Photochemical destruction of cyanide in landfill leachate

The Alien 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.