JPS6245000B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel and rational method for treating human waste septic tank sludge. In recent years, as the number of installed septic tanks has rapidly increased, the amount of septic tank sludge discharged is enormous, and it is currently having a major negative impact on the operation and management of existing human waste treatment plants. Conventionally, septic tank sludge, except for dumping into the ocean, is generally mixed with pumped human waste in many cases at human waste treatment plants.Furthermore, septic tank sludge has a lower concentration of organic matter than pumped human waste, so pumped human waste is especially treated as septic tank sludge. Malfunctions in processing plants that carry out digestion are becoming more and more noticeable. In other words, the following four items have become a problem as digestive disorders that occur when a large amount of septic tank sludge is mixed in. Since it has a lower BOD and organic matter concentration than human waste, the organic matter load on the digester is reduced, reducing digestion efficiency. Septic tank sludge undergoes biological treatment in the septic tank, which causes an imbalance of nutrients and substrates to the microorganisms involved in decomposition.
Adversely affects digestion. Digestive disorders are more likely to occur because there is significantly less alkalinity and other substances that act as a buffer in the digestive tank. Septic tank sludge contains a large amount of inert solids and sand, which increases the accumulation of scum and sediment in the digester tank. As the above-mentioned problems have been identified, recently there have been many cases in which septic tank sludge is not mixed with pumped human waste, and a separate treatment facility is installed exclusively for septic tank sludge (this is called separate treatment of septic tank sludge). )
However, separate treatment naturally requires additional installation space and high construction costs, and for this reason, separate treatment has not become widespread. In view of the current situation, the present invention aims to provide a more rational method for treating septic tank sludge, and another purpose is to provide a method that can also streamline the treatment of pumped human waste. be. That is, the present invention does not require separate treatment of septic tank sludge, can completely resolve the adverse effects of combined treatment, and furthermore aims to streamline the treatment of collected human waste itself. The present invention involves mixing human waste septic tank sludge with human waste anaerobic digestion desorption liquid or aerobic digestion treatment liquid, treating the mixed liquid with activated sludge treatment, and then adding a cationic polymer flocculant to the treated liquid and surplus sludge. It is characterized by the addition of a flocculant mainly consisting of , to perform solid-liquid separation. Next, one embodiment of the present invention will be described with reference to FIG. As shown in Figure 1, the human waste 1 is
It flows into the anaerobic digestion tank 2 without being mixed with the septic tank sludge. The septic tank sludge 3 is mixed into the digestion and desorption liquid 4 or directly thrown into the activated sludge treatment tank 5. Therefore, it is preferable not to dilute the mixture of the two with river water, groundwater, or seawater, and if dilution water is unavoidably added for the purpose of defoaming, it should be kept in a small amount of dilution water as much as possible. , undergo activated sludge treatment. The effluent from the activated sludge treatment tank 5 flows into the final settling tank 6, and the thickened sludge 7 is recycled to the activated sludge treatment tank 5. Next, the surplus sludge 8 from the activated sludge treatment process is mixed with the overflow water of the final settling tank 6 without being extracted out of the system, or the surplus sludge 8 is mixed with the activated sludge treatment liquid from the overflow part of the final settling tank 6. After flowing out in slurry form, a cationic polymer flocculant 9 is added to this slurry liquid,
The structure is such that a dehydrated cake 11 and a dehydrated separated liquid 12 are obtained directly by the dehydrator 10. With this method, the cationic polymer flocculant, which has conventionally been used only for dewatering excess sludge, can also be used for clarifying the liquid. If this dehydrated separated liquid 12 is diluted to about 10 times, the quality of water can be discharged as is in many cases, but if the SS recovery rate of the dehydrator is low, the dehydrated separated liquid 12 may be further diluted with sulfuric acid, etc. After being coagulated and precipitated 14 or floated and separated using an inorganic flocculant 13 or an organic flocculant, it is appropriately diluted and discharged, but as described later, the required amount of the inorganic flocculant is significantly reduced. It has been discovered that savings can be made. In addition, in the case of a treatment plant where water for dilution is not available, by adding unit operations such as activated carbon, ozone, electrolysis, ultrafiltration membrane, etc. to the coagulated and separated liquid, water quality that can be discharged without dilution can be obtained. It has been found that by employing the process of the present invention as described above, the following great effects can be obtained. Since the septic tank sludge is added to the digested liquid without being mixed with the collected human waste before entering the digester in the conventional method, no malfunction of the digester will occur. The activated sludge process can be operated without or close to dilution, so the flow rate is 1/10 to 1/10 that of conventional methods.
1/20, it becomes practical to directly dewater the mixed liquid of activated sludge final settling tank effluent and excess sludge using a dehydrator. Moreover, instead of using the conventional method of extracting surplus activated sludge from the system and separately dewatering it, we can create a mixed slurry of surplus sludge and activated sludge treatment process effluent.
When a cationic polymer flocculant is added and dewatered, colloidal
BOD, COD, chromaticity component, organic nitrogen component,
Since it utilizes the phenomenon discovered by the present inventor that excess sludge coagulated by a cationic polymer flocculant is very effectively adsorbed and removed and transferred to the dewatered cake, subsequent dewatering is possible. It was confirmed that the required amount of flocculants such as sulfuric acid salt during the coagulation and precipitation process of the separated liquid was drastically reduced to less than 1/20 of that of the conventional method. Therefore, the amount of inorganic hydroxide sludge that is difficult to dewater is drastically reduced, making it possible to operate the sludge treatment process rationally, and of course reducing the cost of the inorganic flocculant. Generally, SS and BOD in the anaerobic digestion solution are
Since the amount is about 2000 to 3000mg/, which is less than human waste or septic tank sludge, the amount of surplus sludge generated is naturally small, and the amount of cationic polymer flocculant added to dehydrate this surplus sludge is not enough for the purpose of clarifying the liquid. As a result of experiments, it was found that because the amount of water was too small, the amount of chromatic components in the biological treatment effluent absorbed into the excess sludge was small, and the clarification of the liquid was insufficient. The problem was solved by adopting a new method of increasing the amount of surplus sludge generated from the biological treatment process by mixing septic tank sludge, thereby increasing the concentration of sludge flowing into the dehydrator. Therefore, by using septic tank sludge for rationalizing the treatment of human waste digestion and desorbed liquid, it becomes possible to treat septic tank sludge, and the effect of killing two birds with one stone can be obtained. It becomes possible to rationally process septic tank sludge without significantly modifying or expanding the existing human waste treatment plant. Next, the implementation results of the present invention will be explained in comparison with the conventional method. At the existing human waste treatment plant A, where the amount of human waste processed is 20 Kl/day, and the amount of septic tank sludge brought in is 12 Kl/day, treatment was carried out according to the flow shown in Figure 2, but the original plan of construction was However, since the treatment of septic tank sludge was not planned, the anaerobic digestion tank was significantly impaired in function as mentioned above, and the water quality of the digested liquid was particularly poor as shown in the table below. It is.

