Sotaro Higuchi

Toxicological evaluation of the chemical oxidation methods for landfill stabilization

As the stabilization criteria for landfill sites, only chemical criteria for the leachate discharges from the landfill sites have been used in Japan and many other countries. Recently, chemical oxidation has been developed as a method for the early-stabilization of landfills. However, by-products that are difficult to detect by chemical analysis can be produced by this method. Therefore, toxicity tests are useful tools for detecting the changes of leachate quality after application of this method. The heat source in the A landfill was analyzed by organic position inquiry technology, and ozone-treated leachate was sprayed back to the heat source in the landfill. Toxicity changes of the leachate after the spray were monitored using Microtoxtrade mark, ToxScreen-II, and DaphTox tests. The hardly-degradable organic matter was efficiently removed and toxicities of the leachate in the heat source decreased after the application. These toxicity results were significantly related to chemical oxygen demand (COD) changes. Thus, it was concluded that the toxicity tests were effective for monitoring the leachate quality after applying the chemical oxidation method for landfill stabilization, and its incorporation to establish the criteria for early-stabilization of landfill sites needs to be considered.

Effects of Incinerator Exhaust Gas Treatment Agents and Fly Ash Processing Chelates on MSW Landfill Management

Lime used to treat flue gas from incinerators and organic chelating agents used to remove heavy metals from fly ash create a highly saline and alkaline environment at landfill sites, causing nitrification inhibition that hampers nitrogen treatment and generating refractory COD in the processes of organic stabilization by microbes and leachate treatment. The authors analyzed organic chelating agents and fly ash treated with the chelating agents, and monitored leachate from lysimeters, or simulated landfills. The results showed that organic chelating agents acted as nitrification inhibitors, and that higher water levels in landfill layers resulted in higher concentrations of thiourea and refractory COD, which are chelating compounds, hindering leachate treatment.