3 things to note when treating wastewater using chemical methods

1. What is chemical wastewater treatment?

Chemical wastewater treatment is the process of using chemicals to remove or reduce pollutants in wastewater. The goal of this method is to make wastewater safer before being discharged into the environment or reused. 

Pollutants in wastewater can include organic and non-organic compounds, bacteria, microorganisms, heavy metals, and other toxic compounds.

2. Chemical wastewater treatment methods

There are many chemical wastewater treatment methods used to remove pollutants and make wastewater safer for the environment and human health. Here are some main methods:

2.1. Disinfection and sterilization of wastewater

Wastewater disinfection and sterilization are processes used to eliminate or reduce the presence of bacteria, viruses, pathogens, and harmful microbial particles in wastewater. The goal of this process is to make wastewater safe to discharge into the environment or reuse without endangering humans and the environment.

Disinfection: This process involves eliminating or reducing the number of bacteria and disease-causing microorganisms in wastewater. Disinfection methods include using disinfectants such as chlorine, antibiotics, ultraviolet (UV) light, high temperatures, ozone, and other chemicals to kill or reduce bacterial populations.

Sterilization: The sterilization process is similar to sterilization, but it focuses on eliminating bacteria and disease-causing microorganisms that can be hazardous to human health. Sterilization methods include the use of stronger sterilants such as chlorine, high temperatures, gamma radiation, and biological sterilization methods.

Here are some common wastewater disinfection and sterilization methods:

2.1.1. Use chemical disinfectants such as chlorine, ozone, UV

Chlorination: Use of chlorine or chlorine compounds to disinfect wastewater. This process can kill bacteria and disease-causing microorganisms.

Sterilization with ultraviolet rays (UV): Use of ultraviolet rays to sterilize wastewater. Ultraviolet rays can destroy the DNA of bacteria and viruses.

Ozonation: Use of ozone (O3) to oxidize and destroy bacteria, viruses and organic substances in wastewater.

High temperature: Use of high temperature through simmering or boiling in order to sterilize the wastewater.

Antibiotics: Use of antibiotic compounds to prevent the growth of bacteria and pathogenic microorganisms in the wastewater.

Gamma radiation: Use gamma radiation to destroy bacteria, viruses and pathogens in wastewater.

2.1.2 Advantages and limitations of these methods

Wastewater disinfection and sterilization methods have their own advantages and disadvantages. Here are some key pros and cons of this method:

Advantage:

- Hygienic safety: Disinfection and sterilization help ensure that wastewater is treated safely, without posing a risk to human health and the environment.

- Eliminate pathogens: These methods can remove bacteria, viruses and pathogens in wastewater, helping to prevent the spread of infectious diseases.

- Water reuse: Treating wastewater with disinfection and sterilization can make wastewater suitable for reuse for applications such as watering plants, cooling, or in industrial processes.

- Relative effectiveness: These methods are often effective in minimizing the presence of harmful bacteria and microorganisms.

Defect:

- Create by-products or residue: Some disinfection and sterilization methods can create by-products or residue, affecting the wastewater treatment process or residue management after treatment.

- Environmental impact: Some chemicals used in disinfection and sterilization processes can have negative impacts on the environment if they are not managed carefully.

- Increased drug resistance: The continuous use of antibiotics and disinfectant chemicals can cause the development of drug-resistant bacteria, making the treatment ineffective after a period of time.

- Cost and resources: The disinfection and sterilization methods often require high use of chemicals, energy and resources, leading to relatively large treatment costs.

- Residue and by-product management: The treating and managing residue generated during disinfection and sterilization may also require additional technology and resources.

- Not suitable for all situations: Some methods may not be suitable for special types of wastewaters or in cases with different requirements for post-treated water quality.