[Table] At this human waste treatment plant, this digestive and desorbed liquid is treated with river water.
Diluted 15 times and activated sludge treatment (aeration tank residence time)
After 8 hours), the chromaticity of the activated sludge final settling overflow water,
For the purpose of removing SS and BOD, flocculation was carried out using sulfuric acid clay, but the amount of sludge produced was reduced because the flocculation did not occur properly unless the sulfuric acid clay injection rate was 400 to 500mg/a large amount. There was a lot of sludge, and the dewatering properties were poor, making it difficult to process and dispose of the sludge.
Excess sludge from activated sludge and flocculated sedimentation sludge concentrated in a thickener are mixed to form two cationic polymers.
% (vs. SS) was added and dehydrated using a screw decanter type centrifugal dehydrator, but due to the contamination of coagulated sedimentation sludge, dehydration performance was poor and the water content of the dehydrated cake was as high as 85-86%. . Next, the results of modifying the flow of this treatment plant as in the present invention shown in FIG. 1 will be explained. The modifications and results are as follows. The point where the septic tank sludge was mixed was made into a storage tank for the digestion and desorption fluid. Therefore, the dysfunction of the digestive layer completely disappeared. As a result of stopping the addition of dilution water (river water) and performing activated sludge treatment without dilution, the BOD of the activated sludge treatment tank influent was 5000 to 6000 mg/, higher than the conventional method, but the aeration time was 120 hours. Because we were able to extend the water over a very long time and maintain a high water temperature, there was no deterioration in the quality of the activated sludge treated water.
In fact, the SS removal rate improved as the water area load in the final sedimentation tank was reduced to 1/15. (The final settling overflow water SS of the conventional method is 70 to 150mg/, whereas the SS after modification is 30mg/
It was ~60mg/. After the excess sludge of the activated sludge was mixed with the overflow water of the final settling tank (approximately 10,000 mg/SS), cationic polymer was added at 1.5% per SS and dewatered using a roll press type dehydrator. As a result, a dehydrated cake with a moisture content of 78 to 79% and a clear dehydrated separated liquid were obtained. When the quality of the activated sludge final sedimentation overflow water of the conventional method was compared with the 15-fold diluted water of the above dehydrated separated liquid, the dehydrated separated liquid of the present invention was better as shown in the table below. It should be noted that both correspond to the raw water for subsequent coagulation and precipitation, so they can be compared.

