JPS5959299A - Treatment of waste syrup liquid - Google Patents

Abstract

PURPOSE:To easily treat waste syrup liquid to a high degree at a low cost, by treating the waste syrup liquid in the process of aerobic biotreatment to reduce soluble BOD components below 50mg/l, adding a coagulant to it, adjusting a pH to 3-5.5 and then coagulatively separating it. CONSTITUTION:Waste syrup liquid is introduced through a pipe 1 into a part 2 for aerobic biotreatment, a nutritive seat 3 such as nitrogen or phosphorus is optionally added therein, and said waste liquid is treated in the process of aerobic biotreatment until soluble BOD components in the waste liquid are made below 50mg/l. Thereafter, a coagulant based on ferric salt is added to the treated liquid being agitated in the first mixing tank 4, and then a pH-adjusting agent 7 is added in the first pH-adjusting tank 6 to adjust a pH to 3-5.5. Thereafter, suspended substance, organic substance, colors and coloring components in the treated liquid are coagulated together with the flocks of ferric hydroxide under the addition of a coagulant 9 in an intermediate solid-liquid separation tank 8 and then separated by a proper means such as filtration or precipitation.

Description

[Detailed description of the invention] The present invention relates to a novel and effective method for treating molasses wastewater.

The molasses waste liquid that is the subject of treatment in the present invention is mainly discharged during the process of manufacturing fermented products such as alcohol, amino acids, nucleic acid derivatives, and baker's yeast using the molasses discharged from the sugar refining process as a raw material. This waste liquid is generally BOD in terms of water quality.

5,000 to 100.00011 for COD? ? /l is extremely concentrated, and the amount of discharged liquid is 100 to 3.00.
In many cases, the amount is as large as 0 +yz"/day.

Conventionally, this molasses waste liquid has been treated only by biological methods, but although this method can remove the BOD component in the waste liquid, the removal of COD and chromaticity components is poor.
The COD of biological treatment liquid is 1,500 to 5. OOO■
7t, chromaticity is 3.000-20,000°.

The COD and chromaticity components in this biological treatment solution are mainly composed of biorefractory M organic polymer compounds such as melanoidin, but various methods are available to treat wastewater containing this type of organic polymer compound. It was developed in Japanese Unexamined Patent Publication No. 55-34135.
``Methods for treating organic wastewater'' in this issue is one of them.

In this known method, a coagulant mainly containing A72 iron salt is added to organic wastewater to adjust the pH to a range of 3 to 55, and then suspended solids, organic substances, and color components are removed from ferric hydroxide. The first step is coagulation and separation with flocs, the second step is to add new iron salt and hydrogen peroxide to the water treated in the first step to oxidize and decompose organic substances and color components, and the second step is to add alkali to the oxidized water. and the sixth step in which the iron salt catalyst is precipitated and separated as iron hydroxide flocs at a pH of 4 or above, and the wastewater containing organic substances is treated to remove organic substances and color components in the wastewater. In some cases, biological treatment methods such as activated sludge method, watering hearth method, or anaerobic digestion method are used to reduce the BOD of wastewater to 110%.
It is said that it is necessary for soils to reduce the amount of chemicals used to a large extent by keeping the concentration below 0pp as much as possible.

The present invention utilizes the above-mentioned known method for treating molasses waste liquid, and by combining it with a more appropriate pre-treatment step, it is possible to easily treat molasses waste liquid, which has not been able to be effectively treated up to i'L. It is also low cost and can be processed at an extremely high level.

The advantage of the pretreatment in the present invention is that in the first invention, the molasses waste liquid is treated with an aerobic biological treatment method, and its soluble B
In the second invention, the molasses waste liquid is first heated to 95°C or higher, then cooled, and then treated by the aerobic biological treatment method 11, and the third invention In this case, molasses waste liquid is first treated by methane fermentation method and then treated by aerobic biological treatment method.

Hereinafter, each of the first to third inventions will be specifically explained.

To explain one embodiment of the first invention with reference to FIG. Nutrient salt 3 is added and the waste liquid is treated using an aerobic biological treatment method until the soluble BOD of the waste liquid becomes less than 50 μm (first step).

