JP2007196095A - Organic waste treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost and efficient organic waste treatment method which improves a durability of equipment such as a dehydrator and a conveyor, and cuts down the cost of chemicals such as a flocculant, and its apparatus. <P>SOLUTION: In the organic waste treatment method, organic waste is subjected to anaerobic digestion treatment, and digested sludge yielded by the anaerobic digestion treatment is subjected to aerobic biological treatment, and then introduced into a process for separating and/or recovering magnesium ammonium phosphate particles. The organic waste treatment apparatus comprises an anaerobic digestion tank for carrying out the anaerobic digestion of the organic waste, an aerobic biological treatment tank for treating the digested sludge from the anaerobic digestion tank, and a magnesium ammonium phosphate separation and recovery device for separating/recovering the magnesium ammonium phosphate particles from sludge from the aerobic biological treatment tank. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a system for treating organic waste in various wastewater treatment plants including sewage treatment plants and organic waste treatment facilities, and more specifically, it is composed of simple unit processes, and provides aeration cost and hydrogen donation. The chemical cost of the body, pH adjuster, flocculant, polymer, etc. can be greatly reduced, and phosphorous and ammonia in the form of particles from organic waste containing high concentrations of organic matter, phosphorus and nitrogen. The present invention relates to a method and an apparatus for providing an efficient processing means that can be collected.

Garbage waste such as leftovers and vegetable scraps at home, cut grass, grass scraps and waste paper, all of which are organic waste. Looking outside the home, processing residues at food processing plants and seafood processing plants, food waste such as sake lees, waste milk, okara, black liquor from pulp mills, manure sludge, livestock manure, organic sludge For example, there is no time for organic waste.
Organic waste is often treated by methane fermentation in the presence of anaerobic microorganisms. Such anaerobic treatment is also called anaerobic digestion, and is a method that has been performed for a long time. Unlike aerobic biological treatment, it does not require dilution and aeration, so it saves energy and costs, and the gas generated by anaerobic digestion contains high concentrations of methane gas. The advantage of anaerobic digestion is that this methane gas can be recovered and used as energy, and various organic wastes are being put to practical use as a method for recovering energy.

  By the way, the anaerobic digestion liquid / anaerobic digestion sludge of the organic waste contains a high concentration of SS component, and although it is halved, organic substances such as a relatively high concentration of BOD component and COD component still remain. ing. Furthermore, ammonia and phosphorus produced and eluted during the anaerobic treatment are contained in high concentrations. Therefore, in order to release the anaerobic digestion liquid and anaerobic digestion sludge of organic waste into rivers and sewers, and to make the water quality suitable for the subsequent destination such as using liquid fertilizer, dehydration is first performed and digestion after dehydration is performed. In many cases, organic substances, nitrogen, and phosphorus are removed from the desorbed liquid. In recent years, restrictions on the total amount of COD and regulations on eutrophication substances such as nitrogen and phosphorus are being strengthened, and it is difficult to cope with only anaerobic digestion and conventional secondary treatment (BOD removal).

  In a treatment facility associated with a water treatment process such as a sludge treatment system in sewage treatment, the SS component of the digested sludge is often reduced or removed in the dehydration process, and the digestion desorption liquid is often returned to the water treatment process. There is a side of the tour of the temple where phosphorus removed in the water treatment process is returned to the water treatment process. For this reason, the phosphorus load to a water treatment system is high, and it cannot be said that it is an efficient method. The same applies to the case where the digestion and desorption liquid is treated individually without any water treatment process. First, the SS component of the digestion sludge is removed in the dehydration process, and BOD removal, phosphorus removal, nitrogen removal, etc. are performed on the digestion desorption liquid. There are many cases.

By the way, the cost for dehydration is one of the problems in the treatment of anaerobic digested sludge. The cost of the flocculant and polymer added for dehydration is a very large burden.
In order to add the polymer to the sludge and aggregate it, it is only necessary to add a polymer charged opposite to the plus / minus charge (anion / cation) of the sludge to bring the sludge close to zero charge. Since general organic sludge is charged to the anion (minus side), a cationic polymer may be added.

  The amount of colloidal charge of general aerobic excess sludge is approximately in the range of −0.1 to −0.3 meq / L, whereas anaerobic digested sludge is charged to −0.2 to −1.5 meq / L. The amount is often large, and the polymer addition rate required for dehydration increases accordingly. In addition, anaerobic digested sludge has a high salinity and M-alkalinity, and a large amount of colloidal particles further increases the difficulty of dehydration, and a larger amount of polymer is required. For this reason, the digested sludge may be dehydrated using iron salts and amphoteric polymers. There are various types of dehydrators such as vacuum dehydrators, pressure dehydrators (filter presses), centrifugal dehydrators, belt dehydrators (belt presses), screw dehydrators, etc., but most commonly used. Is a belt press. When iron salt is added, the dehydrating property is improved while the pH is lowered. The addition rate of the iron salt is limited so that it does not damage the dehydrator and remains at pH 4 to 5 or higher. Since iron salt has a coagulation effect on phosphoric acid, it is not suitable for the purpose of recovering the removed phosphorus, although it is two birds with one stone from the viewpoint of removing soluble phosphorus in sludge.

  As for the removal method of phosphorus, the chemical coagulation precipitation method using iron salt and PAC as described above has been developed and put into practical use. However, due to the chemical cost and the generation of a large amount of sludge, introduction in actual facilities is avoided. Tend to. In the 1970s, anaerobic-aerobic methods focusing on excess phosphorus intake in activated sludge and methods aimed at simultaneous removal with nitrogen have been developed and put into practical use as biological phosphorus removal methods. Among these, the anaerobic and anaerobic aerobic method is widely used in Japan because it can skillfully utilize the metabolic action of microorganisms and accumulate a large amount of phosphorus in the cells of the growing microorganisms. However, the anaerobic anaerobic aerobic method has problems such as unstable processing performance due to changes in the water environment and changes in the external environment due to seasonal fluctuations. May be necessary. As a result, there are problems that the processing steps are complicated and the running costs such as chemical costs are high.

On the other hand, as an attempt to recover phosphorus from wastewater, a catalytic dephosphorization method and a crystallization method in which phosphorus is precipitated as phosphate apatite were developed in the 1970s. In recent years, a chemical phosphorus removal method called a MAP crystallization method has attracted attention. In the MAP crystallization method, phosphate ions, ammonium ions, and magnesium ions react in equimolar amounts in water to form magnesium ammonium phosphate hexahydrate crystals (Magnesium Ammonium Phosphate, also referred to as “MAP” as an acronym): The chemical formula is a phosphorus removal / recovery method using the phenomenon of generating MgNH ₄ PO ₄ .6H ₂ O) (MAP crystal). The formation reaction of MAP crystals is shown in the following formula 1.
PO ₄ −P ³ + + NH ₄ ⁺ + Mg ²⁺ + 6H ₂ O → MgNH ₄ PO ₄ .6H ₂ O (1)

  By pulling out the MAP crystal particles generated according to this reaction from the reaction system, it is possible to remove phosphorus from the wastewater and also remove some ammonium ions. The MAP crystallization method is less complicated in operation and can recover phosphorus particularly stably. The recovered MAP contains 13% phosphorus by weight and has the added value of being an excellent fertilizer. The MAP crystallization method can be said to be an excellent technique for removing and recovering phosphorus and nitrogen from the viewpoint of effective use of resources.

As the anaerobic digestion process proceeds, the concentration of phosphate ions and ammonium ions in the sludge increases, and the same phenomenon as that of the MAP crystallization method naturally occurs, usually using magnesium ions as the rate-limiting factor. For this reason, the digested sludge often contains a considerable amount of MAP particles. In many cases, particles containing MAP particles are led to a dehydration step without being separated and collected, and are mixed into a dehydrated cake. In the process, there are problems such as damage to the dehydrator and conveyor, shortening the machine life, and causing phosphorus fly ash troubles during incineration.
The present inventors previously performed anaerobic digestion on excess sludge generated in the organic wastewater treatment process utilizing the metabolism of microorganisms, and added a magnesium source in the treatment process to the sludge. The process of producing magnesium ammonium phosphate from the contained phosphorus or phosphorus and nitrogen, separating and recovering the produced magnesium ammonium phosphate from the digested sludge, and concentrated water or digested sludge of the digested sludge after removal of magnesium ammonium phosphate It has been proposed to produce and recover magnesium ammonium phosphate from the target liquid by adding and mixing a magnesium source and a pH adjuster to at least one of the dehydrated filtrates (Patent Document 1).
To sewage containing ammonia and phosphorus, magnesium ammonium phosphate particles are precipitated by adding a Mg ion source while oxidizing a part of ammonia into nitrous acid in an aerobic tank 2A in which nitrite bacteria exist. Is possible (Patent Document 2).

  On the other hand, in addition to biological nitrification and denitrification methods, ammonia treatment methods such as ammonia stripping method, discontinuous point chlorine injection method and ion exchange method have been devised. Every method of processing is pros and cons. Therefore, removal by a biological nitrification denitrification method is a general method. In this method, depending on the ammonia concentration of various wastewaters to be treated and the pH buffering capacity of the wastewater itself, the pH of the mixed culture solution decreases due to nitrification of ammonia by autotrophic nitrifying bacteria. Since both of the capacities are hindered, pH adjustment is necessary, which naturally increases the cost. In addition, the BOD in the digestion and desorption liquid is usually insufficient to denitrify all of the contained nitrogen. In the denitrification step, it is necessary to add a large amount of organic matter to supplement the hydrogen donor. In most cases, the denitrification organic matter must be purchased as a chemical, which increases the processing cost. For this reason, development of the technique which removes nitrogen in the waste_water | drain which lacks organic substance without the addition of organic substance is required.

The above-mentioned problems of the prior art are enumerated. In the dehydration process, the sludge mixed with MAP particles is dehydrated as it is, and the subsequent equipment such as dehydrators and conveyors wears. Problems of chemical costs such as flocculants, phosphorus fly ash problems when incinerating sludge containing high concentrations of phosphorus, problems of aeration costs in nitrification and denitrification processes, and chemical costs of pH adjusters and hydrogen donors There are problems, etc.
JP 2003-45889 A JP 2003-126877 A

  The present invention solves the above-mentioned problems of the prior art and is constituted by a combination of simple processes, and can greatly reduce the cost of aeration and the cost of chemicals for hydrogen donor / pH adjustment. It is an object of the present invention to provide a low-cost and efficient organic waste processing method and apparatus capable of recovering ammonia in the form of particles.

The present invention has solved the above problems by the following means.
(1) Anaerobic digestion treatment of organic waste, aerobic biological treatment on the digested sludge obtained by the anaerobic digestion treatment, biological nitritation treatment, magnesium ammonium phosphate A method for treating organic waste, characterized in that sludge having undergone a particle separation and / or recovery step is guided to a solid-liquid separation step, and the separated liquid is subjected to ammonia denitrification treatment.
(2) Organic waste is subjected to anaerobic digestion, the digested sludge obtained by the anaerobic digestion is decarboxylated, and the sludge after decarboxylation is guided to the magnesium ammonium phosphate separation and recovery process. Biological nitritation treatment is applied to sludge after separation of magnesium ammonium oxide, leading to a solid-liquid separation process, and the separated liquid is guided to an ammonia denitrification process, and separated and recovered from the sludge after decarboxylation. A method for treating organic waste, wherein part or all of the magnesium ammonium phosphate particles are returned to the decarboxylation treatment step.
(3) Immediately after the anaerobic digestion treatment, a magnesium ammonium phosphate particle separation step is provided, and part or all of the magnesium ammonium phosphate particles separated from the digested sludge is returned to the anaerobic digestion treatment step. The method for treating organic waste according to (2) or (3), which is characterized in that
(4) Anaerobic digestion tank for anaerobically digesting organic waste, nitritation tank for treating digested sludge from the anaerobic digestion tank, and magnesium ammonium phosphate particles from sludge from the nitritation tank An organic waste treatment apparatus comprising a magnesium ammonium phosphate separation / recovery device for separation / recovery.
(5) Anaerobic digestion tank for anaerobically digesting organic waste, decarboxylation tank for decarboxylating digested sludge from the anaerobic digestion tank, and magnesium ammonium phosphate particles from the sludge from the decarbonation tank Magnesium ammonium phosphate separation / recovery device for separation / recovery, nitritation tank for treating sludge passed through the magnesium ammonium phosphate separation / recovery device, solid separation tank for solid-liquid separation of sludge from the nitritation tank, And a return pipe for returning a part or all of the magnesium ammonium phosphate particles separated and recovered by the magnesium ammonium phosphate separation and recovery device to the decarbonation tank. apparatus.

According to the present invention, the following effects can be obtained.
(A) By separating / collecting the MAP particles before the solid-liquid separation, there is no problem of wear of subsequent equipment such as a dehydrator or a conveyor.
(B) Chemical costs such as flocculants and polymers can be reduced by performing aerobic biological treatment on digested sludge having poor dewaterability and then dewatering.
(C) Further, phosphate ions in the sludge are effectively removed / recovered by maintaining the pH in the sludge within a range suitable for MAP particle generation due to the influence of decarboxylation by aeration in aerobic biological treatment. This eliminates the problem of phosphorus fly ash when incinerating sludge containing high concentrations of phosphorus.
(D) By combining aerobic biological treatment with nitrite-type nitrification and ammonia denitrification, it is possible to reduce the problem of aeration costs in the nitrification denitrification step and chemical costs such as pH adjusters and hydrogen donors.
The present invention can provide a low-cost and efficient organic waste processing method and apparatus comprising a combination of simple processes.

The best mode for carrying out the present invention will be described in detail with reference to the drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments and examples.
In the present invention, first, as shown in the flow of FIG. 1, the organic waste 10 to be treated is introduced into the anaerobic digester 1. In digested sludge, an equilibrium is established among Mg, PO ₄ -P, NH ₄ -N, and pH, which are components of MAP. It is well known that MAP crystals can be generated by increasing the concentration of any of Mg, PO ₄ -P, and NH ₄ -N, or by increasing the pH from neutral to alkaline. Yes. The pH is an important condition for MAP generation, and alkaline is preferable for MAP generation. However, if the pH is too high, the degree of supersaturation increases, and the force for promoting crystallization acts too strongly. There is a risk of MAP generation. Fine MAP cannot be separated / recovered. When producing MAP for the purpose of recovery, the pH during production is preferably in the range of 6.8 to 8.0, and more preferably 7.1 to 7.6.

Next, biological treatment is performed under aerobic conditions in the aerobic biological treatment tank 2 communicated with the tank. There are various types of aerobic biological treatment such as standard activated sludge method, batch activated sludge method, fixed bed / moving bed type biofilm method and the like. Any of them can be applied, and not only BOD removal but also a nitrification part of batch / circulation nitrification denitrification and an aerobic part of anaerobic aerobic anaerobic method. Any aerobic biological treatment method is applicable.
By the way, the breakdown of the gas generated in the process of anaerobic digestion is about 3: 7 to 4: 6 for carbon dioxide and methane. Since the anaerobic digestion tank 1 is a closed type, carbon dioxide CO ₂ dissolves in the digested sludge and is almost saturated, and a dissociation equilibrium is established.
CO ₂ ↑ + H ₂ O ← → H ₂ CO ₃ ← → H ⁺ + HCO ₃ ⁻ ← → 2H ⁺ + CO ₃ ²⁻ (2)

Usually, aerobic biological treatment involves aeration. By forcibly bringing the digested sludge into contact with the air by aeration, free carbonic acid (H ₂ CO ₃ ), which is an acid component in the digested sludge, is released, and the pH rises to nearly 8. As a result, the equilibrium of each ion constituting the MAP moves, and MAP crystals are generated in the sludge. It is not easy to raise the pH significantly from 8 by decarboxylation alone. This is effective in preventing the formation of fine MAP.

By introducing the sludge containing MAP crystals into the MAP recovery / separation apparatus 3 in the latter stage (Ogino: JP 2002-045889), phosphorus and ammonia in the organic waste 10 are in the form of MAP particles 4. It can be separated and recovered. By this method, the BOD of the digested sludge can be removed, and at the same time, PO ₄ -P and NH ₄ -N can be fixed in the form of MAP particles 4, and can be easily separated and recovered. When anaerobic digested sludge is targeted, the residence time of the biological treatment tank 2 is about 1 to 2 days for removing BOD by biological treatment, whereas it is 1 for the production of MAP as a chemical reaction. As time is sufficient, decarboxylation / pH increase / MAP generation can be performed by aeration for biological treatment, and the cost is low. Specially, a residence time for MAP generation is secured, and a tank is added. There is no need for design considerations.

In order to further increase the amount of MAP particles 4 to be generated, addition of an alkaline agent after aeration is one option, but this method is not necessarily efficient for those having a high buffering capacity such as digested sludge, As already mentioned, when the fine adjustment is not successful and the pH rises too much, a pH value that is too high is suitable for MAP production but not for recovery purposes. If the pH rises before the microorganisms are affected, the vital biological treatment will not be possible, and it will be a tip-over, so be careful. In the present invention, a method of supplementing Mg having a low content concentration with respect to NH ₄ —N and PO ₄ —P is suitable. Of course, some organic wastes 10 contain high concentrations of Mg, such as waste liquids and wastes related to tofu production, such as okara, so Mg ions in digested sludge, If the concentration balance of PO ₄ -P and NH ₄ -N is in place, sufficient MAP generation and phosphorus removal can be achieved by simply adjusting the pH by decarboxylation by aeration without adding an Mg source. . MgCl ₂ as Mg source is high convenient water solubility. Mg _{(OH) 2} is less expensive than MgC1 _2. In particular, industrial slurry-like Mg (OH) ₂ is much cheaper. Mg (OH) ₂ can also be expected to maintain pH as an alkali. Seawater may be used. If a waste liquid containing Mg at a high concentration can be used as the Mg source, the cost is excellent.

  Since the destination is the aerobic biological treatment tank 2, even if the waste liquid contains a BOD component, it can be used without any problem. The suitability of being put into the anaerobic digestion tank 1 or the biological treatment tank 2 depends on the properties of the waste liquid such as SS concentration and BOD concentration. When adding the Mg source to the biological treatment tank 2, there is a method of directly feeding it into the tank, and a method of adding it from the digested sludge line entering the tank. Considering from the viewpoint of MAP generation, that is, reduction of phosphorus concentration, the MAP generation amount, that is, phosphorus concentration reduction amount is determined by phosphorus, ammonia, magnesium concentration and pH, and the same effect can be obtained by either injection method.

  The above is a device for increasing the amount of MAP generated. On the other hand, in order to increase the recovery rate of MAP, it is necessary to prevent the generation of fine MAP. The highest concentration of phosphorus and ammonia is in the digested sludge injection line before entering the biological treatment tank 2. In this part, the pH is usually higher than 6.8, which is a standard for MAP production. If Mg is injected here, a large amount of fine MAP may be generated and cannot be recovered. In addition, there is a concern that the scaling of the piping part is promoted. On the other hand, although the pH in the biological treatment tank 2 has increased to about 8, the phosphorus and ammonia concentrations have already decreased to some extent, so there is little possibility that fine MAP will be generated even if Mg is directly injected into this. . When adding Mg, it is preferable not to mix with digested sludge but to add to the biological treatment tank 2 separately. Regardless of whether or not Mg is added, returning the collected MAP as a seed crystal to the biological treatment tank 2 again and increasing the surface area of the seed crystal on which MAP precipitates has a great effect on preventing the formation of fine MAP. The MAP particles returned to the MAP production tank as seed crystals preferably have a diameter of φ150 μm or more, and more preferably have a diameter in the range of φ250 to 800 μm.

When performing solid-liquid separation of anaerobic sludge, it was necessary to use a large amount of a flocculant and a polymer. The sludge after aerobic biological treatment and separation of MAP has improved sedimentation separation performance compared to the original anaerobic digested sludge. The amount of drug required can be greatly reduced, leading to cost savings.
The treatment liquid that has undergone aerobic biological treatment and solid-liquid separation can be subjected to nitrogen removal as necessary.

In the present invention, nitrite bacteria floating or immobilized on a carrier are present in the aerobic biological treatment tank 2 shown in FIG. 1, and the aerobic treatment is partially or entirely performed as nitrite type nitrification. By doing so, the cost for nitrification and denitrification can be almost halved. This is shown in FIG.
To sewage containing ammonia and phosphorus, magnesium ammonium phosphate particles are precipitated by adding a Mg ion source while oxidizing a part of ammonia into nitrous acid in an aerobic tank 2A in which nitrite bacteria exist. Is possible (Japanese Patent Laid-Open No. 2003-126887). According to known literature (study on biological denitrification method (I) -examination on factors controlling nitrification-Sewage Association Journal, Vol. 7, No. 4), the optimum pH of nitrite bacteria is 7.0. At ˜8.5, the optimum pH of the nitrifying bacteria is 6.0 to 7.5, and the nitrite bacteria maintain the activity while the nitrite bacteria lose their activity under the condition of pH around 8. It is a preferable state for nitrite type nitrification that pH is maintained at around 8 by decarboxylating digested sludge by aeration. When nitric acid nitrification is performed under this pH condition, NO ₃ requires 1.5 times more oxygen than NO ₂ and the activity of nitrifying bacteria decreases, so the aeration cost increases and is rational. is not. When nitrifying digested sludge, aiming for nitrite-type nitrification is an efficient and rational treatment method.

The first stage of the nitrification reaction is a reaction (Formula 3) that oxidizes NH ₄ -N to NO ₂ -N by nitrite bacteria (also called ammonia-oxidizing bacteria), and the second stage is nitrifying bacteria (nitrite oxidation) oxidizing the _NO 2 -N by also called bacteria) to _NO 3 -N a reaction (equation 4).
NH ₄ ⁺ + 1.5O ₂ → 2H ⁺ + H ₂ O + NO ₂ ⁻ +58 to 84 kca1 (3)
NO ₂ ⁻ + 0.5O ₂ → NO ₃ ⁻ +15.4 to 20.9 kca1 (4)
When nitrification is performed in water treatment, a nitrogen removal process is often provided in the subsequent stage to remove nitrogen. Denitrification in the state where nitrous acid is accumulated often generates a considerable amount of nitrous oxide N ₂ O gas together with nitrogen gas. Nitrous oxide is one of the warming gases, and its warming effect is 310 times that of carbon dioxide of the same weight. Gas that is not allowed to do.

The ammonia denitrification method (anaerobic ammonia oxidation method) has recently attracted attention as an effective technology for the dilemma of energy consumption and the environmental burden of greenhouse gases in the nitrification denitrification process, which is limited to nitrification. : Patent 3460745, Delft University: H03-501099). In this method, ammonia and nitrous acid are denitrified by the action of autotrophic bacteria, and the reaction is an autotrophic reaction using ammonia as a hydrogen donor and nitrite as a hydrogen acceptor (Formula 5).
1.0 NH ₄ ⁺ +1.32 NO ₂ ⁻ +0.066 HCO ₃ ⁻ + 0.13H ⁺ →
1.02N ₂ + 0.26NO ₃ ⁻ + 0.066CH ₂ O _0.5 N _0.15 + 2.03H ₂ O
... (5)

The present inventors examined whether nitrous oxide was generated in the process of ammonia denitrification for artificial wastewater containing ammonium salt and nitrite as main components. As a result, generation of nitrous oxide was not confirmed.
The sludge that has been subjected to the nitrification treatment passes through the MAP recovery / separation device 3, and after removing the SS component to about 100 to 300 mg / L in the solid-liquid separation step, nitrogen is then removed in the ammonia denitrification step. Remove. At this time, ammonia denitrification requires ammonia nitrogen of almost the same amount as nitrite nitrogen as shown in Equation 5, so that it is efficient to adopt processing conditions that stop nitritation in about half. In addition, in the case of ammonia denitrification, the removal rate of nitrogen is about 80%. Therefore, when it is insufficient for the use of treated water, it can be dealt with by separately combining a nitrification denitrification step in the subsequent stage.

By the way, when the BOD of the organic waste 10 to be treated is very high, the residence time of the aerobic biological treatment tank 2 is several days. When the biological treatment tank 2 is in a state close to complete mixing, the presence of high concentrations of NH ₄ -N and PO ₄ -P in the inflowing digested sludge and the increase in pH due to decarboxylation are less effective. In such a case, if the aerobic biological treatment tank 2 is partitioned, MAP is generated and separated and recovered in the previous part, and seed crystals are circulated in some cases, MAP generation and biological treatment can be performed in one tank. Is possible.

Furthermore, in the present invention, as shown in FIG. 3, the digested sludge is guided to the decarbonation tank 7, MAP is generated as the pH increases due to decarboxylation, and the generated MAP is recovered in the subsequent MAP separation and recovery step. Also good. The sludge after MAP separation and recovery is subjected to nitrite type nitrification in the subsequent aerobic biological treatment tank 2 to separate the solid and liquid. In this flow, MAP is generated by decarboxylation of sludge that has just exited the digester and contains NH ₄ -N and PO ₄ -P at high concentrations, so the amount of MAP generated increases. By separately performing MAP generation, which is a chemical reaction that requires only a short residence time, and aerobic biological treatment, which requires a relatively long time, the residence time and residence space of MAP that can cause troubles such as scaling can be reduced. Make it smaller. Since MAP is removed in advance before the aerobic biological treatment tank 2, the possibility of troubles such as scaling is reduced.
By combining ammonia denitrification and nitrification denitrification processes as necessary in the subsequent stage in the treatment water state, the quality of treated water according to the purpose can be satisfied.

  Alternatively, the MAP separation and recovery device 3 may be provided immediately after the anaerobic digester 1 in FIGS. In FIG. 4, after anaerobic digestion of organic waste, a MAP separation and recovery step is provided between the aerobic biological treatment tank 2 and nitrite type nitrification is applied to the sludge after MAP recovery. And a MAP separation and recovery step is provided. Similarly, in FIG. 5, after anaerobic digestion is performed on the organic waste 10, a MAP separation / recovery step is provided, and MAP is generated again in the decarboxylation tank 7, and then passed through the MAP separation / recovery device 3, and then an aerobic organism. Processing, followed by solid-liquid separation and processing. In this case, since the amount of MAP produced in the biological treatment tank 2 is small, it is desirable to return the recovered MAP and circulate it as seed crystals.

  EXAMPLES In the following, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited by these examples.

Example 1
The test was conducted in the manner of one embodiment of the bench scale of the present invention shown in FIG. In treating the garbage 11 taken out from the household, after anaerobic digestion treatment was performed in a methane fermentation tank (anaerobic digestion tank 1), the sludge was guided to a circulating nitrification denitrification treatment step.
(Processing conditions)
The anaerobic digestion tank in this example has a capacity of 20 liters, a temperature of 35 ° C., a residence time of HRT of 20 days, a denitrification tank has a capacity of 6 liters, a temperature of 20 ° C., a residence time of HRT of 6 days, and the nitrification tank has a capacity of 18 liters. The treatment was performed under the conditions of a temperature of 25 ° C. and a residence time of HRT of 18 days.
(Processing result)
The sludge properties of the methane fermentation tank (anaerobic digestion tank 1), denitrification tank 8, and nitrification tank 9 were as shown in Tables 1 and 2, respectively.

  At this time, the MAP particles 4 generated in the sludge in the nitrification tank 9 are separated by a cyclone (not shown), returned to the nitrification tank 9 by about 1 to 1.5 g-MAP / L-tank, and circulated as seed crystals. As a result, MAP particles having a particle size of about 120 to 600 μm can be recovered. The production / recovery amount of MAP reached 2.5 g / L-sludge.

Example 2
The test was performed according to one system of the lab scale embodiment of the present invention shown in FIG. About half of NH ₄ -N in the raw sludge is converted to nitrous acid, and NH ₄ -N and NO ₂ -N in the treated sludge are almost equal to the methane fermentation sludge of agricultural waste 12 by the flow carrier injection method. The nitrite type nitrification treatment is performed by adjusting the conditions. Thereafter, the sludge is guided to the MAP separation / recovery device 3, solid-liquid separation is performed on the subsequent sludge, and ammonia denitrification treatment is performed on the desorbed liquid.

  FIG. 8 is a flow experimented for comparison. In processing the methane fermentation sludge of the same agricultural waste 12 as in Example 2, MAP particles are first separated / recovered, and then solid-liquid separation is performed on the separated sludge. Then, it is a flow which guide | induces desorption liquid to a circulation type nitrification denitrification process.

(Processing result)
Since the agricultural waste 12 used contained okara which is a tofu production waste, the Mg concentration was high, and thus the methane fermentation solution was very easy to produce MAP.
The recovery rate of MAP particles in the comparative control experiment was 0.9 g / L per sludge. Digested sludge is very poor in dehydration, and it was necessary to use a strong cationic polymer for solid-liquid separation. The injection rate of the polymer was 3.5% -DS.
Table 3 shows the properties of the sludge and ammonia denitrification solution in the methane fermentation tank (anaerobic digestion tank 1) and nitritation tank 2A in this example. In the table, the unit of numerical values other than the pH value is “mg / L”.

  In this example, the MAP particles recovered in the MAP separation / recovery tank 3 were returned to a ratio of about 0.8 to 1.2 g-MAP / L-tank and circulated as seed crystals. As a result, MAP particles having a particle size of 100 to 550 μm could be recovered. The recovery rate of MAP particles was about 2.8 g / L per sludge. Also, at this time, the flow rate of solid-liquid separation for the sludge that has been improved aerobic by performing aerobic treatment instead of anaerobic digested sludge, the polymer injection rate becomes 1.8% -DS, The amount of polymer used could be reduced by about 50%. Further, the type of polymer can be switched from a strong cationic polymer to a relatively inexpensive medium cationic polymer, and the cost for chemicals was reduced by about 60%.

  The present invention improves the durability of equipment such as dehydrators and conveyors used in the process of treating organic waste, reduces chemical costs such as flocculants and polymers, and incinerates sludge containing phosphorus. Since the phosphorus fly ash at the time is reduced significantly, the organic waste treatment method and apparatus of the present invention are expected to be introduced into an organic waste treatment facility such as a sewage treatment plant.

It is a figure which shows the processing flow of one embodiment of this invention which introduce | transduces organic waste into an anaerobic digestion tank, processes in an aerobic biological treatment tank, and collect | recovers MAP with a MAP separation-and-recovery apparatus. It is a figure which shows the processing flow of one embodiment of this invention which uses a nitritation tank as an aerobic biological treatment tank, and uses an ammonia denitrification tank after a solid-liquid separation tank. It is a figure which shows the processing flow of one embodiment of this invention which introduce | transduces digested sludge to a decarboxylation tank and collect | recovers the produced | generated MAP in a MAP separation and recovery process. A MAP separation and recovery process is provided between the anaerobic digestion tank and the aerobic biological treatment tank, and between the aerobic biological treatment tank and the solid-liquid separation tank, and an ammonia denitrification tank is used after the solid-liquid separation tank. It is a figure which shows the processing flow of one embodiment of this invention. The MAP separation / recovery step is provided after the anaerobic digestion tank, MAP is further generated in the decarboxylation tank, and after passing through the MAP separation / recovery apparatus, the processing flow of one embodiment of the present invention including the nitrous acid tank and the solid-liquid separation treatment is shown. FIG. FIG. 3 is a diagram illustrating a processing flow of Example 1. FIG. 6 is a diagram illustrating a processing flow of Example 2. It is a figure which shows the flow of the processing method of a comparative example.

Explanation of symbols

1 Anaerobic digestion tank 2 Aerobic biological treatment tank 2A Nitrite tank 3 MAP separation and recovery device 4 MAP
5 Solid-liquid separation tank 6 Ammonia denitrification tank 7 Decarbonation tank 8 Denitrification tank 9 Nitrification tank 10 Organic waste 11 Garbage 12 Agricultural waste 13 Treated water 14 Circulating fluid

Claims (5)

  Anaerobic digestion treatment of organic waste, aerobic biological treatment on digested sludge obtained by the anaerobic digestion treatment, biological nitritation treatment, magnesium ammonium phosphate particle separation and A method for treating organic waste, characterized in that sludge having undergone a recovery step is guided to a solid-liquid separation step, and the separated liquid is subjected to ammonia denitrification treatment.   Organic waste is subjected to anaerobic digestion, the digested sludge obtained by the anaerobic digestion is decarboxylated, and the sludge after decarboxylation is guided to the magnesium ammonium phosphate separation and recovery process. The sludge after separation is subjected to biological nitritation treatment, leading to the solid-liquid separation process, leading the separated liquid to the ammonia denitrification process, and magnesium phosphate separated and recovered from the sludge after decarboxylation A method for treating organic waste, wherein a part or all of ammonium particles are returned to a decarboxylation treatment step.   Immediately after the anaerobic digestion treatment, a magnesium ammonium phosphate particle separation step is provided, and some or all of the magnesium ammonium phosphate particles separated from the digested sludge are returned to the anaerobic digestion treatment step. The processing method of the organic waste of Claim 1 or Claim 2.   Anaerobic digestion tank for anaerobic digestion of organic waste, nitritation tank for treating digested sludge from the anaerobic digestion tank, and separation / recovery of magnesium ammonium phosphate particles from sludge from the nitritation tank An organic waste processing apparatus comprising a magnesium ammonium phosphate separation and recovery apparatus.   Anaerobic digestion tank for anaerobic digestion of organic waste, decarbonation tank for decarboxylation of digested sludge from the anaerobic digestion tank, and separation / recovery of magnesium ammonium phosphate particles from the sludge from the decarbonation tank A magnesium ammonium phosphate separation and recovery device, a nitritation tank for treating the sludge passed through the magnesium ammonium phosphate separation and recovery device, and a solid separation tank for solid-liquid separation of the sludge from the nitritation tank, Furthermore, the organic waste processing apparatus provided with the return pipe which returns some or all of the magnesium ammonium phosphate particle isolate | separated and collect | recovered with the magnesium ammonium phosphate separation-and-recovery apparatus to this decarboxylation tank.

Images