An Overview of Various COD Treatment Methods: Which One Best Suits Your Needs?

 

Common Solutions for COD Removal in Wastewater Treatment

 

In the field of water treatment, COD (Chemical Oxygen Demand) is a key indicator used to measure the concentration of organic pollutants in water. An elevated COD value indicates a higher level of organic contamination. The removal of COD helps reduce environmental pollution, improve water quality, and meet the regulatory standards for industrial or municipal water use.

 

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There are various methods for COD removal. The following sections will provide a detailed overview of commonly used treatment techniques, including Physical Treatment, Chemical Treatment, Biological Processes, Advanced Oxidation Processes (AOPs), Adsorption, and Integrated Methods.

 

 

 

 

1. Physical Treatment

 

Physical Treatment primarily relies on physical mechanisms to remove particles or suspended solids from wastewater. These methods are typically used as a preliminary treatment step and are particularly suitable for wastewater with high concentrations of suspended or particulate matter. The main techniques include the following:

 

1.1 Sedimentation

 

Sedimentation method relies on gravity to allow larger particles to settle at the bottom of the tank, where they are subsequently removed through a sludge discharge system. This method is suitable for treating wastewater with high concentrations of suspended solids and is commonly used in primary sedimentation tanks of municipal wastewater treatment systems. It is a simple process with low equipment costs, but it is less effective for dissolved organic matter and fine particles. Physical treatment methods primarily remove particles or suspended solids from wastewater through physical means and are typically employed as preliminary treatment steps.

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Product Series	Oil/Organic Solvent/AOX	Emulsion Breaking	Decolorization	Flocculation	Water Reuse
Neosorb® GS-AN	+	+	+	+	-
Neosorb® EMU-V DES	+++	++	++	++	-
Neosorb® MB	+	-	-	+	+++
Neosorb® MB-N	+	-	-	+	+++
Neosorb® A2022	+++	+++	+++	++	-
NF-124	++	+++	+++	++	-

 

1.2 Filtration

 

Filtration method adopt different filter media (e.g. sand, activated carbon, or membranes) to remove particles and suspended solids from water. Sand filters are effective for removing larger particles, while membrane filtration technologies (e.g. ultrafiltration, nanofiltration, and reverse osmosis) are capable of eliminating finer contaminants. Membrane filtration can further reduce COD levels; however, it generates concentrated waste streams that require additional treatment considerations.

 

1.3 Dissolved Air Flotation (DAF)

 

DAF method uses fine air bubbles to carry suspended solids to the water surface, where they form a froth that can be removed. This method is particularly effective for treating wastewater containing oils or hydrophobic pollutants. While DAF systems offer operational flexibility, they tend to involve higher equipment costs and are most commonly used as a pretreatment step for industrial oily wastewater.

 

 

2. Chemical Treatment

 

Chemical treatment is suitable for removing organic compounds that are difficult to degrade naturally and typically provides rapid and noticeable results. Common chemical treatment techniques include the following:

 

2.1 Oxidization

 

Oxidation method decomposes organic compounds into carbon dioxide and water through the application of strong oxidizing agents (e.g. ozone, hydrogen peroxide, or hypochlorite). Ozone oxidation is particularly effective for treating refractory organic compounds, such as those containing aromatic ring structures. Although oxidation offers high treatment efficiency and is well-suited for industrial wastewater with high COD concentrations, the associated costs and safety risks of the oxidizing agents require thorough assessment.

 

2.2 Coagulation–Sedimentation

 

Coagulation–sedimentation method involves adding coagulants (e.g. ferric chloride, polyaluminum chloride) to wastewater, causing colloids and fine particles to aggregate into larger flocs that can then be removed through sedimentation. This method is well-suited for wastewater with high levels of suspended solids and colloidal materials. While coagulation–sedimentation is relatively cost-effective, it generates a significant amount of sludge, which requires further treatment.

We offer a variety of compound flocculants tailored for different wastewater characteristics. For more information, please feel free to contact us!

(Further Reading: Wastewater treatment example: SS suspended particulate improvement example! Reappearance of clarified discharge water! Features of one-dose powder flocculant)

 

2.3 Chemical Precipitation

 

Chemical precipitation is a targeted treatment method used for the removal of specific contaminants. For example, to remove phosphates, aluminum or iron salts can be added to the wastewater to form insoluble precipitates that can be separated from the water. This method is particularly effective for removing heavy metals and other inorganic salts, but is limited in its applicability as it can only be used for specific substances.

Our heavy metal capture agents—Plexon® 3315 and KT-N40—can effectively remove chelated metal salts from wastewater, enhancing water quality and delivering greater environmental compliance and safety. For more information or technical support, please feel free to contact us.

(Further Reading: Wastewater Treatment: Are You Familiar with the Timing for Using Heavy Metal precipitants?)

 

 

3. Biological Treatment

 

Biological treatment relies on microorganisms to degrade organic pollutants in water and is well-suited for wastewater with high concentrations of organic matter. This method is characterized by its low cost and operational simplicity; however, the treatment process tends to be relatively slow. Common biological treatment methods include the following:

 

3.1 Aerobic Treatment

 

Aerobic treatment utilizes aerobic bacteria to decompose organic matter under oxygen-rich conditions. The most common systems include the activated sludge process and biofilm systems. The activated sludge process supplies oxygen through aeration equipment, allowing microorganisms to remain suspended in the water as activated sludge to break down pollutants. This method offers high removal efficiency and is widely used in municipal wastewater treatment, though its operation requires stable aeration.

