JPH0134680B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of treating organic carbon compounds that cause BOD in water and wastewater using microorganisms. [Prior art] Biological treatment methods for water or wastewater include:
Various methods are used, such as activated sludge treatment, but in any method, if reduced nitrogen compounds (hereinafter abbreviated as _NH3 ) are contained in the raw water, nitrifying bacteria will occur. May produce NO _x ^- (NO ₂ ^- and/or NO ₃ ^- ). [Problems to be solved by the invention] When NO _x ^- is generated, for example, in activated sludge treatment, the N ₂ gas generated by denitrification in the settling tank adheres to the sludge, causing SS (suspended) in the treated water.
solids) and worsen water quality. In addition, when NO ₂ ^- is generated by nitrification, it is caused by NO ₂ ^- .
This was a problem of concern to water treatment engineers because COD increased and NO ₂ ^- itself was harmful. The present invention was made to eliminate the drawbacks of the conventional biological treatment methods, and provides a method for reducing _NOx in treated water by suppressing the activity of nitrifying bacteria in mixed microorganisms. . [Means for Solving the Problems] The present invention provides a method for treating a liquid containing an organic carbon compound and NH ₃ using microorganisms.
An anaerobic process is provided in which only the returned sludge is introduced, and all or part of the returned sludge is allowed to exist under anaerobic conditions for 20 hours or more in the anaerobic process to increase the activity of microorganisms that oxidize nitrogen compounds and produce NO _x ^- . An organic carbon compound and reduction characterized in that it suppresses the production of NO _x ^- in an aerobic process by reducing the activity of organic carbon compound-degrading bacteria and then circulating it in an aerobic process. This is a method of biologically treating water or wastewater containing nitrogen compounds using an activated sludge method. Next, the present invention will be explained in detail with reference to the drawings. In the drawings, reference numeral 1 indicates a raw water introduction pipe, 2 indicates a sludge return pipe, 3 indicates an aeration tank, 4 indicates a solid-liquid separation tank, 5 indicates a separated water discharge pipe, 6 indicates an excess sludge discharge pipe, and 7 indicates an anaerobic tank. In Figure 1, raw water containing organic carbon compounds and NH ₃ is introduced from a raw water introduction pipe 1 into an aeration tank 3 under aerobic conditions, and after the contained organic carbon compounds are oxidized and decomposed, they solidify. Separated water (treated water) and sludge are separated in the liquid separation tank 4, and separated water discharge pipe 5
is discharged from. On the other hand, the sludge separated in the solid-liquid separation tank 4 is extracted from the lower part of the solid-liquid separation tank 4, a part of which is discharged from the surplus sludge discharge pipe 6 as surplus sludge, and the remainder is returned as return sludge. In the present invention, the sludge is returned to the aeration tank 3 after passing through the sludge return pipe 2 and undergoing anaerobic treatment in the anaerobic tank 7 for 20 hours or more. In the anaerobic tank 7, the sludge sent from the sludge return pipe 2 may be stirred in the atmosphere or left standing. When stirring, it is preferable to stir slowly using a rotating paddle or the like. Naturally, it is more effective to maintain anaerobic conditions by using a closed tank that does not allow air to enter.In this case, stirring with a rotating paddle or gas stirring that circulates the internal gas can provide powerful stirring. It is possible to do so. If NO _x is present in the returned sludge, NO _x
The anaerobic treatment time for returned sludge is determined by taking into account the disappearance time of sludge. For example, if it takes 5 hours for NO _x to disappear, the anaerobic treatment time is at least 25 hours (20
+5 hours) or more is required. Another embodiment of the invention is shown in FIG. FIG. 2 shows an example in which a part of the returned sludge is divided into parts for anaerobic treatment, part of which is returned to the anaerobic tank and the remainder to the aeration tank, and the entire amount of raw water is injected into the aeration tank. Example 1 An activated sludge mixture was collected from an activated sludge aeration tank of organic wastewater undergoing nitrification, and NO _x ^- in the mixture was collected.
The activated sludge washed out by centrifugal washing was stored in an airtight container, and the organic matter oxidation activity and NH ₃ nitrification activity of the activated sludge were measured three times over time. Acetic acid was used as the sample organic substance. The results are shown in Figure 3. In FIG. 3, the dotted line indicates organic matter decomposition activity, and the solid line indicates nitrification activity. The results shown in Figure 3 show that when the nitrification activated sludge is left under anaerobic conditions for about 20 hours, the nitrification activity of the nitrification activated sludge is significantly lower than the organic matter oxidation activity. Additionally, activated sludge kept under anaerobic conditions recovers its nitrification activity when returned to aerobic conditions, but in order to achieve the purpose of the present invention, it is necessary to keep it under anaerobic conditions for at least 20 hours. This was confirmed separately. Example 2 Normal artificial wastewater consisting of NH ₃ , acetic acid, yeast extract, and various metal salts was used as the test raw water.
Activated sludge treatment was performed using the flow shown in FIGS. 1 and 2. The BOD of artificial wastewater, NH ₃ ^- N, capacity of the anaerobic tank, aeration tank, MLSS concentration in the aeration tank, and water temperature in the aeration tank were as follows. BOD of artificial wastewater 2000mg / NH ₃ ^- N of artificial wastewater 500mg / Aeration tank capacity 20 Anaerobic tank capacity 30 (closed type) Aeration tank MLSS 4200-5800ml/g Aeration tank water temperature 29-32℃ Results are calculated based on raw water inflow to both tanks Table 1 shows the amount and the amount of returned activated sludge.

〔Effect of the invention〕

According to the present invention, in the aerobic treatment of wastewater containing _NH3 , an anaerobic step is provided in which only the returned sludge is introduced, and in the anaerobic step, all or part of the returned sludge is kept under anaerobic conditions for 20 hours or more. By returning the sludge to the aeration tank, it is possible to selectively suppress only the nitrification activity of the sludge, thereby suppressing the production of _{NO x} ^{- .}
It is possible to solve various problems associated with the occurrence of

[Brief explanation of drawings]

FIG. 1 is a flowchart for explaining one embodiment of the present invention, and FIG. 2 is a flowchart for explaining another embodiment. Moreover, FIG. 3 is a diagram showing the relative activities of nitrification and organic matter oxidation when activated sludge is subjected to anaerobic treatment, and FIG. 4 is a diagram showing a comparative example. 1...Raw water introduction pipe, 2...Activated sludge return pipe, 3
...Aeration tank, 4...Solid-liquid separation tank, 7...Anaerobic tank.

Claims (1)

[Claims] 1. In a method of treating wastewater containing organic carbon compounds and reduced nitrogen compounds in an activated sludge treatment step, an anaerobic step is provided in which only returned sludge is introduced, and at least a portion of the returned sludge is treated in the anaerobic step. 1. A biological treatment method for organic wastewater, which comprises allowing organic wastewater to exist under anaerobic conditions for 20 hours or more, and then circulating it to the aerobic step of the activated sludge treatment.