JPH06315695A - Pretreatment of activated sludge - Google Patents

Abstract

PURPOSE:To prevent the deterioration of activated sludge, keep the activated sludge highly active and stabilize treatment by using a reaction sludge formed from excess sludge as a microorganism adsorbent. CONSTITUTION:The contaminant in raw water is treated with activated sludge as follows. Namely, 100 parts of raw water and 1-30 parts, preferably 3-15 parts, of return sludge are mixed and agitated, the reaction sludge is floated, concentrated and separated, and a sludge contg. >=0.5%, preferably >=2%, solid and treated water are obtained. The treated water and return sludge are aerated in an activated-sludge aeration tank, solid is separated from liq., and a final effluent and return sludge are obtained. The return sludge is anaerobically and aerobically digested in a concd. sludge digestion tank to biologically decompose the contaminant adsorbed by the reaction sludge, and a digested sludge is obtained. The digested sludge is drawn off as the excess sludge.

Description

Detailed Description of the Invention

[0001]

[Industrial field of application] The present invention relates to a method for treating activated wastewater, which is capable of biodegrading microbial wastewater such as urban sewage, group groundwater, small-scale rural settlement wastewater and food, dyeing, leather, chemical and electrical industries. Therefore, even if the characteristic wastewater flows from each of the activated sludge treatments, it is possible to prevent bulking from occurring in a general-purpose facility by pre-treating it in advance so that unattended automatic operation can be easily achieved. The present invention relates to providing an activated sludge treatment method that not only reduces the installation area of wastewater treatment equipment and reduces the generation of excess sludge, but is also suitable for utilizing excess sludge as an effective resource.

[0002]

2. Description of the Related Art Since activated sludge treatment method is an extremely excellent wastewater treatment method, it is widely used for wastewater treatment, and various treatment methods have been proposed according to the type of raw water.

Conventional activated sludge treatment methods utilize various microorganisms ranging from soil bacteria to large protozoa utilizing the food chain.

In the activated sludge method, as a pretreatment, screens, pressure flotation, and coagulation sedimentation treatment are performed to remove those dispersed in raw water from rough to fine ones, and activate soluble organic components suitable for microbial treatment. After aeration treatment with sludge, the treated water is separated from the activated sludge and discharged, and the concentrated and separated activated sludge is recycled and used as return sludge. Then, excess sludge is extracted by discarding a part of the returned sludge. The sludge discharged to the outside of the system is mixed with the sludge removed by pretreatment and dehydrated as it is, or the dehydrated cake that has been digested in the digestion tank and then dehydrated is landfilled, microbial fertilizer, or incinerated. .

[0005]

As described above, the conventional activated sludge treatment method has a very high degree of perfection, but it still has a problem to be solved. These are described below.

(1) When the inflowing raw water contains a large amount of hardly-decomposable substances (proteins, denatured proteins, cellulose, starch, fats and oils) that are difficult for microorganisms to decompose, activated sludge cannot readily decompose these adsorbed substances. In addition, there is a problem that the filamentous bulking and the occurrence of foaming scum due to actinomycetes and the like cause abnormalities in the treatment due to the generation of filamentous bacteria, which significantly impairs the activated sludge treatment capacity. For this reason, if pressure resistant flotation equipment is installed and these persistent substances are removed, the concentration of organic components in the raw water will drop significantly and the amount of activated sludge to be treated will decrease, while the amount of industrial waste removed will be reduced. And the disposal becomes a problem. In addition, when dewatering floating sludge, in general, cohesiveness is unstable and it is difficult for coagulation and dewatering to reduce the water content, and sludge is prone to spoilage and odors, which may cause work environment problems. . Therefore, as a whole, many problems are concentrated in the treatment of the sludge that has been floated and separated, which causes an increase in wastewater treatment cost and remarkably impairs the advantages of the activated sludge treatment method. In order to avoid these problems, the method of enlarging the aeration tank and aerating for a long time without digesting it has become popular (lagoon method), but this is enormous when the amount of drainage is large or the load is large. Since an aeration tank is required, there are problems such as no site and huge construction costs.