It is an important component of the first invention to treat the soluble BOD in the first step to a size of 5 omg7 or less, and if the soluble BOD is 50 q/ or more, the flocculant in the second step and beyond,
It is not stupid υ that significantly increases the amount of chemicals such as oxidizers injected,
The treatment effect will be extremely poor, and the final treatment limit water quality will rise, making it impossible to achieve the purpose of the present invention. Note that the presence of SS (suspended solids) BOD caused by microbial flocs etc. does not adversely affect the amount of chemical injection and the treatment effect.

The method of aerobic biological treatment is not limited to q and γ, and any of the activated sludge method, watering hearth method, catalytic oxidation method, rotating disk method, etc., or a combination thereof may be used.

However, in order to maintain and manage the BOD of the processing liquid to 50η/ or less, it must be operated at a positive OD volume or a negative OD volume of 6%.
It is necessary to pay close attention to the processing conditions, such as whether the necessary oxygen is being supplied sufficiently and whether the BOD sludge load is appropriate.

In addition, the excess biological sludge generated in the first step has a concentrated content of 19f.
After f L, it may be treated separately, but it can also be treated in the following second step together with the first step treatment solution to coagulate and separate the COD and chromaticity components.

In the second step, first, a predetermined amount of flocculant 5 mainly composed of ferric salt is added to the first step treatment liquid while stirring in the first mixing tank 4, and then, P H adjuster 7
By adding
~ 4.5), in the intermediate solid-liquid separation tank 8, the turbid substances, organic substances, and chromaticity components in the treated liquid are mixed with the ferric hydroxide flocs while adding a coagulation aid 9. Agglomerate and separate by appropriate means such as filtration or sedimentation.

The flocculant mainly composed of ferric salt used here is ferric sulfate.
Any number of tons of iron, ferric chloride, or polyferric nitrate may be used, and the treatment effect will be improved by increasing the amount of iron, ferric chloride, or iron polynitrate; however, it is usually 25 to 2.0 tons in terms of iron atoms. S o mg 7t.

The solid content separated in the intermediate solid-liquid separation tank 8 is discharged through a pipe 10, treated separately if necessary, and then disposed of, and the liquid content is sent to the next sixth step.

In the sixth step, first, in the second mixing tank 11, hydrogen peroxide 12 as an oxidizing agent and iron salt 13 as an oxidation catalyst are added while stirring, and the liquid is led to the oxidation reaction tank 14. An oxidation reaction is carried out to oxidize and decompose organic substances and chromaticity components in the liquid.

The amount of hydrogen peroxide added is not particularly limited, and depends on the composition of the waste liquid,
It is determined depending on the concentration, target water quality, etc., but is usually in the range of 0.1 to 2 times the amount of CODMn in the waste liquid in terms of effective oxygen in hydrogen peroxide.

Iron salts include compounds such as ferrous or ferric sulfate, ferrous or ferric chloride, polyferrous sulfate, and their aqueous solutions, but usually iron salts have high oxidation catalytic ability and are inexpensive. Therefore, ferrous sulfate salt) is required. The amount of iron salt added is determined by the concentration and composition of the waste liquid, the amount of hydrogen peroxide added, the reaction time, and the solid-liquid separation method at the oxidation reaction edge. The larger the amount, the faster the reaction speed, but the amount of sludge generated increases.
IG~2. in terms of iron atoms. a o Q vrq/1. The range shall be .

Iron salt reacts with hydrogen peroxide in the liquid to generate hydroxyl radicals with strong oxidizing properties and is hydrolyzed to reach the optimum reaction P H4υ.
P)1 in the second mixing tank 11 during IIK adjustment
Add modifier 15.

The oxidation reaction tank 14 is agitated by an oil cylinder, mechanical agitation, or air agitation. The oxidation ratio and the reaction time in the tank 14 vary depending on the composition, concentration, reaction temperature, amount of hydrogen peroxide, and amount of iron salt of the waste liquid, but are usually 5 minutes to 24 hours at room temperature.

Note that if the conditions are such that the reaction is completed within a certain amount of time, the reaction in the second mixing tank 11 is sufficient.

The alkaline agent 17 is introduced into the tank 16 and the reducing agent 1 is added as required.
8, and in the final solid-liquid separation tank 19, usually with the addition of a coagulation aid 20, iron ions are precipitated as iron hydroxide flocs, and at the same time, the organic matter of the waste liquid is also coagulated. Separate by appropriate means such as filtration or precipitation.

If unreacted hydrogen peroxide remains in the oxidation reaction, C
COD of n1 detected as COD value during OD measurement
However, in this case, a reducing agent is added to decompose the remaining hydrogen peroxide, and ferrous sulfate, ferrous chloride, sodium sulfite, thiosulfate sorter, etc. are used.

The liquid separated in the final solid-liquid separation tank 19 is taken out through a pipe 21, and after adjusting the pH if necessary, it is either discharged or sent to another treatment step for higher-level treatment. On the other hand, the solid content (hydroxide flocs) is discharged and disposed of in Sai 22, but in some cases, mineral acids such as hydrochloric acid or sulfuric acid are added to dissolve the iron hydroxide, and iron hydroxide is used in the second step. It can also be reused as a salt-based flocculant.

Example The molasses waste liquid discharged from a yeast manufacturing factory and having the liquid quality shown in Table 1 was diluted five times with fresh water, and the treatment method was a batch activation-sludge method using an aeration tank with a volume of 1 oz, BO7! LD load is 2,0Kf-BOD/rn2 days, liquid salt is 65℃
Under the conditions, the aeration amount is 8, 4.5t4), 3/-7 minutes.
When aerobic biological treatment was carried out in three stages, the liquid quality of the treated solution was as shown in Table 2.

Table 1 Table 2 However, BOD is the value of lachrymal fluid filtered with A5C paper.Next, in the second step, for these treatment solutions, the treatment method is batch treatment using 1t B-Maru. , solid-liquid separation is done by sedimentation method,
The amount of ferric chloride added is 500η/ in terms of trivalent iron ion.
In the fifth step, the treatment method was 1.
Batch processing using a t-heater, the amount of hydrogen peroxide added is 100 μ/1 in terms of effective oxygen. The amount of ferrous sulfate added is 500 μ/1 in terms of divalent iron ions. In the fourth step, the reaction time was 60 minutes, the reaction time was 29, the treatment method was batch treatment using a 1 ton beaker, the solid-liquid separation was the sedimentation method, the alkaline agent was 1N sodium hydroxide solution, and the alkali agent was 1N sodium hydroxide solution. When the second to fourth steps in the first invention were carried out under the conditions of pH 7 and no reducing agent added, the liquid quality of the treated liquid was as shown in Table 5.

According to Table 3, it is clear that the removability of COD and chromaticity in the first invention is significantly good.

Next, for the first process treatment solution shown in Table 2, the second
FIG. 2 shows the relationship between the COD value of the process solution and the CODI coagulated and removed by iron flocs.

According to FIG. 2, it can be seen that in the first invention, the ability to remove agglomerates of COD in the second step is significantly improved.

Next, the five gr!s shown in Table 2! The amount of ferric chloride added to the 1-step treatment solution was 300 m'J/l, 450 mY/l, and 500 rw for trivalent iron ion exchange 3'-, respectively.
The COD of the second process treatment liquid treated as 1/l was approximately the same as 580/l and 530/11560/l, respectively. By varying the amount of peroxide (X) added in 6 steps,
We investigated the relationship between the COD of the 4th step processing solution and the earliest addition of hydrogen peroxide in the 6th step when the 3rd and 4th steps were executed (Figure 6).

As is clear from this Figure 3, the CO of the rabbit 2nd process treatment solution is
It can be seen that even when the D value is adjusted to the same level, if the soluble BOD is treated in the first step to less than 50 μ/l, high COD removal performance can be achieved with the addition of a small amount of hydrogen peroxide.

EXAMPLE Activated sludge treatment was performed on the liquid molasses waste liquid shown in Table 1 by varying the amount of aeration, and the treated liquids, which had different soluble BOD, were treated with ferric chloride in the second step. A flocculation treatment was carried out with the amount added being 500 .mu./l in terms of divalent iron ions, and the relationship between the COD value of each second step treatment solution and the BOD value of the first step treatment solution was investigated (FIG. 4).

According to FIG. 4, it can be seen that when the BOD of the first step treatment liquid is 50 square meters or less, the COD treatability in the second step is rapidly improved.

Next, in the second step, the first step treatment solution having different treatability in the second step is treated by changing the amount of ferric hydroxide added, and the second step treatment solution having the same COD value is obtained. Each treatment liquid was oxidized in the third step with the same amount of hydrogen peroxide and catalyst as in Experimental Example 1, and the COD value of each fourth step treatment liquid and the first step were The relationship with the BOD value of the treatment liquid was investigated (Figure 5).

According to Figure 5, the BOD of the first process treatment liquid is 50■/l.
In this case, the COD value of the fourth process treatment solution decreases rapidly.
I understand that.

