JPS58112097A - Dehydration of organic sludge - Google Patents

Abstract

PURPOSE:To lower the water-retaining ratio of cake and to improve the efficiency of recovering solid matter, by adding a cationic organic macromolecular fluocculant and a metal to organic sludge and then an anionic organic macromolecular flocculant to it, followed by flocculation. CONSTITUTION:A cationic organic macromolecular flocculant composed of condensed polyamine and a metal salt are added to and mixed in organic sludge formed in the treatment of sewage or the like. An anionic organic macromolecular flocculant composed of the partially-hydrolyzed product of poly (sodium acrylate) or polyacryl amine is then added to and mixed in said sludge. Thereafter, the sludge is flocculated and mechanically dehydrated. The addition ratio of the cationic organic macromolecular flocculant is preferably at 1-10% calculated as the dried solid matter of the condensed polyamine per dried solid matter of the organic sludge. One of Mg, Ca, Al and Fe salts is used as the metal salt.

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 ferric salt of ferric chloride and slaked lime as dehydration aids. being processed. The amount added is large at 5-20% for ferric chloride and 15-80% for slaked lime, which causes problems such as an increase in the amount of sludge generated and corrosion of the furnace during sludge incineration. Ta.

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 a belt press type is used as a dehydrator, the removability 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, etc. There are problems with processing speed, and with screw press dehydrators, a lot of sludge flows out of the screen, and sufficient pressure is not 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 R 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 the screw press dehydrator, but also uniformly prevents sludge from adhering to the cloth in the vacuum dehydrator.
The object of the present invention is to provide a method for dewatering organic sludge that also improves releasability from cloth and enables the application of organic polymer flocculants to both types of dehydrators.

That is, the present invention involves adding and mixing a cationic polymer made of a condensed polyamine and a metal salt to organic sludge, and then adding and mixing an anionic polymer made of a partially hydrolyzed product of sodium polyacrylate or polyacrylamide to form a floc. , followed by 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., the main reason for reducing the treatment effect is the properties 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, the above-mentioned drawbacks can be overcome by improving these properties of the flocs produced.

The present inventors focused on this point and conducted various experiments to improve the properties of the flocs. As a result, after adding and mixing a cationic polymer made of condensed polyamine and a metal salt to organic sludge, When an anionic polymer consisting of a partial hydrolyzate of sodium polyacrylate or polyacrylamide is added and mixed with stirring, the j! It was found that 1tn7Efftsuk was generated.

Conventionally, flocculation methods using two types of ionic polymer flocculants in combination have not been practiced. For example, it is known that the amount of polymer flocculant used can be reduced by adding anionic polyw- to organic sludge and then adding a cationic polymer to coagulate it (Japanese Patent Publication No. 39-174
92), It is also known to use an anionic organic polymer flocculant and a cationic organic polymer flocculant or a cationic inorganic flocculant together, especially when treating inorganic sludge (% Kaisho 5O -110972). However, it is completely unknown that the combination and order of addition of a cationic polymer, metal salt and anionic polymer as in the present invention is 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 order of addition of cationic polymer and metal salt is
Whichever comes first is fine. 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.

The mechanism of the phenomenon that occurs when treated with the method of the present invention is not necessarily clear, but 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 7-ionic polymer. Judging from phenomena such as the fact that the water content of food cake decreases when 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
It is called a condensed polyamine.

Condensed polyamine is a condensate of alkylene dichloride and alkylene polyamine (the structural formula is -E-NH-R).
-NH-R÷. (same below), condensate of Ayu9run and Forw9n (1,000Nu to 匝Xcn2%)
.

A condensate of alkylene polyamine and epichlorohydrin with air condensation and epichlorohydrin (-f-NH-) is also effective, but among these, those with high cationic strength and large molecular weight are even more effective.

Further, the optimum amount of these additives cannot be specified because it varies greatly depending on the properties of the organic sludge and the composition of the polymer flocculant, and is most definitely determined by preliminary experiments on actual sludge. Addition of a large amount of cationic polymer will reduce the water content of the food cake, but will also increase the processing cost, so it is generally 0.1 g or more in terms of dry coagulant per sludge dry solid, preferably 1 to 10 g6 is selected.

In the present invention, the metal salt used is magnesium salt, calcium salt, aluminum salt, or iron salt. However, since the optimum amount to be added varies depending on the properties of the organic sludge, it cannot be further specified, and it is most certain to determine it through preliminary experiments on actual sludge. Generally, it is added from 0.5 to 3096, preferably from 1 to 20, per dry solid organic sludge.

By adding a cationic polymer and a metal salt in combination, the addition rate of the cationic polymer 9Y can be significantly reduced, and furthermore, the water content of the cake after dehydration can be significantly reduced.

On the other hand, the anionic strength of the anionic polymer used in the present invention is indicated by an anionic strength (indicated by OK).

