JPS591117B2 - How to treat organic wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing organic substances, and more specifically, to a method for treating wastewater containing organic substances. This paper concerns a new treatment method.

In recent years, interest in environmental conservation has increased rapidly, and various legal regulations have been enacted.Although there have been significant advances in pollution prevention technology, there is still a need for an immediate technical and economic solution. There are many areas left unfinished.

In particular, regulations on the quality of water discharged into closed water bodies are becoming increasingly strict, and in particular, chemical oxygen demand (hereinafter abbreviated as CODMn) is normally 1.
0 ppm or less is now required, and combined with the introduction of total CODMn quantity regulations, an immediate solution is desired.

In the biological treatment method normally used to treat organic wastewater, although the biological oxygen demand (BOD5) decreases, CODMn is reduced by the biologically persistent substances in the wastewater or by the biological treatment. Polymer substances mainly consisting of mucopolysaccharide, humic acid, and fulvic acid, which are biometabolic waste substances generated during the process, accumulate in the treated water, which not only does not always give satisfactory results, but also causes the effluent water to become black or brown. Or, the current situation is that it is colored pale yellow.

For example, when looking at waste leached sewage, organic matter in the waste undergoes anaerobic or aerobic decomposition in the landfill layer for a long period of time after food waste or non-combustible materials are landfilled. Organic matter includes some easily biodegradable sugars, proteins, and fatty acids, as well as non-biodegradable substances or the result of biological metabolism.

Most of them are organic polymer substances such as mucopolysaccharide, humic acid, and fulvic acid, which are waste substances that are not excreted.They have a high organic pollution load and are colored black or brown, so biological treatment methods alone cannot treat them. It is not possible to purify to a high degree.

In addition, in the treatment of human waste, which requires advanced treatment, the organic substances contained in large amounts in human waste are usually treated using anaerobic digestion, aerobic digestion, or a combination of these methods, but biological While the organic treatment method decomposes and removes easily biodegradable organic substances, it is difficult to remove CODMn because it is a persistent biodegradable substance contained in human waste or a biometabolic waste substance that newly accumulates during the biological treatment process. The effect is low, and not only is the removal of bile pigments contained in human waste insufficient, but also the removal of chromaticity is difficult due to the chromaticity of biometabolic waste substances accumulated in the biological treatment process. It is less effective and has a brown color.

In addition, wastewater from the brewing and fermentation industries is already a result of fermentation and decomposition of raw organic substances (particularly grains such as soybeans, rice, and wheat) over a long period of time with microorganisms such as yeast and fungi during the production process. Since the wastewater discharged from the process is highly subject to microbial decomposition, biodegradable lower fatty acid saccharides, lower alcohols, proteins, and amino acids are expected to be removed by biological treatment methods, but they are no longer biometabolic waste. It contains a large amount of biodegradable substances and is usually brown to pale yellow in color.

As described above, biological treatment methods are usually used for wastewater treatment due to their low equipment costs and running costs as a treatment method for wastewater, human waste, sewage, and organic waste discharged from various industries. However, although it is an excellent method for decomposing and removing easily biodegradable organic substances, it is of course difficult to treat organic wastewater due to the treatment of non-biodegradable substances and the accumulation of waste substances produced as a result of biological metabolism. This method is not necessarily satisfactory as an advanced processing method.

Various treatment methods have been developed to treat wastewater containing biorefractory substances or biometabolic waste substances.
Typical of these methods include methods based on physical and chemical treatments such as activated carbon adsorption and ozone oxidation.

These methods require large-scale equipment and enormous running costs when treating wastewater with a high pollution load, and they also have problems concerning the essence of treatment technology.

In other words, in the activated carbon adsorption method, the biometabolic waste substances accumulated in biologically treated water are organic polymer compounds with molecular weights of several thousand to tens of thousands, such as glycoproteins, humic acids, and fulvic acids. Adsorption into pores and diffusion are extremely poor, and the organic matter removal effect is low.

Although the ozone treatment method oxidizes and decomposes organic polymer compounds in wastewater and partially reduces CODMn, its treatment effect is low, and the low molecular compounds generated during the oxidative decomposition process are converted into easily biodegradable substances. Both types have been found to have defects that increase BOD5, and have become a major problem in practice.

Under such circumstances, as a result of extensive research, the present inventors have discovered an excellent method that can highly remove suspended solids, organic substances, and chromatic components in organic wastewater, and have completed the present invention. reached.

