JPS6352957B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be applied to urban sewage, human waste, BOD, etc.
The present invention relates to a method for treating organic wastewater containing COD, SS, _NH4 -N, etc. as main pollutants by biological means and chemical means. Conventionally, the mainstream treatment technology for urban sewage or human waste has been the activated sludge method or its modified methods, and by applying these treatment technologies, BOD and SS in the wastewater can be efficiently removed. However, COD,
Removal of nitrogen and phosphorus was difficult, and the removal function of COD was particularly insufficient. Therefore, conventionally, when it is necessary to remove pollutants such as COD, it has been common practice to add a tertiary treatment step after the biological treatment step. The main treatment technologies commonly used in this tertiary treatment step are the coagulation sedimentation method and/or the activated carbon adsorption method, and these treatment technologies are selectively applied depending on the required quality of the treated water. was. Among these tertiary treatment techniques, the coagulation-sedimentation method is usually applied for the purpose of polishing the secondary treated water, and is effective in removing chromaticity components, COD, and SS from the wastewater. The flocculant used in this treatment technique is generally sulfuric acid band [Al ₂
(SO ₄ ) ₂ ], ferric chloride [FeCl ₃ ], or slaked lime [Ca
(OH) ₂ ], but the biggest advantage of this method is
If the chemical injection rate is aimed at the above treatment, it is possible to simultaneously and reliably remove phosphorus dissolved in the wastewater, which is why it is relatively often applied to tertiary treatment. However, the coagulation-sedimentation method has the following serious practical drawbacks that negate the above advantages. In general, the amount of chemical injection is large (Al/P injected into the secondary treated water is 2 to 3, Al/P injected into the aeration tank).
4 to 5), therefore the amount of sludge generated is large (processing cost is high). Sludge flocs have poor settling properties (requires a large land area). Coagulated sludge generally has poor thickening properties (the amount of sludge that must be treated is large). Similarly, sludge has poor dewatering properties (large load on sludge treatment facilities). In the treatment process, large amounts of chemicals and flocculated sludge must be handled (daily operation management and operation are troublesome). The treatment and disposal of phosphorus concentrated in flocculated sludge is not considered at all (it is difficult to evaluate it as a substantial phosphorus removal technology). For the reasons mentioned above, it is possible to overcome these technical limitations and replace the coagulation-sedimentation method, i.e., it does not use chemicals and therefore generates no sludge or only generates very little sludge. There is a need to establish COD removal technology that can be treated at low cost. On the other hand, among the existing technologies, activated carbon adsorption method has received high praise as a technology that can reliably remove COD to a low level without generating sludge that is difficult to treat. Considering this, there are more technical problems than the coagulation-sedimentation method. In other words, the mechanism of COD removal using the activated carbon adsorption method is not a method that biologically decomposes and removes COD components as in biological treatment, for example, but rather uses activated carbon as an adsorption concentration medium to absorb COD components in wastewater through the pores on the surface of the activated carbon. It simply adsorbs and concentrates. Therefore, when the COD component reaches the adsorption saturation amount of the activated carbon, the COD component begins to leak into the wastewater, so it is necessary to regenerate it. A few methods have already been established as activated carbon recycling technology, but in any case, a large amount of chemicals or a large amount of energy must be used, which not only makes the recycling cost extremely high. There is a problem in that recycled wastewater must be treated. In any case, the activated carbon adsorption method is a treatment technology that simply adsorbs and concentrates pollution-causing substances in wastewater, so strictly speaking, it cannot be evaluated sufficiently as a treatment technology, and the drawback is that the treatment cost is high. Therefore, it is difficult to say that this is a processing method that is widely applied in actual processing. As described above, as with the activated carbon adsorption method, there is a strong demand for the development and establishment of improved methods of this technology or alternative technologies. The present inventors have discovered a simple, low-cost, and reliable method that can replace the coagulation-precipitation method or activated carbon adsorption method.
We have been searching for a method to remove COD, but recently we have established a biophysicochemical COD removal technology that adds microbial functions to the physicochemical treatment technology in the most rational and efficient way. We have completed a treatment process that has the ability to remove COD. That is, the process of the present invention consists of two steps of biophysical and chemical treatment steps.
BOD components in the wastewater to be treated are removed as much as possible through a stepwise process, and at this stage, the
BOD/COD (ratio of BOD and COD) should be 0.5 or less,
The wastewater, whose main components are components that are inherently difficult to biodegrade, is introduced into the second stage biophysical and chemical treatment process, and COD is adsorbed and concentrated on the activated carbon surface.
This is a method for removing COD from wastewater, which is characterized by biologically decomposing and removing components under aerobic conditions. The gist of the technical idea of the present invention is to ultimately concentrate COD components contained in wastewater that are difficult to biodegrade on the surface of activated carbon and/or other adsorption media, and to continuously release them through the functions of living organisms. exists in the concept of permanent regeneration, and various process developments can be considered based on this principle, the implementation of which will be described below. So-called secondary treated water obtained by treating municipal sewage by the activated sludge method is first introduced into a solid particle packed bed type biological filtration process. A normal packed bed type filter tower is used in this process, and one type of filter material, such as activated carbon, sand, anthracite, or garnet, is placed inside the tower up to about 1/2 of the operating liquid level. Or it is filled with two or more types. The secondary treated water is passed in a downward flow direction from the upper part of the apparatus, while the inside of the packed bed is maintained under aerobic conditions by air supplied from the lower part of the apparatus. The air supply rate is set in accordance with the particle size of the filled overfill material to such an extent that the overfill material does not flow, and the overfill material in a fixed state provides overfunction. When secondary treated water is introduced into such equipment (process) and passed under aerobic conditions, BOD, nitrogen, and
