JPS6340160B2 - - 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 are used in combination with centrifugal separators, 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, in the present invention, after adding and mixing a cationic polymer made of condensed polyamine to organic sludge,
This method is characterized by adding and mixing an anionic polymer consisting of a partially hydrolyzed product of sodium polyacrylate or polyacrylamide to form a floc, and then subjecting it to mechanical 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. After adding and mixing a cationic polymer consisting of condensed polyamine to the sludge, we added sodium polyacrylate or polyacrylamide to the sludge. It has been found that when an anionic polymer consisting of a partially hydrolyzed product is added and stirred, a floc with high density, high strength, and good dehydration properties is 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 organic polymer flocculant and anionic organic polymer flocculant as in the present invention and the order of addition are particularly effective for dewatering organic sludge. 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 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. Furthermore, the optimum amount to be added cannot be unconditionally determined because it varies greatly depending on the properties of the organic sludge and the composition of the polymer flocculant, and is most certainly determined by preliminary experiments on actual sludge. The larger the amount of cationic polymer added, the lower the cake moisture content will be, but the treatment cost will also increase, so generally the amount is 0.1% or more, preferably 1 to 10% in terms of coagulant dry matter, per sludge dry solids. To be elected. On the other hand, the chemical structure of the anionic polymer flocculant used in the present invention is

[Formula] It is necessary to appropriately select the anion strength (expressed 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. Usually, if y/x+y is 0.2 or more and the molecular weight is about 5 million to 10 million, it is 0.05 to 5% in terms of dry coagulant.
It is recommended to add (per sludge dry solids). The order of addition of the cationic flocculant and anionic flocculant is very important. In other words, it is necessary to add the cationic flocculant first and mix thoroughly, then add the anionic flocculant and mix gently to form a floc. If you do so, the effect will be significantly reduced. The mechanism of the phenomenon that occurs when treated with the method of the present invention is not necessarily clear, but the sludge particle surface is negatively charged, there is no effect unless a cationic flocculant is added first, and cationic flocculation Comprehensively judging from the phenomenon that the cake moisture content decreases as more agents are added, organic sludge particles are denatured and the water content in the particles decreases as cationic organic polymer flocculants are added. It is thought that the surface potential turns positive and then strongly reacts with the added anionic organic polymer flocculant. However, the reason why the effect of the combination in the present invention is particularly remarkable compared to the combination of other anions and cations is currently unknown. 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 discharged from a human waste treatment plant treated with a low dilution two-stage activated sludge method (brown in appearance, PH
6.6, concentration 26g/, ignition loss 74%),
Dehydration treatment was performed using a centrifuge. In the method according to the invention, the cationic polymer was added first and mixed thoroughly, and then the anionic polymer was added. A condensate of hexamethylene diamine and epichlorohydrin as a polyamine (A
) was used as the anionic polymer, and a polyacrylamide partial hydrolyzate (referred to as anion A) was used as the anionic polymer.
(degree of hydrolysis 50 mol%, molecular weight approximately 7 million) was used.
For comparison, Table 1 shows the results of using a strong polyacrylic ester cation (referred to as cation A, cationicity 100 mol%, molecular weight 6 million) alone and in combination with cation A and anion A. In the method according to the invention, polyamine A is added at 0.1%.
Addition of more than
It can be seen that if the order of addition of the cationic and anionic polymers is changed, the effect disappears.

【table】

[Table] Example 2 Excess sludge (PH6.9, concentration 2.3%, loss on ignition 65%) discharged from a human waste treatment plant treated by anaerobic digestion was treated with a roll press type dehydrator. In the method of the present invention, a condensate of aniline and formalin (referred to as polyamine B) is used as the polyamine, and a polyacrylamide partial hydrolyzate (degree of hydrolysis 30 mol%, molecular weight
7 million, called anion B) was used. For comparison, polyacrylic ester medium cation (cation degree 50 mol%, molecular weight 4.5 million, called cation B)
A method was carried out both alone and in combination with cation B and anion B. The results are shown in Table 2.

