JPS6255917B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for removing oil, protein, and BOD contained in wastewater generated during the processing of marine products, and easily recovering high-grade fish oil, fish meal, and fertilizer. At seafood processing plants, thawing, cutting, and
The water quality of seafood processing wastewater generated from processing processes such as washing, boiling, seasoning, surimi, and boiling varies greatly depending on the water amount, season, and processing method. BOD is 3000 to 12000 ppm, and oil content is 1000 ppm. ~
4000ppm, SS is 1000-5000ppm, and has characteristics such as a high content of emulsionized nitrogen-containing substances (amino acids, proteins, peptides, etc.). Therefore, when treating seafood processing wastewater, in order to use biological oxidation as the final step, the oil content in the pretreatment step must be within the allowable concentration range for microbial purification ability.
Effective removal of SS, BOD, etc. is necessary.
If removal is insufficient, the microbial purification ability will decrease due to oil accumulation during the biooxidation process, and a large amount of inert SS will be produced.
Problems such as the outflow of purifying microorganisms due to the influx of water, and the modification of purifying microorganisms due to a decrease in oxygen supply capacity due to overloading occur. On the other hand, the pollutant components contained in seafood processing wastewater are mainly composed of oil, protein, etc., and although resources should originally be recovered effectively, it is complicated to separate the oil and protein and turn them into products. Additional post-processing is required. In general, when treating seafood processing wastewater, the treatment method before the biological treatment process is to remove the solid content in the wastewater with a screen, then allow the oil content in the wastewater to float naturally to remove some of the oil content. , adjust the pH to the isoelectric point of the protein at 3 to 6 using an inorganic acid, turn the protein and oil into coarse flocs by the coagulation effect produced by adding sodium alginate, sodium polyacrylate, etc., and dissolve the air by pressurizing the treated water. A first method in which the recycled water is led to a flotation separation tank and separated into treated water and froth with condensed oil and protein.As a flotation method in the first method, the froth and treated water are separated by air bubbles generated by electrolysis. The second method,
After the oil content in the wastewater is floated and separated using circulating pressurized water, a portion of the excess sludge generated in the biological treatment process is mixed with the wastewater from which the oil content has been removed, and protein is absorbed using the flocculation and adsorption properties of microbial flocs. There is a third method in which mixed flocs of microorganisms and proteins that have been captured are floated and separated using circulating pressurized water; Since it is necessary to increase the amount of circulating water to generate a large amount of air bubbles necessary for flotation, the amount of circulating water increases, and it is inevitable that the flotation separation tank becomes too large. Further, in the second method, since it is necessary to generate a large number of bubbles, the amount of electric power increases, resulting in an increase in running costs. Furthermore, in the first and second methods, the floss separated in the flotation tank contains a large amount of oil, so when dewatering the floss,
Drum filters, press filters, belt filters, etc. are difficult to use, assuming that a flocculant that is approved as a food additive is used, because the oil clogs the cloth and reduces the dehydration effect, and screw filters are difficult to use. In the press, it is necessary to perform a heating operation at the same time and use a method for dehydration. In this case, the extracted oil has already been oxidized by heat and has no value as a high-grade fish oil as it is.
Further reduction operations are required to recover it as high-grade fish oil. The oil and water that has been squeezed out are collected in an oil-water separation tank, and the water is returned to the isoelectric treatment tank or activated sludge treatment tank, but it contains a large amount of soluble protein and BOD generated by heating, and is loaded. will increase. In addition, when solid foods containing protein are dried and used as feed, there is a risk of spontaneous combustion due to the large proportion of fish oil contained in the product, and when mixed with fish meal, the quality of the product is affected by the oil content. causes a decline. In the third method, complete recovery is difficult because proteins are recovered only by the coagulation adsorption power of microorganisms, and wastewater flows into the biooxidation process with a large amount of protein and BOD remaining, which increases the load in the biooxidation process. It has the disadvantage of having a high amount of water and the size of the equipment, and furthermore, the floss contains a mixture of proteins and microorganisms, which should be avoided from hygienic considerations when used as meat meal or feed. The only use left is as fertilizer. The present inventors have conducted repeated research to resolve the drawbacks of the above-mentioned conventional methods for treating wastewater from seafood processing. Completed the present invention by discovering that by separating proteins using the pressure flotation separation method of the entire isoelectric point, the drawbacks of conventional methods can be overcome and fishery processing wastewater can be treated efficiently. This is what I did.
That is, the present invention provides a method for treating wastewater from seafood processing, which includes a step of removing solid matter from the water to be treated using a screen, a circulating pressurized flotation step to remove oil in advance, and a step to remove proteins. For example, seafood processing is characterized by separately collecting oil, protein, and bacterial sludge by sequentially performing a pressure flotation separation process using a special line mixer to remove the entire isoelectric point, and a biological treatment process to remove BOD. It relates to wastewater treatment methods. In the present invention, the following effects can be obtained by using a circulation pressurization method for oil and fat flotation in oil and fat separation, and using so-called total pressure flotation in which wastewater is introduced into a line mixer for protein separation. Oil and fat naturally float to the surface, and in order to remove only oil and fat more effectively, the amount of bubbles needs to be small, and 20 to 30% of the amount of wastewater is used as circulating water.
It is sufficient to simply supply the oil, and problems such as a reduction in floating speed due to finer oil and fat when using the full-volume pressurization method do not occur. In addition, in flotation separation of proteins, there are many proteins and SS in the wastewater, and a large amount of air bubbles are required to float them.In the circulation method, as the amount of circulating water increases, the flotation separation tank also becomes larger. It has its drawbacks. However, in the case of the full-volume pressurized flotation method using a special line mixer, it is possible to supply a sufficient amount of bubbles without increasing the amount of water, and furthermore, the high-efficiency stirring power in the special line mixer improves the isoelectricity of the protein. It is possible to carry out the point aggregation reaction completely, and the refining of protein and SS particles can be sufficiently compensated for by floating them as coarse flocs through the coagulation action of sodium polyacrylate. Next, an example will be shown in which the effects of the above-mentioned oil/fat and protein treatments are specifically clarified. First, in order to compare the effects of the pressurized flotation method using a special line mixer in oil and fat separation,
Using a line mixer with a capacity of 2 and a flotation tank with a capacity of 100, full volume pressurization, partial pressurization, and chemical-free injection are possible.
PH6.5 under circulating pressure, normal hexane extracted substance
Table 1 shows the comparison results for 510ppm seafood processing wastewater.