2.2. Wastewater treatment by chemical precipitation method

2.2.1. Use of coagulants to remove contaminants

Chemical precipitation method is a wastewater treatment method that uses chemicals to create agglomerated residues in wastewater. These residues include dirt particles, impurities and other pollutants in wastewater. Once the residues are created, they easily settle as residue, helping to separate the water during the treatment process. 

Flocculation: Flocculants are substances that can bind small particles together to form larger clumps. Flocculants are usually organic or inorganic polymers.

Coagulation: Coagulants are substances that help to facilitate precipitation by creating sticky particles to connect residues together.

2.2.2. Mechanism of action of chemical precipitation method

The precipitation process in wastewater treatment by chemical precipitation usually takes place through the following steps:

- Adding flocculants and coagulants: First, flocculants and coagulants are added to the wastewater. Flocculants are substances that bind small particles together to form larger clumps. Coagulant facilitate precipitation by creating sticky particles that bind the residues together.

- Precipitation and residue formation: Flocculants and coagulants interact with dirt particles, impurities and other pollutants in wastewater. These agents precipitate into larger particles, creating agglomerated residues in the wastewater.

- Formation of large clumps: The agglomerates become larger and larger as they interact and connect with each other. This process is like bubbles rising and connecting to each other on the surface of the water.

- Sedimentation: Larger agglomerates gradually settle as sludge due to the influence of gravity. This creates a layer of sediment at the bottom, which helps to separate the water during the treatment.

The mechanism of action of the chemical precipitation method involves the interaction between flocculants and coagulants with dirty particles and pollutants in wastewater. When flocculant and coagulant combine with small particles, they create larger particles through the process of flocculation and coagulation. These large particles increase in size as they interact and connect with each other, forming agglomerated clumps.

2.2.3 Advantages and disadvantages of chemical precipitation method

Advantage

- Effective in removing residue: This method is usually effective in removing dirt particles, impurities and other pollutants from wastewater.

- Good integration with other methods: Chemical precipitation method can be easily integrated with other methods such as flocculation, metal reduction or using biological methods to increase the treatment efficiency.

- Adjusting water quality: This method allows to adjust the water quality by removing dirt particles and impurities, helping therefore to increase the transparency of the water.

Disadvantages of chemical precipitation method:

- Chemical requirements: This method requires the use of chemicals such as flocculant and coagulant, which can increase costs and create byproducts.

- Residue management: Residues generated during the precipitation process need to be managed and treated appropriately afterwards.

- Not suitable for all types of wastewater: This method may not be suitable for special types of wastewater or in specific situations.

Chemical precipitation is one of the common wastewater treatment methods used to remove dirt particles and impurities in wastewater to achieve better water quality.

2.3 Treat wastewater by removing heavy metals and toxic substances

2.3.1. Use of the chemical complexation method to remove heavy metals

Using chemical complexation to remove heavy metals in wastewater is a process in which chemicals bind to heavy metals to create chemical complexes. These complexes are often sparingly soluble in water, causing heavy metals to become less soluble and more easily to sediment or separate from the wastewater. The process of using chemical complexation in order to remove heavy metals is explained below:

Operation of chemical complexing method:

Choosing a chelating agent: First, a chelating agent is chosen which can create complexes with heavy metals.

Adding chelating agents to wastewater: Chelating agents are added to wastewater which contains heavy metals. Molecules of chelating agents bind to heavy metal ions in wastewater.

Creating chemical complexes: Heavy metal ions are bound to chelating agents to form chemical complexes. These complexes are usually sparingly soluble in water and may form large particles or precipitates.

Sedimentation or separation from wastewater: Chemical complexes or larger precipitated particles are capable of settling under the influence of gravity or being separated by mechanical methods, for instance with the use of a filter.

Advantages of chemical complexation method:

Effective in heavy metal removal: This method is often effective in removing heavy metals from wastewater by creating sparingly soluble complexes.

pH adjustment is not required: Compared to some other methods, chemical complexation methods usually do not require special pH adjustments to perform the process.

