JPS63214396A - Treatment of returned water in sludge treatment system - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen and phosphorus by regulating returned water generated from a sludge treatment process to a specified pH value, and thereafter adding water soluble magnesium salt and the subjecting it to biological denitrification treatment. CONSTITUTION:A pH modifier 2 such as caustic soda is added to returned water 1 to regulate the pH value to 8-9 and after adding magnesium salt 3, it is introduced into a biological denitrification process of a system for circulating nitrification liquid. The effluent of a denitrification tank 4 is introduced into a nitrification tank 5 and remaining ammoniac nitrogen is changed into nitrate nitrogen and also oxidation and decomposition of BOD component are performed. The effluent of the nitrification tank 5 is subjected to precipitation treatment 7, and thereafter returned or discharged. Further one part 6 thereof is circulated to the denitrification tank 4. Thereby the load of returned water is easily reduced.

Description

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

(Conventional technology) A large amount of organic sludge is generated at sewage treatment plants.

Generally, water is treated through several steps, and the separated liquid generated during each treatment process is returned to one normal water treatment process. However.

The amount and quality of this return water vary depending on the sludge treatment method and operation management method, but generally the BOD and SS are 200
0mg/1 or more, and ammonia nitrogen (Nl+
, ”-N) and phosphoric acid-phosphorus (PO4'-P).

The load associated with this return water contributes to the deterioration of treated water quality, and recently the importance of advanced treatment of return water in sludge treatment systems has been emphasized, and various methods have been proposed with the aim of removing nitrogen and phosphorus in particular. has been done.

In other words, among the factors that deteriorate the treated water quality, BOD and S
Although S has been reduced through the capacity of treatment plant facilities and efforts to maintain and manage them, nitrogen and phosphorus cannot be treated efficiently with the current facilities.

Specifically, the biological denitrification method is used to remove nitrogen, and the coagulation-sedimentation method using Al salts and Ca salts is used to remove phosphorus.Basically, these two treatment methods are combined. The method is currently being used.

(Problems to be Solved by the Invention) Phosphorus removal in this coagulation-sedimentation method involves using phosphates present in water such as aluminum salts such as aluminum sulfate and polyaluminum chloride, ferric sulfate, ferric chloride, etc. This method involves adding a coagulant of slaked lime to form poorly soluble salts, which are then precipitated and removed. However, there are drawbacks to the coagulation and sedimentation treatment method.

(1) The flocs produced by aluminum salts and iron salts are colloidal and have extremely poor settling and concentration properties.
(2) In the case of aluminum salts and iron salts, BOD is also removed, which disrupts the nutritional balance and makes treatment difficult with subsequent biological treatment. (3) Phosphate removal by lime The removal mechanism has drawbacks such as the fact that the higher the pH value, the higher the removal rate, so p) dephosphorization is performed on the high alkaline side where the I value exceeds 10, so neutralization treatment is required after treatment. .

On the other hand, regarding nitrogen removal by biological denitrification, the denitrification process, which utilizes the organic matter itself in wastewater as a hydrogen donor, and the nitrification process are connected in series, and the effluent from the nitrification process (nitrified liquid) is desorbed. A biological denitrification process in which nitrified liquid is recycled into the nitrogen process can be adopted.

However, in the above biological denitrification method, AN salt or F
If e-salt is added and a coagulation-sedimentation treatment is performed, there are problems such as a decrease in pH value, a decrease in alkalinity, and inhibition of the activity of nitrifying bacteria and denitrifying bacteria due to aluminum.

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

The present invention aims to eliminate these drawbacks of the prior art, and its purpose is to provide a method that can efficiently remove nitrogen and phosphorus from wastewater with extremely simple operations.

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

That is, 1 the present invention provides a sludge treatment characterized by adjusting return water generated from a sludge treatment process to a pH value of 8 to 9, first adding a water-soluble magnesium salt, and then performing biological denitrification treatment. The gist of this paper is a method for treating system return water.

The present invention will be explained below with reference to the drawings.

First, in Fig. 1, P of caustic soda etc. is added to the return water 1.
A H regulator 2 is added to adjust the pH value to 8 to 9, and then a magnesium salt 3 which is ionized with an aqueous solution such as magnesium chloride is added, and the mixture is introduced into a biological denitrification process using a nitrification liquid circulation system.

This nitrification liquid circulation system is a nitrification tank 5 that follows the denitrification tank 4.
A part 6 of the nitrification liquid is circulated from the nitrification tank 6 to the denitrification tank 4, and the nitrate nitrogen NO and -N produced in the nitrification tank 5 are reduced to N and gas in the denitrification tank 4. In addition, in the denitrification tank 4, the BOD component in the return water is used as a hydrogen donor for denitrifying bacteria, and NoX
-N gasification (Nt gas) is performed.

At this time, magnesium ions (Mg''), phosphate ions (po4.'-) and ammonium ions (N
The reaction with H4 proceeds in approximately the same molar ratio, producing crystalline particles of magnesium ammonium phosphate.

That is, phosphoric acid and a part of ammonia nitrogen dissolved in the return water are produced as magnesium ammonium phosphate according to the following formula (i1), and are removed as a solid content.

PO,” +Mg” + NH4+→ MgNH
4POt (1) Next, the outflow water from the denitrification tank 4 flows into the nitrification tank 5, and the remaining ammonia nitrogen is converted to nitrate nitrogen.
At the same time as converting it to 0X-N, the BOD component is oxidized and decomposed. The effluent from the nitrification tank 5 is subjected to a precipitation treatment 7 and then returned or discharged. Further, a portion 6 of it is circulated to the denitrification tank 4. At this time, the amount of magnesium salt added to the phosphoric acid concentration in the return water was 0.00 in Mg/P molar ratio.
The range of 5 to 1.0 is preferable. In the present invention, the reaction proceeds according to the molar ratio of 5, so in the subsequent biological nitrification and denitrification treatment, the ratio of BOD to nitrogen to phosphorus is generally approximately 10.
When the ratio becomes 0:5:1, the survival environment for living things becomes better,
Since it is well known that biological treatment can be carried out without any problems, it is possible to adjust the amount added to create the optimum conditions.