The molecular weight (determined by m, y, and l) must be appropriately selected depending on the sludge properties and dehydrator type. In general,
The higher the anionic strength, the lower the cake moisture content, and the larger the molecular weight grain flocs tend to be, the more the moisture content tends to increase slightly. Generally, it is preferable to add a flocculant with a value of 0.2 or more and a molecular weight of 5,000,000 to 10,000,000 degrees in terms of dry coagulant (0.05 to 5 g (per dry solid sludge)).

In addition, in a dehydrator such as a screw press type dehydrator that mechanically dehydrates sludge while heating it, heating and polyhydration in the present invention are not recommended. The synergistic effect of - can dramatically reduce the moisture content of the dehydrated cake.

As described above, according to the present invention, the generated flocs are
It has high texture, high strength, good dewatering properties, and the floc particle size can be adjusted appropriately, so belt press dehydrators have good peelability of the dehydrated cake and a low water content, while screw press dehydrators can remove the dehydrated cake easily. The amount of sludge leaking from the tank is reduced, and the moisture content is lowered. 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, such as the fact that the polymer flocculant can now be applied to vacuum dehydrators and g-g dehydrators, to which it was previously considered impossible to apply a polymer flocculant.

Next, examples of the present invention will be described.

Example 1 Excess activated sludge generated in human waste treatment plant by treatment with low dilution two-stage activated sludge method (pH 6.8, $lI! degree 22.O
f/l.

A dehydration test using a centrifugal separator was conducted using a sample (loss on ignition: 72%).

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.

A condensate of hexamethylene diamine and epichlorohydrin (referred to as polyamine A) is used as a cationic polymer, calcium chloride is used as a metal salt, and a polyacrylamide partial hydrolyzate (referred to as anion A, water freshness 50 mol L molecular weight approximately 7.6 million) is used as an anionic polymer. Using. For comparison, polyacrylic ester-based strong cation (Cation A
(Cation degree: 100 mo1%, m-p amount: 6 million) alone, and the combined use of cation ^ and anion A were tested.

The test results are shown in Table 1.

From Table 1: 1 In the method according to the invention, polyamine A is
．． It can be seen that when 0 or more is added, an increase in throughput, a decrease in cake moisture content, and an increase in SS recovery rate can be achieved.

Example 2 Surplus activated sludge (pH 6.2) generated from a municipal sewage treatment plant
, concentration 18 f/l) was also 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), the metal salt is magnesium sulfate, and the anionic polymer is a polyacrylamide partial hydrolyzate (hydrolyte freshness 605&, molecular weight 5 million, referred to as anion B). ) was used. The order of addition was that the sulfuric acid mag solution was added to and mixed with the sludge, and then polyamine B was added and mixed. Furthermore, anion B was added and mixed to generate flocs. For comparison, a case 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 sludge (pH 6, 8, negative agif/l) generated from a city sewage treatment plant 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 a polyamine, ferric sulfate is used as a metal salt, and polysodium acrylate (anionic degree 100 m
(referred to as anion C) with a molecular weight of 4.5 million was used. As a ratio, polycation ester early strong cation (cation degree 85 mo1 * + molecular weight 5 million, referred to as cation B) alone and in combination with cation B, ferric sulfate and anion C were used to treat smallpox. The order of addition is:
After adding and mixing Boriaquin C or Cation B to the sludge, a ferric sulfate solution was added and mixed, and further anion C was added and mixed to form flocs. The test results are shown in Table 3. It can be seen from the 3rd IN that a reduction in cake moisture content and an increase in solids recovery can be achieved with the method according to the invention.

Example 4 Excess activated sludge generated from a night soil 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 C9 calcium chloride and anion B were used in the method of the 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 chemical combination and heating in the present invention can reduce the moisture content of the cake and improve the recovery rate.

Margin below Table 1 Table 2 Table 3 Table 4

Claims (1)

[Claims] 1. After adding and mixing a cationic organic polymer flocculant consisting of a clamp-type polyamine and a metal 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 method according to claim 1, wherein one of magnesium salts, calcium salts, aluminum salts, and iron salts is used as the metal salt. (5) The addition rate of the cationic organic polymer flocculant is 0.11 or more, preferably 1 to 10 g, in terms of feed type polyamine dry solids per organic sludge dry solids. or the method described in paragraph 2. 4. The method according to claim 1, 2, or 3, wherein the addition rate of the metal salt is 0.5 to 301, preferably 1 to 20 Ist, per dry solid organic sludge. . 1. The addition rate of the anionic organic polymer flocculant in terms of dry solids is 0β5 to 5-5-5% per dry solids of organic sludge.
Claim 1 is: The method according to paragraph 2, paragraph 3 or paragraph 4. & The method according to claim 1, 2, 3, 4, or 5, wherein the mechanical dewatering process is performed while heating the organic sludge.