GB2302328A

GB2302328A - Method of and system for disposing sewage and waste water through thermal oxidation

Info

Publication number: GB2302328A
Application number: GB9612871A
Authority: GB
Inventors: Tae Young An; Kyoung Soo An
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-06-21
Filing date: 1996-06-19
Publication date: 1997-01-15
Anticipated expiration: 2016-06-19
Also published as: CN1150126A; KR0151355B1; KR960037582A; GB9612871D0; GB2302328B

Abstract

There is provided a method of disposing sewage and waste water through thermal oxidation, comprising the steps of: collecting and sedimenting sewage and waste water in a storage tank; adding 100-5,000 mg/l of a first oxidizing agent to the sewage and waste water; reacting the sewage and waste water with the first oxidizing agent in a first reaction vacuum tank at 40 to 90 {C for 15-45 min while stirring; and filtering the resulting sewage and waste water, that contributes to the prevention of water pollution and to the protection of nature.

Description

METHOD OF AND SYSTEM FOR DISPOSING SEWAGE AND WASTE WATER THROUGH THERMAL OXIDATION BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a method of and system for disposing sewage and waste water through thermal oxidation. The "sewage and waste water" here is used to mean all sewage and waste water from factories as well as homes. In more detail, the present invention relates to a thermal oxidation method and system capable of reusing the sewage and waste water with great efficiency and economic advantage.

Description of the Prior Art In order to better understand the background of the invention, a description will be given of a conventional method of waste water disposal, in connection with some drawings. As illustrated in Fig. 1A, waste water is first introduced into a storage tank and then into a pH-control tank at which the waste water has pH values suitable for treatment and next to a reaction tank where various chemicals react with the contaminants contained in the water to detoxicate them. Thereafter, the water is transferred to a coagulation tank and flows into a sedimentation tank or flocculation tank. While undergoing the last two courses, the contaminants are removed.

Alternatively, after the pH-control tank, the waste water enters an aeration tank in which biological treatment is carried out using microorganisms, as illustrated in Fig.

1B. The contaminants are taken out during the experiment in a sedimentation tank. These two methods may be combined.

According to such conventional methods, the removal ratio of organic material (biochemical oxygen demand) is found to be 30 % upon physical treatment, 40-50 % upon chemical treatment and 70-90 % upon biological treatment.

These disposal efficiencies are very low when compared with the expense of the installations and their operation. Such systems are quite poor in disposal efficiency, particularly, for hard-to-decompose waste water including the waste water from dyeing, printing, or tanning processes. The economics of these methods are unfavorable so that they are almost useless in practice.

If even a small amount of the incompletely disposed sewage and waste water is released to neighboring rivulets or rivers, it contaminates the natural circumstance thereof, destructurizes the ecosystem, and finally is a menace to mankind. In addition, the shortage of industrial water, which may be ascribed to such incomplete reuse or other factors, becomes a barrier to the development of industry.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method of disposing sewage and waste water by which the heavy metals and color of the sewage and waste water can be completely removed.

It is another object of the present invention to provide a method for treating and changing sewage and waste water into industrially usable water.

It is a further object of the present invention to provide a method of disposing sewage and waste water which can contribute to the prevention of water pollution and to the protection of nature.

It is still another object of the present invention to provide an economically favorable method of disposing sewage and waste water.

It is still a further object of the present invention to provide a system for disposing sewage and waste water through thermal oxidation.

In accordance with an aspect of the present invention, there is provided a method of disposing sewage and waste water through thermal oxidation, comprising the steps of: collecting and sedimenting sewage and waste water in a storage tank; adding 100-5,000 mg/l of a first oxidizing agent to the sewage and waste water; reacting the sewage and waste water with the first oxidizing agent in a first reaction vacuum tank at a 40 to 90 "C for 15-45 min while stirring; and filtering the resulting sewage and waste water.

In accordance with another aspect of the present invention, there is provided a system for disposing sewage and waste water through thermal oxidation, comprising: a reaction vacuum tank coated with a heat shield material; an inlet port provided at one side of the reaction vacuum tank for supplying the sewage and waste water into the reaction vacuum tank and an outlet port provide at the opposite side of the reaction vacuum tank for draining the sewage and waste water; two semi-circular partitions for steadily maintaining the staying time in the reaction vacuum tank, each being open at the lower part and positioned at the sides of the inlet port and the outlet port; a stirrer positioned at the center of the reaction vacuum tank for homogenizing the sewage and waste water; a means for heating the sewage and waste water inside the reaction vacuum tank; a pressure gauge for monitoring the pressure of the inside of the reaction vacuum tank; and a gas exhaust line connected to the pressure gauge for transferring the gas generated inside the reaction vacuum tank back to a storage tank or an incoming conduit.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which: Figs. 1A and 1B are process schemes showing conventional methods of disposing sewage and waste water; Fig. 2 is a process scheme showing a method of disposing sewage and waste water through thermal oxidation according to the present invention; Fig. 3 is a cross sectional view showing a reaction vacuum tank according to the present invention; and Fig. 4 is a plan view showing the reaction vacuum tank, taken through line A-A of Fig. 3.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a storage tank collecting sewage and waste water is followed by a completely closed, vacuum reaction tank instead of the pHcontrol tank or aeration tank in the prior art, as shown in Fig. 2. Many vacuum reaction tanks, connected in a series, may be employed. The sewage and waste water from the vacuum reaction tank enters a pH-control and sedimentation tank and a solid-liquid-separation tank, where primary treatment is carried out. Thereafter, the water is secondarily treated in an active carbon filtering tank and a effluent tank.

For a more detailed description, a reference will be made to Fig. 3 which schematically shows the vacuum reaction tank. The vacuum reaction tank 10 is equipped with a chemical tank which contains a mixture of oxidizing agents and heavy metal treating agents. When sewage and waste water flow into the vacuum reaction tank 10 through an incoming conduit 16, a quantitative pump 12 is operated to pump the agent mixture into the conduit 16 at which the sewage and waste water is combined with the agents. Here, the expression "vacuum reaction tank" has the same meaning as "reaction bath" or "reaction tank" as used below.

Outside the vacuum reaction tank 10, a heating means is provided to promote the reaction of the oxidizing agents with sewage and waste water by elevating the temperature of the vacuum reaction tank. This reaction temperature is preferably maintained at 40 to 90 C and more preferably at 70 to 90 C. For the heating means 18, an electric heater, a steam boiler and the like are employed.

With regard to the oxidizing agents, two kinds, a first oxidizing agent and a second oxidizing agent, are used according to the present invention.

For the first oxidizing agent, He02, Mono2, HNO3, KMnO4 and the mixtures thereof may be used. It is efficiently preferred that the first oxidizing agent is selected depending on the kind of the sewage and waste water to be treated. In general, a first oxidizing agent mixture of H202 and KMnO4 where H202 amounts to 10-40 mg/liter with 4,000-80,000 mg/liter of KMnO4 can oxidize most sewage and waste water. The suitable concentration of the first oxidizing agent to treat ordinary sewage and waste water is on the order of 100-5,000 mg per liter of sewage and waste water, but may depart from such range depending on the BOD and COD of sewage and waste water.

The second oxidizing agent is at least one selected from the group consisting of NaClo3, KMnO4, NaOCl, KCr207, KNO3, NaNO3, FS208 and H2SO4. Most sewage and waste water can be treated with a mixture consisting of KMnO4, K2S208 and H2SO4, each having a concentration of 4,000-80,000 mg/liter, 1,000-3,000 mg/liter and 70-150 mg/liter, or with a mixture consisting of KMnO4, NaOCl and K2S208, each having a concentration of 4,000-80,000 mg/liter, 1,000-2,000 mg/liter and 1,000-3,000 mg/liter. Like the first oxidizing agent, the second oxidizing agent has a suitable concentration to treat ordinary sewage and waste water ranging from 100 to 5,000 mg per liter. However, this range may be varied with the BOD and COD of the sewage and waste water to be treated.

Optionally, heavy metal-treating agents may be used in combination with the first oxidizing agent. In this case, the heavy metal-treating agent can be adopted from any commercially available agents. Preferably, "EPOFLOC L-l", sold by Yong I1 Chemical Co. Ltd., Korea, "ORITOL-S", sold by An Kook Chemical Co. Ltd., Korea, and NaOH alone or in combination is used for sewage and waste water containing heavy metals. In terms of cost and efficiency, the heavy metal-treating agents are used preferably at an amount of 10 to 100 mg and more preferably 20 to 50 mg per liter of sewage and waste water.

As mentioned above, the kind and concentration of the agents used to treat sewage and waste water may be varied with the kind of the sewage and waste water to be treated but, in most cases, the ranges as set forth above can be preferably applied.

In the vacuum reaction tank 10, sewage and waste water is reacted with various agents introduced together. The reaction is continued for 15 to 40 min in the reaction tank preferably for 30 to 40 min.

During this reaction period, a stirrer 15 which is positioned at the center of the reaction tank 10 is operated to homogenize the reaction system. In this regard, a plurality of stirrers may be provided. After being treated with the agents, the sewage and waste water is drained through an outgoing line 17 which is located at the opposite side of the incoming conduit 16. As shown in Fig. 3, two semi-circular partitions 19, each open at the lower part, are provided at the sides of the incoming conduit 16 and the outgoing line 17. While the sewage and waste water is treated, a vacuum is maintained in the reaction tank 10. For this, the gas generated within the reaction tank 10 during the reaction is exhausted at an upper region through an exhaust valve 14 leading to the storage tank or the incoming conduit, under the monitor of a pressure gauge 13.That is, the gas generated from the reaction of the sewage and waste water with the oxidizing agents within the closed vacuum reaction tank 10 is transferred back to the storage tank or the incoming conduit, thereby preventing secondary contamination. The reaction tank 10 is coated with a heat-insulating material 20 with the aim of reducing heat loss. Any heat insulating material typically used is adequate.

In principle, sewage and waste water, together with oxidizing agents and other proper chemicals, is introduced through the conduit 16 into the inside of the vacuum reaction tank 10, mixed homogeneously by the stirrer 15, reacted with them while the heating means 18 works to maintain the reaction temperature at 40 to 90 C, and drained through the outgoing line 17. During this procedure, the vacuum reaction tank 10 is maintained at a vacuum state by the exhaust valve 14 leading to the storage tank or the incoming conduit.

With reference to Fig. 4, there is a plan view taken through line A-A of Fig. 3. As shown in this figure, the two semi-circular partitions 19, each open at the lower part, are located at the sides of the incoming conduit 16 and the outgoing line 17, respectively, so as to provide enough time to fully react the sewage and waste water with the agents. Thus, the introduced sewage and waste water is supplied from the lower part.

Complete reaction is not accomplished in conventional open reaction tanks or by heating to less than 40 c.

Particularly, open reaction tanks are of no utility value since they are very high in operation cost and show an efficiency as low as 50 % or less.

According to the present invention, if sewage and waste water is collected and introduced into the storage tank, a level switch senses the amount of the sewage and waste water and signals to a central control (not shown).

Then, under the central control, all machines are operated, for example, to automatically pump the sewage and waste water. The sewage and waste water of the storage tank starts to flow into the reaction tank. At the same time, the injecting pump 12 connected to the chemical tank 11 works to transfer the oxidizing agents from the chemical tank 11 to the incoming conduit 16. Hence, the sewage and waste water enters the reaction tank in a mixed state with the oxidizing agents. This mixture is homogeneously mixed by the stirrer in the vacuum reaction tank 10 completely closed. The high temperature maintained by the heating means 18 makes it easy to oxidize the sewage and waste water.After being subjected to pH adjustment in a tank, the sewage and waste water is transferred to a sedimentation tank and next to the solid-liquid separation tank where the sewage and waste water is separated into a supernatant and a sludge. The supernatant is filtered by, for example, an active carbon filter and ionic exchange columns. The water which has undergone the above processes is collected in the effluent tank or the recycling tank.

The resulting water can be used as industrial water as well as when washing toilets or cars. Meanwhile, the sludge left in the sedimentation tank may be treated in an ordinary manner.

In an aspect of efficiency, sewage and waste water is preferably treated for 15 to 40 min. in each reaction tank and more preferably for 30 to 40 min.

The sewage and waste water which have undergone the processes in the reaction vacuum tank(s) is now transferred to the pH-control and sedimentation tank. As a pH-control agent, a mixture of sulfuric acid (H2SO4) and sodium hydroxide (NaOH) is employed.