(2) In carrying out microbial treatment, when the pH of the influent raw water is largely deviated from neutral, an acid or alkali is added to neutralize it in order to maintain the neutral pH. However, the amount of chemicals added increases, the salt concentration in the treated water rises, and problems not only occur when recirculating after the third treatment, but the pH of the treated water shows an abnormal value and promotes corrosion of equipment. Or cause problems. For example, when the pH of the raw water is low, it is neutralized with caustic soda, but if the fatty acids in the raw water are aerated sufficiently to aerate the activated sludge, it becomes alkaline and the activated sludge is damaged, or conversely, the raw water becomes alkaline. In the case of, it is common to neutralize with sulfuric acid,
It promotes the growth of sulfate-reducing bacteria and causes the problem of corrosion due to hydrogen sulfide, and the activated sludge is damaged to cause filamentous bulking. Therefore, the addition of these chemicals not only costs the chemicals but also has an adverse effect, which is a problem in the pH adjusting method of the raw water.

(3) In the activated sludge method, when a substance that sterilizes the activated sludge flows in, the activated sludge is damaged, and it is easy to lose the purification function of raw water or to cause filamentous bacterial bulking. However, it is inevitable to remove a small amount of a sterilizing agent or a substance that has an adverse effect on the activated sludge into the wastewater, so that the removal of these substances is a problem.

[0009]

In order to rationally solve all of the problems mentioned above, the present invention seeks means for a pretreatment method for activated sludge treatment and solves the problems.

First, large solids in the inflowing raw water are removed by a screen or the like, and the reaction sludge (returning sludge) volume of 1 to 30 parts, preferably 3 to 15 parts, relative to the raw water volume of 100 parts, is adjusted to the raw water adjusting tank. If there is any, add it there, or in the raw water pumping pipe, or install a raw water reaction tank, stir and mix with the raw water, respectively, and contact the persistent sludge in the raw water or the substance that destroys the activated sludge with the reaction sludge. After being adsorbed, the reaction sludge is pressure-floated, concentrated and separated to obtain sludge containing 0.5% or more, preferably 1.5% or more of solid content (adsorption-concentrated reaction sludge) and pressure-floating treated water (treated raw water). ) And get. The average mixing ratio of the raw water and the reaction sludge is the amount of activated sludge that grows in the aeration tank, and depends on the returned sludge concentration (excess sludge concentration). The lower limit of the mixing ratio of the reaction sludge is the minimum amount at which the effect of removing harmful substances in the raw water is exhibited, and the effect comes out at 1 part, but is preferably 3 parts. The upper limit depends on the amount of pollutants that are considered to have an adverse effect on activated sludge, such as persistent substances and bactericides, in the raw water inflow. With the above average values, the upper limit must be set so that the sludge concentration in the aeration tank does not adversely affect the water treatment, so the limit is naturally imposed. It depends on the BOD and SS of the treated raw water after returning the sludge under pressure to the treated sludge, and the concentration of the returned sludge. From experience, if the reaction sludge is extracted for more than 1 day for more than 1 day, the concentration of the aeration tank will decrease. May occur, and 3 to 15 parts is preferable for stability.

The treated raw water obtained by mixing the reaction sludge in these mixing ratios and then removing it in the pressure flotation equipment is subjected to aeration treatment with the returned sludge in the activated sludge aeration tank, solid-liquid separated, and finally discharged water. And get back the sludge. Part of the returned sludge is supplied to the raw water reaction tank as reaction sludge. The adsorption-concentrated reaction sludge is anaerobically and aerobically digested in a concentrated sludge digestion tank, and the pollutants adsorbed by the reaction sludge are microbially decomposed to obtain digested sludge.
And it is characterized by using means for extracting and removing this digested sludge.

[0012]

The function of the activated sludge pretreatment of the present invention is unnecessary in the conventional activated sludge method, and excess surplus sludge (return sludge) that has been withdrawn and discarded is used as the reaction sludge as a microbial adsorbent, thereby making it difficult to decompose in the raw raw water. Substances, such as bactericides that adsorb activated sludge to damage activated sludge and substances that adversely affect microorganisms such as strong acid and strong alkali, are selectively adsorbed to the reaction sludge, and the sludge is removed from the system. In order to remove the activated sludge, the activated sludge is prevented from being damaged and the activated sludge is kept in a high activity state, so that the activated sludge is prevented from swelling and the occurrence of abnormal processing phenomenon due to foam scum, and the processing can be stabilized.

