Electrochemical wastewater treatment equipment for coking wastewater treatment

I. Product Overview

Coking wastewater is one of the most difficult wastewaters to treat in the coal chemical industry. It originates from the high-temperature carbonization (coking), gas purification, and chemical product recovery processes of coal, and mainly includes residual ammonia water, final cooling wastewater from coal gas, crude benzene separation water, and tar processing wastewater. Its typical water quality characteristics are: high COD concentration, high ammonia nitrogen concentration, high content of recalcitrant toxic substances (phenols, benzene series compounds, polycyclic aromatic hydrocarbons, heterocyclic compounds such as pyridine, quinoline, carbazole, etc.), extremely poor biodegradability (BOD₅/COD typically 0.10~0.20), high cyanide and sulfide content, oil content (tar), and large fluctuations in water quality and quantity.

The treatment of coking wastewater has long been a core environmental challenge for coking enterprises. Traditional process routes typically follow the pattern of "pretreatment (oil removal, phenol removal, ammonia stripping) → biological treatment (A/O, A²/O, SBR, etc.) → advanced treatment," but face numerous challenges in actual operation: ① Phenolic compounds, cyanides, and heterocyclic compounds strongly inhibit or even kill microorganisms in the biological system, leading to frequent poisoning and bulking of activated sludge, and unstable operation of the biological system; ② Extremely poor biodegradability (B/C < 0.20), limited COD removal rate in the biological stage, and effluent COD far below current discharge standards; ③ Low winter temperatures cause a sharp drop or even halt in the nitrification efficiency of biological systems, leading to significant ammonia nitrogen exceedances. This system employs electrochemical oxidation technology and can be flexibly integrated into multiple stages of the coking wastewater treatment process, undertaking the following core functions:

For phenol removal effluent after ammonia stripping:Direct oxidation and decomposition of toxic substances such as phenols, cyanides, and heterocyclic compounds in the wastewater, completely eliminating biotoxicity within 1-2 hours. The B/C ratio is increased from 0.10-0.20 to over 0.35, creating safe and stable influent conditions for subsequent biological systems and effectively preventing system collapse due to shock.

For advanced treatment of biological effluent:Deep removal of residual COD (recalcitrant humic substances, aromatic polymers, etc.) and color from the biological effluent, completely eliminating COD and color to meet the most stringent emission standards.

For quenching wastewater treatment: After COD and color removal, the wastewater is reused in the quenching system, achieving closed-loop circulation of quenching water and reducing the risk of fresh water intake and external pollution.

The entire process consumes only electricity, without adding any chemical agents, and does not produce hazardous waste such as iron sludge or adsorbed saturated carbon. The electrodes are resistant to scaling and pollution, and can adapt to complex water qualities such as high hardness, high salinity, and oil content in coking wastewater. It operates at normal temperature and pressure (0~40℃) and is not affected by seasonal and temperature changes. It is a key core technology for achieving stable compliance and upgrading of coking wastewater.

II. Difficulties in coking wastewater treatment and solutions with this equipment

III. Working Principle

After pretreatment such as oil removal, precipitation, and ammonia stripping, coking wastewater enters the electrochemical reactor, where the following reactions occur under the action of electrodes:

(1) Direct electro-oxidation The characteristic toxic pollutants in coking wastewater are directly oxidized on the anode surface: Phenols (phenol, cresol, naphthol, etc.): After the benzene ring is hydroxylated on the anode surface, it is further oxidized and ring-opened, transforming into small molecule organic acids, and finally mineralized into CO₂ and H₂O. The oxidative ring-opening process of phenol completely eliminates its cell membrane penetration toxicity to microorganisms. Cyanide (CN⁻): It is directly oxidized to cyanate (CN⁻→CNO⁻) at the anode. The cyanate is further hydrolyzed into ammonia and carbonate, and its high toxicity is completely eliminated. Heterocyclic compounds (pyridine, quinoline, carbazole, indole, etc.): The nitrogen-containing heterocycle is directly ring-opened on the anode surface. N is released from the ring and converted into NH₃ or N₂. The ring system structure is destroyed, and the biotoxicity is greatly reduced. Polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, etc.): The aromatic ring system is gradually oxidized and ring-opened on the anode surface. The macromolecular condensation structure is decomposed into small molecule degradable substances.

