JPH0114838B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a treatment process suitable for organic wastewater, particularly highly concentrated organic wastewater such as human waste. Conventionally, the process that has been evaluated as the most advanced among human waste treatment processes involves biological nitrification and denitrification treatment of human waste, solid-liquid separation of activated sludge in a settling tank, and coagulation and sedimentation of supernatant water. sand filter,
This method further includes ozone treatment, activated carbon treatment, and sterilization treatment. However, this conventional process has the following serious problems. In other words, many unit operations are arranged in series, making the process complex and difficult to maintain. The installation area will also be larger. Coagulation-sedimentation (or flotation) treatment requires a large amount of flocculant such as sulfate clay, which is resource-intensive, and flocculated sludge that is difficult to dewater (Al(OH) ₃ , etc.)
is generated, and its treatment and disposal are difficult and require a large amount of energy and expense. A large amount of electricity is required to generate ozone, approximately 20 to 30 Kwh/Kg・O ₃ , and it is also necessary to process activated carbon.
It costs 500 to 600 yen/Kl - human waste, which is an expensive expense. Recycling waste activated carbon also requires a large amount of energy. The present invention provides a method that can overcome the various drawbacks of the conventional processes as described above. That is, the present invention treats organic wastewater in a biological treatment process, then evaporates the treated water in an evaporation process, and uses condensed water of the evaporated water vapor as highly treated water of the organic wastewater. This is a method for treating organic wastewater characterized by adsorption treatment of odor components in highly treated water with activated carbon. An embodiment of the present invention will be described below with reference to the drawings, taking human waste treatment as an example. The removed human waste 1 (often contaminated with septic tank sludge) is passed into the biological treatment process 2 using the biological nitrification and denitrification method without adding dilution water, which mainly removes BOD, COD, and nitrogen. Biologically remove components. As biological treatment process 2, a method is adopted in which BOD in human waste can be used as a hydrogen donor for denitrifying bacteria, such as a nitrification liquid circulation type, a step-supply type of human waste, an aerobic denitrification type, and a batch treatment type. In biological treatment step 2, a large amount of dilution water (10
It is extremely undesirable to add more than twice the normal amount of water, as this not only lowers the water temperature and deteriorates the activity of microorganisms, but also increases the amount of water to be evaporated. The activated sludge slurry 3 flowing out from the biological treatment process 2 is subjected to solid-liquid separation in a return liquid separation process 4 such as a centrifugal thickener, settling tank, flotation separator, etc., and most of the separated sludge 5 is returned to the sludge 5'. recycled as On the other hand, the surplus activated sludge 6 is processed in a sludge dewatering step 7. However, although BOD, nitrogen components, and SS have been successfully removed from the biologically treated water 8 flowing out from the solid-liquid separation process 4, large amounts of non-biodegradable COD, chromaticity, phosphoric acid, and organic nitrogen remain. ing. Therefore, in the conventional process, COD, chromaticity, phosphoric acid, and organic nitrogen are removed from the biologically treated water 8 through coagulation sedimentation, sand filtration, ozone treatment, and activated carbon adsorption treatment. However, the present invention abandons such conventional means and introduces a completely new technical idea. That is, after preheating the biologically treated water 8 in a heat exchanger 9, it is subjected to an evaporation step 10 (1) using a vapor compression method.
0' is the water vapor 1 supplied to the evaporator) and evaporated.
1 is compressed and heated in a vapor compressor 12, and then guided to an indirect heating section 13 in an evaporator 10', where the latent heat of condensation of the steam is reused as a heat source for evaporation. Since the temperature of the condensed water 14 is approximately 100°C (the pressure inside the evaporator 10' is approximately normal pressure), it is used as a high-temperature heat source for the heat exchanger 9 and then subjected to the activated carbon adsorption step 15.
The water flows out as ultra-highly treated water 16. Since the condensed water 14 is distilled water, the water quality is extremely good, with zero SS, zero color, phosphoric acid, BOD,
The COD and nitrogen content ranges from 0 to several mg/d, indicating the highest quality of undiluted human waste treated water. However, as a result of the demonstration plant operation of the process of the present invention, the following problems were found. That is, it has been found that a small amount of odor components may coexist in the condensed water 14, probably because the odor components are generated during the process of evaporating the biologically treated water 8. This odor component was mainly composed of sulfur-based malodorous substances such as dimethyl sulfide. Therefore, as a result of searching for an effective method for removing malodorous components from the condensed water 14, it was found that a method of adsorption treatment using activated carbon is extremely superior. Since the condensed water flowing into the activated carbon adsorption process contains almost no coexisting substances other than malodorous components, extremely effective adsorption is achieved, and the activated carbon has a sufficiently long life of 6000 to 8000/carbon. As described above, the important point of the present invention is that organic wastewater is first subjected to biological treatment, and a specific target water called biologically treated water is treated by an evaporation process using, for example, the vapor compression method to obtain condensed water of evaporated water vapor. The purpose is to adsorb a specific target water called condensed water using activated carbon. Furthermore, this embodiment includes the following points as one of the important concepts. That is, the temperature of the liquid in the biological treatment tank due to the heat produced by the microbial oxidation reaction (approximately 40,000 Kcal/Kl - human waste) generated when human waste 1 is biologically treated, and therefore the temperature of biologically treated water 8 becomes lower than the temperature of human waste 1. One of the important points is to evaporate the biologically treated water 8 whose temperature has been raised by the heat of microbial oxidation, focusing on the effect that the water temperature increases by 20 to 30°C. As a result, there is an energy-saving effect in that the amount of heat required to heat the inside of the evaporator 10' to the evaporation temperature (usually 90 to 100° C.) can be reduced. The evaporative concentrate 17 (biologically treated water concentrated several tens of times) is disposed of in an arbitrary incineration process 18 such as spray combustion, and the generated thermal energy is transferred to the evaporation process 10 and the vapor compressor 12. , sludge dewatering process 7, etc. In the embodiments described above, the evaporation step 10 is based on a vapor compression method, but it may also be based on a multiple effect evaporation method, and the steam generated from the multiple effect can is compressed by a vapor compressor. The evaporation process may be such that it is supplied to any one of the multi-effect cans. Note that condensed water 14 flowing out from the heat exchanger 9
