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Views: 222 Author: Carie Publish Time: 2025-04-23 Origin: Site
Content Menu
● Introduction to Sewage Treatment
● Overview of Sewage Treatment Stages
● Key Chemicals Used in Sewage Treatment
>> pH Adjusters
>> Disinfectants and Oxidizing Agents
>> Adsorbents (Activated Carbon)
● Chemical Selection: Factors to Consider
● Environmental and Safety Considerations
● Visual Guide: Sewage Treatment Chemical Processes
● FAQ
>> 1. What is the most commonly used chemical in sewage treatment?
>> 2. Why is pH adjustment important in sewage treatment?
>> 3. Are there eco-friendly alternatives to traditional sewage treatment chemicals?
>> 4. What safety precautions are necessary when handling sewage treatment chemicals?
>> 5. Can chemical treatment remove heavy metals from wastewater?
● Citation
Sewage treatment is a vital process that protects public health and the environment by removing contaminants from wastewater before it is released back into nature. Chemicals play a crucial role at various stages of sewage treatment, helping to remove solids, neutralize harmful substances, and disinfect water. This comprehensive guide will explore the chemicals commonly used in sewage treatment, their functions, and considerations for their use.
Sewage treatment involves a combination of physical, biological, and chemical processes designed to remove contaminants from wastewater. The primary goals are to eliminate pathogens, reduce organic load, and minimize the presence of toxic substances before water is discharged or reused. As urban populations grow and industrial activities increase, the volume and complexity of sewage also rise, making effective treatment ever more critical.
Chemicals used in sewage treatment enhance the efficiency of physical and biological processes. They assist in removing suspended solids, neutralizing harmful compounds, and disinfecting water to prevent the spread of diseases. Understanding which chemicals to use, how they function, and their environmental impact is essential for plant operators, engineers, and environmental managers.
Sewage treatment typically occurs in three main stages, each with distinct objectives and treatment methods:
Primary treatment focuses on the physical removal of large solids, grit, and sediments. This stage usually involves screening, sedimentation tanks, and grit chambers. Although chemical use is minimal here, sometimes coagulants are added to improve sedimentation efficiency by aggregating fine particles.
Secondary treatment relies primarily on biological processes where microorganisms break down organic matter in the wastewater. Activated sludge systems, trickling filters, and biofilm reactors are common technologies. Chemicals such as pH adjusters may be used to optimize microbial activity, and anti-foaming agents can control excessive foam generated by biological processes.
Tertiary treatment is the advanced stage designed to remove residual contaminants, including nutrients (nitrogen and phosphorus), heavy metals, pathogens, and organic micropollutants. This stage often involves chemical dosing for coagulation, flocculation, disinfection, and sometimes adsorption. The goal is to produce water that meets stringent regulatory standards for discharge or reuse.
Function:
Coagulants and flocculants are chemicals that help aggregate fine suspended particles into larger clumps called flocs, which can then be easily separated from the water by sedimentation or filtration. This process improves the removal of turbidity, organic matter, and some heavy metals.
Common Coagulants:
- Aluminum Sulfate (Alum): One of the oldest and most widely used coagulants, alum is effective and relatively inexpensive. It works by neutralizing the negative charges on particles, allowing them to clump together.
- Polyaluminum Chloride (PAC): A more efficient coagulant than alum, PAC requires lower dosages and produces less sludge.
- Ferric Chloride and Ferric Sulfate: These iron-based coagulants are highly effective in removing phosphates and heavy metals.
Common Flocculants:
- Polyacrylamide Polymers: Synthetic polymers that enhance floc formation by bridging particles.
- Natural Polymers: Such as starch or cellulose derivatives, used in some eco-friendly applications.
Application Tips:
- The dosage of coagulants and flocculants must be optimized through jar tests or pilot studies to avoid overdosing, which can cause restabilization of particles or excessive sludge.
- Coagulants also help in phosphorus removal by precipitating it as insoluble compounds.
Function:
Maintaining the correct pH is essential for effective treatment and to protect equipment and biological processes. pH influences the solubility of metals, the activity of microorganisms, and the efficiency of chemical reactions.
Common pH Adjusters:
- Acids (to lower pH): Sulfuric acid and hydrochloric acid are commonly used to neutralize alkaline wastewater.
- Bases (to raise pH): Sodium hydroxide (caustic soda), lime (calcium hydroxide), and magnesium hydroxide are used to neutralize acidic wastewater and precipitate heavy metals.
Additional Benefits:
- Lime addition not only adjusts pH but also aids in removing phosphorus and heavy metals by precipitation.
- pH control is critical before disinfection, as some disinfectants are pH-sensitive.
Function:
Disinfectants kill or deactivate pathogenic microorganisms, ensuring treated water is safe for discharge or reuse. Oxidizing agents also break down organic pollutants and reduce odors.
Common Disinfectants:
- Chlorine: The most widely used disinfectant, available as chlorine gas or sodium hypochlorite solution. It is effective against bacteria, viruses, and some protozoa.
- Chlorine Dioxide: A strong oxidant with fewer harmful byproducts than chlorine.
- Ozone: A powerful oxidant that disinfects and breaks down organic compounds but requires on-site generation.
