JP3656895B2 - Biological treatment method and apparatus for exhaust gas - Google Patents

Description

【００２２】
循環水槽に汚泥濃度約１２０００ｍｇ／Ｌの硝化槽汚泥１０Ｌを投入後、循環水を連続的に散水しながら、排ガスを連続的に通気した。通気開始時の充填層の圧力損失は、上流側充填塔５０Ｐａ以下、下流側充填塔５０Ｐａ以下であった。通気開始７目目から、上流側充填塔の硫化水素除去率は９０％以上となった。以後安定した除去率を示したものの、上流側充填塔のみ、充填層の圧力損失が徐々に上昇し、実験開始から１２０日目に、上流側充填塔の圧力損失が５００Ｐａとなった。この時点で、排ガスの流れ方向を逆転した。逆転直後の硫化水素除去率は、上流側充填塔３％、下流側充填塔９０％であった。ガスの流れ方向逆転から６日後、上流側充填塔の硫化水素除去率は９０％以上となり、充填層の圧力損失は、上流側充填塔５０Ｐａ以下、下流側充填塔４５０Ｐａであった。
【００２３】
ここで、下流側充填塔の循環水槽に、初期のｐＨが１１となるように２５％水酸化ナトリウム水溶液を導入し、次いで、初期の有効塩素濃度が０．５％となるように、有効塩素濃度１２％の次亜塩素酸ナトリウム水溶液を導入して、充填層に散水した。この薬液洗浄を１２時間継続した結果、下流側充填層の圧力損失が５０Ｐａまで低下した。引き続き薬液を充填層に散水した結果、２日間経過時の循環水質はｐＨ６．７、有効塩素濃度１ｍｇ／Ｌ以下、ＳＳ濃度３０ｍｇ／Ｌとなった。また、洗浄時及び洗浄直後の上流側＋下流側充填塔の硫化水素除去率は９０％以上であった。以後、充填層の圧力損失の上昇時に同様の工程を繰り返した。
【００２４】
比較例１
比較例に用いる実験装置を図２に示す。図２は、従来法に用いる装置の概略構成図である。
充填塔３、４は、微生物を担持させるための充填材を充填した充填層５、６と、充填層５、６に散水するための散水部１１、１２と、散水するための循環ポンプ９、１０と、循環水を貯留するための循環水槽７、８を備える。
循環水槽７、８に微生物を含む活性汚泥等の種汚泥を添加し、循環水ポンプ９、１０で散水部１１、１２から充填層５、６に対して循環散水する。同時に排ガス１を脱臭塔３から脱臭塔４の順に直列に導入し、被処理物質を除去するための運転を行う。
【００２５】
図２に示す構造の実験装置を用いて実験した。
実験条件は次のとおりである。
排ガスの種類 ：し尿処理場から発生する高濃度臭気
排ガス中の硫化水素濃度 ：１００〜２００ｐｐｍ
排ガス温度 ：１５〜２５℃
処理風量 ：４．８ｍ³／ｍｉｎ
空塔速度 ：７２０ｈ^-1
空塔線速度 ：０．４ｍ／ｓ
散水量（単位処理ガス量あたりの散水量）：３リットル／ｍ³
循環水のｐＨ ：１〜２
充填材の種類 ：直径２ｃｍのポリプロピレン製充填材
充填層高さ ：１ｍ
【００２６】
循環水槽に汚泥濃度約１２０００ｍｇ／Ｌの硝化槽汚泥１０Ｌを投入後、循環水を連続的に散水しながら、排ガスを連続的に通気した。通気開始時の充填層の圧力損失は、上流側充填塔５０Ｐａ以下、下流側充填塔５０Ｐａ以下であった。通気開始７目目から、上流側充填塔の硫化水素除去率は９０％以上となった。以後安定した除去率を示したものの、上流側充填塔のみ充填層の圧力損失が徐々に上昇し、実験開始から１２０日目に５００Ｐａ、２００目目に１０００Ｐａとなった。この時の処理風量は４ｍ³／ｍｉｎ（設定条件の８３％）であり、圧力損失の上昇にともなう処理風量の低下が見られた。
【００２７】
比較例２
図２に示す構造の実験装置を用いて、ガス通気方向の逆転を行わずに、充填層洗浄を実施した。
実験条件は次のとおりである。

【００２８】
循環水槽に汚泥濃度約１２０００ｍｇ／Ｌの硝化槽汚泥１０Ｌを投入後、循環水を連続的に散水しながら、排ガスを連続的に通気した。通気開始時の充填層の圧力損失は、上流側充填塔５０Ｐａ以下、下流側充填塔５０Ｐａ以下であった。通気開始７目目から、上流側充填塔の硫化水素除去率は９０％以上となった。以後安定した除去率を示したものの、上流側充填塔のみ、充填層の圧力損失が徐々に上昇し、実験開始から１２０日目に上流側充填塔５００Ｐａとなった。この時点で上流側充填塔の循環水槽に、初期のｐＨが１１となるように、２５％水酸化ナトリウム水溶液を導入し、次いで初期の有効塩素濃度が０．５％となるように、有効塩素濃度１２％の次亜塩素酸ナトリウム水溶液を導入して、充填層に散水した。この薬液洗浄を１２時間継続した結果、上流側充填層の圧力損失５０Ｐａまで低下した。引き続き薬液を充填層に散水した結果、４日間経過時の循環水質はｐＨ６．７、有効塩素濃度１ｍｇ／Ｌ以下、ＳＳ濃度３０ｍｇ／Ｌとなった。また、洗浄時及び洗浄直後の上流側＋下流側の硫化水素除去率は９０％以上であったものの、洗浄から４日間経過時の硫化水素除去率は２％であった。以後処理運転を継続し、硫化水素除去性能が９０％以上に回復するまでに、洗浄から９日間を要した。
【００２９】
【発明の効果】
本発明の排ガスの生物処理方法及び装置は、直列に接続された複数の充填塔において、少なくとも上流側の２塔を排ガスダクトの切り替えにより、ガスの通気方向を定期的に逆転させるとともに、該逆転操作により、ガスの通気方向に対して、上流側となった充填塔における対象物質の除去性能が向上したのちに、下流側充填塔の充填層内に残留する余剰汚泥の除去を、充填層と薬品を含む水とを接触させて行うことにより、処理に必要な微生物を排出することなく、充填層内の余剰汚泥のみを効率良く排出できるため、半永久的に、充填層の圧力損失を低く維持し、安定した処理性能を得ることができる。
したがって、充填塔式の生物処理装置を余剰汚泥生成量の多い、高負荷処理や揮発性有機化合物の処理まで適用拡大することが可能である。
【図面の簡単な説明】
【図１】本発明の生物処理装置の一例を示す概略構成図。
【図２】比較例に用いた従来の一般的な生物処理装置の概略構成図。
【符号の説明】
