Regeneration of pulp liquors

In a paper mill which produces paper from waste paper by treating the waste paper with aqueous treatment liquors and recovering converted paper and spent treatment liquors, a method of treating the spent treatment liquors which enables the production of paper with the production of no liquid effluent from the paper mill, comprising:

• filtering the spent treatment liquors to remove suspended solids;
• returning some of the filtered spent treatment liquors back to the paper production process and subjecting the remainder of the filtered spent treatment liquor to a biological oxidative treatment which produces a sludge;
• separating the liquid phase from the sludge;
• subjecting the separated liquid phase to microfiltration;
• returning some of the microfiltered liquid phase to the paper production process and subjecting the remainder to reverse osmosis treatment wherein the treated liquid phase is returned to the paper production process.

In a paper mill for producing paper from waste paper in which no liquid effluent is produced which includes the steps of treating the waste paper with aqueous treatment liquors and recovering converted paper and spent treatment liquors, a system for treating the spent treatment liquors comprising:

• a biological treatment unit to oxidize a substantial portion of the organic materials in the spent aqueous treatment liquors to produce a separable sludge;
• a microfiltration unit to remove any undissolved matter remaining in the liquid phase exiting the biological treatment unit;
• a reverse osmosis unit to produce a concentrated solution of salts and a treated liquid phase;
• and
• an evaporation unit suitable to produce a solid waste product from the concentrated solution of salts.