JPS5913278B2 - Method for flocculating organic wastewater sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for flocculating primary sedimentation tank sludge, excess activated sludge, or mixed sludge generated during activated sludge treatment of sewage and other organic wastewater.

Conventionally, organic sludge generated when sewage and other organic wastewater is treated with activated sludge is flocculated using a cationic organic polymer flocculant (hereinafter referred to as cationic polymer), and then subjected to operations such as concentration or dewatering. However, cationic polymers are more toxic than nonionic organic polymer flocculants (hereinafter referred to as nonionic polymers) or anionic organic polymer flocculants (hereinafter referred to as anionic polymers) [48 by Himedaka]. The problem is that the time TLm (48-hour half-death concentration) of cationic polymers is lower than that of anionic and nonionic polymers.

Generally, cationic polymers such as methacrylic acid ester acrylamide copolymer, polyethylene imine, polyamine, polyamine sulfone, polyamide, polyacrylamide cationically modified products are used to prepare organic sludge, such as primary sedimentation tank sludge, surplus activated sludge mixed raw sludge, etc. When dehydrating with a dehydrator, such as a vacuum dehydrator, pressure dehydrator, roll press dehydrator, centrifugal dehydrator, etc., the injection rate is in the range of 2 to 10 kg/1-ss, and the sludge solids concentration is 50 kg/m'', the injection amount per sludge volume is 100 to 500 g/m3 (100 to 500 ppm
), and most of the injected cationic polymer is adsorbed by the sludge, but the amount injected is much higher than the 48-hour TLm value lppm of general cationic polymers, and the p liquid discharged from the dehydrator is Alternatively, there is a possibility that cationic polymers injected into separated water such as furnace cloth cleaning wastewater may remain, and if returned to the original organic wastewater treatment equipment, it is said to have a negative impact on activated sludge in the aeration tank. There is.

Furthermore, it is said that if the separated water discharged from the dehydrator is directly discharged into rivers, the sea, etc., it will have a negative impact on the organisms living in these water bodies.

However, anionic and nonionic polymers, which are said to be much less toxic than cationic polymers or non-toxic, have little effect on flocculating organic sludge.

In other words, the amount of polymer used (consumption) is large, and despite this uneconomical use of a large amount, the strength of the resulting aggregate is small;
The water content is high and the dehydration properties are poor, making post-treatment extremely troublesome and expensive, making it unsuitable for large-scale processing.Currently, these polymers are not injected alone to coagulate or dewater organic sludge. be.

The present invention effectively uses an alkali agent and calcium chloride for nonionic, anionic, or mixture polymers that have little or no effect on the flocculation of organic sludge, and uses a small amount of the polymer to effectively flocculate organic sludge. The purpose is to provide a method that is accurate and efficient.

The present invention applies alkaline agents such as caustic soda, slaked lime, and caustic potash to organic sludge generated when activated sludge treatment is performed on so-called organic wastewater such as primary sedimentation tank sludge, surplus activated sludge, and mixed sludge generated from organic wastewater treatment plants. After adding calcium chloride, an amount corresponding to the amount (weight ratio) of the alkali oxidant added previously in terms of CaC112.2H20 was added.

4 This is a method of coagulating organic wastewater sludge by further adding a nonionic or anionic polymer or a mixed polymer of a nonionic polymer and an anionic polymer (hereinafter referred to as mixed polymer).

In the present invention, first, an alkaline agent such as caustic soda, slaked lime, caustic potash, aqueous ammonia, and soda carbonate is added to organic sludge until the pH of the sludge becomes 10 or more.

Next, add calcium chloride as CaC112.2H20 in an amount corresponding to -~- of the injection rate of the alkali agent added in the previous step 3, and stir and mix slowly or relatively rapidly.
Alternatively, before stirring and mixing, an anionic polymer, a nonionic polymer, or a mixed polymer is further added and then slowly stirred.

