DK127894A - Pulp waste water treatment - Google Patents

Pulp waste water treatment Download PDF

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Publication number
DK127894A
DK127894A DK127894A DK127894A DK127894A DK 127894 A DK127894 A DK 127894A DK 127894 A DK127894 A DK 127894A DK 127894 A DK127894 A DK 127894A DK 127894 A DK127894 A DK 127894A
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peroxidase
waste water
hydrogen peroxide
amount
chlorine
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DK127894A
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English (en)
Inventor
Sven Pedersen
Jens Folke
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Novo Nordisk As
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Description

PULP WASTE WATER TREATMENT FIELD OF INVENTION
This invention relates to a process for detoxicating waste water from bleaching lignocellulosic pulp with chlorine i dioxide.
BACKGROUND OF THE INVENTION
The fear of 2,3,7,8-tetrachloro-p-dibenzodioxin to be found in pulp mill effluents has driven the industry to use smaller amounts of molecular chlorine in the bleaching of kraft ) pulp all over the world up through the SOties. Molecular chlorine has been substituted with chlorine dioxide in an increasing number of mills. Today, up to 100% substitution with chlorine dioxide is used in some mills.
The toxicity of the effluents from the process of i bleaching pulp with chlorine dioxide is of course of great interest. The amount of phenolic groups is an indicator of how toxic a given pulp effluent is.
SUMMARY OF THE INVENTION
We have found that, surprisingly, approximately 50% i of the amount of phenolic groups in the bleach liquor from the process of bleaching pulp with chlorine dioxide can be removed with a phenol oxidizing enzyme system (e.g. peroxidase and hydrogen peroxide).
Accordingly, the invention provides a method of detoxicating waste water from the process of bleaching pulp with chlorine dioxide or with a mixture of chlorine dioxide and molecular chlorine, in which less than 20% of the active chlorine in said mixture is molecular chlorine, the method comprising treatment of said waste water with a phenol oxidi-' zing enzyme system.
BRIEF DESCRIPTION OF DRAWINGS
The present invention is further illustrated by reference to the following drawings, in which
Fig. 1 shows the mortality of eggs/larvae from zebra fish exposed to the following concentrations of untreated D-stage liquor (explained in Ex. 1): 1.25%: ; 2.50%: □; 5.00%: ; 10.00%: 0; 20.00%: a; 40.00%: δ; 80.00%: O; Control: X.
Fig. 2 shows the mortality of eggs/larvae from zebra fish exposed to the following concentrations of peroxidase treated D-stage liquor (explained in Ex. 1): 1.25%: I; 2.50%: □; 5.00%: ; 10.00%: Φ; 20.00%: A; 40.00%: Δ; Control: X.
DETAILED DESCRIPTION OF THE INVENTION
Phenol oxidizing enzyme system
The enzyme system used in the invention consists of a suitable peroxidase together with a hydrogen peroxide source or a suitable oxidase together with 02. Suitable enzymes are those which oxidize and polymerize aromatic compounds such as phenols and lignin.
Examples of suitable enzymes are peroxidase (EC 1.11.1.7), catechol oxidase (EC 1.10.3.1) and laccase (EC 1.10.3.2). Some preferred enzymes are horseradish peroxidase, soybean peroxidase and peroxidase derived from a strain of Coprinus. e.g. C. cinerius or C. macrorhizus, peroxidase from Bacillus. e.g. B. pumilus and laccase from Trametes. e.g. T. versicolor (previously called Polyporus). It may be useful to use two different phenol oxidizing enzymes together.
The amount of peroxidase should generally be in the range 1-200 PODU per ml of waste water (PODU unit of peroxidase activity defined below). The amount of laccase should generally be in the range 1-200 units per ml of waste water (unit of laccase activity defined below).
The hydrogen peroxide source may be hydrogen peroxide or a precursor of hydrogen peroxide, preferably perborate or percarbonate, or a hydrogen peroxide generating enzyme system, e.g. an oxidase and its substrate, or a percarboxylic acid or a salt thereof. The amount of hydrogen peroxide source may be added to the waste water in an amount corresponding to 0.1-100 mM H2Oz, preferably in an amount corresponding to 1-50 mM H202, more preferably in an amount corresponding to 1-10 mM H202.
If the phenol oxidizing enzyme system consists of an oxidase together with 02, molecular oxygen from the atmosphere will usually be present in sufficient quantity.
Determination of Peroxidase Activity iPQDU)
Peroxidase activity is determined from the oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by hydrogen peroxide. The greenish-blue colour produced is photometered at 418 nm. The analytical conditions are 0.88 mM hydrogen peroxide, 1.67 mM ABTS, 0.1 M phosphate buffer, pH 7.0, 30°C, 3 minutes reaction. 1 peroxidase unit (PODU) is the amount of enzyme that catalyses the conversion of 1 /xmol hydrogen peroxide per minute at these conditions.
Determination of Laccase Activity