The operation of the invention will be described in more detail. When the reaction sludge is mixed with the raw water and stirred and then the adsorbed reaction sludge is removed by the pressure flotation equipment, the pH adjustment of the raw water becomes unnecessary. Due to the pH buffering effect of microorganisms, p
Since H is adjusted, the chemicals and equipment necessary for neutralizing acids and alkalis are not needed, so not only can the site be used effectively, but the cost of chemicals can be saved. In addition, even if there is a harmful substance such as a bactericide that adsorbs to the activated sludge and destroys the activated sludge in the raw water, the reaction sludge adsorbs these in advance,
Since it is removed by pressure floatation outside the system, it does not adversely affect the activated sludge in the aeration tank, so stable activated sludge treatment can be performed even when bactericide is mixed in the wastewater.

In the present invention, the activated sludge treatment equipment can be installed in a small installation area by performing two series of parallel treatments. In other words, the activated sludge treatment with a normal sludge concentration (normal activated sludge treatment tank) and the activated sludge treatment with a concentration about 10 times the normal concentration (concentrated sludge digestion tank) are operated in parallel to efficiently drain the water as a whole. Can be processed. Therefore, when the wastewater treatment capacity of the existing equipment is to be improved to about 3 times, the raw water reaction tank and the pressure flotation equipment are installed above the aeration tank, and the thick sludge digestion tank is installed in the existing aeration tank or raw water adjustment tank. By dividing the parts into parts and enlarging the final settling tank if necessary, the treatment capacity of the existing activated sludge treatment equipment can be increased even in a small site area.

Sewerage discharge has progressed in urban areas, but the present invention advantageously works as a simple treatment. In the case of sewage discharge, regulations on oil and fat are strict, but SS (suspended solids concentration) is different depending on each municipality, but it is relatively high, so the water quality that meets the discharge standard is usually the same as the discharged water from the activated sludge treatment tank. Since it is easy to mix with the digested sludge from the thick sludge digestion tank and automatically adjust the water quality to meet the discharge standard value for discharge, it is also useful for reducing the simple treatment cost of activated sludge.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples described herein.

[0017]

[Comparative Example] There is a facility where activated sludge treatment is performed on wastewater with an average water volume of 650 m ³ / day from a food manufacturing factory mainly for processing meat. Annual average water quality of inflowing raw water is BOD of 780p
pm, COD350ppm, SS250ppm and n
-Hexane extraction component is 85ppm, and contains alkaline cleaning liquid for smoking furnace and bactericide in food processing plant.
In this facility, after the inflowing raw water is floated and separated by an oil separation tank, coarse dust is removed by a wedge wire type screen with a 1 mm opening, and the raw water is stored in a raw water adjusting tank and pumped up by a pump. The average amount of raw water is adjusted to 27 m ³ / hour in the raw water metering tank, mixed with the return sludge and subjected to aeration treatment with the activated sludge aeration tank volume of 350 m ³ of the extrusion flow, and then ^two sedimentation tanks with a water area of 64 m ² are used in parallel. The treated water is separated from the activated sludge, the discharged water is taken out, and the activated sludge that has been settled and concentrated is circulated and used as return sludge, and a part of it is extracted as excess sludge for coagulation dehydration to obtain a dehydrated cake, which is disposed off-site. Was.

At this facility, Sphaerotilis and type 021N filamentous bacteria abnormally propagated in the aeration tank, causing bulking, which sometimes caused a state in which treatment could not be performed. Further, since the pH of raw water may exceed 11, the raw water was neutralized with sulfuric acid before being placed in the aeration tank.

Furthermore, when performing coagulation dehydration of excess sludge, the coagulation state varies daily depending on the production items of the factory,
It is hard to be constant. When a bulking occurs, it operates using a spare settling tank, but since a large amount of sludge accumulates here as well, it will circulate as return sludge if the maximum dehydration capacity is not enough, but the inflow of raw water must be temporarily reduced. Frequent situations often occurred.

