Iron-Carbon Microelectrolysis Catalytic Oxidation Unit

The chemical industry is a multi-sector, multi-variety industrial department, encompassing various sectors such as chemical raw materials, fertilizers, inorganic salts, chlor-alkali, pesticides, dyes, organic raw materials, synthetic materials, additives, chemical reagents, coatings, rubber processing, and more.

Industrial products are diverse and complex in composition, resulting in a wide variety of discharged wastewater. Most of it is highly toxic, difficult to treat, accumulates in organisms, exhibits significant oxygen-consuming properties in water bodies, and easily deteriorates water quality.

I. Types of Industrial Wastewater

Industrial wastewater refers to the total wastewater discharged during the production process of chemical products (including process wastewater, cooling water, and exhaust gas scrubbing water).

Chemical industrial wastewater can be categorized into three major types based on composition: the first type is wastewater containing organic substances, mainly from industries such as basic organic raw materials, synthetic materials (including synthetic plastics, synthetic rubber, synthetic fibers), pesticides, and dyes; the second type is wastewater containing inorganic substances, such as wastewater discharged from industries like inorganic salts, nitrogen fertilizers, phosphate fertilizers, nitric acid, and soda ash; the third type is wastewater containing both organic and inorganic substances, such as from chlor-alkali, photosensitive materials, and coatings industries.

If categorized by the main pollutants present, it can be divided into cyanide-containing wastewater, phenol-containing wastewater, sulfur-containing wastewater, fluoride-containing wastewater, chromium-containing wastewater, organic phosphorus compound-containing wastewater, organic substance-containing wastewater, etc.

The main industrial wastewaters and their primary sources are as follows:

II. Iron-Carbon Micro-Electrolysis Process

China's chemical industry involves a wide range of sectors, producing tens of thousands of chemical products. Consequently, pollutants in chemical wastewater are diverse, with complex component structures. Each type of chemical wastewater has its uniqueness, often requiring multiple treatment methods to meet discharge standards. Different water treatment methods are adopted for different pollutants.

For chemical wastewater with high organic concentration, complex composition, high salt content, poor biodegradability, and high toxicity, there is still a lack of economical and effective methods. Due to technical and economic reasons, traditional wastewater treatment methods face significant challenges and can no longer meet increasingly stringent environmental requirements.

The micro-electrolysis process utilizes the principle of metal corrosion, forming a galvanic cell to treat wastewater. It is also known as the internal electrolysis method or multi-phase iron-carbon method. Without electricity, it uses micro-electrolysis fillers in acidic wastewater to generate high and low potential differences for electrolytic treatment, aiming to degrade organic pollutants.

In an acidic environment, the micro-electrolysis system itself and the nascent [H], Fe2+, etc., it produces undergo redox reactions with many components in the wastewater. For example, it can destroy chromophores or auxochromes in colored wastewater, even break chains, reduce COD, and enhance biodegradability. It significantly improves the capacity of subsequent biochemical treatment and is particularly suitable for pre-treatment of high-concentration, hard-to-degrade organic wastewater.

III. Application Case Studies

1. A chemical company produces 10,000 tons of phthalic anhydride and 60,000 tons of dibutyl phthalate annually.

Production wastewater is generated during the production of dibutyl phthalate, a traditional primary plasticizer. The wastewater is organic, complex in composition, high in COD, and contains large amounts of inorganic salts, posing significant challenges for treatment.

Dibutyl phthalate is produced by the reaction of phthalic anhydride and n-butanol under concentrated catalysis, through esterification, neutralization, and de-alcoholization processes. The production wastewater mainly contains phthalic acid, monoester phthalate, diester phthalate, sodium phthalate, alcohols, sodium, etc. The organic components are complex, with B/C = 0.37, indicating good biodegradability. The wastewater quality varies significantly, with COD generally between 30,000–50,000 mg/L. Higher pH correlates with higher COD.

