JPS5835117B2 - Wastewater treatment method - Google Patents

Description

Detailed Description of the Invention Methods for treating wastewater containing organic substances include activated sludge method, trickling filter method, rotating disk method, and catalytic oxidation method as biochemical treatment methods. When the protein is insoluble or poorly soluble in protein, or contains proteins or their decomposition products, coagulation-sedimentation method, coagulation-flotation method, etc. are also used.

The most common and effective method among these is the activated sludge method, but due to restrictions on raw water load and difficulty in maintenance and management, it cannot be directly applied to high-load raw water. It is difficult to treat, and fluctuations in concentration and water volume are minimized.
Must be avoided.

On the other hand, the trickling filter method and the rotating disk method alleviate the drawbacks of the activated sludge method, but have drawbacks such as low treatment efficiency and the tendency to generate bad odors.

In addition, the catalytic oxidation method is mainly limited to low-load raw water, and is often used in combination with other biochemical treatment methods.

As mentioned earlier, coagulation-sedimentation and coagulation-flotation methods, which are physicochemical treatment methods, are not suitable for wastewater containing soluble organic substances, but many of the organic substances contained in raw water are Due to their nature, the scope of application of these methods is limited and cannot be said to be universal.

The present invention is applied to the above-mentioned biological treatment method, improves the treatment efficiency of the biochemical treatment method, and makes it possible to treat particularly high-load raw water and raw water containing difficult-to-decompose substances. It is something.

Although it can be applied to any biochemical treatment method, it is particularly effective when applied to the activated sludge method.

The method of the present invention uses domestic raw water, if it is wastewater containing organic substances,
It is effective for other wastewaters, but particularly effective wastewater includes raw water for fish processing, including fish cleaning, disassembly, surimi, boiling water, etc., raw water for broiler disassembly, raw water for slaughterhouses, raw water for rice storage, raw water for fish meat processing, and raw water for storage facilities. This is wastewater with a very high BOD, and the BOD of these water reaches several thousand PPM to several hundred PPM.

In order to directly biochemically treat such wastewater, it is common to perform primary treatment or dilute it so that the BOD is at least about 1000 PPM.

Of course, BOD1000 P is required for direct biochemical treatment.
Even after the amount of PM has been reduced, treatment is difficult, and even if the activated sludge method is used, it is almost impossible to achieve a BOD removal rate of 80% or more and a treated water BOD of 100 PPM or less through one-step treatment.

Therefore, the two-stage activated sludge method, in which biochemical treatment is carried out in two stages, may result in leakage.

However, no matter what method is adopted, even if the acclimatization is carried out sufficiently and carefully, there is always a risk of bulking due to high loads, and there is a risk of bulking due to high loads.
r High removal rate such as over 90%, especially BOD and 150%
It is difficult to keep it below PPM.

The present inventor has conducted extensive research on methods for treating such wastewater more efficiently, and as a result, the present invention has been achieved.

The method of the present invention will be explained in detail below.

The method of the present invention involves continuously or intermittently adding lower fatty acids or/and salts thereof to raw water or an aeration tank or other treatment tank in a biochemical treatment method.

It goes without saying that the lower fatty acid to be added can be applied to the present invention as long as it is in the form of an acid or a salt or can be easily converted into the substance by hydrolysis.

Among the lower fatty acids, acetic acid is the most preferred, but propionic acid, butyric acid, and formic acid are also the most effective.

Although the method of the present invention is most effective in the activated sludge method, it is of course also effective in other biochemical treatment methods, such as the trickling filter method and the rotating disk method.

Preferable wastewater to which the present invention is applied is the raw water mentioned above, but the reason why it is difficult to remove BOD from these raw waters is not clear, but these wastewaters contain high concentrations of undegraded protein and other substances. This is thought to be because it contains a large amount of molecular weight substances.

In biochemical treatment methods, such as the activated sludge method, microorganisms such as various bacteria, protozoa, microorganisms, and phytoplankton coexist, and these form a food chain.The balance between each microorganism is optimal. When , the overall processing efficiency should be the longest.

From this perspective, the present inventor has researched effective biochemical treatment methods for these wastewaters and has found that adding lower fatty acids is effective for raw water that is difficult to treat due to its high protein content. This discovery led to the present invention.

Lower fatty acids are formic acid, acetic acid, fropionic acid, butyric acid, valeric acid, and caproic acid with 1 to 6 carbon atoms, and can also be added in the form of salts such as sodium salt, potassium salt, calcium salt, and ammonium salt. It is possible.

In the present invention, acetic acid or its salts such as acetic acid, sodium acetate, potassium acetate, ammonium acetate, calcium acetate, etc. are particularly effective.

Furthermore, those that can be easily converted into fatty acids by hydrolysis etc. in wastewater are also included in the present invention.

Addition amount is 1-200 PPM to raw water, 5% to raw water
~60 PPM is preferred, but the appropriate amount is selected depending on the properties of the raw water, especially the substrate.

These compounds may be added to the raw water or to the return sludge or to the aeration tank.

Particularly when treating difficult-to-decompose substances, activated sludge must be acclimated, but an effective method is to continue acclimatization without adding acetic acid or the like during this process.

In other words, acclimatization is generally carried out by reducing the water volume and concentration load at the beginning, and gradually increasing the load one by one after confirming that the activated sludge has been acclimatized, the treated water has not deteriorated, and the SV value of the activated sludge is normal. At this time, the amount of added substances increases at the same rate as acclimatization progresses.

In general, the initial amount added is within 10% of the specified amount, and 2.
It often takes a week to a month, during which time the amount increases to a predetermined amount.

During this period, continuous addition is best, but once a day
Almost no adverse effects are observed even when added in batches.

However, if the addition period is longer than L2, the water quality will fluctuate, which is not preferable in terms of microbial acclimation.

The same holds true after entering steady operation.

Special application methods include cases where the removal rate decreases during biological treatment of raw water containing highly loaded and persistent characteristics such as those mentioned above, or when the SVI becomes abnormally large. On the other hand, it is also possible to improve the processing conditions by temporarily adding about 50 to 200 ppm of lower fatty acids.

Example 1 BOD830 obtained by pressure flotation treatment of fisheries weighted F raw water
ppm of primary treated water to MLS8 according to the standard activated sludge method.
4000 ppm, BOD load 0.61kg/kg,
Processed at SS, D, residence time 8HV.

Acetic acid was added to the aeration tank, and the BOD of the treated water was measured.

The results are shown in Table 1, and it is recognized that the quality of treated water is improved by adding acetic acid.

Example 2 Raw water for seafood processing with a BOD of 1200 ppm was subjected to ML S
82500 ppm BOD load 0.53 ky/kg
, SS, D, *Processed using a long-time aeration method with a residence time of 20 HV.

Pyruvic acid or butyric acid was added to this to see the effect.

The results are shown in Table 2.

Example 3 Pulse sound raw water was filtered through a vibrating sieve, diluted 6 times, and then treated by a long-time aeration method.

BOD of raw water is 880 ppm, MLS8200
0BOD load 0.44 kg/kg, SS, D,
The treatment was carried out by a long-time aeration method with a residence time of 24 HV.

Sodium acetate was added twice a day at 90 ppm.

Example 4 Raw water from a fish processing factory with a BOD of 685 ppm was treated using a rotating disk method.

Treated water with residence time of 6 hours **BOD 174p
It became pm.

At this time, 70 ppm of fropionic acid was temporarily added.

BOD was measured 3HV after addition.

Example 5 Raw water from broiler disassembly was treated using a standard activated sludge method.

BOD of raw water is 420 ppm and ML S 83000
ppm BOD load 0.67kg/kg, SS, D.

At a residence time of 5 HV, the treated water BOD was 67 to 79 ppm.

On the other hand, when acetic acid was added, the treatment efficiency was significantly improved as shown in Table 5.

Claims (1)

[Claims] 1. A method for biochemically treating wastewater containing organic substances, which comprises adding 1 to 200 PPM of a lower fatty acid having 1 to 6 carbon atoms and/or a salt thereof to the wastewater.