JP4335065B2 - Organic wastewater or sludge treatment method and apparatus - Google Patents

Description

  The present invention relates to a system for treating organic wastewater or sludge in a sewage treatment plant or various wastewater treatment facilities. More specifically, the present invention relates to digestion and desorption liquid of human waste and septic tank sludge, sludge digestion liquid, chemical factory wastewater, etc. In a technology for removing phosphorus and the like as crystals of magnesium ammonium phosphate (hereinafter also referred to as “MAP”) from waste water or sludge containing organic substances of high concentration, phosphorus and nitrogen, and recovering the MAP crystals, The present invention relates to a method and apparatus for efficient generation.

  Conventional simultaneous denitrification and dephosphorization simultaneous treatment methods include biological treatment methods such as anaerobic anaerobic and aerobic methods, anaerobic aerobic methods, coagulation precipitation methods, alumina adsorption methods, etc. There is. In recent years, MAP treatment and the like have also been attempted for return water, anaerobic digestion and detachment liquid, etc. generated in the process of human waste treatment and sewage treatment. Among these treatment methods, the anaerobic anaerobic aerobic method has problems such as unstable treatment performance due to changes in water quality and changes in the external environment due to seasonal fluctuations. The combined method has a problem in that the processing steps are complicated and the running cost including chemicals is large. The MAP treatment method is less complicated to operate than the previous two methods, and in particular, it can stably recover phosphorus, and the recovered MAP has an added value as an excellent fertilizer, making effective use of resources. From this point, it can be said that this is an excellent phosphorus and nitrogen removal technique. An example of a conventional method for collecting MAP in the sludge anaerobic treatment step is shown in FIG.

  However, in the case of the MAP method, (1) chemical costs such as sodium hydroxide as a pH adjusting agent and magnesium chloride as an additive are large, and (2) MAP is rapidly crystallized in a short time of less than 1 hour. (Abbreviated as “rapid MAP reaction”), fine MAP particles are generated and leak from the MAP reaction tank, and the MAP recovery rate may be reduced to about 60 to 70%. (3) The rapid MAP reaction is about 400 mg. When SS of more than 1 / liter is mixed in the liquid, SS is entangled with the MAP crystallized product and cannot be recovered as high-purity MAP crystal. (4) In the case where an anaerobic digestion process is adopted before the MAP treatment process In the anaerobic digestion process, the MAP reaction that becomes the rate limiting of the soluble magnesium salt in the sludge has already been carried out in the reaction tank, and the generated MAP particles remain as SS. Therefore, there is a problem that it is disposed of together with the sludge without being recovered in a mixed state with the digested sludge.

  Therefore, in order to solve the above-described conventional problems, the present inventors have disclosed “organic wastewater treatment method and treatment apparatus” disclosed in Japanese Patent Application Laid-Open No. 2002-45889 (patent application number “2000-231633”). A technology for efficiently recovering phosphorus in wastewater as MAP was proposed. That is, anaerobic digestion is performed on surplus sludge generated in the organic wastewater treatment process, and a magnesium source is supplied in the process to generate MAP in the reaction tank, and the generated MAP is separated from the digested sludge. Organic drainage treatment method and treatment comprising a step of collecting, and a step of producing and collecting MAP by adding and mixing a magnesium source and a pH adjuster to the concentrated separated water of digested sludge or the dehydrated filtrate of the sludge A device was proposed. By carrying out the invention, it has become possible to greatly improve the efficiency of collecting phosphorus in the waste water. Accordingly, as a result of detailed studies to improve the invention, the present inventors have further improved and stabilized the MAP recovery rate, increased the purity of the generated MAP, reduced the amount of chemicals used, and simplified the processing system. Efforts were made to enable further improvements.

