JPS643158B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel and rational method for treating organic waste liquids such as human waste, sewage, wastewater, and septic tank sludge. The problem with conventional human waste treatment processes is that biological treatment processes such as activated sludge and biological nitrification and denitrification cannot remove phosphoric acid, non-biodegradable COD, and color. A large amount of an inorganic flocculant such as clay or ferric chloride must be added to perform coagulation sedimentation or flocculation. (For example, in biologically treated water diluted 10 times as much as human waste, it is necessary to add extremely large amounts of sulfuric acid, approximately 800 mg/diluted, or 8,000 mg/diluted.) As a result, a large amount of inorganic sludge, which is difficult to dewater, is added. The treatment and disposal of such waste has become a serious problem, as the running costs are high. Separate chemicals are required for sludge dewatering and flocculation, and this also causes high running costs. The dewaterability of biologically treated surplus sludge is also extremely poor, making it more difficult to treat and dispose of than coagulated sedimentation sludge. For waste liquid flowing into the biological treatment process,
Since it is necessary to add a large amount of clean diluted water (groundwater, river water, etc.), which is approximately double the amount, there is a problem that the human waste treatment itself is difficult to carry out at treatment plants where it is difficult to secure a water source. Although the water quality may appear to be good, it is actually about
Since the water is diluted 10 times, the quality of the treated water is not very good in terms of total load. It is an object of the present invention to provide a method for treating organic waste liquid that fundamentally solves the various conventional problems described above based on a novel idea. That is, the present invention treats organic wastewater in a biological nitrification and denitrification process, and adds iron sulfate and water as an alkaline agent to a mixed slurry of treated water and excess sludge from the biological nitrification and denitrification process. This is a method for treating organic waste liquid, which is characterized in that after adding and mixing magnesium oxide and/or magnesium oxide, solid-liquid separation is performed in a post-treatment step including mechanical dehydration. An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, (organic) waste liquid 1 such as human waste and septic tank sludge flows into a biological treatment process 2 using a biological nitrification and denitrification method. receive. This biological treatment is most preferably carried out undiluted;
This point differs greatly from conventional human waste treatment. However, the slurry (Mixed-
Liquor) is centrifugally concentrated as slurry 6b,
The sludge is allowed to flow through a sludge concentration process 3 such as flotation separation, and the concentrated sludge 4a is recycled to the biological treatment process 2 as return sludge 4b. On the other hand, the concentrated separated water 5 is mixed with the effluent slurry 6a (containing excess sludge) from the biological treatment process 2 to form a mixed slurry 7,
It flows into the storage tank 8. Note that when the wastewater 1 is treated without dilution, the inflow amount of the wastewater 1 and the flow rate of the mixed slurry 7 are equal. The slurry from the storage tank 8 is then transferred to the drug mixing tank 9.
where iron sulfate 10 is added as a flocculant.
is subjected to a chemical reaction treatment by adding and mixing Mg(OH) ₂ or MgO as an alkaline agent 11, and then separated into a dehydrated cake 13 and dehydrated separated water 14 by a mechanical dehydrator 12 such as a filter press. The point that this dehydrated separated water 14 corresponds to the treated water of the wastewater 1 is one of the important elements constituting the present invention. Note that it is not preferable to dilute the wastewater 1 at a high ratio and subject it to biological treatment as in the past because the amount of slurry flowing into the mechanical dehydrator 12 becomes enormous. Therefore, the dehydrated separated water 14 is then transferred to the PH adjuster 3.
After the pH is adjusted to about 6 to 8 by adding 2, it is discharged. If desired, the water may be discharged after being treated with a sand filter 15 or with an activated carbon adsorption device, an ozone treatment device, an aeration treatment device, or the like (none of which are shown). Another embodiment of the present invention is shown in FIG. 2, in which the slurry from the chemical mixing tank 9 is concentrated in advance in a sludge concentration step 16 using a flotation thickener or a gravity thickener to create a thickened sludge. The concentrated sludge 17 is sent to a mechanical dehydrator 12, and the resulting dehydrated separated water 14 and concentrated separated water 18 are used as treated water. In this embodiment, the biological treatment step 2 is unavoidable for purposes such as defoaming.
This is a particularly effective treatment process when dilution water is mixed into the solution. There is no problem if a flotation thickener or a gravity thickener is used as the sludge thickening step 16, but if a centrifugal thickener is used, some amount may be present in the concentrated and separated water 18.
Since the SS content is included, it is necessary to provide a sedimentation tank 19 in front of the sand filter 15 to separate the SS content. Note that the precipitated sludge 20 obtained here is preferably recycled to the storage tank 8. In the present invention, the mixed slurry 7 of biologically treated water and excess sludge has an important meaning, so an embodiment of the method for obtaining this mixed slurry 7 will be described in detail with reference to the drawings. First, in the example shown in FIG. 3, biological treatment step 2
A part of the slurry 6b was extracted from the slurry, centrifugally concentrated,
Introduced into a centrifugal concentrator 3a (a flotation concentrator may also be used) as the sludge concentration step 3 such as flotation concentration,
The entire amount of the obtained thickened sludge 4a is recycled to the biological treatment process 2 as return sludge 4b. Note that the amount of slurry 6b to be extracted may be an amount equivalent to an amount sufficient to maintain a predetermined MLSS within the biological treatment process 2. On the other hand, the outflow slurry 6a from the biological treatment process 2 is combined with the concentrated separated water 5 to form a mixed slurry 7, which flows into the storage tank 8. In the example shown in FIG. 3 2, biological treatment step 2
An amount of outflow slurry 6a corresponding to the total amount of waste liquid 1 and return sludge 4b flowing into the biological treatment process 2 flows out from the biological treatment process 2, the entire amount is treated by the centrifugal thickener 3a, and a part of the thickened sludge 4a is used as the return sludge. 4b, and the remaining sludge 4c is mixed with the concentrated and separated water 5 from the centrifugal thickener 3a to form a mixed slurry 7. Incidentally, when comparing the embodiments shown in FIG. 31 and FIG. 32, the embodiment shown in FIG. 31 is more rational in that the load applied to the sludge concentration step 3 is smaller. Next, in the example shown in FIG. 4, the entire amount of the slurry 6a discharged from the biological treatment process 2 flows into the settling tank 3b serving as the sludge concentration process. In this case, if sludge is not drained from the bottom of the settling tank 3b, the upper part of the settling tank 3b will gradually become filled with sludge, and eventually the slurry will overflow from the water surface of the settling tank 3b. . This overflow slurry corresponds to the mixed slurry 7 in each of the embodiments described above. In this case, in parallel with the overflow, the thickened sludge 4a is recycled to the biological treatment process 2 as return sludge 4b. Figure 4 2 shows the thickened sludge 4a from the bottom of the settling tank 3b.
is pulled out, a part is returned to sludge 4b, and the remaining sludge 4 is
This is the case where c is mixed with the concentrated separated water 5 (overflow water), and the mixture obtained here corresponds to the mixed slurry 7. Figure 4.3 shows the process from biological treatment process 2 to within this process.
Slurry 6b sufficient to maintain the desired concentration of MLSS is extracted and concentrated in settling tank 3b, and the resulting concentrated separated water 5 is mixed with effluent slurry 6a to form mixed slurry 7. In addition, when using the sedimentation tank 3b, FIG. 4 3 is the most preferable among the above-mentioned each aspect. Furthermore, the fifth illustrated example is a case where a rotating disk method is adopted as the biological treatment step 2. In the case of such a biofilm process, the return sludge 4b is not required, so the slurry 6a flowing out from the biological treatment process 2 becomes the mixed slurry 7 as it is, and is used in the centrifugal thickener 3a (or flotation thickener), sedimentation basin, etc. 3
The sludge concentration step 3 such as b is completely unnecessary. This also applies to cases where other biofilm processes such as the sprinkled bed method, immersed bed method, and fluidized medium biological treatment method are employed. Therefore, it has been confirmed that according to the present invention, an innovative treatment result can be obtained in which dewatering of sludge and advanced treatment of biologically treated water are performed simultaneously in one process. As described above, the effects obtained by the present invention are listed below. (1) The process is simplified because sludge dewatering and advanced treatment can be achieved at the same time. (2) By adding the chemicals required for sludge dewatering, the chromaticity, COD, and phosphoric acid in the biologically treated water are removed all at once. This eliminates the need for many chemicals, making it possible to significantly conserve resources. (3) In the process of applying a conventional activated sludge method to the biological treatment process and then adding chemicals for dehydration, almost no nitrogen components are removed and remain in the dehydrated separated water. Even if we try to apply the biological nitrification and denitrification method to dehydrated and separated water, there is almost no BOD component left in the dehydrated and separated water.
This method has a serious disadvantage in that valuable substances such as expensive methanol must be added as an organic carbon source necessary for denitrifying bacteria. In contrast, in the present invention, a biological nitrification and denitrification process is provided before the dehydration process, and a method is adopted in which the BOD component in the raw solution (human waste, etc.) is used as an organic carbon source, so the above-mentioned drawbacks can be completely overcome. This eliminates the need for methanol and the need for nitrification and denitrification of dehydrated and separated water. Therefore, running costs can be reduced and processes can be simplified. (4) Even undiluted wastewater can be treated without problems.
Dilution water becomes unnecessary. (5) Treatment by coagulation sedimentation or coagulation flotation to remove COD, etc., which is difficult to biologically treat, is not necessary, and therefore no coagulated sludge is generated. (6) The moisture content of the dehydrated cake of excess sludge generated in the biological treatment process is reduced. (approximately 60 to 63%) (7) Even when an advanced treatment process such as activated carbon treatment is provided after the mechanical dehydration process, the COD load and chromaticity load associated with the advanced treatment process are reduced.
Construction costs and maintenance costs for advanced treatment processes can be reduced. Next, examples of the present invention will be described. Example Human waste having the following water quality was used as a stock solution and treated according to the flow sheet shown in FIG. 1 using a known nitrified solution circulation biological denitrification process as a biological treatment process.

