JPH0698356B2 - Organic wastewater treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel treatment method capable of treating organic wastewater such as human waste, septic tank sludge, sewage, and various organic industrial wastewater in a significantly energy-saving manner. It is a thing.

[Conventional technology]

Conventionally, taking a representative human waste of organic wastewater as an example, an alkaline agent such as Ca (OH) ₂ is added to the desorbed liquid obtained by anaerobically digesting human waste to raise the pH to 11 or more to ammonia. A method of stripping (NH ₃ strip) is known. Also known is a method in which an alkaline agent is directly added to human waste, NH _{3 is} stripped at a high pH, and then an acid is added to lower the pH to perform biological nitrification and denitrification treatment.

However, in these conventional methods, since the M alkalinity of human waste or the anaerobic digestion and desorption liquid of human waste is extremely high at about 10,000 mg / l, the pH buffering property is high, and as a result, tens of thousands of alkaline agents are added. Unless it is added in a large amount such as / l, the pH cannot be raised to pH 11 or higher, which is suitable for NH ₃ strips, and the running cost of the alkaline agent becomes high, so that it cannot be put to practical use at all. Therefore, as for the human waste treatment, the biological main nitrification denitrification treatment is now the mainstream.

Even if NH ₃ strip is performed, the process is limited to immediately after the anaerobic digestion treatment of human urine or just before the biological nitrification and denitrification treatment of human urine.
There was no concept of doing _three strips. That is,
The application of the conventional NH ₃ strip method to human waste treatment is as follows.
It was limited to flows, and no other attempts existed until now.

[Problems to be Solved by the Invention] However, both of the above flows (a) and (b) have a drawback that the cost required for the alkaline agent for NH ₃ strip is high, and further, in the flow (b), NH ₃ strip is used. Then B
Since OD is not removed at all, there is a fatal drawback that the aeration power in the subsequent biological nitrification and denitrification step is large, so it is recognized that flow (b) is not a technique that is practically applicable. It has not been put to practical use.

Further, the above-mentioned flow (a) has a drawback that the reaction rate of anaerobic digestion is extremely low and the energy required for heating is large.

The present invention aims to completely solve the drawbacks of the prior art, specifically, significantly reduces the running cost of the alkaline agent for NH ₃ strip, and,
BOD very energy saving removing, and, COD, chromaticity, and an object of the invention to provide a new process for PO ₄ ^3- possible highly removed.

[Means for Solving the Problems]

The present invention is based on the new concept of arranging decarboxylation treatment and NH ₃ strip treatment in series connection before the methane fermentation treatment with immobilized methanogens.

Methane fermentation treatment with immobilized methanogens is different from conventional anaerobic digestion in a digester, and utilizes the flocculation function of the microorganisms themselves to generate granular aggregates of anaerobic cells in which the proportion of methanogens is high. A biofilm of methanogenic bacteria is grown on the surface of a granular medium such as zeolite, and a blanket layer (fluidized bed) is formed with this, and liquid is passed through this blanket layer to decompose and remove organic substances with high efficiency. It is a typical method to perform, a methane fermentation treatment method that requires almost no internal mechanical equipment and is easy to maintain and manage.
An example is the method called the UASB method.

That is, in the present invention, a hydrogen ion dissociating substance is added to organic wastewater, decarboxylation treatment is performed under acidic conditions, an alkaline agent is added to the decarboxylation treatment liquid, and ammonia stripping is performed under alkaline conditions. The method for treating organic sewage is characterized by performing methane fermentation treatment with immobilized methanogens, and is characterized in that solid-liquid separation is further performed before or after the decarboxylation treatment. In these treatments, the organic sewage treatment method is characterized in that after the methane fermentation treatment with the fixed methanogen, biological nitrification denitrification treatment is performed.

[Action]

First, the operation of the present invention will be described for a system showing one embodiment.
With reference to the drawings, the following description will be given by taking an example of a human waste water, which is a typical organic waste water.

To the human waste water 1 such as human waste and septic tank sludge, a cationic polymer or a polymer 2 of both cationic and anionic polymers is added to aggregate SS and colloid in the waste water to flocculate it, and to set it to an arbitrary solid such as a screen. The flocculation flocs are separated in the liquid separation step 3 and divided into sludge 4 and separated liquid 5.

