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Views: 222 Author: Carie Publish Time: 2025-04-22 Origin: Site
Content Menu
● Understanding Conventional Sewage Treatment
>> Overview of Conventional Treatment Stages
● Three Ways to Improve Conventional Sewage Treatment
>> 1. Enhanced Biological Nutrient Removal (BNR)
>>> Why Focus on Nutrient Removal?
>>> Advanced Biological Processes for Nutrient Removal
>>> Case Study: AAO Implementation in a Municipal Plant
>> 2. Advanced Chemical Treatment
>>> Role of Chemical Treatment in Sewage Plants
>>> Chemical Coagulation and Flocculation
>>> Carbon Adsorption for Micropollutants
>>> Chemical Precipitation for Phosphorus
>> 3. Process Integration and Automation
>>> Why Integration and Automation Matter
>>> Integrated Treatment Systems
>>> Automation and Real-Time Monitoring
● Additional Considerations for Improving Conventional Sewage Treatment
>> Sludge Management and Resource Recovery
>> Addressing Emerging Contaminants
● Comparative Table: Key Improvement Strategies
● FAQ
>> 1. What are the main pollutants targeted by sewage treatment plants?
>> 2. Why is nutrient removal (nitrogen and phosphorus) so important?
>> 3. What are the drawbacks of chemical treatment in sewage plants?
>> 4. How does automation improve sewage treatment efficiency?
>> 5. Can existing sewage treatment plants be upgraded with these improvements?
● Citation
Conventional sewage treatment is fundamental for protecting public health and the environment. However, as urban populations grow and environmental regulations tighten, traditional methods often struggle to meet stricter discharge standards, particularly concerning nutrients like nitrogen and phosphorus. This article explores three key strategies to enhance the effectiveness of conventional sewage treatment, integrating advanced technologies and best practices. Visual aids and video resources are provided throughout to illustrate concepts and solutions.
Conventional sewage treatment typically involves three stages:
- Preliminary Treatment: Removal of large solids and grit.
- Primary Treatment: Sedimentation to remove suspended solids.
- Secondary Treatment: Biological processes (e.g., activated sludge, trickling filters) to degrade organic matter and reduce biochemical oxygen demand (BOD).
- Tertiary (Advanced) Treatment: Further purification to remove nutrients and pathogens, often required to meet modern standards.
Preliminary Treatment:
The first step involves removing large debris such as sticks, plastics, and rags using screens and grit chambers. This prevents damage to downstream equipment and reduces clogging.
Primary Treatment:
Wastewater flows into sedimentation tanks where heavier solids settle to form primary sludge, and oils and grease float to the surface for removal. This stage typically removes 30-40% of suspended solids and 25-35% of BOD.
Secondary Treatment:
Biological treatment uses microorganisms to consume organic pollutants. The activated sludge process is the most common, where air is supplied to aeration tanks to support aerobic bacteria that degrade organic matter. Secondary clarifiers then separate biomass from treated water.
Tertiary Treatment:
This stage targets nutrients (nitrogen and phosphorus), pathogens, and other pollutants not fully removed by secondary treatment. Methods include filtration, disinfection (chlorination, UV), and nutrient removal processes.
While conventional treatment effectively reduces organic matter and suspended solids, it often falls short in removing nutrients and emerging contaminants. Enhancing these plants is critical for environmental protection and regulatory compliance.
Nitrogen and phosphorus are essential nutrients but become pollutants in excess. When discharged into water bodies, they cause eutrophication—excessive algae growth, oxygen depletion, and fish kills. Conventional secondary treatment removes only a fraction of these nutrients.
Anaerobic-Anoxic-Oxic (AAO) Process:
This process creates three distinct zones in the treatment reactor:
- Anaerobic Zone: No oxygen or nitrate present; phosphorus-accumulating organisms (PAOs) release phosphorus.
- Anoxic Zone: Nitrate is present but no free oxygen; denitrification occurs where nitrate is converted to nitrogen gas.
- Oxic Zone: Oxygen is supplied; PAOs uptake phosphorus and nitrification converts ammonia to nitrate.
This sequence promotes simultaneous nitrogen and phosphorus removal.
Membrane Bioreactor (MBR):
MBR combines activated sludge with membrane filtration (microfiltration or ultrafiltration). Membranes retain suspended solids and microorganisms, producing high-quality effluent.
- Advantages: Smaller footprint, excellent solids separation, and enhanced nutrient removal.
- Challenges: Membrane fouling requires regular cleaning and increases operational costs.
Sequencing Batch Reactor (SBR):
SBR treats wastewater in timed batches through fill, react, settle, and decant phases. This flexibility allows precise control of aerobic and anoxic conditions to optimize nutrient removal.
- Advantages: Adaptable to varying flows and loads, efficient nutrient removal.
- Limitations: Batch operation may require larger tanks and more complex controls.
A mid-sized city upgraded its conventional activated sludge plant to an AAO system. After the upgrade, total nitrogen removal improved from 40% to over 90%, and phosphorus levels dropped below regulatory limits. This resulted in improved water quality in the receiving river and reduced algae blooms.
While biological processes remove organic matter and some nutrients, chemical treatment is often necessary to meet stringent phosphorus limits and remove trace contaminants.
- Process: Chemicals like aluminum sulfate (alum), ferric chloride, or lime are added to wastewater. These chemicals neutralize charges on particles and cause them to aggregate into larger flocs.
- Outcome: Flocs settle more easily, removing suspended solids and phosphorus bound to particles.
- Application: Often used after secondary treatment or integrated into tertiary treatment.
Advantages:
- Rapid phosphorus removal to very low concentrations (often <0.1 mg/L).
