In kraft softwood mills, tall oil soap is a valuable by-product as well as a toxin in the wastewater treatment system. Thus it is necessary to properly manage foam and soap within the mill.
Managing this issue requires a number of steps including the handling and deaeration of foam, separation of soap from liquor, and the separation of liquor from soap. Once the soap is separated from the system, it should be kept separate and not remixed with the liquor.
New technologies emerging from the by-product recovery of black liquor soap include conversion of the soap to bio-diesel fuel (SDRF process) and the extraction of other valuable by products such as sterols.