JPH0130560B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for dewatering organic sludge produced when treating sewage, human waste, various industrial wastewater, and the like. Conventionally, organic sludge generated from the treatment of urban sewage, human waste, industrial wastewater, etc. is dehydrated using a vacuum dehydrator or a pressure dehydrator by adding iron salts such as ferric chloride and slaked lime as dehydration aids. has been done. The amount added was large, at 5-20% for ferric chloride and 15-80% for slaked lime, causing problems such as an increase in the amount of sludge generated, corrosion of the furnace during sludge incineration, and an increase in ash. . In recent years, in order to solve these problems, various organic polymer flocculants have been developed as dehydration aids, and after centrifugation, they are used in combination with belt press type dehydrators and the like. However, dehydration methods using organic polymer flocculants also have many drawbacks. For example, when using a belt press as a dehydrator, the releasability of sludge to cloth, solids recovery rate, processing speed, etc. are not sufficient, and even with a centrifugal separator, the solids recovery rate, cake moisture content, processing speed, etc. There are problems with screw press type dewatering machines, where a large amount of sludge flows out from the screen and insufficient pressure is transmitted to the sludge, making it virtually impossible to process. In addition, with a vacuum dehydrator, it is difficult to uniformly adhere sludge to which an organic polymer flocculant has been added onto the cloth, and with a pressure dehydrator, it is difficult to peel off the dehydrated cake. Another serious drawback is that organic polymer flocculants cannot be applied. The present invention solves these conventional drawbacks, increases the processing speed, lowers the moisture content of the cake, increases the recovery rate of solids, and improves the peelability of sludge in a belt press type dehydrator. It not only prevents sludge from leaking in screw-press type dehydrators, but also uniformizes the adhesion of sludge to the cloth of vacuum dehydrators and improves the peelability from the cloth of pressure dehydrators. The purpose of this invention is to provide a method for dewatering organic sludge that enables the application of organic polymer flocculants to sludge. That is, the present invention provides organic sludge with a cationic polymer made of a condensed polyamine and a magnesium salt,
After adding and mixing at least one kind of metal salt among calcium salt, aluminum salt, and iron salt, an anionic polymer consisting of a partial hydrolyzate of sodium polyacrylate or polyacrylamide is added and mixed to form a floc. It is characterized by dehydration treatment. To explain the present invention in detail below, as mentioned above, after adding an organic polymer flocculant to sludge containing a large amount of organic substances to flocculate the solid content in the sludge, a centrifugal dehydrator, a belt press type When dehydrating with a dehydrator, screw press type dehydrator, etc., a major factor that reduces the treatment effect is the nature of flocs produced when an organic polymer flocculant is added and mixed. That is, the density of the produced flocs is low, the strength is low, and the dewatering property (water permeability) is poor. Another cause is that the flocs produced in the vacuum dehydrator are too large. Therefore, by improving these properties of the produced flocs, the above-mentioned drawbacks can be overcome. The present inventors focused on this point and conducted various experiments to improve the properties of the floc. As a result, they added a cationic polymer made of condensed polyamine, magnesium salt, calcium salt, aluminum salt, and iron to organic sludge. After adding and mixing at least one type of metal salt among the salts, an anionic polymer consisting of a partial hydrolyzate of polyacrylic acid or polyacrylamide is added and mixed with stirring. It was found that good flocking was produced. Conventionally, flocculation methods using two types of ionic polymer flocculants in combination have not been carried out. For example, it is known that the amount of polymer flocculant used can be reduced by adding an anionic polymer to organic sludge and then adding a cationic polymer to flocculate it (Japanese Patent Publication No. 17492-1973). It is also known to use an anionic organic polymer flocculant and a cationic organic polymer flocculant or a cationic inorganic flocculant in combination when treating (JP-A-50-110972). However, it is completely unknown that the combination of a cationic polymer, a metal salt, and an anionic polymer and the order of addition as in the present invention are particularly effective for dewatering organic sludge. In the present invention, the order of addition of the cationic polymer, metal salt and anionic polymer is extremely important. That is, it is necessary to add the cationic polymer and the metal salt to the organic sludge and mix them thoroughly, and then add and mix the anionic flocculant. The cationic polymer and metal salt may be added in any order. Further, the cationic polymer and the metal salt may be added at the same time. Furthermore, the cationic polymer and the metal salt may be dissolved in the same solution, and the dissolved liquid may be added to the organic sludge. In any case, in the present invention, it is important to add the anionic polymer after adding and mixing the cationic polymer and the metal salt. Although the mechanism of the phenomenon that occurs when treated with the method of the present invention is not necessarily clear, it is important to note that the surface of the sludge particles is anionically charged, and that the cationic polymer and metal salt must be added and mixed before adding the anionic polymer. Judging from the phenomena that the moisture content of the cake decreases as more cationic polymers and metal salts are added, it is concluded that cationic polymers and metal ions modify the particles contained in sludge into particles with good dewatering properties. This is thought to be due to the fact that the particles become cationic due to the cationic polymer and metal ions and react strongly with the anionic polymer. The cationic polymer flocculant used in the present invention is called a condensed polyamine. Condensed polyamines include condensates of alkylene dichloride and alkylene polyamines (the structural formula is -[NH-R-NH-R'-] _o ; the same applies hereinafter);
Condensate of aniline and formalin