[Table] The above test shows that the circulating pressure flotation method of around 20% is optimal for oil and fat separation. The concentration of floating oil is 8-12%, and it can be recovered as fish oil. The total volume pressurization method is a method in which the entire volume of wastewater is pressurized and air is dissolved in the pressurized water.
The partial pressurization method is a method in which a portion of the wastewater is pressurized and air is dissolved in the pressurized water, and the circulation pressurization method is a method in which a portion of the treated water is pressurized and air is dissolved in the pressurized water. be. For example, in 30% partial pressurization, the ratio of partially pressurized water is 0.3 and the flotation tank inlet water volume is 1 to the total amount of wastewater, and in the case of 30% circulation pressurization, the ratio is 0.3 of the circulating water and 1.3 of the flotation tank inlet water volume to the total amount of wastewater. becomes. Next, we will examine the performance of the full-volume pressurized flotation method using a special line mixer for protein separation. Using wastewater from which oils and fats have been separated, a line mixer with a capacity of 50 and a flotation tank with a capacity of 1670 were used, with a line mixer pressure of 3 kg. Table 2 shows the results of a performance test conducted by changing the amount of sodium polyacrylate added at /cm ² ·G.

[Table] As seen from Table 2, SS removal rate is 99.5%, BOD
A removal rate of 85% and an oil removal rate of 95% were obtained. In addition, the concentration effect of protein floss at this time is very good,
The moisture content of protein floss is 93 to 95%, and the effect of fine bubbles generated evenly and in large quantities by the full-volume pressurized flotation method using a special line mixer is evident. Table 3 shows the results of a dehydration test on the protein floss using a screw press using a screen with an overarea of 1 m ² and a pore diameter of 1 mmφ.