To comply with China's environmental protection policies and local regulations, the plant plans to build a wastewater treatment facility to ensure that, after centralized treatment, the wastewater meets the third-grade standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) and the grade standards of the "Water Quality Standard for Discharge into Urban Sewers" (CJ 343-2010).

(1) Designed wastewater treatment capacity:

Comprehensive influent volume of the wastewater treatment plant is 200 m³/d.

(2) Raw water quality:

Designed influent:

COD < 50,000 mg/L

BOD5 < 18,000 mg/L

SS: 2,000 mg/L

pH: 6–9

Designed effluent: After treatment, the effluent must meet the third-grade standards of "Integrated Wastewater Discharge Standard" (GB 8978-1996) and the grade standards of "Water Quality Standard for Discharge into Urban Sewers" (CJ 343-2010).

Specific effluent quality indicators:

COD: 500 mg/L

BOD5: 300 mg/L

SS: 400 mg/L

To achieve compliance and reduce operating costs, Jieyao Technology conducted experimental verification and successfully applied its core technology to treat the existing wastewater. Considering cost-effectiveness and process optimization, the company adopted a main process of "micro-electrolysis oxidation + multi-phase catalytic oxidation + flocculation sedimentation" for pre-treatment of the wastewater.

The raw wastewater is a colorless, semi-transparent liquid with a pH of around 5.18.

After micro-electrolysis oxidation and catalytic oxidation treatment, the effluent data are as follows:

Raw water: COD: 45,488 mg/L;

Micro-electrolysis effluent: 33,193 mg/L, removal rate 27.03%;

After multi-phase catalytic oxidation: COD: 26,973 mg/L, removal rate 40.70%.

After micro-electrolysis oxidation, COD removal is about 27%. After further catalytic oxidation, COD is further reduced, with a removal rate of about 40%.

Based on past engineering experience, the B/C ratio of wastewater can generally be increased to above 0.30, improving biodegradability, facilitating subsequent biochemical treatment, and reducing the burden on end-of-pipe treatment.

2. A fine chemical plant in Xuzhou produces high-concentration and low-concentration wastewater during the production of chemical products such as curing agents and flame retardants. The main sources are reaction mother liquor from reactors and workshop cleaning wastewater.

(1) Designed wastewater treatment capacity:

According to data provided by the manufacturer, daily wastewater production is 500 m³/d, including 170 m³/d of high-concentration wastewater and 330 m³/d of low-concentration wastewater.

Based on wastewater quality and past engineering investments in chemical wastewater treatment, an "iron-carbon micro-electrolysis catalysis + A/O combined process" was adopted.

Process flow is as follows:

After two months of operation, the system stabilized, with COD removal gradually increasing to around 80%, showing good treatment效果. Even with significant fluctuations in water volume, the system maintained good shock load resistance. Since iron-carbon micro-electrolysis generates oxygen during operation, ventilation and exhaust devices should be installed at the tower top to prevent accidents.

(1) Fine chemical production wastewater is uneven. By setting up an adjustment tank with aeration devices, water volume and quality can be effectively regulated.

(2) This treatment process separates and treats concentrated and dilute wastewater in stages. High-concentration wastewater, mainly reaction mother liquor, is treated first with micro-electrolysis oxidation and neutralization sedimentation, then mixed and homogenized with low-concentration wastewater before biochemical treatment. Staged influent treatment reduces the dosage of iron-carbon and lime milk, lowering investment and operating costs. Meanwhile, centralized treatment of high-concentration wastewater with iron-carbon micro-electrolysis oxidation reduces treatment difficulty and improves efficiency.

(3) As a redox process, iron-carbon micro-electrolysis oxidation does not significantly remove COD but can破坏 functional groups of large organic pollutants in high-concentration wastewater. Simultaneously, Fe2+ generated at the anode and its oxidation product Fe3+ can form various basic salts with strong adsorption and flocculation activity, adsorbing and flocculating部分 dissolved organic substances and微小 suspended particles. In the subsequent neutralization sedimentation tank, after adding lime milk, iron salts吸附 with pollutants form flocs and are removed from the water, achieving COD removal while preventing filler scaling.