Laccase activity is determined by a similar method without addition of hydrogen peroxide. 1 unit of laccase activity is defined as the amount of enzyme that catalyses the oxidation of 1 μιτιοί ABTS per minute.
Process Conditions
After the pulp bleaching with chlorine dioxide or with a mixture of chlorine dioxide and chlorine, in which less than 20% of the active chlorine in said mixture is molecular chlorine, the effluent is treated with the phenol oxidizing enzyme system. Additionally an oxidizable substrate such as an organic compound , such as a phenolic compound, e.g. p-hydroxy-benzene sulphonate, may be added in order to enhance the effect of the phenol oxidizing enzyme system. The amount of oxidizable substrate may correspond to a concentration in the waste water of between 0.1 μΜ and 100 μΜ. pH may be adjusted to neutral (pH 6 - pH 8); reaction time will normally be from 10 minutes to 5 hours; the temperature will normally be from 10°C to 50°C.
Many pulp mills have different lines for softwood and hardwood. The phenol oxidizing enzyme system is useful in effluents both from softwood and from hardwood.
The present invention is further illustrated in the following examples which are not in any way intended to limit the scope of the invention as claimed. EXAMPLE 1
Treatment of Bleached Pulp Mill Effluent A D-stage sample from bleaching softwood pulp was collected from a Swedish Kraft pulp mill. The D-stage is the bleach liquor from the bleaching stage in which chlorine dioxide or a mixture of chlorine dioxide and chlorine is used, in this case 100% chlorine dioxide was used. To 3 litres of this sample 15 ml of recombinantly produced peroxidase derived from Coprinus cinereus (rCiP), described in WO 92/16634, having an activity of 10000 PODU/ml, were added together with 30 ml of 0.5 M HjOj (giving 50 PODU/ml and 5 mM H20? in the effluent) . pH was adjusted to 7.0. Reaction time: 3 hours. The amount of phenolic groups in the untreated D-stage sample and the peroxidase treated D-stage sample was determined.
Phenol Content
The amount of phenolic groups in the untreated and peroxidase treated effluents was determined using the spectro-photometric, 4-amino-antipyrine method originally described by Emerson et al ("The Condensation of Antiaminopyrine II. A new Colour Test for Phenolic Compounds". J.Ora.Chem 8, 1943, p.417) .
Results
Untreated D-stage sample had an OD500 of 0.123.
Peroxidase treated D-stage sample had an OD500 of 0.061.
It is believed that the phenol oxidizing enzyme system causes a polymerisation of low molecular mass material in the bleach liquor. It can be seen from the above mentioned results that 50% of the phenolic groups are removed. EXAMPLE 2
Toxicity Tests
Mortality of eggs/larvae from zebra fish in untreated and peroxidase treated D-stage samples (described in Ex. 1) was analyzed in the following way:
Fertilized eggs of zebra fish (Brachydanio rerio) in the blastula stage were obtained from a stock laboratory culture (< 8 h after spawning) . The eggs were collected and placed in 150 ml test vessels filled with 100 ml of test solution (described below). The method followed is described by Landner et al, in "Short-term Test for Predicting the Potential of Xenobiotics to Impair Reproductive Success in Fish", Ecotoxicol. Environ. Safety 9, 1985, pp. 282-293. The embryo larval stages were exposed in a semistatic manner (this implies that a minimum of 2/3 of the test solution is renewed daily) to the following test solutions: 1.25%; 2.50%; 5.00%; 10.00%; 20.00%; 40.00% and 80.00% of untreated and peroxidase treated D-stage solutions. (80.00% test solution was only performed with untreated D-stage solution). The toxicity tests were carried out for 10 days in a thermostatic room at 24.9°C ± 0.1°C and a photo period of 12 h. Dead eggs and larvae were counted and removed daily. The results of the tests are presented in Fig. 1 (untreated D-stage solutions) and Fig. 2 (peroxidase treated D-stage solutions) using the following symbols: 1.25%: I; 2.50%: □; 5.00%: ♦; 10.00%: 0; 20.00%: a; 40.00%: a; 80.00%: 0; Control: X.
It can be seen from Fig. 1 and 2 that the survival of eggs/larvae was significantly affected by higher concentrations of untreated D-stage solutions, whereas the eggs/larvae in the peroxidase treated D-stage solutions were unaffected. The slight mortality seen in the peroxidase treated D-stage solutions is quite arbitrary with zero response in 2.50%, 10.00% and 20.00% test solutions, and an insignificant mortality in 1.25%, 5.00% and 40.00% test solutions.
DK127894A 1994-11-04 1994-11-04 Pulp waste water treatment DK127894A (da)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006126983A1 (en) * 2005-05-04 2006-11-30 Novozymes North America, Inc. Chlorine dioxide treatment compositions and processes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006126983A1 (en) * 2005-05-04 2006-11-30 Novozymes North America, Inc. Chlorine dioxide treatment compositions and processes

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