JPH0753279B2 - Sludge treatment system Return water treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for efficiently and efficiently removing nitrogen and phosphorus contained in return water generated in a sludge treatment process.

(Prior art) A large amount of organic sludge generated in a sewage treatment plant is treated through several steps, and the separated liquid generated in each treatment process is normally returned to the water treatment process. Was generally done. However, the amount and quality of the returned water differ depending on the sludge treatment method and operation management method, but generally BOD and SS are 2000 mg / or more, and ammonia nitrogen (NH ₄ ⁺ -N) and phosphoric acid-phosphorus-phosphorus. since high concentrations of (PO ₄ ^3- -P), the return load of the flowing water contribute treated water quality deterioration, it is emphasized the importance of advanced treatment in running water return in sludge treatment system recently, especially Various methods have been proposed for the purpose of removing nitrogen and phosphorus. That is,
Regarding BOD and SS among the above factors that deteriorate the quality of treated water,
This has been reduced by the capacity of the treatment plant facilities and efforts for maintenance, but nitrogen and phosphorus cannot be treated sufficiently efficiently in the current facilities.

Specifically, the biological denitrification method is adopted as the nitrogen removal method, and the coagulation precipitation method using Al salt or Ca salt is adopted as the phosphorus removal method. Basically, these two treatment methods are combined. This method is currently adopted.

(Problems to be Solved by the Invention) Phosphorus is removed by the coagulation-precipitation method by adding phosphates existing in water to aluminum salts such as aluminum sulfate and polyaluminum chloride, ferric sulfate and ferric chloride, and This is a method of forming a sparingly soluble salt by adding a flocculant of slaked lime to remove the precipitate. However, the disadvantages of coagulation-precipitation treatment are: (1) The flocs produced by aluminum salts and iron salts are colloidal, and their precipitation and concentration properties are extremely poor.
Poor dehydration (2) In the case of aluminum salts and iron salts, BOD is also removed together, which impairs the nutritional balance and makes it difficult to treat by treatment methods that follow biological treatment. (3) Phosphorus by coal The higher the pH value,
Since the removal rate increases, there is a drawback that the dephosphorization treatment is performed on the high-alkali side where the pH value exceeds 10 and thus neutralization treatment is required after the treatment.

On the other hand, regarding nitrogen removal by biological denitrification, denitrification process that uses organic matter in wastewater itself as a hydrogen donor → Nitrification process is connected in series to remove effluent (nitrification liquid) from the nitrification process. A nitrification solution circulation biological denitrification process of recycling to a nitrogen process can be adopted.

However, in the above-mentioned biological denitrification method, when Al salt or Fe salt was added and coagulation-precipitation treatment was performed, the pH value decreased, the alkalinity decreased, and the nitrifying bacteria caused by aluminum,
There are problems such as inhibition of activity against denitrifying bacteria.

Thus, despite the established technology for removing phosphorus and nitrogen, there are currently problems in practical use.

The present invention is intended to eliminate such drawbacks of the prior art, and an object thereof is to provide a method capable of efficiently removing nitrogen and phosphorus in wastewater by an extremely simple operation.

(Means for Solving Problems) The inventors of the present invention have arrived at the present invention as a result of earnest research for solving the above problems.

That is, in the present invention, the return water generated from the sludge treatment process is adjusted to a pH value of 8 to 9, and the water-soluble magnesium salt is then added to the return water in a Mg / P molar ratio of 0.5.
The gist is a treatment method for returning water in a sludge treatment system, which is characterized by adding biological denitrification treatment after adding it so that it becomes ~ 1.0.

Hereinafter, the present invention will be described with reference to the drawings.

First, as shown in Fig. 1, the pH of caustic soda, etc. is
Adjusting the pH value to 8-9 by adding regulator 2 and then ionizing magnesium salt with an aqueous solution of magnesium chloride, etc. 3
Is added, and the solution is introduced into the biological denitrification process of the nitrification solution circulation system.

This nitrification liquid circulation system is a nitrification tank 5 that follows the denitrification tank 4.
Part 6 of the nitrification liquid from the
Nitrate nitrogen NO _X -N generated by those reduced to N ₂ gas in the denitrification tank 4. In addition, in the denitrification tank 4,
Utilizing BOD components as hydrogen donors denitrifying bacteria gasification of NO _X -N an (N ₂ gas) performed. At this time, the reaction of magnesium ion (Mg ²⁺ ), phosphate ion (PO ₄ ³⁻ ) and ammonium ion (NH ₄ ⁺ ) proceeds in the returning water almost at the molar ratio, and the crystal of magnesium ammonium phosphate crystal Particles are produced.

That is, the phosphoric acid and a part of the ammoniacal nitrogen dissolved in the return water form magnesium ammonium phosphate according to the following formula (1), and are removed as a solid content.

PO ₄ ³⁻ + Mg ²⁺ + NH ₄ ⁺ → MgNH ₄ PO ₄ (1) Next, the outflow water of the denitrification tank 4 flows into the nitrification tank 5, and the residual ammoniacal nitrogen is converted to nitrate nitrogen NO _X −N. The BOD component is oxidatively decomposed while being changed. The effluent of the nitrification tank 5 is returned or discharged after the precipitation treatment 7. Further, a part 6 thereof is circulated to the denitrification tank 4. At this time, the amount of magnesium salt added relative to the concentration of phosphoric acid in the return water must be in the range of 0.5 to 1.0 in terms of Mg / P molar ratio. In the present invention, since the reaction proceeds in a molar manner, in the subsequent biological nitrifying and denitrifying treatment, when the ratio of BOD to nitrogen and phosphorus is generally about 100: 5: 1, the microbial survival environment is It is well known that the biological treatment will be improved and biological treatment will be performed without any problems, and it will be possible to create the optimum conditions.

