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Views: 222 Author: Carie Publish Time: 2025-05-18 Origin: Site
Content Menu
● Overview of Sewage Treatment Processes
● How Sewage Treatment Removes Bacteria
>> 3. Secondary Treatment: The Core of Bacterial Removal
>> 4. Tertiary Treatment and Disinfection
● Microbial Removal Efficiency in Sewage Treatment
● Advanced Biological Treatment Technologies
>> Sequencing Batch Biofilter Granular Reactors (SBBGRs)
● Role of Beneficial Bacteria in Sewage Treatment
● Challenges in Bacterial Removal
● Environmental and Health Implications
● FAQ
>> 1. What is the most effective stage for removing bacteria in sewage treatment?
>> 2. Does primary treatment remove all bacteria from sewage?
>> 3. How does UV light disinfect sewage water?
>> 4. Can treated sewage water be reused safely?
>> 5. What role do bacteria play in sewage treatment?
Sewage treatment is a vital process in modern sanitation systems, designed to remove contaminants, including harmful bacteria, from wastewater before it is released back into the environment or reused. Understanding which stages and methods in sewage treatment effectively remove bacteria is crucial for ensuring public health and environmental safety.
Sewage treatment typically involves multiple stages, each targeting different types of pollutants, including solids, organic matter, and microorganisms such as bacteria. The main stages are:
- Pre-Treatment: Removal of large debris and grit.
- Primary Treatment: Settling of solids and removal of fats and scum.
- Secondary Treatment: Biological degradation of organic matter using bacteria.
- Tertiary Treatment: Advanced processes including disinfection to remove remaining pathogens.
Each stage contributes to reducing bacterial loads in wastewater, but their effectiveness varies significantly.
The initial step screens out large solids like sanitary products, leaves, and rags that could hinder subsequent treatment processes. Sand and grit are also removed by sedimentation tanks. This stage does not directly remove bacteria but prevents damage and blockages in the system.
In primary treatment, wastewater is held in large settling tanks allowing heavy solids to sink as sludge and lighter materials like fats to float as scum. Some bacteria are removed as they attach to these solids and settle out. However, primary treatment typically only removes about 10-20% of bacteria and viruses because many microorganisms remain suspended in the water.
Secondary treatment is a biological process where aerobic bacteria are introduced to break down organic matter in the sewage. This stage is highly effective in reducing bacterial populations:
- Activated Sludge Process: Air is pumped into aeration tanks where bacteria consume organic pollutants, converting them into harmless by-products. Excess bacteria settle out in secondary clarifiers.
- Trickling Filters: Sewage passes over media colonized by bacteria that digest organic matter.
Secondary treatment can remove 85-99% of bacteria through natural die-off, predation by other microorganisms, and sedimentation of bacterial biomass.
Tertiary treatment includes filtration, nutrient removal, and crucially, disinfection processes such as chlorination, ultraviolet (UV) light, or ozonation. These methods specifically target and kill remaining bacteria and other pathogens:
- UV Light Disinfection: UV light damages bacterial DNA, preventing reproduction without altering water chemistry or appearance.
- Chlorination: Chlorine compounds kill bacteria effectively but require careful dosing to avoid harmful by-products.
- Ozonation: Ozone is a strong oxidant that destroys bacteria and viruses.
Tertiary treatment can achieve near-complete bacterial removal, making effluent safe for discharge or reuse.
| Treatment Stage | Approximate Bacterial Removal Efficiency |
|---|---|
| Primary Treatment | 10-20% (1-2 log units) |
| Secondary Treatment | 85-99% (up to 4 log units) |
| Tertiary Treatment | Near 100% (disinfection step) |
Studies show that secondary treatment reduces bacterial pathogens by 3–6 log units, and tertiary treatment further ensures safety by removing almost all remaining bacteria.
A pilot-scale study showed that SBBGRs removed over 90% of suspended solids and significantly reduced bacterial indicators like *Escherichia coli* by up to 4 log units. When combined with sand filtration, the effluent met World Health Organization (WHO) criteria for safe reuse in agriculture.
SBBGRs operate in cycles, alternating between aeration and settling phases within a single reactor, enhancing bacterial degradation and sedimentation efficiency. This process is highly compact and energy-efficient, making it suitable for decentralized wastewater treatment systems.
Interestingly, bacteria themselves are the primary agents of sewage treatment. Beneficial aerobic bacteria metabolize organic pollutants, reducing biochemical oxygen demand (BOD) and outcompeting pathogenic bacteria. This natural microbial competition helps control harmful bacteria populations.
However, some pathogenic bacteria can survive in sewage treatment plants, especially if the process is incomplete or the system is overloaded. This is why tertiary disinfection is essential to ensure complete pathogen removal.
Despite advances, several challenges remain in bacterial removal from sewage:
- Antibiotic-Resistant Bacteria: Some bacteria have developed resistance to antibiotics and disinfectants, posing a risk if released untreated.
- Biofilm Formation: Bacteria can form biofilms on treatment surfaces, protecting them from disinfection.
- Viral and Protozoan Pathogens: Viruses and protozoa may be more resistant to treatment than bacteria, requiring specialized processes.
Ongoing research focuses on optimizing treatment conditions, combining multiple disinfection methods, and developing novel technologies like membrane bioreactors (MBRs) and advanced oxidation processes (AOPs).
Proper bacterial removal in sewage treatment is critical to prevent waterborne diseases such as cholera, typhoid, and dysentery. Untreated or poorly treated sewage can contaminate drinking water sources, recreational waters, and agricultural fields.
By effectively removing bacteria, sewage treatment plants protect ecosystems, reduce public health risks, and enable water reuse, contributing to sustainable water management.
Sewage treatment removes bacteria through a combination of physical, biological, and chemical processes. While primary treatment removes some bacteria by sedimentation, the majority are eliminated during secondary biological treatment where bacteria degrade organic matter and compete with pathogens. Tertiary treatment, especially disinfection methods like UV light and chlorination, ensures near-total removal of harmful bacteria, making treated wastewater safe for discharge or reuse. Advanced technologies such as SBBGRs and sand filtration further enhance bacterial removal, supporting sustainable water management and public health protection. Continuous innovation and monitoring are essential to address emerging challenges like antibiotic resistance and ensure safe, effective sewage treatment worldwide.
Secondary treatment is the most effective stage for removing bacteria, achieving 85-99% removal through biological processes involving aerobic bacteria.
No, primary treatment removes only about 10-20% of bacteria, mainly those attached to settleable solids. Most bacteria remain suspended and require further treatment.
UV light disinfects by damaging the DNA of bacteria and other pathogens, preventing their reproduction without affecting water's taste, smell, or pH.
Yes, with proper secondary and tertiary treatment, including disinfection, treated sewage water can meet safety standards for reuse in agriculture and other applications.
Beneficial bacteria in secondary treatment break down organic pollutants, reducing contaminants and outcompeting harmful bacteria, thus cleaning the wastewater biologically.
