JPS6235836B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating a suspension containing sulfate ions, and in particular to a method for treating an organic suspension. Cationic organic polymer flocculants are used in the flocculation treatment of suspensions, especially organic suspensions, but if the suspension contains sulfate ions, certain cationic organic polymer flocculants are used. With polymer flocculants,
The flocs produced become smaller and the flocculation effect worsens. Conventionally, the cause of this problem is unknown, and countermeasures have been taken by simply treating sludge with poor coagulability by increasing the amount of flocculant added, or by combining treatment with other flocculants. This invention was made based on the new knowledge that sulfate ions are the cause of poor flocculation of such suspensions.It is possible to efficiently perform flocculation treatment by adding a certain type of compound. The purpose of this study is to propose a method for processing suspensions that can be used. This invention applies chitosan, polyethyleneimine, polyvinylpyridine, a condensate of dicyandiamide and formalin, a condensate of melamine and formalin, a co-condensate of melamine, urea and formalin, and aniline to a suspension containing sulfate ions of 50 mg/l or more. In a method of flocculating by adding a cationic flocculant selected from condensates of for sulfate ion
This is a suspension aggregation treatment method characterized by adding 0.2 equivalent or more and aggregating the suspension. The suspension to which the flocculation treatment method of the present invention is applied includes all types of suspensions, including what is normally called sludge, but particularly organic suspensions. Examples of organic suspensions include:
Sewage, sewage precipitated sludge, human waste, anaerobic or aerobic digested sludge of human waste, human waste septic tank sludge, organic industrial wastewater (e.g. food factory wastewater, seafood processing wastewater, slaughterhouse wastewater, etc.), various types of sewage including the above wastewater. This includes surplus sludge from activated sludge treatment. Further, examples of other suspensions include, but are not limited to, coagulated sedimentation sludge of paper pulp wastewater. If such sludge contains sulfate ions of 50 ml/l or more, the flocculation effect will worsen, but sulfate ions are originally contained in suspensions such as chemical factory wastewater, paper and pulp factory wastewater, etc. Although there may be cases where
It may be included by adding it later. Examples of cases where the sludge is added later include flocculation treatment using an inorganic flocculant containing sulfate ions such as sulfuric acid band, resulting in flocculated sedimentation sludge, or such flocculation sedimentation sludge mixed with the above-mentioned sludge. The mixed sludge etc. that are collected will be treated. The cationic flocculant used in the present invention is
Chitosan, polyethyleneimine, polyvinylpyridine, condensate of dicyandiamide and formalin,
These flocculants are a condensate of melamine and formalin, a co-condensate of melamine, urea and formalin, and a condensate of aniline and formalin.
Since the presence of sulfate ions in the suspension reduces the flocculation effect, in the present invention the alkali earth metal compound is added to perform flocculation. The alkaline earth metal compounds used in the present invention are calcium, magnesium and barium salts other than sulfates and hydroxides, and examples of the salts include chlorides and nitrates. The flocculation method is to add the alkaline earth metal compound to a suspension containing sulfate ions before adding the flocculant, stir it, and then add the flocculant, or add the alkaline earth metal compound to the flocculant. Add at the same time as the flocculant and stir to perform flocculation. In the latter case, the alkaline earth metal compound and the flocculant may be added as a mixture or may be added separately. The alkaline earth metal compound and flocculant may be used alone or in combination of several types. The cationic flocculant is usually added as a 0.05 to 0.5 wt% aqueous solution. The alkaline earth metal compound is added as an aqueous solution or suspension. The amount of flocculant added may be the same as in the case where sulfate ions are not included, and the flocculation stirring conditions may be the same as those for normal flocculation treatment. The amount of the alkaline earth metal compound added is 0.2 equivalent or more, preferably 1 equivalent or more relative to the amount of sulfate ions contained. Further, after adding the alkaline earth metal compound, it is desirable to perform stirring and mixing. As a method for flocculating a suspension, in addition to a flocculating treatment using only the cationic flocculant, a combination treatment with other flocculants is possible. In addition to combination treatment with other cationic flocculants, combination treatment with anionic flocculants is also possible. For combination treatments with anionic flocculants, a flocculant with an opposite charge to that of the suspension is added to neutralize the charge, and then another flocculant with an opposite charge is added. A method in which the aggregation is carried out is preferred. For example, in the case of a suspension having an anionic charge such as an organic suspension, the cationic flocculant is added first, and then the anionic flocculant is added to perform flocculation. In the case of a suspension having a cationic charge such as flocculated sludge caused by an agent, an anionic flocculant is added first, and then the cationic flocculant is added to perform flocculation. In either case, the metal compound is added simultaneously with or prior to the addition of the cationic flocculant. In addition, in the case of such a combination treatment, it is preferable to use a natural polymer or its derivative as one flocculant, and after adding the first flocculant, strong stirring is performed, and then the second flocculant is added. After that, it is preferable to stir the mixture to form a floc.
Strong stirring is such strong stirring that no flocs are observed or the diameter of the flocs is 2 mm or less.The means for achieving this is not limited, but in the case of a stirring tank equipped with an agitator, as a guideline, The circumferential speed is 1 to 5 m/sec (normal stirring is 0.1 to 0.5
m/sec). The flocs produced by the above coagulation are separated by solid-liquid separation means such as precipitation and filtration, and are treated like sludge.
If the SS concentration is high, it can be dehydrated as is or after removing separated water using a dehydrator. When performing flocculation treatment by adding the above-mentioned cationic flocculant to a suspension, if the suspension contains sulfate ions, the flocs will be smaller and the flocculation effect will be worse than when the suspension does not contain sulfate ions. do. In such a case, if the alkaline earth metal compound is added to perform flocculation, the flocs will become larger and the sedimentation rate and filtration rate will increase. The dehydration effect is improved, such as the moisture content of the dehydrated cake being reduced. The flocculation effect when an alkaline earth metal compound is added is almost equivalent to that when sulfate ions are not present. The results of flocculation treatment by adding various sulfates to suspensions show that, as shown in the examples below, the degree of deterioration varies depending on the type of salt, and the reason for the deterioration of the flocculation effect due to sulfate ions is clear. isn't it. Furthermore, the amount of alkaline earth metal compound required to completely recover the flocculation effect is approximately 20% equivalent of sulfate ion in the case of calcium chloride and magnesium chloride, and approximately the same amount in the case of barium chloride. , although the reason for the increased agglomeration effect is not clear,
In either case, the effect appears within the range of solubility of the sulfate of the added metal, so it is clear that the effect is not solely due to the removal of sulfate ions as insoluble precipitates such as calcium sulfate. Next, experimental examples and examples of the present invention will be explained. The flocculants used in each experimental example and example are shown in Table 1.

