JPS6216716B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for neutralizing iron salts used as catalysts and recovering and reusing precipitated ferric hydroxide during the treatment of organic wastewater. The present invention relates to a method for treating organic wastewater in which organic matter remaining in biologically treated water is adsorbed and removed using the ferric hydroxide sludge recovered as described above. Traditionally, biological treatment methods have been widely used to treat wastewater containing organic substances because of their simple equipment and low running costs. Regulations are becoming increasingly strict in order to prevent eutrophication of closed water areas such as inner bays and to protect the environment. In particular, biological treatment removes easily biodegradable substances from wastewater, but it also removes biodegradable substances or biometabolic waste substances produced during the biological treatment process, such as humic acid and fulvic acid. Acids accumulate and reduce the chemical oxygen demand (below) in the wastewater.
COD _Mo ) is kept at a high level.
Methods have been developed to lower COD _Mo. However, each method has advantages and disadvantages,
There is a need for a more excellent treatment method, and the present inventors have completed the present invention as a result of extensive research. The present invention involves the first step of adding ferric hydroxide to biologically treated water of organic wastewater to adsorb organic matter, and then coagulating and separating it together with suspended solids. By adding an iron salt catalyst along with hydrogen,
A second step of oxidatively decomposing the organic matter still contained in the treated water, and a third step of adding an alkali to the treated water of the second step to precipitate and separate the iron salt catalyst as ferric hydroxide sludge. The gist of the present invention is a method for treating organic wastewater, characterized in that ferric hydroxide sludge recovered from the third step is used as an adsorbent in the first step at a pH of 3 or higher. The present invention will be explained in detail below. The technology for reducing COD _Mo in biologically treated water generally uses acid salts of iron and aluminum as flocculants to coagulate and separate organic matter along with the metal hydroxides generated by neutralization. ing. However, since metal acid salts and neutralizing agents are used as chemicals, when used for large amounts of organic wastewater, not only are running costs problematic, but the treatment performance is not always satisfactory. The present inventors added ferric hydroxide to biologically treated water of organic wastewater to adsorb organic matter, and then added ferric hydroxide to the treated water in the first step, in which the organic matter was coagulated and separated along with suspended solids. A second step in which an iron salt catalyst is added together with hydrogen peroxide to oxidize and decompose organic matter still contained in the treated water, an alkali is added to the treated water in the second step, and the iron salt catalyst is converted into ferric hydroxide. In a method for treating organic wastewater consisting of a third step of precipitation and separation as sludge, the ferric hydroxide sludge recovered in the third step is strongly oxidized by a catalyst using hydrogen peroxide, which has a high redox potential. Therefore, it was confirmed that it is harmless as it does not contain any partial oxides of organic substances, and has the property of strongly adsorbing organic substances in the acidic range of PH3 or higher. The ferric hydroxide sludge with excellent adsorption capacity as described above is produced from the acidic iron salt used as a catalyst in the second step, so there is no need to use expensive ferric salt as an adsorbent; Industrial wastes such as ferrous sulfate and ferrous chloride, which are discharged in large quantities from the iron and steel industry and titanium manufacturing industry, can be used as acidic iron salts, and are extremely effective in preventing pollution. There is a huge amount to gain from this. A feature of the present invention is that the ferric hydroxide sludge precipitated and separated in the third step is recovered and reused as an adsorbent in the first step. In the third step, the collected ferric hydroxide sludge is used to adsorb organic matter in the biologically treated water, and then a coagulation aid is added to the coagulated and separated first step treated water, and in the second step Hydrogen peroxide is added at the same time as new fresh iron salt is added as an oxidation catalyst with stirring. The iron oxide salt added as an oxidation catalyst in the second step is Fe such as ferrous sulfate and ferrous chloride.
Fe such as () ions, ferric sulfate, ferric chloride, etc.
(2) A compound containing ions or an aqueous solution thereof, ferrous sulfate is used because of its oxidation catalytic activity and low price. Acidic iron salts react with hydrogen peroxide to generate hydroxyl radials with strong oxidizing properties, and are hydrolyzed to the optimum reaction pH of 4 or less, but if necessary, the reaction pH can be adjusted to the optimum reaction pH. , a PH regulator is added, and the reaction is allowed to proceed. The amount of acidic iron salt added as an oxidation catalyst can be determined depending on the type and concentration of the oxidizable substance, the amount of hydrogen peroxide injected, and the reaction time.
Usually, it is determined according to the effective amount of iron that is reused as an adsorbent in the first step, and as in the first step, it is added in the range of 10 ppm to 5000 ppm in terms of iron atoms. In addition, the amount of hydrogen peroxide added is determined depending on the type and concentration of oxidizable substances in the wastewater, the target quality of the treated water, etc., although there are no particular limitations _.
0.1 in terms of effective oxygen in hydrogen peroxide
It is added in a range of 2 to 2 times. The oxidation reaction time varies depending on the type and concentration of the oxidizable substance in the wastewater, the reaction temperature, the amount of iron salt catalyst, and the amount of hydrogen peroxide, but it is usually 5 minutes to 5 minutes at room temperature.
