KR960003921B1 - Method for treatment of waste water from cold rolling plant - Google Patents

Abstract

The waste water treatment comprises (A) well mixing oil-containing waste water, alkali-containing waste water, sulfur-containing waste water, and organic substances-containing waste water ; (B) adding acid heavy metal-containing waste water to above mixture to adjust thiocyan concentration of the mixture at lower than 30 mg/l ; (C) adding sulfuric acid to adjust the pH of the mixed waste water at 6.5-8.0 ; (D) adding coagulant to the neutralized waste water to remove oil and suspensions ; and (E) biologically oxidizing, absorbing and adsorbing the treated water from (D) in an aerating tank.

Description

Wastewater Treatment Method from Cold Rolling Mill

1 is a schematic diagram of a cold rolling mill wastewater treatment method according to the conventional method

2 is a system diagram of a cold rolling mill wastewater treatment method according to the present invention

3 is a graph showing the change of COD and thiocyanate concentration according to the reaction time in the aeration tank in the present invention.

4 is a graph showing a change in thiocyanate ion concentration according to the reaction time in the aeration tank in the present invention.

5 is a graph showing a change in sulfuric acid input according to the acid heavy metal wastewater inflow compared to the mixed wastewater in the present invention

6 is a graph showing the change of COD and thiocyanate concentration with reaction time in the conventional method.

7 is a graph showing the change of COD and thiocyanate concentration according to the amount of FeCl ₃ input in the conventional chemical method.

The present invention relates to a wastewater treatment method generated in a cold rolling mill, and more particularly, to a method for effectively treating oil-containing wastewater, alkali-containing wastewater, deflowing wastewater, organic matter-containing wastewater and acid heavy metal-containing wastewater generated in a cold rolling mill. will be.

Waste water generated in cold rolling mill is made of hot rolled coil produced in hot rolling mill, which is pickled, cold rolled, electro-cleaned, annealed and plated to produce cold-rolled and plated products with surface roughness. Organic wastewater containing chromium, chromium containing wastewater and organic wastewater are generated in various ways.

As a conventional method for treating wastewater generated in a cold rolling mill, as shown in FIG. 1, the oil-containing wastewater and the alkali-containing wastewater are collected in a collection tank, and then flowed into a reaction tank to adjust pH by sulfuric acid, and then aggregate. In the tank, the pollock is improved by the inorganic flocculant, the oil material is removed by the skimmer in the floating separation tank, and the oil-containing wastewater, the alkali-containing wastewater treated in the first stage in two stages, and the organic-containing wastewater and the dehydration liquid COD, SCN- After reducing the ions, these treated water, chromium-containing wastewater and acid-heavy metal-containing wastewater are introduced into the acid wastewater collection tank in three stages, and then transferred to a pH adjusting tank for pH adjustment. A method for treating by; Wastewater treatment processes and processes are the same as those described above, but methods of chemically treating the wastewater alone, which are the most adversely affected by the contaminant treatment by the microorganisms in the aeration tank, do not flow into the aeration tank.

However, these conventional methods are not only difficult to neutralize alkali-containing wastewater (pH 11-12.2) in the reaction tank by sulfuric acid, but also consume a lot of sulfuric acid, and in particular, by treating the demineralization waste liquid directly into the aeration tank, High concentrations of thiocyan (approximately 50,00mg / L) directly contact microorganisms in the aeration tank, which impacts the microorganisms and lowers the activity of the microorganisms, resulting in insufficient COD and thiocyanate ions. It causes the death of microorganisms has become a big problem in wastewater treatment.

In addition, the sole chemical treatment of the effluent waste to minimize the effect of the aeration tank microorganism by the thiocyanate in the effluent waste is not suitable because it is insufficient in the treatment efficiency and acts as a factor of increasing the COD concentration of the final effluent.

Accordingly, the present invention is to equalize the wastewater by mixing the acid-heavy metal-containing wastewater in the mixed wastewater mixed with oil-containing wastewater, alkali-containing wastewater, dehydration wastewater and organic-containing wastewater, so as to reduce the amount of sulfuric acid and calcined lime, as well as COD in mixed wastewater The present invention aims to provide a method for effectively and stably treating contaminants by microorganisms in an aeration tank by stabilizing thiocyan ions contained in the demineralization wastewater before entering the aeration tank.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention relates to a method for treating wastewater generated in a steel mill and a cold rolling mill, comprising the steps of: sufficiently mixing an oil-containing wastewater, an alkali-containing wastewater, a deflowing waste liquid and an organic-containing waste liquid; Mixing acid heavy metal-containing wastewater in these mixed wastewater so as to adjust the thiocyanate concentration in the mixed wastewater to 300 mg / l or less; Neutralizing the wastewater to pH 6.5-8.0 by adding sulfuric acid to the thiocyanate adjusted wastewater; Removing oil and suspended solids by adding a flocculant to the neutralized wastewater; And it relates to a method for treating the wastewater generated in the cold rolling mill of the steel mill, including the step of oxidizing, absorbing, and adsorption of the wastewater from which oil and suspended solids have been removed by the aeration tank.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In order to treat the wastewater generated in the cold rolling mill in accordance with the present invention, oil-containing wastewater, alkali-containing wastewater, demineralization wastewater and organic matter-containing wastewater are first mixed sufficiently in the wastewater mixing tank as shown in FIG. This results in a mixed wastewater having a pH of 11.2-12.0, a COD of about 400 mg / l and a thiocyanate ion concentration of about 350 mg / l.