[Formula] Condensate of alkylene diamine and epichlorohydrin

[Formula] Condensate of ammonia and epichlorohydrin

[Formula] etc., and those having any composition are effective, but among them, those with high cationic strength and large molecular weight are even more effective. In addition, the optimum amount of these additives cannot be determined unconditionally because it varies greatly depending on the properties of the organic sludge and the composition of the polymer flocculant, and it is most reliable to determine it through preliminary experiments on actual sludge. . The higher the amount of cationic polymer added, the lower the cake moisture content will be, but the treatment cost will also increase, so generally it is 0.1% per sludge dry solids, calculated as coagulant dry matter.
Above, preferably 1 to 10% is selected. Furthermore, in the present invention, at least one of magnesium salt, calcium salt, aluminum salt, and iron salt is used as the metal salt, but the optimum amount to be added varies depending on the properties of the organic sludge, so it cannot be generally specified. The most reliable method is to conduct preliminary experiments on actual sludge. Generally, it is added in an amount of 0.5 to 30%, preferably 1 to 20%, based on the organic sludge dry solids. By adding a cationic polymer and a metal salt together, the addition rate of the cationic polymer can be significantly reduced, and furthermore, the moisture content of the cake after dehydration can be significantly reduced. On the other hand, the chemical structure of the anionic polymer flocculant used in the present invention is

