JPH0148840B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating sludge, and particularly to a method for treating surplus sludge generated when wastewater containing phosphates is treated with activated sludge. The biological dephosphorization method, which removes phosphorus from wastewater by repeatedly bringing wastewater and activated sludge into contact under anaerobic and aerobic conditions, is widely practiced, and BOD is removed by releasing phosphorus from returned sludge under anaerobic conditions. phosphorus is incorporated into the sludge under aerobic conditions. In the case of the biological method, there are problems with the handling of the sludge generated, mainly the sedimentation and dewatering properties of the sludge, but with the biological dephosphorization method mentioned above, there are not only these problems but also the problem of leaching of phosphorus from excess sludge. There is. In other words, the surplus sludge generated in the biological dephosphorization method itself has a high water content, and if it is placed in an anaerobic environment, the phosphorus in the sludge will be eluted, and if it is dehydrated as it is, it will contain a high concentration of phosphorus. There was a problem that a liquid was generated and it needed to be disposed of. Various methods have been proposed to solve these problems, including (1) using a cationic polymer alone, (2) using a cationic polymer and an anionic polymer together, and (3) for dewatering sludge. )
This method uses ferric chloride and slaked lime together. However, in method (1), the flocs produced are weak and sufficient dewatering is difficult, and the elution of phosphorus from the sludge cannot be inhibited. Although method (2) produces strong flocs and poses no problem in terms of dehydration, it cannot prevent the elution of phosphorus as described above; (3)
Although it is possible to suppress the elution of phosphorus using the method described above, the amount of flocculant used is extremely large (FeCl ₃ 6H ₂ O 20%/SS, Ca(OH) ₂ 70-80%/
SS), and also unsatisfactory results in terms of dewatering speed and moisture content. As described above, the methods proposed so far have not been able to effectively dewater excess sludge generated from biological dephosphorization. An object of the present invention is to provide a sludge treatment method that not only has sufficient sludge sedimentation and dewatering properties, but also can sufficiently suppress the elution of phosphorus from surplus sludge generated in the biological dephosphorization method. be. That is, the present invention provides a method for treating surplus sludge generated when treating phosphate-containing wastewater by an activated sludge treatment method including an anaerobic process and an aerobic process, which includes adding a metal salt to the sludge. After mixing, an acrylic acid hydrazide-based polymer compound and a polymer compound containing an amino group or a quaternary ammonium salt are further added, and then dehydrated. The acrylic acid hydrazide polymer compound (hereinafter referred to as AH polymer) used in the present invention has the general formula (In the formula, R represents H or CH ₃ , A represents a monomer unit of acrylamide, methacrylamide, acrylic ester, methacrylic ester, and B represents acrylic acid or its salt, methacrylic acid or its salt, or the above-mentioned A It represents a monomer unit copolymerizable with , and l, m and n have the following relationship: 0 mol%<l≦100 mol% n+m+l=100 mol%) is preferred. Examples of the B unit copolymerizable with the A unit include vinyl chloride, vinyl acetate, butadiene, styrene, acrylonitrile, and the like. The polymerization form of the AH polymer may be block type, alternating type, or random type. Further, the intrinsic viscosity of the AH polymer is preferably [η] 30° C. 1N-NaNO ₃ >0.1 (dl/g). An example of producing the AH polymer is shown below, but the method for producing the AH polymer is disclosed in detail in JP-A-55-144004. The polymer compound containing an amino group or a quaternary ammonium salt (hereinafter referred to as AA polymer) used in the present invention includes aminoalkyl acrylates such as dimethylaminoethyl acrylate;
Examples include aminoalkyl methacrylates such as dimethylaminoethyl methacrylate, aminoalkyl acrylamides such as dimethylaminopropylacrylamide, aminoalkyl methacrylamides such as dimethylaminopropyl methacrylamide, and quaternized products thereof. In addition, copolymers with other monomers that can be copolymerized with these can also be used, and examples of other monomers include acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl acetate, acrylic ester, and methacrylic ester. etc. The intrinsic viscosity of the AA polymer is [η] 30°C 0.1N-NaCl desirably 5 dl/g or more. As the metal salt used in the present invention, aluminum or iron salts are preferred, and aluminum salts are particularly preferred from the viewpoint of handling. Examples of aluminum salts include aluminum chloride and polyaluminum chloride (PAC), and examples of iron salts include ferrous sulfate, ferric sulfate, and polyferrous sulfate. It is thought that the use of the above-mentioned chemicals can suppress the elution of phosphorus from the sludge mainly due to the following effects. That is, when a metal salt (for example, aluminum salt) is added to sludge, the phosphorus released into the liquid becomes insolubilized by the reaction PO ₄ ^3- + Al ³⁺ → AlPO ₄ , and the generated AlPO ₄ is transferred to the sludge floc. It is thought that it is taken in and turned into a flock. It is also believed that Al ³⁺ forms a polynuclear complex in the sludge or reacts electrically with the sludge particles themselves, and it is presumed that these reactions occur simultaneously or in relation to each other. If the above-mentioned AH polymer and AA polymer are further added after this metal salt is added, a very strong sludge floc is formed. In the present invention, the amount of metal salt added is determined by the SS of sludge.
0.5 to 10%, preferably 1.0 to 3.0%.
Also, the usage ratio of AH polymer and AA polymer is
Weight ratio of 1:9 to 9:1, preferably 2:8 to
The ratio is 8:2. The amount of these polymers added is preferably 0.3 to 5.0% in total based on the SS of the sludge. To carry out the method of the present invention, metal salts are first added to the sludge, appropriately stirred to uniformly disperse the metal salts in the sludge, and then the above polymers are added to the sludge in the same solution or separately at the same time. The water may be added, stirred as appropriate, and then dehydrated. Dewatering is carried out by known means such as a belt press, centrifuge, screw press, filter press, etc. Note that it is not preferable to add the metal salt and the polymer to the sludge at the same time because the effect is inferior. According to the present invention, the metal salt and the AH polymer and
By using AA polymer, it is possible to form large and dense sludge flocs, and the sludge has sufficient settling and dewatering properties. This can be sufficiently suppressed and the complexity of treating sludge separated water can be eliminated. Therefore, by carrying out the present invention, it is possible to improve the amount of sludge dewatered, and the present invention can be effectively used in wastewater treatment equipment that generates a large amount of sludge. Next, the effects of the present invention will be specifically explained using manufacturing examples and examples. The Preparation Example is an example of the preparation of the AH polymer used in the Examples. Polyacrylamide was added to the 4-necked flask in Production Example 3.
1 kg of 10% aqueous solution and 1 kg of 80% hydrazine hydrate aqueous solution were added and reacted at 55° C. for 3 hours with stirring. After the reaction was completed, the resulting viscous solution was poured into about 15 times the volume of methanol to obtain a white precipitate. This was taken, purified by reprecipitation, and dried under reduced pressure at 60°C to obtain an acrylic acid hydrazide polymer compound (hereinafter referred to as A1). Examples and Comparative Examples 1 to 3 A sludge dewatering test was conducted using the above A1 and other specific polymers and metal salts. The physical properties of these polymers are shown in Table 1.