For example, 40 to 70 r, p, m, preferably 60 r,
When the sludge particles are stirred for 1 to 5 minutes, preferably for 2 to 3 minutes, at speeds around p and m, the sludge particles gradually become larger flocs, and when the stirring is stopped and left as is, they immediately settle and concentrate, increasing the solids concentration in the sludge.

Note that even if organic sludge or organic sludge to which only anionic or nonionic polymers are added is left to stand after being slowly stirred, the sludge will settle and thicken, but the rate of this will be very slow, and the solid concentration in the sludge will also be alkaline. The method of the present invention is extremely useful in that the value is very low and impractical compared to the case of using a combination of calcium chloride and calcium chloride.

In addition, in the method of the present invention, the particles of the coagulated organic sludge become flocs and the dewatering properties are improved, so when the coagulated sludge is dewatered using a dehydrator, the dewatering speed of the sludge is high and the dewatering is completed more quickly.

On the other hand, when using a dehydrator to dewater organic sludge as it is, or organic sludge with nonionic polymers, anionic polymers, or mixed polymers added, the dewatering speed is low because the sludge particles are dispersed compared to coagulated flocs. In particular, when nonionic polymers, anionic polymers, or mixed polymers are added to organic sludge, the sludge particles become more dispersed, and the viscosity of the water increases due to the injected polymer, resulting in poor dewatering properties and a long time for dewatering. The superiority of the method of the present invention is also recognized from the viewpoint of the following points.

Furthermore, the nonionic polymers, anionic polymers, etc. used in the method of the present invention have no or almost no toxicity compared to cationic polymers, so when these coagulated sludges are dehydrated using a dehydrator, the separated water discharged can be directly recycled into rivers, oceans, etc. Even if the polymer is discharged into the water or returned to an organic wastewater treatment facility, toxicity problems due to the polymer are unlikely to occur.

The type of nonionic polymer or anionic polymer used in the present invention varies depending on the type of organic sludge and the treatment plant where it is generated, and it is necessary to select an appropriate type, but mainly sodium polyacrylate, polyacrylamide, or polyacrylamide are used. Partial hydrolysates are suitable, and the injection rate range varies depending on the type of organic sludge and the treatment plant where it is generated.
The effective range is 0.5 to 6 kg/1-ss.

Theoretical explanation of the effects of the alkaline agent and calcium chloride in the present invention has not yet been made, but the phenomenon is that by raising the pH of organic sludge to 10 or higher with an alkaline agent, the organic sludge swells and its viscosity decreases. When calcium chloride is added to this, the organic sludge returns to a state similar to its original appearance, but the surface of the sludge particles has changed to a state where it is easier to adsorb and crosslink anionic polymers, nonionic polymers, or mixed polymers. It is estimated that
When these polymers are added and slowly stirred, the sludge particles coagulate into large flocs, and the alkaline agent and calcium chloride play an important role in coagulating the sludge.

That is, although it is estimated, even if a nonionic polymer or anionic polymer is directly injected into organic sludge, the polysaccharide present on the surface of the sludge particles may be
The polymer is not adsorbed to the sludge particles or cross-linked, and agglomeration does not occur because the adsorption and cross-linking phenomenon of the anionic polymer is obstructed, or because the surface charge of the sludge particles and the charge of the nonionic and anionic polymers themselves repel each other. It is estimated that if an alkaline agent is added to the sludge in advance to make the sludge pH 10 or higher, the sludge particles will swell or some of them will dissolve, and if calcium chloride is added to this, the swelled or eluted sludge will shrink or shrink again. This seems to be due to the existence of a phenomenon in which the surface of the sludge particles becomes more active or new parts are precipitated, which makes them more likely to be adsorbed with anionic or nonionic polymers, and aggregation progresses.

Furthermore, an alkaline agent is added to the organic sludge to bring the sludge pH to 10.
Even if an anionic polymer, a nonionic polymer, or a mixed polymer is added to the above solution without adding calcium chloride, the sludge will flocculate to some extent, but the sludge particles will swell due to the alkaline agent, and the solids concentration reached will be lower. The addition of calcium chloride is also important because it does not cause much concentration.