In other words, the present invention provides a method for treating organic substances such as biorefractory substances and biometabolic waste substances and color components in organic wastewater using a simple method, low processing cost, and extremely high efficiency. It relates to a method that can be removed.

The organic wastewater to be treated by the present invention includes sewage leached from a waste landfill, treated water that has been subjected to biological treatment,
Sewage, human waste, and organic industrial wastewater are preferable, and if the organic wastewater contains biologically easily degradable various sugars, fatty acids, alcohols, and other water-soluble and organic substances, activated sludge, BOD5 using biological treatment methods such as watered p-beds, rotating disks or anaerobic digestion.
It is important to reduce the amount to 100 ppm or less as much as possible.
This pretreatment is necessary to greatly reduce the amount of chemicals used such as iron salt catalysts and hydrogen peroxide.

Specifically, the method of the present invention consists of the following steps.

(b) After adding a flocculant mainly containing ferric salt to organic wastewater and adjusting the pH to 3 to 5.5, suspended solids, organic matter, and color components are removed together with ferric hydroxide flocs. 1st step of coagulation and separation; (0) 2nd step of adding new iron salt and hydrogen peroxide to the water treated in the 1st step to oxidize and decompose organic matter and chromatic components; (c) oxidation-treated water as it is; Or, if unreacted hydrogen peroxide remains, add a reducing agent to decompose and remove the hydrogen peroxide, and at the same time add an alkali to neutralize to pH 4 or higher, and precipitate and separate iron salts as iron hydroxide flocs. The third step consists of:

In particular, the present invention is characterized by a processing method that includes a series of steps as shown from the first step to the third step, so embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, organic wastewater to be treated is led to a first mixing tank 1 through a pipe 8, and while being stirred, a predetermined amount of a flocculant 16 mainly composed of ferric salt is added, and a first pH adjustment is performed. In tank 2, the pH is adjusted to a predetermined value, and organic matter and chromaticity components in the wastewater coagulate together with iron hydroxide flocs.

The flocculant mainly composed of ferric salt used here can be ferric sulfate, ferric chloride, ferric nitrate or polyferrous sulfate, but usually ferric nitrate is used. 2
Iron is not used due to its impact on treated water.

Although the amount of coagulant, mainly ferric salt, added varies depending on the amount of organic matter contained in the wastewater, the treatment effect improves in proportion to the amount of ferric salt added. , is usually added in an amount of 10 ppm to 11,000 ppm in terms of iron atoms.

It is also possible to add acid or alkali to the first mixing tank 1 at the same time as the addition of the ferric salt to generate ferric hydroxide flocs, but the pH at the time of aggregation is preferably 3 to 5.5. Since it is an important component of the present invention to strictly maintain the pH within the range of 4 to 4.5, the first pH
An adjustment tank 2 is provided to adjust the pH.

For pH adjustment in the first pH adjustment tank 2, either acid or alkali is added depending on the nature of the waste water to maintain the optimum pH.

Biological treatment of organic wastewater is performed using sulfuric acid, hydrochloric acid, etc., if the pH does not drop to the optimum pH value of 3 to 5.5 even after adding strongly acidic ferric salts due to the pH buffering property of NH4+. A mineral acid is added, but since the pH usually drops to 4 or less with the addition of a ferric salt, an alkali is added to adjust the pH to an optimal value.

The alkali used for neutralization may be any strong alkali such as caustic soda, caustic potash, slaked lime, quicklime, etc., but slaked lime is used in consideration of cost, settling properties, etc.

The time required for neutralization is the same as for normal strong acid/strong alkali neutralization reactions, and is completed in about 1 to 20 minutes. It aggregates with persistent substances, biometabolic waste substances, and chromaticity components.

The pH adjustment liquid is led to the intermediate solid-liquid separation tank 3 through a pipe 10, where a flocculation aid 18 is added and the ferric hydroxide flocs which flocculate organic substances or color components by flocculation sedimentation or flocculation pressure flotation are produced. The sludge is separated and removed through a pipe 22, concentrated in a sludge concentration tank provided as needed, dehydrated, mixed with a neutralizing agent to make it neutral, and then disposed of.

