JPS6231637B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for biologically treating and purifying organic wastewater, such as sewage, human waste, industrial wastewater, and other wastewater, and in particular for denitrification deposited on the medium of the denitrification process. This paper relates to a biological denitrification method for wastewater that uses nitrogen bacteria. This biological denitrification method consists of activated sludge method, granular,
It is broadly divided into biological fixed bed methods, which use microorganisms attached to lump-like, plate-like, net-like, rod-like, fibrous, and tubular media. A fixed bed method has been put into practical use that can maintain purity and high concentration and allow for downsizing of equipment. Conventional fixed bed denitrification treatment usually converts nitrogen compounds in wastewater, such as NH ₄ , into NO ₂ or NO ₃ during the nitrification process.
After nitrification to NOx (hereinafter referred to as NOx), NOx is reduced and decomposed to _N2 gas (denitrification) in a denitrification process in which a fixed bed or fluidized bed is formed by a medium to which denitrifying bacteria are attached. It is. In order to reuse the medium in this method, the medium is removed from the denitrification process, the bacteria adhering to the medium are separated from the medium, and the medium is returned to the denitrification process. On the other hand, the bacterial cells are dehydrated, dried, and incinerated, but this method requires a large amount of energy to detach because the bacterial cells adhere strongly to the medium, and the detached bacterial cells are pure cultures. Therefore, it has drawbacks such as extremely poor dehydration properties. There is also a method that uses anaerobic digestion to solubilize the bacterial cells on the medium and separate them from the medium, but this also requires a long time to solubilize the medium and requires reprocessing of the digestion fluid. It has the disadvantage of being All of these conventional methods for treating surplus bacteria are complicated in operation and have the above-mentioned drawbacks, which are problems that are of concern to the industry. In particular, improving the treatment method for surplus denitrifying bacteria has become a major issue, but this is because the growth rate of the nitrifying bacteria used is 0.1 growth rate/NH ₄ -N (g/g). The growth rate of denitrifying bacteria is 0.4 bacterial growth/NO ₃ -N (g/g), which is four times the amount of nitrifying bacteria per nitrogen removed, even for methanol-assimilating denitrifying bacteria with a small bacterial cell yield. It's for a reason. The present invention eliminates the various drawbacks of these conventional methods, and allows denitrification to be carried out efficiently and extremely easily without pulling out the bacteria from the denitrification process or separating the bacteria from the medium. The purpose of this study is to provide a biological denitrification method for wastewater that enables economical treatment and disposal of surplus denitrifying bacteria. The present invention provides a denitrification treatment system in which a plurality of denitrification processes are connected in series, and the amount of organic carbon source injected in each denitrification process is sufficient for the growth of each denitrification bacteria,
By alternately adjusting the amount to zero or insufficient for the growth of denitrifying bacteria, the denitrifying bacteria grown on the medium by methanol denitrification reaction (exo-breathing denitrification reaction) can be reduced by methanol. Excess denitrifying bacteria that have grown on the medium are reduced through a denitrification reaction using the constituent components of the denitrifying bacteria themselves as reducing agents (endo-respiration type denitrifying reaction), and then the denitrifying bacteria are removed again by a denitrifying reaction using methanol. This is a biological denitrification method that utilizes multiple denitrification steps to propagate the bacteria so that a constant amount of denitrification bacteria is maintained throughout the process. Next, an embodiment of the present invention will be described based on the drawings. The waste water 1 containing NH ₃ is completely or partially nitrified to NO ₃ in the nitrification step 2, and the nitrified water 3 containing only NO ₃ is directly It flows into the denitrification step 4 together with methanol 6, and most of the NO ₃ is denitrified, and the remainder is denitrified in the denitrification step 5 without methanol 6, and after the denitrification is completed, it is discharged as treated water 7. In this case, part or all of the wastewater 1 can be directly flowed into the denitrification process 4 through the bypass channel 1' and treated, if necessary. On the other hand, in the denitrification step 4, denitrifying bacteria proliferate due to the denitrification reaction with methanol 6, and in the serial denitrification step 5, the bacterial cells gradually grow due to the endorespiratory denitrification reaction using the bacterial component itself as a reducing agent. Decrease. The denitrification rate of endorespiration type is approximately 1/5 to 1/10 of that of methanol 6. Therefore, the denitrification step 4,