(Further reading: Struggling with Industrial Wastewater COD Treatment? Meet KB-660W-100: Your Eco-Friendly Solution for Non-Toxic Bioremediation. (v2))

 

3.2 Anaerobic Treatment

 

Anaerobic treatment utilizes anaerobic microorganisms to break down organic matter in an oxygen-free environment, producing methane, carbon dioxide, and water. This method is suitable for high-strength organic wastewater and has the advantage of generating biogas that can be used as an energy source. However, it typically requires a longer treatment time and is more appropriate for large-scale industrial wastewater treatment.

 

 

4. Advanced Oxidation Processes (AOPs)

 

Advanced Oxidation Processes (AOPs) utilize highly reactive oxidizing radicals, (such as hydroxyl radicals (•OH)) to achieve deep oxidation of organic pollutants. This method is particularly effective for refractory organic compounds and is well-suited for high-COD industrial wastewater. Common AOPs include:

 

4.1 Ozone Oxidation

 

Ozone oxidation works by decomposing ozone to generate reactive radicals that further oxidize organic pollutants. This method is suitable for high-strength organic wastewater, but the equipment required for ozone generation and its operational costs are relatively high. Therefore, it is typically applied in specialized industries.

 

4.2 Photocatalytic Oxidation

 

Photocatalytic oxidation utilizes catalysts such as titanium dioxide (TiO₂) under ultraviolet or visible light to generate reactive radicals that degrade organic compounds in wastewater. This method produces no secondary pollution and is effective for refractory organic pollutants. However, it requires a strong light source, and the catalyst must be periodically replaced or regenerated.

 

4.3 Electrochemical Oxidation 

 

Electrochemical oxidation produces oxidants like hypochlorous acid and hydroxyl radicals via electrochemical reactions, which break down organic pollutants. This technology is suitable for small-scale applications or wastewater with high concentrations of contaminants, although it generally involves relatively high operational costs.

 

 

5. Adsorption

 

Adsorption primarily relies on adsorbent materials to remove organic pollutants from water. Common adsorbents include activated carbon, zeolite, and other porous materials. This method is characterized by high removal efficiency, but the adsorbent must be periodically replaced or regenerated, making it more suitable for the advanced treatment of low-COD wastewater. Adsorption is effective for wastewater containing low concentrations of organics, especially in the final process in order to meet the discharge standard.

(Further reading: COD Removal Using Oil-Absorbent Materials in Wastewater Treatment)

 

Comparison of cod treatment methods based on their characteristics and applicability:

 

Treatment Method	Principle	Advantages	Disadvantages	Applicable Scope	Efficiency	Cost	Environmental Impact
Physical Treatment	Uses mechanical processes such as filtration and sedimentation to separate suspended solids	Simple operation, low maintenance cost	Cannot remove dissolved COD; limited treatment efficiency	Wastewater containing suspended solids or particulate pollutants	Medium to Low	Low to Medium	Low environmental impact; sludge generated after treatment requires proper disposal
Chemical Treatment	Uses chemical oxidants (e.g., ozone, chlorine) to degrade organic matter	High removal efficiency; rapid COD reduction	High cost of chemicals; potential secondary pollution	High-COD wastewater, such as industrial effluents	High	High	May produce harmful by-products, such as chlorinated organics
Biological Treatment	Uses microorganisms to biologically degrade organic pollutants	Eco-friendly, sustainable, and low operating cost	Requires strict operational conditions; long treatment time	Domestic sewage and biodegradable industrial wastewater	High	Medium to Low	Environmentally friendly, but may be affected by toxic substances
Advanced Oxidation Method	Generates free radicals via strong oxidants (e.g., UV/H₂O₂, Fenton reagent) to degrade organics	Capable of degrading persistent organic pollutants	High cost; strict operational requirements	Wastewater with hard-to-degrade pollutants	Very High	High	Requires caution to avoid harmful effects of radicals on humans and the environment
Adsorption Method	Uses adsorbents (e.g., activated carbon) to adsorb organic matter in wastewater	Suitable for low-concentration pollutants; easy to operate	High cost for regenerating spent adsorbents; limited capacity	Wastewater with low concentrations of organic pollutants	Medium	Medium	Requires treatment or replacement of saturated adsorbents to prevent secondary pollution

 

 

6. Integrated Methods

 

Given the advantages and disadvantages of each COD treatment method, integrated treatment processes that combine multiple techniques are commonly adopted in industrial applications. A typical sequence involves physical treatment to remove coarse particles and reduce suspended solids, chemical oxidation to significantly lower organic pollutant levels, and biological processes for complete mineralization. Such combined systems are widely implemented to ensure regulatory compliance and cost-effectiveness, representing a prevailing trend in industrial wastewater treatment.

 

 

Conclusion

 

COD removal plays a vital role in wastewater treatment, and choosing the right method depends on the specific properties of the wastewater and the desired treatment goals. The key to effective COD removal lies in choosing suitable methods tailored to specific water quality conditions. Physical, chemical, and biological treatments each have their own advantages and limitations, and can be flexibly selected or combined based on the nature of the wastewater.

With advancements in water treatment technologies, advanced oxidation processes (AOPs) and next-generation adsorbent materials have significantly improved treatment efficiency, providing more effective COD control solutions for industrial wastewater. While physical, chemical, and biological methods are suitable for different types of wastewater, AOPs and adsorption are particularly effective for high-COD or refractory organic pollutants.

As water treatment continues to evolve, the development and application of novel catalysts and adsorbents are bringing more efficient solutions for COD removal. In practical applications, a combination of multiple technologies is often employed to achieve high COD removal efficiency while also minimizing treatment costs.

 

If you have any questions or needs regarding COD reduction in wastewater treatment, feel free to click the “Contact Form” button at the lower-left side. Alternatively, you may call our service hotline. Our professional team is ready to provide you with effective solutions and assist you in achieving optimal water quality improvement.