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Views: 222 Author: Carie Publish Time: 2025-05-17 Origin: Site
Content Menu
● Overview of Sewage Treatment Plant Stages
● Biological Treatment in Sewage Plants
>> What Is Biological Treatment?
>> Why Use Biological Treatment?
● The Biological Treatment Process
● Microbial Ecology in Biological Treatment
● Importance of Biological Treatment
>> Innovations in Biological Treatment
● Environmental and Economic Benefits
● FAQ
>> 1. What microorganisms are used in biological sewage treatment?
>> 2. How does the activated sludge process differ from trickling filters?
>> 3. What is the role of oxygen in biological treatment?
>> 4. Can biological treatment remove nutrients like nitrogen and phosphorus?
>> 5. What happens to the sludge produced during biological treatment?
Sewage treatment plants are critical infrastructures designed to clean wastewater from homes, industries, and communities before releasing it back into the environment. Among the various stages of sewage treatment, the part that utilizes biological factors is the secondary treatment, also known as the biological treatment stage. This article explores in detail the role of biological factors in sewage treatment plants, how they work, the processes involved, and their significance in maintaining environmental and public health.
A typical sewage treatment plant consists of multiple stages:
1. Preliminary Treatment – Removal of large debris and grit.
2. Primary Treatment – Sedimentation to remove suspended solids.
3. Secondary Treatment (Biological Treatment) – Use of microorganisms to degrade organic matter.
4. Tertiary Treatment – Advanced cleaning to remove nutrients and pathogens.
5. Sludge Treatment – Processing of solids removed during treatment.
The biological factors come into play mainly during the secondary treatment stage.
Biological treatment involves using living microorganisms-primarily bacteria and other microbes-to break down organic pollutants in wastewater. These microorganisms consume the organic matter as their food source, converting it into simpler, less harmful substances such as carbon dioxide, water, and biomass (microbial cells).
- Efficiency: Microorganisms can degrade complex organic compounds that physical or chemical methods cannot.
- Cost-effectiveness: Biological processes reduce the need for expensive chemical treatments.
- Environmental friendliness: It mimics natural purification processes, reducing toxic pollutants without harmful residues.
Biological treatment is a natural and sustainable approach that leverages the metabolic processes of microbes to cleanse wastewater, making it a cornerstone of modern sewage treatment plants.
One of the most common biological treatment methods is the activated sludge process. Here's how it works:
- Wastewater is mixed with a concentrated suspension of microorganisms (activated sludge) in an aeration tank.
- Oxygen is supplied continuously to support aerobic bacteria.
- The bacteria metabolize organic pollutants, converting them into carbon dioxide, water, and new bacterial cells.
- The mixture then flows to a secondary clarifier where solids (biosolids) settle out.
- Part of the settled sludge is recycled back to maintain microbial population; the rest is removed for further sludge treatment.
This process is highly effective in removing organic matter and is widely used in municipal and industrial wastewater treatment plants worldwide.
Another biological method is the trickling filter:
- Wastewater is sprayed over a bed of porous media (stones, plastic media).
- A biofilm of aerobic microorganisms grows on the media surface.
- As sewage trickles down, microbes consume organic matter.
- The treated water is collected at the bottom and sent for further treatment.
Trickling filters are simpler in design and operation compared to activated sludge systems and are often used in smaller or rural treatment plants.
- Sequencing Batch Reactors (SBR): A batch process where aeration and settling occur in the same tank sequentially. SBRs offer flexibility and control over treatment cycles.
- Moving Bed Biofilm Reactor (MBBR): Uses plastic carriers suspended in the aeration tank for biofilm growth, combining advantages of suspended and attached growth systems.
- Anaerobic Digestion: For sludge treatment, anaerobic bacteria break down organic solids producing biogas (methane) as energy. This process is essential for sludge stabilization and energy recovery.
The success of biological treatment depends heavily on the microbial community structure. Different microbes play specific roles:
- Aerobic bacteria: Degrade organic carbon compounds using oxygen.
- Nitrifying bacteria: Convert ammonia to nitrate (nitrification).
- Denitrifying bacteria: Convert nitrate to nitrogen gas (denitrification), removing nitrogen.
- Phosphorus-accumulating organisms (PAOs): Uptake and store phosphorus for removal.
Maintaining a balanced and healthy microbial ecosystem is key to effective treatment. Factors such as temperature, pH, oxygen concentration, and toxic substances affect microbial activity.
- Removal of BOD and COD: Biological treatment significantly reduces Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), indicators of organic pollution.
- Nutrient Removal: Processes like nitrification and denitrification reduce nitrogen compounds, preventing eutrophication in water bodies.
- Pathogen Reduction: Microbial competition and environmental conditions reduce harmful pathogens.
- Energy Recovery: Anaerobic digestion of sludge produces biogas, a renewable energy source.
By reducing organic pollutants and nutrients, biological treatment protects aquatic ecosystems from oxygen depletion and harmful algal blooms, safeguarding biodiversity and water quality.
While biological treatment is effective, it faces several challenges:
- Toxicity: Industrial pollutants such as heavy metals and chemicals can inhibit microbial activity.
- Oxygen Supply: Maintaining adequate oxygen levels is energy-intensive and critical for aerobic microbes.
- Sludge Management: Excess sludge requires proper treatment and disposal.
- Process Control: Biological systems are sensitive to changes in influent composition and environmental conditions.
- Microbial Fuel Cells: Devices that generate electricity from wastewater using bacteria.
- Hybrid Systems: Combining activated sludge with biofilm reactors for improved efficiency.
- Advanced Biofilm Carriers: New materials that enhance microbial growth and pollutant degradation.
- Automation and Sensors: Real-time monitoring and control to optimize biological processes.
These innovations aim to make biological treatment more resilient, energy-efficient, and adaptable to varying wastewater characteristics.
Biological treatment not only cleans wastewater but also offers:
- Reduced Chemical Usage: Minimizes the need for chemical additives.
- Lower Energy Consumption: Especially with anaerobic digestion producing biogas.
- Resource Recovery: Nutrients like nitrogen and phosphorus can be recovered for fertilizer production.
- Sustainability: Supports circular economy principles by converting waste into resources.
The secondary treatment stage of a sewage treatment plant is where biological factors are most actively used. Through processes such as the activated sludge method, trickling filters, and biofilm reactors, microorganisms play a vital role in breaking down organic pollutants, reducing toxicity, and protecting the environment. Understanding and optimizing these biological systems is essential for effective wastewater management and sustainable urban living.
Biological treatment represents a natural, cost-effective, and environmentally friendly approach to sewage treatment. As technology advances, integrating innovative biological processes will further enhance the efficiency and sustainability of wastewater treatment plants worldwide.
Microorganisms include aerobic bacteria, fungi, protozoa, and sometimes anaerobic bacteria in sludge digestion. Aerobic bacteria are the primary agents in activated sludge and trickling filters.
Activated sludge uses suspended microbial biomass in an aeration tank, while trickling filters rely on biofilms growing on a fixed media over which sewage flows.
Oxygen supports aerobic microbes that metabolize organic matter. Without sufficient oxygen, microbial activity decreases, reducing treatment efficiency.
Yes, biological processes such as nitrification and denitrification remove nitrogen, and specific bacteria can remove phosphorus, helping prevent water eutrophication.
Sludge is either recycled to maintain microbial populations or sent to anaerobic digesters where it is broken down to produce biogas and reduce volume.
