Oxidative treatment of bleach plant effluent
AssigneeInternational Paper Company
InventorsCaifang Yin, Christopher P. Hung, Hugh P. Gallagher, Jasper H. Field
Life of this patent
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Abstract
The invention described in the specification relates to a process and apparatus for the reduction of adsorbable organic halide (AOX), chemical oxygen demand (COD) and color bodies from the filtrates generated in a chlorine compound-containing pulp bleaching sequence. The method involves vigorously and intensely mixing certain pulp bleaching filtrates in order to lower the AOX content of the filtrate and the use of a peroxy compound and a ferrous salt catalyst to treat a combined filtrate streams thereby significantly reducing the level of AOX, COD and color in the effluent leaving the pulp bleaching plant.
Claims25
A method for treating effluent from a kraft pulp bleaching sequence having a chlorine and/or chlorine dioxide stage generating an organic chloride compound-containing filtrate (F.sub.D) and an alkaline extraction stage generating an extraction stage filtrate (F.sub.E) wherein the F.sub.D and F.sub.E filtrates contribute to the amount of the chemical oxygen demand (COD), adsorbable organic halides (AOX), color bodies, and toxicity in the bleach plant effluent, the method comprising:
- contacting F.sub.D filtrate with the F.sub.E filtrate at a pH above about 10 to provide an F.sub.D F.sub.E mixture;
- vigorously mixing the F.sub.D F.sub.E mixture for a mixing interval sufficient to reduce the AOX of the F.sub.D ;
- lowering the pH of the F.sub.D F.sub.E mixture to from about 3.0 to about 5.0;
- contacting the F.sub.D F.sub.E mixture prior to any biological treatment thereof with from about 0.2 to about 2.0 grams per liter of peroxy compound in the presence of a catalytic amount of a metal catalyst;
- and
- holding the F.sub.D F.sub.E mixture in contact with the peroxide compound and catalyst in a hold vessel for a reaction time sufficient to substantially reduce the amount of AOX, COD, color bodies and/or toxicity initially present in the F.sub.D and F.sub.E filtrates.
A system for reducing pollutants from an elemental chlorine-free pulp bleaching plant, comprising:
- a mixer for mixing an F.sub.D filtrate from a chlorine dioxide bleaching stage with an F.sub.E filtrate from an alkaline extraction stage to form an F.sub.D F.sub.E mixture;
- a peroxide contact system for contacting the F.sub.D F.sub.E mixture with a peroxide in the presence of a metal catalyst prior to any biological treatment system;
- and
- a biological treatment system for treatment of the contacted mixture from the peroxide contact system.
A process for reducing organic halide (AOX), chemical oxygen demand (COD) and color bodies in an effluent from a pulp bleaching sequence having a chlorine and/or chlorine dioxide stage generating an organic chloride compound-containing filtrate (F.sub.D) and an alkaline extraction stage generating an extraction stage filtrate (F.sub.E), the process comprising:
- vigorously mixing the F.sub.D filtrate from a first chlorine dioxide bleaching stage with the F.sub.E filtrate from a first alkaline extraction stage of the bleaching sequence at a pH above about 10.0 to provide an F.sub.D F.sub.E mixture;
- contacting the F.sub.D F.sub.E mixture prior to any biological treatment thereof with an amount of peroxide in the presence of a catalytic amount of iron-containing catalyst at a pH in the range of from about 3.0 to about 5.0;
- and
- holding the contacted F.sub.D F.sub.E mixture in the presence of the peroxide and catalyst for a period of time ranging from about 1 minute to about 60 minutes to assure essentially complete reaction between the peroxide and the mixture whereby the AOX, COD and color bodies initially present in the F.sub.D and F.sub.E filtrates are substantially reduced.
Dependencies are inferred from the claim text.