If the amount of bacteria in step 5 is the same, it will be efficient to remove 80 to 90% of the NOx flowing into denitrification step 4, and remove the remaining 20 to 10% of NOx in the next denitrification step 5. Can be denitrified. Before the denitrification bacteria in denitrification processes 4 and 5 increase or decrease excessively, injection of methanol 6 in denitrification process 4 is stopped or reduced, and methanol 6 is injected in denitrification process 5 to denitrify the bacteria. Before the denitrifying bacteria in denitrifying processes 4 and 5 excessively decrease and increase again, injection of methanol 6 in denitrifying process 5 is stopped, and methanol 6 is again injected into the previous denitrifying process 4. By repeating the denitrifying operation, the amount of denitrifying bacteria in the entire denitrifying process can be quantitatively maintained. Note that the number of bacterial cells that have proliferated can be reduced by reducing the injection amount to an amount insufficient for the growth of bacterial cells in the denitrification process, without necessarily stopping the injection of methanol 6 completely. However, the rate of decrease is slower than when methanol is not injected. However, it is effective when the number of bacterial cells in the denitrification process is relatively small overall. Furthermore, the purpose of the denitrification process can be achieved if at least two processes are connected in series, but it is better to further connect the denitrification process 8 after the latter denitrification process 5, and to have three or more processes, to reduce the amount of methanol injected and the bacteria in the process. Preferable for regulating body mass. Methanol 6' may also be injected into the subsequent denitrification steps 8 and below, if necessary. Switching between methanol injection and non-injection can be performed manually by observing with the naked eye the increase or decrease in the amount of denitrifying bacteria attached to the medium. In this case, the method of determining the amount of organic carbon source to be injected that is insufficient for the growth of denitrifying bacteria during visual observation is determined empirically by looking at the amount of denitrifying bacteria attached to the medium. If the amount is sufficient, the amount of bacteria will increase and a biofilm will grow. On the other hand, if the amount is insufficient, the biofilm will shrink and become smaller, and all you have to do is notice that it flows out with the runoff water. For example, when treating small-scale wastewater, a transparent or translucent plastic structure is used in the denitrification process, so the amount of growth can be observed from the outside, and the amount of growth can be observed from the outside.
In addition, when using a structure made of opaque materials such as steel plates, it is possible to increase the growth of denitrifying bacteria inside the tower by attaching a viewing window vertically on the side of the denitrification tower, such as the one installed in sand filter towers. The amount can be observed. By the method described above, while observing the amount of denitrifying bacteria in the tower, it is possible to determine by trial and error the amount of organic carbon source to be injected that is insufficient for the growth of denitrifying bacteria.
That is, the amount of organic carbon source injected may be reduced so that the amount of denitrifying bacteria gradually decreases, or the injection may be stopped. In particular, the amount insufficient for growth is an amount that is sufficient if an organic carbon source is added and the bacteria grow, and an insufficient amount if the bacteria do not grow, but it should be determined based on economic changes. . In other words, based on the state of the bacteria at one time, judgments are made based on the state of the bacteria at the next time.
In other words, if the next time there are more bacteria than before and the biofilm is growing, it is sufficient, and the bacteria will decrease (shrink).
If the biofilm is unstable, it is determined that the amount is insufficient. In addition, when the medium is a granular medium, the height of the medium layer increases or decreases depending on the growth rate of denitrifying bacteria on the medium. If detected using an interfacial (interface) meter, it is possible to control whether methanol is injected or not injected unattended. It is also possible to set the medium transfer time using a timer and transfer the medium intermittently. In this case, it is sufficient to empirically set the optimum transfer time based on the increase/decrease in the layer height which varies depending on the set time. The amount of bacterial cells and the amount of denitrification in each of the denitrification steps can be adjusted by adjusting and controlling the distribution of the methanol injection step and non-injection step and the increase/decrease of the methanol injection amount simultaneously or individually. I can do it. Furthermore, when the amount of organic carbon source injected is alternately adjusted to an amount sufficient for the growth of each denitrifying bacteria and an amount insufficient for the growth of the denitrifying bacteria to zero, each is performed in at least a separate denitrification process. It is better to
It is considered that the organic carbon source is injected when the number of denitrifying bacteria in the denitrification process decreases, and when the number of denitrifying bacteria increases, the amount of the organic carbon source is stopped or the amount of injection is reduced. In this way, if the amount of organic carbon source added is controlled in accordance with the growth rate of denitrifying bacteria, the amount of bacteria in the denitrifying process can be maintained within an appropriate range, which eliminates the inconveniences that may occur during uncontrolled operation. be able to. That is, in a denitrification tower into which a sufficient amount of organic carbon source has been injected, denitrification bacteria multiply excessively during the operation period and separate from the adhesion medium or flow out of the tower together with the adhesion medium.