[Table] The operating conditions for the biological nitrification and denitrification process were set as follows, and the raw human waste was not diluted and treated without dilution. Water temperature…30~32℃ MLSS…18000~20000mg/ Nitrification tank DO…3~5mg/Nitrifying solution circulation ratio…100 times the raw solution inflow 1st denitrification tank retention time…2 days Nitrification tank retention time…4 days 2nd Denitrification tank retention time...2 days Sludge return method...centrifugal concentrator (manufactured by Tomoe Kogyo) Final sedimentation tank...unnecessary, so not used Separated water from the centrifugal concentrator is mixed with the effluent slurry from this biological nitrification and denitrification process To the mixed slurry (SS concentration 12,000 to 15,000 mg/), 5,000 to 6,000 ppm of ferrous sulfate _FeSO4 was added as the iron sulfate, and then magnesium hydroxide was added as the alkali agent to adjust the pH to 8 to 9. After stirring for a minute, the mixture was dehydrated using a fully automatic filter press equipped with a squeezing mechanism, with overpressure set at 3 Kgf/cm ² and squeezing pressure set at 15 Kgf/cm ² . As a result, a dehydrated cake with an extremely low water content of 65 to 70% and dehydrated separated water having the following water quality were obtained, and the quality of this dehydrated separated water was so good that it could be discharged as it was.