[Table] As shown in the above table, according to the present invention, the amount of dilution water used is the same as that of the conventional method, that is, the dehydrated separated liquid is
It was found that by diluting the activated sludge treated water to a factor of 15, the quality of the water was much better than that of activated sludge treated water diluted 15 times using the conventional method, and the treated water could be discharged as is. Next, the dehydrated separated liquid was coagulated and precipitated with sulfuric acid salt. (equivalent to 6,000 to 7,500 mg/in the case of treated water).On the other hand, when coagulation precipitation is performed on the dehydrated separated liquid as in the present invention, in the case of the dehydrated separated liquid that is not diluted with dilution water, sulfuric acid Good flocculation is achieved at 100 to 150 mg/diluted water, and coagulation and precipitation treatment is possible with a very small amount of 15 to 20 mg/diluted water for 15 times dilution of the dehydrated separated liquid. An injection rate of less than /20 was found to be sufficient. As a result, the amount of coagulated and precipitated sludge mainly composed of aluminum hydroxide was reduced to 1/20 of the conventional method, and the amount of dehydrated cake and water content were also reduced. It should be noted that the flocculant added to the slurry flowing into the dehydrator is not limited to a cationic polymer alone, but may also be a combination of two or more types of polymers or an inorganic flocculant. In order to remove the residual cationic polymer in the separated liquid, it is possible to use an anionic polymer and an inorganic flocculant together as a flocculant in the coagulation-sedimentation process, or to oxidize the dehydrated separated liquid to a biofilm method such as a tube catalytic oxidation method. Naturally, it is not possible to circumvent the scope of the claims of the present invention by carrying out a coagulation-sedimentation treatment after the treatment and biologically degrading the residual cationic polymer.

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing an embodiment of the present invention, and FIG. 2 is a system explanatory diagram showing a conventional example. 1... Extracted human waste, 2... Anaerobic digestion tank, 3... Septic tank sludge, 4... Digestion and desorption liquid, 5... Activated sludge treatment tank,
6...Final settling tank, 7...Thickened sludge, 8...Excess sludge,
9... Cationic polymer flocculant, 10... Dehydrator, 1
DESCRIPTION OF SYMBOLS 1... Dehydrated cake, 12... Dehydrated separated liquid, 13... Inorganic flocculant, 14... Coagulation precipitate, 15... Dilution water.

Claims (1)

[Scope of Claims] 1. After mixing human waste septic tank sludge with a human waste digestion solution and treating the mixed solution with activated sludge treatment, a flocculant containing at least a cationic polymer flocculant is added to the treated solution and excess sludge. 1. A method for treating human waste septic tank sludge, characterized in that solid-liquid separation is performed by adding. 2. The method for treating human waste septic tank sludge according to claim 1, wherein the digestion treatment liquid is an anaerobic digestion desorption liquid or an aerobic digestion liquid. 3. Claim 1 or 2 in which a cationic polymer flocculant is used alone as the flocculant.
Method for treating human waste septic tank sludge as described in section. 4. The method for treating human waste septic tank sludge according to claim 1 or 2, wherein a cationic polymer flocculant, another polymer flocculant, and/or an inorganic flocculant are used in combination as the flocculant. 5 Claims 1, 2, 3, or 4, wherein the solid-liquid separation is mechanical dehydration.
Method for treating human waste septic tank sludge as described in section. 6. The method for treating human waste septic tank sludge as set forth in claim 1, 2, 3, or 4, wherein the solid-liquid separation is performed by mechanically dewatering and then coagulating solid-liquid separation of the dehydrated separated liquid. . 7. The human waste septic tank according to claim 1, 2, 3, or 4, wherein the solid-liquid separation is performed by performing mechanical dehydration, biologically treating the dehydrated separated liquid, and then coagulating solid-liquid separation. How to treat sludge.