JPS6218236B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating organic wastewater. In the advanced treatment of organic wastewater, especially sewage and human waste, due to environmental issues at the destination, the concentration of the final effluent should be BOD 10 mg/or less, COD 30 mg/or less, T-N 10 mg/or less, and chromaticity 30 degrees or less. That is what is required. In order to obtain such treated water, activated carbon adsorption treatment as a polisher is essential after so-called secondary treatment such as biological treatment and coagulation-sedimentation treatment. In this activated carbon adsorption treatment, conventionally, when secondary treated water is passed through an activated carbon adsorption tower for a long period of time, organic matter in the wastewater is adsorbed to the activated carbon and accumulated as the number of days the water passes through the activated carbon layer. It becomes anaerobic, and sulfur compounds such as hydrogen sulfide are generated, emitting a foul odor. Furthermore, the treated water often becomes cloudy or colored, and the target quality of the treated water cannot be obtained. The causes of these are not confirmed, but it is believed that sulfate ions contained in wastewater are reduced by sulfate-reducing bacteria generated under anaerobic conditions, and that organic matter adsorbed on activated carbon undergoes anaerobic digestion. It is believed that. It is known that the generation of sulfate-reducing bacteria in the activated carbon layer can be prevented if nitrate ions are present in the water flowing into the activated carbon adsorption tower. One of the methods is to continuously add chemicals such as sodium nitrate and potassium nitrate to the water flowing into the activated carbon adsorption tower. The present invention deals with the treatment of organic wastewater generated during the treatment process.
The aim is to solve these problems by effectively utilizing NO ₂ ^- and NO ₃ ^- (hereinafter abbreviated as NOx) without adding chemicals such as sodium nitrate and potassium nitrate from outside the system. be. In other words, in the nitrification process effluent of the biological nitrification and denitrification treatment process of organic wastewater, the amount of water contained in the raw water is
NH ₄ ⁺ is oxidized by the action of nitrifying bacteria under aerobic conditions, and a considerable amount of NOx is produced. The present invention is characterized in that the activated carbon treatment is carried out under the condition that this NOx is allowed to exist as it is in the inflow water of the activated carbon treatment process. The nitrification and denitrification process, in which human waste is treated by the biological nitrification and denitrification method, consists of a nitrification process and a denitrification process. ₄ ⁺ is oxidized to NO ₃ ^- via NO ₂ ^- , and in the denitrification process, the nitrifying solution, that is, the NO ₃ ^--rich liquid, is brought to an anaerobic state, and the denitrifying action of denitrifying bacteria is used to release NO. ₃ ^- is reduced to _N2 . The nitrification liquid circulation type nitrification and denitrification method has been developed as the most effective biological nitrification and denitrification method. In this nitrification and denitrification method, the conventional one-stage denitrification process is divided into two stages: a first denitrification process and a second denitrification process, which are located before and after the nitrification process, and NO ₃ produced in the nitrification process is Most of the ^- is returned to the first denitrification process along with the mixed liquid, where it is denitrified using the BOD of raw human waste that flows in as reducing organic matter.
The remaining NO ₃ ^- is denitrified (NOx, up to 1 to 2.0 mg/) in the second denitrification step using added methanol. In such a processing process, the BOD of raw human waste
The majority of this is removed by oxidation during denitrification in the first denitrification process, and the remaining part is removed in the second denitrification process.
Since this is a process for removing NO ₃ ^- , by omitting this second denitrification treatment process, it is possible to reduce the BOD content in the influent water of the activated carbon adsorption treatment process, and also allow it to contain NOx. I found that. The NOx remaining in the activated carbon-treated water can be completely removed by further biological denitrification after the activated carbon treatment. Further describing one embodiment of the present invention, human waste is first treated by biological nitrification and denitrification. The biological nitrification and denitrification treatment consists of a denitrification step followed by a nitrification step, and as shown in the example, the BOD of the denitrification tank supernatant water is 1.365 mg/, COD 580 mg/,
NOx―N3.2mg/, BOD of sedimentation tank supernatant water420mg/
, COD460mg/, and NOx-N46.5mg/. Next, a cationic polymer is added to a slurry of the biological nitrification and denitrification process effluent and excess sludge, and a dehydrated cake and a dehydrated separated liquid are obtained by a dehydrator. Next, the dehydrated separated liquid is subjected to coagulation sedimentation and sand filtration, and then used as activated carbon treated influent water. Since the solid-liquid separation process after biological treatment has no effect on the increase or decrease of NOx, any of the solid-liquid separation processes, such as coagulation sedimentation, flotation separation, excess membrane treatment, or sand filtration, can be used. The quality of treated water in each treatment process was as shown in Table 2. The flocculation-sedimentation supernatant water that flows into the activated carbon adsorption tower (strictly speaking, it is sand-filtered water, but the treated water quality is almost the same) has a BOD of 40 mg/,
COD was 125 mg/, NOx-N was 46.4 mg/. In the conventional treatment method, as mentioned above, the biological treatment effluent contains only a trace amount of NOx, and this becomes the inflow water to the activated carbon adsorption tower. Trouble will occur due to the following. The treated water from the activated carbon adsorption tower is as shown in Table 2.
BOD3.7mg/, COD3.1mg/, NOx―N30.4
mg/. If the target quality of the final treated water is satisfactory, there is no need for further treatment, but recently there has been a strong desire to reduce the nitrogen content as much as possible.
In order to reduce the NOx-N content, NOx-N can be efficiently removed by further denitrifying the activated carbon-treated water and adding methanol according to the NOx-N content. Denitrification treatment uses a known biological denitrification method, but methods using biofilms such as a fluidized bed method, a rotating disk method, and a gravity sand filter method are preferred because they are easy to control. In this way, the present invention makes the biological nitrification and denitrification process a denitrification process, followed by a nitrification process, and performs the activated carbon treatment in a state where NOx is present in the inflow water of the activated carbon treatment process. It suppresses the anaerobic state inside the activated carbon tower, makes full use of the adsorption effect of activated carbon, and does not remain in the activated carbon treated water.
By performing denitrification treatment following activated carbon treatment, NOx can be removed and the target quality of treated water can be obtained at all times. An example of the present invention is shown. Example An experiment was conducted using human waste having the water quality shown in Table 1 according to the flow shown in Figure 1. In the case of raw water treatment amount of 0.5 m ³ /day, the specifications of the experimental equipment were set as follows. 1 Biological treatment (1) Residence time Denitrification tank 14 hours Nitrification tank 18〃 (2) Nitrification tank load Sludge load V-N base
0.05Kg-N/Kg・SS・Japan BOD base
0.12 〃 Volume load T-N base
0.32Kg―N/m ³・day BOD base
0.78 〃 (3) Others MLSS 9000~10000mg/ Dilution ratio 7 times Water temperature 25~27℃ 2 Dehydrator Processing capacity ^1m3 /day (MAX) Rotation speed 3000rpm Cationic polymer addition amount 1.5~2.0% (Flownatsu) (vs. SS) ) 3 Coagulation and precipitation treatment Ferric chloride (hexahydrate 300-350mg/) Polymer (Sunpoly N-500) 1mg/ Stirring residence time 0.2 hours Sedimentation tank 〃 4 〃 4 Sand filter Anthracite + sand 2 layers Water flow rate LV =2~5m/H 5 Activated carbon treatment Column size 5.0cm〓×100cm ^L flow rate SV=2 A, C 1 6 Denitrification using biofilm Fluidized bed denitrification method Biological media (filling material), sand (particle size 0.6mm) depth 1m Methanol addition ratio CH ₃ OH/N = 2.5 to 3.0 Volume load NO ₃ -N, 5KgN/m ³ -day residence time 7 to 10 minutes Human waste is diluted 2 times with the above specifications As a result, the treated water quality of biological nitrification and denitrification process is shown in Table 1.
It was like that.

