Please Choose Your Language
Views: 222 Author: Carie Publish Time: 2025-04-20 Origin: Site
Content Menu
● Introduction to Sewage Treatment Chemicals
● Main Stages of Sewage Treatment
● Chemicals Used in Sewage Treatment Plants
>> Precipitants
>> Other Specialized Chemicals
● Advanced Chemical Treatment Technologies
>> Advanced Oxidation Processes (AOPs)
>> Nutrient Recovery Chemicals
● Environmental and Health Safety Considerations
>> Chemical Storage and Handling
● FAQ
>> 1. What are the most commonly used chemicals in sewage treatment plants?
>> 2. How do coagulants and flocculants work in wastewater treatment?
>> 3. Why is pH adjustment important in sewage treatment?
>> 4. How are chemicals safely stored and handled in sewage treatment plants?
>> 5. Are there environmental risks associated with chemical use in sewage treatment?
● Citation
Sewage treatment plants play a vital role in protecting public health and the environment by removing contaminants from wastewater before it is released back into nature. This complex process relies on a range of chemicals, each with specific functions in treating and purifying water. In this comprehensive article, we will explore the main chemicals used in sewage treatment plants, their roles, handling considerations, and the science behind their application. Visual diagrams and video explanations are included to enhance understanding, followed by a conclusion and a detailed FAQ section.
Sewage treatment plants (STPs) are engineered systems designed to remove physical, chemical, and biological contaminants from wastewater. While biological processes play a significant role, chemicals are essential at various stages to enhance efficiency, ensure regulatory compliance, and safeguard the environment.
The global increase in urbanization and industrialization has led to more complex wastewater streams, requiring advanced chemical treatments to meet stringent discharge standards. Chemicals help accelerate processes, remove difficult contaminants, and ensure the treated water is safe for discharge or reuse.
Understanding the role of chemicals requires familiarity with the main treatment stages:
1. Preliminary Treatment: Removal of large solids, grit, and debris through screening and grit chambers. Chemicals are generally not used here but may be applied for odor control.
2. Primary Treatment: Sedimentation tanks allow suspended solids to settle. Chemicals like coagulants can be added to improve settling efficiency.
3. Secondary Treatment: Biological processes degrade organic matter using microbes. Chemicals may be added to control pH, provide nutrients, or inhibit unwanted microbial growth.
4. Tertiary Treatment: Advanced treatment to remove nutrients (nitrogen, phosphorus), heavy metals, and micropollutants. Chemicals play a major role here in precipitation and oxidation.
5. Disinfection: Final step to kill pathogens before discharge or reuse, typically using chlorine, ozone, or UV light.
Suspended particles in wastewater are often very fine and carry electrical charges that keep them dispersed. Coagulants neutralize these charges, allowing particles to come together, while flocculants bind these particles into larger aggregates (flocs) that settle more easily.
- Aluminum Sulfate (Alum):
Alum is one of the most widely used coagulants. It reacts with water to form aluminum hydroxide precipitates that trap suspended particles. Alum is effective in removing turbidity and phosphorus.
- Ferric Chloride and Ferric Sulfate:
Iron salts are effective coagulants, especially for phosphorus removal. They form iron hydroxide flocs that adsorb phosphates and other contaminants.
- Polyacrylamide (PAM):
PAM is a synthetic polymer used as a flocculant to enhance the aggregation of particles. It is available in anionic, cationic, and nonionic forms, selected based on wastewater characteristics.
- Natural Polymers:
Some plants use natural polymers like chitosan, derived from crustacean shells, as eco-friendly flocculants.
Disinfectants
Disinfection is critical to eliminate pathogens such as bacteria, viruses, and protozoa. Chemicals used must be effective, safe, and leave minimal harmful residuals.
- Chlorine (Gas or Hypochlorite):
Chlorine is the most common disinfectant due to its strong oxidizing properties and low cost. It kills pathogens by disrupting cell membranes and enzymatic systems. However, chlorine can form harmful disinfection by-products (DBPs) such as trihalomethanes.
- Sodium Hypochlorite:
A liquid form of chlorine, easier and safer to handle than chlorine gas. It is widely used for on-site disinfection.
- Chlorine Dioxide:
More selective and effective against certain resistant pathogens like Cryptosporidium. It produces fewer DBPs.
- Ozone:
A powerful oxidant that destroys microorganisms and organic contaminants. Ozone decomposes quickly, leaving no residual chemicals, but requires on-site generation and higher energy input.
- Ultraviolet (UV) Light:
UV radiation damages microbial DNA, preventing replication. UV is chemical-free but does not provide residual disinfection, so it is often combined with chemical disinfectants.
pH Adjusters
Maintaining the correct pH is essential for optimal chemical reactions and biological activity.
- Sodium Hydroxide (Caustic Soda):
Used to raise pH in acidic wastewater, improving coagulation and biological treatment efficiency.
- Sulfuric Acid or Hydrochloric Acid:
Added to lower pH when wastewater is too alkaline, protecting downstream processes and equipment.
- Lime (Calcium Hydroxide):
Besides pH adjustment, lime can precipitate heavy metals and phosphates, and aid sludge dewatering.
- Magnesium Hydroxide:
Used as a safer alternative for pH correction, especially in large-scale plants.
Precipitants chemically convert dissolved contaminants into insoluble solids that can be removed by sedimentation or filtration.