[Table] Next, when we conducted the same mechanical dehydration test as above using a combination of various iron sulfates and various alkaline agents, the water content of the dehydrated cake at the optimum chemical dosing rate was as shown in the table below. It was confirmed that the combination of sulfate and a magnesium-based alkaline agent resulted in a dehydrated cake with a low moisture content and a small amount of moisture generated. Note that when slaked lime was used as the alkaline agent, the water content of the dehydrated cake decreased, but the amount generated tended to increase.

【table】 [Brief explanation of drawings]

The drawings show embodiments of the present invention, with FIGS. 1 and 2 being explanatory views of the entire system, and FIGS. 3 to 5 being explanatory views of partial systems showing a method for obtaining a mixed slurry. 1... Waste liquid, 2... Biological treatment process, 3... Sludge concentration process, 3a... Centrifugal thickener or floating concentration device, 3b... Sedimentation tank, 4a... Thickened sludge, 4b...
...Return sludge, 4c...Sludge, 5...Concentrated separated water,
6a...Outflow slurry, 6b...Slurry, 7...
... Mixed slurry, 8 ... Storage tank, 9 ... Chemical mixing tank, 10 ... Iron sulfate, 11 ... Alkali agent,
12... Mechanical dehydrator, 13... Dehydrated cake, 14
... Dehydrated separated water, 15 ... Sand filter, 16 ... Sludge concentration process, 17 ... Thickened sludge, 18 ... Concentrated separated water, 19 ... Sedimentation tank, 20 ... Sedimented sludge, 21
...PH adjuster.

Claims (1)

[Claims] 1 Organic waste liquid is treated in a biological nitrification and denitrification process, and iron sulfate, magnesium hydroxide and/or magnesium oxide are added to a mixed slurry of treated water and surplus sludge from the biological nitrification and denitrification process. 1. A method for treating organic waste liquid, which comprises adding and mixing and then performing solid-liquid separation in a post-treatment process including mechanical dehydration.