JPS5841118B2 - Valve drain deodorization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention targets drains containing odor components such as so-called steam condensed water from accumulators, evaporators, turpentine coolers, etc. in the pulp manufacturing process. The present invention relates to a method for removing .

BACKGROUND ART Conventionally, anaerobic digestion of organic wastes such as waste liquid and waste sludge discharged from pulp manufacturing processes and waste liquid treatment processes has been carried out by a mixed treatment method.

However, these various wastes have significantly different physical and chemical characteristics, and there are cases where the mixed treatment method is not necessarily the optimal treatment method depending on the characteristics of these various wastes.

The present inventors focused on making the most effective use of the characteristic that the steam drain is a heat-soluble waste liquid, and discovered that most of the odors that are a problem in pulp mills are contained in these drains. The present invention was arrived at through the process of researching these individual anaerobic biological treatments.

Specifically, the effective use of the characteristics as a heat-soluble waste liquid means the following.

In conventional methane fermentation treatment of pulp waste liquid, it is not treated alone, but is treated after mixing bleached sludge, unbleached sludge, surplus activated sludge, different types of fermentation residue, etc.

In this case, the steam drain is generally between 50'C and 70'C.
Since it is discharged at a high temperature of about 1000 yen, it is possible to perform high-temperature anaerobic digestion treatment with no heating or minimal heating. Depending on the ratio, the temperature will drop by about 3°C to 30°C, and a larger amount of energy will be consumed for heating than when no mixing is done.

In addition, since there are few solid organic substances in the steam drain, there is no need for the liquefaction and decomposition process of organic substances that is required to decompose organic waste containing other sludge-like solid substances. Minute digestion time can be shortened, enabling higher-speed processing.

Therefore, it is considered advantageous to carry out the anaerobic digestion treatment of steam drains having the above-mentioned characteristics, rather than the conventional mixing treatment, so that even if contamination cannot be avoided, It is important that the temperature reduction and solids content increase are such that they do not substantially prolong the digestion time required for steam drain treatment alone.

FIG. 1 shows the results of an experimental example conducted to reach the above conclusion.

In this experiment, biological sludge in the treated liquid from the anaerobic digestion tank was sedimented and separated, and the sludge was returned to the digestion tank using a continuous digestion device using the anaerobic contact method. Below is the residence time of each waste in the digestion tank.
This was done in stages.

Experiments at each residence time lasted for two months, with the first
The plot shown in the figure shows the average value of the amount of methane gas generated in each steady state, but the minimum residence time required when the evaporator drain is normally used alone (graph ■) is 0.5 While it was a day,
Evaporator drain and excess activated sludge are converted into C0D-Cr
If the weight ratio is 1 (graph ■), it will take 1.5 days, and the evaporator drain, excess activated sludge and unbleached sludge will be mixed at a C0D-Cr weight ratio of 1.
: When digested with a 1:1 ratio (graph ■), even if the residence time was 4.0 days, the amount of methane gas generated per weight of input COD-Cr was insufficient, and the biodegradation reaction was carried out by steam drain. It can be seen that anaerobic digestion of the evaporator drain alone progresses at the highest rate.

As mentioned above, the steam drain discharged from the pulp manufacturing process contains a large amount of sulfur-containing odor components in a concentrated manner. Conventionally, only the odor components were selected using the steam stripping method to remove the odor components in this drain. Many methods are used to strip the waste and incinerate it together with steam.

However, there are no reports of anaerobic biodegradation of steam drains in pulp mills for the purpose of deodorizing, and no knowledge has been found regarding the possibility of decomposing sulfur-containing odor components and deodorizing ability by anaerobic digestion. It has not been.

In addition to the steam stripping method, conventional biological deodorization methods use soil decomposition methods, activated sludge methods, watered P bed methods, etc. as basic components and send odor-containing exhaust or wastewater to these components. biologically decomposes while
This method belongs to the so-called aerobic biological deodorizing treatment method.