１：排ガス、２：処理ガス、３、４：充填塔、５、６：充填層、７、８：循環水槽、９、１０：循環ポンプ、１１、１２：散水部、１３、１４、１５、１６：ダンパ、１７、１８：洗浄用薬液注入管、１９：連通ダクト、２０、２１：排泥管、２２、２３：マノメータ、２４、２５：ｐＨ計、２６、２７：悪臭物質及び／又は揮発性有機化合物濃度計[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a biological treatment method of exhaust gas containing malodorous substances and / or volatile organic compounds, in particular, malodorous substances and / or volatile organic compounds generated from sewage treatment plants, human waste treatment plants, various factories and the like. The present invention relates to a method and apparatus for biological treatment of exhaust gas containing it.
[0002]
[Prior art]
A method of biologically deodorizing a odor gas by aeration through a packed bed to which microorganisms are attached is known as a packed tower type biological deodorization method. Since the deodorization principle of this method is decomposition of malodorous substances by microorganisms, microorganisms grow and surplus sludge is generated as a result of the deodorization treatment. In a water treatment to which a biological treatment method is widely applied, a process for discharging such excess sludge is usually provided. However, the conventional packed tower type biological deodorization device is mainly operated under a condition where the load of malodorous substances is low, and part of the sludge in the packed bed is peeled off and discharged by watering. In general, there is no surplus sludge discharge function / discharge process.
Originally, a packed tower type biological treatment apparatus can retain a large amount of microorganisms in the packed bed, and therefore can perform a high-load treatment corresponding to these microorganism activities. Further, not only hydrogen sulfide but also various volatile organic compounds can be removed. However, under such conditions, the amount of excess sludge generated is extremely large, and when high concentration hydrogen sulfide is targeted, precipitation of elemental sulfur, which is an intermediate of the oxidation reaction of hydrogen sulfide, is significant. Therefore, these sludges accumulate in the packed bed, and as a result, when a long-term continuous treatment is performed, the packed bed is clogged, resulting in a problem that the operation becomes impossible.
[0003]
When the packed bed is clogged with a conventional apparatus, it is necessary to take out the filler from the apparatus and replace it with a new one, or to take out and clean it. However, this operation requires a lot of time and labor. Moreover, since the microorganisms necessary for the treatment are removed together with the excess sludge, the treatment performance deteriorates after washing.