The treated water separated into solid and liquid in the first step passes through the pipe 11 and passes through the second
While being led to the second mixing tank 4 of the process and being stirred, iron salt 19 as an oxidation catalyst and hydrogen peroxide 20 as an oxidizing agent are newly added.
Add.

The iron salts added as oxidation catalysts include Fe(If) ions such as ferrous sulfate salts and ferrous chloride salts, and Fe(III) ions such as ferric sulfate salts, ferric chloride salts, and polyferrous sulfate salts. Although nitrates such as ferrous nitrate and ferric nitrate are expected to have sufficient oxidation catalytic activity, they are not used except in special cases due to problems such as eutrophication. First, ferrous sulfate is usually used because it has high oxidation catalytic ability and is inexpensive.

Iron salt, which is an oxidation catalyst, reacts with hydrogen peroxide in waste water to generate hydroxyl radicals with strong oxidizing properties and is hydrolyzed, resulting in the optimum reaction pH of 4 or less, but it can be adjusted to the optimum reaction pH as necessary. To do this, pH adjuster 17 is added.

The amount of iron salt added as an oxidation catalyst is determined by the type of oxidizable substance, the amount of hydrogen peroxide injected, the reaction time, and the solid-liquid separation method after the oxidation reaction. The amount of addition of iron becomes effective from a few ppm, and the larger the amount, the better the effect of removing organic substances and chromaticity components in wastewater becomes.However, on the other hand, the amount of sludge generated increases, so it is usually It is added in a range of 5 ppm to 11,000 ppm in terms of conversion.

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. It is added in an amount of 0.1 to 2 times the amount of oxygen.

The mixed liquid is led to the oxidation reaction tank 5 through the pipe 12, where an oxidation reaction is carried out.

The oxidation reaction tank is mechanically or air agitated.

The oxidation reaction time in the reaction tank 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.

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.
The reaction temperature is not particularly limited, and the reaction time is sufficient for the reaction in the second mixing tank in the case of wastewater where the reaction is completed in a short time, such as waste water leached from a physical wastewater tank. However, when an oxidation reaction tank is installed, the reaction is usually completed within a residence time of 5 minutes to 24 hours at room temperature.

Next, the oxidation reaction treated water is led to the neutralization tank 6 through a pipe 13 while being stirred, and an alkaline agent 17' or a reducing agent 21 is added thereto as required.

The alkaline agent 17' can be anything that dissolves in water and exhibits alkalinity, such as caustic soda, caustic potash, slaked lime, or quicklime.
Alternatively, Fe (if loss ions are mixed in, iron ions are precipitated as iron hydroxide flocs at pH 9 or higher, and at the same time, organic matter in the waste water is also coagulated and separated.

゛ Also, if unreacted hydrogen peroxide remains in the oxidation reaction, the reducing agent will reduce CODMn during CODMn measurement.
Fe(I) ions of ferrous salts, ferrous sulfate, ferrous chloride, ferrous sulfate, or sodium sulfite, to increase the apparent CODMn value.
A reducing agent such as sodium thiosulfate is added to decompose residual unreacted hydrogen peroxide, but normally even if an excess of reducing agent is injected, Fe(
A ferrous salt that is oxidized to 110 and separated and removed as ferrous hydroxide at pH 9 or higher is used.

The neutralized water passes through a pipe 14, and a flocculation aid 18 is usually added to the final solid-liquid separation tank 7, where it is separated into solid-liquid by sedimentation or flotation, and separated into iron hydroxide flocs and treated water. The treated water is then discharged through the pipe 15 after readjusting the pH if necessary, or is sent to another treatment process for the purpose of higher-level treatment.

On the other hand, the iron hydroxide separated in the final solid-liquid separation tank is carried out through pipe 23 and disposed of.

As described above, the present invention provides an industrial treatment method for the advanced treatment of wastewater containing organic substances such as biorefractory substances, biometabolic waste substances, and color components, which have been extremely difficult to treat in the past. 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 Waste physical condition FeCA3 was added as a ferric salt to biologically nitrified and denitrified treated water of leachate wastewater at 600 p in terms of iron atoms.
pm was added, the pH was adjusted to 4 with caustic soda, and the organic matter and chromaticity components in the leached wastewater were coagulated and separated together with ferric hydroxide flocs. e S 04 in terms of iron atoms is 600
After adding 50 ppm of hydrogen peroxide in terms of effective oxygen, adjust the pH of the solution to 3 (carry out oxidation reaction treatment for 15 minutes while stirring gently, then add caustic soda to the oxidation reaction treated water to maintain pH 7). Table 1 shows the results of analyzing the quality of the water treated in the third step, in which ferrous iron was oxidized to ferric hydroxide by air stirring for 30 minutes, and the ferric hydroxide flocs were separated by sedimentation.