The amount of excess sludge drawn out is 1110 m ³ per month on average because the compaction in the settling tank does not increase and the returned sludge is 3500 ppm on average per month, which is 37 m ³ on average per day, which is a relatively large operating time of the dehydrator. The monthly average is as long as 19 hours / day, and the addition amount of the coagulant can be reduced to some extent with respect to the excess sludge, but the operating time of the dehydrator is long. On a monthly average, the cationic polymer flocculant is 2.5% and the anionic polymer flocculant is 0.7%, which is a large addition rate, so the monthly average amount of the flocculant used is 98 kg / kg of the cationic polymer flocculant. The amount of the anionic polymer coagulant was 27 kg / month. In addition, the water content of the dehydrated cake discharged from the dehydrator is relatively high with a monthly average value of 86%, so the dehydrated cake contains a lot of undecomposed substances, so it decomposes and gives off a bad odor. I was in trouble. Furthermore, since the dehydrated cake has a high water content, the average amount of dehydrated cake generated was as high as 29 tons per month, and the sludge disposal cost was insignificant. Especially when the water content exceeds 85%, there is a problem in collecting sludge.

[0021]

[Example] In the activated sludge facility of the comparative example, a raw water reaction tank with an 8 m ³ stirrer was installed after the raw water measuring tank to pretreat the raw water, and 6 parts of the reaction sludge was added to 100 parts of the raw water. Continuous addition was performed with a metering pump. A chemical-free injection type pressure levitation facility KF800 (manufactured by Alcy Japan Co., Ltd.) was installed and 100 kg of this mixed raw water was 5 kg / cm ² without chemical injection.
In a partial pressure flotation tank in which 80 parts of pressurized water is mixed and circulated,
Reactive sludge was concentrated and floated to 1.8%, removed, and separated from the settling tanks that were prepared in advance for bulking by dividing the two settling tanks into two tanks by dividing them into a 186 m ³ thick sludge digestion tank. did. One of the 120 m ³ tanks was equipped with a stirrer and the top was sealed, and the generated gas was treated with alkali and acid to recover the gas.
The other 66 m ³ tank is equipped with an air diffuser and a stirrer, and the digested sludge obtained by anaerobic and aerobic aeration of the pollutants adsorbed in the reaction sludge is automatically controlled by the liquid level of the thick sludge digestion tank. With a screw press dehydrator (NSP-manufactured by Nippon Alsee Co., Ltd.).
300) and dehydrated.

On the other hand, the treated water obtained in the chemical-free injection pressure flotation equipment was treated using an activated sludge treatment tank and a sedimentation tank in the same manner as in Comparative Example to obtain discharged water. However, in this case, Sphaerotilis and type 021N filamentous bacteria that were constantly generated in the comparative example were hardly seen, sludge concentration was improved in the settling tank, and the returned sludge concentration exceeded 6000 ppm. Was operated at 100% to maintain MLSS at 3300 ppm, the activated sludge treatment was satisfactory. Therefore, we reduced the number of sedimentation tanks by one, but there was no need to worry at all.

The reaction sludge that adsorbed the contaminants floated and concentrated to about 1.8% on a monthly average by pressure flotation generated 13 tons / day on a monthly average, and this was generated in a thick sludge digestion tank with an improved settling tank. Digested. Since the reaction sludge stays in the digestion tank for about 14 days, the indigestible substances, fats and oils, natural polymers, etc. adsorbed by the reaction sludge were digested, and the conversion to bacterial cells was significantly progressed. Therefore, the monthly average digested sludge removal rate is 9 tons / day, and the solid conversion rate is 0.17 tons / day, and the monthly average operating time of the dehydrator is 5 hours / day, which is about the same as in the comparative example. It became 1/4. The amount of the flocculant used was 42 kg / month for the cationic polymer flocculant and 17 kg / month for the anionic polymer flocculant, which was about half that of the comparative example. The water content of the dehydrated cake was drastically reduced to 81% on a monthly average, and the odor of the dehydrated cake was reduced compared to the comparative example, so that it was not necessary to use a deodorant. The amount of dehydrated cake generated was 14 tons / month on average, which was less than half that of the comparative example.

Since the odor of the dehydrated cake was reduced, the dehydrated cake was dried and examined as a fertilizer, and it was found that it can be effectively used not only as a mature fertilizer but also as a soil conditioner.

[0025]

The effect obtained by the present invention is a technology for recovering pollutants dissolved in water as solids or gas in wastewater treatment, and these recovered solids are used as industrial wastes on the earth. From the viewpoint of not causing environmental problems, it is an excellent effect that the amount of recovered solids can be reduced and a method of using it as an effective resource can be easily provided.

