black liquor, , liquor pulping
Pulp waste liquor is a by-product of the paper and cardboard industry emitted from paper mills.
The liquid effluent from the digestion of wood during pulping; contains wood chemicals (for example, lignin) and spent digestant (caustic, sulfite, or sulfate, depending on the process used). It is used as an energy source to feed back into pulp production. (Wikipedia)