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Cyanide Generation During Preservation of Chlorinated Wastewater Effluent Samples 1 November 2005

Cyanide Generation During Preservation of Chlorinated Wastewater Effluent Samples 1 November 2005. Los Angeles County Sanitation Districts Joseph Khoury, Connie Young, Anita Pandit, Jorge Garcia, Keith Magers, Steve Carr, Chris Wissman, Maria Pang, and Dwayne Fischer. The Cyanide Problem.

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Cyanide Generation During Preservation of Chlorinated Wastewater Effluent Samples 1 November 2005

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  1. Cyanide Generation During Preservation of Chlorinated Wastewater Effluent Samples 1 November 2005 Los Angeles County Sanitation Districts Joseph Khoury, Connie Young, Anita Pandit, Jorge Garcia, Keith Magers, Steve Carr, Chris Wissman, Maria Pang, and Dwayne Fischer

  2. The Cyanide Problem • Effluent levels exceed NPDES limits • Not detected in the influent • Disinfection by-product? • Artifact of sample handling and analytical technique?

  3. Cyanide Chemical Species • Free: HCN H+ + CN- • Complexed: M(CN)6-n • Strongly bound: Nitriles R-CN, Isonitriles R-NC • Oxidized: Thiocyanate SCN-, Cyanate CNO-, etc..

  4. Acute Toxicity to Aquatic Life

  5. NPDES discharge limits approach detection limits

  6. Effluent levels exceed discharge limits

  7. Cyanide Compliance Program • Plant Operations: UV disinfection • Analytical Methods • Sample Collection Protocols

  8. Analytical Methods • Total Cyanide by acid distillation • Weak acid dissociable cyanide • Acid distillation, colorimetric detection • Available cyanide by flow injection • Ligand exchange, amperometric detection • HPLC methods • Chemical derivatization • Metal cyanides by ion chromatography • Total cyanide by flow injection analysis

  9. Hold for less than 2 weeks Dechlorinate, add NaOH to pH=12 Analyze Sample handling for CN analysis Sample Chlorinated Wastewater

  10. Necessary conditions for CN formation • Wastewater effluent matrix • Chlorine • Reducing agent (dechlorination) • High pH

  11. Cyanide Results from 8 Water Reclamation Plants • Chlorinated Final Effluent, Thiosulfate, pH=12 pH=11 pH=10 • Outfall, pH=12. • Chlorinated Final Effluent, Arsenite, pH=12 Stored at 4ºC, and analyzed within 14 days

  12. Valencia WRP

  13. Saugus WRP

  14. Long Beach WRP

  15. Los Coyotes WRP

  16. Pomona WRP

  17. Whittier Narrows WRP

  18. San Jose Creek East WRP

  19. San Jose Creek West WRP

  20. ConclusionsTreatment Plant Monitoring • Four plants (Valencia, Saugus, SJC East and West) are usually above the reporting limit, and 4 others are usually below. • Arsenite dechlorination consistently produces high results. • Outfall sampling usually only slightly lower than final effluent. • Low pH preservation yields lower results.

  21. KCN spike Holding Time Study • No Cyanide loss due to volatilization • Apparent CN demand in our final effluent

  22. Conclusions • No Cyanide loss due to volatilization • Apparent CN demand in our final effluent Immediate analysis with no pH adjustment

  23. Preservation Studies • Sodium Thiosulfate with no pH adjustment • Sodium Thiosulfate, and NaOH to pH = 12 • Sodium Arsenite with no pH adjustment • Sodium Arsenite, and NaOH to pH = 12 All samples were analyzed immediately(distilled within 15 minutes of sampling)

  24. Temporal Studies SJC East All samples analyzed immediately

  25. Temporal Studies SJC East All samples analyzed immediately

  26. San Jose Creek WestAveraged Results San Jose Creek East Averaged Results All samples analyzed immediately

  27. Valencia Averaged Results andSaugusAveraged Results All samples analyzed immediately

  28. Four Preservation Protocols

  29. Four Preservation Protocols

  30. Summary • Approved methods for total CN analysis give conflicting results. • Final effluent CN level < 5 µg/L reporting limit. • High CN level generated in samples that were dechlorinated and preserved at high pH. • Amount of CN generated increases with pH. • Some dechlorinating agents magnify the effect. • Immediate analysis of cyanide without addition of NaOH is preferable.

  31. Immediate Analysis

  32. Ongoing Studies: • Identify the matrix precursor(s) • Propose chemical reaction pathways • Assess other methods • Lower our reporting limits

  33. Credits • Pearl Ang-Tiu, Pamela Brey, Emmanuel Akpu, Peter Corral • Connie Young, Anita Pandit, Jorge Garcia, Joseph Khoury • Maria Pang, Steve Carr, Chris Wissman, Keith Magers, and Dwayne Fischer

  34. Contact Sanitation Districts of Los Angeles County 1955 Workman Mill Rd Whittier CA 90601 Maria Pang, Asst. Manager of Laboratories mpang@LACSD.org Steve Carr, Lab Supervisor scarr@LACSD.org Joseph Khoury, Chemist jkhoury@LACSD.org

  35. Holding Time and pH Study

  36. Calculated Loss of HCN “…cyanide air emissions can be estimated on the basis of equilibrium levels of cyanide in the air over solutions at various temperature and pH values from the following:” [HCN]air = [(1470/T)e(9.275-2992/T) ]/[1+10(pH-9.3)] Where HCN = mg HCN/m3 air per ppm NaCN in solution, and T = temperature, Kelvin U.S. Environmental Protection Agency (2000) Managing Cyanide in Metal Finishing; EPA 625/R-99/009, section 4.0; Cincinnati, Ohio

  37. Calculated Loss of HCN [HCN]air = [(1470/T)e(9.275-2992/T) ]/[1+10(pH-9.3)] Where HCN = mg HCN/m3 air per ppm NaCN in solution, and T = temperature, Kelvin

  38. vs.Chloramination San Jose Creek WestBreakpoint Chlorination All samples Analyzed Immediately

  39. Outfall StudiesSaugus & Valencia All samples Analyzed Immediately

  40. Precursor,Chlorine,Arsenite at high pH Precursor,Chlorine,Arseniteintermediates? Analyze Arsenite Reaction Studies Matrix Precursor+Chlorine Timing between • Sample collection and Dechlorination • Dechlorination and NaOH addition • NaOH addition and Analysis

  41. A few days between preservation and analysis Immediate analysis Immediate Analysis vs. Preserved Samples

  42. Precursor Study - past • Precursors that have been tested • Solids, Polymer, Ascorbic acid, humid acids, Urea, and Hydantoin • Experimental conditions • High dosage of target organics, at least 1 mM • In DI matrix, chlorine, nitrite/nitrate, chloramine were applied • In post ammonia Secondary, chlorine was applied • Dechlorinating agents and pH adjustment were applied • Inconclusive at this time

  43. Immediate analysis Arsenite at ambient pH Arsenite at pH=12 Arsenite Dechlorination C8 SDB-XC SDB-XC Oil&Grease • Adjust to pH=12 • analyze immediately • reanalyze 24 hrs later Final Effluent Sample Extractable Precursors

  44. Problems • Effluent concentrations exceed limits • Effluent conc. exceeds influents • Effluent 5 – 20 µg/L • Influent < 5 µg/L • Discharge limits approach MDLs

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