JPH05138193A - Mehtod for biologically removing nitrogen in waste water - Google Patents

Abstract

PURPOSE:To prevent the outflow of sulfur denitrification bacteria and to promote denitrification velocity by introducing sulfur denitrification bacteria into water absorptive resin and inclusively immobilizing the same when the water absorptive resin absorbs water and is swelled. CONSTITUTION:Both incineration ash 2 of sewage sludge and suspension of incineration ash wherein a small amount of acid is added to incineration ash 2 are added to sludge 1 containing sulfur denitrification bacteria and this mixture is agitated and mixed. Water absorptive resin 4 is added and the mixture is agitated and mixed. Water absorptive resin 4 absorbs water and is swelled and simultaneously sulfur denitrification bacteria are introduced into the inside of water absorptive resin 4 and inclusively immobilized. The inclusively immobilized sulfur denitrification bacteria 5 are introduced into a biological nitrification sulfur denitrification treatment device 6 and treatment is performed. Furthermore an NaOH solution is added to incineration ash 2 and then exhaust gas high in the concentration of carbon dioxide is blown thereinto. Thereby bicarbonate liquid containing HCO3<->, at high concentration is prepared and used as a carbonate source in sulfur denitrification reaction. In such a way, necessary inorganic carbon is supplied by utilizing waste such as combustion exhaust gas and cost reduction is contrived.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biological nitrogen removal method for wastewater, and more particularly to a denitrification method in which denitrifying bacteria are entrapped and immobilized to improve nitrogen removal efficiency.

[0002]

2. Description of the Related Art As a biological nitrogen removal method for wastewater, a method of combining a nitrification reaction and a denitrification reaction is generally adopted. Since ordinary denitrifying bacteria are polytrophic bacteria, it is better to supply an organic carbon source such as methanol as a hydrogen donor from the outside when carrying out the denitrification reaction by using the organic matter in the inflowing wastewater as a hydrogen donor. The denitrification rate is higher and the total nitrogen removal rate is higher than when used. Therefore, there is an advantage that the capacity of the denitrification tank can be reduced, but there is a drawback that the running cost becomes high due to the cost of chemicals such as methanol.

On the other hand, as another example of nitrogen removal from wastewater, a sulfur-filled aerobic / anaerobic activated sludge method is known. This method uses granular sulfur instead of methanol as a hydrogen donor for denitrifying bacteria, and NaH as a carbon source.
By supplying CO ₃ , the processing cost has been successfully reduced. The denitrifying action in this method is different from the normal denitrifying bacteria, and the autotrophic sulfur denitrifying bacteria play a major role. In the sulfur denitrification reaction, the stoichiometric formula when sulfur alone is supplemented can be represented by the following formula (1).

1.114S + NO ₃ ⁻ + 0.669H ₂ O + 0.337CO ₂ + 0.0842HC O ₃ ⁻ + 0.0842NH ₄ ⁺ → 0.0842C ₅ H ₇ O ₂ N + 0.5N ₂ +1.114 SO ₄ ²⁻ + 1.228H ⁺・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1) On the other hand, methane bacteria A comprehensive immobilization method using a water-absorbent resin for sludge containing water is known (for example, water treatment technology Vo1.27.No. 9.1986). This method involves adding water-absorbent resin (acrylic synthetic polymer resin) and calcium carbonate to sludge containing methane bacteria to absorb water and swell the resin, and at the same time to incorporate anaerobic microbial cells into the resin, and then to crosslink the agent. Is a method of immobilizing bacterial cells by adding a calcium chloride aqueous solution, which is a cross-linking agent, to cross-link the carboxyl groups in the resin molecule. In this method, calcium carbonate acts as a neutralizing agent for the acid and has the effect of maintaining a pH range suitable for the growth of methane bacteria.

[0005]

Despite the fact that about 10 years have passed since the development of the sulfur-filled aerobic / anaerobic activated sludge method, it has not yet been put to practical use. There are three possible reasons for this.

The first reason is that the denitrification rate does not increase as expected even if sulfur is supplemented as a hydrogen donor. That is, in the sulfur denitrification reaction, any reduced sulfur having a sulfur oxidation number of −2 to +4 can be used as a hydrogen donor, but the fastest denitrification rate is S ₂ O ₃ ^2−. Ion. However, although Na ₂ S ₂ O ₃ has a high denitrification rate, it has a drawback that it is quite expensive in price. On the other hand, elemental sulfur is inexpensive, but has the disadvantage that the denitrification rate is lower than that of S ₂ O ₃ ²⁻ ions. Therefore, there is currently no suitable reduced sulfur chemical agent as a hydrogen donor in the sulfur denitrification reaction.

