JPS6391107A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To reduce the consumption of an inorg. flocculant and to remove COD, BOD, etc., with high efficiency by adding an iron-based flocculant to industrial waste water to previously regulate the pH of the waste water, and then adding an aluminum-based flocculant to regulate the pH of the waste water. CONSTITUTION:An iron-based flocculant such as iron polysulfate and ferric chloride (material contg. trivalent iron is preferable) is added in an appropriate amt. to industrial waste water with highly variable qualities to previously regulate the pH. An aluminum-based flocculant such as aluminum sulfate and PAC is then added to control the pH. When the pH of the waste water is adjusted to 4.5-6.5, the rejection ratio of COD can be increased, and the variations in the water quality can be coped with. Besides, coloration is reduced by the joint use of the iron-based and aluminum-based flocculants as compared with the case where the iron-based flocculant alone is used, the rejection ratio of COD is also increased by 5-15%, and the treating cost is decreased.

Description

[Detailed description of the invention] This invention is a method for coagulating and settling wastewater discharged from various factories using a combination of an iron-based flocculant and an aluminum-based flocculant. This is a wastewater treatment method in which the pH of wastewater is pre-adjusted by adding an iron-based coagulant, and the pH of the wastewater is controlled to a predetermined value using an aluminum-based coagulant.

Polyaluminum chloride has traditionally been used as a coagulation and sedimentation treatment method for wastewater discharged from various factories.

There are methods using aluminum-based flocculants such as aluminum sulfate, and methods using iron-based flocculants such as polyferric sulfate and ferric chloride.

These factory wastewaters (hereinafter referred to as wastewater) have large water quality fluctuations, and the quality of the water after coagulation and sedimentation treatment is affected by the water quality fluctuations of this wastewater.As a way to prevent this, the aforementioned water quality can be improved by enlarging the wastewater storage tank. Methods such as absorbing fluctuations or constantly adding a sufficient amount of flocculant to treat wastewater, which is the most difficult to treat, are used.

Some factories treat wastewater by controlling the pH of the wastewater, but these methods use acid or alkali to keep the pH value of the wastewater after treatment within the discharge standard range (generally pH 5.8 to 8.5). In most cases, the pH is adjusted by adding .

Problems to be Solved by the Invention When wastewater is treated by the above method, (1) B in the wastewater is
The removal rate of OD and COD is low; (2) equipment becomes larger due to larger storage tanks to absorb fluctuations in wastewater water quality; and (3) the amount of wastewater required is 1.0 cm to treat wastewater, which is always the most difficult to treat. Since a flocculant is added to the treatment, the flocculant is used in vain, and the pH shift caused by the flocculant added more than necessary may be adjusted with acid or alkali, which increases the processing cost. There was a drawback.

Solving the Problems The inventors of the present invention conducted various inspections to solve these problems. As a result, (a) iron-based flocculants have a higher removal rate of COD and BOD than aluminum-based flocculants, but they may color the wastewater after treatment; and (b) iron-based flocculants and (c) When an aluminum-based flocculant is used in combination, there is no coloration, and the COD removal rate is 5 to 15% higher than when only an aluminum-based flocculant is used alone.
It is possible to remove hydrogen sulfide contained in wastewater generated in paper mills, human waste treatment plants, sewage treatment plants, etc., and (d) as shown in Figure 1, the COD removal rate is high when the pH is 4.5 to 6.5. (v) Even if the water quality of the wastewater fluctuates, we found that efficient wastewater treatment is possible if the wastewater is treated by adjusting the pH to 4.5 to 6.5. .

This invention is based on these findings, and includes a method for coagulating and settling wastewater discharged from various factories using an iron-based flocculant and an aluminum-based flocculant. This method of treating wastewater is characterized by adjusting the pH of the wastewater to a predetermined level by using a combination of preliminary adjustment of the pH of the wastewater by adding a coagulant and adjusting the pH of the wastewater by adding an aluminum-based coagulant.

The iron-based flocculant used in this invention is ferric sulfate.

Ferric chloride, polyferrous sulfate, ferrous sulfate, ferrous chloride, etc. may be used, but in consideration of cohesive force, hydrolysis pH, and appropriate pH during coagulation and sedimentation, one containing trivalent iron. Good.

Further, polyferric sulfate having basicity is preferred in order to reduce the decrease in pH during addition.

An example of an aluminum-based flocculant is sulfuric acid.

In addition to polyaluminum chloride, aluminum chloride, waste band, and high aluminum chloride are used.