  An object of the present invention is to solve the above-described problems of the prior art and further improve the invention of Japanese Patent Application Laid-Open No. 2002-45889 (patent application number “2000-231633”). That is, the present invention is an organic wastewater treatment system, particularly wastewater containing organic matter, nitrogen and phosphorus, such as digestion and desorption liquid of human waste and septic tank sludge, sludge digestion liquid, chemical factory wastewater, etc. In a MAP treatment method that employs an anaerobic treatment process for waste water containing organic matter, phosphorus, and nitrogen, and removes phosphorus as magnesium ammonium phosphate crystals, the amount of drug used is reduced, nitrogen, and While greatly improving the phosphorus removal efficiency, the processing performance realized in the invention of JP-A-2002-45889 can be achieved by improving and stabilizing the MAP recovery rate, increasing the purity of the generated MAP, and reducing the amount of chemical used. The present invention relates to a technique for further improving and simplifying the processing system.

  In order to further improve the phosphorus recovery process disclosed in the invention of JP-A-2002-45889, the present inventors have studied using various types of liquids or slurries as Mg-containing water added to the digester as the Mg source. Has been repeated. Among them, it is possible to start up the system quickly and efficiently at the time of starting up the system, to maintain the processing performance at the lowest possible chemical cost, and the ratio of MAP particles with high purity, high separability and high handling properties. The system has been improved with these points as new issues.

  That is, the present invention can efficiently set up a system, maintain processing performance at a low chemical cost, and maintain high generation and recovery of high-purity, high-separation and high-handling MAP particles. It is an object of the present invention to provide a method and apparatus for treating organic wastewater or sludge. In the present specification, organic sludge is simply referred to as “sludge”.

The present invention was able to solve the above problems by the method or apparatus shown below.
(1) Anaerobic digestion treatment of organic wastewater or sludge, and a magnesium source added in the anaerobic digestion step to produce magnesium ammonium phosphate generated from phosphorus or phosphorus and nitrogen in wastewater or sludge In the treatment method having a process and a process of taking out the produced magnesium ammonium phosphate out of the system, a magnesium compound solution that is easily soluble in water is added as a magnesium source at the start of the magnesium ammonium phosphate production process , A method for treating organic wastewater and sludge characterized by switching to a slurry-like or powdery addition of a magnesium compound that is sparingly soluble in water as a magnesium source after a predetermined period of time for the production of magnesium ammonium oxide .
(2) As said easily soluble magnesium compound solution, magnesium hydroxide is dissolved with hydrochloric acid or sulfuric acid and adjusted to pH 4.5 to 6.9 for use, and the organic as described in (1) above Wastewater and sludge treatment methods.

(3) Anaerobic digestion treatment of organic wastewater or sludge, adding a magnesium source in the anaerobic digestion step to produce magnesium ammonium phosphate generated from phosphorus or phosphorus and nitrogen in wastewater or sludge, In an organic wastewater and sludge treatment apparatus having a step of taking out the produced magnesium ammonium phosphate out of the system, it has a magnesium source mixing tank in the previous stage of the anaerobic digestion step, and magnesium hydroxide is added to hydrochloric acid or hydrochloric acid in the mixing tank. A mechanism for preparing an easily soluble magnesium compound solution by dissolving in sulfuric acid and adjusting the pH to 4.5 to 6.9, a mechanism for adding the easily soluble magnesium compound solution, and a process for producing magnesium ammonium phosphate are predetermined. After a period of time, the magnesium source is added in a slurry or powder form of a magnesium compound that is sparingly soluble in water. Organic wastewater, and sludge treatment apparatus characterized by having a structure.

  The present invention is a technology for efficiently separating and recovering particles of inorganic compounds such as MAP produced in an anaerobic digestion tank in the treatment of organic wastewater and sludge. It is possible to increase the ratio of MAP particles having a high purity, a high separation property and a high handling property, and the like.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of the present invention, and the present invention is not limited to this embodiment.
In FIG. 1, primary sedimentation sludge 5 and surplus activated sludge 6 discharged from the organic wastewater treatment system are concentrated and separated by a sludge concentrator 20, and concentrated sludge 7 is introduced into a Mg source mixing tank 21. Especially in the Mg source mixing tank 21, a predetermined amount of easily soluble magnesium chloride, magnesium hydroxide hydrochloric acid neutralized water, magnesium hydroxide sulfuric acid neutralized water, or the like as the Mg source at the time of system startup is linked to the sludge supply amount. Add and mix. In terms of cost, it is more advantageous to use a liquid obtained by neutralizing magnesium hydroxide with hydrochloric acid or sulfuric acid than magnesium chloride. However, since the neutralized Mg solution recrystallizes magnesium hydroxide on the alkali side, It is desirable to add in the acidic to weakly acidic region. However, mixed raw sludge to be mixed usually has acid fermentation in many cases and may be slightly acidic, so there may be no problem even if some magnesium hydroxide particles remain. . The use of easily soluble magnesium prevents the tendency of the MAP reaction to proceed rapidly when magnesium ions are locally increased, to capture SS (sludge) during MAP generation, and to lower the purity of the generated MAP. Because. The start-up period varies depending on the sludge properties, digestion tank residence time, and the like, but it is often about 5 to 60 days.

