Deep wastewater treatment: comparison of advanced oxidation technologies

Removal of CODcr in water advanced oxidation process there are three main, namely, Fenton oxidation process, ClO2 catalytic oxidation process and O3 catalytic oxidation process, now for the above three catalytic oxidation process for economic and technical selection.

Fenton oxidation process

The combination of ferrous salt and hydrogen peroxide is called Fenton reagent, it can effectively oxidize and remove the traditional wastewater treatment technology can not remove the difficult to degrade organic matter, in essence, H2O2 in the Fe2 + catalytic effect of the generation of highly reactive hydroxyl radicals (-OH), -OH can be used with most of the organic role of its degradation.

Fenton oxidation process characteristics

(1) Oxidization is non-selective and has a strong ability to remove organic matter. 2;

(2) Organic matter eventually decomposed into CO2 and H2O, no toxic and harmful intermediate products, safe and environmentally friendly;

(3) Need the pH value of the sewage between 2 ~ 4, need to adjust the sewage into acidic, oxidation end and then adjusted to neutral. 4. completely degradation of COD and its oxidizing effect;

(4) High consumption of chemicals for complete degradation of COD, resulting in high treatment costs. 5) Rapid reaction time;

(5) rapid reaction time is short.

(6) Fenton oxidation applicable occasions high, resulting in high treatment costs;

Fenton reagent oxidation method due to the need to adjust the acid, alkali, pharmaceutical unit consumption, reaction time is long, the amount of sludge is large, difficult to apply in large and medium-sized sewage treatment plants.

Fenton reagent oxidation method is suitable for small and micro sewage treatment plants with acidic water, especially suitable for acidic sewage treatment of some dyestuffs, pesticides and pharmaceutical intermediates enterprises.

ClO2 catalytic oxidation process

Chlorine dioxide catalytic oxidation is one of the advanced oxidation techniques for water treatment, which is improved and developed on the basis of chemical oxidation method. The principle of chlorine dioxide catalytic oxidation is in the presence of surface catalyst conditions, the use of strong oxidants - chlorine dioxide catalytic oxidation of organic pollutants in wastewater at room temperature and pressure, directly oxidize organic pollutants into carbon dioxide and water, or oxidize the large molecules of organic pollutants into small molecules of organic pollutants, to improve the biochemistry of wastewater, and can better remove the organic pollutants. Pollutants.

1.Features of ClO2 catalytic oxidation process

(1) The oxidizing ability of ClO2 is lasting;

(2) The reaction between ClO2 and organic matter almost does not produce fugitive organic chlorides, and does not produce trichloromethane with carcinogenic effect;

(3) The reaction with organics has significant selectivity, and the oxidizing ability is highly correlated with the type of substituent group on the organics. The use of efficient catalysts overcomes its selectivity for the oxidation of organics;

(4) The degradation of organic matter to generate oxygen groups of small molecule compounds, which can increase the value of sewage BOD5, improve the biochemical properties;

(5) The pH value of the sewage needs to be acidic (around 6), the sewage needs to be adjusted to be acidic, and then adjusted to be neutral at the end of oxidation.

(6) Reaction time: 45~60min.

2. Application of ClO2 catalytic oxidation

Due to the catalytic oxidation of chlorine dioxide technology requires acidic pH value of sewage (around 6), the sewage needs to be adjusted to acidic, and then adjusted to neutral at the end of oxidation, which limits its application in large and medium-sized sewage treatment plants.

And because of the reaction between chlorine dioxide and organic matter has significant selectivity, need to choose the right catalyst, the selection of the catalyst in the actual application of the work is complex and difficult, but also limited its popularization and application in industrial wastewater.

At present, chlorine dioxide catalytic oxidation technology is successfully applied in the following fields:

(1) in the coal gas wastewater, high concentration of cyanide wastewater, p-aminoanisole wastewater, phenol formaldehyde wastewater and printing and dyeing wastewater treatment have achieved good results, can remove most of the difficult to degrade organic pollutants, and improve the biochemistry of sewage;

(2) It can remove most of the difficult organic pollutants and improve the biochemistry of wastewater. (2) It has good effect of decolorization and COD removal for easily oxidized water-soluble dyes such as cation dyes, azo dyes and easily oxidized water-insoluble dyes such as sulfur dyes.

Ozone catalytic oxidation process

Ozone catalytic oxidation is to use the hydroxyl radical [-OH] generated by ozone under the action of catalyst to oxidize and decompose the organic pollutants in water. Due to the strong oxidizing ability of -OH and the non-selective nature of the oxidizing reaction, it can rapidly oxidize and decompose the majority of the organic compounds (including some highly stable and difficult to degrade organic substances).

Metal-loaded activated carbon catalysts are complexes consisting of a mixture of tiny crystalline and non-crystalline parts, with a large number of acidic or basic groups on the catalyst surface. The presence of these acidic or basic groups, especially hydroxyl and phenolic hydroxyl groups, gives the catalyst not only adsorption capacity but also catalytic capacity. In the process of ozone/catalyst synergism, ozone decomposition under the action of the catalyst produces [-OH] and thus triggers a chain reaction, which also produces very active monatomic oxygen [-O] with strong oxidizing ability.

Ozone catalytic oxidation characteristics

(1) The oxidizing ability of organic pollutants is very strong, and the ability to remove organic matter is strong;

(2) The participation of catalyst, oxidation selectivity is greatly reduced, almost broad-spectrum application;

(3) Organic matter eventually decomposed into CO2 and H2O, no toxic and harmful intermediate products, safe and environmentally friendly;

(4) The pH value can be neutral or alkaline, no need to adjust the pH value of sewage;

(5) The ozone generator produces ozone by electric energy and air, without chemicals, safe and hygienic on site;

(6) The oxidation reaction time is short, generally controlled in about 30min, the reactor volume is small.

Ozone catalytic oxidation applicable occasions

Due to the above characteristics, ozone catalytic oxidation technology is suitable for CODcr degradation in large, medium and small wastewater treatment plants with almost all kinds of wastewater. Through the comparison of the above three oxidation processes, ozone catalytic oxidation process has good treatment effect, wide range of application, mature technology, and at the same time, there are a large number of successful applications in domestic and foreign sewage treatment plants.

As the wastewater to be treated in depth is the effluent from the sedimentation tank after biological aerobic treatment, the BOD/COD ratio of wastewater is already quite low, and if we want to further reduce the COD value, we have to utilize the method of advanced treatment, and among all the methods of advanced treatment, ozone-catalyzed oxidation has good treatment effect, wide range of application, mature technology, and has a large number of successful application examples in domestic and foreign wastewater treatment plants. Ozone catalytic oxidation process has been successfully applied in a large number of sewage treatment plants at home and abroad. Compared with other advanced oxidation methods, it has the advantages of low investment cost, large degree of tolerance to changes in water quality, easy operation and maintenance, and low operating costs.