In addition, in this invention, an appropriate amount of iron-based flocculant is added to preliminarily adjust the pH of the waste water, and an aluminum-based flocculant is also added in combination to adjust the pH.

The reason for this is (1) iron-based flocculants have a low P I-I and are rapidly hydrolyzed when added to wastewater;
(2) Iron-based flocculants have a higher COD and BOD removal rate than aluminum-based flocculants, but after treatment (3) Hydrogen sulfide in the waste water can be removed by using an aluminum-based product in combination with the waste water, which is colored.

In addition, the target value for adjusting the drainage PTT in this invention is 4
．． If it is set to 5 to 6.5, the COD removal rate will be high, and efficient wastewater treatment will be possible even if there are fluctuations in water quality.

The specific processing method of the present invention will be explained below based on examples.

Figure 2 is a block diagram showing the operating system for carrying out the present invention. In the figure, reference numeral 1- is a drainage channel, and the drainage PII value is measured by the P H electrode 2 in this drainage channel.

The P T-I value measured by this PH electrode 2 is P
The H instruction transmitter 3 sends it as an electrical signal to the control room.

Next, this PH indication transmitter 3 is equipped with a function that allows the upper and lower limits of the PI value to be arbitrarily set, and the measured wastewater PH is
It is determined where the value is in the PH region divided by the upper and lower limit setting values, and this determination signal is transmitted to the control room together with the PH signal. Next, this discrimination signal and the PH signal are inputted to the comparison circuit 4 to determine the amount of iron-based flocculant to be injected, and this signal is inputted to the drive circuit 5.

The drive circuit 5 drives the iron-based flocculant injection pump 6 to inject the flocculant in the iron-based flocculant storage tank 7 into the drainage channel 1 so as to achieve the determined injection amount.

This drive circuit 5 is provided with several stages of manual flow rate setting devices, and commands the iron-based flocculant injection pump 6 about the required injection amount.

The number of manual flow rate setters is determined by the discrimination function of the PH indication transmitter 3. For example, if the upper and lower limits are set, there are three stages, and when only the upper or lower limits are set, there are two stages, and the number can be changed as necessary.

On the other hand, the PH value multiplied signal from the PH indication transmitter 3 is input to the PH value multiplication signal adjuster 8. The regulator 8 determines the amount of aluminum-based coagulant to be injected based on the difference between the input pH value and the adjustment target value, and inputs this signal to the drive circuit 9.

The drive circuit 9 drives the aluminum-based flocculant injection pump 10 so that the injection amount is determined, and injects the flocculant in the aluminum-based flocculant storage tank 11 into the drainage channel.

By the way, the upper and lower limit setting values that determine the amount of iron-based flocculant to be injected and the drainage PH that determines the amount of aluminum-based flocculant to be injected
The correlation between the adjustment target values is, for example, when the target PH value is set to 6.0.
If the pH value of the wastewater is 6 when using an aluminum-based flocculant,
．． Inject so that it becomes 0. -Right upper and lower limit setting values are target P
H value, for example, the upper limit is set to 5.5 and the lower limit is set to 5.0, and as the wastewater pH value becomes lower, the injection amount of the iron-based coagulant is decreased. Further, a lower limiter is provided in the regulator 8 so that the aluminum-based coagulant is always injected in a minimum amount or more, and the iron-based coagulant and the aluminum-based coagulant are injected together.

Next, Table 1 shows the results of treating wastewater from a paper mill.

Table 1 (Data are average values for 30 days, upper and lower limit set values for the method of the present invention are 5.5 and 5.0) Lessons Learned According to this invention, the removal rate of COD and BOD is high, and the inorganic flocculant Compared to conventional methods, the amount of hydrogen sulfide used is reduced, the treatment cost is reduced, and hydrogen sulfide can be removed, which has great effects.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the COD removal rate in wastewater and the treatment PH, and FIG. 2 is a diagram showing the operating system for carrying out the present invention. 1... Drain channel 2... PH electrode 3... PHH indicator 4... Comparison circuit 5... Drive circuit 6... Iron-based coagulant injection pump 7... Iron-based coagulant Storage tank 8...Adjuster 9...Drive circuit 10...Aluminum flocculant pump 11...Aluminum flocculant storage tank PH i, i=mi]-

Claims (1)

[Claims] In the method of coagulation sedimentation treatment of wastewater discharged from various factories etc. using iron-based flocculants and aluminum-based flocculants, preliminary adjustment of wastewater pH by addition of iron-based flocculants and aluminum-based flocculants are used. A method for treating wastewater, characterized in that the pH of the wastewater is adjusted to a predetermined value by adjusting the pH of the wastewater by adding a flocculant.