TWI426054B - Wastewater treatment methods - Google Patents

Description

Wastewater treatment method

The invention relates to a wastewater treatment method, in particular to a wastewater treatment method for cold-rolled oily wastewater in a steel plant.

In the cold rolling process of the steel industry, a large amount of waste water is discharged, which is generally called cold-rolled wastewater, and among them, the cold-rolled oily wastewater with high oil content is due to oil content and chemical oxygen demand (Chemical oxide demand, The following is abbreviated as COD), which is more difficult to handle and has poorer biodegradability. Therefore, cold-rolled oily wastewater must be further processed. Traditionally, cold-rolled oil-containing wastewater is mainly treated by physical chemistry and biological treatment: physical and chemical methods: First, the cold-rolled oily wastewater is subjected to quenching and squeezing oil to remove the oil slick, and then the emulsified oil is removed by emulsification and air-floating system, and then the emulsified oil and the dissolved oil are removed by chemical coagulation, and finally the water quality is discharged to the discharge standard through the filtration system. The disadvantages of this method are complicated process, large dosage, poor safety, high operating cost, and it is still difficult to meet the discharge standard after the treated effluent, and there is a problem of secondary pollution.

Biological treatment method: the cold-rolled oily wastewater treated by scraping oil and air floatation is introduced into the activated sludge system containing microorganisms, and the microorganisms are used to decompose the organic matter in the wastewater, and then introduced into the sedimentation tank to precipitate, so that the water quality can be discharged. Standard, and the disadvantages of this method are that the treatment efficiency is not high, the effluent water quality is poor, and the treatment site has a large area.

In addition, although the biological treatment method has the aforementioned shortcomings, it is a commonly used procedure for treating general oily wastewater at present, and the current practical application of the oily wastewater treatment process proposed by the American Petroleum Institute (API) will also treat biological treatment. The method is planned into a standard method, and it is obvious that the treatment of oily wastewater by microorganisms has become a development trend.

Therefore, how to combine the biological treatment method to develop a cold-rolled oily wastewater treatment process with a small footprint, more efficient, more economical, more simplified and safer treatment process, is the direction of the steel industry.

Accordingly, it is an object of the present invention to provide a wastewater treatment method which is effective for reducing suspended solids (S.S.) and biological oxygen content (COD) of cold-rolled oily wastewater.

Accordingly, the present invention provides a wastewater treatment method for cold-rolled oily wastewater of a steel plant, comprising a nucleation step, a precipitation step, a preparation step, and an organic matter removal step.

The nucleation step is to introduce the pre-treated cold-rolled oil-containing wastewater into a first tank, and the molten iron sulfate is added to the cold-rolled oil-containing wastewater and continuously stirred to condense the suspended solids in the cold-rolled oil-containing wastewater.

The precipitating step is: adding the cationic polymer to the cold-rolled oily wastewater containing the polyferric sulfate, stirring, and allowing the solidified cement to be condensed and precipitated at the bottom of the first tank to form the cold-rolled oily wastewater. a first liquid having a high suspended solids content and a second liquid having a low suspended solids content, wherein the second liquid has a suspended solids content of not more than 5% based on 100% of the suspended solids content in the cold-rolled oily wastewater .

The preparation step is to prepare a thin film bioreactor device, including a second receiving tank, and a filter module, wherein the second receiving groove defines an accommodating space, and has a water inlet connecting the outside and the accommodating space. The filter module is disposed in the accommodating space, defines a filter chamber capable of accommodating liquid, has a predetermined pore for the liquid to pass through the filter membrane entering the filter chamber, and a connection between the filter chamber and the outside Water nozzle.

The organic matter removing step, the activated sludge having microorganisms is placed in the accommodating space, and the second liquid is introduced into the second tank from the water inlet and mixed with the activated sludge to obtain a filter to be filtered. A negative pressure is applied to the water outlet to allow the filter to pass through the filter membrane to the filtration chamber with a predetermined film flux, thereby obtaining a reclaimed water in the filtration chamber, and chemically aerating the cold-rolled oily wastewater. The amount of chemical oxygen demand removal of the reclaimed water is not less than 90%, based on 100%.