Stable over time: Chemical complexes are often stable over time, helping heavy metals not re-dissolve and being safely stored.

Disadvantages of the chemical complexing method:

Requires chelating agent: This method requires the use of high quality and effective chelating agent to form the chemical complex.

Reusability: Some chemical complexes can be difficult to recycle or reuse, leading to waste management problems.

Potential interaction with other substances: Chelating agents can interact with other substances in wastewater and cause adverse effects.

The chemical complexation method is one of the most useful methods to remove heavy metals in wastewater. However, a careful selection and management of the chelating agent is necessary to ensure the effectiveness and safety of the process.

2.3.2. Applications in industrial wastewater treatment

Chemical precipitation method is widely used in industrial wastewater treatment to remove pollutants, impurities and dirty particles from wastewater. Below are some specific applications of chemical precipitation methods in industrial wastewater treatment:

Heavy metal removal: This method is used to remove heavy metals such as lead, cadmium, mercury, and nickel from industrial wastewater. Chemicals are added to wastewater to create agglomerated residues, in which heavy metal ions adhere and settle.

Chromium plating wastewater treatment: Industries that use chromium plating often generate wastewater containing chromium ions. Chemical precipitation can be applied to convert chromium from dissolved form to residue, helping to remove chromium from wastewater.

Removal of organic matter: Organic substances, such as grease, organic toxic substances and other organic compounds in industrial wastewater, can be removed using chemical precipitation to form agglomerated residues.

The treatment of wastewater containing phosphorus: Industries such as food, pharmaceutical, and fertilizer production often generate wastewater containing large amounts of phosphorus. Chemical precipitation methods can be used to form chemical complexes with phosphorus and to remove it from the wastewater.

Wastewater treatment from paper and textile industries: These industries often generate wastewater containing dirty particles, colors and organic matter. The chemical precipitation method can be used to remove dirt particles and impurities, making the wastewater more transparent.

Wastewater treatment from the electroplating industry: Industries that use electroplating often generate wastewater containing heavy metals. Chemical precipitation can be used to form chemical complexes with heavy metals and to remove them from the wastewater.

3. Practical applications of chemical wastewater treatment

Chemical wastewater treatment has many practical applications in different fields. Below are some examples of practical applications of chemical wastewater treatment:

Urban wastewater treatment:

In urban areas, wastewater from households, manufacturing facilities and service establishments needs to be treated before being discharged into the environment. Chemical methods such as chlorination and precipitation to remove impurities and organic matter can be used to ensure wastewater is safe and in compliance with environmental standards.

Industrial wastewater treatment: Manufacturing industries, such as the chemical, food, paper, textile and electronics industries, often generate wastewater containing dirty particles, organic pollutants and heavy metals. Precipitation, flocculation and the use of chemicals to remove heavy metals are common ways to treat the wastewater from these industries.

Gold particle wastewater treatment: In gold mining industries, wastewater often contains gold particles and toxic chemicals. Chemical precipitation can be used to separate gold particles from wastewater, helping to minimize negative impacts on the environment.

Wastewater treatment from electroplating technology: Electroplating technologies often create wastewater containing heavy metal ions. Chemical complexation methods can be applied to form insoluble complexes with heavy metals, causing them to sediment and remove from wastewater.

Wastewater treatment from oil and gas production industry: Oil and gas production industries often create wastewater containing grease and organic substances. Flocculation and the use of chemicals can help to create clumps and to remove grease from wastewater.

Water reuse: Chemical wastewater treatment can also facilitate water reuse. Once treated, the wastewater can be purified and reused in applications that do not require purified water.

Thus, chemical wastewater treatment has many important practical applications in many different industries, helping to protect the environment and freshwater resources.

Chemical methods in wastewater treatment are important in removing pollutants. However, using chemical methods requires high technical knowledge to select and apply appropriate chemicals and to adjust process parameters. Hopefully the environmental knowledge FEC provides will help the readers to treat the wastewater using chemical methods.