Separation liquid 5 is SS, colloidal except soluble BOD in wastewater.
Although BOD is effectively removed, HCO ₃ ^- alkalinity by the solubility of ions and low molecular weight, such as PO ₄ ^3- ions B
OD has not been removed. Especially, since the alkalinity component based on HCO ₃ ⁻ ion remains in an extremely large amount of 8000 to 10000 mg / l in the case of human waste, next, H ⁺ ion dissociation substance 6 such as FeCl ₃ , AlCl ₃ , HCl is added. Add to lower the pH to 3-4 (eg Fe ³⁺ ions are Fe ³⁺ + 3H ₂ O → Fe (OH) ₃ ↓ + 3H ⁺
As a result, the Al ³⁺ ion becomes Al ³⁺ + 3H ₂ O → Al (OH) ₃ ↓ +
3H ⁺ dissociates the H ⁺ ion by a hydrolysis reaction), and the following chemical reaction proceeds to transfer the HCO ₃ ⁻ ion to CO ₂ .

_{^{HCO 3 - + H + → CO}} 2 ↑ + H 2 O ...... (1) Thereafter, exposed gas in the decarboxylation step 7, such gas-liquid contact,
Dissipates CO ₂ . 8 is air for air exposure blown into the decarbonation step 7. At this time, H ₂ S in the wastewater is also diffused and removed. When Fe ³⁺ is used as the H ⁺ ion dissociation substance, H ₂ S is precipitated and removed as FeS ↓. This will bring about a great effect on the methane fermentation treatment as described later.

As the H ⁺ ion dissociation substance 6, H ₂ SO ₄ , Fe ₂ (SO ₄ ) ₃ , Al
Compounds containing SO _{4 3−} ions such as ₂ (SO ₄ ) ₃ and ferric polysulfate are not very preferable. This is because, when the SO ₄ ^3- ions is added, in the methane fermentation step 19 to be described later, SO ₄
^{The 3-} ions are anaerobically transformed into H ₂ S by the action of sulfate-reducing bacteria.
In addition to being toxic to methanogens, a large amount of H ₂ S gas is mixed in the generated CH ₄ gas, which hinders the effective use of CH ₄ gas. Polyaluminum chloride (PAC) cannot be recommended because its pH lowering power is significantly weaker than that of FeCl ₃ . In addition, after the SS in the wastewater is coagulated and removed by a polymer in advance, Fe ³⁺ or
When Al ³⁺ is added, Fe ³⁺ or Al ³⁺ is not consumed for SS agglomeration, so lower Fe ³⁺ or Al ³⁺ lowers pH, COD, P
O ₄ ³⁻ has the advantage that chromaticity can be effectively removed.

After that, SS mainly composed of flocs such as Fe (OH) ₃ and Al (OH) ₃ is separated in any solid-liquid separation step 9 such as precipitation,
HCO ₃ ⁻ (alkalinity), PO ₄ ³⁻ , soluble COD, and chromaticity are removed, and a clear liquid 10 having a clear appearance is obtained. 11 is separated sludge. The appearance of the clear liquid 10 is clear, but NH ₄ ⁺ and soluble BOD in the wastewater remain as they are.

Next, the clarified liquid 10 is heated to 30 ° C or higher, and NaOH, Ca (OH) ₂ , M is added.
adding an alkali agent 12, such as g (OH) _2, pH was raised to alkaline (preferably pH 10-11) a, NH ₄ ^{+ +} OH ^- by a chemical reaction _{→ NH 3 ↑ + H 2 O} ...... (2), NH ₄ ⁺ is transferred to free NH ₃ and supplied to the NH ₃ strip process 13 by gas-liquid contact such as a packed tower, a plate tower, and a leak tower.

If a large amount of alkalinity component is present in the clarified liquid 10 flowing into the NH ₃ strip process 13, the reaction of HCO ₃ ⁻ + OH ⁻ → CO ₃ ^{2 −} + H ₂ O (3) proceeds and OH ⁻ ions are consumed. Therefore, unless a large amount of alkali agent is added, the reaction of the above formula (2) cannot proceed, but in the present invention, decarbonation is carried out by a unique method in the previous stage to remove HCO ₃ ⁻ . Therefore, the interference reaction of the above formula (3) does not occur. As a result, by adding a remarkably small amount of alkaline agent, NH ₃
The liberation reaction proceeds effectively.