The utility model has the advantages that: by using a two-stage treatment method, the suspended solid in the cold-rolled oil-containing wastewater is firstly precipitated and precipitated by using the ferric sulfate and the cationic polymer, and then the second liquid is used in the membrane bioreactor unit. Chemical oxygen demand (COD) removal, and a reclaimed water with a suspended solids (SS) content of less than 5% and a chemical oxygen demand removal rate of not less than 90% can be obtained, which is not only simple in treatment but also effective in reducing wastewater treatment. Site area.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to Fig. 1, a preferred embodiment of a wastewater treatment method for cold-rolled oily wastewater in a steel plant subjected to scraping and air-floating treatment comprises the following four steps.

First, the nucleation step 11 is performed, the cold-rolled oil-containing wastewater is introduced into a first tank, and a molten iron sulfate solution is added to the cold-rolled oil-containing wastewater and continuously stirred at a predetermined rotation speed to condense the suspended solids in the wastewater. .

It is to be noted that the cold-rolled oil-containing wastewater of the present embodiment refers to a pre-treatment step of oily and alkali-washed wastewater discharged in a cold rolling process of a general steel plant by first scraping oil and air floating, and preliminary removal of oil slick and emulsified oil. After the cold-rolled oil-containing wastewater discharged, the pre-treatment step of the scraping and air-floating is a well-known technique of the general steel industry, and therefore no further description is made. In the preferred embodiment, the source of the cold-rolled oily wastewater is China. The mixed waste water of oil and alkali washing in the second cold-rolled wastewater field of the Iron and Steel Co., Ltd., after the oil scraping and air-floating steps, removes the cold-rolled oily wastewater discharged from the oil and emulsified oil.

In detail, the polyferric sulfate is used to condense the suspended solids in the cold-rolled oily wastewater to facilitate the subsequent process. When the concentration of the ferric sulfate is too low, the nucleation effect is not good, and the stirring speed is too slow. Dispersing the polyferric sulphate unevenly will also cause the nucleation effect of the suspended solids (SS) to be poor, the stirring speed is too fast, and the nucleation point is too small. Therefore, preferably, the stirring speed of the step is between 60~ Between 100 rpm, and the content of the polymerized ferric sulfate relative to the cold-rolled oily wastewater is 100 to 200 ppm.

Next, a precipitation step 12 is carried out, and the cationic polymer is added to the cold-rolled oil-containing wastewater containing the polyferric sulfate, and stirred at a predetermined rotation speed for a predetermined time, and then allowed to stand, so that the coagulated nucleated suspended solid cement is precipitated in the first a bottom of the tank, the cold-rolled oily wastewater is formed into a first liquid having a high suspended solid content and a second liquid having a low suspended solid content, wherein the suspended solids (SS) content in the cold-rolled oily wastewater is The second liquid has a suspended solids (SS) content of not more than 5% based on 100%.

Specifically, the cationic polymer is used to make the suspended solid which is condensed and nucleated in the cold-rolled oily wastewater, and can be cemented into a larger agglomerate to settle at the bottom of the first tank by the action of the cationic polymer. A second liquid having a low suspended solid content can be directly obtained. If the content is too low, the cementation effect is insufficient, and further, the stirring speed in this step is too fast, and the cemented agglomeration effect of the suspended solids is not good. It is not easy to precipitate. Therefore, preferably, the stirring speed of the step is not more than 60 rpm, and the content of the cationic polymer relative to the cold-rolled oily wastewater is 1 to 10 ppm.

In the present embodiment, the cationic polymer is a weak cationic coagulant selected from Taiwan Kurita Co., Ltd., and the water content is less than 10%, and the pH of the 0.2% aqueous solution is between 3 and 4, and the amount of charge is 1.5~1.9C/mg, suitable for pH range from 1~9.

