JPS59162994A - Treatment of waste water containing organic substance - Google Patents

Abstract

PURPOSE:To efficiently treat waste water with the small amounts of hydrogen peroxide and a ferrous salt to be added, by oxidatively treating said waste water containing organic substance, adjusting its pH to precipitate flocks, and circulatively mixing a part of treated water after being subjected to solid-liquid separation in the waste water. CONSTITUTION:Treated water 3 circulated from a solid-liquid separation tank 2 is mixed in waste water 1 containing organic substance, and the resulting liquid mixture is supplied to a reaction tank 4. Hydrogen peroxide 5, a ferrous salt 6 such as ferrous sulfate and optionally a pH adjusting agent 7 are charged in the reaction tank 4 to adjust a pH to about 2-4, and the liquid mixture is agitated therein for a predetermined time to oxidatively decompose dissolved organic substance. After the oxidative reaction is finished, the oxidatively treated water 8 is sent to a coagulation tank 9, wherein pH is adjusted to about 5-8 by the addition of an alkali agent 10 to precipitately coagulate flocks based on ferric hydroxide. Thereafter, the liquid mixture is separated into treated water 3 and sludge 11 in the precipitation tank 2, and a part of said treated water 3 is circulated to raw waste water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing organic substances, and more specifically, the present invention relates to a method for treating wastewater containing organic substances. This article relates to a wastewater treatment method for removing wastewater using.

The method for treating wastewater containing organic substances using hydrogen peroxide and iron salts utilizes free radicals with strong oxidizing power that are generated when hydrogen peroxide, an oxidizing agent, reacts with an iron salt catalyst. ,
Since it is an effective method, it has been applied to actual wastewater treatment.

The conventional method is to add hydrogen peroxide and a ferrous salt such as ferrous sulfate to organic substance-containing wastewater to oxidize and decompose organic substances under acidic conditions of pn 2 to 4, and then add alkali to adjust the pH.
Coagulates and separates with iron hydroxide produced by adjusting to 5 to 8,
This is a method of obtaining treated water.

In the treatment of wastewater containing organic substances using this conventional method, large amounts of hydrogen peroxide and iron salts are required when the wastewater contains high concentrations of organic substances or persistent organic substances. Furthermore, there is a problem that even if a large amount of these chemicals is added, the organic substances cannot be removed sufficiently. This is due to the fact that hydrogen peroxide is ineffectively consumed in the oxidation reaction and the oxidation produced by the reaction with iron salts is caused by the attempt to treat organic substances in wastewater down to low concentrations by adding large amounts of chemicals at once. This is thought to be due to the fact that free radicals do not work effectively on organic substances, or that undecomposed organic substances cannot be sufficiently coagulated and separated by iron hydroxide produced by adding alkali after the oxidation reaction. .

The above-mentioned problems can be solved to some extent by the already known method of treating wastewater in two stages (Japanese Unexamined Patent Publication No. 163796/1983). This two-stage processing method is
This is a method in which the treated water obtained by treating wastewater by the above conventional method is further treated by the conventional method, by adding hydrogen peroxide and iron salt in portions and repeating the oxidative decomposition and coagulation separation of organic substances twice. The chemicals can be used more effectively than the conventional method in which the entire amount of these chemicals is added at once, and relatively high processing efficiency can be obtained. However, since each stage of the two-stage process is performed using the conventional method, the above-mentioned problems have not been sufficiently resolved, and there is a limit to the improvement in processing efficiency compared to the conventional method. However, the treatment process is complicated and the equipment costs for the treatment equipment are high.

In addition, multi-stage treatment (in which wastewater is treated in three or more stages)
It is conceivable that higher treatment efficiency can be obtained by repeating oxidative decomposition and coagulation separation of organic substances three or more times, but the treatment process is more effective than the two-stage treatment method because hydrogen peroxide and iron salts work more effectively. The purpose of this invention is to provide a wastewater treatment method that has excellent treatment efficiency, a simple treatment process, and low equipment costs.

To achieve this objective, the present invention adds hydrogen peroxide and iron salt to organic substance-containing wastewater in a reaction tank to oxidize and decompose organic substances, and then adds an alkali to coagulate them together with iron hydroxide in a flocculation tank. , characterized in that the treated water obtained by separating the produced flocs in a solid-liquid separation tank is mixed with the wastewater. In particular, the treated water obtained by oxidatively decomposing organic substances in the wastewater and then coagulating and separating the wastewater. The key is to mix it with raw wastewater and treat it.

According to the method of the present invention, by diluting the raw wastewater with treated water, hydrogen peroxide and iron salts added to the raw wastewater can be used at low concentrations, so that these chemicals and the oxidizing free radicals generated can be used. It works effectively in the oxidative decomposition and coagulation separation of organic substances in wastewater without being wasted, and because the organic substances are repeatedly oxidized and decomposed and coagulated and separated many times by circulating the treated water. Also, wastewater containing highly concentrated or persistent organic substances can be efficiently treated with a small amount of chemicals added.

