JPH0137199B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for dewatering organic sludge by adding a flocculant to it. A cationic polymer flocculant is added to organic sludge such as sewage treatment sludge or human waste treatment sludge and stirred, then an anionic polymer flocculant is added and stirred to form flocs and dewatered. A method has been proposed. In this method, if a natural polymer, especially chitosan, is used as a cationic polymer flocculant, the moisture content of the dehydrated cake can be dramatically reduced, but since chitosan is produced from crab shells, etc. There were concerns about stable supply, and there was a desire for a synthetic cationic polymer flocculant to replace chitosan. In response to such demands, the present invention aims to provide a method for dewatering sludge using a synthetic cationic polymer flocculant instead of chitosan. In the present invention, a cationic polymer flocculant is added to organic sludge and a first stirring is performed, and an anionic polymer flocculant is then added to the organic sludge and a second stirring is performed,
In a method for dehydrating the generated flocs, a Hofmann decomposition product of an acrylamide polymer is used as a cationic polymer flocculant, and the first stirring is performed until flocs are not generated, or even if flocs are generated, the floc diameter is 2 mm. This method of dewatering organic sludge is characterized in that strong stirring is performed as follows, and the second stirring is normal stirring that is weaker than the first stirring. Organic sludge in the present invention includes anaerobic digested sludge of human waste, aerobic digested sludge of human waste, human waste septic tank sludge, human waste digested desorbed liquid, surplus sludge in activated sludge treatment of sewage and other various sewage, and initial sedimentation of sewage. These include pond sludge, human waste, flocculated sludge generated during tertiary treatment of sewage, etc. These sludges can be treated alone or in combination. In the present invention, a Hofmann decomposition product of an acrylamide polymer is used as a cationic polymer flocculant that is first added to such organic sludge. The acrylamide polymer may be polyacrylamide or polymethacrylamide, or may be a copolymer of acrylamide or methacrylamide with another monomer copolymerizable. Acrylamide-based polymers include acrylamide monomer alone, methacrylamide monomer alone, or other monomers copolymerizable with these monomers, such as acrylonitrile, acrylic acid methyl ester, acrylic acid ethyl ester, methacrylic acid methyl ester, methacryl A mixture with acid ethyl ester, etc.
Dissolved in water or organic solvents such as methanol,
Obtained by adding a polymerization initiator and polymerizing. As a polymerization initiator, hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide,
Azobisisobutyronitrile and other commonly used compounds can be used alone or in combination. Alternatively, a lidox-based polymerization initiator may be used in combination with a reducing agent. Hoffman decomposition products of acrylamide polymers are
Acrylamide polymer is made into an aqueous solution, and hypohalites such as sodium hypochlorite, sodium hypobromite, and calcium hypochlorite are applied in the coexistence of alkali such as sodium hydroxide and potassium hydroxide. can get. The amount of Hofmann decomposed acrylamide polymer added varies depending on the properties of the sludge (PH, SS, VSS, electrical conductivity, etc.), but is generally 0.5 to 6 wt%.
(vs. SS) is sufficient. First, a Hofmann decomposition product of an acrylamide polymer is added to the organic sludge as a cationic polymer flocculant, and a first stirring is performed to perform primary flocculation.
The first stirring allows the sludge and flocculant to sufficiently react,
Since the purpose is to neutralize the electric charge, the stirring should be strong enough not to generate flocs or so that the diameter of the flocs generated is 2 mm or less. The stirring method is not particularly limited, and may include stirring using a stirring blade in a stirring tank, stirring by a flow in piping, stirring by passing through a pump such as a centrifugal pump, and the like. As for the degree of stirring, when using a stirring tank equipped with a stirrer, as a rough guide, strong stirring can be performed at a circumferential speed of a stirring blade of about 1 to 5 m/sec. In the present invention, the entire sludge is reacted by strong stirring after adding the Hofmann decomposition product of the acrylamide polymer, and the electric charge of the sludge is neutralized.
Adding a flocculant to improve the dehydration properties of the flocs produced. In order to neutralize the electric charge of the sludge, it is better not to generate flocs during agitation and mixing, and even if flocs are generated, the generation should be limited to small flocs of 2 mm or less. For this reason, as described above, the first stirring is a more intense stirring than the normal stirring for generating flocs. After neutralizing the charges as described above, an anionic polymer flocculant is added and a second stirring is performed to form flocs. The amount of anionic polymer flocculant added also varies depending on the properties of the sludge, but is generally 0.2 to 3 wt% (based on
SS) level. Examples of anionic polymer flocculants include polyacrylic acid or its salt, a partial hydrolyzate of polyacrylamide, a copolymer of acrylic acid (salt) and acrylamide, acrylic acid (salt), and 2-acrylamide-2. - A copolymer with methylpropanesulfonic acid (salt), a terpolymer of acrylic acid (salt), acrylamide, and vinylsulfonic acid (salt), etc. can be used. Since the second agitation generates flocs, it is weaker than the first agitation, and has an agitation intensity that is normally used for flocculation of sludge. The stirring means is not limited, but when a stirring tank equipped with stirring blades is used, the circumferential speed of the stirring blade can be 0.1 to 0.5 m/sec. By performing such agitation and mixing, the sludge particles whose charge has been neutralized by reacting with the Hofmann decomposition product of the acrylamide polymer coagulate to form flocs, resulting in the formation of strong and large flocs. , the dehydration properties are extremely improved. The flocs produced by the above coagulation are fed to a dehydrator as is or after removing the separated water, and dehydrated in the same manner as in the conventional method. As the dehydration method, centrifugal dehydration, vacuum dehydration, compression dehydration, etc. can be adopted. As a dehydrator for performing such dehydration, conventionally used dehydrators such as a centrifugal dehydrator, a vacuum dehydrator, a belt press type dehydrator, a screw press, or a filter press can be used. According to the present invention, the first stirring is performed by adding the Hofmann decomposition product of the acrylamide polymer, and the neutralization reaction of the charge of the sludge is appropriately performed, and then the anionic polymer flocculant is added. When the flocs are generated by performing the second stirring, the flocs are large in size, have low viscosity, are smooth and non-sticky, and have low adhesion to filter cloth, etc., so they have excellent filtration and dehydration properties.
The amount of sludge treated can be increased, and the moisture content of the cake is low, allowing for efficient dewatering at low cost. In particular, in the case of a belt press type dehydrator using a filter cloth, a high pressure of 1 kg/cm ² or more can be applied, and a dehydrated cake with a low moisture content can be obtained depending on the pressing pressure. This dehydrated cake is disposed of by drying, incineration, composting, etc., but since the moisture content of the dehydrated cake is low, less auxiliary fuel is required for drying and incineration, and when composting, it is necessary to adjust the moisture content. Additives such as sawdust, rice husks, and straw can be used in small amounts. Further, since there is a wide allowable range for the amount of the cationic and anionic polymer flocculants added, and a wide allowable range for the ratio of the two flocculants, it is easy to adjust the amount added in actual processing. moreover,
A stable dewatering treatment effect can be obtained despite changes in sludge properties. Next, examples of the present invention will be described, and the flocculants used in each example are as shown in Table-1.