It will be completed in 24 hours. The higher the reaction temperature, the more quickly and efficiently the reaction tends to occur, but the purpose of the present invention can be sufficiently achieved even at room temperature, so it is not particularly limited. When precipitating and separating the iron salt catalyst in the oxidation reaction treatment water, if the iron salt catalyst exists in the form of Fe() ions, it will generate ferric hydroxide flocs at pH 4 or above, so this is separated and Used as an organic adsorbent in processes. However, if the iron salt catalyst in the oxidation reaction treatment water exists in the form of unreacted Fe() ions, while maintaining the pH at 7 or higher,
Aeration is performed to change Fe() ions to Fe() ions, which are precipitated and separated as ferric hydroxide, which is used as an adsorbent in the first step. If unreacted hydrogen peroxide remains in _the oxidation reaction treated water, it will be
Ferrous salts, i.e. ferrous sulfate, are detected as COD _Mo values and increase the apparent COD _Mo value.
Fe() ions such as ferrous chloride are added to reduce and remove hydrogen peroxide. At this time, the Fe() ions are oxidized to produce ferric hydroxide, which can be reused as an organic matter adsorbent in the first step together with the ferric hydroxide produced from the iron salt catalyst. The alkaline agent required for neutralization in the third step may be caustic soda, caustic potash, or slaked lime, which dissolve in water and exhibit alkalinity, but slaked lime is used in consideration of sedimentation properties, cost, etc. The neutralized treated water is separated into solid-liquid by precipitation or flotation by adding a coagulation aid, and separated into ferric hydroxide flocs and treated water, and the treated water is either discharged or After PH adjustment, it is sent to other processes for more advanced treatment. On the other hand, the coagulated and separated ferric hydroxide is sent to the first step after its concentration is adjusted in a sludge concentration tank and used as an adsorbent. In the first step, biologically treated water from sewage, human waste, waste landfill leachate, and organic industrial wastewater containing COD _Mo , such as persistent biodegradable substances and biometabolic waste materials, is collected in the third step. The resulting ferric hydroxide is added as an adsorbent, the pH is adjusted to 3 or more, and organic substances are adsorbed and removed while stirring. The amount of recovered ferric hydroxide sludge used to adsorb organic matter in biologically treated water is proportional to the amount of recovered ferric hydroxide sludge, although the amount added varies depending on the type and concentration of organic matter contained in the wastewater. do,
The treatment effect is good, but usually in terms of iron atoms.
Added from 10ppm to 5000ppm. The PH adjuster for adjusting the PH to acidic in the first step may be any mineral acid exhibiting strong acidity, but sulfuric acid or hydrochloric acid is usually used in consideration of eutrophication of the treated water. The reason for maintaining the pH during adsorption at an acidic level in the first step is that it varies depending on the type of adsorbed substance, but biologically treated water of organic wastewater mainly contains biorefractory substances and biometabolic waste substances. This is because organic polymeric substances having a molecular weight of several thousand to tens of thousands can be adsorbed well at a pH of 3 or higher, preferably a pH of 4 to 5. The time required for adsorption varies depending on the type of substance to be adsorbed and PH conditions, but adsorption is completed in 5 to 300 minutes. The treated water adsorbed by the ferric hydroxide sludge is removed together with suspended solids in the wastewater by coagulation sedimentation or condensation pressurized flotation with the addition of a condensation aid. The sludge separated and removed from the treated water is dehydrated and neutralized before being disposed of, while the treated water is sent to the second process. As described above, in the present invention, in the first step,
Biologically treated organic wastewater The ferric hydroxide sludge recovered in the third process is effectively used to remove biologically persistent substances and biologically metabolic waste substances that are extremely difficult to treat in the past. Since the amount of organic matter can be greatly reduced by adsorption and removal, the amount of hydrogen peroxide added during oxidative decomposition in the presence of an iron salt catalyst in the second step is greatly reduced. enable. In addition, since ferrous iron, which is discharged in large quantities as industrial waste, can be effectively used as an iron salt catalyst, the present invention can be applied to an industrial wastewater treatment method that will require increasingly sophisticated treatment in the future. It is of extremely high value. Next, the method of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Example 1 According to the present invention, the ferric hydroxide sludge separated by sedimentation in the third step was changed to 100 to 4000 ppm in terms of iron atoms for the biologically nitrified and denitrified treated water of waste landfill leachate sewage. and add
Organic substances are adsorbed and removed by stirring for 60 minutes.
Furthermore, a flocculation aid was added and the quality of the supernatant water after static sedimentation was measured and the results are shown in FIG. At this time, the pH at the time of aggregation was adjusted to PH7 with caustic soda. Furthermore, in the first step, 600 ppm of ferric hydroxide sludge from the third step was added in terms of iron atoms to adsorb and coagulate the treated water, and in the second step, ferrous sulfate was added as an iron salt catalyst to the treated water. in
Table 1 shows the quality of the treated water when oxidative decomposition treatment was carried out by adding 600 ppm and 50 ppm of hydrogen peroxide (effective oxygen equivalent) and stirring for 3 hours at acidic pH.