As a method for discharging the excess sludge without taking out the packed bed, there is a method in which the packed bed is submerged and air is back-washed. This method has the following problems although the sludge peeling performance from the filler is extremely high.
(1) In order to flood the packed bed, it is necessary to increase the strength of the packed tower.
(2) A large amount of water is required for flooding.
(3) Gas treatment must be temporarily stopped during cleaning.
(4) Processing performance decreases after washing.
[0004]
As a method of replacing the air backwash method with such problems, a method of peeling and discharging excess sludge by adjusting the watering method has been proposed. For example, the amount of water spray is adjusted to intentionally cause flooding in the packed bed, and excess sludge is peeled off from the filler. Further, water is sprayed not only on the packed bed but also on the lower layer to remove elemental sulfur accumulated at the bottom of the packed bed. In addition, a method has been proposed in which a large amount of water is sprinkled temporarily to remove sludge from the filler.
Although these methods of adjusting the amount of water spray can solve or alleviate the problems of the above-described backwashing method, it is difficult to obtain excess sludge discharge performance equal to or higher than that of the backwashing method.
[0005]
As a method for obtaining surplus sludge discharge performance equivalent to or higher than that of the backwashing method, there is a method of bringing a filler and water containing chemicals into contact with each other. However, chemicals with high performance for removing and decomposing sludge adhering to the filler are generally highly reactive chemicals, which adversely affect the activity of microorganisms. For example, by using hydrogen peroxide having a relatively low persistence among chemicals, it is possible to suppress a decrease in performance after cleaning.
In any of the above-described cleaning methods, excess sludge is forcibly separated and discharged together with highly active microorganisms, so that it is difficult to suppress a decrease in processing performance immediately after cleaning.
[0006]
As a method of efficiently removing elemental sulfur deposited on the filler without forcibly discharging sludge, a plurality of treatment zones are provided, and one of the treatment zones is suspended for a certain period, thereby stopping the suspension period. Microbial decomposition of sulfur. In this method, when the main component of the deposit is elemental sulfur, the removal effect is high, but when the main component of the deposit is microbial sludge, the self-digestion rate of sludge is higher than the microbial decomposition rate of sulfur. Is slow and difficult to remove.
As described above, the exhaust gas packed tower biological treatment apparatus has no practical means capable of discharging excess sludge accumulated in the packed bed without degrading the treatment performance. Therefore, even though high-efficiency deodorization treatment and volatile organic compound treatment are inherently possible, high-efficiency removal of the target substance is possible, but clogging of the packed bed resulting from long-term operation is an obstacle. Therefore, application to such conditions was considered difficult.
[0007]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems of the prior art, efficiently discharges / removes excess sludge, and prevents a temporary decrease in processing performance resulting from the discharge / removal operation of excess sludge, making it semi-permanent. It is an object of the present invention to provide a biological treatment method and apparatus for exhaust gas that can maintain stable treatment performance.
[0008]
[Means for Solving the Problems]
  In order to solve the above-described problems, in the present invention, biological oxidation treatment is performed under sprinkling through exhaust gas containing malodorous substances and / or volatile organic compounds through packed beds of packed towers arranged in series in stages. In the biological treatment method of exhaust gas, when the pressure loss in the uppermost packed bed does not exceed 1000 Pa, at least the upstream two-stage packed tower packed bed is vented by reversing the order and direction of the packed bed. In the packed towerImproved processing performanceThen, a chemical treatment method for exhaust gas is characterized in that a chemical solution is sprinkled into the packed bed of the packed tower that is located downstream in the reverse aeration to remove surplus microorganisms in the packed bed.
  Further, in the present invention, a packed tower arranged in multiple stages in series, a passage for passing an exhaust gas containing malodorous substances and / or volatile organic compounds through the packed tower, and watering means for sprinkling water in the packed bed of the packed tower. In the biological treatment apparatus for exhaust gas, the at least two upstream stages of the packed tower have means for enabling the flow order and direction of the exhaust gas to be reversed, and these packed towers have pressure loss detecting means. And a biological treatment apparatus for exhaust gas, characterized in that it has processing capacity detection means, circulating water quality measurement means, and chemical supply means.
[0009]
  In the present invention, the pressure in the uppermost packed columnLoss is, Not exceeding 1000 Pa, preferably around 500 Pa,Improved processing performanceIs the removal rate of malodorous substances and / or volatile organic compounds in the exhaust gasThe removal rate determined byIs 80% or more, preferably 90% or more, and, Improve processing performanceIs the pressure loss in the manometer installed in the uppermost packed tower.AccordingOr,Measured value with pH meter or conductivity meter installed in circulating water tank of uppermost packed towerJudged bycan do.