The second reason is that sulfur-denitrifying bacteria are ubiquitous bacteria, but they have a slightly lower growth rate than ordinary denitrifying bacteria and that sulfur-denitrifying bacteria have a floating property. Therefore, it is considered that the outflow of bacteria is likely to occur when the treatment efficiency is increased, and it is difficult to increase the concentration of the bacteria.

The usual denitrification reaction can be expressed by the following equations (2) to (4).

2NO ₃ ⁻ + 10H → N ₂ + 4H ₂ O ... (2) 2NO ₂ + 6H → N _{2 ^{+ 2H 2 O + 2OH - ······················}} (3) N 2 O + 2H → N 2 + H 2 O ············・ ・ ・ ・ ・ ・ ・ ・ ・ (4) It is considered unavoidable that the reaction rate of sulfur denitrifying bacteria is slow, but it is necessary to increase the concentration of cells. Can be improved by means of immobilization. For example, as described above, entrapping immobilization of general nitrifying bacteria such as sludge containing methane bacteria is applied to a standard activated sludge method treatment facility, and various means have been developed for entrapping immobilization methods. There is. However, all of these immobilization means have problems that they are difficult to operate on a large scale and the cost of the immobilization material becomes high.Therefore, a method for actually immobilizing sulfur denitrifying bacteria has been put to practical use. Absent.

A third reason is that it is necessary to supplement inorganic carbon for sulfur denitrification. This inorganic carbon exists as an alkalinity in the inflowing sewage, and therefore, when the alkalinity is insufficient, the inorganic carbon must be replenished independently. In the biological denitrification method, nitrification is usually performed in combination with denitrification, but alkalinity is consumed also in this nitrification process. That is, alkalinity is unilaterally consumed in the nitrogen removal treatment by sulfur denitrification and nitrification, and therefore, it is often required to supplement inorganic carbon. As this inorganic carbon, NaHCO ₃ is usually used, but the increase in drug cost due to the use of NaHCO ₃ cannot be ignored.

The usual nitrification reaction can be expressed by the following equations (5) to (6).

[0012] ^{_{2NH 4 + + 3O 2 → 2NO}} 2 + 2H 2 O + 4H + ················ (5) 2NO 2 - + O 2 → 2NO 3 - ······· (6) Since hydrogen ions are generated in the process of the above formula (5) ammonia being oxidized to nitrous acid, When the inflow water has an alkalinity, the nitrification reaction consumes the alkalinity, whereas the denitrification reaction produces an alkalinity on the contrary. There is no need to replenish the drug. Therefore, with respect to the supplementation of inorganic carbon, the sulfur denitrification reaction is obviously disadvantageous as compared with the normal denitrification reaction.

The present invention has been made in view of the above circumstances, and it is possible to accelerate the denitrification rate by preventing the outflow of sulfur denitrifying bacteria, and to burn the inorganic carbon required for the sulfur denitrification reaction. It is an object of the present invention to provide a biological nitrogen removal method for waste water, which can reduce the cost by supplying waste gas such as exhaust gas.

[0014]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention firstly sets forth a claim 1 for sludge containing sulfur-denitrifying bacteria, incinerating ash of sewage sludge and a small amount of this incinerated ash. After adding an acid and partially dissolving the incineration ash suspension and stirring and mixing, add water-absorbent resin to this mixture and stir-mix it to absorb water and swell the water-absorbent resin, and at the same time perform sulfur denitrification. Incorporate bacteria into the water-absorbent resin and immobilize them comprehensively.
A method for biological nitrogen removal of wastewater is provided, wherein the entrapped and immobilized sulfur denitrifying bacteria flow into a biological nitrifying sulfur denitrification treatment apparatus for treatment.

Further, according to claim 2, a small amount of a NaOH solution is added to the incinerated ash to make it alkaline, and a gas having a high carbon dioxide concentration is blown from the combustion exhaust gas supply means, whereby bicarbonate containing HCO ₃ ⁻ ions at a high concentration is added. Provided is a method for biological nitrogen removal of wastewater by preparing a salt solution and using the bicarbonate solution as a carbon source in a sulfur denitrification reaction.