Aerobic microorganisms gradually proliferate on the surface of the overmaterial due to nutrient substances such as phosphorus, and BOD in the liquid is decomposed and removed as much as possible by the metabolic activities of these microorganisms.
At the same time, the SS contained in the secondary treated water is also effectively removed by the biological overaction of the filled overfill material. The treatment conditions for the biological process should be such that BOD, which is easily biodegradable, is preferentially degraded, that is, the effluent from this process should be
It is important to set the BOD/COD so that it is significantly reduced relative to the inflow water. In this process
If the BOD removal function is insufficient and the BOD/
When COD is larger than a certain value, that is, when the amount of BOD is too large relative to the amount of COD, the COD removal ability in the next adsorption step using the fluidized medium method is significantly reduced. The reason for this is that microorganisms inherently have a so-called dioxy effect, and for example, in secondary treated water, there are substances that are easily assimilated by microorganisms (easily biodegradable) and substances that are difficult to assimilate (hardly biodegradable). This is because when substances are present at the same time, the microorganisms preferentially decompose and utilize substances that are easily assimilated, and therefore substances that are difficult to assimilate remain in the liquid until the end. Therefore, when a liquid with a large BOD/COD flows into the fluidized medium adsorption step, which is the second step of the present invention,
Although COD removal is expected, BOD (substances that are easily biodegradable) is preferentially decomposed, and COD (substances that are difficult to biodegrade), which is the target of removal, is hardly decomposed. As mentioned above, the secondary treated water treated by the biological filtration process which is the first step in the present invention
It is essential that BOD/COD be kept below a certain value, but as a result of various studies on this issue, we have found that
When processed so that BOD/COD is 0.5 or less,
The COD removal function of the adsorption process, which is the second step, does not deteriorate and maintains high COD for an extremely long period of time.
It was confirmed that the removal rate was maintained. Therefore, BOD/COD is reduced by biological processes.
The secondary treated water determined to be ≦0.5 is then introduced into the adsorption step. The equipment that is the core of this process is
A draft tube for airlift is built into a normal circular tank or square tank, and air is introduced from the bottom end of the draft tube. The zeolite etc. to be used is 10~
30% is added, and the inflow water and adsorption medium are sufficiently circulated and mixed by air lift action. Furthermore, this device is equipped with a mechanism that separates the liquid and fluid medium and extracts only the liquid. As mentioned above, BOD/
When the secondary treated water that has been treated to COD≦0.5 is passed through the adsorption process for a certain period of time under BOD starvation conditions, COD
Microorganisms that can decompose and assimilate the components naturally proliferate, and COD is effectively removed from the secondary treated water. As described above, according to the present invention, the following industrially outstanding effects can be obtained, and COD, which has been extremely difficult to remove in the past, can be effectively removed at low cost. It is an extremely rational treatment technology that combines physicochemical treatment technology with the metabolic action of microorganisms, and is capable of removing not only persistent COD but also other pollutants such as BOD and SS at a high rate. can. Since no chemicals are used, processing costs are extremely low, and no sludge, which is difficult to process, is generated, as is the case with the coagulation-sedimentation method. The energy required for biological regeneration of the fluidized medium (activated carbon, zeolite, etc.) for the adsorption process can be replenished simply by supplying the oxygen necessary for respiration of microorganisms, resulting in significant energy savings compared to conventional methods. Since the fluid medium is bioregenerated, it can be used repeatedly on a semi-permanent basis. Representative examples of the present invention are shown below. Examples Experimental example 1 in which secondary treated water obtained by treating underground water by the activated sludge method was treated by the process of the present invention as a common test raw water, and Experimental example 2 in which it was treated only by the adsorption step of the present invention. We compared their COD removal abilities. Comparison of the performance of both processes will be conducted only after the microorganisms have naturally grown sufficiently in the medium of each process and the functions corresponding to each process have been fully recognized (by passing the sample raw water through the medium). This study was conducted using data from approximately 3.5 months after the start of the study. The treatment exclusion conditions for each experimental example are shown in Table 1, and the treatment results are shown in Tables 2 and 3. In addition, in these tables, the first step means the biological permeation step, and the second step means the adsorption step.

【table】

【table】

[Table] Measurement A comparison of Tables 2 and 3 shows that the COD of the water treated by the process of the present invention is significantly lower.

Claims (1)

[Claims] 1. Organic wastewater containing BOD, SS and COD is passed through a solid particle packed bed under aerobic conditions.
Performs partial removal of BOD, SS, and COD.
An organic wastewater treatment method comprising a first step in which the COD is reduced to 0.5 or less, and a second step in which the effluent from the first step is introduced into an adsorption step using a fluidized medium under aerobic conditions for treatment. How to remove COD. 2. Claim 1, wherein the first step is performed using one or more selected from activated carbon, sand, anthracite, and garnet as the solid particles forming the solid particle packed bed. The method described in section. 3. The method according to claim 1 or 2, wherein the second step is performed using at least one of activated carbon and zeolite as the fluidizing medium.