Then, in the NH ₃ strip process 13, air 14 is supplied to bring the liquid 10 into gas-liquid contact with the clarifying liquid 10 to strip (dissipate) NH ₃ ↑. Reference numeral 15 is the released NH ₃ gas, which is disposed of by oxidation 16 to N ₂ by catalytic combustion or absorption 16 ′ into H ₂ SO ₄ and H ₃ PO ₄ liquids. 17 is clean gas, which is discharged into the atmosphere.

Next, the NH ₃ strip effluent 18 from which NH ₃ was highly removed (removal rate of 90% or more) in the NH ₃ strip step 13 was supplied to the mesophilic methane fermentation step 19 by the immobilized methanogen ( With a BOD load of 30 to 50 kg BOD / m ³ · day), soluble BOD is subjected to methane fermentation treatment at extremely high speed, and decomposed and removed into CH ₄ and CO ₂ gas. This "immobilized methanogen" utilizes the phenomenon in which a methanothric methanogen granulates itself into aggregates (called self-immobilization), zeolite,
Methane-forming bacteria adhered to the surface of microbial adhesion media such as sand, granular ceramics, granular activated carbon, and honeycomb tubes, and methane in organic polymer gels such as calcium alginate, polyvinyl alcohol, polyacrylamide, and photocurable resins. It means the generic name of the ones that comprehensively immobilize the producing bacteria. The illustrated example is one of the most preferred upflow anaerobic sludge blanket method (also called UASB method) using a bracket layer of self-immobilized methanogen.

20 is a particle size of 0.5 to 2 formed in the methane fermentation treatment step 19.
mm is a blanket layer of self-immobilized methanogen aggregates, with extremely high concentrations of methanogens (5000-100000mg /
lMLSS) is maintained. Reference numeral 21 is a collection chamber for the generated gas containing CH ₄ as a main component, 22 is a precipitation separation unit, and 23 is a baffle for guiding the generated gas to the gas collection chamber 21.

As a result of experiments, the present inventor has obtained the following important findings.

That is, in the high-speed methane fermentation treatment with immobilized methanogens,
High concentrations of SS and NH ₄ ^{+ in the} influent inhibit the immobilization of methane bacteria.

Sulfides in the influent also have a detrimental effect on methane bacteria.

However, in the present invention, removal of the SS in preceding processing by immobilized methanogens, because they are processed and NH ₃ removal by simultaneous removal and improved NH ₃ strip method of H ₂ S in the decarbonation unit, the fixed It was experimentally confirmed that the inhibitory factors to the methanogenic bacterium can be sufficiently eliminated, and the high-speed treatment by the immobilized methanogen such as UASB progresses under the ideal situation. This is one of the extremely important points in the process configuration of the present invention.

Then, the generated methane gas 24 is recovered and the heating source for heating the clarified liquid 10 flowing into the NH ₃ stripping step 13, the drying of the sludge dewatering cake, the auxiliary fuel for incineration, and the stripped NH ₃
It is effectively used as auxiliary fuel for catalytic combustion of gas 15.

Methane fermentation effluent 25 from the methane fermentation step 19, is already ^{_{SS, BOD, PO 4 3-,}} COD, because NH ₄ ⁺ majority of has been removed, the discharge can be treated water in public water However,
In the case of further advanced treatment as desired, the methane fermentation effluent 25 is introduced into a biological nitrification denitrification treatment step 26, or a known activated sludge treatment or an aerobic biological bed (not shown),
A small amount of BOD, nitrogen components, etc. remaining in the methane fermentation effluent 25 may be biologically removed.

Note that 27 is a solid-liquid separation means such as an ultrafiltration membrane (UF membrane) for separating activated sludge, and is not necessary when applying an aerobic biological bed. 28 is returned sludge, 29 is excess sludge, and 30 is highly treated water. Further, 31 is surplus methane bacteria, and the generation amount thereof is extremely small like the surplus sludge 29.

For the purpose of extremely highly removing the non-biodegradable COD and chromaticity of the methane fermentation effluent 25, activated carbon powder should be used.
32 is added to the aeration tank of the subsequent activated sludge treatment process,
Alternatively, by adding it to the NH ₃ strip effluent 18, it is possible to effectively prevent foaming and achieve the purpose.

Furthermore, it is extremely interesting to note that when activated methane fermentation is performed by immobilized methanogens, activated carbon powder 32 is treated with UA.
It was confirmed that when it was supplied into the methane fermentation treatment step 19 such as the SB method, the formation of aggregates due to self-immobilization of methanogenic bacteria was significantly promoted, which is a finding that has not been known until now.

