When people refer to high strength leachate they are normally referring to the landfill leachate from a sanitary landfill which has percolated slowly through the waste. That is leachate and has been extracted by the leachate collection and pumping system.
Usually high strength leachate has ammoniacal nitrogen concentrations above 500 mg/l up to 3.500 mg/l, and Chemical Oxygen Demands in the range 1,000 mg/l to 25,000 mg/l for a large landfill when fresh leachate is discharged direct from an acetogenic landfill, before the landfill (or landfill cell) gas production starts.
High strength leachate is usually leachate which has been recirculated through methanogenic cells of the same landfill in which it was created.
We have provided more information about high strength leachate in our leachate composition section which you can click here to see.