Method for recycling paper mill waste water
OwnerRichard C. O'Brien, deceased, by Elva R. O'Brien, executrixinventors
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Abstract
Disclosed is a method for coagulating the suspended solids in paper mill waste water so that the coagulated solids may be easily separated from the waste water and the clarified waste water reused in the paper making process. Coagulation is induced by first adding sulfuric acid to lower the pH to below 4, mixing thoroughly, and then adding calcium hydroxide to raise the pH to above 10. The coagulated solids separated from the waste water may be used as a landfill, used as a low grade pulp source, or dewatered and burned as a fuel.
Claims10
In a paper-making process a method for treating paper mill waste water to remove the suspended material therein so that the clarified waste water may be reused in the paper-making process, comprising the steps of:
- (a) adding a sufficient amount of sulfuric acid to reduce the pH of the waste water to less than 4.0,
- (b) mixing thoroughly, then,
- (c) adding a sufficient amount of calcium hydroxide to rapidly drive the pH of the acidified waste water to above 10 and cause coagulation of the solid matter in said waste water,
- (d) separating the coagulated solid material from the waste water to clarify it, and
- (e) treating the clarified waste water to return the pH to approximately neutral.
In a paper making process utilizing large quantities of water for stock preparation and the like, a method of providing the major part of water needed in such process by treatment and recycling of waste water therefrom comprising the steps of
- (a) continuously collecting waste water from the several steps of the paper-making process;
- (b) passing the collected waste water through a first treatment stage and adding thereat sufficient sulfuric acid to reduce the pH of the mixture to at least 4.0;
- (c) mixing thoroughly,
- (d) then passing the acidified waste water through a second treatment stage and adding thereat sufficient calcium hydroxide to raise the pH of the mixture quickly to at least 10 causing coagulation of solids in the mixture;
- (e) removing the coagulated solids from the mixture to clarify the waste water;
- (f) restoring the pH of the clarified waste water approximately to neutral;
- and
- (g) recycling the neutralized, clarified waste water into the paper-making process as the major source of water for that process.
Dependencies are inferred from the claim text.