As is clear from the results of the above two experiments, according to the first invention in which the soluble BOD of the waste liquid in the aerobic biological treatment in step 1 is particularly set to 50 μ/1, it is possible to The ability to remove COD is remarkable, and a significant reduction in the amount of chemical additives can be expected, and the effect far exceeds the range expected from the above-mentioned known examples.

Next, referring to FIG. 6, an embodiment of the second invention will be described. The molasses waste liquid to be treated is guided through a pipe 23 to a heating section 24, where it is heated to a temperature of 995° C. or higher by a heating medium 25. After being heated, it is cooled by the cooling medium 27 in the cooling section 26 (first step).

In the second invention, the heating temperature of the waste liquid in the first step is important, and unless the waste liquid is heated to a temperature of 95°C or higher, the object of the invention will not be achieved. If the heating temperature is 95° C. or lower, the amount of chemicals such as flocculants and oxidizing agents added in subsequent steps will increase, the treatment effect will be poor, and the final treatment limit water quality will increase. On the other hand, by heating the waste liquid to 95°C or higher, not only can the amount of chemicals added be expected to be reduced, but also high levels of organic matter can be removed in subsequent steps without necessarily having to remove a high degree of BOD in the second step. Removability can be maintained.

There are no particular limitations on the heating method, and direct flame, steam, or other heating medium may be used. In addition, the longer the time the waste liquid is kept at 95°C or higher, the better the effect, and the higher the holding temperature, the sufficient effect can be obtained in a short time, but usually it is kept at 95°C for 1 hour or more, 105°C. ℃, 10 minutes or more is sufficient.

The purpose of cooling is to lower the temperature of the waste liquid to a temperature that allows biological treatment in the second step, and any means may be used.

Next, the first process treatment liquid is led to the biological treatment section 28,
'T1' Here, if necessary, nutrient salts 29 such as nitrogen and phosphorus are added and subjected to aerobic biological treatment (second step).

The purpose of this second step is to remove BOD components in the waste liquid, and the higher the BOD removal rate here, the better, but normally, if the BOD of the second process treatment liquid is less than 200 μ/cm, then the We can expect advanced COD and chromaticity processing in the process. There are no particular limitations on the method of aerobic biological treatment.

The second step treatment liquid is subsequently subjected to the fifth step to the fifth step, which is exactly the same as the second to fourth steps of the first invention, so the explanation thereof will be omitted. .

Example The molasses waste liquid discharged from the yeast factory and having the liquid quality shown in Table 1 was used as gr! of the second invention. After processing in the first step (heating at 95 ° C. for 1 hour) and diluting this treated liquid 5 times with fresh water, the second step is performed using a batch activated sludge method using an aeration tank with a capacity of 10 tons. Ta. In addition, the BOD load at this time is 2 K
? -BOD /n (day, liquid temperature is 35℃, aeration amount is 3
It was 7/min.

On the other hand, the stock solution was diluted 5 times with M and subjected to aerobic biological treatment under the same conditions as above (comparative example).

The liquid quality of these treatment liquids is as shown in Table 4, and it can be seen that there is no major difference in water quality, and the liquid quality is of the same level.

Table 4 Next, the amount of ferric salt added to these treatment solutions is fil.
! The third step in the second invention was carried out by changing h, and the relationship between the COD value of the above-mentioned treatment liquid and the amount of COD coagulated and removed by the iron flocs was determined (FIG. 7).

From FIG. 7, in the second invention. It is clear that the COD coagulation removal performance in the 6th step is significantly improved compared to the comparative example, and in the second invention, 300
■/1. In the comparative example, it is also 1, o o o my7t
The ferric salt of
D showed almost the same value of 510 g/l in the second invention and 480 g/l in the comparative example.

Next, the amount of hydrogen peroxide added to the third step treatment solution having the same COD value was changed in proportion, and the processing in the fourth punch of the second invention was carried out. The relationship between COD and hydrogen peroxide addition in the treated area was determined (Figure 8).

From FIG. 8, it is clear that the second invention, in which the stock solution was heat-treated in the first step, shows a small amount of hydrogen peroxide-added boiling COD removed.

As is clear from the above experimental results, according to the second invention, in which the first step of heating the stock solution to 95°C or higher is added, the amount of coagulant and hydrogen peroxide used is significantly lower, and the processing It is possible to treat liquid COD to much lower levels.