Among these, the soil decomposition method is mainly aimed at deodorizing exhaust gas, and it involves sending odor-containing exhaust gas (usually containing oxygen gas) into permeable soil from pipes buried in the soil to remove odor components. This method deodorizes by adsorption → ingestion by microorganisms → biodegradation.

The activated sludge method type is used for both exhaust gas and deodorization from wastewater, and is used in culture solutions for aerobic microorganisms (usually grown in suspended form, but in fixed or fluidized bed materials). This is a method in which odor-containing exhaust gas or wastewater is injected into a microorganism (in which the odor components are absorbed and biologically decomposed).

A water sprinkling P bed method type can also be used for both exhaust gas and wastewater deodorization.

When deodorizing exhaust gas using this method, exhaust cleaning water is circulated and sprinkled on the P material layer, and the odor-containing exhaust gas is passed through the P material layer in a direction opposite to the direction of the water flow and is cleaned while being in contact with the P material layer. This is a method in which odor components are decomposed by microbial slime adhering to the surface of the f-material.

In addition, when removing odor components from wastewater, the odor-containing wastewater is circulated and sprinkled instead of washing water, and air is passed in opposition to this flow to remove the odor components dissolved in the liquid under aerobic conditions. A method of decomposition is used.

The deodorizing method that utilizes the metabolic activity of aerobic microorganisms as described above decomposes odor components in the solution while supplying molecular oxygen to the solution. Although this is often done, there are cases in which some odor components migrate into the surplus air exhausted from the deodorizing device, and this becomes a secondary source of odor.

In order to prevent this situation, it is effective to reduce the amount of air used as much as possible and recycle it. It is also possible to take measures to reduce the volume of gas used by ~% by circulating air to the deodorizing device, reduce the amount of exhaust gas by that amount, and prevent secondary odor pollution.

However, the supply of molecular oxygen to a solution itself is a process that requires a considerable amount of energy, and the production of high-purity oxygen gas also requires a considerable amount of energy, making it an economical issue. These methods may be adopted only in cases where it is appropriate to do so.

Conventionally, the steam stripping method described above has been mainly used to deodorize evaporator drains, accumulator drains, and other odor-containing drains discharged during the pulp manufacturing process, but biological deodorization treatment methods have also been used. Several have been considered.

However, all of these belong to the category of so-called aerobic deodorization treatment using aerobic organisms, and there is no research on how to biologically deodorize such money-making odor drains without supplying any molecular oxygen. No review report was found.

The present inventors found that anaerobic microorganisms have a greater ability to decompose odor components than aerobic microorganisms, and that the biological deodorizing ability of these anaerobic microorganisms is greater than that of steam drains in pulp mills. The present invention was achieved by obtaining the knowledge that a more effective added value can be added to a substantial single anaerobic digestion treatment.

Below, the research process that led to the present invention will be explained in detail, and its characteristics, effects, etc. will be clarified.

Research on deodorization initially began with basic experiments using synthetic wastewater containing money-making odor components to learn the characteristics and differences in the ability of aerobic and anaerobic microorganisms to decompose various money-making odor components. Both batch and continuous methods were used.

Regarding the microorganisms used as inoculum used in the experiment, those subjected to aerobic biodegradation were activated sludge used for municipal sewage treatment with glucose and yeast extract for a biological solid retention time of 2.5. It was further cultured for 2 months in an aerobic chemostat incubator with a reaction volume of 21 per day,
Digested sludge collected from an anaerobic digester of municipal sewage sludge was subjected to anaerobic biodegradation using glucose and yeast extract for a biological solid retention time of 151 El.
.

In an anaerobic chemostat incubator with a reaction volume of 21, add 2 more
It was cultivated for a month.

In batch experiments, after adjusting the MLSS concentration to 20,001r19/l for both aerobic and anaerobic cultures, continuous supply of the medium was stopped, and endogenous respiration was allowed to occur, resulting in a glucose concentration of almost zero. After confirming this, methyl sulfide was added to each chemostat reactor at a concentration of 500 μL/l, and the temperature was adjusted to 30°C.
Next, we started a batch experiment by keeping plf at 7.5, and observed the decrease in methyl sulfide over time, and obtained the results shown in Figure 2.