It is represented by the following formula: It is necessary to appropriately select the anion strength (represented by y/x+y) and the molecular weight (determined by x, y, and n) depending on the sludge properties and the type of dehydrator. Generally, the higher the anionic strength, the lower the cake water content, and the larger the molecular weight, the larger the floc and the slightly higher water content. ordinary,
It is preferable to add a flocculant with a ratio of 0.2 or more and a molecular weight of about 5 million to 10 million in an amount of 0.05 to 5% (per dry solid sludge) in terms of dry coagulant. In addition, in a dehydrator such as a screw press type dehydrator that mechanically dehydrates sludge while heating it, the water content of the dehydrated cake can be dramatically reduced by the synergistic effect of heating and the polymer of the present invention. As described above, according to the present invention, the resulting flocs have high density, high strength, and good dewatering properties, and since the floc particle size can be adjusted appropriately, the belt press type dehydrator has good peelability of the dehydrated cake. The water content decreases, and the amount of sludge leaking from the screen in screw press dehydrators decreases.
Moisture content decreases. In addition, centrifugal separators have been shown to have effects such as improved sludge recovery, increased treatment capacity, and reduced water content. In addition, many effects have been recognized, including the fact that polymer flocculants can now be applied to vacuum dehydrators and pressure dehydrators, to which it was previously considered impossible to apply polymer flocculants. Next, examples of the present invention will be described. Example 1 Excess activated sludge (PH6.8, concentration 22.0
g/, ignition loss 72%) was used to conduct a dehydration test using a centrifuge. In the method according to the present invention, the cationic polymer and the metal salt were added simultaneously and mixed thoroughly, and then the anionic polymer was added. The cationic polymer is a condensate of hexamethylene diamine and epichlorohydrin (referred to as polyamine A), the metal salt is calcium chloride, and the anionic polymer is a polyacrylamide partial hydrolyzate (referred to as anion A, degree of hydrolysis).
(50 mol% molecular weight approximately 7 million) was used. For comparison, polyacrylic ester strong cation (cation A
(Cation degree: 100 mol%, molecular weight: 6 million) alone and in combination with cation A and anion A were tested. The test results are shown in Table 1. From Table 1, it can be seen that in the method according to the present invention, when polyamine A is added in an amount of 1.0 or more, an increase in throughput, a decrease in cake moisture content, and an increase in SS recovery rate can be achieved. Example 2 Excess activated sludge (PH
6.2, concentration 18 g/) was processed using a roll press type dehydrator. In the method of the present invention, the polyamine is a condensate of aniline and formalin (referred to as polyamine B),
Magnesium sulfate was used as the metal salt, and polyacrylamide partial hydrolyzate (degree of hydrolysis 60%, molecular weight 5 million, referred to as anion B) was used as the anionic polymer. The order of addition was that the magnesium sulfate solution was added and mixed with the sludge, and then the polyamine B was added and mixed. Further, anion B was added and mixed to form a floc. For comparison, a method in which magnesium sulfate was not added and a method in which cation A was added alone were tested. The test results are shown in Table 2. From Table 2, it can be seen that the cake moisture content is dramatically reduced by the present invention. Example 3 Mixed raw sewage (PH
6.8, concentration 36.4 g/) was dehydrated using a screw press type dehydrator. In the method of the present invention, the polyamine is a condensate of tetraethylene pentamine and ethylene dichloride (referred to as polyamine C), the metal salt is ferric sulfate, and the anionic polymer is sodium polyacrylate (anionic degree 100 mol%, molecular weight 4.5 million, anionic (referred to as C) was used. For comparison, a method using a polycation ester-based strong cation (cationicity 85 mol %, molecular weight 5 million, referred to as cation B) alone and a method using a combination of cation B, ferric sulfate, and anion C were performed. The order of addition was that polyamine C or cation B was added and mixed to the sludge, then ferric sulfate solution was added and mixed, and then anion C was added and mixed to form flocs. The test results are shown in Table 3. From Table 3 it can be seen that a reduction in cake moisture content and an increase in solids recovery can be achieved by the method according to the invention. Example 4 Excess activated sludge generated from a human waste treatment plant treated by a low dilution two-stage activated sludge method was mechanically dehydrated while being heated in a screw press (sludge temperature was 65 to 70°C). Polyamine C, calcium chloride and anion B were used in the method of the present invention. As a comparison, a method using cation B alone was tested. The results are shown in Table 4. Table 4 shows that the synergistic effect of the combination of chemicals and heating in the present invention can reduce the moisture content of the cake and improve the recovery rate.

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Claims (1)

[Claims] 1. After adding and mixing a cationic organic polymer flocculant made of condensed polyamine and at least one metal salt among magnesium salt, calcium salt, aluminum salt, and iron salt to organic sludge, A method for dewatering organic sludge, which comprises adding and mixing an anionic organic polymer flocculant consisting of a partial hydrolyzate of sodium polyacrylate or polyacrylamide for flocculation treatment, followed by mechanical dewatering treatment. 2 The addition rate of the cationic organic polymer flocculant is 0.1% or more in terms of condensed polyamine dry solids per organic sludge dry solids, preferably 1% or more.
10. The method of claim 1, wherein the amount is 10%. 3. The method according to claim 1 or 2, wherein the addition rate of the metal salt is 0.5 to 30%, preferably 1 to 20%, based on the organic sludge dry solids. 4. The addition rate of the anionic organic polymer flocculant in terms of dry solids is per dry solids of organic sludge.
The method according to claim 1, 2 or 3, wherein the amount is 0.05 to 5%. 5. Claim 1, wherein the mechanical dewatering step is performed while heating the organic sludge.
The method according to paragraph 2, paragraph 3 or paragraph 4.