The soluble Mg well mixed in the Mg source mixing tank 21 spreads uniformly in the sludge and the local concentration gradient is reduced. The more the digested tank sludge 8 having a uniform solubility Mg concentration, the lower the frequency of local occurrence of MAP supersaturation when contacting the digested sludge when the digester 22 is charged. In addition, as a means for suppressing local occurrence of supersaturation, it may be effective to circulate digested sludge and mix the digested tank input sludge 8 with the circulating flow. When the start-up period is over, the amount of MAP in the digestion tank 22 or the total surface area of MAP is sufficiently large, and the PO ₄ -P in the digested sludge is sufficiently small, the added Mg source is hardly dissolved from the readily soluble Mg source Switch to a natural Mg source. As a poorly soluble Mg source, 35% magnesium hydroxide slurry, etc., which is generally inexpensive and has a relatively large amount of circulation, is often used. An Mg source that is soluble may be used. After that, it is possible to continue operation using these relatively inexpensive hardly soluble Mg sources, but it is necessary if you want to control the purity of MAP particles or increase the particle size. Accordingly, it may be possible to control the properties of the MAP particles by increasing the use frequency of the easily soluble Mg source.

The digested sludge 9 containing MAP particles is separated from the MAP separation and concentrator 26 by the MAP concentrated sludge 15 containing a large amount of particles mainly composed of MAP having a particle size of about 100 μm or more and a specific gravity of about 1.5 g / cm ³ or more. 10 is separated. As the MAP separator / concentrator 26, a liquid cyclone, an electric sieve, a screen-like separator, a precipitation separator, a MAP cleaning device, a device combining these device principles, or the like can be used (for example, “organic” Wastewater and sludge treatment method and treatment apparatus ": by the process disclosed in Japanese Patent Application No. 2002-328336). If impurities remain in the digested sludge 9, they may be removed by a impurities removing device (not shown) before being introduced into the MAP separation and concentration device 26. In addition, in the MAP separation / concentration device 26, in addition to MAP, metal sulfide particles generated in the anaerobic digestion tank 22 may be removed in some cases. As a means for intentionally separating the metal sulfide, impurities are present. A removal device may be used. The MAP desorption sludge 10 (the sludge mixed with the dust smashing sludge when the contaminant removal device is used) is dehydrated in the dewatering device 25, the dewatered cake 12 is discharged, and the dehydrated filtrate 13 is first put in the sedimentation tank 17. Will be returned.

  As described above, as the Mg source to be added, an easily soluble Mg source such as a hydrochloric acid neutralization solution of magnesium hydroxide is used at the time of start-up, and after a predetermined period of time, the added Mg source is changed to a magnesium hydroxide slurry or the like. By switching to an inexpensive and hardly soluble Mg source, the system can be quickly and efficiently started up, the processing performance can be maintained at the lowest possible chemical cost, and the ratio of MAP particles with high purity, high separation and high handling can be maintained at a high level. And so on.

  Next, an example of the operation result of the experimental plant that actually incorporates the wastewater treatment technology of the present invention will be described. However, the present invention is not limited to this embodiment.