[Table] Experimental example Sewage mixed sludge (PH6.0, SS: 1.93%, SO ₄ ^2- : 28
mg/, electrical conductivity: 2500 μS/cm) with Na ₂ SO ₄
The SO ₄ ^2- concentration of the sludge was changed by adding
Add and mix with a hand mixer (1 beater)
The floc was generated by stirring at 250 rpm (0.5 m/sec) for 15 seconds, and the floc was poured onto a Buchner funnel lined with a 100-mesh nylon filter cloth, and the amount of filtrate was measured. The results are shown in the graphs in the drawing. From the above results, sulfate ions in sludge are 50mg/
It can be seen that when the amount exceeds this value, the amount of filtrate deteriorates rapidly. _Example 1 Sewage mixed raw sludge (PH5.8, SS: 2.70%, ^SO2-4 :
23mg/, electrical conductivity: 1980μS/cm) 200ml
After adding the sulfate, stirring and mixing, adding the metal compound and stirring and mixing, then Table-1
After adding the flocculant and stirring strongly for 30 seconds at 500 rpm (peripheral speed 1 m/sec) with a hand mixer (2 beaters), add the flocculant and stirring at 250 rpm (0.5 m/sec) with a hand mixer (1 beater).
The flocs were flocculated by stirring for 15 seconds, and the diameter of the flocs produced was measured.The flocs were poured onto a Buchner funnel lined with a 100-mesh nylon filter cloth to measure the amount of filtrated water. The results are shown in Table-2. For comparison, the results are also shown when no alkaline earth metal compound is added, when common salt is added in place of sulfate, and when neither sulfate nor alkaline earth metal compound is added.

