Treatment of pulp mill effluents

[Detailed Description of the Invention]

The present invention relates to the disposal method of pulp mill waste fluid. It is known that the waste fluid of intensity contamination nature will be discharged from a paper pulp manufacture factory. In this specification, the waste fluid of this intensity contamination nature is called "papermill waste fluid." This waste fluid arises mainly from the bleaching work of paper pulp. Generally this bleaching process consists of at least two steps, and in order that that first process may remove chlorine treatment and the 2nd process may already remove Noodle compounds by sodium hydroxide processing in the end of Then and these processes as it is meltable, it washes paper pulp with water, as known as a matter of fact. Thus, chlorine treatment liquid (this comes out from Ushiro's pulp washing bleached by chlorine) and a soda treating solution (this comes out from Ushiro's pulp washing bleached by sodium hydroxide) arise. These liquid, especially a soda treating solution constitute the main part of the contamination waste fluid from a pulp mill. And they are products which arise in most quantity. Because, about 30 m per manufacture of 1 ton of paper pulp³A Of chlorine treating solution and 10 m³It is because a of soda treating solution arises. However, a certain thing [ that grade change can be carried out ] of these values is clear by the clear kind of manufacture pulp, manufacture, and a bleaching process. The character thru/or kind of pulp mill waste fluid changes with the delignification processes (lignin is extracted in the form of lignosulfonic acid salt) preceded with the character of the wood (a deciduous tree or the department plant of resin) used for manufacturing pulp, and bleaching of pulp. having described such a matter -- the present invention -- it is going to solve -- although it is for emphasizing an essential problem, it must be understood that it is not what limits the present invention only to special mention To waste fluid upwards. It is quite complicated in itself [ of pulp mill waste fluid / contamination ], and is a thing of the character which is hard to define. However, it is appropriate to discriminate BOD (namely, biological need for oxygen) in these waste fluid, COD (chemical oxygen demand), and a color from an actual standpoint. The main pollution characteristics are constituted by these three elements. There is another method of determining degree of contamination in measuring the concentration of the organic carbon (namely, carbon which originates from an organic molecule) in waste fluid. As what processes pulp mill waste fluid, many methods are already proposed. In particular, processing by calcium hydroxide or an active charcoal is mentioned. Some researchers tried to apply this device to processing of papermill waste fluid by development of a film device recently. In this way, Vida (Beder) has reported processing of the papermill waste fluid by reverse osmosis [TAPPI, and 53(5)883~May, 1970 [ 7 or ]]. However, the actual reverse osmosis of this waste fluid has already been reported before it, it Therefore and the extra fault of essential deluxe edition paper-making place waste fluid is described in the above-mentioned report. This extra fault and reverse osmosis are actually distinguished today. That is, while the former is characterized by suspending only a far bigger Solute molecule than a solvent with a film, in the latter reverse osmosis, the Solute molecule which has a particle size comparable as a solvent is also YOU HOLD(ed) by the film. However, the interest which could be shown in the film method of these at the beginning carried out the considerable fall by many difficult problems. The following can be mentioned especially among these difficult problems. (1) A reverse osmosis method has a fault surely in that it must use very high pressure. It is because liquid pressure must be made higher than the osmotic pressure of waste fluid. (2) Use of a cellulose acetate film needs the pretreatment by acid, in order to avoid hydrolysis of the acetate ester, but by the strong alkalinity of a soda treating solution, a lot of acid is required and, in the result, a lot of salt forms it. It is not desirable, when it Therefore and this also tends to discharge also and waste fluid in a river. (3) Get it clogged depending on a film, therefore a flow decreases sharply. (4) The contamination by the color material of industrial waste fluid is not fully removed, when