JP2008188488A - Wastewater treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment system for effectively actualizing wastewater treatment in a shorter period of time and more inexpensively compared to conventional equipment when treating, in particular, PVA wastewater. <P>SOLUTION: The wastewater treatment system mixes common salt with the wastewater containing polyvinyl alcohol, electrolyzes the resultant mixture, merges the wastewater of the bleaching process of a cellulose based fiber structure and/or a liquid ammonia manufacturing process and the electrolyzed wastewater, and subjects the merged wastewater to denitrification and activated sludge treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment system including electrolysis of industrial wastewater, and more particularly to a wastewater treatment system that economically and effectively treats industrial wastewater mainly containing polyvinyl alcohol.

  Polyvinyl alcohol (PVA) contained in industrial wastewater is a substance discharged from bleaching and dyeing factories such as woven fabrics and knitted fabrics, but its biodegradability is poor, and when treated by the activated sludge method, it is treated for a long period of 20 days or longer. Is needed.

  Therefore, it is often concentrated and incinerated at present, but incurs incineration costs and incineration ash processing costs, and is regarded as a problem from the viewpoint of carbon dioxide emission by incineration.

<1> As disclosed in JP-A-11-309468, many methods for oxidizing an organic substance by adding an oxidizing agent in the presence of a metal catalyst are also disclosed. However, these methods are difficult to handle because the oxidizing agent used is a deleterious substance, and the cost is high.

Next, an electrolysis method has also been proposed.
<2> For example, in Japanese Patent Application Laid-Open No. 6-254568, by generating a direct current through a waste liquid that is an electrolyte solution or an electrolyte solution, the generated radical active oxygen generated thereby is oxidized in the waste liquid. A method having a waste liquid treatment process that reacts with a substance and oxidatively decomposes the substance is proposed.
<3> In Japanese Patent Laid-Open No. 2000-254650, oxygen-containing gas is supplied to the cathode to generate hydrogen peroxide, and inorganic acid is supplied to the anode from the acid solution addition port to oxidize and generate hypochlorous acid or the like. The product to be treated is treated with the two compounds. As a result, a water treatment method and apparatus have been proposed in which the sterilizing power is improved and the vicinity of the cathode surface is maintained from neutral to acidic due to the acidity of the coexisting oxidation product, thereby suppressing the precipitation of metal hydroxide.

<4> In Japanese Patent Application Laid-Open No. 2003-326263, the concentrated electrolyzed water treatment method includes a concentration step of concentrating water to be treated to obtain a concentrated liquid to be treated, and electrolysis of the concentrated liquid to be treated after the concentration step. An electrolysis process to be treated, and preferably, after the electrolysis process, further includes a dilution process for diluting the treated liquid after electrolysis with separated water other than the concentrated liquid to be treated obtained in the concentration process. . Furthermore, a concentrated electrolyzed water treatment method including a biodegradation treatment step for biodegradation treatment of water to be treated before the concentration step has been proposed.

  However, when the PVA is performed only by electrolysis, the PVA is not sufficiently decomposed. In general, in the method using electrolysis, the investment of the apparatus is required to secure a sufficient reaction area of the electrode. There is a problem that it becomes expensive.

JP 11-309468 A JP-A-6-254568 JP 2000-254650 A JP 2003-326263 A

  As a result of intensive studies to achieve the above object, the present inventors have developed a wastewater treatment system that effectively realizes wastewater treatment in a short period of time and at a low cost, particularly when treating PVA wastewater. The issue is to provide.

  In view of the above problems, the present inventors perform electrolysis by adding sodium chloride to waste water containing several mass% of PVA. A wastewater treatment system is found that combines wastewater from a bleaching process or liquid ammonia processing process and the electrolyzed wastewater, and passes the combined wastewater through a denitrification and activated sludge treatment process, thereby completing the present invention. It came to.

The present invention
<1> Salt water is mixed with wastewater containing polyvinyl alcohol and electrolyzed, and the wastewater from the bleaching step of the cellulosic fiber structure and / or the liquid ammonia processing step is combined with the electrolyzed wastewater, and the combined wastewater is removed. A wastewater treatment system characterized by treating nitrogen and activated sludge;
<2> The waste water containing the electrolyzed polyvinyl alcohol and the waste water from the bleaching step and / or the liquid ammonia processing step of the cellulosic fiber structure are combined at a ratio of 1:25 to 1:35 to remove nitrogen and activity. <1> The wastewater treatment system according to <1>, characterized by sludge treatment.
<3> The treatment conditions for one set of electrodes in the above electrolysis are as follows: the treatment time (residence) is 30 to 60 minutes, the current is 400 to 500 A, the voltage is 6 to 10 V, and the treatment amount per pair of electrodes is 2 to 3 m. ³ / day, the wastewater treatment system according to <1>, <2>, wherein the sodium chloride (NaCl) concentration is 3000 to 5000 mg / L,
It is.

