JPS643156B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rational treatment process for organic waste liquid. A typical example of the treatment of organic waste liquid by the conventional method is explained using Figure 1 using the human waste treatment process as an example.The human waste 1 is treated in the biological treatment process 2, and the treated liquid is sent to the final sedimentation tank 3 to be made into supernatant water. A portion of the drawn sludge 4 becomes return sludge 5, and the remainder becomes surplus sludge 6. The supernatant water flows into the stirring tank 7, where an inorganic flocculant 8 and a polymer flocculant 9 are added, and then flows into a flocculation sedimentation tank 10 where it is separated into flocculated separation water 11 and flocculated sludge 12. The flocculated and separated water 11 is passed through a sand filter 13, oxidized with ozone 15 in an ozone treatment device 14, and finally adsorbed in an activated carbon adsorption device 16.
It is discharged outside the system as highly treated water 17. on the other hand,
The flocculated sludge 12 is treated with a polymer flocculant (cationic polymer) 19 together with excess sludge 6 in an auxiliary agent mixing tank 18.
is added, and then separated into dehydrated separated water 21 and dehydrated cake 22 by a mechanical dehydrator 20. In such conventional processes, the following major problems remain. In biological treatment such as activated sludge method and anaerobic digestion method, color components in human waste and difficult-to-biodegradable
Since COD components and phosphoric acid can hardly be removed,
It is necessary to add a large amount of an inorganic flocculant such as sulfuric acid chloride to the biologically treated water (in the example in Figure 1, this corresponds to the supernatant water of the final sedimentation tank 3) for coagulation and sedimentation. Therefore, running costs are high, and a large amount of hard-to-drain coagulated sludge is generated, making it difficult to treat and dispose of it. Excess biological sludge generated from the biological treatment process also has poor dewatering properties, making it difficult to reduce the moisture content of the dehydrated cake to below 85%. The running cost of the sludge dewatering process is high because a large amount of dewatering aids such as cationic polymers are required for sludge dewatering. The actual situation is that An object of the present invention is to provide a method for treating organic waste liquid that can fundamentally solve the problems in the conventional processes. The present invention biologically treats organic wastewater in a biological treatment process, obtains a mixed slurry of surplus sludge from the biological treatment process and treated water, retains the mixed slurry under anaerobic conditions, and at least A part or all of the ferric ions are reduced to ferrous ions by adding an iron-based flocculant, separated into thickened sludge and separated water in the concentration process, and the separated water is led to the oxidation process. This is a method for treating an organic waste liquid, which is characterized by oxidizing ferrous ions into ferric ions, and further separating the oxidized liquid into solid and liquid. In other words, the present invention enables Fe ³⁺ once added to be used as a chemical for dehydration modification of sludge and for advanced treatment of biologically treated water, and also improves sludge modification by maintaining it under anaerobic conditions. The quality is Fe ³⁺ , and the advanced treatment of the concentrated separated water is configured so that it can be reacted in the Fe ²⁺ state. To explain this specifically, surplus biological sludge generated from the biological treatment process is mixed with biologically treated water, and after this mixed slurry is maintained under anaerobic conditions, at least dichloride is added to the mixed slurry. Adding a ferric flocculant such as iron or ferric sulfate to improve the sludge in the mixed slurry (treatment to improve sludge dewatering properties) and convert at least a portion of the ferric iron into ferrous iron. Ferrous iron (Fe ²⁺
The first point is that the sludge is separated into separated water containing water and thickened sludge. Note that after adding the ferric flocculant to the mixed slurry, this mixed slurry may be maintained under anaerobic conditions, and the same effect can be obtained. In the present invention, as described later (see FIG. 2),
The mixed slurry 37 is retained in the anaerobic retention tank 38 to reduce the redox potential.
Since an iron-based flocculant coexists, the Fe ³⁺ of this flocculant
There is an advantage that the amount of reduction from Fe ²⁺ to Fe 2+ can be increased, and that this flocculant can therefore be used more effectively. In addition, in combination with the ferric coagulant, slaked lime,
By adding an alkaline agent such as magnesium hydroxide and a polymer flocculant, the concentration effect of the concentration step can be enhanced and corrosion of equipment materials can be prevented. Then, an oxidizing agent such as air, oxygen, ozone, chlorine, hydrogen peroxide, etc. is added to the separated water containing ferrous Fe ²⁺ , and the separated water (biologically treated water) is subjected to advanced treatment by Fuenton treatment. with Fe ²⁺
The second method was to oxidize to Fe ³⁺ and change it to SS precipitates such as Fe(OH) ₃ and FePO ₄ , and then remove the precipitates in a solid-liquid separation process such as precipitation and filtration. That's the point. Next, one embodiment of the present invention will be described with reference to the drawings. In FIG. 2, human waste 31 flows into a biological treatment process 32 such as biological nitrification and denitrification. In order to maintain activated sludge at a desired concentration in the biological treatment process 32, a part of the MLSS flows into the sludge thickening section 33, where it is separated into thickened sludge 34 and concentrated separated water 35, and the thickened sludge 34 is sent to the biological treatment process 32. It will be sent back. On the other hand, the concentrated separated water 35 is mixed with the effluent slurry 36 from the biological treatment process 32 to form a mixed slurry 37.
becomes. This mixed slurry 37 means a slurry containing excess sludge generated in the biological treatment process 32. Note that when a biofilm process such as a rotating disk method is employed in the biological treatment step 32, the sludge concentration section 33 for returning sludge is naturally unnecessary, and the outflow slurry 36 directly corresponds to the mixed slurry 37. Therefore, the mixed slurry 37 is transferred to the anaerobic retention tank 3.
After being retained at 8 for a predetermined time, ferric chloride (FeCl ₃ ) 40 is added in a stirring tank 39, and preferably an alkali agent and a polymer flocculant are added next.
The sludge is separated into a concentrated sludge 42 and separated water 43 in a flocculated sludge concentration process 41 such as a screen or gravity sedimentation concentration. This concentration step 41 is preferably carried out under acidic conditions (optimally pH 4 to 5). The reason for this is PH4
This is because under the acidic conditions of ~5, the COD component resulting from organic matter in the separated water 43 is the least, and Fe ²⁺ tends to remain as an ion. Subsequently, the separated water 43 flows into an oxidizing tank 45, where an oxidizing agent 44 such as air, oxygen, hydrogen peroxide, ozone, or chlorine is added to oxidize Fe ²⁺ to Fe ³⁺ .
At this time, the reaction Fe ³⁺ +3OH ^- →Fe(OH) ₃ ↓ occurs, and the same effect as when fresh ferric chloride flocculant is added to the separated water 43 can be obtained. In this case, when hydrogen peroxide (H ₂ O ₂ ) or ozone (O ₂ ) is used as the oxidizing agent 44, Fe ²⁺ becomes an oxidation reaction catalyst for these oxidizing agents, and at the same time a coagulation reaction occurs in the oxidizing tank 45. A very important effect is obtained that chemical oxidation such as oxidation reaction can be achieved in the same process. The outflow water from the oxidation tank 45 becomes highly treated water 47 after SS is removed in an SS removal step 46 by sand filtration, sedimentation, etc. On the other hand, the dewatering properties of the thickened sludge 42 have been significantly improved by the addition of ferric chloride 40, and it is directly dehydrated by the filter press 49 without chemical injection, with a low content (usually 60 to 65%). dehydrated cake 51
is obtained. In addition, in the figure, 48 is separated sludge, and 50 is dehydrated separated water. As described above, the effects of the present invention are surprising, and this is due to the advanced treatment that removes color, COD, and phosphoric acid from the treated water from the biological treatment process 32, and the removal of excess biological sludge generated from the biological treatment process 32. This means that the dehydration-improving treatment of 20% is achieved with the same agent. In the biological treatment step 32, when a process that simply removes BOD is adopted, a large amount of nitrite nitrogen NO ₂ -N is often generated in the treated water, and this is mixed with H ₂ O ₂ and O ₃ added to the oxidation tank 45. reacted with,
This will lead to an increase in the consumption of H ₂ O ₂ and O ₃ , and if ammonia nitrogen NH ₃ -N remains in the treated water, chloramine will be produced when chlorine is added to the oxidation tank 45, and Cl Since this results in the phenomenon of consuming a large amount of _{NO 2 -N} , a biological nitrification and denitrification process is adopted as the biological treatment step 32 to ensure that NO ₂ -N,
It is highly preferred to prevent _NH3 -N residue. In this way, the mixed slurry 37 is consumed because the alkalinity is consumed by the biological nitrification reaction.
Another effect that cannot be overlooked is that the pH buffering property is weakened and it becomes easy to set the optimum pH (4 to 5) for the flocculation reaction by the ferric flocculant. As described above, according to the present invention, advanced treatment of biologically treated water (removal of COD components, chromaticity components, phosphoric acid, etc.) and treatment to improve the dewaterability of surplus biological sludge are performed.
Since the process is carried out using the same chemical (ferric flocculant in the present invention), there is no need to add a sludge dewatering agent such as a cationic polymer separately from the advanced treatment flocculant as in conventional processes. This makes it possible to streamline the process and significantly reduce maintenance and management costs.Thus, the thickened sludge discharged from the thickening process (the first stage of the oxidation process) can be dehydrated without any chemical injection, and the thickened sludge of the mixed slurry can be dehydrated. When the ferric ion Fe ³⁺ added as a pre-treatment agent for ferric sludge comes into contact with anaerobically maintained excess biological sludge flowing out from the biological treatment process, it is reduced with high efficiency.
We discovered a new phenomenon in which Fe ²⁺ ions change into Fe 2+ ions, and use these Fe ²⁺ ions as oxidation catalysts for the Fenton treatment of the concentrated and separated water in the concentration process, so the treatment can be performed without adding additional Fe ions from the outside. Important industrial benefits can be obtained, such as improved water quality. Next, examples of the present invention will be described. EXAMPLE Residue-free human waste having the water quality shown in Table 1 was treated by a known nitrified solution circulation biological denitrification process without adding dilution water.

[Table] The operating conditions for the biological nitrification and denitrification process were set as shown in Table 2.

【table】

[Table] Mixed slurry (SS8000~
12000mg/, M alkalinity 800~1000mg/, PH
8.2) was allowed to stay anaerobically for 4 hours, then FeCl ₃
After adding 3000mg/stir and stirring for 10 minutes (at this time
PH was 2.5), adjusted to PH5.0 by adding Ca(OH) ₂ , and then added nonionic polymer (Acofrost).
After adding 40mg of N100) to form large particle flocs, they were flowed into an inclined wedge wire screen (mesh opening 0.3mm, screen length 60cm, screen width 20cm), which effectively drained the water. The concentration of thickened sludge on the screen was as high as 3.8%. On the other hand, in the screen separation water
It contained 50-100 mg/Fe ²⁺ ion. This is presumed to be due to part of Fe ³⁺ in FeCl ₃ being reduced by biological sludge. Then screen separated water with _hydrogen peroxide _H2O2
After adding 200mg/1 hour and stirring for 1 hour, the pH was re-neutralized to 5.0, and the generated SS, mainly composed of Fe(OH) ₃ , was removed by sand filtration. It was extremely good.

[Table] When 3000 mg/FeCl ₃ is added to the mixed slurry flowing out from the biological nitrification and denitrification process,
The solid line graph A in FIG. 3 shows the results of investigating how Fe ²⁺ in the screen-separated water changes depending on the SS concentration in the mixed slurry. From this graph, it is recognized that as the SS concentration of the mixed slurry increases, the Fe ²⁺ ion concentration in the screen-separated water also increases. Note that the broken line graph B in Fig. 3 shows that the mixed slurry is not anaerobically retained, but rather is aerated with air for 4 hours before adding _FeCl3 .
in screen separated water when 3000mg/additional
This shows the Fe ²⁺ concentration. These results indicate that it is effective to anaerobically retain the mixed slurry in order to actively reduce and elute Fe ²⁺ into the screen-separated water and use it as a flocculant or oxidation catalyst. found. Next, Table 4 shows the COD-Mn of the sand filter treated water when various substances were used as oxidizing agents to oxidize Fe ²⁺ in the screen separated water.

[Table] On the other hand, when the thickened sludge (concentration 3.8%) on the wedge wire screen was left for more than about 12 hours, the dewatering performance deteriorated significantly, and there was a tendency for it to become difficult to dewater without chemical injection. If the time is within a few hours, it can be easily dehydrated using a filter press without chemical injection, with an overpressure of 4 kg/cm ² and an overtime of 10
As a result of dehydration under the conditions of 12 Kgf/cm ² , compression pressure of 12 kgf/cm 2 , and 20 minutes of pressing time, a dehydrated cake with an extremely low moisture content of 65 to 68% was obtained, and this cake can be self-combusted in a fluidized bed incinerator. It was hot.

[Brief explanation of the drawing]

Fig. 1 is a system explanatory diagram showing a typical example of the conventional method, Fig. 2 is a system explanatory diagram showing an embodiment of the present invention, and Fig. 3 is a system explanatory diagram showing a typical example of the conventional method.
The figure shows SS of mixed slurry in an example of the present invention.
It is a graph showing the relationship between the concentration and the Fe ²⁺ ion concentration of screen-separated water. 31... Fresh urine, 32... Biological treatment process, 33
... Sludge concentration section, 34 ... Thickened sludge, 35 ... Concentrated separated water, 36 ... Effluent slurry, 37 ... Mixed slurry, 38 ... Anaerobic retention tank, 39 ... Stirring tank, 40 ... Chloride phase 2 Iron, 41...Concentration process, 4
2... Thickened sludge, 43... Separated water, 44... Oxidizing agent, 45... Oxidation tank, 46... SS removal process, 4
7...Highly treated water, 48...Separated sludge, 49...
Filter press, 50...Dehydrated separated water, 51...
...Dehydrated cake.

Claims (1)

[Claims] 1. Organic waste liquid is biologically treated in a biological treatment process,
A mixed slurry of surplus sludge and treated water from the biological treatment process is obtained, and the mixed slurry is allowed to stagnate under anaerobic conditions, and at least a ferric flocculant is added to remove some or all of the ferric ions. is reduced to ferrous ions, separated into concentrated sludge and separated water in a concentration step, and the separated water is led to an oxidation step to oxidize the ferrous ions in the separated water to ferric ions. A method for treating organic waste liquid characterized by solid-liquid separation of the treated liquid. 2. The method according to claim 1, wherein the concentration step is carried out under acidic conditions of pH 4 to 5.