Referring to Table 1, Table 1 shows cold-rolled oily wastewater with a chemical oxygen demand (COD) of 1574 ppm and a suspended solids concentration (SS) of 270 ppm. The nucleation is carried out by adding different amounts of polymeric ferric sulfate and cationic polymers. In step 11, the mixture was stirred at 90 rpm for 10 minutes, and the suspended solid (SS) content and chemical oxygen demand of the second liquid obtained after stirring for 15 minutes at the rotation speed of 30 rpm in the precipitation step 12 for 30 minutes. (COD) removal rate results.

It is known from Table 1 that when the concentration of polyferric sulfate is insufficient, the removal rate of suspended solids (SS) in cold-rolled oily wastewater is poor, and when the concentration of polyferric sulfate is greater than 100 ppm, the removal rate of suspended solids (SS) is It can reach more than 90%, and the removal rate of chemical oxygen demand (COD) can be maintained at less than 35%; since the main purpose of the nucleation step 11 and the precipitation step 12 is to minimize the concentration of suspended solids and avoid the second liquid The concentration of suspended solids is too high to cause troubles in the subsequent treatment process, but it is also necessary to avoid excessive reduction of the chemical oxygen demand concentration of the second liquid in order to provide the nutrient source required by the microorganisms in the subsequent biological treatment process. Preferably, the content of the polyferric sulfate is 100-150 ppm, and the removal rate of the chemical oxygen demand of the second liquid is not more than 30%.

Referring to FIG. 2, a preparation step 13 is performed to prepare a thin film bioreactor device including a second tank 2, an aeration tray 3, and a filter module 4.

The second tank 2 defines an accommodating space 21 and has a water inlet 22 that communicates with the outside and the accommodating space 21 .

The aeration disc 3 is disposed at the bottom of the second tank 2, and can introduce gas from the outside into the second tank 2 to generate fine bubbles for providing microorganisms in the activated sludge 5 for decomposing organic matter. The oxygen introduced in the embodiment of the aeration disk 2 is air.

The filter module 4 is placed on the aeration disc 3 perpendicular to the bottom of the second tank 2, and defines a filter chamber 41 for accommodating liquid. The filter chambers 41 are spaced apart from each other, and the average pore diameter is not more than 0.7 μm. a filter membrane 42 made of polytetrafluoroethylene as a material, a water outlet 43 connecting the filter chamber 41 and the outside, and an aeration tube 44 for allowing liquid to pass into the filter chamber 41. The aeration tube 44 is disposed at the bottom of the two filtering membranes 42 for introducing gas from the outside, scraping and removing the biofilm and other impurities adsorbed on the filtering membranes 42 to slow the blocking of the filtering membranes 42. The frequency of the aeration tube 44 introduced in the present embodiment is air.

Then, the organic matter removing step 14 is performed, an activated sludge 5 is placed in the accommodating space 21, and the second liquid is introduced into the accommodating space 21 and the activated sludge 5 from the water inlet 22 of the second tank 2 Mixing, the microorganisms of the activated sludge 5 decompose the organic matter in the second liquid to obtain a filter to be filtered, and then apply a negative pressure through the water outlet 43 of the filter module 4 to allow the filter to pass through a predetermined film flux. After the filter membrane 42 reaches the filtration chamber 41, a reclaimed water is obtained to complete the wastewater treatment method of the cold-rolled oily wastewater of the present invention, and the reclaimed water can be further outputted through the water outlet, and the cold-rolled oil is used. The chemical oxygen demand of the wastewater is 100%, and the chemical oxygen demand removal rate of the reclaimed water is not less than 90%.