The wastewater treatment system of the present invention is
<1> The period of PVA wastewater treatment can be significantly shortened compared to the case of biodegradable treatment alone, shortened from about 20 days to 2 to 4 days.
<2> Operation and maintenance costs of PVA wastewater treatment equipment can be significantly reduced.
<3> Processing costs can be reduced more than incineration of PVA.
Etc. are obtained.

The wastewater treatment system of this invention is demonstrated using FIG.
In the wastewater treatment system of the present invention, salt is added to electrolyze wastewater containing several mass% of PVA. The wastewater from the bleaching process or liquid ammonia processing process and the electrolyzed wastewater are merged, and the combined wastewater is passed through a denitrification and activated sludge treatment process to quickly decompose pollutants such as PVA. .

The electrolyzer according to the present invention will be described with reference to FIG.
When electrolysis is performed by mixing sodium chloride in waste water 1, the dissolved chlorine ions are oxidized at the anode to produce chlorine ions, and some of the chlorine further reacts with water to produce hypochlorite ions. This chlorine and hypochlorous acid oxidatively decompose the COD component to produce a COD _Mn value reduced and biodegradable component.
The waste water 1 is introduced into the apparatus from the upper part in FIG. 2, and flows through the water channel 6 of the electrode part formed in an inverted U shape. By arranging the convex electrode 5a of the water channel 6 as an anode and the concave electrode 5b as a cathode, the waste water 1 flows between the electrodes, and flows between the electrodes to which voltage is applied. The salt put in is electrolyzed. Although the water channel 6 can be linear or curved, in order to control the time during which the wastewater 1 flows between the electrodes and is electrolyzed, and to increase the contact area between the wastewater 1 and the electrodes, It is preferable to change the flow direction of the waste water 1 as in FIG.

水質基準の指標の一つである水質汚濁負荷量はＣＯＤ（Chemical Oxygen Demmand：化学的酸素要求量）濃度と排水流量との積で定義されており，一日平均排水量が５０ｍ^３以上の事業所はその汚濁負荷量を測定するとともに，その規制値を遵守することを義務づけられている。 In order to determine the setting conditions of the electrolyzer for wastewater containing PVA, the conditions when the COD _Mn concentration of the PVA wastewater is 27,000 mg / L are as follows: voltage about 9V, current 500A, throughput 100L, electrode 1set, The experiment of Table 1 was conducted.

Water pollution load which is one indicator of the water quality standards COD (Chemical Oxygen Demmand: Chemical Oxygen Demand) concentration and is defined by the product of the wastewater flow, the average daily wastewater is 50 m ³ or more establishments Is obliged to measure its pollutant load and to comply with its regulation values.

From Table 1 above, when the COD _Mn concentration of the PVA waste water is about 27,000 mg / L, the electrolysis treatment conditions are voltage 9V, current 500A, treatment amount 100L / electrode 1set, NaCl concentration 3,000mg / L, electrolysis. It was found that 45 minutes was preferable in view of the processing time.

The electrolysis apparatus uses PVA wastewater 1 containing about 2% by mass of polyvinyl alcohol (PVA). The treatment time is 30 to 60 minutes, and the treatment time may be untreated in less than 30 minutes, and more than 60 minutes. And the efficiency becomes worse. The current and voltage are 400 to 500 A and 6 to 10 V. Under this condition, the processing capacity is lowered, and when this condition is exceeded, the water temperature rises and the life of the electrode is shortened. The treatment amount per electrode set is 2 to ³ m ³ / day, and the sodium chloride (NaCl) concentration is 3000 to 5000 mg / L. When the treatment amount is less than 3000 mg / L, the treatment capacity decreases and exceeds 5000 mg / L. Unused portion will increase and efficiency will decrease.

  For the electrode, carbon, iron, titanium, stainless steel or the like is used depending on the pollutant in the wastewater, and titanium is more preferably used because of corrosion resistance.

The PVA waste water 1 contains a suspension other than PVA, and this suspension adheres to fine bubbles generated by electrolysis and floats. The floated foam containing the suspension overflows from the electrolytic treatment tank and is sent to the next treatment.
About 100 ton / day of electrolyzed PVA wastewater is combined with about 2,900 ton / day of bleaching process and liquid ammonia processing wastewater, and about 3,000 ton / day of wastewater is combined with denitrification and activity in the next process. It is subjected to sludge treatment.