In the figure, a indicates an aerobic biological reaction, and b indicates an anaerobic biological reaction.

The results shown in Figure 2 were also obtained regarding the behavior of odor components other than methyl sulfide, that is, methyl mercaptan and hydrogen sulfide.

The concentration of each odor component in the biological reaction solution was determined by extracting the reaction mixture with benzene to obtain a benzene solution of the odor component, and then using a gas chromatograph equipped with an FPD (flame photometric detector).

In addition, the cumulative amount of gas generated per 100 rL of reaction liquid from the anaerobic biodegradation reactor after 8 hours was 27
．． 077LA', and the final concentration composition ratio of the generated gas was 54% methyl mercaptan, 35% methane, and 11% carbon dioxide.

In addition, the increase in the concentration of inorganic carbon in the reaction solution in this case is 1.
Since it was 85 mw ol/l, it is estimated that methyl sulfide was decomposed in the anaerobic reactor based on the following formula from the relationship with the generated gas.

1 (CH3)2S→CH3SH+-CH4+-C022 It is also known from Figure 2 that a part of the generated methyl mercaptan dissolved and further decomposed to hydrogen sulfide, but most of it was in gaseous form. It was released to the outside of the reaction solution as a product.

The rapid decrease in methyl sulfide concentration during the first 15 minutes in the aerobic reactor in the results shown in Figure 2a is not considered to be due to biodegradation, considering the subsequent slow concentration decrease, and is due to physical dissipation due to aeration. This release into the atmosphere predicts the occurrence of secondary odor pollution during aerobic biological treatment.

Next, the decomposition characteristics of methyl disulfide were investigated using the same preculture conditions as above, and the results shown in FIG. 3 were obtained.

The experimental procedure was almost the same as that for methyl sulfide, except that the initial methyl disulfide concentration was 30,011 Ig/l.

In the figure, a is the result in the aerobic bioreactor, and b is the result in the anaerobic bioreactor.The cumulative value of gas generation from the anaerobic bioreactor after 10 days is 10077
171! It was 15.47d, of which 37
% is methyl mercaptan, 28% is hydrogen sulfide, and 23% is methane.

12% is carbon gas, and the concentration of inorganic carbon in the liquid is 0.
．． Since the increase was 7 smmol/l, it was found that anaerobic decomposition of methyl disulfide follows the following formula.

A similar batch experiment was conducted with ethyl mercaptan, and the results shown in FIG. 4 were obtained.

In the figure, a shows the results in the aerobic bioreactor, and b shows the results in the anaerobic bioreactor.

As for ethyl mercaptan, almost no emission was observed due to aeration in the aerobic reactor, and although there is no problem of secondary odor pollution due to the emission of ethyl mercaptan, it is thought that methyl mercaptan generated during the reaction process was emitted. Furthermore, since methyl mercaptan has an even lower olfactory threshold than ethyl mercaptan, secondary odor pollution due to atmospheric emissions of methyl mercaptan is expected to pose a more difficult problem.

Regarding the gas generated in the anaerobic reactor, only the concentrations of hydrogen sulfide and methyl mercaptan were measured, and hydrogen sulfide was 0.2
5% and 62% methyl mercaptan, but the amount of hydrogen sulfide produced, including the amount dissolved in the liquid, was about 1/1 o per mole of the initial odor component compared to the case of methyl disulfide. This means that hydrogen sulfide is not produced by direct decomposition of ethyl mercaptan;
It is presumed that part of the methyl mercaptan as an intermediate product was further decomposed to produce hydrogen sulfide.

An increase in the concentration of sulfate radicals in the reaction solution in the aerobic reactor in the above three batch experiments was not shown in any of the cases, and the sulfur in the decomposed odor components was not oxidized to sulfuric acid, and the decomposition It is thought that it was released into the atmosphere from the solution as a volatile substance generated during the route.