[Table] Normally, the same moisture content as 70% is obtained when dehydrating by heating to 60-80℃, but this is due to the low moisture content of the protein floss mentioned above and the fact that the oil content has been removed beforehand. This is because what is being done is working effectively. The seafood processing wastewater treatment method of the present invention will be explained in detail with reference to the accompanying drawings. Wastewater generated from seafood processing is introduced into a first wastewater storage tank 1, supplied to a screen 2 by a pump a to separate solids (), and treated water is introduced into a second wastewater storage tank 3. The wastewater is guided from the storage tank 3 by the pump b to the oil separation tank 5 via the connected pipes 15 and 16, and the colloidal oils and fats in the wastewater are separated.
The separated wastewater is pressurized and introduced from the storage tank 5' into the special line mixer 4 using pump C, and mixed with pressurized circulating water that has been dissolved to saturation concentration by blowing in compressed air A. Oils and fats are separated by the floating action of microbubbles created by the reduced pressure of pressurized circulating water (). Here, the special line mixer 4 has a double cylinder structure with an inner cylinder, and is a device that can dissolve air in the introduced liquid to its saturated solubility in about 30 seconds by rapid mixing and agitation using an impeller. Used at ~5Kg/cm ²・G. Next, the wastewater from which the fats and oils have been separated is temporarily stored in the oil and fat separated liquid storage tank 6, and after aeration is performed to prevent spoilage, it is introduced into the isoelectric point coagulation tank 7 using the pump d, and hydrochloric acid is added dropwise from the acid storage tank 18. The mixture is aerated and mixed to adjust the pH to 4 to 6, and then introduced under pressure into the special line mixer 8 using pump e. Compressed air A is supplied to the special line mixer 8, and it is made into a pressurized air saturated liquid in the same manner as described above. After the pressure is reduced by the pressure reducing valve 22, sodium polyacrylate is supplied from the auxiliary agent storage tank 19, and it is used for the coagulation effect. Coarse protein flocs are thus formed and introduced into the flotation separation tank 9, where the proteins are floated by the flotation action of fine bubbles generated by the reduced pressure. The treated water from which proteins have been removed in this way is temporarily stored in the protein separation liquid storage tank 10, then introduced into the PH adjustment tank 10' by the pump f, and an alkaline agent is dripped from the tank 20, allowing for the next biological oxidation treatment. After adjusting the pH, the sludge is aerated and mixed with the sludge for a certain period of time in the aeration tank 11 sent by the pump f', and is separated into final treated water and sludge in the settling tank 12. Existing methods may be used for the biological oxidation treatment, and standard activated sludge method, biofilm method, rotating disk method, etc. can also be used. The sludge pulled out from the bottom of the settling tank 12 is returned to the aeration tank 11 by the pump g, and a portion is taken out of the system as surplus sludge, and after drying, bacterial cell sludge for fertilizer is obtained. On the other hand, flotation separation tank 9
Protein floss F collected by scraping rake from the upper surface of the separation tank is stored in the floss storage tank 13, and sodium polyacrylate is dropped therein from the auxiliary agent storage tank 21, and introduced into the screw press 14 by pump h for dehydration. do. The liquid separated from the screw press is returned to the oil/fat separated liquid storage tank 6 by pump h', and the dehydrated cake is used as a raw material for fish meal after drying. As described above, the method of the present invention reduces the oil content of the floss generated from the isoelectric focus flotation process, enables dehydration of the floss without heating, and separates oil, protein, and bacterial cell sludge. They can be separated and taken out of the system and easily recovered as resources as high-temperature fish oil, fish meal, and fertilizer. Therefore, the method of the present invention can solve the pollution problem in the seafood processing industry, which has various problems such as a sudden increase in oil and fat content due to a change in fish species, an increase in BOD due to an increase in dissolved organic content, and various problems in floss treatment. It's a big contribution. Example Table 4 shows the treatment effects of each process in a seafood processing wastewater treatment plant with a daily wastewater volume of 1900 m ³ and a treatment time of 8 hours (240 m ³ /h) up to the biological treatment process.

【table】 [Brief explanation of the drawing]

The accompanying drawing is a flow sheet outlining the method of the present invention.

Claims (1)

[Claims] 1 In the treatment of seafood processing wastewater, the process of removing solids in the wastewater with a screen, the process of removing oil by a circulating pressure flotation method, the process of removing proteins, etc. by a total isoelectric point pressure flotation method , and a method for treating seafood processing wastewater, the method comprising sequentially treating each step of the process of removing BOD by biological oxidation treatment.