  In the biological treatment apparatus for exhaust gas according to the present invention, the pressure loss detecting means is provided in at least two upstream stages of the packed tower.change ofDetectWhen the detected change does not exceed 1000 PaThe means for enabling the reversal of the aeration sequence and the aeration direction is activated to reverse the aeration, and the processing capacity detection means or pressurePowerlossMissing detection meansOr water quality measuring meansImprovement in processing performance of packed tower, which has become the most upstreamIt is also possible to have control means for controlling the chemical supply means of the packed tower that has become the downstream side by the reverse aeration to operate so that the chemical is introduced into the sprinkling water.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the packed tower type exhaust gas biological treatment method of the present invention, a plurality of packed towers connected in series are provided, and at least two upstream towers are periodically reversed by switching the exhaust gas duct. At the same time, after the processing performance of the packed tower on the upstream side is improved by the reverse operation, the excess sludge in the packed bed of the downstream packed tower is removed by bringing the packed bed and water containing chemicals into contact with each other. It was decided.
In the packed tower used in the present invention, the distribution of microorganisms in the packed bed corresponds to the load of malodorous substances and volatile organic compounds, and the amount of microorganisms is large near the exhaust gas inflow part, and the microorganisms move toward the gas outlet side. The amount is reduced. That is, the portion close to the inflow portion of the gas to be treated is a place having a very high oxidative decomposition activity where most of the target substance is removed by oxidation. Therefore, the growth of microorganisms is most remarkable, and therefore, it is also a place where clogging of the packed bed is likely to occur due to accumulation of excess sludge.
[0011]
In addition, when processing high-concentration hydrogen sulfide-containing odors, the portion close to the inflow portion of the gas to be treated in the packed bed contains elemental sulfur, which is an intermediate in the oxidation reaction of hydrogen sulfide, in addition to the growth of microorganisms. Since it is easy to precipitate, the increase in deposits is extremely remarkable.
As described above, in the packed tower type biological treatment apparatus, the portion responsible for oxidative decomposition removal of the target substance and the portion where the increase in the amount of filler deposit sludge is substantially coincided with each other. The removal leads to a decrease in processing performance.
According to the method of the present invention, the gas aeration direction is periodically reversed between at least two upstream columns. Following this environmental change, the part with high microbial activity gradually shifts, and finally the microbial distribution with respect to the gas flow direction is in reverse phase to the distribution before the gas flow direction is reversed. . Thus, the microorganism distribution can be shifted by the reversal operation of the gas aeration direction. Even in this transition period, the exhaust gas always passes through a portion having a high oxidative decomposition activity, so that the processing performance is not significantly reduced by the reverse operation.
[0012]
A portion close to the inflow portion of the exhaust gas before the reverse operation becomes downstream with respect to the gas flow by the reverse operation. Therefore, since the load becomes lower, elemental sulfur generated by oxidation of hydrogen sulfide, for example, is oxidatively decomposed by microorganisms. Some of the sludge derived from microorganisms is self-digested. However, microorganism-derived sludge remains in the packed bed for a long period of time because of its poor degradability. Therefore, the decomposition and discharge of such hardly decomposable sludge is performed by bringing the filler and water containing chemicals into contact with each other.
As described above, in the present invention, the microbial distribution in the packed bed is intentionally moved by the reversal operation of the exhaust gas aeration direction, and the oxidative decomposition activity of the target substance in the upstream packed tower is improved. In view of the fact that the packed bed no longer contributes to the oxidative decomposition reaction of the target substance, chemical cleaning of the packed bed is performed only for the packed tower on the downstream side. Therefore, since microorganisms with high activity are always present in the packed bed of any packed tower among the plurality of packed towers, there is no significant decrease in processing performance after the excess sludge discharging step. Further, gas treatment can be continuously performed during the excess sludge discharging step. Furthermore, the method of the present invention can be applied to a conventional multi-column system by modifying the duct portion.
[0013]
Switching of the exhaust gas duct for reversing the gas flow direction is performed based on the measured value of a manometer attached for measuring the pressure loss of the packed bed. When the pressure loss of the packed bed rises to 1000 Pa or more, there are many cases where the drift of exhaust gas and the reduction of the air flow rate are often caused. Therefore, it is preferable to operate so that the pressure loss of the upstream packed bed does not exceed 1000 Pa. In the present invention, after the gas flow direction is reversed, until the treatment performance of the upstream packed tower is improved, for example, the removal rate is 80% or more, preferably 90% or more, without discharging the sludge of the downstream packed tower. Since the operation is continued for a certain period, the pressure loss of the downstream packed tower rises also during this period. Therefore, the reversal of the aeration direction is preferably performed with a margin of preferably around 500 Pa before the pressure loss of the packed bed rises to 1000 Pa.