The operation of the present invention has been described above with reference to one embodiment.
Further, another embodiment of the present invention will be supplementarily described.

That is, by adding the H ⁺ ion dissociation substance 6 such as Fe ³⁺ to the solid-liquid separation step 3 in the preceding stage, the solid-liquid separation step 9 in FIG.
How to get rid of.

A method in which a H ⁺ ion dissociation substance 6 is added and a decarboxylation process 7 is provided in a stage preceding the solid-liquid separation process 3.

Omitting the addition of polymer 2 and solid-liquid separation step 3 in FIG. 1,
A method of directly adding H ⁺ ion dissociation substance 6 to sewage 1 and performing decarboxylation treatment. (This method is suitable for the case where SS of sewage 1 is not high concentration like sewage.) Odor (H ₂ S
Etc.) is removed by biological deodorization.

A method of adding the dehydrated separated liquid of the septic tank sludge to the biological treatment step after the methane fermentation processing step 19 when the human waste and the septic tank sludge are treated in combination. Since the solubility BOD of septic tank sludge is only about 1/10 of that of human waste, it is disadvantageous to allow it to flow into the methane fermentation treatment step 19.

When the raw water SS is relatively small such as sewage (SS number 10
0 mg / l) omits the solid-liquid separation steps of 3 and 9 in FIG.
After the decarboxylation step 7, the NH ₃ strip step 13 may be directly introduced. However, as H ⁺ ion dissociation substance 6, Fe ³⁺ , A
In the case of using l ³⁺ , it is much more preferable to provide a solid-liquid separation step 9 to separate flocs and remove COD and PO ₄ ³⁻ as the pH decreases.

Are recommended as an embodiment of the present invention.

〔Example〕

 Experiments of the present invention were conducted according to the embodiment of FIG.

250 mg / l [Eva Gloss C104G (trade name)] of cationic polymer was added to human waste having water quality shown in the left column of Table 1 below.
After stirring for a minute, large-sized flocs were produced, so
This was separated with a 1 mm wedge wire screen. FeCl ₃ (4000 mg / l) and HCl (1000 mg / l) were added to the separated liquid, and the mixture was decarbonated by aeration for 1 hour and then allowed to stand for 0.5 hour in a settling tank.
1 The right column shows the water quality, and the alkalinity of human waste, SS, COD, BOD, PO
₄ ^{3 ,,} H ₂ S was largely removed.

Next, after heating the decarboxylation solution in the right column of Table-1 to 55 ° C and adding NaOH, the pH easily rose to 10.5 at only 800 mg / l, and the optimum pH for NH ₃ strip was reached. I was able to set it. This alkali addition rate is about 1 of the conventional NH ₃ strip method.
It was / 10. For the NH ₃ strip, a 7 m high packed column filled with terraret was used, and the air stripping method by gas-liquid countercurrent was adopted. Gas-liquid ratio is (liquid volume / air volume) = 0.25
And

As a result, the NH ₃ strip treatment liquid flowing out from the NH ₃ strip step had the water quality shown in the left column of Table 2 below. When this solution was subjected to methane fermentation (temperature 30 ° C) with a residence time of 0.7 days by the UASB method using a self-immobilized methanogen, BOD was removed very rapidly and the water quality shown in the right column of Table-2 is shown. A treatment liquid was obtained. In addition, a small amount of the screen separation liquid was added to the UASB method inflow liquid to remove PO ₄ in the UASB treatment.
^3-Prevented shortage.

The NH ₃ strip treatment liquid at a temperature of 52 ° C. was heat-exchanged with decarbonated treatment water, cooled to 30 ° C. to 35 ° C. suitable for medium-temperature methane fermentation treatment, and supplied to a UASB treatment tank.

Next, the UASB treatment liquid in the right column of Table 2 was treated by a known biological nitrification denitrification method. This nitrification denitrification method uses a nitrification solution circulation type, MLSS concentration of 10,000 to 12000 mg / l, and residence time of 0.
It was set on 4 days and a limiting membrane (molecular weight cutoff of 100,000) was used for solid-liquid separation of activated sludge. For nitrification and denitrification, 600 mg / l of powdered activated carbon and 300 mg / l of FeCl ₃ were added.

As a result, highly-treated water having extremely good water quality shown in Table 3 below was obtained.