【table】

[Table] The treated sludge and dewatering test methods are as follows. <Sludge> Surplus sludge from biological dephosphorization of sewage PH6.8, SS=1.04%, VSS/SS=83.8% <Dehydration test method> (1) 200 ml of sludge was collected. (2) A predetermined amount of a predetermined metal salt (PAC) was added and stirred. (3) A predetermined amount of predetermined polymers (A1 and B2) were added separately and simultaneously, and appropriate stirring was performed. (4) The produced floc was poured into a Buchner funnel lined with 100 mesh nylon cloth, and the liquid volume was measured after 10 seconds. (5) The concentration of PO ₄ -P in the liquid was also measured to evaluate the hand wringability of the cake remaining on the cloth. (6) After another 2 minutes, the sludge was sandwiched between a belt press dehydrator cloth (polyester, herringbone weave) and a sponge, and the water was compressed and dehydrated for 60 seconds at a pressure of 1 kg/ ^cm2 , and the water content of the dehydrated cake was measured. . The results were as shown in Table 2. As a comparative example, when polymer B1 was added and stirred properly with a spatula (comparative example 1), polymer B3 was added and stirred vigorously for 30 seconds with a hand mixer, and then polymer B4 was added and stirred properly. Also shown are cases in which PAC was added and stirred gently with a spatula for 10 seconds, and then polymer B1 was added and proper stirring was performed (Comparative Example 3).

[Table] Hand drawing property: ○ indicates that good dehydration is possible with a belt press, △ indicates that dehydration with a belt press is difficult.
From the results shown in Table 2, the present invention can satisfy both the settling and dewatering properties of sludge compared to the conventional method, and
It can be seen that the amount of phosphorus leaking into the liquid is extremely reduced. Comparative Examples 4 to 7 Performance tests were conducted in the same manner as in the previous example except that the chemicals shown in Table 3 were used. The results are shown in Table-3.

[Table] Hand drawing property: ○ has the same meaning as above, × indicates that dehydration by belt press is not possible.
From Table 3, it can be seen that the effects of methods other than those of the present invention are significantly worse.

Claims (1)

[Claims] 1. A method for treating surplus sludge generated when treating phosphate-containing wastewater by an activated sludge treatment method including an anaerobic process and an aerobic process, the method comprising adding a metal salt to the sludge. 1. A method for treating sludge, which comprises: mixing the sludge, and then further adding an acrylic acid hydrazide-based polymer compound and a polymer compound containing an amino group or a quaternary ammonium salt. 2 Acrylic acid hydrazide polymer compound has the general formula (In the formula, R represents H or CH ₃ , A represents a monomer unit of acrylamide, methacrylamide, acrylic ester, methacrylic ester, and B represents acrylic acid or a salt thereof, methacrylic acid or a salt thereof, or the above-mentioned A represents a monomer unit copolymerizable with , and l, m and n have the following relationship: 0 mol%<l≦100 mol% n+m+l=100 mol%) according to claim 1, which is a compound represented by How to treat sludge. 3. The polymer compound containing an amino group or a quaternary ammonium salt is an aminoalkyl acrylate,
The method for treating sludge according to claim 1 or 2, wherein the sludge treatment method is a compound selected from aminoalkyl methacrylate, aminoalkylacrylamide, aminoalkylmethacrylamide, or a quaternized product thereof. 4. The sludge treatment method according to any one of claims 1 to 3, wherein the metal salt is an aluminum or iron salt.