[0016]

According to the method of the present invention, incineration ash of sewage sludge or a suspension of incineration ash and an acid is added to sludge containing sulfur denitrifying bacteria, and then the water-absorbent resin is mixed and stirred. As a result, this water absorbent resin absorbs water and swells, and the sulfur denitrifying bacteria are entrapped and immobilized in the water absorbent resin, preventing the outflow of the sulfur denitrifying bacteria in the biological nitrifying sulfur denitrifying treatment equipment. And the denitrification rate is accelerated.

Further, according to the method of claim 2, a small amount of alkali is added to the incinerated ash, and a gas having a high carbon dioxide concentration is blown from the combustion exhaust gas supply means, whereby a bicarbonate containing a high concentration of HCO ₃ ⁻ ions. Since the liquid is prepared, the bicarbonate liquid can be used as a carbon source in the sulfur denitrification reaction.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a sulfur-denitrifying bacteria-enriched culture sludge. For 1 m ^{3 of} sludge containing this sulfur-denitrifying bacterium, 1 kg of incinerated ash 2 of sewage sludge and a small amount of hydrochloric acid (HCl) is added to this incinerated ash. ) Is added to the incinerated ash suspension 3 and mixed by stirring. Next, a water absorbent resin, for example, acrylic synthetic polymer resin 4 (viscosity 10 to 32 mesh) is added to this mixture for 1 k.
By adding g and stirring and mixing for about 30 minutes, the water-absorbent resin 4 swells with water, and at the same time, the sulfur denitrifying bacteria are taken into the water-absorbent resin 4, and the sulfur denitrifying bacteria are entrapped and immobilized.

Then, fresh water is flowed into the obtained mixture to wash the mixture. At this time, when the washing clear water becomes clear and the washing is stopped when the pH becomes neutral,
Sulfur denitrifying bacteria are settled in the form of small spheres having a diameter of 2 to 3 mm and are entrapped and immobilized.

The entrapped immobilized sulfur denitrifying bacterium 5 obtained as described above is introduced into a biological nitrifying sulfur denitrification treatment device 6 to be subjected to denitrification treatment. This biological nitrification and denitrification treatment device 6
Is equivalent to the denitrification tank based on the above-mentioned sulfur-filled aerobic-anaerobic activated sludge method.

According to this embodiment, when the water-absorbent resin 4 absorbs water and swells, the sulfur denitrifying bacteria are taken into the water-absorbent resin 4 and are entrapped and immobilized. The effect that the outflow of sulfur denitrifying bacteria in the device 6 is prevented and the denitrification rate is accelerated is obtained.

Among the materials for entrapping immobilization shown in the above examples, the cost of materials other than the water-absorbent resin can be neglected, so this example can be achieved at a lower cost than other entrapping immobilization methods. It has the feature of being

As the incineration ash 2, it is preferable to use ferric chloride and slaked lime added as a dehydration aid. Table 1 shows an example of the composition of the incineration ash 2.

[0025]

[Table 1]

When a small amount of acid is added to the incineration ash having the above composition, it becomes possible to substitute calcium chloride, which is a cross-linking agent for the water absorbent resin. Further, since the incinerated ash has a high calcium content, it is taken in by the entrapping immobilization microbial cells, and thus it can be used as a substitute for calcium carbonate, which is a neutralizing agent for acids.

Further, in the present invention, the method described below was carried out in order to obtain the carbon source required for promoting the sulfur denitrification reaction. That is, in the sulfur denitrification reaction, it is necessary to supply inorganic carbon in addition to reduced sulfur. As a method of supplying this inorganic carbon, a small amount of NaOH solution is added to the incineration ash to make it alkaline, and sludge incinerator waste gas or Is blown with gas with high carbon dioxide concentration such as waste gas generated by combustion of nitrifying gas generated from sludge anaerobic nitrification tank,
A bicarbonate solution containing a high concentration of O ₃ ⁻ ions is produced, and this bicarbonate solution is used as a carbon source in the sulfur denitrification reaction.

FIG. 2 is a schematic view showing the sulfur denitrification method in which the above-mentioned inorganic carbon is supplied, 11 is a bicarbonate liquid preparation tank, and 12 is
Is a stirrer, 13 is an incineration ash supply means, 14 is a NaOH supply means, 15 is a combustion exhaust gas supply means, and 16 is a sulfur denitrification tank or a first settling tank.

