filter media. 3) Evaluate interferences associated with the adsorption capacity of the metal oxide coating. adsorption capacity of the metal oxide coating. METHODOLOGYMETHODOLOGY Materials used for Objective 1 Filter Media – Portsmouth, NH WTP sand – Philadelphia, PA WTP sand Characterization Methods – SEM analysis – Electron microprobe analysis Portsmouth, NH Philadelphia, PA AverageAverage MetalMetal CoatingCoating ContentContent ofof SelectedSelected RapidRapid SandSand FiltersFilters –– SEMSEM picturepicture Portsmouth, 1996 AverageAverage MetalMetal CoatingCoating ContentContent ofof SelectedSelected RapidRapid SandSand FiltersFilters ––SEMSEM picturepicture Philadelphia, 2006 AverageAverage MetalMetal CoatingCoating ContentContent ofof SelectedSelected RapidRapid SandSand FiltersFilters ––SEMSEM picturepicture Philadelphia, 1996 AverageAverage MetalMetal CoatingCoating ContentContent ofof SelectedSelected RapidRapid SandSand FiltersFilters Electron Microprobe picture A B C D Silica grain E F G Philadelphia, 1996 AverageAverage MetalMetal CoatingCoating ContentContent ofof SelectedSelected RapidRapid SandSand FiltersFilters Weight Oxide Percent 120 100 80 Al2O3 MnO 60 FeO SiO2 40 Percent of Oxid of Percent 20 0 ABCDEFG Layer Level Philadelphia, 1996 RESEARCHRESEARCH OBJECTIVESOBJECTIVES Explore the Arsenic removal potential of ‘naturally’ coated, regenerable sand filter media. 1) Assess coating characteristics of ‘aged’ rapid sand filter media. sand filter media. 2) Quantify Arsenic removal potentials using ‘aged’ sand filter media. ‘aged’ sand filter media. 3) Evaluate interferences associated with the adsorption capacity of the metal oxide coating. adsorption capacity of the metal oxide coating. METHODOLOGYMETHODOLOGY Experimental Set-Up Backwash (BW) Procedure – 50/100 mL sand in 500/1000 mL buffered water – Backwash at target pH’s for 1 hour Equilibration Procedure – Buffered water at the pH of the Challenge solution Challenge Procedure – Arsenic Solution according to the array Backwash/RegenerationBackwash/Regeneration SetSet--UpUp Motor with paddle pH controller Pumps Buffered Water Media (Sand) Base Acid ChallengeChallenge SetSet--UpUp pH controller Pump Filter Filter Filter Filter 1 2 3 4 Reservoir Base Acid Effluent to Autosampler RESEARCHRESEARCH OBJECTIVESOBJECTIVES Explore the Arsenic removal potential of ‘naturally’ coated, regenerable sand filter media. 1) Assess coating characteristics of ‘aged’ rapid sand filter media. sand filter media. 2) Quantify Arsenic removal potentials using ‘aged’ sand filter media. ‘aged’ sand filter media. 3) Evaluate interferences associated with the adsorption capacity of the metal oxide coating. adsorption capacity of the metal oxide coating. METHODOLOGYMETHODOLOGY LL 1616 ORTHOGONALORTHOGONAL ARRAYARRAY 5 parameters – EBCT – pH of the challenge solution – Presence of sulfate – Presence of natural organic matter – pH of the backwashing 2 levels RESULTSRESULTS ARSENIC REMOVED / BED VOLUME at 95 BV (g/m3) [As]removed/ BV RUN/BV EBCT pH SO4 NOM BW 95 RUN1 2.5 6 0 0 8 3363 RUN2 2.5 6 0 6 8 3176 RUN3 2.5 6 200 6 8 3593 RUN4 2.5 6 200 6 11 3502 RUN5 2.5 8200611 2302 RUN6 2.5 6 200 08 3361 RUN7 2.5 6 0 0 11 3521 RUN8 2.5 8 008 2351 RUN9 5 6 200 6 11 3413 RUN10 5820068 3011 RUN11 580 611 1755 RUN12 5 6008 5873 RUN13 58008 4216 RUN14 580011 3980 RUN15 582000 11 4531 RUN16 5 8 200 6 11 3327 RESULTSRESULTS ARSENIC REMAINING VERSUS BED VOLUME arsenic restant vs bed volume 1,7 RUN1 1,6 RUN2 1,5 RUN3 1,4 RUN4 1,3 1,2 RUN5 1,1 RUN6 L 1 RUN7 0,9 0,8 RUN8 0,7 RUN9 [As] (mg/[As] 0,6 RUN10 0,5 RUN11 0,4 0,3 RUN12 0,2 RUN13 0,1 RUN14 0 RUN15 0 20 40 60 80 100 120 RUN16 bed volume feed average INTERPRETATIONINTERPRETATION PREDICTIONPREDICTION PROFILERPROFILER 6004.27 3809.291 ±728.51 BV (mg/L) 1729.2 arsenic removed/ 2 1 2 1 2 1 2 1 2 1 EBCT pH SO4 NOM BW EBCT(0.0113) > pH (0.0186) > NOM (0.0227) >> SO4 (0.3028) > BW (0.6037) INTERPRETATIONINTERPRETATION MODELMODEL EQUATIONEQUATION 6000 5000 4000 3000 2000 1000 arsenic removed/ BV (mg/L) Actual 1000 2000 3000 4000 5000 6000 arsenic removed/ BV (mg/L) Predicted P=0.0284 RSq=0.67 RMSE=670.91 Y = - 608,5*EBCT + 549,8*pH + (-213,7*SO4) + 526,7*NOM + 99,7*BW + 3454,6 SUMMARYSUMMARY Sand coating composed mainly with aluminum, manganese oxide with a beginning of small ratio of iron oxides EBCT, pH and NOM: most important effect Slight positive impact with the presence of sulfate No significant effect of BW pH: in the range of recommended pH for aluminum coated sand RecommendationsRecommendations Additional experiments to analyze more precisely effect of sulfate but also others anions like phosphate Additional experiments to determine durability of coatings, test raw water Pilot or Full scale demonstration Analyse Portsmouth sand with Electron microprobe .