And, in the second invention, B in the aerobic biological treatment step
Another major feature is that it can perform advanced OD and chromaticity processing without being subject to many restrictions on OD processing performance.

Next, an embodiment of the fifth invention will be explained with reference to FIG. 9. Molasses waste liquid to be treated (BOD of 10.00
The organic matter in the waste liquid from the methane fermentation method is removed by adding nutrients 32 such as nitrogen and sulfur as necessary to the pipe 30 and the methane fermentation section 31. The material is processed (first step).

In the sixth invention, an important component is that the waste liquid is treated by a methane fermentation method in the first step, and this structure reduces COD in the fifth and fourth steps.

Chromaticity removability is improved.

There are no restrictions on the method of methane fermentation, and any fermentation process can be used.

The gas generated in the fermentation section 31 is led out of the system through a pipe 33 and, after being appropriately treated, is used as a heat source for fermentation, etc. The sludge is collected by solid-liquid separation by an appropriate means, and is recycled into a new container. The waste liquid is used for fermentation treatment, but excess sludge is led out of the system through a pipe 34, subjected to appropriate treatment as necessary, and then disposed of.

The first step treatment liquid is treated in the aerobic treatment section 35 by an aerobic biological treatment method by adding dilution water from the inlet pipe 36 if necessary (second step).

This step is to remove residual BOD and reducing substances such as hydrogen sulfide and reduce the amount of chemicals added such as flocculant and oxidizing agent in the sixth and fourth steps. It is desirable that the soluble BOD of the process treatment liquid is less than 300 tJJ.

There is no particular limitation on the method of aerobic biological treatment in this step.

Incidentally, the excess sludge generated in this step can be led to the methane fermentation section 31 of the first step to reduce Kl, and can be led to the third step along with the second step treatment liquid depending on the size. It is also possible to perform coagulation separation along with COD and chromaticity separation.

The second process treatment solution is sequentially subjected to the processes of the third process to the fifth process, but since these are completely the same as the second process to the fourth process of the first invention, the explanation thereof is as follows. Omitted.

EXAMPLE The molasses waste liquid discharged from the alcohol manufacturing process and having the liquid quality shown in Table 5 was treated by batch treatment using a fermenter (B).
OD load is 4 K9-BOD/, day, liquid temperature is 53℃
The methane fermentation treatment was carried out under the following conditions, and the first step treated liquid was diluted 5 times with seedlings, and the waste liquid was directly diluted 5 times, and the second step of the fifth invention was carried out under the following conditions. When the fifth step was carried out, the liquid qualities of the fifth and fourth step treatment solutions were as shown in Table 6.

Table 5 Treatment Conditions In the second step, the treatment method was a batch activated sludge method using an aeration tank with a volume of 107, and the BOD burden i was j Kq-BOrl.
/m, 1 day, liquid temperature 65℃, aeration rate 5t/min.

In the fifth step, the processing method is batch processing using a 1-ton beaker, solid-liquid separation is by sedimentation method, the amount of ferric chloride added is 5007η/7 in terms of trivalent iron ions, the XPH adjustment agent is 1N sodium hydroxide solution, and flocculation. In the fourth step, when the pH at the time was 0, the treatment method was batch treatment using a 1 ton beaker, and the amount of hydrogen peroxide added was 150η7 ton with an effective oxygen exchange of 31-
, the amount of ferrous sulfate added is 450 ■/ in terms of divalent iron ion.
1. Reaction pH was 2-9 and reaction time was 60 minutes.

In the 5th step, the L1 treatment method is batch treatment using 14 beakers, solid-liquid separation is by sedimentation method, alkaline agent is 1N hydroxide) IJum solution, pH at the time of aggregation is 7, and no reducing agent is added.

In addition, Figure 10 shows the COD value and removal C of the third process treatment solution when the amount of iron chloride added in the sixth process was varied.
It is a figure showing the relationship with OD amount.

According to the sixth invention, by performing methane fermentation before the aerobic biological treatment, the BOD components are
BOD in the aerobic treatment process is removed by approximately 70%.
Not only is the load reduced and it is easy to prepare a processing solution having an OD of 50η/or less, but also
In the process, organic components other than those removed by aerobic biological treatment are also treated, so the composition and properties will be different from that of the treated solution that is only subjected to aerobic biological treatment, and this will cause problems in later treatment steps. It brings good results and can be expected to provide advanced COD and chromaticity processing effects.