In particular, since methyl mercaptan is observed to be emitted as methyl mercaptan, this indicates that aerobic treatment has the potential risk of generating secondary odor pollution as mentioned above. This shows that.

On the other hand, in anaerobic biological reactions, the maximum decomposition rate of odor components is about 13 times that of methyl sulfide, about 10 times that of methyl disulfide, and about 1.5 times that of ethyl mercaptan compared to aerobic reactions. We obtained the new knowledge that anaerobic biological reaction shows higher ability than aerobic biological reaction in terms of total odor component decomposition activity per unit amount of bacterial cells.

Furthermore, in the anaerobic reactor, there is no air diffusion such as aeration, so there is no release of odor components into the atmosphere.

Therefore, in this case, it is possible to adopt a method of removing the odor components from the solution by separating and accumulating them as methyl mercaptan gas and hydrogen sulfide gas in the generated gas, as shown in this experimental example. The method of the present invention has been developed in which, in principle, the odor-containing drain discharged from the pulp manufacturing process is deodorized using anaerobic organisms.

The basic research for the completion of the present invention was further continued by the method described below as to whether the anaerobic biodegradation treatment of lucrative odor components in odor-containing drains could be sustained in a continuous bioreactor.

The odor component synthesis waste liquid used was water mixed with methyl disulfide 20011.
I9/l, methyl sulfide 200"i'/l, ethyl mercaptan 200mg/l added, yeast extract 12.5M/l, methanol 600wIfV1
It is prepared by adding trace amounts of inorganic nutritional salts.
This synthetic effluent was fed to an anaerobic chemostat reactor with a liquid volume of 21 at a rate of 0.51/day.

As a result, the biological residence time was set at 4.0 days, but
Initially, this reactor was inoculated with an anaerobic mixed culture bacteria that was cultivated with glucose and yeast extract and was actively generating methane gas, as in the previous batch experiment, and then the air in the headspace was purged with nitrogen gas. It was sealed and continuous operation started.

The pH of the reaction solution was adjusted to 7.0, and the reaction solution temperature was maintained at 35° C. throughout the experiment.

Among the experimental data obtained in this experiment, the concentration of odor components in the reactor effluent water is shown in FIG.

As shown in FIG. 5, the processability was stable over a 90-day continuous experimental period, and under steady-state conditions approximately 95% of the input odor components could be removed from the synthetic effluent.

Therefore, it was found that deodorization treatment using anaerobic biological reactions can be continued even in a continuous reactor, and it was confirmed that this method can be applied to the continuous removal of odor components without replanting. .

Based on the results obtained in the above basic research, we have developed a method for using anaerobic biodegradation to deodorize various drains containing odor components discharged from pulp manufacturing plants, and we have developed a method for applying anaerobic biodegradation and optimal operating conditions. As a result of conducting an investigation based on the method shown below, we found that there are both cases in which the ability to decompose odor components through anaerobic biological reactions can be demonstrated sustainably, and cases in which it is not possible. Obtained.

That is, a trace amount of inorganic nutrients were added to the vacuum evaporator drain (steam train from the surface condenser) discharged from a kraft pulp mill as test wastewater, and biological Solids were continuously added under a residence time of 4.0 days, and the pH of the reaction solution was adjusted to 6.5. When the odor component was decomposed while maintaining the temperature at 55°C, the results shown in Figure 6 were obtained.

In addition, the composition of the above input drain is L methyl disulfide 550
■/lc or less, all units are m9/l), methyl sulfide 2
15, methyl mercaptan 73, and hydrogen sulfide 2.7.

The results shown in FIG. 6 show that when the wastewater to be deodorized is a vacuum evaporator drain, continuous deodorization treatment is possible without removing generated sulfides from the reactor.

On the other hand, when the same experiment was conducted using a turpentine drain, which is an odor drain from the process of recovering terpenes from condensed steam, as the sample wastewater, the results shown in FIG. 7a were obtained.

In addition, when biodegrading the odor components in the anaerobic biological reactor, the results were shown in Figure 7b when continuous treatment was performed while removing hydrogen sulfide gas generated from the generated gas in the head space of the reactor. .