Since the water temperature is still around 50° C., it is highly desirable to adopt a method of not allowing the water to directly flow into the activated carbon adsorption step 15 but instead using it as a heat source for the drying step of the dehydrated cake 7'. In addition, when the organic wastewater 1 contains a large amount of ammonia nitrogen components such as human waste, it is preferable that the biological treatment step 2 is a biological nitrification method or a biological nitrification denitrification method. If the biological treatment step 2 has only a BOD removal function, ammonia nitrogen in the biologically treated water will evaporate together with the evaporated water vapor, and a large amount of ammonia will be mixed into the condensed water. According to the present invention as described above, many important effects such as those described below can be obtained. All of the steps that were essential in conventional processes, such as coagulation sedimentation of biological treatment liquid, filtration, ozone oxidation, COD/chromaticity removal through activated carbon adsorption, and sterilization, are no longer necessary, and are far superior to conventional processes. Treated water with high quality can be obtained. As a result, it not only has a significant effect on preventing environmental pollution, but also simplifies the process. The purpose of activated carbon adsorption is only to adsorb and remove low concentrations of odor components, and there is no need to remove COD and chromaticity with activated carbon as in the conventional process.The life of activated carbon is extremely long at over 6000/・carbon. Life of activated carbon for COD and color removal in process: 500 to 1000/・carbon
significantly longer than . Therefore, the cost of activated carbon treatment is less than 1/6 of the conventional process. Since there is no need for flocculants, ozone generation electricity, or chlorine for sterilization, there is a significant resource and energy saving effect. Since coagulation and sedimentation treatment is not necessary, no flocculation and sedimentation sludge is generated and only excess activated sludge needs to be treated. As a result, sludge treatment costs are reduced and sludge treatment facilities are also saved. The calorific value of the dehydrated cake is 4000K because the dehydrated cake of surplus activated sludge from the biological treatment process does not contain coagulated sedimentation sludge mainly composed of inorganic substances.
It has excellent fuel properties with a high cal/kg/ds and easily self-combustes, so it does not require auxiliary fuel such as heavy oil. This effect also greatly contributes to energy saving. Since human waste contains extremely large amounts of highly concentrated ammonia, organic acids, and odor components, direct evaporation treatment of human waste according to the present invention results in extremely large amounts of ammonia and volatile components in the generated water vapor and water vapor condensation. Since the water contains organic acids and odor components, it is impossible to use water vapor condensate as highly treated water as in the present invention. Moreover, there is a problem in that the evaporation process of human waste generates an intolerable odor that is stronger than the odor of raw human waste. Since human waste contains a high concentration of SS of 10,000 to 20,000 mg/, the concentration of SS increases extremely due to evaporation and concentration, resulting in loss of fluidity.
There is an essential problem that the evaporator gets clogged. In contrast, in the present invention, the human waste is first biologically treated to remove ammonia, volatile organic components, and odor components sufficiently before being evaporated, so that the condensed water of evaporated water vapor contains BOD, COD, nitrogen,
Phosphoric acid, chromaticity component, SS are all zero or several
mg/, indicating extremely excellent water quality. Furthermore, the odor concentration in the condensed water is extremely low, several thousand times lower than in the case of direct evaporation treatment of human waste. Furthermore, since the SS content of the liquid to be evaporated is as small as several 10 to 100 mg/ml, there is an important effect that fluidity does not deteriorate due to an increase in the SS concentration. The chloride ion Cl ^- concentration of conventional undiluted human waste treatment water is extremely high at around 3000mg/, so it is not recommended for forest spraying.
It was almost impossible to use the water for irrigation in fields due to salt damage, but the water treated by the present invention can be used for irrigation.
Since the Cl ^- ion concentration is extremely small, ranging from 0 to several mg/, it can be easily used for forest spray water and irrigation water. If a liquid containing a volatile organic acid is directly evaporated, there is a high possibility that the evaporator, vapor compressor, etc. will be corroded by the organic acid, but in the present invention, the organic acid that is easily assimilated by microorganisms is biologically treated in advance. Since it is removed during the process, troubles such as those described above cannot occur. Next, examples of the present invention will be described. Example: Human waste (containing 15% septic tank sludge) transported to the H human waste treatment plant in Fujisawa City, Kanagawa Prefecture is removed using a rotary screen, and the amount of human waste processed is 1
No-dilution treatment was carried out using nitrified fluid circulation biological denitrification method at a scale of Kl/day. The reason for non-dilution treatment is to raise the liquid temperature by utilizing the heat of microbial oxidation and to save energy by reducing the amount of water flowing into the evaporation process. MLSS of biological treatment process is 19000~22000mg/,
The length of stay was 7 days. The water temperature in the biological treatment tank is 42℃ in summer and 42℃ in winter due to the oxidation heat of microorganisms such as BOD assimilating bacteria and nitrifying bacteria.
It was maintained at 33-34°C. A chemical-free centrifugal concentrator is used for solid-liquid separation of the biological treatment tank effluent slurry, and most of the thickened sludge (concentration 5-6%) is recycled to the denitrification tank, and excess activated sludge is dehydrated using a filter press. A dehydrated cake with a moisture content of 65-67% was obtained. However, centrifugal concentrated separated water (SS300~400mg/
) into the sedimentation tank to further remove SS.
Supernatant water of less than 100 mg SS is supplied to a vapor compression evaporator and concentrated to a concentration ratio of 40 times, resulting in a concentrated liquid of 25 mg/day.
975/day of steam condensed water (corresponding to undiluted ultra-highly treated human waste water) was obtained. The water quality of the filtered human waste, biologically treated water (evaporator inflow water), and condensed water (highly treated water) was as shown in the table below.