Example 2 FeSO4 as an oxidation catalyst in the second step of Example 1
The results shown in Table 2 were obtained by using the same method and conditions as in Example 1, except that FeCl3 was used instead of FeCl3.

Example 3 Instead of the biologically nitrified and denitrified treated water of the waste physical leachate wastewater of Example 1, the activated sludge treated water of the frozen ground digestion tank desorbed liquid was treated in the same manner as in Example 1 with FeCl3 (100%
The 1st step treated water becomes coagulated water with 100 ppm of hydrogen peroxide (30 ppmash) and Fe504 (100 ppmas Fe) as an iron salt catalyst is added.
Table 3 shows the quality of the water treated in the 3rd step after the oxidation reaction.
Shown below.

Example 4 Biologically treated water of base human waste treatment plant (COD112mV/11
FeSO4 and FeSO4 as iron salt catalysts were added to the first step treated water, which was subjected to coagulation and precipitation after adjusting the pH to 4 with caustic soda and coagulating and precipitating. Hydrogen peroxide was added and an oxidation reaction was carried out for 10 minutes with gentle stirring, then caustic soda was added to adjust the pH to 7, and the precipitated ferric hydroxide was separated by sedimentation in the third step. Figure 2 shows the measurement results of water COD.

At the same time, as a comparative example, the measurement results of the amount of FeCl3 flocculant added and the COD of the treated water when the coagulation-sedimentation treatment at pH 4 consisting of only the first step of the present invention was performed on the same human waste biologically treated water were also shown. Shown in Figure 2.

In addition, the first method of the present invention targets the same urine biologically treated water.
Without performing any process, FeSO4 and hydrogen peroxide were directly injected, the pH was adjusted to 3 with sulfuric acid, the oxidation reaction was carried out for 10 minutes, and the pH was adjusted to 7 by adding caustic soda to the oxidation reaction treated water.
FIG. 2 also shows the COD measurement results of the treated water that was adjusted to 100% and subjected to only the second and third steps in which ferric hydroxide flocs were separated by sedimentation.

As a result, compared to the treatment using only the first step and the treatment using only the second and third steps, the treatment according to the method of the present invention not only reduces the amount of chemicals added, but also significantly improves the treatment limit value of COD. Ta.

For example, Table 3 shows the amount of chemical injection and the amount of sludge generated required to bring the COD of treated water to 25 .mu./l.

As described above, in the method of the present invention, the amount of Fe salt added is 1/3 and the amount of sludge generated is 172.6 compared to when only the coagulation treatment in the first step is performed, and only in the second and third steps. Compared to the treatment method, the amount of Fe salt added is 1/1.6,
The amount of H20□ added was 1/2.5, and the amount of sludge generated was 1/1.7.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the process of the present invention, Figure 2 is the COD of treated water
and H20□ addition amount or FeCl3 or FeS
04 is a diagram showing the relationship with the amount added. 1...1st mixing tank, 2nd...1st pH
Adjustment tank, 3... Intermediate solid-liquid separation tank, 4...
・Second mixing tank, 5... Oxidation reaction tank, 6...
...Second pH adjustment tank, 7...Final solid-liquid separation tank,
8-15...Tube, 16...Flocculant, 1
7...pH adjuster, 17'...alkaline agent, 18...coagulation aid, 19...iron salt, 20... Hydrogen peroxide, 21...Reducing agent, 22-23...Tube.

Claims (1)

[Claims] 1 In a method for treating organic wastewater, a flocculant mainly containing ferric salt is added to organic wastewater to adjust the pH to 3 to 5.5.
Iron salt and hydrogen peroxide are newly added to the treated water of the 1st step and 9th step, in which suspended solids, organic substances, and color components are coagulated and separated together with ferric hydroxide flocs. A series of steps consisting of a second step of oxidatively decomposing organic substances and color components, and a third step of adding an alkali to the oxidized water and precipitating the iron salt catalyst as iron hydroxide flocs at pH 4 or higher and coagulating and separating them. A method for treating organic wastewater, comprising: