JP2002316192A - Method and apparatus for treating organic foul water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic foul water treatment process which can greatly decrease the amount of generated excess activated sludge, can remove nitrogen stably to a high degree, can remove phosphorus to a high degree, can recover phosphorus as a resource, and can increase the amount of energy recovered from organic foul water. SOLUTION: Organic foul water is mixed with a cationic polymeric flocculant and subjected to solid-liquid separation to give a flocculate and separated water. The separated water is supplied to a biological nitration denitrification activated-sludge treatment step and mixed with a particulate chemical phosphorus-removal agent to solidify a phosphorus component. Then, the separated water is supplied to a solid-liquid separation step, and the resultant supernatant is obtained as treatment water. A part of separated sludge obtained in the separation step is taken out, subjected to an alkali treatment by the addition of NaOH, and subjected to solid-liquid separation. Thus separated sludge is returned to the denitrification step. Ca or Mg ions are added to the separated liquid obtained in the solid-liquid separation step to precipitate phosphorus ions as a solid, which is recovered by solid-liquid separation, and the separated liquid is returned to the denitrification step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for highly purifying organic sewage such as sewage, and in particular, can significantly reduce the amount of surplus activated sludge generated, can recover phosphorus in sewage as a resource, and can further reduce sewage. The present invention relates to a processing technique capable of increasing the amount of energy recovered from wastewater.

[0002]

2. Description of the Related Art Sewage will be described below as a typical example of organic wastewater. The latest sewage treatment method at present is as shown in FIG.
After removing a part of the sludge, biological treatment is performed in a biological nitrification and denitrification step 34 to remove BOD and nitrogen, and then the activated sludge is settled and separated in a final sedimentation tank 36 to separate the settled sludge 38, from which the sludge is separated. A process is performed in which an inorganic coagulant 39 is added to the effluent water 37 to cause coagulation and precipitation to remove phosphorus, SS, and COD. In addition, the inorganic coagulant 39 was added to the final sedimentation basin 36.
In some cases, the floc in which phosphorus has been insolubilized by being added to the slurry flowing into the reactor is precipitated together with the activated sludge. Note that FIG.
, 40 is a coagulation sedimentation tank, 42 is a coagulation sedimentation sludge,
1 is treated water, 43 is returned sludge, and 33 is raw sludge.

[0003]

However, the conventional sewage treatment process as shown in FIG. 2 has the following disadvantages. B) Since the SS removal rate of the first sedimentation basin is only about 40%, the amount of surplus activated sludge generated from the biological treatment process increases, and this burdens the sludge treatment. In addition, since the amount of organic SS removed in the first settling basin is small, there is a problem that the amount of methane gas generated is small when the first settled sludge is anaerobically digested. B) If a method of adding an inorganic coagulant such as ferric chloride or aluminum sulfate to the first sedimentation tank to apply coagulation and sedimentation is applied, SS and phosphorus removal rates in the first sedimentation tank are greatly improved, and the above-mentioned problems are solved. On the other hand, on the other hand, on the other hand, there arises a further problem that a large amount of hardly dewaterable coagulated sediment sludge is generated.

[0004] Further, if the removal rate of SS is increased by adding a flocculant to the first settling basin, the removal rate of SS-BOD becomes too high. Insufficient BOD source (hydrogen donor) degrades the denitrification effect. D) Phosphorus flocculated sediment sludge cannot be used effectively and must be discarded. Therefore, precious phosphorus in sewage cannot be recovered and used as a resource.

The present invention solves all the drawbacks of the conventional organic sewage treatment method, makes it possible to significantly reduce the amount of excess activated sludge (substantially zero), and to provide a stable and stable BOD source of denitrifying bacteria. Ideal organic wastewater treatment process suitable for the 21st century, capable of removing nitrogen at a high level, further removing phosphorus, recovering phosphorus as a resource, and increasing energy recovery from organic wastewater The task is to provide

[0006]

Means for Solving the Problems The present inventors have conducted investigations and studies in order to solve the above-mentioned disadvantages of the prior art.
If the sewage in which SS is highly coagulated and separated by the cationic polymer is treated in a biological denitrification process in which a phosphorus remover and activated sludge coexist, the subsequent treatment process proceeds smoothly, and the amount of excess activated sludge generated The present invention has been found to be extremely effective in all of the problems of recovering phosphorus and recovering energy such as methane gas, and has completed the present invention.

That is, the present invention provides an organic wastewater treatment process comprising the following basic flow. (1) Aggregates formed by adding a cationic polymer flocculant to organic wastewater are separated into solids and liquids to obtain separated water and coagulated separated sludge, and the separated water is formed by the chemical phosphorus remover particles and activated sludge. Supply to the coexisting biological nitrification denitrification activated sludge treatment process,
The BOD and nitrogen are removed and the phosphorus content is solidified, the sludge mixture in the treatment step is supplied to a solid-liquid separation step, and the supernatant liquid from which the sludge substance has been separated is discharged out of the system as treated water. Pull out part of the separated sludge in the separation process, phosphorus, BO
D, NaOH is added to the sludge containing nitrogen to adjust the pH to 1
After being adjusted to 0 or more, solid-liquid separation is performed, and the separated sludge is returned to the denitrification step. On the other hand, Ca or Mg ions are added to the separated liquid from the solid-liquid separation to precipitate phosphorus ions as solids. A method for treating organic sewage, comprising: collecting phosphorus by solid-liquid separation, and returning the separated liquid to the denitrification step. (2) The method according to (1), further comprising a step of anaerobically digesting the coagulated and separated sludge with the cationic polymer coagulant and mixing the digested and separated liquid with the solid-liquid separated liquid after the addition of the NaOH. ) Described processing method.

(3) An aggregating / separating apparatus for adding a cationic polymer flocculant to organic sewage to perform solid-liquid separation of an agglomerated product, and supplying the separated water from the aggregating / separating apparatus to a chemical phosphorus removing agent A biological nitrification denitrification apparatus for removing phosphorus, BOD and nitrogen, a solid-liquid separation tank for introducing effluent from the nitrification denitrification apparatus and separating it into treated water and sludge, and a solid-liquid separation tank Alkali treatment tank that introduces a part of the separated sludge from the above to release phosphorus, a solid-liquid separation device that separates the alkali-treated sludge from the alkali treatment tank into solid and liquid and separates the separated liquid and the separated sludge, Or a precipitation tank that adds Mg ions to precipitate phosphorus as a solid, a separation pipe of the solid-liquid separation device, and a return pipe that sends a separated liquid from the precipitation tank to the nitrification denitrification device. Organic wastewater treatment equipment.

[0009]

FIG. 1 is a flow chart showing an embodiment of the present invention. In FIG. 1, sewage 1 which is an example of organic wastewater
, At least a cationic polymer 2 which is an example of a polymer flocculant (this term is used to mean an amphoteric polymer flocculant having a cationic group and an anionic group in a molecule) is added,
The sewage SS is agglomerated, and the formed floc is sedimented in the aggregating / separating tank 3 or separated by filtration through a coarse particle size filter medium packed bed. The meaning of "adding at least a cationic polymer" means that a cationic polymer flocculant may be used in combination with an anionic, nonionic, or amphoteric polymer flocculant. In addition, it is not suitable to add an anionic or nonionic polymer alone, since the organic SS in the sewage cannot be sufficiently flocculated. At this time, when mineral particles having a large specific gravity, such as fine sand, are added to the flocculation / separation tank 3 to which the cationic polymer is added, flocs adhere to the particles, and extremely large sedimentable flocs are formed. / M
Very high-speed sedimentation separation of in or more is very preferable. As a result, the SS in the sewage 1 was high (90%
Above) The sewage that has been removed and has very little SS and SS-based BOD flows into the subsequent biological nitrification denitrification process.

On the other hand, SS (agglomerated and separated sludge 5), which is agglomerated and removed by the cationic polymer, is mainly composed of organic matter, and when supplied to the anaerobic digestion tank 25 for performing the anaerobic digestion step, the methane gas 26 is effectively converted Occurs and the amount of energy recovered from the sewage 1 can be increased. That is, in the present invention, the SS of the sewage 1 can be removed to a high degree without generating inorganic sludge, and the solid-liquid separation efficiency is increased about twice, and this can be taken to the anaerobic digestion step. The amount of generated methane gas 25 can be approximately doubled.

Further, since the anaerobic digestion and desorption solution 27 discharged from the anaerobic digestion tank 25 contains a large amount of phosphorus and ammonia, the solid-liquid separation after the alkali treatment tank 15 for performing the NaOH solubilization step described later is performed. Solid-liquid separation liquid 19 that exits the device 18
And ammonia and MAP (recovered phosphorus 2
Collect as 4). Further, the digested sludge 28 from the anaerobic digestion tank 25 is sent to a dehydrator 29, and the dehydrated separated liquid 30 obtained there contains a large amount of phosphorus and ammonia. The resulting solid-liquid separation liquid 20 is mixed. Thus, the sewage 1 in which the SS is highly coagulated and separated by the cationic polymer 2 flows into the denitrification tank 6 in the biological nitrification denitrification step, and further flows into the nitrification tank 7 in the nitrification step, and The soluble BOD and nitrogen components are removed. The activated sludge is separated from the effluent 9 in a solid-liquid separation tank 11 to obtain treated water 12. In this nitrification denitrification step, a part of the effluent 9 is
It is circulated to the denitrification tank 6 as 0. As the solid-liquid separation tank 11, a precipitation tank and a membrane separation tank can be considered. In FIG. 1, the biological nitrification method of the nitrification liquid circulation type is shown. However, the step-type nitrification denitrification method, the aerobic denitrification method, and the biological dephosphorization performed by providing an anaerobic tank before the denitrification tank Any biological nitrification denitrification method, such as a method, can be employed.

Since the phosphate ions in the sewage 1 are not removed in the coagulation / separation tank 3 by adding the cationic polymer 2,
The effluent from the cationic polymer coagulation separation step contains a large amount of phosphate ions. An important point in the present invention is that a phosphorus removing agent 8 capable of chemically removing phosphorus is added to the biological nitrification denitrification step for receiving the coagulated and separated water from the cationic polymer to coexist with activated sludge. . Phosphate ions can be removed using a phosphorus remover (ferric chloride, ferric sulfate,
Iron, iron hydroxide, aluminum sulfate, aluminum chloride,
Biological nitrification denitrification process by adding polyaluminum chloride, aluminum hydroxide, activated alumina, sodium aluminate, titanium chloride, titanyl sulfate, titanium hydroxide, titanium oxide, zirconium chloride, zirconium hydroxide, zirconium oxide) In the above, since the water is highly removed by coagulation or adsorption, the phosphate ion of the treated water flowing out from the final solid-liquid separation tank 11 is 0.1 to 0.2 m
It can be extremely reduced to about g / liter.

The phosphorus removing agent added to the biological treatment step includes:
In the process of staying in the biological nitrification denitrification treatment process, iron hydroxide in the state of adsorbing phosphorus, hydrated iron oxide, aluminum hydroxide, hydrated aluminum oxide, zirconium hydroxide,
It is present in a state of zirconium oxide, titanium hydroxide, titanium oxide and the like. Most of the separated sludge 13 separated in the solid-liquid separation tank 11 after the biological nitrification denitrification step is returned to the denitrification tank 6 as return sludge 14. It is important that the remaining sludge (the amount of surplus activated sludge generated by a conventional ordinary activated sludge method not applying the present invention is at least three times or more, and an amount of sludge equal to the amount of surplus activated sludge generated is treated with alkali. Even if it is treated, the excess sludge reduction effect is small) is sent to the alkali treatment tank 15.

NaOH 16 is added to the alkali treatment tank 15 and the pH is 10 or more (preferably 10.5-11.
It is adjusted to 5) and stirred for about 1 to 2 hours. As a result, the activated sludge is hydrolyzed by the alkali and solubilized, and the soluble BOD is eluted from the activated sludge. Activated sludge cells themselves have been damaged by cell walls due to alkali and are susceptible to biodegradation. In addition, the alkaline p
Under the H condition, the hydroxyl group is more easily coordinated than the phosphate ion, so that the phosphate ion is desorbed from the iron hydroxide, aluminum hydroxide, zirconium hydroxide, or the like that has adsorbed the phosphate ion. The sludge to be supplied to the alkaline tank is
Part of the activated sludge may be withdrawn from the nitrification tank 7 and the denitrification tank 6.

The alkali-treated sludge 17 is separated into a solid-liquid separator 18
Separation liquid 19 obtained by solid-liquid separation contains phosphate ions and soluble BOD.
Ion 21 is added to precipitate as magnesium ammonium phosphate (MAP) and calcium phosphate, and sedimentation-separation is carried out. The ammonium ion for producing MAP is
Digestion and desorption solution 27 in the anaerobic digestion step of coagulated and separated sludge 5,
By mixing with the dehydration separation liquid 30 (containing a high concentration of ammonium ions), a sufficient amount of ammonium ions for MAP generation can be supplied. Next, the separated sludge 20 solid-liquid separated by the solid-liquid separator 18 after the alkali treatment
And the separated liquid 23 in the phosphorus precipitation step are returned to the denitrification tank 6, and the BOD eluted by the alkali treatment is used as an organic carbon source (hydrogen donor) for the denitrifying bacteria.

Therefore, according to the present invention, the SS in the sewage 1
Even if the sewage from which the SS BOD has been removed by coagulation separation is supplied to the denitrification step, the organic carbon source for the denitrifying bacteria does not run short, and efficient denitrification is performed. This is one of the important effects of the present invention. This is because the conventional removal of SS by adding a flocculant to sewage,
This is because the S-BOD is also removed at the same time, and a large problem that the denitrification effect deteriorates due to the shortage of the organic carbon source in the subsequent denitrification step could not be solved conventionally.

Since the alkali-treated sludge 17 has a weakened cell wall and improved biodegradability, when supplied to the biological nitrification denitrification step, about 30% of the sludge is decomposed by microorganisms into carbon dioxide and water. , 70% remain as growing sludge.
Therefore, when the sludge of about 3 times or more the amount of the excess activated sludge generated in the ordinary activated sludge method to which the present invention is not applied is alkali-treated, the excess activated sludge is not substantially generated from the biological nitrification denitrification step. .

In the present invention, the organic SS in the sewage 1 is used.
Almost all are removed by the coagulation separation step using the cationic polymer 2, so that the organic SS hardly flows into the biological nitrification denitrification step. However, the amount of surplus activated sludge is reduced. As a result, the amount of activated sludge supplied to the alkali treatment step can be reduced, and as a result, there is a great effect that the required amount of alkali is reduced.

There is still another great effect. That is, in the present invention, since almost all of the organic SS in the sewage 1 is removed by the coagulation separation step using the cationic polymer 2, the organic SS hardly flows into the biological nitrification denitrification step. The SRT (sludge age) of the nitrifying bacteria in the nitrification step becomes large, and the nitrifying bacteria are not washed out out of the system. Therefore, unlike the related art, it is not necessary to fix nitrifying bacteria to a carrier such as a gel carrier, which is a great effect that the carrier cost can be eliminated.

However, the alkaline separation liquid 23 in the phosphorus precipitation step contains phosphorus-desorbed iron hydroxide, aluminate ion, aluminum hydroxide, aluminum oxide, titanium hydroxide, titanium oxide, zirconium hydroxide and the like. Therefore, when this is returned to the biological nitrification denitrification step, it again has a function of effectively removing phosphate ions in the sewage 1. Therefore, the fresh phosphorus removing agent 8 to be added to the biological nitrification denitrification step only needs to be in the initial operation. In other words, after the start of operation, iron hydroxide,
Alternatively, after aluminum hydroxide, titanium hydroxide, zirconium hydroxide, etc. accumulate at about 1000 to 3000 mg / liter as SS, the necessity of adding a fresh phosphorus removing agent 8 can be substantially reduced, and phosphorus removal can be achieved. Lumber 8
In this case, only the loss that escaped from the system may be added to the aeration tank and replenished. In FIG. 1, reference numeral 29 denotes a dehydrator for digested sludge 28, 31 denotes dehydrated sludge, and 10 denotes a circulation slurry.

[0021]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) A verification test of the present invention was performed on sewage (average water quality is shown in Table 1) according to the process shown in FIG. Table 2 shows the test conditions.

[0023]

[Table 1]

[0024]

[Table 2]

As a result of the experiment, the quality of the treated sewage cationic polymer coagulated sedimentation water was SS 5 to 12 mg / L, BO
D40-45mg / liter, T-P3.2-3.6m
g / L, T-N 21-25 mg / L, and the organic SS in the sewage was highly removed. Two months after the operation started, the average of the quality of the treated water from the sedimentation tank after the treatment condition became stable was as shown in Table 3 in which phosphorus, BOD and nitrogen were highly removed. Although the excess sludge was not disposed of outside the system during the one-year test, the MLVSS of the biological nitrification denitrification tank was 3600 to 4000 m.
Since the g / liter was maintained, it was found that the generation of excess sludge was negligibly small.

[0026]

[Table 3]

[0027]

As described above, according to the present invention, the following remarkable effects can be exhibited, and an organic sewage treatment process such as sewage treatment can be innovated. (1) Phosphorus concentration of biologically treated sewage can be extremely low, and valuable phosphorus can be recovered from sewage as MAP and HAP. Therefore, it is not necessary to remove phosphorus by a tertiary treatment facility such as coagulation sedimentation, so that the facility can be greatly reduced. (2) Since almost no surplus activated sludge is generated from the biological treatment plant 1, dehydration and incineration of the surplus activated sludge are greatly streamlined. (3) Since organic SS in sewage is highly removed in the first sedimentation basin and brought into the methane fermentation (anaerobic digestion) process, the amount of methane gas recovered from sewage increases.