Specifically, in this step, an activated sludge having a microbial concentration of 7000 to 10000 ppm is placed in the accommodating space, and mixed with the second liquid, and the second liquid is used by microorganisms in the activated sludge. The organic matter is decomposed and filtered through the filtration membrane to obtain regenerated water with high COD removal rate. Therefore, the biological treatment efficiency of the activated sludge directly affects the chemical oxygen demand and treatment efficiency of the reclaimed water, and the membrane flux and scraping The amount of air in the biofilm on the filter membrane also affects the processing efficiency of the step. Although the higher the concentration of the microorganism, the higher the membrane flux, the better the treatment efficiency, but when the microbial concentration is greater than 10000 ppm or the membrane pass When the amount is too high, the filter membrane is easy to block, and the filtration membrane is blocked more severely, and the transmembrane pressure (TMP) rises faster, thus increasing the frequency of filtration membrane cleaning; in addition, due to activated sludge A biofilm is formed on the filter membrane, and the biofilm also biodecomposes the organic matter. However, the thickness of the biofilm is too large to cause the pressure on the membrane. Therefore, the biofilm should be scraped in a timely manner to avoid an increase in the membrane pressure of the membrane; therefore, the concentration of the microorganisms, the flux of the membrane, and the amount of air that scrapes the biofilm on the membrane must be matched to each other. Achieve the most stable and optimal wastewater treatment efficiency.

Preferably, the concentration of the microorganism of the activated sludge is controlled at 8000 to 9000 ppm, and the membrane flux is 0.15 to 0.4 m ³ /m ² ‧day, and the amount of air introduced into the filter membrane from the aeration tube 34 is 3~6L/min, in addition, in order to maintain the microbial concentration in the decomposition process of organic matter at 8000~9000ppm, the chemical oxygen demand load (COD loading) of the second liquid is 1~5kgCOD m ³ ‧day.

Referring to Figures 3 to 5, Figures 3 to 5 are mixed wastewater containing oil and caustic wash from the second cold-rolled wastewater field of China Steel Corporation during a predetermined test period, before degreasing and air flotation. The cold-rolled oily wastewater obtained by the treatment is subjected to preliminary precipitation to obtain a second liquid having a COD concentration of 1175±418 ppm, an average SS concentration and a standard deviation of 137±119 ppm, and introducing the second liquid into the film prepared in the foregoing step 13. The bioreactor device performs the average COD concentration, the oil concentration, and the SS concentration of the reclaimed water discharged after the organic matter removing step 14, wherein the membrane bioreactor device has a pore size of 0.7 μm, and the activated sludge microorganism The concentration was 8000 ppm, the film flux was controlled at 0.35 m ³ /m ² ‧day, and the COD loading was 2.87 ± 1.44 kg COD m ³ ‧ day

It can be seen from Fig. 3 that the regenerated water obtained by the reaction and filtration of the membrane bioreactor device has an average concentration of COD of less than 60 ppm (40±17 ppm) during the detection period, which has met the standard of direct discharge, and is determined by the standard in FIG. The oil content comparison shows that the oil content and standard deviation of the second liquid is 70±73ppm, and the standard deviation of the oil content of the reclaimed water obtained by biological treatment and filtration is 0.99±0.81ppm, which has reached the direct discharge standard (<60ppm). , indicating that the organic matter of the second liquid can be quickly and efficiently removed by the condition control of the thin film bioreactor device of the present invention.

From the results of FIG. 5, the standard deviation of the suspended solids concentration (SS) of the second liquid obtained by the reaction and filtration of the membrane bioreactor device has been reduced from the initial 137±119 ppm to 2.31±2.97 ppm. It is much smaller than the standard of direct discharge (<30ppm), indicating that the solid-liquid separation efficiency of the membrane bioreactor device is excellent under this process condition and parameter setting.

The invention adopts a two-stage treatment step, firstly, after the cold-rolled oily wastewater is subjected to coagulation and sedimentation, a second liquid having a suspended solid content removal rate of not less than 90% and a chemical oxygen demand removal rate of less than 35% is obtained, and then The second liquid is subjected to biological treatment and filtration in the second stage to obtain a reclaimed water having a suspended solid content removal rate of not less than 95% and a chemical oxygen demand removal rate of not less than 90%, and can be directly applied to general secondary water. For example, cleaning water, watering water, water spray, or as the influent water of the wastewater recovery system, not only the treatment process is remarkable, but also the COD removal efficiency is high, so the object of the present invention can be achieved; and the amount of fixed wastewater is treated. Under the standard, the wastewater treatment method of the present invention can reduce the footprint required by the conventional activated sludge method by about 60%, and another purpose of reducing the floor space can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