Next, the denitrification and activated sludge treatment apparatus will be described.
The waste water 2 from the bleaching process, liquid ammonia processing process, etc. and the electrolyzed PVA waste water 1 are removed from the waste water by decomposing nitrogen and ammonia by the denitrification and activated sludge treatment equipment after both waste waters are combined. At the same time, PVA and water pollutants are decomposed and precipitated by microorganisms (bacteria) and separated from water.
The denitrification and activated sludge treatment apparatus propagates various bacteria inside the treatment tank and decomposes the pollutants with the bacteria. What is necessary is just to select the optimal bacteria in decomposing | disassembling the contaminant in water.

  PVA waste water 1 containing about 2% by mass of PVA (about 100 ton / day) is passed through an electrolysis apparatus set to the following conditions, and waste water 2 (about 2,900 ton from the bleaching process or liquid ammonia processing process). The combined waste water 3 of about 3,000 ton / day was passed through the denitrification and activated sludge apparatus.

Various conditions of the electrolysis apparatus were set as follows.
Condition Wastewater treatment amount: 100 m ³ (ton) / day Treatment amount per electrode pair: 2-3 m ³ / day

Current / voltage: 500A / 9V / electrode 1 set NaCl concentration: 3,000mg / L

Table 2 shows the wastewater COD _Mn value after the electrolysis treatment and before the denitrification and activated sludge treatment and the treated water COD _Mn value after the denitrification and activated sludge treatment. In Table 2, the days when there is no PVA wastewater are not measured because the factory is closed every two days.

The COD _Mn of the waste water 3 was between 600 and 1,000 mg / L, but the COD _Mn of the treated water 4 after denitrification and activated sludge treatment was 80 mg / L or less. The treated water 4 is then subjected to treatment such as a pressure levitation device and pH adjustment, and is drained to the outside. Here, COD _Mn was set to 80 mg / L or less, but when draining from the factory, it is intended to clear the regulation daily average 20 mg / L or less and the maximum 25 mg / L or less.

Comparative Example For comparison with the examples, PVA wastewater 1 was treated with denitrification and activated sludge treatment equipment, combined with wastewater from bleaching and liquid ammonia processing processes, without electrolysis treatment, and mixed for 6 days. COD _Mn (mg / L) of waste water 3 and treated water 4 was measured. The measurement time was 10:00 every day, and the measurement method was based on JIS K 0102 17 (oxygen consumption by potassium permanganate at 100 ° C.).

表３から、電気分解処理されないＰＶＡ含有廃水が混合廃水３として現れたのが第２日目の測定時であり、これが処理水４として現れたのが第５日目のため、混合廃水３は脱窒素及び活性汚泥処理装置内において約３日間で処理され、その後廃水される。このことから、ＰＶＡは脱窒素及び活性汚泥処理装置内において約３日間で分解処理されていることが解る。

From Table 3, the PVA-containing wastewater that was not electrolyzed appeared as the mixed wastewater 3 at the time of measurement on the second day, and since this appeared as the treated water 4 on the fifth day, the mixed wastewater 3 was It is processed in a denitrification and activated sludge treatment apparatus in about 3 days, and then is drained. From this, it is understood that PVA is decomposed in about 3 days in the denitrification and activated sludge treatment apparatus.

Explanatory drawing of the waste water treatment system of this invention. Schematic explanatory drawing of the electrolyzer used for the waste water treatment system of this invention.

Explanation of symbols

1 PVA wastewater 2 Bleaching wastewater 3 Mixed wastewater 4 Treated water 5a Electrode a
5b Electrode b
6 waterway

Claims (3)

Salt water is mixed with the waste water containing polyvinyl alcohol and electrolyzed, and the waste water from the bleaching process of the cellulosic fiber structure and / or the liquid ammonia processing process is combined with the electrolyzed waste water, and the combined waste water is denitrogenated and activated. A wastewater treatment system characterized by sludge treatment. The electrolyzed waste water containing polyvinyl alcohol and the waste water from the bleaching step and / or the liquid ammonia processing step of the cellulosic fiber structure are combined at a ratio of 1:25 to 1:35 to perform denitrification and activated sludge treatment. The wastewater treatment system according to claim 1. In the electrolysis, the treatment conditions per electrode set are as follows: waste water COD _Mn is 20000 to 30000 mg / L, treatment time (retention) is 30 to 60 minutes, current is 400 to 500 A, voltage is 6 to 10 V, electrode 1 The wastewater treatment system according to claim 1, wherein the treatment amount per group is 2 to ³ m ³ / day, and the salt (NaCl) concentration is 3000 to 5000 mg / L.

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