Next, the mixed wastewater is transferred to the adjusting tank and mixed with an appropriate amount of acid heavy metal-containing wastewater having a pH of 0.6-2.0 to equalize the mixed wastewater, wherein the pH of the wastewater is in the range of 10.5-8.0, and the thiocyanate ion concentration is 300 mg / l. Is maintained below.

Next, the equalized wastewater is transferred to a neutralization tank and neutralized to pH 6.5-8.0 by sulfuric acid.

Next, the neutralized mixed wastewater is transferred to a coagulation tank, where the inorganic coagulant such as poly aluminum chloride (PAC) is added to coagulate, and then, the flocculation tank is floated to separate oil and suspended solids.

Next, the mixed wastewater in which oil, suspended solids, etc. are separated and floated is introduced into the aeration tank, whereby the microorganisms are oxidized, absorbed, and adsorbed.

As described above, the process after the wastewater treatment by the microorganisms in the aeration tank is performed by a conventional method.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

As shown in FIG. 2, the oil-containing wastewater, the alkali-containing wastewater, the dehydration wastewater and the organic-containing wastewater generated in the cold rolling mill are sufficiently mixed in the wastewater mixing tank in one step, and then the appropriate amount is contained in the acid heavy metal when transported to the adjusting tank. Wastewater was mixed and stabilized.

In the second step, the neutralization tank was neutralized to pH 6.5-8 by sulfuric acid, and then floc was formed by PAC in the flocculation tank to remove oil and suspended matter.

Wastewater containing 325 mg / l of COD and 287 mg / l of thiocyan ion inflow into the aeration tank was reacted for 12 hours, and the COD and thiocyan ion concentrations were changed according to the reaction time. It observed and the result is shown in FIG.

As shown in FIG. 3, when the wastewater pretreated according to the present invention is reacted in the aeration tank for 12 hours, COD of 26 mg / l and thiocyne of 14.4 mg / l are 92% and 95%, respectively, by the aeration tank. It can be seen that it is removed.

In addition, the wastewater having thiocyanate concentrations of 203 mg / l, 423mg / l and 514mg / l obtained in the first and second steps was introduced into the aeration tank and reacted for 24 hours. The results are shown in FIG.

As shown in FIG. 4, when the thiocyanate concentration is 400 mg / L or more in the mixed wastewater introduced into the aeration tank, the thiocyanate reduction effect is insufficient even if the reaction time due to the microorganism is 12 hours or more.

However, it can be seen that when the thiocyanate concentration in the mixed wastewater is 300 mg / L or less as in the present invention, these substances can be stably treated.

In addition, the decrease of sulfuric acid injection amount according to the acid heavy metal-containing wastewater injection into the mixed wastewater was observed and the results are shown in FIG.

As shown in FIG. 5, when the amount of sulfuric acid input when the acid heavy metal-containing wastewater is not mixed is 100, the amount of sulfuric acid input when the acid heavy metal-containing wastewater is mixed at 6.5%, 12.5%, 25%, and 37.5%, respectively, compared to the mixed wastewater. It can be seen that the reductions are almost linearly reduced to 20%, 31%, 42% and 51%.

Comparative Example 1

The cold rolled wastewater as in Example was treated by the conventional method as in the first degree, where the COD of the wastewater before entering the wood tank was 438 mg / l and the thiocyanate concentration was 375 mg / l.

The pretreated wastewater was introduced into the aeration tank and reacted for 16 hours, and the COD and thiocyanate concentration changes according to the reaction time were observed. The results are shown in FIG.

As shown in FIG. 6, it can be seen that even after the microbial treatment in the aeration tank, the COD is 271 mg / l, and the thiocyanate ion concentration is 157 mg / l, and the removal efficiencies are 38% and 52%, respectively.

These results indicate that dehydration waste, which is a thiocyan ion-containing wastewater of about 50,000, flows directly into the aeration tank, which not only impacts the microorganisms, but also reduces the microbial activity or causes death if severe. This is because it is difficult to adjust the pollutant load because the fluctuations in the flow rate and the thiocyanate concentration in the demineralized waste liquid are severe.

Comparative Example 2

COD and thiocyan ion removal experiments were performed by using FeCl ₃ , which is one of the iron salt forms alone, in the cold wastewater as in Example only, and the results are shown in FIG. 7.

As shown in FIG. 7, COD and thiocyan ion concentrations were 2324 mg / l and 21250 mg / l, respectively, even after chemical treatment of the initial 2826 mg / l and 25432 mg / l, respectively, resulting in very low treatment efficiency. It can be seen.

Claims (1)

CLAIMS 1. A method for treating wastewater generated in a cold mill in a steel mill, the method comprising: thoroughly mixing an oil-containing wastewater, an alkali-containing wastewater, a deflowing waste liquid and an organic matter-containing waste liquid; Mixing acid heavy metal-containing wastewater in these mixed wastewater to adjust the thiocyanate concentration in the mixed wastewater to 30 mg / l or less; Neutralizing the pH of the wastewater to 6.5-8.0 by adding sulfuric acid to the thiocyanate adjusted wastewater; Removing oil and suspended solids by adding a flocculant to the neutralized wastewater; And oxidizing, absorbing, and adsorbing the wastewater from which oil and suspended solids have been removed by the microorganism in the aeration tank.