In addition, the injection rate of this calcium chloride is CaC112*
13 2H20, if the amount corresponding to the alkaline agent injection rate is appropriate and the injection rate is too low, the swelled or eluted sludge particles will not shrink or precipitate, and the polymer will be added to them. However, the solids concentration achieved is low and it does not concentrate much.

In addition, if the injection rate is too high, the sludge particles will completely return to their original state, and even if an anionic polymer, nonionic polymer, or mixed polymer is added, flocculation will not occur, resulting in a lower solids concentration and poor concentration. Therefore, the injection rate should be kept within the above range.

As described above, according to the method of the present invention, an alkaline agent is added to organic sludge to make the sludge pH 10 or more, and then 3 parts of salt and 4 parts of calcium chloride are added, which corresponds to the injection rate of the alkaline agent. Furthermore, by adding a nonionic polymer, an anionic polymer, or a mixed polymer to flocculate the sludge particles, the sludge particles become flanked, and the thickening and dewatering properties of the sludge are improved. Unlike polymers, they have little or no toxicity, so even if polymers remain in the supernatant water after sludge concentration or in the separated water from the dehydrator, they can be discharged directly into the original wastewater treatment equipment or into rivers, oceans, etc. If you do, there will be no problem.

Next, the sludge analysis values and experimental examples used in the experiment are shown.

The properties of the sludge, polymer, etc. used in this experiment are shown below.

■) Organic sludge analysis value (sludge generated from sewage treatment plants) ■) Organic polymer flocculant ■ Cationic polymer Product name Himoroku Mp-373 (Kyoritsu Organic ■ product) Main component: Concentration of methacrylic acid ester amide copolymer used 1g/l @ Nonionic polymer Product name Acofloc N-700 (Mitsui Suiana Mitsui product) Main component Polyacrylamide Usage concentration 19/1 ■ Anionic polymer Product name Acofloc A-110 (Mitsui Sui Anamitsu product) Main component Polyacrylamide partially hydrated Concentration of decomposition product used: 1 g/l Experimental example-1 (Experimental example using conventional method) Cationic polymer, nonionic polymer,
Anionic polymers or mixed polymers of nonions and anions are directly injected and stirred into sludge, and caustic soda is injected as an alkali agent into surplus activated sludge to adjust the sludge pH.
A sedimentation concentration column test was conducted on sludge etc. in which anionic polymers, nonionic polymers, and mixed polymers were injected and stirred into the sludge with a concentration of 10 or more.

The sedimentation column used was 70mmφX 1.100mtnH
, a column with a rake.

The experimental results are shown in Table 1 below.

As shown in Table 1, even if nonionic polymer, anionic polymer, or mixed polymer is injected directly into excess sludge, or by injecting caustic soda into excess sludge, the sludge pH
Even if a nonionic polymer, an anionic polymer, or a mixed polymer is injected after the value is set to 10 or more, sludge flocculation hardly occurs and the settling property of sludge is not improved.

That is, FIG. 1 shows the relationship between the value of pH adjustment using an alkaline agent, the sludge concentration reached after 24 hours, and the isokinetic settling rate using the sludge properties in Table 1 and the data in Table 2.

From FIG. 1, it can be seen that it is effective to make the sludge pH alkaline, but the effect is particularly significant in the pH range of 10 or more, and it is not possible to obtain a satisfactory result simply by making the sludge alkaline to a pH of 7 to 10.

Experimental example 2 (Experimental example using the method of the present invention) Caustic soda was added to the same excess activated sludge used in Experimental example 1 to make the sludge 10 or more, and then calcium chloride was injected, and nonionic polymer and anion were added. A sedimentation concentration column test was conducted on sludge that was stirred and flocculated by injecting polymers, mixed polymers, etc.

The experimental results are shown in Table-2.

The column used was the same as in Experimental Example-1.

As shown in Table 2, the effect of the method of the present invention is on dogs.