Fig. 2 is an example of an activated sludge method of aeration-non-aeration intermittent aeration as a biological denitrification method, in which pH adjusting agent 2 is added to return water 1 and then water-soluble Mg salt is added to return water. Is introduced into the aeration tank 8 of the intermittent aeration type activated sludge method. In the aeration tank, the aerobic-anaerobic state alternates due to the ON / OFF operation of the aeration device, and the BOD component in the return water is removed. Also, NH ₄ ⁺ −
Nitrification of N, phosphate ion of added magnesium ions Mg ²⁺ and return running water with the gas of the NO _X -N occurs
PO ₄ ^3- reacts with ammonium ion NH ₄ ⁺ to form magnesium ammonium phosphate crystals, which are removed together with the drawn sludge 10 and returned to the aeration tank as partly returned sludge 9. Thus, the soluble phosphorus and NH ₄ ⁺ -N in the return water are removed as a solid. This solid-liquid separation treatment may be performed in the precipitation tank as described above, or after adding water-soluble magnesium to the return water, stirring treatment is performed for 10 to 30 minutes, and the return water is poured into the aeration tank. The generated magnesium ammonium phosphate may be precipitated and separated before being collected, and then recovered, and then biological treatment by intermittent aeration may be performed.

As described above, the important constitution of the method of the present invention is:
Excess ammonium ion and phosphate ion are removed by precipitation in the form of magnesium ammonium phosphate by addition of magnesium ion, and the remaining ammonium ion and phosphate ion necessary for microbial assimilation are treated by biological nitrification and denitrification. It is to remove in.

(Operation) According to the method of the present invention, it is possible to efficiently remove nitrogen and phosphorus contained in the return water generated in the sludge treatment process. The reason for this is not necessarily clear, but the present inventors presume as follows.

That is, the mechanism for removing phosphorus in the return water is to precipitate it as magnesium ammonium phosphate, as seen in the qualitative analysis of phosphate ions, but the addition amount of magnesium salt was 0.5 in terms of Mg / P molar ratio. In the range of up to 1.0, the concentration of phosphoric acid remains at a level that does not interfere with the subsequent biological nitrification and denitrification treatment. Thus, instead of removing all of the phosphorus in the return water, the subsequent biological nitrification denitrification treatment
PO ₄ ³⁻ ions are consumed for assimilation of organisms, while NH ₄ ⁺ ions can be biologically denitrified by nitrifying and denitrifying bacteria under anaerobic and aerobic conditions. According to the method of the present invention, NH ₄ ⁺ ions are
Since most of it is removed, the load will be reduced, and it is considered that denitrification can be sufficiently performed in the subsequent biological treatment.

(Example) Hereinafter, the specific description of the present invention will be described by way of examples.

Example 1 Sludge anaerobic digester desorption solution [pH value = 7.4, BOD = 2470 mg /
_{, SS = 6860mg /, NH 4} + -N = 560mg /, phosphate (PO ₄ ^3-
-P) = 140mg /] 2.5m ³ / day with sodium hydroxide
After adjusting the ph value to 8.3, magnesium chloride was added as Mg ²⁺ at a concentration of 107 mg / min and introduced into the biological denitrification process by the nitrification solution circulation system shown in FIG. The operating conditions of this biological denitrification process were as follows.

Denitrification tank MLSS 4700 mg / retention time 6 hours Nitrification solution circulation ratio 4 times Nitrification tank MLSS 4600 mg / retention time 6 hours Next, the return water that flows into this denitrification tank is filtered and SS and magnesium ammonium phosphate in the return water are filtered. When the analyzed water quality after removal of the crystals, BOD = 290 mg /, phosphate ion ^{_{(PO 4 3- -P) = 3.8mg}} /, ammonium ion (NH ₄ ⁺ -N) = 480mg was /. Furthermore, analysis of the effluent from the settling tank after the biological denitrification, BOD = 20 mg /, phosphate ion ^{_{(PO 4 3- -P) = 0.8mg}} /
, Ammonium ion (NH ₄ ⁺ -N) = 0.9 mg /, and the water quality was extremely good.

(Effects of the Invention) According to the present invention, it is possible to remove phosphorus and nitrogen in return water generated from a sludge treatment process with extremely high efficiency, and it is extremely easy to load return water, which has been a problem in the past. It can be solved by various technologies and is a technology that can be widely used as wastewater treatment technology.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the dephosphorization denitrification process in the nitrification solution circulation system of the present invention, and FIG. 2 is an explanatory diagram of the dephosphorization denitrification process in the intermittent aeration system. 1 ... Return water, 2 ... pH adjuster 3 ... Magnesium salt, 4 ... Denitrification tank 5 ... Nitrification tank 6 ... Partial return of nitrification liquid 7 ... Precipitation treatment, 8 ... Aeration tank 9 ... … Returned sludge, 10 …… Extracted sludge

Claims (1)

[Claims] 1. The pH of the return water generated from the sludge treatment process
The value is adjusted to 8-9, and then water-soluble magnesium salt is added so that the Mg / P molar ratio becomes 0.5-1.0 with respect to the phosphoric acid concentration in the return water, followed by biological denitrification treatment. A method for treating return water of a sludge treatment system, which is characterized by carrying out.