- Effective for removing colloidal and dissolved phosphorus forms.
Disadvantages:
- Increased sludge volume requiring disposal.
- Chemical costs and handling considerations.
- Potential pH adjustments needed.
Activated carbon adsorption removes trace organic compounds such as pharmaceuticals, personal care products, and endocrine disruptors that resist biological degradation.
- Types: Powdered activated carbon (PAC) is added directly; granular activated carbon (GAC) is used in filters.
- Benefits: Significantly reduces micropollutants and improves effluent quality.
- Challenges: High operational costs and periodic carbon regeneration or replacement.
In some cases, chemical precipitation is combined with biological phosphorus removal to achieve ultra-low phosphorus levels.
Conventional plants often operate with fixed parameters and manual controls, leading to inefficiencies and suboptimal performance. Integrating processes and automating controls can significantly enhance treatment outcomes.
Combining multiple treatment technologies into a single, compact system improves efficiency and flexibility.
- Integrated Fixed-film Activated Sludge (IFAS): Combines suspended growth (activated sludge) and attached growth (biofilm on media) to increase biomass and nutrient removal.
- Denitrification Filters: Use biofilters to remove nitrate in a compact footprint.
- Modular Plants: Prefabricated units that integrate biological and chemical treatment, ideal for small communities or plant upgrades.
Modern plants use sensors to continuously measure parameters such as dissolved oxygen, ammonia, nitrate, pH, turbidity, and flow rates. These data feed into control systems that adjust aeration, chemical dosing, and sludge wasting automatically.
Benefits:
- Optimizes energy use by adjusting aeration based on oxygen demand.
- Reduces chemical use by dosing only as needed.
- Improves effluent quality by maintaining optimal conditions.
- Enables predictive maintenance and reduces downtime.
A wastewater treatment plant integrated automation and remote monitoring, resulting in a 20% reduction in energy consumption and a 15% decrease in chemical use. Real-time alerts allowed operators to respond quickly to process upsets.
Improving sewage treatment is not only about effluent quality but also about managing by-products sustainably.
- Anaerobic Digestion: Converts sludge into biogas (methane), which can be used for energy generation.
- Nutrient Recovery: Technologies are emerging to recover phosphorus from sludge or wastewater as struvite, a valuable fertilizer.
- Dewatering and Drying: Advanced methods reduce sludge volume, lowering disposal costs.
Wastewater treatment is energy-intensive, especially aeration. Strategies to improve energy efficiency include:
- Using fine bubble diffusers for better oxygen transfer.
- Variable frequency drives (VFDs) on pumps and blowers.
- Recovering energy from biogas.
- Implementing energy management systems.
Conventional treatment often fails to remove pharmaceuticals, microplastics, and personal care products. Advanced oxidation processes (AOPs), membrane filtration, and activated carbon adsorption are promising solutions.
| Strategy | Main Benefit | Main Challenge | Typical Application |
|---|---|---|---|
| Enhanced Biological Nutrient Removal | High N and P removal | Higher complexity | Urban/municipal plants |
| Advanced Chemical Treatment | Low phosphorus, micropollutant | Increased sludge/cost | Stringent discharge locations |
| Process Integration & Automation | Efficiency, flexibility | Upfront investment | New/upgraded plants |
Improving conventional sewage treatment is essential to meet the growing challenges posed by population growth, urbanization, and stricter environmental standards. The three most effective ways to enhance conventional treatment are:
- Implementing advanced biological nutrient removal processes (e.g., AAO, MBR, SBR) to target nitrogen and phosphorus.
- Incorporating advanced chemical treatment (e.g., coagulation-flocculation, carbon adsorption) for further removal of phosphorus and trace organics.
- Integrating treatment steps and automation to optimize plant performance, reduce costs, and ensure regulatory compliance.
Beyond these, sustainable sludge management, energy efficiency, and tackling emerging contaminants are critical complementary strategies. By adopting these approaches, municipalities and utilities can achieve higher effluent quality, protect water resources, and operate more sustainably in the face of evolving challenges.
Sewage treatment plants primarily aim to remove biochemical oxygen demand (BOD), suspended solids (SS), ammonia, nitrogen, and phosphorus, as well as pathogens and trace organic contaminants.
Excess nitrogen and phosphorus in treated effluent can cause eutrophication in receiving waters, leading to algal blooms, oxygen depletion, and harm to aquatic life.
Chemical treatment can significantly increase sludge production and operational costs and may require careful management of chemical dosing to avoid negative environmental impacts.
Automation allows for real-time monitoring and adjustment of treatment processes, optimizing chemical and energy use, improving effluent quality, and reducing operational errors.
Yes, many existing plants can be retrofitted with advanced biological and chemical treatment units, integrated systems, and automation to enhance performance and comply with stricter regulations.
[1] https://www.atlantis-press.com/article/125974486.pdf
[2] https://publications.parliament.uk/pa/cm199798/cmselect/cmenvtra/266ii/et0210.htm
[3] https://www.fao.org/4/t0551e/t0551e05.htm
[4] https://mrforum.com/product/9781644901151-1/?srsltid=AfmBOopFvTtJPHAUWkwxRi2-U1DMIkG6ifGNTmmgrWeUqoqkHPWSw4Gx
[5] https://ijettjournal.org/assets/year/2017/volume-45/number-3/IJETT-V45P226.pdf
[6] https://www.fehrgraham.com/about-us/blog/what-is-the-best-method-for-wastewater-treatment-fg
[7] https://pubmed.ncbi.nlm.nih.gov/35359231/
[8] https://onlinelibrary.wiley.com/doi/10.1002/9781119641353.ch2