(4) Since organic SS in sewage is highly removed in the first sedimentation basin, the SRT of nitrifying bacteria in the biological nitrification and denitrification step can be increased, and even if a nitrifying bacteria-immobilized carrier is not used. The SRT of nitrifying bacteria can be increased, and the cost of adding a carrier can be eliminated. (5) If the organic SS of the wastewater is removed too much, the BOD is insufficient due to the denitrification bacteria in the biological denitrification step, and the denitrification effect is deteriorated. , And the BOD is eluted from the sludge, which can be used as an organic carbon source for denitrifying bacteria. Therefore, even if organic SS is highly coagulated and removed in advance, the denitrifying effect does not deteriorate. (6) The alkali agent (NaOH) is economical because it can be used for a combined purpose of desorbing phosphate ions from phosphorus-removed particles and solubilizing activated sludge.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a method for treating organic wastewater of the present invention.

FIG. 2 is a block diagram showing a conventional sewage treatment method.

[Explanation of symbols]

 Reference Signs List 1 sewage 2 cationic polymer 3 coagulation separation tank 4 effluent 5 coagulation separation sludge 6 denitrification tank 7 nitrification tank 8 phosphorus remover 9 effluent water 10 circulation slurry 11 solid-liquid separation tank 12 treated water 13 separation sludge 14 return sludge 15 alkali treatment Tank 16 NaOH 17 Alkali-treated sludge 18 Solid-liquid separator 19 Separation liquid 20 Separation sludge 21 Mg or Ca ion 22 Precipitation tank 23 Separation liquid 24 Recovered phosphorus 25 Anaerobic digester 26 Methane gas 27 Digestion / desorption liquid 28 Digestion sludge 29 Dehydrator Reference Signs List 30 Dehydration separation liquid 31 Dehydration sludge 32 First sedimentation basin 33 Raw sludge 34 Biological nitrification denitrification process 35 Effluent 36 Final sedimentation basin 37 Outflow water 38 Sedimentation sludge 39 Inorganic coagulant 40 Coagulation sedimentation tank 41 Treated water 42 Coagulation sedimentation sludge 43 Return sludge 44 Excess activated sludge

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshihiro Tanaka 11-1 Haneda Asahimachi, Ota-ku, Tokyo F-term in EBARA CORPORATION (reference) 4D015 BA23 BB05 BB17 CA01 DC06 DC07 DC08 EA32 EA35 FA02 FA03 FA26 4D038 AA08 AB45 AB48 BA04 BB18 BB19 4D040 BB05 BB15 BB32 BB57 BB72 4D059 AA03 AA06 AA19 BA12 BE00 BE49 BF14 BK12 CA28 DA01

Claims (3)

[Claims] 1. A method of adding a cationic polymer flocculant to organic wastewater to separate solids and liquids into aggregates formed into separated water and coagulated separated sludge. The separated water is used as a chemical phosphorus remover particle and activated sludge. Is supplied to the biological nitrification denitrification activated sludge treatment step coexisting with BOD, nitrogen is removed and the phosphorus is solidified, and the sludge mixture of the treatment step is supplied to the solid-liquid separation step,
The supernatant obtained by separating the sludge substance is discharged as treated water to the outside of the system, while a part of the separated sludge in the separation step is extracted, and NaOH is added to the sludge containing phosphorus, BOD and nitrogen to adjust the pH to 10 or more. After the adjustment, solid-liquid separation is performed, and the separated sludge is returned to the above-mentioned denitrification step. On the other hand, Ca or Mg ions are added to the separated liquid from the solid-liquid separation to precipitate phosphorus ions as solids and then solid-liquid separation. And recovering the phosphorus, and returning the separated liquid to the denitrification step. 2. An anaerobic digestion of the coagulated and separated sludge by the cationic polymer coagulant, and the digested and separated liquid is treated with the N
The processing method according to claim 1, further comprising a step of mixing the solid-liquid separation liquid after the addition of aOH. 3. An aggregating / separating apparatus for solid-liquid separating an agglomerate formed by adding a cationic polymer flocculant to organic wastewater.
Supplying the separated water from the coagulation separation device, adding a chemical phosphorus removing agent, introducing a biological nitrification denitrification device for removing phosphorus, BOD, and nitrogen, and introducing effluent from the nitrification denitrification device; A solid-liquid separation tank for separating into treated water and sludge, an alkali treatment tank for introducing a part of the separated sludge from the solid-liquid separation tank to release phosphorus, and an alkali-treated sludge from the alkali treatment tank for solid-liquid separation. Solid-liquid separation device that separates into separated liquid and separated sludge,
A separation tank for adding Ca or Mg ions to the separation liquid to precipitate phosphorus as a solid, a return pipe for sending the separation sludge of the solid-liquid separation device and the separation liquid from the separation tank to the nitrification denitrification apparatus are provided. An organic wastewater treatment device characterized by the following.