Figure 2 shows an example of an activated sludge method using an aeration-non-aeration intermittent aeration method as a biological denitrification method.
The return water to which the conditioner 2 was added and then the water-soluble Mg salt was added is allowed to flow into the aeration tank 8 of the intermittent aeration type activated sludge method. In the aeration tank, aerobic and anaerobic conditions occur alternately by ON-OFF operation of the aeration device, and BOD components in the return water are removed. In addition, the nitrification effect of NH,''-N and the gasification of NOX-N occur, and the added magnesium ion Mgz
``'' reacts with phosphate ions PO43- and ammonium ions NH,'' in the return water to form magnesium ammonium phosphate crystals, which are removed together with the drawn sludge 10 and partially returned to the aeration tank as return sludge 9. In this way, soluble phosphorus and NO, -N in the return water are removed with solid matter. In addition.

This solid-liquid separation treatment may be performed in a settling tank as described above, or after adding water-thin magnesium to the return water, stirring is performed for 10 to 30 minutes, and the return water is flowed into the aeration tank. The previously produced magnesium ammonium phosphate may be separated by precipitation and recovered once, followed by biological treatment by 8 intermittent aerations.

As mentioned above, the important components of the method of the present invention are:
Excess ammonium ions and phosphate ions are precipitated and removed in the form of magnesium ammonium phosphate by adding magnesium ions, and the remaining ammonium ions and phosphate ions necessary for assimilation by microorganisms are subjected to biological nitrification and denitrification treatment. It is to be removed by

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

In other words, the mechanism for removing phosphorus from the return water is to precipitate it as magnesium ammonium phosphate, as seen in the qualitative analysis of phosphate ions, but the amount of magnesium salt added is 0 at the Mg/P molar ratio. .5-1.0
It is preferable to add the phosphoric acid so that the concentration of phosphoric acid remains at a level that does not interfere with the subsequent biological nitrification and denitrification treatment. Instead of removing all the phosphorus in the return water like this.

In the subsequent biological nitrification-denitrification process, po, '- ions are consumed by living organisms, while NH, + ions are used for biological denitrification by nitrifying and denitrifying bacteria under anaerobic and aerobic conditions. According to the method of the present invention, it is possible to treat NH4”
Since most of the ions are removed by adding magnesium ions, the load is reduced, and it is thought that the subsequent biological treatment will be able to perform sufficient denitrification treatment.

(Example) A detailed explanation of the present invention will be given below with reference to examples.

Example 1 Sludge anaerobic digestion tank desorbed liquid CpH value = 7.4. BOD
=2470mg/β, SS=6860mg/l,
NH*”-N=560mg/l.

Phosphoric acid (PO*'-P) -140mg/l) 2
．． 5 m”/day to a PTT value of 8 with sodium hydroxide.
．． After adjusting the amount of magnesium chloride to M g 2 +
107 mg/1 was added and introduced into the biological denitrification process using the nitrification solution circulation method shown in FIG. The operating conditions for this biological denitrification process were set as follows.

Denitrification tank M L S 3 4700 mg/1 residence time 6 hours Nitrification liquid circulation ratio 4 times Nitrification tank M L S S 4600 mg/1 residence time 6 hours Next, the return water flowing into this denitrification tank is filtered and returned When the water quality was analyzed after removing the SS and magnesium ammonium phosphate crystals in the water, BOD = 290
+sg/l, phosphate ion (Pot'-P) = 3
．． 8mg/l.

Ammonium ion (NH, “-N) = 480mg
/ l te, 1) ff:=.

Furthermore, when we analyzed the water flowing out from the settling tank after biological denitrification treatment, we found that ROD = 20 mg/l.
, phosphate ion (PO4'-P)-0.8mg/j2,
77moni'7muio7 (NH4"-N) = 0.9mg
/l of extremely good water quality.

(Effects of the Invention) According to the present invention, it is possible to remove phosphorus and nitrogen from the return water generated from the sludge treatment process with extremely high efficiency, and it is possible to extremely easily reduce the load on the return water, which has been a problem in the past. This can be solved using advanced technology, and this technology can be widely used as a wastewater treatment technology.

4. Description of the Drawings FIG. 1 is an explanatory diagram of the dephosphorization and denitrification treatment in the nitrification liquid circulation method of the present invention, and FIG. 2 is an explanatory diagram of the dephosphorization and denitrification treatment in the intermittent aeration method.

1----------1 return water 2----------
pH adjuster 3--1--magnesium salt 4-
-----One theory Nitrogen tank 5---One nitrification tank 6---11 Partial return of nitrified solution 7---One precipitation treatment 8--------- One aeration Tank 9------1 Return sludge 10------
---Ichipu sludge patent applicant Unitika Co., Ltd. Figure 1

Claims (2)

[Claims] (1) Return water generated from the sludge treatment process has a pH value of 8.
~9, then add water-soluble magnesium salt,
A method for treating return water of a sludge treatment system, which is characterized in that biological denitrification treatment is subsequently performed. (2) The method for treating return water of a sludge treatment system according to claim 1, characterized in that the Mg/P molar ratio when adding the water-soluble magnesium salt is 0.5 or more and 1.0 or less. .