[0014]
  As a result of the reversal of the aeration direction, the cleaning of the packed bed downstream of the aeration direction is based on the indication value of the continuous monitor of the target substance concentration that detects the processing capacity attached to the outlet of the upstream packed tower. It is good to do it. In addition, the change in the removal characteristics of the material to be treated due to the reversal of the gas flow direction appears in the pressure loss in the manometer installed in the uppermost packed tower.ForCan be.
  in this case,Pressure lossThe value of can be 50 Pa or more and 500 Pa or less. The reason for this is that when malodorous substances and / or volatile organic compounds begin to be removed in the uppermost packed tower, microorganisms increase in the packed bed and the pressure loss rises. . On the other hand, it is not preferable to leave it until it reaches 500 Pa or more because the time until the next reverse ventilation is shortened.
  If the change in the removal characteristics of the substance to be treated due to the reversal of the gas flow direction appears as a change in the circulating water quality, the measured value of the circulating water quality, for example, a pH meter or conductivity meter installed in the circulating water tank Based on the above, it is possible to determine the cleaning time of the packed bed, and these can also be used as index values. For example, when removing hydrogen sulfide under low pH conditions, sulfate ions generated as a result of the oxidation reaction lower the pH of the circulating water and increase the conductivity.
[0015]
Therefore, since the change in the hydrogen sulfide removal characteristics between the plurality of columns due to the reversal of the aeration direction appears as a change in the pH or conductivity of the circulating water, the washing time may be determined based on these values.
In this case, the value of the predetermined value B can be 3 or less for pH and 5 mS / cm or more for conductivity.
Circulating water quality is an important indicator, especially when removing hydrogen sulfide (currently the mainstream target substance). When hydrogen sulfide begins to be oxidized and removed in the uppermost packed tower, sulfuric acid, which is an oxidation product, is added to the circulating water. Since it accumulates, the pH decreases and the conductivity increases. Only hydrogen sulfide can be sufficiently removed even under conditions of pH 3 or lower and conductivity 5 mS / cm or higher, and thus steady operation is performed under such low pH conditions.
As a result, the amount of alkaline agent used to neutralize the pH of the circulating water and the supply amount of neutral water in the pH can be saved, and the pH is more stable at low pH, that is, for microorganisms. There is an advantage that the environment is easy to stabilize.
[0016]
As described above, the method of the present invention can effectively use indicator instruments, such as manometers, exhaust gas continuous monitors, pH meters, and conductivity meters, which have been attached to conventional devices for condition confirmation, for operation control. . Moreover, it is also possible to perform the method of this invention by automatic control using these measuring instruments.
Examples of the chemical solution for cleaning the packed bed include water containing chemicals such as sulfuric acid, sodium hydroxide, potassium hydroxide, hydrogen peroxide, sodium hypochlorite, ozone, and the like. When using ozone, ozone gas may be introduced directly. Moreover, in order to raise cleaning efficiency, you may combine a chemical | medical agent or implement multiple washing | cleaning by a different chemical | medical solution. However, if the packed tower is connected further downstream than the packed tower that performs packed bed cleaning, in consideration of the effect on the downstream packed tower, a non-volatile chemical or highly reactive gas should be added. It is better to use drugs that do not occur.
The concentration of the chemical solution may be determined by confirming the sludge stripping / decomposing performance in advance with a beaker test or the like, or may be adjusted while actually cleaning the packed bed. The cleaning efficiency is high when the acid concentration and the aqueous alkali solution are adjusted to pH 10 or higher, sodium hypochlorite is used at an effective chlorine concentration of 300 mg / L or higher, and hydrogen peroxide is used at 300 mg / L or higher. The cleaning time may be determined based on the state of sludge peeling from the packed bed and the decrease in pressure loss of the packed bed.