- Hydrogen Peroxide: Used in advanced oxidation processes, often combined with UV light or ozone.
- Ultraviolet (UV) Light: Not a chemical but an effective physical disinfectant used alongside chemical methods.
Dechlorination Agents:
- To neutralize residual chlorine before discharge, chemicals like sodium bisulfite or sodium thiosulfate are used to prevent toxicity to aquatic life.
Considerations:
- Chlorine can form harmful disinfection byproducts (DBPs) such as trihalomethanes; alternatives like ozone or UV are preferred in sensitive environments.
- Disinfection efficacy depends on contact time, concentration, pH, and water quality.
Function:
Foam formation can disrupt aeration and biological treatment processes. Anti-foaming agents reduce surface tension and collapse foam bubbles.
Common Anti-Foaming Agents:
- Silicone-based Compounds: Highly effective and widely used.
- Polyethylene Glycol Derivatives: Used in some applications for their biodegradability.
Application:
- Dosed carefully to avoid interference with microbial activity.
- Often added in small quantities during secondary treatment.
Function:
Activated carbon adsorbs dissolved organic compounds, trace pollutants, and odors, especially in tertiary treatment. It is effective in removing pesticides, pharmaceuticals, and other micropollutants.
Types:
- Powdered Activated Carbon (PAC): Added directly to the water and removed by sedimentation or filtration.
- Granular Activated Carbon (GAC): Used in fixed-bed filters for continuous adsorption.
Benefits:
- Improves water taste and odor.
- Reduces toxic organic compounds.
Limitations:
- Activated carbon must be replaced or regenerated periodically.
- High operational costs compared to other treatments.
Choosing the right chemicals for sewage treatment depends on multiple factors:
- Type and Concentration of Contaminants: Industrial wastewater may need specialized chemicals to handle heavy metals or toxic organics.
- Treatment Plant Size and Capacity: Larger plants may benefit from automated dosing systems and bulk chemical supplies.
- Regulatory Requirements: Discharge standards for nutrients, pathogens, and toxic substances guide chemical use.
- Chemical Compatibility and Safety: Avoid chemicals that create harmful byproducts or interfere with biological processes.
- Cost and Environmental Impact: Sustainable chemical choices reduce sludge volume and environmental footprint.
- Chemical Handling: Proper training and personal protective equipment (PPE) are essential to prevent accidents.
- Storage: Chemicals must be stored securely to prevent leaks and contamination.
- Disposal: Sludge containing chemical residues must be managed according to environmental regulations.
- Sustainability: Advances in green chemistry and process optimization aim to reduce chemical consumption and waste.
How a Sewage Treatment Plant Works
Chemical treatment is a cornerstone of modern sewage management, enabling the safe and efficient removal of a wide range of contaminants. The selection and application of chemicals—such as coagulants, flocculants, pH adjusters, disinfectants, anti-foaming agents, and adsorbents—must be tailored to the specific needs of the wastewater and regulatory requirements. Sustainable practices and technological advancements continue to improve the safety, efficiency, and environmental compatibility of chemical sewage treatment. Understanding the role of each chemical and optimizing their use ensures effective treatment, protects public health, and preserves natural water bodies for future generations.
The most commonly used chemicals are coagulants (such as aluminum sulfate and polyaluminum chloride) and disinfectants (such as chlorine and sodium hypochlorite), which are essential for solid removal and pathogen control.
pH adjustment ensures optimal conditions for biological processes, enhances the effectiveness of other chemicals, and prevents corrosion or scaling in the treatment system.
Yes, research is ongoing into bio-inhibitors, advanced oxidation processes, and optimized dosing strategies to reduce chemical consumption and minimize environmental impact.
Proper training, use of personal protective equipment (PPE), secure storage, and adherence to handling protocols are essential to prevent chemical exposure and accidents.
Yes, chemical precipitation (using reagents like lime or sodium hydroxide) can convert dissolved heavy metals into insoluble forms that can be filtered out.
[1] https://camachem.com/en/blog/post/top-10-sewage-treatment-chemicals
[2] https://www.operatorsunlimited.net/6-main-roles-of-chemicals-in-wastewater-treatment/
[3] https://www.membracon.co.uk/blog/biological-and-chemical-wastewater-treatment-processes/
[4] https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/14:_Water/14.08:_Wastewater_Treatment
[5] https://beta.co.id/en/blog/chemical-treatment-of-sewage
[6] https://www.thomasnet.com/articles/chemicals/wastewater-chemical-treatment/
[7] https://www.bmluk.gv.at/en/topics/water/water-quality-and-water-protection/how-does-a-sewage-treatment-plant-work.html
[8] https://jalamrut.com/news/what-chemicals-does-an-stp-sewage-treatment-plant-use/
[9] https://pubmed.ncbi.nlm.nih.gov/37257296/
[10] https://chem.libretexts.org/Courses/De_Anza_College/CHEM_10:_Introduction_to_Chemistry_(Parajon_Puenzo)/12:_Water/12.08:_Wastewater_and_Sewage_Treatment
[11] https://chem.libretexts.org/Courses/Maryville_College/Essential_Chemistry_for_Poisons_Potions_and_Pharmaceuticals/08:_Water/8.08:_Wastewater_and_Sewage_Treatment
