KR100371870B1 - Process and apparatus for recovering and removing orthophosphates from sewage and wastes - Google Patents

Abstract

The present invention provides a method and apparatus for recovering and removing phosphorus in sewage and wastewater, which is capable of stable phosphorus removal, obtains a recoverable phosphorus resource instead of waste sludge, and has a long replacement cycle of crystallization material supplied to the end of crystallization reaction. It is used to crush the steel converter slag generated as a by-product of the steel industry and use an average particle diameter of about 0.1mm as a material, which can be applied to liquor for the second treatment water of sewage and wastewater treatment processes. In addition, the performance of recovering and removing phosphorus by the fully mixed batch system applied to the return flow from the sludge treatment process is excellent.

Description

Process and apparatus for recovery and removal of phosphorus in sewage and wastewater {PROCESS AND APPARATUS FOR RECOVERING AND REMOVING ORTHOPHOSPHATES FROM SEWAGE AND WASTES}

The present invention relates to a method for recovering and removing orthophosphates (hereinafter referred to as phosphorus) as a crystal structure in a wastewater treatment process of a main stream and a return flow, and a completely mixed batch device.

The commonly used phosphorus recovery and removal methods are classified into (1) biological treatment methods and (2) chemical methods using coagulants, which are widely used in the world, and in recent years, (3) physicochemical method, crystallization The law is being tried, and the crystallization method is divided into calcium phosphate method and struvite method.

The state of the art for crystallization is well summed up in the conclusion of the international conference on “recycling technology for sewage and livestock wastewater” first held in the UK on 6-7 May 1998. It is known that the calcium phosphate method has a greater resource value of phosphorus recovery than the method, and it is evaluated that the calcium phosphate method has no value as a phosphorus resource when using a coagulant of iron or aluminum salt.

Seeding material is important in the phosphorus recovery technology of the calcium phosphate method, and currently available technology uses Crystallactor ^® of DHV Co., Ltd., which is manufactured using sand as a raw material in Europe. However, this method has a problem of low resource value due to the low phosphorus content of about 11%. In addition, in laboratory-scale studies, hydroxyapatite is used to increase phosphorus content, or magnesium oxide powder and calcite (CaCO ₃ ) are used as materials, and in Japan, small scales using phosphate or bone char are used. Fixed bed crystallization process is commercialized.

General filter type (fixed) crystallization technique using converter slag is described in Japanese Laid-Open Patent Publications No. 57-94392, No. 59-14274, No. 61-271087, etc. of Japan Steel Pipe Co., Ltd. The slag particles have a large particle size of about 0.5 to 3.0 mm.

In the case of conventional biological removal, there are many difficulties in stable removal of phosphorus, while chemical removal by chemical injection is stable, but it has disadvantages of generating large amount of sludge and increasing treatment cost due to the use of chemicals.

Accordingly, the present invention has been made to solve the above disadvantages, it is possible to remove the stable phosphorus, to obtain a recoverable phosphorus resource rather than waste sludge, the replacement cycle of crystallization material supplied as the end of the crystallization reaction is very long sewage and wastewater Another object of the present invention is to provide a method for recovering and removing phosphorus from wastewater and wastewater, while having a simple structure and operation. It is to provide this easy fully mixed batch device.

1 is a cross-sectional view of a fully mixed batch device for phosphorus recovery and removal according to an embodiment of the invention.

First, in the present invention, the steelmaking converter slag generated as a by-product of the steel industry is crushed, and the particle diameter of 0.075 to 0.15 mm (average of about 0.1 mm) that passes through # 100 and remains in # 200 is as it is, or It is used for washing and drying to recover and remove phosphorus from sewage and wastewater.

In the present invention, the steelmaking converter slag used as a raw material for the recovery and removal of phosphorus in the calcium phosphate method generates a large amount of industrial waste in the steelmaking process of the steel mill (for example, about 3,000 tons per day in Pohang Steel) It is a waste discharged while injecting quicklime into molten iron in order to separate and remove P ₂ O ₅ , which is contained as an impurity in the steelmaking process of the converter, and producing steel at a high temperature of 1500 to 1600 ° C. For this reason, some free lime and a large amount of CaO are contained in the steel converter slag, and high concentrations of calcium are eluted in water, especially in the early weeks, which is the most desirable performance for the recovery and removal of phosphorus from the calcium phosphate method. Caused to have.

The theoretical content of apatite recovered from the phosphorus resources using these materials is 18.5%. This value is about 1% annually, considering that the average phosphorus content of present ore gemstones is about 20%. Considering the tendency that the phosphorus content rate is falling, sufficient resource value is expected.

The present invention is a method for recovering and removing phosphorus from sewage and wastewater using converter slag that has undergone a predetermined steelmaking process as described above, and is applied to liquor for the secondary treated water of the sewage and wastewater treatment process, An object of the present invention is to provide a treatment method by a fully mixed batch type device applied to a conveyed stream returned from a sludge treatment step.

The method for recovering and removing phosphorus in sewage and wastewater according to the present invention is the final sedimentation effluent of the biological treatment (secondary treatment) or the return flow from the sludge treatment process as inflow water in the sewage and wastewater treatment, and the steelmaking converter slag When the reactor for the recovery and removal of a fully mixed batch of phosphorus phosphorus at a proper concentration and a proper pH and a concentration of calcium is operated for a long time, crystallization in the form of calcium hydroxyapatite (Ca ₅ OH (PO ₄ ) ₃ ) on the surface of the steelmaking converter slag After growing to a certain size and growing to a certain size, the crystal grains are taken out to the ore ore, and then the new steelmaking converter slag is replaced and introduced again, and the phosphorus in the sewage and wastewater is repeatedly reduced. For example, it can be removed to 0.5 to 10 mg / L or less, as well as to recover and use as a phosphorus resource.

In addition, the fully mixed batch crystallization reaction tank according to the present invention has a circular or polygonal cross section, and two or more baffles having an appropriate size are symmetrically attached to the inner wall of the sewage and wastewater treatment plant. Inflow of the final settling effluent of the second treatment step or the return flow from the sludge treatment step to the converter slag to about 2 to 20w / v%, while driving the mixer (mixer) installed in the upper center of the reactor It has a hydraulic retention time (HRT) of about 1 to 5 hours, and is configured to quickly discharge a large amount of treated water from a few minutes after stopping mixing periodically by using the excellent sedimentation characteristics of the converter slag.

The converter slag is not discharged, and only the treated water from which phosphorus is recovered and removed is discharged through the discharge pipe. In the initial stage of operation of the reactor, a sufficient amount of calcium is eluted from the slag and the proper pH is maintained, so no additional measures are required, but after two to three weeks or more, calcium in an external calcium reservoir (usually calcium chloride or lime solution) It is necessary to gradually increase the injection amount. Including the concentration of calcium contained in the secondary treated water (usually 30 to 40mg / ℓ) to maintain the calcium concentration in the reaction tank to 30 to 80mg / ℓ, the pH of the reactor effluent is 8.5 to 9.5 (about 9.0 Since it is important for high efficiency recovery and removal of phosphorus, the pH automatic control device is operated for proper injection of alkali chemicals such as NaOH. As a result, even when the phosphorus concentration introduced is 5 to 10 mg / L, the phosphorus concentration of the effluent may be stably maintained at 0.5 to 1.0 mg / L or less.

The converter slag used in these reactors will continue to grow more than several times in its own volume when the operating period is more than a few months, so when it grows to a resource-worthy size, it must be discharged out of the field. On the other hand, as the operation period elapses, a part of the apatite already formed on the surface of the crystallization due to the collision in the process of complete mixing is released and acts as a new seed. do. Moreover, when the regulation value of effluent pH is 8.5 or less, it is preferable to separately install the apparatus which injects a small amount of acids, such as sulfuric acid, into the reactor effluent.

In addition, a return stream composed of a general digester stripping solution, a dewatering solution, a concentrated tank supernatant, and the like contains a high concentration of phosphorus, which often causes problems in liquor treatment. In particular, the sludge that has undergone a biological dephosphorization treatment process is a serious problem as phosphorus is re-dissolved and returned to a high concentration in the course of the sludge treatment process, such as concentrated tank, anaerobic digestion tank.

Therefore, according to the method of the present invention, when the ratio of the input slag concentration to the initial phosphorus concentration in the batch operation is 0.03 (% / mg / L) or more, the phosphorus recovery and removal rate of 80% or more can be obtained in the reaction time of 5 hours. In particular, when the digester desorbent is subjected to decarbonation treatment, the recovery and removal efficiency can be somewhat improved, and the initial crystallization pH range can be maintained even if the pH is not adjusted in the beginning of operation. In the case of a completely mixed reactor in the return stream, the pH of the reactor is not required because the effluent is returned to the inlet of the water treatment system and mixed with the influent sewage.

The fully mixed batch crystallization tank for phosphorus recovery and removal of phosphorus in sewage and wastewater of the present invention can be applied to the return flow (including digestion tank desorbent) of sewage and wastewater treatment plant, and at this time, if a high concentration of steelmaking converter slag is used High concentration of phosphorus contained in the stream can be removed or recovered with high efficiency.

In the method and apparatus used in the present invention, there is no inhibition in the phosphorus recovery reaction even when nitrification is performed in the biological treatment step and NO ₃ ⁻ is discharged at a high concentration in the final sedimentation effluent. Therefore, in the design for biological treatment, only BOD and denitrification are considered, and phosphorus is effective for recovery and use even when discharged at a high concentration, and unlike the case of using a flocculant, it is economical because no separate sludge is generated. It is possible to design treatment.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a cross-sectional view of a fully mixed batch device for phosphorus recovery and removal according to an embodiment of the present invention, which has a crystallization desulfurization reactor 40 of circular or polygonal cross section, which is introduced into the reactor 40. The pipe 43 and the discharge pipe 45 are formed. The fully mixed batch phosphorus recovery and removal reactor (40) of the present invention has a baffle (47) of the appropriate size to suppress the generation of swirl flow due to the rotation of the plurality of impellers (46) via the mixing motor (41). Two or more are symmetrically fixed to the inside of the wall surface of this reaction tank 40, and are installed. In addition, when the mixing motor 41 is stopped, the converter slag 42 is settled by gravity within a few minutes, after which the supernatant is discharged at a time, and the inflow water is filled again to have an operation pattern.

Minimization of the mixing energy is essential in the operation of the reaction tank 40 of FIG. 1. For this purpose, the shape of the reaction tank may be a circular or square structure and an egg shape, a half egg type, or a polygon corresponding thereto in cross section.

When the apparatus of the present invention is installed in the mainstream, the final sedimentation basin effluent after biological treatment is introduced through the inlet pipe 43, or when the side stream is installed in the side stream, the sludge thickening vessel supernatant, the digester desorption solution and the dehydration liquid are combined. Influent water is also introduced into the batch reactor 40 through the inlet pipe 43.

The hydraulic retention time of the fully mixed batch reactor 40 is standard for 2 hours, and can be shortened to about 1 hour if the design value of the phosphorus concentration in the effluent is slightly increased. In addition, in the case of containing a high concentration of phosphorus, as in the return flow, a residence time of about 5 hours may be required.

As an operation element of the crystallization reaction, it is very important to maintain the pH in the reaction tank 40 at 8.5 to 9.5, and the pH is adjusted using the automatic pH control device 44. Other operating factors that determine the phosphorus concentration of the reactor effluent include calcium ion concentration in the reactor 40, converter slag concentration (reaction surface area), and water temperature, and the effects of alkalinity are practically neglected in a typical sewage treatment step. Possible element.

In particular, it has been found that the influence of temperature is sensitive, and the reaction rate as well as the crystallization reaction rate change simultaneously with the temperature, so it is essential to consider the temperature as a design element in the design.

Although the size of the reaction tank 40 is not limited, it can be appropriately selected according to treatment conditions such as inflow water amount, mixer capacity, and site conditions, and is preferably divided into two or more tanks. For example, a reactor having a diameter of 5 m and a depth of about 5 m has a treatment capacity of about 1,000 m 3 / day, and can be designed by connecting a plurality of devices in parallel or in series. In the case of a large-capacity treatment facility, a method of increasing the diameter and depth of the unit reactor while using a plurality of reactors and installing a plurality of mixers may be employed.