[0017]
Of the above chemicals, when an alkaline agent and an oxidizing agent are combined, the sludge peeling / decomposing performance often increases. In addition, in the case of these chemicals, when the initial concentration is the above-mentioned concentration, when the water is poured into the circulating water tank and the packed bed is continuously sprinkled, most of the alkali and oxidant in the chemical solution are decomposed due to sludge decomposition, Is consumed. In addition, by spraying this chemical solution while introducing exhaust gas after washing, the residual alkali content in the chemical solution is neutralized by an acidic gas such as carbon dioxide in the gas, and the residual oxidant is contained in the exhaust gas. It is removed by reducing substances contained in. Furthermore, in the biological treatment apparatus for gas treatment, since the inflow amount of insoluble inorganic components is extremely small, the proportion of organic components in the excess sludge is high. Therefore, the sludge solubilization rate by the oxidizing agent is high, and the insoluble components remaining in the washing waste liquid are extremely small. From the above, even if the cleaning waste liquid is discharged to the attached water treatment step, the load applied to the water treatment is low, and if the waste water cannot be discharged, it can be used as circulating water as it is. From the above, the value of using a chemical solution in which an oxidizing agent or an alkaline agent and an oxidizing agent are combined in the method of the present invention is great.
[0018]
In the method of the present invention, the conditions for cleaning the packed bed are close to the conditions of a chemical cleaning and deodorizing method that is currently generally performed. Since the conventional packed tower type biological deodorization apparatus is often designed based on the specifications of the chemical liquid cleaning deodorization apparatus, the resistance of the apparatus to chemicals is sufficient. Can be applied. In addition, it is necessary to use a chemical-resistant filler as the filler, but since many of the fillers currently applied to the packed tower type biological deodorization apparatus are chemical-resistant, the method of the present invention is employed. Furthermore, the type of filler is not greatly limited.
[0019]
Next, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an apparatus used in the method of the present invention.
The packed towers 3 and 4 include packed layers 5 and 6 filled with a filler for supporting microorganisms, sprinkling units 11 and 12 for sprinkling the packed layers 5 and 6, and a circulation pump 9 for sprinkling water. 10, circulating water tanks 7 and 8 for storing the circulating water, and pipes 17 and 18 for introducing a cleaning chemical into the circulating water tank. The packed towers 3 and 4 are provided with manometers 22 and 23 across the packed beds 5 and 6, the circulating water tanks 7 and 8 are provided with pH meters 24 and 25, and the exhaust gas introduction path and the communication path are provided. Densitometers 26 and 27 are installed.
The packed tower 3 and the packed tower 4 are connected by a communication duct 19, and a duct for introducing the exhaust gas 1 and a duct for discharging the processing gas 2 are connected in parallel for each tower. The duct for introducing the exhaust gas 1 is provided with a damper 13 on the packed tower 3 side and the damper 14 on the packed tower 4 side, and the duct for discharging the processing gas 2 is filled with a damper 15 on the packed tower 3 side. Dampers 16 are respectively installed on the tower 4 side.
[0020]
When the gas flows in series from the packed tower 3 to the packed tower 4, the dampers 13 and 16 are opened and the dampers 14 and 15 are closed. When flowing gas in series from the packed tower 4 to the packed tower 3, the dampers 14 and 15 are opened and the dampers 13 and 16 are closed.
At the start of operation, seed sludge such as activated sludge containing microorganisms is added to the circulating water tanks 7 and 8, and the circulating water pumps 9 and 10 circulate water from the sprinkling parts 11 and 12 to the packed beds 5 and 6. At the same time, the exhaust gas 1 is introduced in series from the packed tower 3 to the packed tower 4 in order, and an operation for removing the target substance is performed. After a long period of treatment operation, when the microorganisms in the packed bed 5 grow and the pressure loss in the packed bed 5 increases, the exhaust gas 1 is introduced in series from the packed tower 4 to the packed tower 3 by opening and closing the damper. Then, processing operation is performed. After the treatment performance of the packed tower 4 is improved, a cleaning chemical solution is introduced into the circulating water tank 7 through the chemical solution introduction pipe 17 to remove / decompose and remove excess sludge in the packed bed 5. If necessary, drain the washing waste liquid in the circulating water tank, replace it with new water, and continue the treatment operation. After the treatment operation for a long time, when the microorganisms in the packed bed 6 grow and the pressure loss of the packed bed 6 increases, the above process is repeated.
[0021]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to this Example.
Example 1
Experiments were performed using an experimental apparatus having the structure shown in FIG.
The experimental conditions are as follows.

[0022]
After introducing 10 L of nitrification tank sludge having a sludge concentration of about 12000 mg / L into the circulating water tank, exhaust gas was continuously ventilated while continuously circulating the circulating water. The pressure loss of the packed bed at the start of aeration was 50 Pa or less for the upstream packed tower and 50 Pa or less for the downstream packed tower. From the seventh start of ventilation, the hydrogen sulfide removal rate of the upstream packed column was 90% or more. Thereafter, a stable removal rate was exhibited, but the pressure loss of the packed bed gradually increased only in the upstream packed column, and the pressure loss of the upstream packed column became 500 Pa on the 120th day from the start of the experiment. At this point, the flow direction of the exhaust gas was reversed. The removal rate of hydrogen sulfide immediately after the reverse rotation was 3% in the upstream packed column and 90% in the downstream packed column. Six days after the reversal of the gas flow direction, the hydrogen sulfide removal rate of the upstream packed column was 90% or more, and the pressure loss of the packed bed was 50 Pa or less for the upstream packed column and 450 Pa for the downstream packed column.