performing the continuous extra fault of the waste fluid. One object of the present invention is to Dissolution the fault of the known method wholly or partially. The another object of the present invention is to provide the method of processing simply pulp mill waste fluid, especially a soda treating solution. To the soda treating solution in which the method of the present invention was discharged from the bleaching process of paper pulp, By adding the flocculant used in a quantity smaller than the quantity which brings about suitable condensation, the soda treating solution is pretreated and it consists of subsequently performing the extra fault of this pretreated waste fluid (mixture of a soda treating solution and a flocculant). The quantity of the flocculant used is 2~50% of the weight preferably of a quantity required generally to obtain suitable condensation, i.e., transparent (decolorized at least 60%) supernatant liquid, and 7~15%. Supernatant liquid does not have the after [ Decantation ] cloudy weather from a sediment (namely, condensation lump). The flocculant of Then is good with a single compound, or its Then is also good with the mixture of a compound. In the case of the latter, it can add simultaneously to waste fluid, or can add the ingredients of a mixture one by one. The system which brings about the extensive formation of a system, especially a sediment which brings about formation of a sediment into a water medium as a flocculant system which may be used for the present invention is preferred. In this way, the in general inorganic compound or the mixture of a compound which brings about formation of insoluble salt or hydroxide precipitate is advantageously used into a water medium. There is in general optimal PH that makes a sediment form intentionally in each flocculant system. It is known by the person skilled in the art about how to select the ingredient, PH, and the amount of ingredients of a flocculant system. As a flocculant system with especially interest, (a) The system which consists of calcium hydroxide and aluminum sulfate, (b) Calcium hydroxide and CO₂(CO₂The system which consists of carrying out the bubble of the gas, (c) the system which consists of a calcium chloride and sodium carbonate -- and (d) Chlorosulfuric acid aluminum To list -- things are made. A condensation auxiliary agent, for example, sodium acrylate/acrylamide copolymer, can be made to mix in each of the above-mentioned system. The quantity of an auxiliary agent is often 0.1~10 % of the weight for the non-machine part of a flocculant system. The extra fault film used for the present invention has a cutoff limit of 4000~100000, preferably 5000~25000 to protein. (When a cutoff limit means the marginal molecular weight about protein and this is exceeded here, the degree of refusal in which a film is more expensive than 95% is shown). It is preferred to use the film which consists of a stable polymer by PH higher than 8, especially PH higher than 10. It is a 2-bar basis among effective films at pure water, and they are a 700-/day andm.²more -- desirable -- a 2000-/day andm²It is preferred to choose the film which brings about more flows. Generally an extra fault is carried out under differential pressure (0.5~20 bars, preferably 1~6 bars) (pressure difference membranous one side and by the side of other). According to the advantageous embodiment, processing waste fluid flows in sec in 1~3 m /preferably with linear velocity earlier 0.1 m /than sec in a film surface. The following example illustrates the present invention and does not limit Then and this. the inside of an example, and COD -- Ahner (Afnor) standards No.T90-101 -- therefore, it measured. The color of waste fluid was measured, without performing PH regulation using a calibration To spectrum photometer about a platinum-cobalt reference sample (the sample is defined as ASTM standards D1209-62). the concentration of organic carbon -- mg per waste fluid 1 -- it expresses with a number. This concentration is computed from the measured value of the amount of carbon which obtained the sample by burning by 900 degreeC (index of total carbon), and 150 degreeC (index of inorganic carbon). Example 1 The pulp mill waste fluid which consists of a bleaching factory of the "craft" paper pulp which used the tree of the department plant of resin as materials from a discharge To soda treating solution is given to the present invention at Followed processing. 