[Table] Next, add 1.5 _to 2.0% (10,000 to 12,000 mg of SS) of a cationic polymer (trade name, Flownatsu) to the slurry liquid obtained by mixing surplus sludge generated from the biological treatment process with the overflow water of the sedimentation tank supernatant water S1 (10,000 to 12,000 mg/SS). versus
SS) was added and dehydrated using a decanter-type centrifugal dehydrator. Next, 200 mg of ferric chloride (hexahydrate) was added to the dehydrator separated liquid having the water quality shown in Table 2 for flocculation treatment. The clear water _S2 from the sedimentation tank was subjected to sand filter treatment, and then used as inflow water to the activated carbon adsorption tower. Furthermore, the activated carbon-treated water was subjected to denitrification treatment by a fluidized bed biofilm method, and then discharged via a sand filter tower. The results are shown in Table-2.

【table】

This is the average value of [Table].
As shown in Table 2, the activated carbon adsorption tower did not generate any bad odor, which is a concern with conventional treatment methods, and there was no outflow of colored water. Also, the quality of the final discharged water is
BOD4.2mg/, COD3.2mg/, T-N2.3mg/
The target treated water quality was achieved.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 1... Human waste, 2... Denitrification tank, 3... Nitrification tank, 4... Sedimentation tank supernatant water (S ₁ ), 5... Cationic polymer, 6...
Dehydrator, 7... Ferric chloride etc., 8... Coagulation tank, 9... Sedimentation tank supernatant water (S ₂ ), 10... Sand filter tower, 11... Activated carbon tower, 12... Biofilm denitrification, 13... Sand filter tower, 1
4... Treated water, 15... Nitrification liquid circulation, 16... Returned sludge, 17... Excess sludge, 18... Cake.

Claims (1)

[Scope of Claims] 1. In a method in which organic wastewater is treated by a biological nitrification-denitrification method, treated water is subjected to solid-liquid separation and then treated with activated carbon, the treatment step of the biological nitrification-denitrification method is a denitrification step. 1. A method for advanced treatment of organic wastewater, characterized in that nitrite nitrogen or nitrate nitrogen is caused to exist in the inflow water in the activated carbon treatment by first carrying out a nitrification step. 2. The method for advanced treatment of organic wastewater according to claim 1, wherein a denitrification step is added subsequent to the activated carbon treatment. 3. The advanced treatment method for organic wastewater according to claim 2, wherein the denitrification step subsequent to the activated carbon treatment utilizes a biofilm.