Therefore, for example, the utilization rate of hydrogen peroxide, which can be obtained by dividing the amount of COD removed by the amount of hydrogen peroxide added, can be extremely increased by increasing the circulation rate of treated water (the ratio of the amount of circulation to the amount of raw wastewater). , it is possible to obtain higher processing efficiency than the two-stage processing method.

However, the treatment efficiency can be changed by changing the circulation rate of the treated water, so if the quality of the continuously flowing wastewater fluctuates, simply adjusting the amount of hydrogen peroxide or iron salt added can be used. Another major feature that conventional methods and two-stage treatment methods do not have is that by changing the water circulation rate, it is possible to cope with relatively large fluctuations in the quality of wastewater and to obtain stable treated water quality.

Next, the present invention will be explained in detail based on the drawings.

FIG. 1 is a flow sheet showing an embodiment of the method of the present invention.

The raw wastewater 1 is treated water 3 which is circulated from the solid-liquid separation tank 2 without being separated.
and flows into the reaction tank 4. In the reaction tank 4, hydrogen peroxide 5, an iron salt 6 such as ferrous sulfate, and, if necessary, a p)l adjuster 7 are added, and are stirred for a predetermined period of time under acidic conditions of usually pH 2 to 4 to dissolve. Organic substances are oxidized and decomposed. In this case, the time for the oxidation reaction depends on the concentration of the wastewater, the water temperature,
Although it varies depending on the concentration of hydrogen peroxide and iron salt, the stirring time can be determined by experiment. The oxidized water 8 that has undergone the oxidation reaction in the reaction tank 4 flows into the coagulation tank 9 and is adjusted to a pH of about 5 to 8 by adding an alkali agent 10, and flocs mainly composed of iron hydroxide precipitate and coagulate. In the settling tank 2, the treated water 3 and sludge 11 are separated.

As explained above, according to the present invention, wastewater containing difficult to decompose organic substances or highly concentrated organic substances, which conventionally required large amounts of hydrogen peroxide and iron salts, can be treated with a small amount of hydrogen peroxide and iron salts. The addition of iron salts allows for extremely efficient treatment.

In particular, it is possible to obtain higher treatment efficiency than a method of treating wastewater in two stages (two-stage treatment method), and it is also possible to cope with large fluctuations in the quality of inflowing wastewater.

In addition, compared to the two-stage treatment method, the treatment process is simpler and the equipment cost for wastewater treatment equipment is lower.Furthermore, since the amount of iron salts added can be reduced, the amount of sludge generated is small, making it less difficult to use in real life. Suitable for wastewater treatment.

Application example 1 Figure 2 shows a system in which the reaction tank 4 in Figure 1 is partitioned into multiple tanks,
1 is a flow sheet showing an applied method of the present invention configured to add hydrogen peroxide 5 and/or iron salt in portions to each tank. In reaction 1, by adding the required amount of hydrogen peroxide and iron salt to the tank and allowing the reaction to occur little by little, the ineffective consumption of hydrogen peroxide is further suppressed and the process becomes effective for the oxidative decomposition of organic substances. The processing efficiency can be further increased.

Application Example 2 The method of the present invention is also effective for wastewater treatment when the concentration of organic substances in continuously flowing wastewater fluctuates greatly, but in this case, the treatment efficiency increases as the circulation rate of the treated water increases. The quality of treated water can be controlled to be kept constant by changing the circulation rate in response to changes in the concentration of organic substances. FIG. 3 is a flow sheet showing an embodiment in which the present invention is applied to control of wastewater treatment. After the flow rate of the raw wastewater 1 is measured with a flowmeter 12, a part of it is introduced into a flow cell of an absorption photometer 13, and the absorbance at a specific wavelength that correlates with the chromaticity and the concentration of persistent organic substances is measured. Ru. Furthermore, the flow rate (circulation amount) and absorbance of the circulated treated water 3 are similarly measured by the flowmeter 12' and the absorption photometer 13'. These raw wastewater 1
The circulation amount is adjusted by the control pulp 15 via the control device 14 having an arithmetic function according to the absorbance and flow rate of the pulp and the absorbance of the treated water. At this time, when the absorbance is large, that is, when the chromaticity or organic matter concentration is high, the amount of circulation increases and treatment efficiency is increased, and conversely, when the absorbance is small, the amount of circulation is adjusted to decrease, resulting in constant stability. Treated water can be obtained.

Example 1 As raw water, supernatant water obtained by coagulating and precipitating treated water obtained by biologically treating a pyrolysis liquid of sludge with a ferric salt flocculant of 700 rl] g/i (as Fe atoms) was used.

CODMn is 52011 Ig/l. When this raw water was treated by the method of the present invention shown in Figure 1, the circulation rate of the treated water (the ratio of the amount of circulation to the amount of raw water), hydrogen peroxide (H
The amounts of added ferrous sulfate (FeSO2) and ferrous sulfate (FeSO), and the treated water CODMn are summarized in Table 1. However, the residence time in the reaction tank was 30 minutes, the pH was set to 3.5, and the pH in the coagulation tank was set to 5 using Ca(OH)2 as an alkaline agent. In addition, in order to compare the processing efficiency at each circulation rate, COD
The value obtained by dividing the amount of Mn removed by the amount of H2O2 added (in terms of O atoms) was determined and shown as the H2O2 utilization rate.

The higher the circulation rate, the higher the treatment efficiency, and the higher the circulation rate, the higher the treatment efficiency, and the smaller the amount of H2O2 and F e S 04.
The same quality of treated water was obtained by adding .

The H2O2 utilization rate may exceed 100% because of C.
This is because ODM is removed not only by oxidative decomposition using H2O2 in the reaction tank but also by coagulation and separation using iron hydroxide in the coagulation tank and solid-liquid separation tank.

Table 1 Example 2 As raw water, supernatant water obtained by coagulating and precipitating treated water obtained by biologically treating machine factory wastewater with a ferric salt coagulant of 60 mg/1 (as Fe atoms) was used. CODMn is 55.3mg/l
It is. The relationship between the circulation rate of treated water and the treated water COD M n when this raw water is treated by the method of the present invention shown in Figure 1 is shown by curve A in Figure 4, and for comparison, the same raw water was treated by the conventional method. Treated water C when treated with a two-stage treatment method in which the treated water treated with (first stage) is further treated with the conventional method (second stage)
OD M n is indicated by a broken line B.

However, in the method of the present invention, H2O
In the two-stage treatment method, equal amounts of H2O2 and FeSO4 were added in the first and second stages, and the total amount of addition was 30rrvllll.

The concentration was adjusted to 120 mg/l.

In addition, the residence time in the reaction tank is 30 minutes (in the two-stage treatment method, the residence time is 30 minutes).
total residence time of the first and second stage reaction tanks), p of the reaction tank
H is set to 3.5, and the flocculation tank contains Ca(OH) in the alkaline agent.
)2 to bring the pH to 5.

When the same amount of H2O2 and FeSO4 is added, the method of the present invention provides better treated water quality than the conventional method (circulation rate 0%). The quality of treated water was better than before.

Example 3 As raw water, supernatant water obtained by coagulating and precipitating treated water obtained by biologically treating chemical plating factory wastewater with a ferric salt coagulant of 800 mg/l (as Fe atoms) was used.

COD M n is 446rr@/l. This raw water is processed using the method of the present invention shown in Figure 1, and by dividing the reaction tank into three tanks (1st tank to 3rd tank) and adding the required amount of H2O2 and F to each phase.
FIG. 5 shows the relationship between the circulation rate of treated water and the treated water CODMn when treated by the method of application example 1 in which eSO4 is added in portions.

In FIG. 5, the curve C is the result obtained by the method of the present invention, the curved line is the result obtained by the method of Application Example 1, and for comparison, the CODMn of the water treated by the two-stage treatment method is shown by the broken line E.

The processing conditions for these methods are that the residence time in the reaction tank is 1 hour (two-stage treatment method, the method of application example 1 is the total residence time of each reaction tank), the pH of the reaction tank is 3.5, The pH of the coagulation tank was adjusted to 5 using Ca(OH)2 as an alkaline agent. Also, H2(,) in each method
The amounts of i and FeSO4 added are shown in Table 2.

Even better treatment results were obtained by applying the method of the present invention, and better treated water quality was obtained than in the two-stage treatment method with 100 cycles of treated water circulation.

Table 2 Example 4 Treated water obtained by biologically treating pyrolysis liquids of three types of sludge with different CODMn as raw water was treated with a ferric salt flocculant of 80%
0 ■#! Supernatant water coagulated and precipitated (as Fe atoms) was used. COD Mn is 46 srng,/l respectively
, 52 orrv:/1.61 orrrg/l. When each raw water was treated under the same reaction tank residence time and pH conditions as in Example 1, the results shown in Table 3 were obtained. Even when the CODM n of the raw water was different, equivalent treated water quality was obtained by adding the same amount of H,02 and FeSO4 by changing the circulation rate.

Table 3

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an embodiment of the method of the present invention;
2 and 3 show flow sheets illustrating an embodiment of the applied method of the present invention. Figures 4 and 5 show the results of Example 2 and Example 3, respectively. 1... Raw wastewater, 2... Solid-liquid separation tank, 3... Treated water, 4... Reaction tank, 5... Hydrogen peroxide, 6... Iron salt, 7... pH Conditioner, 8... Oxidized water, 9...
Coagulation tank, 10... Alkaline agent, 11... Sludge,
12 and 12'...flow meter, 13 and 13'...
・Absorption photometer, 14...control device with calculation function,
15...Control pulp. Japan Peroxide Co., Ltd. 1st

Claims (1)

[Claims] 1. Oxidative decomposition of organic substances by adding hydrogen peroxide and iron salt to wastewater containing organic substances. A method for treating wastewater containing organic substances, characterized in that a part of the treated water obtained by coagulation and separation with iron hydroxide produced by adding an alkali is circulated and mixed with the wastewater. 2. The method for treating organic substance-containing wastewater according to claim 1, characterized in that by changing the circulation rate, the COD of the treated water is kept constant regardless of changes in the quality of the inflowing wastewater.