[Table] Example 1 Mixed sludge of sewage primary sedimentation tank sludge and surplus sludge from activated sludge treatment (PH5.3, SS: 1.91%,
Take 200 ml of VSS: 85.4% vs. SS), add Hoffman decomposition product (CI) of polyacrylamide or other cationic polymer flocculant, and stir first for 30 seconds at 500 rpm with a stirrer (two plate flat blades). and
The floc diameter was measured. Next, the anionic polymer flocculant shown in Table 2 was added and stirred using a stirrer.
A second stirring was performed at 250 rpm for 20 seconds, and the resulting floc was poured onto a Puchner funnel lined with a 100 mesh nylon filter cloth, and the amount of filtrate was measured after 10 seconds (Nutsche test). In addition, 15g of the sludge after filtration was collected, and 0.5kg/
The moisture content of the sludge cake was measured after it was squeezed for 60 seconds at a pressure of cm ² (press test). Table 2 of the results
Shown below. In addition, for comparison, Hofmann decomposition products of polyacrylamide (Test No. 14, 15) and other cationic synthetic polymer flocculants (Test Nos. 10 to 13, 18, 19) were added alone, and the Table 2 also shows the case where stirring was performed using a stirrer at 250 rpm for 20 seconds.

[Table] From Table 2, it can be seen that when Hofmann decomposition product of polyacrylamide is used as a cationic polymer flocculant, (Test Nos. 1 to 4) It was found that the filtration performance was excellent and the moisture content of the dehydrated cake was lower than when using the combined polyacrylamide (Test Nos. 5 to 8) and when Mannitzchi modified polyacrylamide was used (Test Nos. 16 to 19). Recognize. Example 2 A Nutsuchie test was conducted on the sludge of Example 1 under the same conditions using the flocculant shown in Table 3, and a press test was conducted on the filtered sludge by changing the press pressure. Table 3 shows the relationship between water content and press pressure when the weight of wet cake that can be peeled off is 95% or more (releasability) when the filter cloth is peeled off. Regarding the press pressure in Table 3, the - mark indicates that compression dehydration was impossible due to insufficient strength and poor peeling of the dehydrated cake.

[Table] From Table 3, it can be seen that when Hofmann decomposition product of polyacrylamide is used as a cationic polymer flocculant, a dehydrated cake with good peelability even under high pressure and a low water content commensurate with the press pressure can be obtained. Example 3 Mixed sludge (PH6.7, SS: 1.82%,
VSS: 72.1% vs. SS) was subjected to Nutsuchie test and press test in the same manner as in Example 1 using the flocculants shown in Table 4. The results are also shown in Table-4.

[Table] From Table 4, it can be seen that when Hofmann decomposition products of polyacrylamide are used as the cationic polymer flocculant (Test Nos. 1 to 4), the filterability and dehydration performance are excellent. Example 4 The stirring intensity was changed by changing the rotation speed and stirring time of the stirrer for excess sludge (PH6.3, SS: 2.13%, VSS: 74% vs. SS) in activated sludge treatment of food factory wastewater. A Nutsuie test and a press test were conducted using the flocculant shown in Table 5 under the same conditions as in Example 1, except that the first stirring was carried out at the same time. Display the results -
5.

[Table] From Table 5, the floc diameter after the first stirring is 2 mm.
It can be seen that the dehydration effect is excellent when strong stirring is performed as shown below. In addition, test No. 5 was performed when the first stirring was gentle and the second stirring was strong, and test No. 6 was when both the first and second stirring were strong, and both had good dehydration effects. It turns out that there isn't.

Claims (1)

[Claims] 1. A cationic polymer flocculant is added to organic sludge and a first stirring is carried out, an anionic polymer flocculant is then added and a second stirring is carried out, and the generated flocs are In the dehydration method, a Hofmann decomposition product of an acrylamide polymer is used as a cationic polymer flocculant, and the first stirring does not produce flocs, or even if it does, the flocs have a diameter of 2 mm or less. A method for dewatering organic sludge, characterized in that the second stirring is a normal stirring that is weaker than the first stirring. 2. The method for dewatering organic sludge according to claim 1, wherein the organic sludge is surplus sludge generated by biologically treating sewage, or a mixed sludge of surplus sludge and other sludge.