[0023]
Here, a 25% aqueous sodium hydroxide solution was introduced into the circulating water tank of the downstream packed tower so that the initial pH was 11, and then the effective chlorine concentration was adjusted so that the initial effective chlorine concentration was 0.5%. A sodium hypochlorite aqueous solution having a concentration of 12% was introduced and sprinkled into the packed bed. As a result of continuing this chemical | medical solution washing | cleaning for 12 hours, the pressure loss of the downstream packed bed fell to 50 Pa. As a result of continuously spraying the chemical solution into the packed bed, the circulating water quality after 2 days was pH 6.7, effective chlorine concentration 1 mg / L or less, and SS concentration 30 mg / L. Moreover, the hydrogen sulfide removal rate of the upstream side + downstream side packed column immediately after the cleaning was 90% or more. Thereafter, the same process was repeated when the pressure loss of the packed bed increased.
[0024]
Comparative Example 1
An experimental apparatus used in the comparative example is shown in FIG. FIG. 2 is a schematic configuration diagram of an apparatus used in the conventional method.
The packed towers 3 and 4 include packed layers 5 and 6 filled with a filler for supporting microorganisms, sprinkling units 11 and 12 for sprinkling the packed layers 5 and 6, and a circulation pump 9 for sprinkling water. 10 and circulating water tanks 7 and 8 for storing the circulating water.
Seed sludge such as activated sludge containing microorganisms is added to the circulating water tanks 7 and 8, and the circulating water pumps 9 and 10 circulate water from the sprinkling units 11 and 12 to the packed beds 5 and 6. At the same time, the exhaust gas 1 is introduced in series in the order of the deodorization tower 3 to the deodorization tower 4, and an operation for removing the substance to be treated is performed.
[0025]
Experiments were performed using an experimental apparatus having the structure shown in FIG.
The experimental conditions are as follows.
Type of exhaust gas: High concentration odor generated from human waste treatment plant
Hydrogen sulfide concentration in exhaust gas: 100-200 ppm
Exhaust gas temperature: 15-25 ° C
Treatment air volume: 4.8m^Three/ Min
Sky speed: 720h^-1
Empty line speed: 0.4 m / s
Water sprinkling amount (water sprinkling amount per unit processing gas amount): 3 liters / m^Three
Circulating water pH: 1-2
Type of filler: Polypropylene filler with a diameter of 2 cm
Packing layer height: 1m
[0026]
After introducing 10 L of nitrification tank sludge having a sludge concentration of about 12000 mg / L into the circulating water tank, exhaust gas was continuously ventilated while continuously circulating the circulating water. The pressure loss of the packed bed at the start of aeration was 50 Pa or less for the upstream packed tower and 50 Pa or less for the downstream packed tower. From the seventh start of ventilation, the hydrogen sulfide removal rate of the upstream packed column was 90% or more. After that, although a stable removal rate was exhibited, the pressure loss of the packed bed gradually increased only in the upstream packed tower, and became 500 Pa on the 120th day from the start of the experiment and 1000 Pa on the 200th day. The processing air volume at this time is 4m^Three/ Min (83% of the set condition), and a decrease in the processing air volume accompanying an increase in pressure loss was observed.
[0027]
Comparative Example 2
The packed bed cleaning was performed using the experimental apparatus having the structure shown in FIG. 2 without reversing the gas aeration direction.
The experimental conditions are as follows.

