Photochemical Destruction of Cyanide in Landfill Leachate

The Allen Park Clay Mine Landfill, owned by Ford, produces a leachate that occasionally contains cyanide at levels marginally below the discharge limit. The form of the cyanide in the leachate was found to be iron-cyanide complexes that resist oxidation by a conventional treatment method, alkaline oxidation. Furthermore, the leachate also was found to contain a relatively large amount of organics (>1,000 mg L of chemical oxygen demand), which would exert additional demand for oxidizing agents (e.g., chlorine). A study was performed to determine what treatment technology could be employed in the event treatment becomes necessary because of potential changes in the leachate characteristics and or discharge limits. In this study, among several chemical oxidation methods, ultraviolet (UV) irradiation with or without ozone was investigated as a treatment option. The following are the primary findings: (1) UV irradiation alone was effective for removing the iron-cyanide complex in both the leachate and the clean water; (2) the demand for UV or ozone by chemical oxygen demand was relatively low for this leachate; (3) ozone alone was not effective for removing the iron-cyanide complex; and (4) UV irradiation alone and UV irradiation with ozone resulted in the same removal for total cyanide in clean-water experiments, but the UV irradiation alone left some free cyanide whereas the UV irradiation with ozone did not.