[Table] Example 2 Ferric hydroxide sludge, which was sedimented and separated in the third step according to the present invention, was added to biologically nitrified and denitrified treated water of waste landfill leachate to a concentration of 100 to 4000 ppm in terms of iron atoms. Figure 2 shows the results of measuring the water quality of the supernatant water after adding a different amount of water, adsorbing and removing organic substances by stirring for 60 minutes, adding a coagulation aid, and allowing the mixture to settle. Note that the pH at the time of aggregation was adjusted to 4 using sulfuric acid. Furthermore, in the first step, the treated water, which was adsorbed and coagulated by adding recovered ferric hydroxide sludge (iron addition amount 600 ppm (iron atom equivalent)) from the third step, is treated with sulfuric acid as an iron salt catalyst in the second step. Table 2 shows the quality of the treated water when oxidative decomposition treatment was carried out by adding 600 ppm of iron as iron atoms and 50 ppm of hydrogen peroxide (in terms of available oxygen) and stirring for 3 hours at acidic pH.

【table】 [Brief explanation of the drawing]

FIG. 1 is a graph showing the quality of supernatant water in the first step of Example 1, and FIG. 2 is a graph showing the quality of supernatant water in the first step of Example 2.

Claims (1)

[Claims] 1 The first step is to add ferric hydroxide to the biologically treated water of organic wastewater to adsorb organic matter, and then coagulate and separate it along with the suspended solids. A second step in which a salt catalyst is added to oxidize and decompose organic substances still contained in the treated water, an alkali is added to the treated water in the second step, and the iron salt catalyst is precipitated and separated as ferric hydroxide sludge. A method for treating organic wastewater comprising a third step, characterized in that ferric hydroxide sludge recovered from the third step is used as an adsorbent in the first step at a pH of 3 or higher.