Examples and Comparative Examples 1 to 3
A present Example is an Example by the experimental plant performed using the sludge of A sewage treatment plant, and a flow is the same as the flow of FIG. 1 shown previously. A treatment plant adopts activated sludge treatment by anaerobic aerobic method. In the example experimental plant, the first settling sludge and surplus sludge collected from the treatment plant A are mixed at about 1: 1 and concentrated by a centrifugal concentrator. The anaerobic digestion tank 22 was digested at an intermediate temperature of 35 ° C., and the residence time was 25 days. The amount of Mg added was 0.4 g (as Mg) per liter of supplied sludge. Moreover, all the added Mg sources used the solution or slurry which contains 7% in a component as Mg.
In this experiment, an experiment for 6 months was performed in four series. The difference in the four series of experimental conditions is that different Mg sources were used on the start-up day 60 and the 61st-180th day as the Mg source to be added. Table 1 shows the differences between the four series of experimental conditions.

  From the four series of experimental results, the MAP recovery performance of Examples, Comparative Examples 2 and 3 is almost the same, MAP recovery rate: 85.9-86.4%, MAP purity: 80.1-80.9 %Met. In Comparative Example 1 where only water mug (magnesium hydroxide) was used as the Mg source until the 180th day from the start of the experiment, the MAP recovery rate was 82.5%, the MAP purity was 72.8%, and the MAP recovery performance was slightly lower than others did. In addition, since the total chemical cost during the experiment period was in the order of Comparative Example 3> Comparative Example 2> Example> Comparative Example 1, considering both MAP recovery performance and chemical cost, the example method was The most balanced and efficient.

  The organic wastewater or sludge treatment method and apparatus of the present invention is a technology for efficiently separating and recovering particles of inorganic compounds such as MAP produced in an anaerobic digestion tank, so that a sewage treatment plant, various wastewater treatment facilities, etc. Is a technique useful as a method and apparatus for treating wastewater containing high concentrations of organic matter, phosphorus and nitrogen.

It is a flowchart of one Embodiment of the processing apparatus of this invention. It is a flowchart of one Embodiment of the conventional processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Influent water 2 First sedimentation basin effluent 3 Biological reactor effluent 4 Treated water 5 Initial sedimentation sludge 6 Excess sludge 7 Concentrated sludge 8 Digestion tank sludge 9 Digested sludge 10 MAP desorption sludge 11 Contamination sludge 12 Dehydrated cake 13 Dehydrated filtrate 14 Concentrator desorption liquid 17 First sedimentation tank 18 Aeration tank 19 Final sedimentation tank 20 Sludge concentration apparatus 21 Mg source mixing tank 22 Anaerobic digestion tank 25 Dehydration apparatus 26 MAP separation apparatus 27 Recovery MAP

Claims (3)

An anaerobic digestion treatment of organic waste water or sludge, and a production step of adding magnesium source in the anaerobic digestion step to produce phosphorous or magnesium ammonium phosphate produced from phosphorus and nitrogen in the waste water or sludge, and In a treatment method having a step of taking out the produced magnesium ammonium phosphate out of the system, a magnesium compound solution that is easily soluble in water is added as a magnesium source at the start of the production step of the magnesium ammonium phosphate, and the magnesium ammonium phosphate A method for treating organic wastewater and sludge, characterized by switching to addition of a magnesium compound that is sparingly soluble in water as a magnesium source in the form of a slurry or powder after a predetermined period of time has elapsed . 2. The organic wastewater and sludge according to claim 1, wherein magnesium hydroxide is dissolved in hydrochloric acid or sulfuric acid and adjusted to pH 4.5 to 6.9 as the easily soluble magnesium compound solution. Processing method. Organic wastewater or sludge is subjected to anaerobic digestion treatment, and a magnesium source is added in the anaerobic digestion step to produce magnesium ammonium phosphate produced from phosphorus or phosphorus and nitrogen in wastewater or sludge. In an organic wastewater and sludge treatment apparatus having a step of taking out magnesium ammonium acid out of the system, it has a magnesium source mixing tank in the previous stage of the anaerobic digestion process, and magnesium hydroxide is dissolved in hydrochloric acid or sulfuric acid in the mixing tank Then, a mechanism for adjusting the pH to 4.5 to 6.9 to prepare an easily soluble magnesium compound solution, a mechanism for adding the easily soluble magnesium compound solution, and a magnesium ammonium phosphate production step have passed for a predetermined period of time. Later, as a magnesium source, a mechanism of adding in a slurry or powder of a magnesium compound that is sparingly soluble in water; Organic wastewater, and sludge treatment apparatus, characterized in that it comprises.

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