The textile and dyeing industry is one of the industries with wastewater sources with very high COD characteristics and high color levels that have been and will cause damage to the water environment if untreated water is discharged directly into the water. the sources. Due to the presence of difficult-to-decompose compounds, the effective treatment method for textile wastewater is advanced oxidationusing the Fenton method. strong>
Image of chemicals in the textile and dyeing industry
What is the origin and pollution of textile dyeing industry wastewater?
All stages in the textile and dyeing industry generate wastewater, from the fiber sizing, bleaching, and bleaching stages to the yarn mercerization, dyeing, printing, and product finishing stages. Of which, the amount of water used in the production process accounts for 72.3%, mainly in the dyeing and finishing stages.
Textile industry wastewater has unstable Pollution composition. This pollution component changes according to technology and production items. Therefore, determining the composition and properties of wastewater is very difficult. Normally, the pH value in wastewater ranges from 7 to 9, the wastewater has a high temperature of about 40oC, the indices BOD5, COD, color and suspended residue content are many times higher than standards.
Pollution parameters in textile wastewater
BTNMT, Column B
Table of pollution parameters of textile wastewater
Let’s learn about advanced oxidation and the Fenton process
Advanced oxidation processes are defined as oxidative decomposition processes that rely on the reactive hydroxyl radical *OH generated during processing . The hydroxyl radical is the strongest oxidizing agent known to date, capable of oxidizing all organic substances, even the most difficult to decompose, turning them into compounds. Non-toxic inorganic substances such as CO2, H2O, inorganic acids…
The Fenton process is an advanced oxidation process that uses iron ions as a hydrogen peroxide catalyst to oxidize organic substances by generating OH* free radicals.
Fenton process in wastewater treatment and influencing factors
The Fenton process occurs in four stages: pH value adjustment, oxidation reaction, neutralization and flocculation and finally sedimentation.
Stage 1: Adjust pH value
The Fenton process is greatly affected by the pH value. This process takes place favorably at low pH levels ranging from 2 to 5.
Stage 2: Oxidation reaction
The Fenton oxidation reaction takes place under the influence of a catalyst of two iron salts and an oxidant of hydrogen peroxide. When slowly adding the catalyst, it will react with the oxidant to form OH* radicals that can oxidize difficult-to-decompose organic substances. OH* radical groups will break the chains of difficult-to-decompose organic substances. , forming organic substances with shorter chains. If the reaction occurs completely, organic substances can be completely converted into CO2 and H2O. The mechanism of the process is as follows:
Fe2+ + H2O2 → Fe3+ + OH- + OH*
CHC(high molecular) + OH* → CHC(low molecular) +CO2 + H2O +OH-
Stage 3: Neutralization and flocculation
After stages 1 and 2 are over, the wastewater has low pH, we need to raise the pH to neutral by neutralizing the oxidized water with NaOH. Besides, OH- will react with triple iron ion to form a precipitate. Then the following two reactions will occur:
NaOH + H+ → Na+ + H2O
3NaOH + Fe3+ → Fe(OH)3↓ + 3Na+
Along with that, Fe(OH)3 will participate in the process of flocculation, coagulation and partial adsorption of macromolecular organic substances.
Phase 4: Settling
After the process of precipitation, flocculation, and coagulation, the flocs will settle to the bottom of the tank, reducing COD, color, and TSS of wastewater.
The factors that affect the Fenton process that we need to pay attention to are:
- Catalyst concentration
- Oxidant concentration
Treating textile wastewater by Fenton method
The advantage of the Fenton process is that the iron salt H2O2 agent is relatively cheap and readily available. At the same time, it is non-toxic and easy to transport and use. The enhanced oxidation efficiency is much higher than using H2O2 alone.
Applying the Fenton process to water and wastewater treatment can lead to complete mineralization of organic matter into CO2, H2O2 and inorganic ions. However, under those conditions, a lot of chemicals must be used, making treatment costs high.
Therefore, in many cases, the Fenton process should only be applied for partial decomposition, converting organic substances that cannot or are difficult to biodegrade into new biodegradable substances for convenient application. subsequent biological treatment.
And below is the technology line for textile wastewater treatment using theFenton method in practice:
Waywater treatment line diagram using Fenton combined biological method
Technology line for textile dyeing wastewater treatment using Fenton method
Textile wastewater passes through a trash screen to remove large coarse substances.
Wastewater is collected and concentrated into the collection pit. This is the place that helps stabilize the concentration and flow of waste stream. A submersible pump is located here, pumping wastewater from the tank into the physical and chemical treatment system behind.
Adjust the pH of wastewater with acid solution, add chemicals FeSO4, H2O2. In the tank, the Fenton process will occur, hydrogen peroxide reacts with iron (II) sulfate to create hydroxyl free radicals capable of destroying organic substances.
NaOH and Polymer are added in a certain amount to precipitate iron, increasing the size and volume of flocs, creating favorable conditions for the sedimentation process to take place in the sedimentation tank, and at the same time bringing the pH of wastewater to neutral. count.
Settlement tank 1:
The mixture of flocs and water after the reaction flows into settling tank 1. Here, the flocs will settle to the bottom of the tank while the wastewater flows out to the intermediate tank.
This is a place that helps stabilize the concentration and flow of wastewater to help the biological system behind it work well. An aerator is arranged here to avoid sedimentation and anaerobic decomposition at the bottom of the tank.
Some organic substances that are difficult to decompose after the Fenton process will be transformed into easily decomposable organic substances. Some are completely converted to CO2 and water. The aerotank will process the remaining organic matter under the action of aerobic microorganisms.
Settlement tank 2:
The mixture of sludge and wastewater after treatment in the aerotank is transferred to settling tank 2, where the sludge flocs will settle and the settled wastewater will go out. Part of the excess sludge will be circulated to the aerotank, and the rest will be pumped to the sludge tank.
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