JPS6041999B2 - Wastewater purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying wastewater with ozone.

In recent years, the need for advanced treatment of industrial wastewater, urban sewage, etc. has increased in order to prevent water pollution and secure water resources, and attempts have been made to develop various advanced treatment technologies.

In advanced treatment of industrial wastewater and urban sewage, one of the major technical issues is the effective removal of soluble organic matter. Activated sludge method,
There are biological treatment methods such as the watering hearth method, biological filtration method, rotating disk method, and contact oxidation method, but these treatment methods are difficult to perform sophisticated treatment in principle, especially when COD (chemical oxygen demand) may not be able to be removed sufficiently.

Moreover, if more advanced treatment is required, steps such as activated carbon adsorption and ozone treatment must be added. Ozone treatment uses the strong oxidizing power of ozone to oxidize and decompose organic substances.

Ozone is a molecule consisting of three oxygen atoms, and it can be easily obtained by electrical discharge using oxygen or air as a raw material, and even if it remains in wastewater, it is decomposed into oxygen molecules in a relatively short time, so it does not cause secondary pollution. It has excellent properties as a chemical used for water treatment, such as being worry-free. However, even with the acid power of ozone, it is not possible to oxidize and decompose all organic substances.

Generally speaking, it is effective in cleaving unsaturated bonds such as ethylene bonds, but there is a limit to the oxidation of saturated compounds due to its reaction kinetics. This is reflected in the evaluation that although it is effective in decolorizing dye factory wastewater and other colored wastewater, there is a limit to the removal of COD and TOC (total organic carbon). In addition, in advanced treatment to treat wastewater with a low concentration of pollutants, if a practical ozone reaction tank such as a bubble column is used, the absorption rate of ozone into the wastewater will be poor.
There was a practical problem with the effective use of ozone. The inventors have already learned that the problems in ozone treatment can be overcome by ultraviolet irradiation or the addition of hydrogen peroxide.

Among these, the ozone treatment method in which hydrogen peroxide is added is a practically effective method because it only requires adding a hydrogen peroxide addition device to conventional ozone treatment equipment. The hydrogen peroxide addition ozonation method attempts to utilize active chemical species generated by the reaction between ozone and hydrogen peroxide to initiate the oxidation of pollutant components.

In this case, if hydrogen peroxide is present in an excessive amount, the active species may react with each other or react with hydrogen peroxide, resulting in increased ineffective consumption of ozone and hydrogen peroxide. Therefore, in this type of ozone treatment method, it is practically essential to adjust the amount of hydrogen peroxide added. Therefore, the present inventors investigated in detail the ozone absorption rate, treatment effect, etc. in the presence of hydrogen peroxide for various wastewaters, and as a result, found that it is desirable to obtain a predetermined ozone absorption rate in a certain ozone reaction tank. It was found that the amount of hydrogen peroxide added increased.

Although the predetermined absorption rate differs depending on the state of gas-liquid contact in the reactor, for example, when a bubble column is used, it can be 95% or more by appropriately selecting the effective liquid depth. This invention was made based on the above research results, and by appropriately controlling the amount of hydrogen peroxide added, wastewater can be purified with the minimum necessary amount of ozone and water peroxide. The purpose is to provide a purification method. Embodiments of the present invention will be described below based on the drawings.

The drawing shows the wastewater purification process; 1 is an ozone reaction tank;
2 is a perforated plate for dispersing ozone-containing gas as fine bubbles in water; 3 is an ozone-containing gas inlet pipe; 4 is an excess ozone discharge pipe; 5 is a to-be-treated water inlet pipe; 6 is a treated water outlet; 7
8 is an ozone concentration meter that measures the ozone concentration of the gas flowing through the excess ozone discharge pipe 4, and 8 is a hydrogen peroxide injection pump, the flow rate of which is controlled according to the detection output of the ozone concentration meter 7. ing.

9 is a hydrogen peroxide storage tank.

The water to be treated is mixed with hydrogen peroxide whose flow rate is controlled by the hydrogen peroxide injection pump 8, and this flows into the reaction tank 1 through the water to be treated pipe 5.

Here, it reaches the bottom of the reaction tank 1 while coming into countercurrent contact with the fine bubbles containing ozone rising from the porous plate 2, and is discharged from the outlet 6 as treated water. Ozone in the bubbles dispersed in the water in the reaction tank 1 moves into the water as it rises, and the ozone concentration in the gas phase gradually decreases.

The bubbles rising as the ozone concentration decreases reach the water surface in the upper part of the reaction tank 1 and flow into the ozone concentration meter 7 via the excess ozone discharge pipe 4. Here, the ozone concentration is measured, and the flow rate of the injection pump 8, ie, the amount of hydrogen peroxide added, is controlled according to the measurement result. For example, if the measurement result is below a predetermined concentration, the injection pump 8 is controlled to reduce its flow rate, and as a result, the amount of hydrogen peroxide added is automatically reduced; , the injection pump 8 is controlled to increase the flow rate and the amount of hydrogen peroxide added increases. By automatically controlling the amount of hydrogen peroxide added, the amount added is always appropriate, and hydrogen peroxide and ozone are used effectively to purify wastewater. In addition, although the above description was made regarding the case where a bubble column was used as the ozone reaction tank, a reaction tank other than a bubble column may be used. Also,
When the ozone concentration in the ozonized gas introduced from the ozone-containing gas introduction pipe 3 changes, the ozone dissipation rate (excess ozone concentration/introduced ozone concentration) can be used instead of the excess ozone concentration. The amount of hydrogen oxide added can be appropriately controlled. As described above, according to the present invention, the amount of hydrogen peroxide added can be easily maintained at an appropriate level, and costs can be reduced through effective use of chemicals.

In addition, since the amount of hydrogen peroxide added is simply controlled according to the ozone absorption rate detected by excess ozone concentration, the control system is simple and the process is stable, which has great practical effects. It is.

[Brief explanation of drawings]

The drawing shows the configuration of a wastewater treatment facility that implements the method of this invention. 1...Ozone reaction tank, 2...Porous plate,
3...Ozone-containing gas introduction pipe, 4...
Excess ozone discharge pipe, 5... Treated water introduction pipe, 6
...Processed water outlet, 7 ...Ozone concentration meter, 8 ...Hydrogen peroxide injection pump, 9 ...
・Hydrogen peroxide storage tank.

Claims (1)

[Claims] 1. When treating pollutants contained in wastewater with ozone in the presence of hydrogen peroxide, the amount of hydrogen peroxide added is controlled according to the ozone absorption rate detected by the excess ozone concentration in the ozone reaction tank. A wastewater purification method characterized by: