Treatment of dye wastewater and pesticide wastewater

The wet oxidation method is mainly used to treat wastewater whose concentration is too low for combustion treatment, too high for biodegradation treatment, or wastewater with greater toxicity
.

Therefore, the current application of wet oxidation is mainly in two aspects: one is for the pretreatment of high-concentration refractory organic wastewater biochemical treatment to improve biodegradability; the other is for the treatment of toxic and harmful industrial wastewater

3.
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1 Treatment of dye wastewater

China’s dye industry is developing vigorously, and its output accounts for 1/5 of the world’s total output.
As far as Shanghai is concerned, the dyes produced by 13 dye plants include more than 500 in ten categories including disperse dyes, cationic dyes, and reactive dyes.
It has an annual output of 13,000 tons and an annual waste water discharge of 15.
6 million tons
.

Pollutants contained in wastewater include benzene, phenol, naphthalene, naphthalene, aldehydes, nitro compounds, amines, sulfonates, halides, etc.

Studies have found that reactive dyes and acid dyes are suitable for wet oxidation, while direct dyes are slightly difficult to oxidize in air
.

Most dyes are of acidic type, so the wet oxidation method has great potential for treating dye wastewater

Cu-Fe and Cu-Ce/FSC are optimized homogeneous and heterogeneous catalysts.
They are applied to the research of CWAO treatment of actual printing and dyeing wastewater to investigate the practical performance of the catalyst and the treatment effect of CWAO method on actual printing and dyeing wastewater
.

The research results show that the CWAO method treats printing and dyeing wastewater, the COD and BOD of the effluent meet the third-level standard, the chroma and pH meet the first-level standard, and the dissolution concentration of heterogeneous Cu reaches the third-level standard; while the effluent BOD is treated

Reaction temperature, oxygen partial pressure, wastewater pH, catalyst dosage, etc.
are all factors that affect the effect of catalytic wet oxidation (CWAO)
.

For example, a heterogeneous catalytic oxidation system with Fe/AC as catalyst and O ₂ as oxidant is used to treat azo dye reactive red 2BF.

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2 Treatment of pesticide wastewater

China is a large agricultural country, and the consumption of pesticides is quite large.
According to incomplete statistics, China produces more than 100 kinds of pesticides, including pesticides and herbicides, with an annual output of more than 200,000 tons, of which organophosphorus pesticides are the main ones
.

The characteristics of pesticide wastewater are:

①Less water;

②High concentration (COD above 5000mg/L);

③ Great changes in water quality;

④Complex composition and high toxicity
.

Most domestic treatment methods are biochemical treatment after pretreatment
.

Commonly used pretreatment methods include alkaline hydrolysis, acid-base method, precipitation extraction method, solvent extraction method, etc.

It is reported in the literature that foreign researchers have used wet oxidation technology to test a variety of pesticide wastewater.
When the temperature is in the range of 204～316℃, the decomposition rate of hydrocarbon organics and their halides in the wastewater reaches or exceeds 99%, even general chemical The chlorinated substances that are difficult to be oxidized, such as polychlorinated biphenyls (PCB) and DDT, are reduced by 99% in toxicity through wet oxidation, which greatly improves the biodegradability of the treated effluent, so that the subsequent biochemical treatment can be carried out smoothly
.

Many people in China have done research in this field.