1 / 63

Arsenic Removal by Coagulation & Precipitation Processes

Arsenic Removal by Coagulation & Precipitation Processes. Presentation Prepared by: Joe Chwirka - Camp Dresser & McKee (chwirkajd@cdm.com) Bruce Thomson - University of New Mexico (bthomson@unm.edu) Presented by: YuJung Chang – HDR Engineering, Inc. Introduction.

rebekah
Download Presentation

Arsenic Removal by Coagulation & Precipitation Processes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Arsenic Removal by Coagulation & Precipitation Processes Presentation Prepared by: Joe Chwirka - Camp Dresser & McKee (chwirkajd@cdm.com) Bruce Thomson - University of New Mexico (bthomson@unm.edu) Presented by: YuJung Chang – HDR Engineering, Inc. Coagulation-Filtration - Chwirka & Thomson

  2. Introduction • Arsenic removal by coagulation & filtration is effective for many applications • Presentation will discuss: • Chemistry of the process • Variables affecting process performance (especially pH & coagulant dose) • Process variations • Coagulation & granular media filtration • Coagulation & membrane filtration • Design considerations Coagulation-Filtration - Chwirka & Thomson

  3. Acid-Base Chemistry of As(V) Coagulation-Filtration - Chwirka & Thomson

  4. Acid-Base Chemistry of As(III) Coagulation-Filtration - Chwirka & Thomson

  5. Redox Chemistry of As Coagulation-Filtration - Chwirka & Thomson

  6. Solubility of As(III) Compounds Coagulation-Filtration - Chwirka & Thomson

  7. Solubility of As(V) Species Coagulation-Filtration - Chwirka & Thomson

  8. Important Points • As has two oxidation states - As(III) & As(V) • As(III) • Non-ionic (H3AsO3) at neutral pH • High solubility • More toxic to many organisms • As(V) • Ionic (H2AsO4-/HAsO42-) at neutral pH • Some phases are less soluble • More reactive in solution: • Membranes • IX • Adsorption Coagulation-Filtration - Chwirka & Thomson

  9. Coprecipitation • Coprecipitation involves removal of two or more constituents by a precipitation reaction. Coprecipitation of As with Fe(OH)3 is an effective treatment process: FeCl3 + 3H2O = Fe(OH)3(s) + 3H+ + 3Cl- Points: • Produces HCl which will lower pH • Typical Fe dose ~10-4 M, whereas As conc. ~10-7 M, hence As is minor component within precipitate • As likely removed by adsorption onto Fe(OH)3 surface with subsequent enmeshment as floc particle grows • Al(OH)3 also effective Coagulation-Filtration - Chwirka & Thomson

  10. Solubility of Fe(OH)3 Coagulation-Filtration - Chwirka & Thomson

  11. Effect of pH on Surface Charge of Fe(OH)3 Coagulation-Filtration - Chwirka & Thomson

  12. Covalent Bond Formation(Grossl et al., 1997) Coagulation-Filtration - Chwirka & Thomson

  13. pH of Zero Point of Charge • Electrostatic attraction is important first step in adsorption • pHzpc = pH at which net surface charge = 0 • Surface is positive at pH < pHzpc • Most clay minerals have pHzpc < 6 • Hence poor adsorption • Clays dominate surface chemistry of soils • Fe(OH)3 and Al2O3 have relatively high pHzpc • Good adsorbents of As(V) Coagulation-Filtration - Chwirka & Thomson

  14. As Removal by Conventional Treatment (McNeill & Edwards 1997) • Survey of conventional coagulation-flocculation water treatment plants • Correlate As removal to removal of Fe, Mn, & Al • [Fe] = Iron Precip. Formed (mM) Coagulation-Filtration - Chwirka & Thomson

  15. As Removal by Conventional Trt. - 2 Coagulation-Filtration - Chwirka & Thomson

  16. As Removal by Conventional Trt. - 3 • Strong correlation to removal of Fe & use of FeCl3 as coagulant • Weaker correlation to removal of Al & use of Alum • Possible sorption onto colloidal Al(OH)3 which passes through granular media filters • Improved As removal achieved by minimizing effluent total Al concentration • Note the importance of particulate As Coagulation-Filtration - Chwirka & Thomson

  17. Arsenic Removal vs FeCl3 Dose, Albuquerque NM Coagulation-Filtration - Chwirka & Thomson

  18. Ambient pH: FeCl3 vs As Leakage, NAS Fallon Coagulation-Filtration - Chwirka & Thomson

  19. El Paso Jar Testing Coagulation-Filtration - Chwirka & Thomson

  20. pH Adjustment with CO2, NAS Fallon, NV Coagulation-Filtration - Chwirka & Thomson

  21. Silica Impacts Arsenic Removal at pH 7.0 and Above pH 8.5 pH 7.5 pH 6.5 FeCl3 Dose: 4 mg/L After Clifford and Ghurye Coagulation-Filtration - Chwirka & Thomson

  22. Silica Speciation with pH Coagulation-Filtration - Chwirka & Thomson

  23. Silica in US Water Supplies (NAOS) After Davis and Edwards Coagulation-Filtration - Chwirka & Thomson

  24. Polymeric Silica 50 mg/L 17 mg/L 5 mg/L After Davis and Edwards Coagulation-Filtration - Chwirka & Thomson

  25. Coagulation/ Filtration • Use pressure filters • Direct Filtration frequently used for iron and manganese removal. • Limited to low ferric dose applications. • High coagulant dose will result in frequent backwash requirements • Increased residuals production & handling costs • Increased production of wastewater Coagulation-Filtration - Chwirka & Thomson