According to this structure, the bicarbonate liquid preparation tank 1
In addition to the incineration ash of the sewage sludge from the incineration ash supply means 13 in 1 at the same time NaOH from the NaOH supply means 14
Combustion exhaust gas supply means 15 while stirring by the stirrer 12.
By bubbling a gas containing a high concentration of CO ₂ from the above, a liquid containing a high concentration of HCO ₃ ⁻ ions is generated. This liquid is supplied to the sulfur denitrification tank or the first settling tank 16 and used as inorganic carbon for promoting the sulfur denitrification reaction.

Further, the chemical change of the calcium content abundantly contained in the incinerated ash is represented by the following reaction formula.

CaO + 2H ₂ O → Ca (OH) ₂ (7) Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O ··· (8) CaCO ₃ + H ₂ O + CO ₂ → Ca (HCO ₃ ) ₂ ···· (9) The CaCO ₃ is sparingly soluble, but by blowing excessive CO ₂ , it becomes water-soluble calcium hydrogen carbonate, which serves as a means for supplying inorganic carbon required for sulfur denitrification reaction. The HCO ₃ ⁻ ion concentration can be set to a level that can be used.

Further, according to this embodiment, CaO, Ca (OH) ₂ , CaCO ₃ and Ca contained in the incineration ash are included.
Due to the acid neutralizing action of (HCO ₃ ) ₂ etc., the optimum growth pH of sulfur denitrifying bacteria is maintained even in wastewater with low alkalinity, and the pH is prevented from lowering even in the nitrification process combined with the sulfur denitrification reaction. The effect of increasing the nitrification rate is obtained, and the total nitrogen removal rate can be increased accordingly.

[0033]

As described in detail above, according to the present invention, when the water-absorbent resin is swollen by water absorption, sulfur denitrifying bacteria are incorporated into the water-absorbent resin and entrapped and immobilized.
The outflow of sulfur denitrifying bacteria in the biological nitrifying sulfur denitrification treatment device can be prevented, and the denitrification rate can be accelerated. Moreover, the acid neutralization effect of the incineration ash surrounded by the entrapping immobilization cells can maintain the optimum growth pH of the nitrifying bacteria even in the case of waste water having low alkalinity, and can improve the nitrification rate.

Since a small amount of alkali is added to the incinerated ash and a gas having a high carbon dioxide concentration is blown from the combustion exhaust gas supply means, a bicarbonate solution containing a high concentration of HCO ₃ ⁻ ions is prepared. The bicarbonate solution can be used as a carbon source in the sulfur denitrification reaction. Therefore, it becomes possible to supply the inorganic carbon necessary for the sulfur denitrification reaction by utilizing waste such as combustion exhaust gas, and it is not necessary to use an expensive chemical agent, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a chart illustrating an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a denitrification method in which inorganic carbon is supplied as another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sulfur denitrifying bacteria accumulated culture sludge, 2 ... Incinerated ash, 3 ... Incinerated ash suspension, 4 ... Water absorbing resin, 5 ... Entrapping immobilization sulfur denitrifying bacteria, 6 ... Biological nitrification sulfur denitrification treatment equipment , 11 ... Bicarbonate solution preparation tank, 12 ... Stirrer, 13 ... Incineration ash supply means, 1
4 ... NaOH supply means, 15 ... combustion exhaust gas supply means, 1
6 ... Sulfur denitrification tank (or first settling tank).

Claims (2)

[Claims] 1. An incinerator ash of sewage sludge and an incinerated ash suspension obtained by partially dissolving a small amount of acid in the incinerator ash are added to and mixed with sludge containing sulfur-denitrifying bacteria. After that, a water-absorbent resin was added to this mixture and mixed by stirring, and at the same time the water-absorbent resin was swollen by water absorption and at the same time, the sulfur denitrifying bacteria were incorporated into the water-absorbent resin to be entrapped and immobilized, and thus entrapped and immobilized. A biological nitrogen removal method for wastewater, which comprises treating sulfur denitrifying bacteria by flowing them into a biological nitrifying sulfur denitrification treatment device. 2. A bicarbonate solution containing a high concentration of HCO ₃ ⁻ ions is obtained by adding a small amount of a NaOH solution to the incinerated ash to make it alkaline and blowing a gas having a high carbon dioxide concentration from a combustion exhaust gas supply means. The biological nitrogen removing method according to claim 1, wherein the prepared bicarbonate solution is used as a carbon source in a sulfur denitrification reaction.