In addition, in FIG. 7a and b, the composition of the drain is 890 μm/lc or less of methyl disulfide, and all units are 11I9.
/l), methyl sulfide 5101 methyl mercaptan 137
, hydrogen sulfide 4.2.

As a result of these two factors (in cases where the concentration of odor components in the wastewater to be treated is high and the total amount of sulfur contained is high, the amount of dissolved hydrogen sulfide produced as a result of anaerobic biological reactions exceeds the allowable amount). This indicates that it has an inhibitory effect on biological reactions in the decomposition of odor components.

This inhibitory effect of dissolved sulfide becomes noticeable when dissolved hydrogen sulfide in the reaction solution exceeds 30 μ/l, and therefore, in the deodorizing treatment of wastewater containing high concentrations of odor components, the above-mentioned inhibitory effect is In order to prevent this, it is effective to provide some kind of desulfurization equipment to reduce the dissolved sulfide concentration to 30 μ/l or less.

In the experimental example shown in Figure 7, hydrogen sulfide was removed with a caustic soda solution during the circulation of the headspace gas, and the concentration of sulfide dissolved in the biological reaction solution was reduced to 30 μm.
/l or less.

As mentioned above, the method of using caustic soda as a desulfurizing agent is
When deodorizing the odor-containing drain from the pulp manufacturing process, there is an advantage that sodium sulfide obtained as a by-product after the desulfurization process can be effectively used as a cooking aid in the pulp manufacturing process.

The experimental results described above are summarized as follows.

(1) The odor component can be decomposed by anaerobic bacteria under anaerobic conditions, and can be accumulated in the generated gas mainly as methyl mercaptan, which can be removed from the solution.

In addition, such anaerobic biological reactions are more active than conventional aerobic biological reactions, and can constitute a more efficient biological deodorization treatment technology, reducing the odor emitted during the pulp manufacturing process. It can be applied to deodorizing treatment of drains containing it.

(2) When treating odor-containing drains that contain high concentrations of odor components, if the hydrogen sulfide produced by the anaerobic biological deodorization reaction exceeds the permissible limit, remove the hydrogen sulfide produced by the reaction. Therefore, it is necessary to suppress the concentration of dissolved sulfide in the reaction solution to an inhibitory concentration of 30 μ/l or less.

Next, for the purpose of understanding the optimal conditions for deodorizing odorous drains using the method of the present invention, vacuum evaporator drains and turpentine drains were examined.

The decomposition characteristics of odor components under various anaerobic biological reaction conditions were investigated by batch experiments using mixed wastewater from the accumulator drain, and the results shown in Figures 8a, b, and 0 were obtained.

The experimental conditions were: initial bacterial cell concentration was 1500 Wi/l, initial odor component concentration was methyl disulfide 525 m9/l (hereinafter referred to as the same unit), methyl sulfide 174, and ethyl mercaptan 23.
, methyl mercaptan 135, hydrogen sulfide 4.5 a, b
, c, the temperature of the reaction solution in b and c was controlled at 55°C (constant), and the pH of the reaction solution in C was buffer-controlled at 6.5.

The unit of "maximum specific methyl mercaptan gas generation rate" shown in the graph (■) is mm01)-methyl mercaptan gas/g bacterial cells/day.

Figure 8a (in the figure, the inoculum used in ranges I, II, and III were cultured at 15°C, 230°C, and 260°C, respectively.

In addition, graph ■ represents the concentration of dissolved methyl mercaptan in the reaction solution (IIIg#).

) is related to temperature characteristics, but from this result, 5
25℃~40℃ than the so-called low temperature digestion condition of ℃〜20℃
The production activity of methyl mercaptan gas per unit seedling is high under meso-temperature digestion conditions of °C, and the conversion activity to methyl mercaptan is higher under high-temperature digestion conditions of 45 to 70 °C than under meso-temperature digestion conditions. It is known that because the residual amount of methyl mercaptan is smaller in high-temperature digestion, more methyl mercaptan is accumulated in the generated gas, and the solution is efficiently deodorized.