The aeration blower was not necessary because the residual pressure of the liquid supply pump to the ultra-supermembrane was used for the aeration and the aeration was performed by the waterfall effect by the drop of the pump discharge liquid to the water surface.

The above-mentioned experiment proves the outstanding effect of the present invention. That is, because there are no factors that inhibit methane fermentation by immobilized methanogens (SS, NH ₄ ^+, and H ₂ S), extremely high-speed methane fermentation can be performed, and BOD and NH ₄ -N in the methane fermentation treatment liquid are remarkably high. Due to the low volume, a high volume of nitrification and denitrification was performed in a small volume biological nitrification and denitrification tank. It was also confirmed that the alkali cost for NH ₃ strip and the acid cost for decarboxylation can be significantly reduced.

〔The invention's effect〕

As described above, the present invention, contrary to the conventional method,
"We performed NH ₃ strip before the methane fermentation process,
Also, an alkalinity removal step (by decarboxylation) is placed in front of the NH ₃ strip, and as a methane fermentation treatment,
Applying immobilized methanogens ”As the process adopts the new concept, the following important effects are obtained.

Methane fermentation treatment with immobilized methanogens such as the UASB method is adversely affected by high concentrations of NH ₄ ⁺ and SS, H ₂ S, but in the present invention, such a negative factor was completely eliminated, so immobilized methane It is possible to perform high-speed methane fermentation treatment under an ideal environment for producing bacteria.

As a result, 1/10 of the required volume of the biological treatment tank of the state-of-the-art state-of-the-art, undiluted, high-load biological nitrification and denitrification method
The treatment can be done in the tank, and the construction cost and space can be greatly reduced.

Aeration power is not required for BOD removal, resulting in a large energy saving effect.

The alkali cost for pH increase for NH ₃ strip can be significantly reduced.

As H ⁺ ions for decarboxylation, it is possible to utilize the hydrolysis reaction of Fe ₃ ⁺ , Al ³⁺ , so that COD,
There is a combined effect that PO ₄ ³⁻ , SS, and colloid can be removed at the same time, and the chemical cost for decarboxylation can be greatly reduced.

High-speed methane fermentation treatment with immobilized methanogens (for example, UASB method) can significantly reduce the size of the treatment tank, and as a result, heat loss due to the amount of heat released from the walls of the methane fermentation tank is reduced. Therefore, the surplus amount of CH ₄ gas increases, and the surplus amount can be used for drying and incineration of sludge, etc., so that a further energy-saving process can be realized.

Since the amount of excess sludge generated from the methane fermentation process by the immobilized methanogen is extremely small, sludge treatment can be performed rationally.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention. 1 …… Shiria wastewater, 2 …… Polymer, 3,9 …… Solid-liquid separation process, 4 …… Sludge, 5 …… Separation liquid, 6 …… H ⁺ ion dissociation material, 7 …… Decarboxylation process, 8 …… Air for air explosion, 10 …… Clarification liquid, 11 …… Separation sludge, 12 …… Alkaline agent, 13 …… NH ₃ strip process, 14 …… Air, 15 …… NH ₃ gas, 16 …… Oxidation, 16 '... absorbent, 17 ... clean gas, 18 ... NH ₃ strip effluent, 19 ...... methane fermentation step, 20 ... blanket layer, 21 ... collecting chamber, 22 ... sedimentation separation unit, 23 …… Baffle, 24 …… Methane gas, 25 …… Methane fermentation effluent,
26 …… Biological nitrification denitrification process, 27 …… Solid-liquid separation means, 28 …… Return sludge, 29 …… Excess sludge, 30 …… Highly treated water, 31 …… Excess methane bacteria, 32 …… Powder Activated carbon.

Claims (3)

[Claims] 1. A hydrogen ion dissociating substance is added to organic wastewater, decarboxylation treatment is performed under acidic conditions, an alkaline agent is added to the decarboxylation treatment liquid, and ammonia stripping is performed under alkaline conditions. A method for treating organic sewage, which comprises performing methane fermentation treatment with immobilized methanogens. 2. The method for treating organic wastewater according to claim 1, wherein solid-liquid separation is performed before or after the decarboxylation treatment. 3. The method for treating organic wastewater according to claim 1 or 2, wherein after the methane fermentation treatment with the immobilized methanogen, a biological nitrification denitrification treatment is performed.