A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed as the limit of the present invention.

Dyeing Waste Water Waste water taken out of an end disposal station of the Panwol industrial complex, Ansan, Korea, was treated according to a conventional method and the present method.

The waste water largely resulted from bleaching, refining and washing. Panwol industrial complex generates such waste water at an amount of 100,000 m3 per day.

Following is the analysis result of the waste water having an average concentration.

pH : 6-7 BOD (Biochemical Oxygen Demand) : about 300 mg/l COD (Chemical Oxygen Demand) : about 400 mg/l SS (Suspended Solid) : about 120 mg/l N-H (Normal Hexane) : about 35 mg/l Color : 800 COMPARATIVE EXAMPLE I The waste water collected in a tank was treated with NaOH, to adjust pH into 6-8. It was biologically treated by a standard active sludge method, followed by a secondary chemical method using a mixture of equivolumes of H2O2, Fell3 and Al2(SO4)3 17H2O.

However, the resulting water was found to have a BOD of 50 mg/l and a color index of 100 e and was virtually impossible to reuse. Further, another significant problem of such a conventional method was that the disposal efficiency was very low. This limit has restrained the investment for production facilities. In addition, such a method requires a large site for disposing waste water.

EXANPLE I According to the method of the present invention, the waste water was treated in two reaction vacuum tanks connected in a series and subjected to solid liquid separation. The results are given as shown in Table 1 below. The first oxidizing agent which was introduced to the first reaction vacuum tank, together with the waste water, contained a volume ratio of 1:20 of 35 % H202 to 2.5 N KMnO4. As the second oxidizing agent, a mixture comprising 2.5 N KMnO4, 0.01 M FS208 and 17 t H2SO4 at a volume ratio of 10:1:2.5 was used. For the heavy metaltreating agent, "EPOFLOC L-l", commercially available from Yong I1 Chemical Co. Ltd., Korea, "ORITOL-S", commercially available from An Kook Chemical Co.Ltd., Korea, and 0.1 N NaOH were combined in a volume ratio of 1:1:100. While the first oxidizing agent and the heavy metal-treating were used in the first reaction vacuum tank, the second oxidizing agent was added in the second reaction vacuum tank. Each reaction tank was maintained at 70 to 90 C and operated for 30 min. to react the agents with the waste water. In the conventional method, solid-liquid separation was accomplished by using a coagulation agent and promoter, prior to the sedimentation tank. By contrast, the waste water was left to sediment sludge, after pH adjustment.

TABLE 1

Conc. Effic. of Chemicals (mg/l) Untreated Treated Disposal 11 1st Oxidizing II Agent 1,100 pH 4-10 7 100 % Heavy metal BOD BOD 300 mg/l 2 mg/l 99.4 % Treating 50 COD COD400 mg/l 4 mg/l 99.0 % 2nd Oxidizing SS 120 mg/l 0 100 % Agent 1,100 N-H 35 mg/l 0 100 % NaOH 100 Color 100 0 100 % EXAMPLE II Waste water having a BOD of 240 mg/l was disposed in the method according to the present invention. The results are given as shown in Table 2 below. As apparent from this table, the disposal efficiency was improved when the reaction temperature increased. Only the same second oxidizing agent as used in Example I and a neutralizing agent were employed because the waste water did not contain heavy metals. Thus, only one reaction vacuum tank was necessary.

TABLE 2 Disposal Efficiencies according to Reaction Temperatures BOD (mg/l) 2nd Oxidi. Neutral. Reac. Reac.

Untreated Treated Effici. Agent Agent Temp. Time 240 2 99.2 % 400 mg/l 50 mg/l 80"C 40min 240 10 95.8 % 400 mg/l 50 mg/l 60"C 40min 240 20 91.7 % 400 mg/l 50 mg/l 40 C 40min EXAMPLE III Waste water having a COD of 400 mg/l was disposed in the method according to the present invention. The procedure of Example I was repeated using the same oxidizing agents. The results are given as shown in Table 3 below. From the table, it is apparent that longer reaction time had better effect.

TABLE 3 Disposal Efficiencies according to Reaction Time BOD (mg/l) Reaction Reaction.

Untreated Treated Efficiency Temperature Time Color 400 2 99.0 % 80 C 40 min 0 400 4 97.5 % 80 C 35 min 0 400 10 97.5 % 80 C 30 min 100 400 100 75.0 % 80 C 25 min 200 As informed from Tables 1, 2 and 3, the disposal efficiency is affected by the concentrations of the first, the second and the heavy metal-treating agents, the reaction temperature and time. That is, the concentrations of the oxidizing agents must be appropriately adjusted depending on the contamination level of waste water and the necessary cleanness of the water released. Longer time and higher temperature are required for reusable industrial water.

For example, when disposing waste water having a COD of 400 mg/l, 1,100 mg/l is required for the first oxidizing agent, 1,000 mg/l for the second oxidizing agent and 100 mg/l for the neutralizing agent. In order to remove COD and color completely, the reaction should be carried out at 80 C or higher for at least 35 min. For the waste water containing heavy metals, 10-100 mg/l of heavy metaltreating agent is necessary for good disposal efficiency.

As described hereinbefore, sewage and waste water can be disposed economically and efficiently into reusable industrial water by the method of the present invention.

Therefore, the present invention contributes to the prevention of water pollution and to the protection of nature.

The present invention has been described in an illustrative manner, and it is to be understood the terminology used is intended to be in the nature of description rather than of limitation.

Many modifications and variations of the present invention are possible in light of the above teachings.

Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

WHAT IS CLAIMED IS:

1. A method of disposing sewage and waste water through thermal oxidation, comprising the steps of: collecting and sedimenting sewage and waste water in a storage tank; adding 100-5,000 mg/l of a first oxidizing agent to the sewage and waste water; reacting the sewage and waste water with the first oxidizing agent in a first reaction vacuum tank at a 40 to 90 C for 15-45 min while stirring; and filtering the resulting sewage and waste water.

2. A method in accordance with claim 1, further comprising the step of adding 10-100 mg/l of a heavy metaltreating agent to said first oxidizing agent, prior to the reacting step.

3. A method in accordance with claim 1, further comprising the steps of adding 100-5,000 mg/l of a second oxidizing agent to the sewage and waste water coming from said first reaction vacuum tank in a second reaction vacuum tank and reacting the sewage and waste water with the second oxidizing agent at a 40 to 90 C for 15-45 min while stirring, prior to the filtering step.

4. A method in accordance with claim 1, wherein said first oxidizing agent is at least one selected from the group consisting of H202, MnO2, HNO3 and KMnO4.

5. A method in accordance with claim 1 or 4, wherein said first oxidizing agent comprises H202 and KMn04 at an amount of 10-40 mg and 4,000-80,000 mg per liter of water, respectively.

6. A method in accordance with claim 3, wherein said second oxidizing agent is at least one selected from the group consisting of NaClo3, KMnO4, NaOCl, KCr207, KNO3, NaNO3, K2S208 and t2SO4.

7. A method in accordance with claim 3 or 6, wherein said second oxidizing agent comprises 4,000-80,000 mg of KMnO4, 1,000-30,000 mg of K2S208, and 70-150 mg of H2SO4 per liter of water.

8. A method in accordance with claim 3 or 6, wherein said second oxidizing agent comprises 4,000-80,000 mg of KMnO4, 1,000-2,000 mg of NaOCl and 1,000-3,000 mg of K2S208 per liter of water.

9. A method in accordance with claim 1, wherein said filtering step comprises the use of active carbon and ionic exchange resin.

10. A system for disposing sewage and waste water through thermal oxidation, comprising: a reaction vacuum tank coated with a heat shield material; an inlet port provided at one side of the reaction vacuum tank for supplying the sewage and waste water into the reaction vacuum tank and an outlet port provided at the opposite side of the reaction vacuum tank for draining the sewage and waste water; two semi-circular partitions for steadily maintaining the staying time in the reaction vacuum tank, each being open at the lower part and provided at the sides of the inlet port and the outlet port; a stirrer provided at the center of the reaction vacuum tank for homogenizing the sewage and waste water; a means for heating the sewage and waste water inside the reaction vacuum tank; a pressure gauge for monitoring the pressure of the inside of the reaction vacuum tank; and a gas exhausting line connected to the pressure gauge for transferring the gas generated inside the reaction vacuum tank back to a storage tank or an incoming conduit.