  26. Schematic of Coagulation/ Filtration FeCl3 Pressure Filter CO2 CO2 Treated Water Raw Water Aeration Rapid Mix Solids to Dewatering Solids to Landfill Coagulation-Filtration - Chwirka & Thomson

  27. Calculation of Filter Loading Limitation • Rule of Thumb, no more than 10 mg/L of FeCl3 • Limit Solids Loading to 0.1 lbs/SF • May need to add sedimentation Coagulation-Filtration - Chwirka & Thomson

  28. Vertical Pressure Filter Coagulation-Filtration - Chwirka & Thomson

  29. Direct Filtration Performance(Based on 0.1 lbs Solids/sf) Coagulation-Filtration - Chwirka & Thomson

  30. Backwash Water as Percent of Production(Based on 250 gal/sf) Coagulation-Filtration - Chwirka & Thomson

  31. C/F O&M Issues • Large backwash volume (20 gpm/sf for 10 minutes) • Tanks may need internal painting, 10 yr intervals. Use 316 SST. • Standby filters, typically provided, but need to evaluate. • Pneumatic or electric valve operators. Coagulation-Filtration - Chwirka & Thomson

  32. Coagulation/ Pressure Filtration • Particle size • Particle breakthrough • backwash requirements • filter ripening • Backup Filters Coagulation-Filtration - Chwirka & Thomson

  33. Coagulation/ Microfiltration • Pilot tested in Albuquerque, 1998 • Pilot tested in NAS Fallon, NV, 2001 • Pilot tested in El Paso, TX, 2001/2002 • Fallon Paiute Shoshone Tribe: 0.5 mgd • City of Albuquerque: 2.3 mgd Coagulation-Filtration - Chwirka & Thomson

  34. Microfiltration General Concepts • Low Operating Pressure, 5 - 30 psi • 0.1 to 0.2 micron pore size • Water flow from Outside to the Inside • Air-Water Backwash • Backwash Every 25 to 30 minutes (95% recovery) • Flux rate defined as Gallons/SF/Day (GFD) • Chemical Cleaning Frequency > 30 days Coagulation-Filtration - Chwirka & Thomson

  35. What is C/MF? FeCl3 CO2 Microfiltration Unit CO2 Treated Water Raw Water Aeration Rapid Mix Solids to Dewatering Solids to Landfill Coagulation-Filtration - Chwirka & Thomson

  36. Pressure Driven Membranes 0.001µ 0.01µ 0. 1µ 1.0µ 10µ 100µ 1000µ Sand Dissolved Organics Bacteria Viruses Cysts Salts Colloids Media Filtration Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis Coagulation-Filtration - Chwirka & Thomson

  37. MF Process Operates in Direct Filtration Mode Filtrate Feed Feedwater (with contaminants) Filtrate Coagulation-Filtration - Chwirka & Thomson

  38. Solids are Removed from Module by an Air-Water Backwash Air Feedwater Air (100 psig) 1 2 3 Coagulation-Filtration - Chwirka & Thomson

  39. Coagulation/ Microfiltration • Pilot tested in Albuquerque, 1998 • Pilot tested in NAS Fallon, NV, 2001 • Pilot tested in El Paso, TX, 2001/2002 • Fallon Paiute Shoshone Tribe: 0.5 mgd • City of Albuquerque: 2.3 mgd Coagulation-Filtration - Chwirka & Thomson

  40. What is C/MF? FeCl3 CO2 Microfiltration Unit CO2 Treated Water Raw Water Aeration Rapid Mix Solids to Dewatering Solids to Landfill Coagulation-Filtration - Chwirka & Thomson

  41. Pressure Driven Membranes 0.001µ 0.01µ 0. 1µ 1.0µ 10µ 100µ 1000µ Sand Dissolved Organics Bacteria Viruses Cysts Salts Colloids Media Filtration Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis Coagulation-Filtration - Chwirka & Thomson

  42. MF Process Operates in Direct Filtration Mode Filtrate Feed Feedwater (with contaminants) Filtrate Coagulation-Filtration - Chwirka & Thomson

  43. Solids are Removed from Module by an Air-Water Backwash Air Feedwater Air (100 psig) 1 2 3 Coagulation-Filtration - Chwirka & Thomson

  44. Pall Microfilter Coagulation-Filtration - Chwirka & Thomson

  45. Memcor PerformanceNAS Fallon, 15 mg/L FeCl3 32 GFD 27 GFD 27 GFD 38 GFD (No FeCl3) 25 GFD (No FeCl3) Coagulation-Filtration - Chwirka & Thomson

  46. Memcor Cleaning EfficiencyNAS Fallon, Citric Acid Coagulation-Filtration - Chwirka & Thomson

  47. Pall PerformanceNAS Fallon, FeCl3 45 mg/L Coagulation-Filtration - Chwirka & Thomson

  48. El Paso C/MF Pilot Studies Coagulation-Filtration - Chwirka & Thomson

  49. El Paso Pilot Studies • Only Pall MF tested • Ferric dose 10 mg/L • pH lowered to 6.8 with CO2 Coagulation-Filtration - Chwirka & Thomson

  50. El Paso Pall Performance Coagulation-Filtration - Chwirka & Thomson

More Related