Therefore, in the deodorizing treatment of odor-containing drain discharged in the pulp manufacturing process, it is possible to perform the deodorization treatment under medium temperature digestion conditions, but preferably under the temperature conditions of high temperature digestion of 45 ° C to 65 ° C. An efficient method is to decompose the components and recover them as methyl mercaptan gas.

On the other hand, the results of investigating the pH conditions of the reaction solution are shown in Figure 8, and the decomposition of the money-making odor components was achieved even with anaerobic bacteria at a low pH of 4.0, but preferably at a pH of 5.0 to 6. Degradation while controlling the pH to 9 is necessary in order to exhibit highly active biodegradation ability.

In other words, it is known that the concentration of dissolved methyl mercaptan in the reaction solution increases rapidly when the pH exceeds 6.9. It turns out that the operation is undesirable.

The results of investigating the oxidation-reduction potential (ORP) conditions in the reaction solution are shown in Figure 8C, and it can be seen that methyl mercaptanization of profitable odor components by anaerobic bacteria occurs in the ORP region under a wide range of anaerobic conditions. It is known that this occurs in

However, it is effective to maintain an ORP value of -300 to -800 mV, which is suitable for methane fermentation in normal anaerobic digestion, in order to proceed with the decomposition of odor components using a mixed anaerobic bacteria ecosystem. I understand that.

A problem with the above deodorizing method is that odor components remain in the treatment solution due to gas-liquid equilibrium or dissociation and dissolution.

If the dissolved concentration of methyl sulfide, methyl mercaptan, etc. exceeds the level that would cause problems as a source of odor,
This can be prevented by cold stripping in a closed system.

It is sufficient to use air as the stripping gas, and the stripping device is also conventional technology.
Any form of odor dissipation device such as an IJ topping tower or the like may be used.

Figures 9a and 9b show the results of examining various conditions for air stripping.

However, a is when the reaction liquid pH is set to 6.5, and b is when the reaction liquid temperature is set to 50°C, both of which are based on the reactor outflow water volume IA in the experiment shown in Figure 6. On the other hand, it shows the concentration of the odor component after 5 minutes of aeration with air at a flow rate of 1/min.

As is known from the results shown in Figure 9a, the higher the liquid temperature during air stripping, the more effective it is, but it is possible to dissipate a considerable amount even at room temperature; Even with heating, no further effect was obtained.

Therefore, even in the case of air stripping while heating, it is economical to limit the heating temperature to 70°C.

Figure 9 shows the influence of the liquid pH value on the air stripping effect. The lower the liquid pH, the greater the methyl mercaptan and hydrogen sulfide dispersion effect. It is considered desirable to perform stripping while adjusting.

The air after IJ wrapping can be disposed of by using it as burner air for boiler combustion, but it can also be used as combustion air for gas engines and other engines, and the air after IJ wrapping can be disposed of by using it as burner air for boiler combustion. This is possible if sufficient measures are taken to prevent corrosion of equipment due to NOx contained therein.

As is clear from the above-mentioned experimental results, the present invention is a method for deodorizing a steam drain containing odor components discharged from a pulp manufacturing process, either alone or substantially alone. The pH of the charged reaction solution in the fermenter is set within the range of 5.0 to 6.9 and subjected to anaerobic digestion treatment to biodegrade and vaporize the odor components mainly into methyl mercaptan and hydrogen sulfide. It is characterized by:

Next, an example of an embodiment of the present invention will be described in detail based on FIG. 10.

Although the process shown in this figure belongs to the anaerobic contact method in terms of form, it is also possible to use other types of processes as described later.

Odor-containing drain 1 discharged during the pulp manufacturing process is input into an anaerobic biological reaction tank 4 as inflow water.

In the contact method such as this embodiment, the residence time in the reaction tank 4 is usually about 0.5 days to 7.0 days, and this time depends on the type and concentration of organic matter contained in the inflow water. It is desirable that the value be similar to that selected in normal methane fermentation depending on the conditions.

