How to Treat High - Concentration COD Wastewater?

 Introduction

Statistics show that each ton of untreated high - COD wastewater can consume the dissolved oxygen in about 14 tons of clean water. If such wastewater is directly discharged, it will pollute waterways and water sources, cause water bodies to become oxygen - deficient, and even threaten ecological security. Therefore, reducing the COD in wastewater is crucial for protecting the aquatic ecosystem. In this article, AquaSust will discuss its types and treatment technologies, to provide you with reference in the wastewater treatment process.

 

What is High - Concentration COD Wastewater？

In environmental chemistry, Chemical Oxygen Demand (COD) is an indicator for measuring the amount of oxygen that can be consumed by reactions in a certain solution. High - concentration COD wastewater refers to sewage with a very high COD content. It contains a large number of organic pollutants, including human excrement, food waste, fats, and oils.

Common Forms of High - Concentration COD Wastewater

This type of wastewater has diverse sources, generally involving multiple fields such as chemistry and environmental protection. It has a high potential for polluting the environment, and common types are as follows:

1. Chemical Industry Wastewater: This kind of wastewater contains various complex organic compounds, such as benzene, toluene, phenols, aldehydes, ketones, etc. These substances have stable chemical structures and are difficult to be naturally degraded. Sometimes they are also toxic.

2. Dyeing Wastewater: Different types of dyes, such as reactive dyes, acid dyes, disperse dyes, etc., all contain complex organic molecular structures, resulting in a high COD value in the wastewater. Moreover, these dyes can also affect the light transmittance of water bodies and hinder the photosynthesis of aquatic plants.

3. Papermaking Wastewater: It mainly comes from the pulping and paper - making processes. It contains a large amount of organic substances such as lignin, cellulose, and hemicellulose. The decomposition of these substances in water will consume a large amount of dissolved oxygen, causing the water body to be oxygen - deficient. This wastewater also contains some alkalis and sulfides, making it highly alkaline and corrosive.

4. Food Processing Wastewater: The food processing industry includes meat processing, dairy processing, winemaking, sugar - making, etc. These wastewaters are rich in oils, starches, and proteins, and the pH value fluctuates greatly (4.0 - 10.5). It can cause lakes to become eutrophic rapidly, with excessive algae growth. Eventually, fish, shrimp, and other aquatic plants die due to oxygen deficiency.

Common Treatment Methods

Efficient treatment of high - COD wastewater can reduce the pollution discharge costs of enterprises and help us recycle organic matter resources, such as biogas and biodiesel, for a circular economy. We generally treat it in the following ways:

1. Pretreatment Stage

Pretreatment aims to adjust the physical and chemical properties of wastewater to make it more stable in subsequent processes:

(1) Neutralization Reaction: By adding lime or sulfuric acid, we can control the pH of the wastewater between 6.5 - 8.5 to avoid equipment corrosion caused by acid - base.

(2) Toxic Substance Removal: Activated carbon adsorption or Fenton oxidation (with an H₂O₂/Fe²⁺ molar ratio of 3:1) can effectively degrade toxic substances such as cyanides and heavy metals.

(3) Macromolecule Interception: We also use microfiltration membranes (with a pore size of 0.1 - 1 μm) or air - flotation processes to remove colloids and suspended solids in the wastewater.

2. Main Treatment Stage

(1) Flocculant Method: Adding polyaluminium chloride or polyacrylamide to the wastewater can promote the destabilization and aggregation of colloids. When the pH of the sewage is between 6 - 7, the flocculation efficiency reaches the highest. However, excessive addition of flocculants will increase the viscosity of the sludge and affect the dewatering efficiency.

(2) Microbial Method

 Anaerobic Treatment: Anaerobic microorganisms are used to decompose the organic matter in the wastewater into substances such as methane and carbon dioxide under anaerobic conditions. This method can produce biogas as an energy source, but the treatment time is long and the requirements for water quality are strict.

 Aerobic Treatment: The MBR membrane bioreactor can reduce the COD to below 100 mg/L. The microorganisms on its surface can decompose the organic matter into carbon dioxide and water in an aerobic environment. But this method consumes a large amount of oxygen during operation.

(3) Electrochemical Method: Through electrode reactions, the organic matter in the wastewater undergoes redox reactions and is decomposed. This method has a fast reaction speed and does not require the addition of chemical agents, but the power consumption cost is relatively high.

(4) Micro - electrolysis Method: Using iron - carbon micro - electrolysis fillers, countless tiny primary batteries are formed in the wastewater to carry out redox and flocculation precipitation of organic matter. We often use it in different wastewaters, but a small amount of sludge is generated during the treatment process.

(5) Adsorption Method: Adding adsorbents to the water to adsorb the organic matter in the water and remove them. Common adsorbents include activated carbon, zeolite, etc. These adsorbents can also remove dyes and odors in the wastewater.

 

AquaSust - Customized Solutions for High - Concentration COD Wastewater

As a leading water treatment supplier in the industry, AquaSust provides you with customized high - concentration COD wastewater treatment solutions. This covers services such as pretreatment optimization, core process matching, and sludge resource utilization. Our technical advantages include modular systems and intelligent control systems, and we are always ready to turn your ideas into feasible realities.