JPS6229115B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wastewater treatment method that uses bone char to simultaneously chemically and biologically remove phosphate ions and ammonia ions present in secondary treated water such as sewage and human waste, as well as other waters. Secondary treated water such as sewage and human waste contains organic phosphorus compounds, inorganic phosphates, organic nitrogen compounds, ammonia, etc., but in normal biological treatment processes, some of the organic phosphorus compounds and organic nitrogen compounds are removed. It is biologically treated and converted into inorganic phosphoric acid compounds, ammonia, etc., but some of these are only used as nutrients for microorganisms, and the excess remains in the treated water. These phosphate ions and ammonia ions cause eutrophication of environmental waters, contaminate water quality, and cause pollution. The conventional method for removing phosphate ions is to add metal ions to sewage and remove the dissolved phosphate ions by precipitation as poorly soluble salts. or due to a side reaction in which the added metal salt is hydrolyzed by the alkali dissolved in the sewage.
It is necessary to use a larger amount of metal ions than the theoretical amount, which increases the cost and requires treatment of the precipitated sludge. The slaked lime method is also used. In the conventional slaked lime method, the reaction takes place at a pH of 10 to 11, and carbonate and phosphate ions dissolved in sewage are removed as precipitates of calcium carbonate and aluminum phosphate. This precipitate becomes sludge that must be treated, and other chemicals are required to neutralize the treated water, both of which lead to high costs. In addition, as a method for removing phosphate ions, in a dephosphorization tower filled with bone char of a certain diameter, the pH of the bone char packed bed is adjusted to 6 or more, preferably 8 to 9, by using an alkaline agent (calcium hydroxide, sodium hydroxide, etc.). By adjusting and circulating a portion of the treated water, a constant fluidity state is maintained within the bone char packed bed, and phosphate ions are removed by crystallization and growth on bone char, the activated calcium hydroxyapatite crystals that are its main component. There is a way to do that. Compared to the conventional slaked lime method, this method has the advantage that only a small amount of alkaline agent such as calcium hydroxide is required, the operating cost is low, and no sludge is generated. However, even in such a dephosphorization method using a bone char packed bed, when secondary treated sewage water is used as the water to be treated, organic substances present in the water adhere to the surface of the bone char, reducing the surface activity and reducing the dephosphorization effect. This will hinder the Therefore, in order to increase the dephosphorization effect, it is necessary to oxidize and decompose such organic substances. On the other hand, biological nitrification and denitrification is the most efficient treatment method for removing ammonia ions, which is another causative agent of eutrophication. It is generally known that If the water to be treated contains phosphate ions and ammonia ions at the same time, it is desirable to remove both from the viewpoint of preventing eutrophication. In view of the above problems, the present invention eliminates the drawbacks of the conventional slaked lime method, allows the water to be treated to flow through a bone char packed bed, crystallizes phosphate ions into bone char as calcium hydroxyapatite, and removes the treated water. Supplying oxygen by aeration with oxygen, etc., circulating a part of this aerated water to circulate inside the bone charcoal packed bed along with the water to be treated, and maintaining the inside of the bone charcoal packed bed in a sufficiently aerobic condition, This method oxidizes and decomposes organic matter in the water to be treated, increasing the effect of removing phosphate ions, and nitrifies ammonia ions in the water. Next, an example of an apparatus used to carry out the present invention will be described with reference to the accompanying drawings. Reference numeral 1 denotes a dephosphorization reaction tower in which a bone char packed bed 2 is formed, and above and below the packed bed 2 a clear water outlet part 3 and a treated water inlet part 4 are formed. Furthermore, a treated water introduction pipe 5 is connected to the introduction part 4 , and a treated water delivery pipe 6 is led out from the delivery part 3 .
a diffuser pipe 8 connected to an air or oxygen supply pipe 7;
is inserted. Further, a circulation pipe 9 led out from the outlet part 3 is communicated with an introduction part 4 of the reaction column 1 or an introduction pipe 5 near the introduction part 4 through a circulation pump 10 in the middle. In addition, the PH electrode 1 is installed in the lead-out part 3.
1 is inserted and a PH indicator controller 12 is inserted into this PH electrode 11.
This PH indicator controller 12 is connected to an alkali injection pump 14 provided in the middle of the alkali injection pipe 13, and the alkali injection pipe 13 is connected to the reaction tower 1.
It is communicated with the introduction part 4 of , or the middle of the circulation pipe 9 near this introduction part 4 . Next, an embodiment of the present invention using the above-described apparatus will be described. The water to be treated flows into the lower part of the dephosphorization reaction tower 1 through the introduction pipe 5, and while passing through the bone char packed bed 2 from the bottom to the top, it comes into contact with the bone char, and the phosphate ions contained in the water to be treated are Calcium is crystallized into hydroxyapatite crystals on the surface of bone charcoal and removed, leading to extraction section 3.
is discharged. Air or oxygen is aerated through the supply pipe 7 from the aeration pipe 8 inserted into the outlet part 3 at the upper part of the packed bed 2, and the oxygen is dissolved in the treated water. A part of the treated water in which oxygen has been dissolved is introduced into the introduction section 4 of the dephosphorization reaction tower 1 through the circulation pipe 9 by the circulation pump 10, and together with the treated water introduced from the introduction pipe 5, the upward flow linear velocity inside the tower is increased. 10m/hr~100m/hr
Preferably, by setting the speed to 25 m/hr to 60 m/hr, the bone char packed bed 2 filled with bone char having a constant particle size of 0.1 mm to 3.0 mm is expanded and fluidized. The amount and flow rate of the circulating treated water added to the water to be treated are determined by using the circulating pump 11 as a variable capacity liquid pump.
This is done by adjusting the valve No. 1. Furthermore, the PH electrode 1 inserted into the lead-out part 3 at the upper part of the packed layer 2