During this retention period, the odor components in the drain are mainly converted into methyl mercaptan by the anaerobic bacteria group as described above, and transferred to the generated gas 14 where it is deodorized.

The mixed liquid 2 flowing out from the reaction tank 4 is degassed by passing through a vacuum chamber 5 whose pressure is reduced by a vacuum pump 10, and then guided to a precipitation separation tank 6, but the degree of pressure reduction in the vacuum chamber 5 is different from that of the conventional one. It is appropriate to set it to the same level as the contact method used for methane fermentation treatment of organic wastewater, etc.

Further, in some cases, it is possible to omit the degassing operation, but this selection must be made after confirming that the solid-liquid separability in the precipitation separation tank 6 will not be extremely deteriorated.

In the settling separation tank 6, settled sludge (settled biological sludge) 1
2 and a supernatant liquid 3, and this supernatant liquid 3 is passed to the next stage of treatment as deodorized water or directly discharged.

The residence time in the sedimentation separation tank 6 must be kept to the minimum necessary to obtain sufficient sedimentation of biological sludge. It is also effective to install a sludge scraper.

A part of the settled sludge 12 is transferred to the reaction tank 4 by the return pump 11.
The remaining sludge is sent back to
This quantitative ratio is determined based on the basic condition that the biological sludge in the reaction tank 4 is maintained at a concentration that is sufficiently stable for the deodorization reaction.
The concentration is controlled to be constant between 01119/l and 20000/l.

An in-tank stirring device 8 is provided in the reaction tank 4, and in this embodiment, it is desirable to carry out constant stirring.

However, when the odor-containing drain 1 is periodically and intermittently added, the state of gas generation after the odor-containing drain 10 is introduced is monitored, and when gas generation has almost stopped, the stirring device 8 is stopped and the reaction tank It is also possible to adopt the conventional so-called semi-batch contact method, in which the biological sludge is sedimented and separated in Drain 4, and only the supernatant liquid is extracted as deodorized water, and the odor-containing drain 1 is introduced again for recycling. be.

In this case, the installation of the decompression chamber 5 and the precipitation separation tank 6 for degassing can be omitted, and the residence time in the reaction tank 4 can be further shortened.

In either case, the stirring device 8 does not need to be a mechanical stirring device as shown in the figure, and can be selected from various types such as gas stirring method and liquid circulation method conventionally used in anaerobic digestion tanks, such as tank volume, shape, etc. The most appropriate method can be selected depending on the situation.

Providing a desulfurization device to remove hydrogen sulfide from the generated gas 14 from the reaction tank 4 is advantageous because, as described above, the concentration of odor components in the odor-containing drain 1 is high, and the hydrogen sulfide in the generated gas 14 increases. This is important when the concentration of dissolved hydrogen sulfide exceeds the permissible value for anaerobic biological deodorization reactions.

Using caustic soda as a desulfurization agent is the most advantageous method because it can also fix methyl mercaptan in the digestion gas, and as mentioned above, sodium sulfide, which is a product after desulfurization, can be used in the pulp manufacturing process. Any desulfurizing agent conventionally used for anaerobic digestion gas may be used.

The gas circulation path for desulfurization is not necessarily limited to the method shown in the figure, but can be created by, for example, inserting the tip of the air pipe from the circulation pump 9 into an appropriate position in the reaction liquid.
It becomes possible to further reduce the concentration of hydrogen sulfide dissolved in the liquid than by gas circulation only in the head space.

However, in this case, the amount of condensed water in the gas circulation piping inside the desulfurization device 7 and outside the reaction tank 4 increases, so it is necessary to suppress the amount of condensed water by heating the desulfurization device 7 and heating the piping. come out.

Further, in such desulfurization, the gas circulation for desulfurization can also be used for stirring the gas in the reaction tank 4.