The installation of the fully mixed batch reactor 40 shown in FIG. 1 is a circular or square reactor in a single reactor, and the converter slag 42 filled therein is symmetrical baffle 47 attached to the inside of the wall of the reactor 40. It is good to maintain the complete mixing state by However, in the case of a batch phosphorus removal facility using activated sludge, the sludge occupies a large volume even after precipitation because of the high concentration of microorganisms, and the sedimentation rate of the sludge is very slow. 2 hours), the treatment efficiency of the batch reactor is actually very low. In the batch reactor for phosphorus recovery and removal of the present invention, the volume occupied by slag is at most about 10% at the beginning of the injection, and is recovered to the phosphorus resource. For long-term operation (about 1 year), the volume of solids will gradually increase, but still within 30% of the volume. The amount of effluent can be easily up to 50% of the reactor capacity while increasing the outflow rate It can be a very useful device to increase the processing efficiency.

In FIG. 1, reference numeral 48 is a calcium chloride solution bath, 49 is a caustic soda solution bath, and 50 is a calcium automatic control device.

Hereinafter, the present invention will be described in more detail based on the experimental examples.

Experimental Example

The injection rate of the steelmaking converter slag having a particle diameter of 0.15 mm was maintained at about 5w / v%, the reaction temperature was maintained at 25 ° C., the pH was 9.5, and the initial concentration of PO ₄ -P was 50 mg-P / L. When the fully mixed batch crystallization reactor was operated for 5 hours at a stirring strength of 200 rpm or more, 0.57 mg of phosphorus was recovered per 1 g of converter slag when calcium was not added, but 0.74 when 60 mg / l calcium was added. mg of phosphorus was recovered.

According to the simple batch-type apparatus which concerns on this invention, it turns out that phosphorus in sewage and wastewater is crystallized by the hydroxyapatite on the surface of this slag using steelmaking converter slag, and it becomes clear that phosphorus removal and collection | recovery performance are excellent. In addition, the apatite generated on the surface of the converter slag during the operation period is partially separated by the collision during the complete mixing process and continues to grow into pure apatite, thereby increasing the purity of the recovered phosphorus. .

Claims (6)

delete Inflow of the final sedimentation effluent or the sludge from the sludge treatment process as inflow water into the reactor for recovery and removal of phosphorus in the sewage and wastewater treatment process, and inputting steelmaking converter slag to the reactor; After discharging the crystallized grains in a predetermined size in the form of calcium hydroxy apatite (Ca ₅ OH (PO ₄ ) ₃ ) on the surface of the steelmaking converter slag and then discharged, the crystallized particles formed In the method of recovering and removing phosphorus in the waste water, comprising the step of taking out to the ore to the ore ore, and the operation of the reactor by replacing and adding a new steelmaking converter slag, The reactor with 2 to 20 w / v% steelmaking converter slag was operated for a long time at a pH of 8.5 to 9.5 and a calcium concentration of 30 to 80 mg / l, with the residence time of the influent being 1 to 5 hours. A method for recovering and removing phosphorus from sewage and wastewater, characterized in that to remove phosphorous at 0.5 to 10 mg / l or less. delete delete It has a circular or elliptical or polygonal cross section and has a reaction tank 40 which is a crystallization declination accommodating the steelmaking converter slag 42, which is formed with an inlet pipe 43 and a lower discharge pipe 45. In order to suppress the generation of swirl flow caused by the rotation of the plurality of impellers 46 via the mixing motor 41, two baffles 47 of appropriate size are symmetrically disposed inside the wall of the reactor 40. In the above-described wastewater and wastewater recovery and removal apparatus in wastewater, The reaction tank 40 is in communication with the calcium chloride solution tank 48 via the calcium automatic regulator 50, and is connected to the caustic soda solution tank 49 via the pH automatic regulator 44, 2 The reactor 40 into which the steelmaking converter slag 42 of 20 w / v% was injected can be operated for a long time at a pH of 8.5 to 9.5 and a calcium concentration of 30 to 80 mg / l, while the influent is held for 1 to 5 hours. Phosphorus recovery and removal apparatus in sewage and wastewater, characterized in that configured to discharge through the discharge pipe (45). delete