【table】

[Table] *6-stage intensity display method This condensed water is collected using an activated carbon adsorption tower (Tsurumicol GL).
−30 and distributed with SV1.0),
Odor components in condensed water were removed. Regarding the water quality of activated carbon effluent, SS, chromaticity, Cl ^- , and PO ₄ are all zero, COD is 0 to 1 mg/, BOD is 0 to 2 mg/,
TN was 1-3 mg/, and the odor intensity was zero. Activated carbon has an extremely large ability to remove malodor components.
Even when 6000/·carbon was passed through the water, the odor intensity of the activated carbon-treated water was zero. The evaporator concentrate was incinerated in a spray combustion furnace.

[Brief explanation of drawings]

The drawings are flow sheets illustrating embodiments of the invention. 1... Human waste, 2... Biological treatment process, 3... Activated sludge slurry, 4... Solid-liquid separation process, 5... Separated sludge, 5'
...Return sludge, 6... Surplus activated sludge, 7... Sludge dewatering process, 7'... Dehydrated cake, 8... Biological treatment water, 9... Heat exchanger, 10... Evaporation process, 10'... Evaporator, 11
...Steam, 12...Vapor compressor, 13...Indirect heating section, 14...Condensed water, 15...Activated carbon adsorption step, 16
...Ultra-highly treated water, 17. Evaporation concentrate, 18. Incineration disposal process.

Claims (1)

[Claims] 1. Organic wastewater characterized by treating the organic wastewater in a biological treatment process, then treating the treated water in an evaporation process, and subjecting the condensed water of the evaporated steam to activated carbon adsorption treatment. processing method. 2. The method according to claim 1, wherein the evaporation step is based on a vapor compression method. 3. The method of claim 1, wherein the evaporation step is by a multiple effect evaporation method. 4. The evaporation step is a combination of an evaporation step using a vapor compression method and an evaporation step using a multiple effect evaporation method, in which at least a part of the water vapor generated in the multiple effect tank is compressed by a compressor, and the pressure is increased. 2. The method according to claim 1, wherein water vapor is supplied to at least one of said multiple effect cans. 5. Claims 2 and 3, wherein the organic wastewater contains ammonia nitrogen, and the biological treatment step is based on a biological nitrification method.
or the method described in paragraph 4. 6. Claim 2, wherein the organic wastewater contains ammonia nitrogen, and the biological treatment process is based on a biological nitrification and denitrification method.
3. The method described in Section 3, Section 3, or Section 4.