[Table] Example 2 Excess sludge in activated sludge treatment of food factory wastewater (PH6.7, SS: 1.7%, ^SO2-4 : _17mg /, VSS: 80
% (vs. SS), electrical conductivity: 1980μS/cm) 200
ml, add 0.05N of sodium sulfate and stir.
After mixing, add the alkaline earth metal compound, stir and mix, then add the flocculant at 1.1% (vs.
SS) was added, and the usual stirring of Example 1 was performed to perform the agglomeration treatment. The generated flocs were filtered in the same manner as in Example 1, the amount of filtrate was measured after 20 seconds, and 15 g of the sludge after filtration was collected and sandwiched between a belt press dehydrator filter cloth (polyester herringbone weave) and a sponge. The water content of the dehydrated cake after being squeezed for 2 minutes at a pressure of 0.5 Kg/cm ² was measured. The results are shown in Table-3. For comparison, the results are also shown when no alkaline earth metal compound was added and when neither sulfate nor alkaline earth metal compound was added.

[Table] Additive-free Example 3 Mixed sludge (PH6.2, SS: 2.1%, VSS:
72% (vs. SS), electrical conductivity: 2350μS/cm,
Take 200 ml of SO ^2- ₄ :159 mg/), add calcium chloride (CaCl _{2.2H 2} O), stir and mix, add a flocculant, stir normally, and filter and as in Example 2. After 20 seconds of dehydration, the amount of filtrate and the water content of the dehydrated cake were measured. Display the results.
4.

[Table] Example 4 Mixed sludge (PH7.4, SS: 1.38%, VSS:
67.6% (vs. SS), electrical conductivity: 2830μS/cm,
Take 200 ml of SO ^2-4 : 181 _mg /), add calcium chloride (CaCl _{2.2H 2} O) and mix with stirring, then add a flocculant and perform strong stirring as in Example 1 to further flocculate. After 20 seconds, the amount of filtrate and the water content of the dehydrated cake were measured. The results are shown in Table-5. The table also shows the case where only flocculant is added without adding calcium chloride.
Also listed in 5.

[Table] Example 5 Suspension in aeration tank in activated sludge treatment of chemical factory wastewater (PH6.2, SS: 4200mg/, VSS: 67%
_{(vs. SS) Electrical conductivity: 5650 μS/cm, SO 2-4} ^: 340
mg/) in a test tube with a stopper, add magnesium chloride (MgCI ₂ 6H ₂ O) and a flocculant, stir it upside down 5 times, let it stand, and after 1 minute collect the sludge volume. It was measured. The results are shown in Table-6.

[Table] From the above results, flocculation with the addition of alkaline earth metal compounds increases the floc diameter and improves sedimentation, filtration and dewatering properties, compared to the case without sulfate ions. It can be seen that the same agglomeration effect is exhibited. As described above, according to the present invention, the flocculation effect can be improved during flocculation treatment of a suspension containing sulfate ions, and treatments such as sedimentation, filtration, and dehydration can be efficiently performed.

[Brief explanation of the drawing]

The drawing is a graph showing the results of experimental examples.

Claims (1)

[Claims] 1. Chitosan, polyethyleneimine, polyvinylpyridine, a condensate of dicyandiamide and formalin, a condensate of melamine and formalin, a condensate of melamine, urea and formalin, a suspension containing 50 mg/l or more of sulfate ions, In a method of flocculating by adding a cationic flocculant selected from condensates and condensates of aniline and formalin, an alkali selected from calcium, magnesium and barium salts (excluding sulfates) and hydroxides is added to the suspension. A method for flocculating a suspension, which comprises adding an earth metal compound in an amount of 0.2 equivalent or more to sulfate ions and flocculating the compound. 2. The method for flocculating a suspension according to claim 1, wherein the suspension is a mixed sludge of surplus sludge generated when sewage is subjected to biological treatment and flocculated sludge using an inorganic flocculant containing sulfate ions. 3. The method for flocculating a suspension according to claim 1 or 2, wherein the alkaline earth metal compound is added prior to adding the cationic flocculant. 4. The method for flocculating a suspension according to claim 1 or 2, wherein the alkaline earth metal compound is added at the same time as the cationic flocculant.