4500 and a color of COD are [ 10000 and PH of this waste fluid ] 10. The viscosity is equal to it of a real waterworks. 300 cm of this waste fluid³It is alike and is calcium hydroxide Ca (OH) of 0.075g/.₂Aluminum sulfate aluminum of 0.3g/₂(SO₄)₃·18H₂The sodium acrylate/acrylamide copolymer of O and 0.4 mg/are added one by one. The mixture of these three sorts of compounds constitutes the flocculant mixture which produces condensation for 10 times in waste fluid by To rise dosage, and brings transparent supernatant liquid to a naked eye by a suitable Decantation speed (1 / 2 hours). About the mixture of a soda treating solution + flocculant, it is 39.2 cm.²It introduces into extra Over bath which was alike and was provided with the film of equal surface area. This film consists of a complicated polymer electrolyte (mixture of two sorts of acrylonitrile copolymers in which the method of one has a cation machine, and others have an anion machine), and they are a 9800-/day andm under 2 bars in water.²Bringing about Flow rate, a cutoff limit is 15000. By churning in a film surface, the boundary layer effect in waste fluid can be eliminated. Differential pressure is 2 bars. Color is 270 cm of extra liquid of 1200 (this is equivalent to 88% of color reduction).³To obtain. As for the COD, Then and this show 78% of fall by 950. Example 2 The pulp mill waste fluid consisting of the soda treating solution discharged from the bleaching factory of paper pulp gives the present invention at Followed processing. Color of this waste fluid is 8000. PH is 12.4. Calcium hydroxide Ca (OH) of 0.08g/₂aluminum of 0.4g/₂(SO₄)₃·18H₂It is 300 cm of this waste fluid one by one about O, and sodium acrylate/acrylamide copolymer of 0.5 ppm.³It is alike and adds. The dosage exceeding 10 times of three sorts of these compounds constitutes a quantity required for suitable condensation and Decantation. As for the point that even free differ although the extra fault of the mixture of a soda treating solution and a flocculant was carried out to having indicated for Example 1 and it was processed under the same conditions with it, the flows in the 2-bar basis about pure water are a 4000-/day andm.²It comes out and a cutoff limit is having used the film made from sulfonation polysulfone which is 10000. Color obtains the extra fault of 2800. The same result as the time of not using an acrylics polymer is obtained. Example 3 The soda treating solution discharged from the bleaching factory of the pulp for textiles (pulp for viscose) which obtained the deciduous tree tree by the heavy sulfite salt method as materials is given to the present invention at Followed processing. A color is 40000 and PH of this waste fluid is 9.2. Calcium hydroxide Ca (OH) of 0.65g/₂aluminum of 2g/₂(SO₄)₃·18H₂It is 300 cm of this waste fluid one by one about O, and sodium acrylate/acrylamide copolymer of 2 ppm.³It is alike and adds. The dosage exceeding 10 times of three sorts of these compounds constitutes a quantity required for suitable condensation and Decantation. Under the conditions of a statement, the extra fault of the mixture of the waste fluid of soda processing and a flocculant is carried out to Example 2, and it is processed for it. The color of an extra fault is 16000 and it is equivalent to 60% of color reduction. Example 4 A discharge To soda treating solution is given to the present invention at Followed processing from the bleaching factory of the kraft pulp which used the tree of the department plant of resin as materials. A color is 25000 and PH of this waste fluid is 12.3. The organic carbon concentration is 1420. Na of 1.5g/₂CO₃CaCl of 1.5g/₂And sodium acrylate/acrylamide copolymer of 1 ppm are added in this waste fluid 20 one by one. The dosage exceeding 10 times of three sorts of these compounds constitutes a quantity required for suitable condensation and Decantation. It processes with the extra fault device containing the film of four sheets which accumulated the mixture of a soda treating solution and a flocculant. Each film is 1.1dm.²It is a product made from sulfonation polysulfone which has Surface area, and they are 4000/of 2-bar bases day, andm to pure water.²Flow rate is brought about and a cutoff limit is a film of 10000. Differential pressure is 1 bar. The flow velocity in a film surface is 1.5 m/sec. The extra liquids of 18 is a 1600-/day andm.²It is obtained by the fixed flow to say. The color is 6000 (76% of reduction), and organic carbon concentration is [ 600 ] equal. The same result is obtained when not using an acrylics polymer.