However, if the injection rate of alkaline agents, calcium chloride, polymers, etc. is higher than the appropriate range, the effect will not be much apparent.

Figure 2 shows the influence of the amount of calcium chloride added using the data in Clothing-1 and Table-2. From Figure 2, it can be seen that the amount of calcium chloride added has an optimal range with upper and lower limits. It can be seen that, in terms of CaC112.3 2H20, the injection rate of alkaline agent other than 1 to -4 gives extremely poor results.

Experimental Example 3 (Experimental example according to the present invention, conventional method experimental example) First sedimentation tank sludge, mixed raw sludge, etc. were flocculated by the method of the present invention, and a sedimentation concentration column test was conducted.The results obtained are shown in the table below.
Shown in 3.

As shown in Table 3, even if the initial sedimentation tank sludge and mixed raw sludge are flocculated using the conventional method and a sedimentation concentration test is performed, little effect is obtained. When done, the effect is a dog.

Experimental Example-4 (Regarding the method of the present invention and the type of alkaline agent) Harvest: The surplus activated sludge used in Experimental Example-1 was treated with caustic soda, caustic potash, slaked lime, aqueous ammonia, soda carbonate, etc. as the alkaline agent in the method of the present invention. The sludge was flocculated and a sedimentation concentration column test was conducted.

The results obtained are shown in Table 4 below.

As shown in Table 4, although the effects of these alkaline agents differed somewhat depending on the type, they were all more effective than conventional methods.

Furthermore, the sludge pH can be adjusted at the injection rate of the alkali agent shown in Table 4 above.
were all 10 or higher.

Experimental example-5 (Dewatering test of flocculated sludge produced by the method of the present invention) Experimental example-1
Add 10m9 of caustic soda to the same surplus activated sludge used in
Add 9-ss and stir, then add calcium chloride to CaCl2
・As 2H20, add 5 m9/j; l-ss and stir, and further add 2.0 m9/El-ss of nonionic polymer.
A dewatering test was conducted on the sludge that had been added and flocculated after stirring.

The dehydrator used in the experiment was a roll press type dehydrator, and the test conditions were a filter cloth of 20 crrL, a P cloth speed of l, and m.
/min, F cloth tension pressure is 4. It was Okgf/i.

The test results are shown in Table-5.

As shown in Table 3, the sludge flocculated by the method of the present invention is
Compared to conventional sludge, the dewatering speed was faster and the moisture content of the cake was lower, both of which yielded good results.

As described above, in the present invention, after the pH of organic sludge is raised to 10 or more, nonionic, anionic, or mixture polymers thereof, which have little or no effect on coagulation of organic sludge, are combined with an alkaline agent and calcium chloride, etc. to produce organic sludge. By flocculating sludge, sludge treatment can be carried out with a significant reduction in the amount of organic polymer flocculant consumed, and the resulting flocculates can be separated and treated as having high strength and low water content. Not only does it significantly improve efficiency, it also makes it possible to accurately and efficiently separate and generate aggregates with good dehydration properties from liquid, which helps simplify post-processing, and also makes processing work simple and economical. It has beneficial features such as the ease of agglomeration and increased throughput.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the influence of sludge pH, and Fig. 2 is a diagram showing the influence of the amount of calcium chloride added.

Claims (1)

[Claims] 1. Organic sludge such as primary sedimentation tank sludge, excess activated sludge, or mixed sludge (mixed raw sludge) generated from so-called organic wastewater treatment plants such as sewage treatment plants or industrial wastewater treatment plants. After adding an alkali agent to make the sludge pH 10 or more, the amount corresponding to the amount of the added alkali agent injection (weight ratio), that is, the amount in terms of CaCl2.2H20, is the amount of the alkali agent with an injection rate of 1 to 3. It is characterized by adding calcium chloride equivalent to (weight ratio) and further adding a small amount of anionic, nonionic, or a mixture of these organic polymer flocculants to flocculate organic sludge. A method for coagulating organic wastewater sludge.