[0028]
After 10 L of nitrification tank sludge having a sludge concentration of about 12000 mg / L was charged into the circulating water tank, exhaust gas was continuously ventilated while continuously circulating the circulating water. The pressure loss of the packed bed at the start of aeration was 50 Pa or less for the upstream packed tower and 50 Pa or less for the downstream packed tower. From the seventh start of ventilation, the hydrogen sulfide removal rate of the upstream packed tower was 90% or more. After that, although a stable removal rate was exhibited, the pressure loss of the packed bed gradually increased only in the upstream packed column, and reached the upstream packed column 500 Pa on the 120th day from the start of the experiment. At this point, a 25% sodium hydroxide aqueous solution is introduced into the circulating water tank of the upstream packed tower so that the initial pH is 11, and then the effective chlorine concentration is 0.5% so that the initial effective chlorine concentration is 0.5%. A sodium hypochlorite aqueous solution having a concentration of 12% was introduced and sprinkled on the packed bed. As a result of continuing this chemical cleaning for 12 hours, the pressure loss of the upstream packed bed was reduced to 50 Pa. As a result of continuously spraying the chemical solution into the packed bed, the circulating water quality after 4 days was pH 6.7, effective chlorine concentration 1 mg / L or less, and SS concentration 30 mg / L. Further, the hydrogen sulfide removal rate at the upstream side and the downstream side immediately after washing was 90% or more, but the hydrogen sulfide removal rate after 4 days from the washing was 2%. Thereafter, the treatment operation was continued, and it took 9 days from the cleaning until the hydrogen sulfide removal performance recovered to 90% or more.
[0029]
【The invention's effect】
The exhaust gas biological treatment method and apparatus of the present invention periodically reverses the gas aeration direction by switching exhaust gas ducts in at least two upstream towers in a plurality of packed towers connected in series. After the operation improves the removal performance of the target substance in the packed tower on the upstream side with respect to the gas flow direction, the excess sludge remaining in the packed bed of the downstream packed tower is removed with the packed bed. By contacting with water containing chemicals, only the excess sludge in the packed bed can be discharged efficiently without discharging the microorganisms required for treatment, so the pressure loss in the packed bed is kept low permanently. In addition, stable processing performance can be obtained.
Therefore, it is possible to expand the application of the packed tower type biological treatment apparatus to a high load treatment and a treatment of a volatile organic compound that generate a large amount of excess sludge.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a biological treatment apparatus of the present invention.
FIG. 2 is a schematic configuration diagram of a conventional general biological treatment apparatus used in a comparative example.
[Explanation of symbols]
1: exhaust gas, 2: treatment gas, 3, 4: packed tower, 5, 6: packed bed, 7, 8: circulating water tank, 9, 10: circulating pump, 11, 12: sprinkling unit, 13, 14, 15, 16: Damper, 17, 18: Cleaning chemical injection pipe, 19: Communication duct, 20, 21: Mud pipe, 22, 23: Manometer, 24, 25: pH meter, 26, 27: Malodorous substance and / or volatilization Organic compound concentration meter

Claims (5)

In the biological treatment method of exhaust gas, in which the exhaust gas containing malodorous substances and / or volatile organic compounds is passed through the packed bed of the packed tower arranged in series in the stage and biologically oxidized under watering, the uppermost packed bed After the pressure loss in the air does not exceed 1000 Pa, at least the upstream two-stage packed tower of the packed bed is vented by reversing the aeration sequence and the aeration direction of the packed bed, and the processing performance in the packed tower which is the most upstream is improved A method for biological treatment of exhaust gas, characterized in that a chemical solution is sprinkled into a packed bed of a packed tower on the downstream side in the reverse aeration to remove surplus microorganisms in the packed bed. Improvement of the processing performance, biological treatment method of exhaust gas according to claim 1, wherein the removal rate of malodorous substances and / or volatile organic compounds in the exhaust gas is when it becomes 80% or more. Improvement of the processing performance, you judged by measurements in the most upstream Luke by the pressure loss in the installed manometer in packed column, or most upstream pH meter installed in the circulation water tank packed column or conductivity meter The biological treatment method for exhaust gas according to claim 1.   Biological treatment apparatus for exhaust gas having packed towers arranged in multiple stages in series, a passage through which exhaust gas containing malodorous substances and / or volatile organic compounds is passed, and water sprinkling means for sprinkling the packed bed of the packed tower In addition, at least two stages upstream of the packed tower have means for enabling the flow order and direction of the exhaust gas to be reversed, and these packed towers include pressure loss detecting means and processing capacity detecting means. And a biological treatment apparatus for exhaust gas, comprising: water quality measuring means for circulating water; and chemical supply means. The biological treatment apparatus for exhaust gas according to claim 4, wherein a change in the pressure loss detection means is detected at least in the two upstream stages of the packed tower, and when the detected change does not exceed 1000 Pa, the ventilation sequence and operating means for the reversible ventilation direction reversed aeration, change of the capacity detecting means or pressure loss detecting means or water measuring means detects the improvement of the processing performance of the packed column became the most upstream Then, the biological treatment apparatus for exhaust gas, characterized by comprising control means for controlling the chemical supply means of the packed tower that has become the downstream side by the reverse aeration to operate so that the chemical is introduced into the sprinkling water.

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