[Brief explanation of the drawing]

Figure 1 is a process explanatory diagram of the first invention, Figure 2 is a relationship diagram between the treated water COD and the amount of COD removed in the second process of the first invention and comparative example, and Figures 3 and 3 are the first invention and comparative example. Figure 4 shows the relationship between the amount of hydrogen peroxide added and the COD of the treated water in the first invention.
D, FIG. 5 is a diagram of the relationship between the first process liquid BOD and the fourth process liquid COD in the first invention, FIG. 6 is a process explanatory diagram of the second invention, and FIG. A relationship diagram between the treatment liquid COD and the amount of removed COD in the sixth step of the invention and the comparative example, FIG. 8 is a relationship diagram between the hydrogen peroxide addition in the second invention and the comparative example; The figure is a process explanatory diagram of the third invention, and FIG. 10 is a diagram showing the relationship between the treatment liquid COD and the amount of COD removed in the third process of the sixth invention and a comparative example. 2...Aerobic biological treatment section, 4...1st mixing tank, 6...
1st P)l adjustment tank, 8... intermediate solid-liquid separation tank, 11...
・Second mixing tank, 14... Oxidation reaction tank, 16... Neutralization tank, 19. Final solid-liquid separation tank, 24... Heating section, 25.
...Cooling section, 28...Biological treatment section, 31...Fermentation section, 35...Aerobic treatment section 11, ...Patent applicant
Kankyo Engineering Co., Ltd. Agent Patent Attorney Some
Hiroshi Tani Figure 1 Figure 6 Figure 9 Figure 2 Kuz * f < co o (r + y ) Figure 3 Sakae 1 Bamboo (m(]/j!) Figure 4
Figure 5'&17-J" processing 5'?, -BODC"'Aμ)
Fig. 7 Hitoshiba Iso COD (mclμ) Fig. 8 □ Seiba h Kuko, I L book t9 shi ladder 7 y 灁 Reyo ura sword Yutashi Amu Q (m9/j2) Fig. 10 50 TOo 200 500
1000 2000 Kuri Las COD (mci/))

Claims (1)

[Claims] 1) A first step in which molasses waste liquid is treated by an aerobic biological treatment method to reduce the soluble BOD of the waste liquid to 50 μ/t J-,); After adding a flocculant mainly consisting of diiron salt and adjusting the pH to a range of 3 to 5.5, suspended solids,
A second step in which organic substances and chromaticity components are coagulated and separated together with ferric hydroxide flocs, and a second step in which hydrogen peroxide and iron salt as an oxidation catalyst are added to the treatment liquid to separate organic substances and chromaticity components. A molasses waste liquid characterized by comprising a sixth step of reducing the oxidized content, and a fourth step of adding an alkali to the oxidized solution to precipitate and separate the iron salt as ferric hydroxide at a pH of 4 or higher. processing method. 2) The first step of heating the molasses waste liquid to 95°C or higher and then cooling it.
a second step in which the first step treatment liquid is treated with an aerobic biological treatment method; and a flocculant mainly containing ferric salt is added to the second step treatment liquid to bring the LPH in the range of 3 to 5.5. After the adjustment, there is a 6th step in which suspended solids, organic substances, and color components are coagulated and separated together with ferric hydroxide flocs, and hydrogen peroxide and iron salt as an oxidation catalyst are added to the 5th step treatment solution. a fourth step in which organic substances and chromaticity components are oxidized and decomposed; and a fifth step in which an alkali is added to the oxidation treatment solution to precipitate and separate the iron salt as ferric and ferric hydroxide at a pH of 4 or higher. A method for treating molasses waste liquid in which inclusion is an erectile symptom. 3) A first step in which molasses waste liquid is treated with a methane fermentation method to remove organic substances in the waste liquid, a second step in which the first step treated liquid is treated with an aerobic biological treatment method, and a second step treated liquid is After adding a flocculant mainly consisting of ferric salt and adjusting the pH to a range of 3 to 5.5, suspended solids, organic substances, and color components are coagulated and separated together with ferric hydroxide flocs. A third step, a fourth step in which hydrogen peroxide and an iron salt as an oxidation catalyst are added to the third step treatment solution to oxidize and decompose organic substances and chromaticity components, and an alkali is added to the oxidation treatment solution. A method for treating molasses waste liquid, comprising a fifth step of precipitating and separating the iron salt as ferric hydroxide at a pH of 4 or higher.