(2) Indirect electro-oxidation Anode electrolysis of water produces hydroxyl radicals (·OH). At the same time, active chlorine (Cl₂, H₂O) is generated by electrolysis of naturally occurring chloride ions in coking wastewater. OCl, OCl⁻): Hydroxyl radicals perform non-selective oxidative attacks on various recalcitrant organic compounds, especially showing significant ring-opening effects on polycyclic aromatic hydrocarbons and heterocyclic compounds. Activated chlorine further diffuses into the solution, rapidly oxidizing ammonia nitrogen, while simultaneously supplementing the oxidation of organic compounds that have not directly contacted the anode.

(3) Ammonia nitrogen oxidation removal: The concentration of ammonia nitrogen in coking wastewater is high, and electrochemical removal is achieved through an indirect oxidation pathway: Chloride ions are electrolyzed at the anode to generate activated chlorine. Activated chlorine rapidly oxidizes ammonia nitrogen into nitrogen gas. Chloride ions are regenerated and circulated in the reaction, continuously participating in ammonia nitrogen oxidation. The ammonia nitrogen removal rate can reach 80%~99%.

(4) Co-removal of COD and improvement of biodegradability: After direct and indirect oxidation, macromolecular aromatic and heterocyclic organic compounds in coking wastewater undergo: ring opening of aromatic rings/heterocyclic rings → chain breaking of macromolecules → conversion into small molecule organic acids, alcohols, aldehydes, etc. These small organic molecules can be utilized by microorganisms in BOD₅ detection, thus increasing BOD₅; at the same time, some organic matter is completely mineralized into CO₂, causing COD to decrease. The B/C ratio increases from 0.10~0.20 to over 0.35, providing a high-quality biodegradable carbon source for subsequent biochemical systems.

IV. Core Advantages (Targeting Coking Wastewater)

V. Technical Parameters (Customizable)

VI. Process Location

Option 1: Pre-treatment and Detoxification Before Biochemical Processing

Coking Wastewater → Oil Removal and Sedimentation (Removal of Tar and SS) → Electrochemical Treatment Equipment (Removal of Phenolics, Cyanides, Heterocyclic Compounds, and Improvement of B/C Ratio) → Intermediate Tank/Equalization Tank → Biochemical System → Secondary Sedimentation Tank → Discharge Meeting Standards

Explanation: This is the most critical and core application configuration in coking wastewater treatment. The electrochemical detoxification unit is placed before the biochemical system, undertaking the core functions of "oxidative decomposition of phenols/cyanides/heterocyclic compounds + improvement of the B/C ratio." If coking wastewater without electrochemical detoxification directly enters the biochemical system, microorganisms will be in a state of long-term toxicity inhibition, leading to extremely unstable system operation. After detoxification, the COD removal rate of the biochemical stage is significantly improved, and the system operates stably throughout the year, unaffected by fluctuations in influent toxicity.

Option 2: Advanced Biochemical Treatment of Effluent

Coking Wastewater → Pretreatment → Biochemical System → Secondary Sedimentation Tank → Electrochemical Treatment System (Removal of Residual COD and Color) → Discharge Meeting Standards

Option 3: Pre-Biochemical Detoxification + Post-Biochemical Advanced Treatment

Coking Wastewater → Pretreatment → Electrochemical Treatment System (Pre-Biochemical) → Biochemical System → Electrochemical Advanced Treatment Unit (Post-Biochemical) → Discharge Meeting Standards/Reuse

Note: For newly built coking wastewater treatment plants or comprehensive upgrading projects, one electrochemical unit is set up before and after the biochemical treatment. The front end is responsible for detoxification and improving biodegradability, ensuring stable and efficient biochemical treatment; the back end is responsible for advanced removal of residual COD and color, ensuring stable effluent compliance. The two electrochemical units work together, making the coking wastewater treatment system most resilient to shocks, with the most stable effluent and optimal operating costs. Although the equipment investment is slightly higher than a single-unit configuration, the reliability of the biochemical system and the certainty of final effluent compliance are significantly improved, resulting in the best overall cost-effectiveness.