1, the PH indicator controller 12 reads the PH value and sets the PH in the packed bed 2, operates the alkali injection pump 14 according to the setting, and the alkali agent is dephosphorized through the alkali injection pipe 13. It is introduced into the introduction section 4 at the bottom of the reaction tower 1. Next, the operation of this embodiment will be explained. Calcium hydroxyapatite crystals are in an equilibrium relationship through the solubility product of calcium ion concentration, phosphate ion concentration, hydroxide ion concentration, and the higher the calcium ion concentration and hydroxide ion concentration, the lower the phosphate ion concentration. Further, the rate of removal of phosphate ions by crystallization increases as the concentration of calcium ions and hydroxide ions increases, and also increases in proportion to the specific surface area of the calcium hydroxyapatite crystals on the surface of the filler. Normal secondary sewage treatment water contains enough calcium ions to crystallize phosphate ions as calcium hydroxyapatite, so if you only want to increase the hydroxide ion concentration, add sodium hydroxide. However, it is recommended to use calcium hydroxide because of the cost and because it lowers the concentration of calcium ions in the water to be treated and lengthens the reaction time, and because it adds calcium ions to the water to be treated. is advantageous. In addition, by adding an alkaline agent, if the pH is adjusted to 6 or more, preferably 8 to 9, than the neutral pH of the secondary treated sewage water, the solubility of calcium hydroxyapatite will be greatly reduced by several times. The reaction speed can be increased more than ten times and the device can be made smaller. PH6
Below, the solubility of calcium hydroxyapatite increases rapidly. In addition, the amount of calcium hydroxide required to adjust the pH is sufficient at several tens of mg/300mg/~400mg/ as in the case of the conventional coal flocculation method.
There is no need to add either. In addition to bone char, there are other substances that contain calcium hydroxyapatite crystals, such as phosphate rock, but the active crystal specific surface area on the surface is small, at most only a few percent of bone char, making it inefficient and requires a large device. Furthermore, when the concentration of each ion in the water to be treated increases and the degree of supersaturation increases, flocs of calcium phosphate salts such as calcium hydroxyapatite and calcium phosphate are generated and flow out into the treated water. For this purpose, a part of the treated water from which phosphate ions have been removed is circulated and mixed with the treated water at a ratio of 1 to 20 times, thereby lowering the phosphate ion concentration in the treated water and preventing the formation of flocs. . Furthermore, by supplying and circulating oxygen to the treated water, the inside of the bone charcoal packed bed is kept under aerobic conditions, which effectively oxidizes and decomposes the nitrified organic matter of ammonia ions, and removes the nitrified organic matter that is attached to the surface of the bone charcoal. Organic substances that reduce surface activity are removed, and phosphate ion removal efficiency is improved. Also, when comparing the removal time of phosphate ions and the nitrification time of ammonia ions when removing phosphate ions from treated water and nitrifying ammonia ions, it is found that when secondary treated sewage water is used as the water to be treated, Since the removal time for phosphate ions is longer and the scale of the equipment is determined by the removal of phosphate ions, the treatment time will not be extended even in the winter when the nitrification rate of ammonia ions decreases. In addition, if the water to be treated contains a large amount of phosphate ions, even if calcium ions are added, including calcium hydroxide necessary for nitrification, the amount necessary to remove the phosphate ions as calcium hydroxyapatite will not be enough. If this is not achieved, calcium ions may be added to the water to be treated in a stoichiometric weight ratio of 1:0.7 or more to phosphate ions. According to the present invention, by passing sewage, secondary treated human waste water, or other water to be treated containing phosphate ions and ammonia ions through a bone char packed bed, the phosphate ions contained in the water to be treated are removed from bone char. Upon contact with active calcium hydroxyapatite crystals on the surface, calcium hydroxyapatite [Ca ₅
(PO ₅ ) ₃ OH] and can be removed from the water to be treated without generating sludge. Furthermore, after the treated water that has passed through the bone charcoal bed is aerated, a portion of this treated water is passed through and circulated again from the bottom of the bone charcoal bed along with the treated water to maintain a uniform pH within the bone charcoal bed. In addition, the bone char packed bed expands and becomes fluidized, promoting contact between the water to be treated and the bone char. Furthermore, by mixing the treated water from which phosphate ions have been removed with the water to be treated, it is possible to prevent the formation of calcium phosphate flocs caused by supersaturation of the phosphate ion concentration. Furthermore, by circulating treated water that has been aerated and dissolved in oxygen, oxygen is supplied into the bone char packed bed, and by placing the packed bed under aerobic conditions, ammonia is removed using microorganisms attached to the bone char surface. Nitrification and oxidative decomposition of organic matter are performed to reduce the concentration of organic matter in the water to be treated, prevent the deposition of organic matter on the surface of bone charcoal, and increase the surface activity of calcium hydroxyapatite crystals on the surface of bone charcoal for dephosphorization. It can increase efficiency. Furthermore, by adjusting the pH within the bone char packed bed to 6 or more, the solubility of precipitated calcium hydroxyapatite can be kept low and the reaction rate can be accelerated. Furthermore, by adding calcium ions to the water to be treated so that the atomic ratio of phosphorus (P) and calcium (Ca) is 3:5 or less, sufficient calcium ions are supplied for the production of calcium hydroxyapatite. This supply amount is approximately 1/10 of the calcium ions added in the conventional lime flocculation method, which is sufficient, and because the amount of lime added is small, the processing cost is low and no sludge is generated, which reduces the sludge processing cost and sludge processing equipment. It is also economical. Next, a comparative experiment was conducted between the method of the present invention and a method without aeration, and the results were examined. 1 Experimental Method Experimental Example 1 Bone charcoal 2 with a particle size of 0.54 mm to 0.99 mm was packed into a cylindrical column with a diameter of 5 cm and a height of 200 cm. (The height of the packed bed is approximately 105 cm.) Secondary treated sewage water is used as the water to be treated, and this is supplied at a flow rate of 4/hr. Calcium hydroxide is used as the alkaline agent to adjust the pH in the packed bed to 8-8.
9, and the liquid linear velocity in the packed bed was set to 40 m/hr using a circulation pump. In addition, aeration with air was performed at the top of the packed bed. Experimental Example 2 The same method as Experimental Example 1 was used without aeration. 2 Experimental results are shown in Table-1.

[Table] From Table 1, when comparing treated water with aeration to treated water without aeration, the remaining amount of phosphate ions is approximately 1/2, and all ammonia nitrogen is converted to nitrate nitrogen. It can be seen that both TOC and BOD are small.

[Brief explanation of the drawing]

The figure is an explanatory diagram illustrating an example of implementation of the present invention. 2...Bone charcoal filling layer.

Claims (1)

[Scope of Claims] 1. Water to be treated containing phosphate ions and ammonia ions is passed from the lower part of the bone char packed bed and led to the upper part, and the treated water led out to the upper part is aerated with air, oxygen, etc. A wastewater treatment method characterized in that a part of the treated water is then circulated by flowing it together with the water to be treated from the lower part of the bone char packed bed. 2. Calcium hydroxide,
The method for treating wastewater according to claim 1, wherein the pH is adjusted to 6 or higher using an alkaline agent such as sodium hydroxide. 3 The treated water mixed with the treated water is treated water 1
2. The wastewater treatment method according to claim 1, wherein the liquid linear velocity flowing upward through the bone charcoal packed bed is 10 m/hr to 100 m/hr. 4. Any one of claims 1 to 3, characterized in that calcium ions are added so that the atomic ratio of phosphorus (P) to calcium (Ca) in the water to be treated is 3:5 or less. The wastewater treatment method described in