Treating High-COD Chemical Wastewater: A Technology Overview

High-concentration chemical oxygen demand (COD) chemical wastewater poses a significant challenge to industrial environmental protection. This type of wastewater typically contains complex, recalcitrant organic matter, highly toxic substances, and strong acids and alkalis, with COD concentrations exceeding those of ordinary domestic sewage by hundreds of times. Efficient treatment of this wastewater requires a multi-level, multi-technology combination process tailored to its characteristics.

I. Basic Principles of Technical Treatment

Treating high-concentration COD chemical wastewater generally follows a core process: "Pretreatment + Main Treatment + Advanced Treatment."

Pretreatment removes suspended solids, equalizes flow, recovers resources, and improves biodegradability (B/C ratio) via hydrolysis of complex molecules. Main treatment undertakes the core task of degrading most organic pollutants, while advanced treatment is used to achieve high-standard discharge or reuse.

II. Detailed Explanation of Key Treatment Technologies

1. Physical and Chemical Pretreatment Technologies

Physical and chemical pretreatment is crucial before wastewater enters the biological treatment system.

Ammonia stripping, phenol removal, and oil separation: Used for coke-making and similar wastewaters to recover ammonia, phenols, and free oil.

Coagulation sedimentation and flotation: By adding coagulants, fine suspended solids and colloids in the water are first coagulated and destabilized, then flocculated into larger particles, which are subsequently separated by sedimentation or flotation, effectively removing some COD and color.

Micro-electrolysis (iron-carbon method): Utilizing the numerous tiny galvanic cells formed by iron and carbon in wastewater, an electrochemical reaction occurs, which can destroy the complex organic structure, improve biodegradability, and remove some color and heavy metals.

Physical coalescence technology: Utilizing the difference in affinity of polymeric coalescing materials for oil and water, the surface properties of the materials are optimized. During the cross-flow process of oily wastewater, fine oil droplets (as small as 10μm) aggregate and merge into larger oil droplets or oil films, ultimately achieving efficient oil-water separation. The entire process is physical, requiring no chemical additives, fundamentally eliminating the disposal costs of oily sludge.

2. Core Oxidative Degradation Technologies

This is a crucial step in treating high-concentration, recalcitrant COD, especially represented by advanced oxidation technologies.

Fenton and Fenton-like Oxidation: Utilizes ferrous ions to catalyze hydrogen peroxide to generate highly oxidizing hydroxyl radicals. Derivative processes such as photo-Fenton and electro-Fenton can improve efficiency and reduce sludge. This technology has strong oxidation capabilities but suffers from high reagent consumption and the generation of iron sludge.

Ozone Catalytic Oxidation: Ozone, under the action of a catalyst, generates more free radicals, significantly enhancing the decomposition efficiency of recalcitrant organic matter. Coupled technologies, such as UV/ozone coupling processes, can achieve synergistic effects and improve treatment efficiency.

Wet Catalytic Oxidation and Supercritical Water Oxidation: Under high temperature and pressure conditions, organic matter is completely oxidized into carbon dioxide and water using air or oxygen. The latter, under supercritical conditions, reacts more thoroughly and is suitable for treating extremely high-concentration organic wastewater, but requires extremely high equipment investment and operational requirements.

Electrocatalytic Oxidation: Degrades pollutants through direct or indirect oxidation reactions on the electrode surface. Novel three-dimensional electrodes and boron-doped diamond membrane electrodes can significantly improve current efficiency and treatment effect.

3. Biological Treatment Technology After pretreatment to improve biodegradability, biological treatment is the main economical and effective process for COD removal.

High-efficiency anaerobic reactors: such as upflow anaerobic sludge blanket (UASB) and anaerobic expanded granular sludge blanket (EGSB), can withstand high organic loads, decomposing large organic molecules into methane, achieving significant COD reduction and energy recovery.

Enhanced aerobic and anoxic processes: such as membrane bioreactors (MBR) and moving bed biofilm reactors (MBBR), can maintain high concentrations of activated sludge and combine anaerobic/anoxic/aerobic stages to enhance the simultaneous removal of total nitrogen and COD.

Special microorganisms and enzyme preparations: Adding strains or enzyme products domesticated for specific toxic and recalcitrant organic matter can effectively improve the stability and treatment efficiency of the biological system.

Upflow Anaerobic Sludge Blanket Structure Diagram

4. Advanced Treatment and Resource Utilization Technologies

To ensure stable effluent quality and reuse, advanced treatment is essential.

Advanced Oxidation Technology Combination: Connecting different oxidation technologies (such as ozone and hydrogen peroxide) in series serves as a "polishing" step after biological treatment, thoroughly decomposing residual trace amounts of recalcitrant organic matter.

High-Efficiency Adsorption Technology: Using adsorbents such as activated carbon, resin, or mesoporous molecular sieves to deeply remove dissolved organic matter and color from water.

Membrane Separation Technology: Such as nanofiltration and reverse osmosis, which can almost completely retain organic matter and salts, producing high-quality permeate for reuse, while simultaneously generating concentrated wastewater requiring further treatment.

Our WYS horizontal oil-water separator uses purely physical coalescence, integrating cyclone separation, coarse coalescence, polymer coalescence, and corrugated plate coalescence into a compact, high-efficiency system. It can be used as a pre-treatment oil removal device for COD coagulation sedimentation and flotation treatment. A single unit replaces multiple treatment steps, simplifying operation and maintenance while achieving high process integration. It significantly reduces the load on the biological treatment system, decreases reagent dosage and sludge production, lowers the treatment pressure on subsequent coagulation, sedimentation, and flotation stages, provides a stable influent to the biological treatment system, and reduces operating costs.

There is no single, universal formula for treating high-concentration COD chemical wastewater. The key lies in accurately analyzing the wastewater characteristics and flexibly combining the aforementioned technical units to form a customized technical solution, ultimately achieving a balance between environmental and economic benefits.