Electrolysis + Fenton treatment for high chemical wastewater

As the demand for chemical products in daily production and life continues to rise, the chemical industry has experienced rapid development. However, this growth has also led to increasingly serious environmental issues, particularly the significant discharge of wastewater from chemical production that has resulted in severe water pollution in rivers surrounding chemical parks.

According to relevant studies, chemical wastewater mainly comes from the following sources:

1. Leakage during the use of chemical raw materials and products.
2. Wastewater from washing the workshop floor.
3. Wastewater from equipment cleaning and pollution treatment.
4. Cooling discharge water, etc.

According to the analysis of the sources of chemical wastewater, it can be divided into three types: organic, inorganic, and organic-inorganic mixed chemical wastewater, which have the following common characteristics:

1. Toxic and irritating, such as halogenated compounds, bactericidal dispersants or surfactants, etc.
2. The wastewater components are complex, and a certain amount of by-products and unreacted raw and auxiliary materials and additives will be produced during the chemical production process.
3. The pollutant content is high and difficult to degrade. Nitro compounds are one of the main pollutants in chemical wastewater and have the characteristic of being difficult to biodegrade, which brings great difficulty to the subsequent treatment of wastewater.
4. The color changes quickly and the chromaticity is high.
5. The water quality and quantity change greatly.
6. The ecological restoration and management are difficult. The water area polluted by chemical wastewater is difficult to restore its original system functions and the cost is high.

Chemical Wastewater Treatment Technology

Chemical wastewater contains a variety of components, and the types of pollutants in different chemical wastewater vary. The treatment of chemical wastewater requires the combination of multiple technologies to achieve the desired treatment effect. Existing treatment solutions can be classified according to principle into physical methods, chemical methods, and biological treatment methods, among others. The process of separating toxic and harmful substances contained in chemical wastewater, or converting them into stable and harmless substances, is called harmless treatment.

According to the degree of wastewater treatment, the water treatment process can be divided into pretreatment, biochemical treatment, and deep treatment.

The main purpose of pretreatment is to intercept suspended solids, regulate water volume, adjust pH, etc., usually using physical and chemical methods, with facilities such as wastewater equalization tanks and screens.

Biochemical treatment is the main process of wastewater treatment. The selected treatment process varies according to water quality. The main methods include traditional activated sludge method, oxidation ditch method, AB method, A/O method, A2/0 method, and SBR method, among others.

Deep treatment is a deep treatment measure after preliminary treatment and medium biochemical treatment. After the effluent reaches the specified requirements, it can be discharged. Advanced treatment methods such as activated carbon adsorption devices, membrane separation methods, advanced oxidation methods, photocatalytic oxidation methods, electrochemical oxidation methods, ultrasonic radiation degradation methods, and radiation methods can be used to ensure stable and qualified effluent quality.

In practical applications, these three stages are overall unified and relatively independent. In some cases, there may also be cross-over. On the other hand, since the integrated treatment cost of the biochemical treatment stage is significantly lower than that of the deep treatment stage, and the treatment effect of the deep treatment stage is easily interfered by water quality factors, the biochemical treatment stage is generally required to remove pollutants as much as possible.

High COD Chemical Wastewater Treatment Technology

Compared with general industrial wastewater, high COD chemical wastewater has much deeper coloration and features poor biodegradability, strong corrosiveness, and difficult treatment after pollution. Enterprises that can produce high COD chemical wastewater mainly include pharmaceutical enterprises, fine chemical enterprises, petrochemical enterprises, pesticide production enterprises, and others. After such wastewater is discharged into water bodies, the toxic substances are numerous, and the water quality changes greatly, causing serious ecological damage. The toxic and harmful substances in chemical wastewater can enter the organism through multiple ways and accumulate in the organism, causing diseases such as chronic poisoning and brain damage.

According to research, high COD chemical wastewater treatment methods mainly include advanced oxidation methods, biochemical methods, photocatalytic methods, adsorption methods, incineration methods, and others.

In summary, choosing the appropriate high COD chemical wastewater treatment technology can not only help enterprises achieve standard discharge, but also promote the coordinated development of regional environment and economy.

Electrolysis + Fenton treatment for high chemical wastewater

High-COD chemical wastewater often contains a significant amount of refractory pollutants that are difficult to biodegrade. A pre-treatment process using a micro-electrolysis Fenton system can be employed to break down and destroy large organic molecules, thereby reducing their toxicity and enhancing their biodegradability. The mechanism of action involves several aspects:

Micro-electrolysis reaction:

In an iron-carbon micro-electrolysis system, iron scraps (mainly composed of iron and carbon) are placed in acidic wastewater. Due to the 1.2V potential difference between Fe and C, a large number of micro-electrochemical cells are formed in the wastewater. The reaction products of the micro-electrochemical cells have adsorption and filtration effects, thereby reducing and removing pollutants in the wastewater. During the micro-electrolysis process, the anode is oxidized to produce Fe, Fe³⁺, and Fe³⁺ hydrolysis precipitates, forming adsorption flocculants. The cathode generates [H] and [O] that continue to undergo oxidation reactions, breaking down large organic molecules in the wastewater and increasing its biodegradability. During the reaction process, OH is generated at the cathode, which increases the pH of the treated wastewater.

Fenton reaction:

After the iron-carbon micro-electrolysis reaction, H₂O₂ is added to form a Fenton reagent oxidation system with Fe²⁺. Due to the catalytic decomposition of H₂O₂ by Fe²⁺, OH˙ (hydroxyl radical) is generated, and the oxidation electrode potential is as high as 2.8V. This gives the Fenton reagent extremely strong oxidation ability, which can oxidize and break down refractory organic matter in wastewater into small organic and inorganic molecules, achieving degradation of the organic matter.

Neutralization and precipitation:

By adjusting the pH of the effluent from the micro-electrolysis Fenton system to around 8 and adding a coagulant, the removal of suspended solids from the wastewater is achieved. The neutralization and precipitation process can independently remove pollutants from wastewater and also improve the effectiveness of wastewater treatment as an intermediate process.

Chemical parks inevitably generate high-COD chemical wastewater. The “micro-electrolysis Fenton oxidation system + neutralization and precipitation” process effectively reduces the impact of high-COD wastewater on the biochemical treatment system of the park, ensuring the stable operation of the park’s wastewater treatment plant.