If the pipes become blocked or solids in the treated water increase, or if denitrifying bacteria proliferate excessively in the denitrification process where a sufficient amount of organic carbon source has been injected, all of the inflowing NOx will be denitrified, resulting in The denitrification tower in the stage tower becomes completely anaerobic and the denitrifying bacteria rot and die (especially when the water temperature is high), so the quality of the treated water deteriorates and once the denitrifying bacteria die, it takes a considerable amount of time for them to grow again. Since it takes several days, there are problems such as methanol is not used during that time and the processing deteriorates further, but the present invention can be processed without these drawbacks. According to the present invention, in a denitrification process in which a plurality of denitrification processes are connected in series, the amount of organic carbon source injected in each denitrification process is sufficient for the growth of each denitrification bacteria, By alternately adjusting the amount of methanol to be insufficient for the growth of methanol, the denitrifying bacteria grown on the medium by methanol denitrification reaction (exo-breathing denitrification reaction) are reduced in methanol, that is, the composition of the denitrifying bacteria. A method in which excess denitrifying bacteria that have grown on the medium are reduced by a denitrifying reaction using the component itself as a reducing agent (endo-respiration type denitrifying reaction), and then the denitrifying bacteria are grown again by a denitrifying reaction using methanol. By using multiple denitrification processes, a constant amount of denitrifying bacteria is maintained throughout the process, so there is no need for equipment for separating excess bacteria, dehydration, drying equipment, incinerators, etc. Moreover, the purification efficiency of the denitrified water has been significantly improved, and the processing operation is extremely simple, as the treatment of excess bacteria can be done by simply operating valves, etc., and operation management is also easy. Since purification can also be performed, the conventional drawbacks associated with the treatment and disposal of surplus denitrifying bacteria can be eliminated, and the denitrification treatment can be significantly improved, eliminating the need for processing costs for surplus bacteria, and further improving the internal respiration type. Denitrification also saves methanol, making it possible to significantly reduce processing costs. Next, an embodiment of the present invention will be described. Experimental equipment Fluidized bed denitrification tower 2 cylindrical columns (φ200mm, height 1600mm, effective volume 50.2) Experimental conditions Experimental wastewater Artificial nitrification solution NO ₃ -N 30mg/ (adjusted by adding NaNO ₃ to dechlorinated tap water) Wastewater treatment amount 2000/day Fluidized bed medium Sand The amount of bacteria in the fluidized bed varied with the height of the fluidized bed Fluidized bed height at the start of the experiment 1st column 600mm 2nd 1000mm Methanol injection at the start of the experiment Amount 1st tower 130g/day 2nd 0g/day Experimental results [Table]

[Brief explanation of the drawing]

The drawing is a flow sheet of an embodiment of the method of the invention. 1...wastewater, 2...nitrification process, 3...nitrified water, 4,
5, 8...Denitrification process, 6,6'...methanol, 7...
treated water.

Claims (1)

[Scope of Claims] 1. When performing denitrification treatment to remove oxidized nitrogen (NOx-N) from wastewater using denitrification bacteria attached to a medium, wastewater is subjected to multiple denitrification processes in series. The amount of organic carbon source injected in each denitrification process is adjusted alternately to an amount sufficient for the growth of each denitrifying bacteria and an amount that is zero or insufficient for the growth of the denitrifying bacteria. A biological denitrification method for wastewater characterized by the following. 2. The method for denitrifying wastewater according to claim 1, wherein the denitrification step involves treating the wastewater through at least three steps. 3. In the denitrification step, the amount of organic carbon source injected is sufficient for the growth of denitrifying bacteria in at least one of the plurality of denitrification steps, and the amount is reduced from zero to the growth of denitrifying bacteria in at least one step. A method for denitrifying wastewater according to claim 1 or 2, wherein the wastewater is treated in an insufficient amount. 4. In the denitrification process, the organic carbon source is injected when the number of denitrifying bacteria in the denitrification process decreases, and when the number of denitrifying bacteria increases, the process is stopped or the amount is reduced to be insufficient for the growth of the denitrifying bacteria. A method for denitrifying wastewater according to claim 1, 2, or 3. 5. A patent claim in which the denitrification step is performed using a granular medium, and the amount of organic carbon source injected is controlled by increasing or decreasing the layer height of the medium caused by increasing or decreasing the number of denitrifying bacteria. A method for denitrifying wastewater according to item 1, 2, 3 or 4.