The generated gas 14 discharged outside the system from the reaction tank 4 and the precipitation separation tank 6 is stored in a gas tank (not shown) and then used as fuel for a boiler or other fuel, or the sulfur component is mainly converted into methyl sulfide and methyl mercaptan. Because it contains large amounts in the form of

However, the highly concentrated methyl mercaptan gas generated by the deodorizing method of the present invention is itself an expensive substance, and can be separated separately and effectively used as some kind of raw material.

As this method, the above-mentioned method of fixing in a caustic soda solution can be adopted.

In addition, when the generated gas is combusted, it contains 10 times more sulfur dioxide than heavy oil or other combustion exhaust gas, so this exhaust gas is heated to 100%, which is the boiling point of sulfur dioxide under normal pressure. It is possible to easily and efficiently produce a large amount of liquefied sulfur dioxide gas by cooling it below ℃ or pressurizing it to about 4 to 10 atm at room temperature (15 to 258 C). Sulfur dioxide gas has the advantage of being usable as a cooking additive in the sulfite pulp manufacturing process.

In the method of the present invention, in addition to the above-mentioned embodiments, depending on the water quality of the odor-containing drain to be treated, the form of the anaerobic biological deodorizing reactor may be one belonging to the upward flow anaerobic P-bed method or a fluidized bed anaerobic reaction. Most of the devices that have been invented for the purpose of improving the efficiency of methane fermentation technology can be applied, such as those that belong to the methane fermentation method and those that belong to the upflow anaerobic sludge blanket method.

As described above, the present invention provides anaerobic digestion treatment by maintaining the pH at 5.0 to 6.9 when substantially independently deodorizing the steam drain discharged from the pulp manufacturing process and containing odor components. By vaporizing and releasing the above-mentioned odor components mainly as methyl mercaptan and hydrogen sulfide, deodorization can be performed significantly faster and more efficiently than conventional methods using aerobic organisms, and it also There is no need to worry about secondary odor pollution, and since the heat retained in the steam drain can be used effectively for anaerobic digestion, deodorization can be carried out in an extremely energy-saving manner.Furthermore, the released sulfur-containing gas can be used as raw material gas. It can be used for various purposes and has many benefits.

[Brief explanation of the drawing]

FIGS. 1 to 9 are graphs showing the results of basic experiments conducted to complete the present invention, and FIG. 10 is a system explanatory diagram showing one embodiment of the present invention. 1... Odor-containing drain, 2... Effluent mixed liquid, 3... Supernatant liquid, 4... Reaction tank, 5... Decompression chamber, 6... Sedimentation separation tank,
7... Desulfurization device, 8... Stirring device, 9
... Circulation pump, 10 ... Reduction pump, 11 ... Return pump, 12 ... Precipitated sludge, 13 ... Surplus sludge, 14 ...Generated gas.

Claims (1)

[Claims] 1. When substantially independently deodorizing steam drain discharged from the pulp manufacturing process and containing odor components, pH
A method for deodorizing pulp drains, which comprises performing an anaerobic digestion treatment while maintaining the odor component at 5.0 to 6.9, and vaporizing and releasing the odor components mainly as methyl mercaptan and hydrogen sulfide. 2. The deodorizing method according to claim 1, wherein the anaerobic digestion treatment is carried out while maintaining the dissolved hydrogen sulfide concentration of the fermenter internal liquid at a predetermined value or less. 3 In the anaerobic digestion treatment, the hydrogen sulfide concentration was reduced to 30■
3. The deodorizing method according to claim 2, wherein the deodorizing method is performed while maintaining the deodorizing concentration at or below /l. 4 In the anaerobic digestion treatment, the temperature of the liquid in the fermenter was set to 45%.
Claim 1: The temperature is maintained within the range of ℃ to 70℃.
2. The deodorizing method according to item 2, item 3, or item 3. 5. The deodorizing method according to claim 1, 2, 3, or 4, wherein the anaerobic digestion treatment is carried out by maintaining the redox potential of the fermenter internal liquid at -300 mV to -800 mV. . 6. Deodorization according to claim 1, 2, 3, 4, or 5, in which residual odor components in the treated liquid after the anaerobic digestion treatment are removed by IJ popping. Law.