Further, in the conventional activated sludge treatment, if the organic concentration and the type of the inflowing raw water are not constant and greatly fluctuate, or if a harmful substance to the activated sludge sometimes flows in, a serious obstacle is given to the bacteria of the activated sludge. It is apt to cause deterioration of water quality and to cause an unprocessable phenomenon due to occurrence of bulking by filamentous bacteria. According to the present invention, in a treatment plant treating such raw wastewater, components that adversely affect the activated sludge out of the pollutants in the inflowing raw water are adjusted in advance by adjusting the supply ratio of the reaction sludge amount to the raw water. The water quality of the raw water can be adjusted arbitrarily and easily by adsorbing it to and removing it, so that the activated sludge treatment can be performed stably and the water quality after the activated sludge treatment is stabilized,
Moreover, the frequency of occurrence of bulking is significantly reduced. further,
If the occupancy site of the wastewater treatment plant is limited and the influent raw water has a high organic content load and is unlikely to be treated in the aeration tank, the present invention disperses the organic content load in the aeration tank and the thick sludge digestion tank for parallel processing. Therefore, the absolute activated sludge holding amount can be increased by 5 to 10 times even in the same area, and the microbial treatment capacity can be greatly increased in that proportion, so that an excellent effect can be exhibited. This was obtained because of the combination of the two following advantages of the activated sludge treatment method. One of them is that in activated sludge treatment, solid-liquid separation is easier as the concentration of activated sludge is thinner, so that ordinary activated sludge treatment equipment is treated with a low concentration of activated sludge by reducing the organic content load. Secondly, when solid-liquid separation is not required, the higher the concentration of organic components and the concentration of activated sludge, the higher the digestion ability. Floating and concentrating with, and then sending it to the thick sludge digestion tank, facultative anaerobic bacteria and facultative aerobic bacteria efficiently promote the digestion of the organic components adsorbed in the sludge, and finally, there is less foul odor. It is easy to obtain fully-ripened activated sludge.

The most problematic point of the wastewater treatment plant is the treatment of excess sludge. Usually, excess sludge is pulled out and coagulated and dehydrated,
If the undegraded organic matter concentration in the excess sludge is high, the organic matter, which is an advantage of microbial decomposition, is not converted to inorganic matter (carbon dioxide gas and water), so not only the amount of waste sludge increases but also the use of coagulant. The amount increases or the agglomeration state is greatly affected by the type of undecomposed substance and becomes unstable, which significantly impairs the performance of the dehydrator and increases the water content of the dehydrated cake, which significantly impairs the economic effect. The invention efficiently decomposes microbial cells by digesting concentrated sludge and has a small amount of undecomposed substances, so that the digestion of sludge progresses, the solid content of generated sludge is small, and the coagulant consumption is small and stable for coagulation and dehydration. The dewatering efficiency of the dewatering machine is improved due to the high coagulation, and the water content of the obtained dewatering cake is low. There. In addition, when it contains little harmful substances and is suitable as a fertilizer, it can be returned as a fully-ripened organic fertilizer and as a global resource effective as a soil conditioner, thereby producing an economic effect. Therefore, according to the present invention, the amount of industrial waste generated by wastewater treatment is small, and when the inflowing raw water does not contain harmful substances, it becomes sludge that can be utilized as an effective resource, so there is little environmental destruction and earth-friendly wastewater treatment. A method can be provided.

Claims (1)

[Claims] 1. When treating pollutants in raw water with activated sludge, 1 to 30 parts, preferably 3 to 15 parts, of returned sludge (reactive sludge) is mixed and stirred in advance with respect to 100 parts of raw water, and then the reaction sludge is pressurized. Float concentration and separation, 0.5%
More preferably, sludge containing 2% or more of solid content (adsorption / condensation reaction sludge) and treated raw water are obtained. The treated raw water is subjected to aeration treatment together with the returned sludge in the activated sludge aeration tank and then solid-liquid separated to obtain final discharged water and returned sludge. The adsorption-concentration reaction sludge is anaerobically and aerobically digested in a concentrated sludge digestion tank, and the pollutants adsorbed by the reaction sludge are microbially decomposed to obtain digested sludge. Then, an activated sludge treatment method of extracting and removing digested sludge as excess sludge.