[Table] According to the present invention, it can be seen that when approximately 0.05% to 5% of anion B is added, the throughput increases, the peelability is improved, and the moisture content of the cake is reduced. Example 3 Surplus sludge (PH) discharged from a certain urban sewage treatment plant
6.2, concentration 10 g/) was dehydrated using a screw press type dehydrator. In the method of the present invention, a condensate of tetraethylenepentamine and ethylene dichloride (referred to as polyamine c) is used as the polyamine, and polysodium acrylate (with anionic degree of
100 mol%, molecular weight 4.5 million, referred to as anion c) was used. For comparison, polyacrylic ester strong cation (cation degree 85 mol%, molecular weight 5 million,
A single method (referred to as cation c) and a combination method of cation c and anion c were performed. The results are shown in Table 3.

[Table] In the method of the present invention, the material could be treated satisfactorily using a screw press type dehydrator, but in the conventional method, a large amount of floc leaked from the screen, making it practically impossible to treat. Example 4 Anaerobic digested sludge (PH7.3, concentration 23.5g/, loss on ignition 63%) discharged from a certain urban sewage treatment plant was dehydrated using a vacuum filtration machine. In the method of the present invention, a condensate of ammonia and epichlorohydrin (referred to as polyamine D) is used as the polyamine, and a polyacrylamide partial hydrolyzate (degree of hydrolysis 20 mol%, molecular weight
7 million, called anion D) was used. For comparison, a chitosan-based polymer flocculant (referred to as cation D)
A single method and a combination method of cation D and anion D were used. The results are shown in Table 4.

[Table] In the method of the present invention, the treatment could be performed satisfactorily using a vacuum filtration machine, but in the conventional method, the adhesion of flocs was poor and treatment was practically impossible. Example 5 Mixed raw sludge (PH
6.5, concentration 45g/, ignition loss 70%) is second chloride
Processed in a pressure dehydrator by adding 5% iron and 30% slaked lime, cake moisture content 75% (Net), overspeed
Obtained 2.0Kg/m ²・h. On the other hand, Table 5 shows the results of a dewatering experiment conducted on the sludge from the same treatment plant using a polymer coagulant as a dewatering aid. In the method of the present invention, polyamine A and anion A are used together, and as a comparative example, cation A alone method,
A combination method of cation A and anion A was carried out.

[Table] It can be seen that according to the method of the present invention, dehydration treatment equivalent to or better than the method of adding slaked lime and iron chloride is possible even with the addition of a polymer flocculant. Example 6 Excess activated sludge (PH
6. Concentration: 13.0g/) was mechanically dehydrated while heating (sludge temperature: 60-65°C) using a screw press. In the method of the present invention, a condensate of polyamine, tetraethylenepentamine, and ethylene dichloride (polyamine C) was used, and sodium polyacrylate (anion C) was used as the anionic polymer. For comparison, a polyacrylic ester strong cation (cation C) was used alone. The results are shown in Table 6.

[Table] From the above results, it can be seen that the moisture content of the cake is dramatically reduced due to the synergistic effect of heating and the addition of the polymer in the present invention.

Claims (1)

[Claims] 1. After adding and mixing a cationic organic polymer flocculant made of a condensed polyamine to organic sludge, an anionic organic polymer flocculant made of a partial hydrolyzate of sodium polyacrylate or polyacrylamide is added and mixed. 1. A method for dewatering organic sludge, which comprises adding and mixing agglomeration 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 addition rate of the anionic organic polymer flocculant in terms of dry solids is per dry solids of organic sludge.
Claim 1 or 2 that is 0.05 to 5%
The method described in section. 4. Claim 1, wherein the mechanical dehydration treatment step is performed while heating the organic sludge.
3. The method described in Section 2, Section 2, or Section 3.