- Aluminum and Iron Salts:
These salts precipitate phosphates as aluminum phosphate or iron phosphate, reducing eutrophication risks in receiving waters.
- Calcium Compounds:
Calcium carbonate precipitation helps remove hardness and some heavy metals.
- Dicyandiamide (DCD):
Used in biological nutrient removal to inhibit nitrification temporarily, improving nitrogen removal efficiency.
- Thiourea Dioxide:
Reduces iron and manganese ions to insoluble forms, aiding their removal.
Oxidizing agents break down complex organic molecules and control odors.
- Hydrogen Peroxide (H₂O₂):
Used in advanced oxidation processes (AOPs) often combined with UV or ozone to degrade micropollutants.
- Potassium Permanganate (KMnO₄):
Oxidizes iron, manganese, and some organic compounds, improving water quality and reducing odors.
- Peracetic Acid:
A strong disinfectant and oxidizer used as an alternative to chlorine with fewer harmful by-products.
- Acetic Acid:
Used as an external carbon source to enhance biological phosphorus removal and denitrification.
- Polyacrylonitrile:
Applied in membrane filtration systems to improve separation efficiency.
- Dimethyl Sulfide:
Used in some industrial wastewater treatments to remove sulfur compounds responsible for odors.
Modern sewage treatment plants increasingly incorporate advanced chemical processes to meet stricter environmental standards and enable water reuse.
AOPs use combinations of oxidizing agents (e.g., ozone, hydrogen peroxide) and UV light to generate highly reactive hydroxyl radicals that degrade persistent organic pollutants, pharmaceuticals, and endocrine disruptors.
Membrane bioreactors (MBRs) use membranes to separate solids from treated water. Chemicals such as acids, alkalis, and detergents are periodically used to clean membranes and restore permeability.
Emerging technologies recover phosphorus and nitrogen from wastewater as marketable fertilizers. Chemicals like magnesium chloride and calcium hydroxide are used to precipitate struvite (magnesium ammonium phosphate), a valuable slow-release fertilizer.
- Storage: Chemicals must be stored in corrosion-resistant tanks with secondary containment to prevent leaks.
- Labeling and Training: Proper labeling and staff training reduce risks of accidents.
- Dosing Control: Automated dosing systems ensure precise chemical addition, minimizing overdosing and waste.
- Emergency Preparedness: Spill kits, neutralizing agents, and emergency response plans are essential.
- Residual Chemicals: Overuse of disinfectants can lead to toxic residuals in effluent.
- Disinfection By-Products (DBPs): Some chemicals form DBPs harmful to aquatic life and human health.
- Sludge Management: Chemicals used in treatment affect sludge characteristics and disposal options.
- Personal protective equipment (PPE) such as gloves, goggles, and respirators are mandatory.
- Ventilation systems reduce inhalation risks from volatile chemicals.
- Regular health monitoring and safety audits help maintain a safe working environment.
Chemicals are indispensable in modern sewage treatment plants, enabling the removal of a wide array of contaminants and ensuring that treated water meets stringent environmental standards. From coagulants that clarify water to disinfectants that safeguard public health, each chemical plays a critical role in the complex treatment process.
Advancements in chemical treatment technologies, such as advanced oxidation and nutrient recovery, are making sewage treatment more efficient, sustainable, and aligned with circular economy principles. However, the use of chemicals must be carefully managed to minimize environmental impact and ensure worker safety.
As global water challenges intensify, understanding and optimizing chemical use in sewage treatment will remain a priority for engineers, operators, and policymakers worldwide.
The most commonly used chemicals include coagulants (aluminum sulfate, ferric chloride), flocculants (polyacrylamide), disinfectants (chlorine, sodium hypochlorite), pH adjusters (sodium hydroxide, lime), and precipitants for nutrient and heavy metal removal.
Coagulants destabilize suspended particles by neutralizing their charges, while flocculants help these particles aggregate into larger flocs, making them easier to remove by sedimentation or filtration.
pH adjustment ensures optimal conditions for chemical reactions and biological processes, improving treatment efficiency and protecting infrastructure from corrosion.
Chemicals are stored in compatible tanks with secondary containment, labeled fill lines, and spill control measures. They are dosed at points of maximum mixing to ensure safety and effectiveness.
If not properly managed, chemicals can pose risks such as toxic residuals or accidental spills. Plants follow strict protocols to minimize these risks and ensure chemicals do not harm the environment or public health.
[1] https://www.echemi.com/cms/539788.html
[2] https://longchangchemical.com/sewage-treatment-chemicals-used-in-sewage/
[3] https://www.netsolwater.com/chemicals-to-treat-sewage.php?blog=4386&srsltid=AfmBOorZpnV_1BhNeOPEGrCDPrBFdxubtvIVDiij2iuysYmQSEnEOv2j
[4] https://www.ontario.ca/document/design-guidelines-sewage-works/handling-chemicals
[5] https://www.netsolwater.com/which-chemicals-are-used-in-sewage-and-water-treatment.php?blog=1252&srsltid=AfmBOoreLKUK2n42CmYASXHEKDiFFXhVKzYflo0opQK4onECy_yCrNBm
[6] https://www.jeeng.net/Keyword-sewage+treatment+plant/32787
[7] https://pmc.ncbi.nlm.nih.gov/articles/PMC3893653/
[8] https://safetyculture.com/topics/sewage-treatment-plant/