11. . . Nucleation step

12. . . Precipitation step

13. . . Preparation step

14. . . Organic removal step

2. . . Second pocket

twenty one. . . Housing space

twenty two. . . water inlet

3. . . Aeration tray

4. . . Filter module

41. . . Filtration chamber

42. . . Filter membrane

43. . . Outlet

44. . . Aeration tube

5. . . Activated sludge

1 is a flow chart showing a preferred embodiment of a wastewater treatment method for cold-rolled oily wastewater according to the present invention;

Figure 2 is a schematic view showing a thin film bioreactor apparatus in a preferred embodiment of the present invention;

Figure 3 is a graph showing a COD concentration and time of the regenerated water and the second liquid obtained after the treatment of the steps 13 to 14 of the present invention;

Figure 4 is a graph showing a graph of oil concentration and time of the regenerated water and the second liquid obtained after the treatment of the steps 13 to 14 of the present invention;

Figure 5 is a graph showing the concentration and time of suspended solids (S.S.) of the regenerated water and the second liquid obtained after the treatment of the steps 13 to 14 of the present invention.

11. . . Nucleation step

12. . . Precipitation step

13. . . Preparation step

14. . . Organic removal step

Claims (7)

A wastewater treatment method for treating cold-rolled oily wastewater produced by a steel plant to obtain reclaimed water, comprising: a nucleation step of introducing cold-rolled oily wastewater into a first tank and mixing the polyferric sulfate to make the cold-rolled oily wastewater The suspended solid in the condensed nucleation, and the content of the polyferric sulphate relative to the cold-rolled oily wastewater is 100-200 ppm; in a precipitation step, the cationic polymer is added to the cold-rolled oily wastewater mixed with the polyferric sulphate, and the condensed The suspended solids of the core are precipitated at the bottom of the first tank to obtain a first liquid and a second liquid having high and low suspended solid contents, respectively, wherein the cationic polymer is relative to the cold-rolled oily wastewater. It is 1~10ppm, and the chemical oxygen demand of the cold-rolled oily wastewater is 100%, the chemical oxygen demand removal rate of the second liquid is not more than 30%, and the suspended solid content in the cold-rolled oily wastewater is 100%. The second liquid has a suspended solids content of not more than 5%; in a preparation step, a thin film bioreactor device is prepared, including a second tank, and a filter module having a predetermined pore, The second receiving slot defines an accommodating space, and has a water inlet connecting the outside and the accommodating space. The filter module is disposed in the accommodating space to define a filtering chamber capable of accommodating the liquid, having a a predetermined membrane for the liquid to pass through the filter membrane entering the filtration chamber, and a water outlet connecting the filtration chamber to the outside; and an organic matter removing step to set the activated sludge with microorganisms And entering the accommodating space, and introducing the second liquid from the water inlet into the second tank and mixing with the activated sludge to obtain a filter to be filtered, and applying a negative pressure through the water outlet of the membrane bioreactor device Allowing the filtrate to pass through the filtration membrane into the filtration chamber with a predetermined membrane flux, thereby obtaining a reclaimed water in the filtration chamber, and the chemical oxygen demand of the cold-rolled oily wastewater is 100%, the reclaimed water The chemical oxygen demand removal rate is not less than 90%. The wastewater treatment method according to claim 1, wherein the chemical oxygen removal rate of the reclaimed water obtained by the organic matter removal step is not less than 95%. The wastewater treatment method according to claim 1, wherein the organic matter removal step controls the film flux to be 0.1 to 0.4 m ³ /m ² . Day. The wastewater treatment method according to claim 3, wherein the activated sludge microorganism concentration in the organic matter removal step is between 7500 and 10000 ppm. The wastewater treatment method according to claim 1, wherein the filtration membrane has an average pore diameter of not more than 0.7 μm and is composed of polytetrafluoroethylene. The wastewater treatment method according to claim 5, wherein the filter module further has an aeration tube for supplying gas. The wastewater treatment technology of claim 1, wherein the membrane bioreactor apparatus further comprises an aeration tray installed at the bottom of the second tank for supplying gas.