Microbial Wastewater Treatment: Types of Microorganisms, Functions, and Applications for Reclaiming Wastewater

Introduction

Wastewater treatment has become one of the most critical environmental challenges of the 21st century. As urbanization increases and industrial activities expand, the volume and complexity of wastewater requiring treatment have grown exponentially. Among the various wastewater treatment methods available, microbial wastewater treatment stands out as one of the most effective, economical, and environmentally sustainable approaches to cleaning polluted water and recovering valuable resources. This comprehensive guide explores the multifaceted role of microorganisms in wastewater treatment, their functions, types, and practical applications for reclaiming wastewater.

Microbial wastewater treatment harnesses the natural metabolic processes of bacteria, fungi, protozoa, algae, and other microorganisms to break down organic pollutants, remove nutrients, degrade toxic compounds, and transform wastewater into reusable water. This biological approach is not only more economical than purely chemical or physical methods but also more sustainable, producing minimal toxic byproducts while recovering valuable biosolids and biogas that can be repurposed as fertilizers and energy sources.

What is Microbial Wastewater Treatment?

Microbial wastewater treatment is a biological process that utilizes living microorganisms to purify wastewater by metabolizing pollutants and converting them into simpler, non-toxic substances. These microorganisms consume organic matter in the wastewater as their food source, converting it into energy, new microbial biomass, and gases like carbon dioxide and methane.

The Principle of Microbial Wastewater Treatment

The fundamental principle underlying microbial wastewater treatment is straightforward: microorganisms naturally consume and transform organic matter. In a wastewater treatment facility, conditions are optimized—through controlled aeration, temperature, pH, and nutrient balance—to maximize this natural biological process at an industrial scale.

The process works because:

• Organic pollutants serve as carbon and energy sources for microbial growth and metabolism

• Microorganisms can break down complex compounds into simpler, less harmful substances

• The process produces stable end products that are either non-toxic or can be further treated

• Multiple microorganism types work synergistically to degrade a wide range of pollutants

Why Microbial Treatment Matters

Traditional wastewater treatment using only physical and chemical methods is expensive, energy-intensive, and can produce toxic byproducts. Microbial treatment offers significant advantages:

• Cost-effectiveness: Biological processes are 50-70% cheaper than purely chemical treatment

• Environmental sustainability: Produces minimal hazardous waste

• Resource recovery: Generates biosolids (fertilizer) and biogas (energy)

• Efficacy: Can treat complex industrial and municipal wastewaters

• Scalability: Adaptable from small decentralized systems to massive municipal plants

• Low chemical requirements: Reduces dependency on synthetic chemicals

Types of Microorganisms in Wastewater Treatment

The effectiveness of microbial wastewater treatment depends on the diverse microbial populations present in treatment systems. Different microorganisms perform specialized functions, working together in complex ecological relationships.

1. Bacteria – The Primary Treatment Workhorses

Bacteria are the most abundant and important microorganisms in wastewater treatment plants, accounting for the majority of pollutant degradation activity.

Aerobic Bacteria

Aerobic bacteria require oxygen to survive and are the dominant microorganisms in most wastewater treatment systems.

Function: These bacteria oxidize organic pollutants using oxygen as the terminal electron acceptor, converting biodegradable organic matter into carbon dioxide, water, and new bacterial biomass.

Common aerobic genera:

• Pseudomonas species – versatile degraders of complex organics

• Bacillus species – degraders of proteins and cellulose

• Acinetobacter species – phosphorus-accumulating organisms

• Nitrosomonas species – ammonia-oxidizing bacteria (nitrifiers)

• Nitrobacter species – nitrite-oxidizing bacteria

Application: Activated sludge systems, trickling filters, aerated lagoons, sequencing batch reactors

Removal efficiency: Aerobic bacteria can remove 85-95% of biochemical oxygen demand (BOD) and chemical oxygen demand (COD)

Anaerobic Bacteria

Anaerobic bacteria thrive in oxygen-free environments and perform essential functions in wastewater treatment.

Function: These bacteria break down complex organic matter in the absence of oxygen, producing methane gas (biogas), carbon dioxide, and stabilized sludge. They're essential for sludge digestion and treatment of high-strength industrial wastewaters.

Common anaerobic genera:

• Methanobacterium species – methane-producing archaea

• Clostridium species – fermentative bacteria

• Bacteroides species – cellulose degraders

• Desulfovibrio species – sulfur-reducing bacteria

Application: Anaerobic digesters, anaerobic lagoons, treating high-strength wastewater

Process products: Biogas (60-70% methane), which can be captured and used as renewable energy

Facultative Bacteria

Facultative bacteria possess the remarkable ability to survive in both aerobic and anaerobic conditions, adapting their metabolism based on available oxygen.

Function: These versatile organisms can switch between aerobic respiration and anaerobic fermentation, allowing them to function in variable treatment environments.

Common facultative genera:

• Enterobacter species

• Escherichia coli (E. coli)

• Salmonella species

Application: Transition zones between aerobic and anaerobic regions, systems with fluctuating oxygen availability

2. Protozoa – Nature's Quality Controllers

Protozoa are single-celled eukaryotic organisms that play a critical but often underappreciated role in wastewater treatment.

Functions of Protozoa

Predation on bacteria: Protozoa feed on dispersed bacteria and bacterial particles, effectively clarifying the treated water and improving effluent quality.

Nutrient recycling: Through their metabolic processes, protozoa recycle nutrients and make them available to bacteria in more usable forms.

Sludge settleability: By consuming excess dispersed bacteria, protozoa improve the settling characteristics of activated sludge.

Treatment indicator: The presence and abundance of specific protozoal species indicate treatment efficiency and system health.

Common protozoal types

Ciliates: The dominant protozoa in wastewater treatment, including:

• Tetrahymena species

• Paramecium species

• Vorticella species

Flagellates: Small protozoa that thrive under stressed conditions with high organic loading.

Amoebae: Carnivorous protozoa that feed on bacteria and are indicators of stable treatment systems.

Protozoal importance

Research shows that systems with healthy protozoal populations achieve superior effluent quality compared to systems with reduced protozoal diversity. A diverse protozoal community indicates stable, mature treatment systems.

3. Fungi – Decomposers of Complex Organics

Fungi are more complex organisms than bacteria, often composed of thread-like hyphae organized into networks.

Fungal capabilities

Degradation of complex compounds: Fungi excel at breaking down complex biopolymers including:

• Lignin (wood component)

• Cellulose (plant cell walls)

• Other resistant organic compounds

Biofilm formation: Fungal hyphae form robust biofilm matrices that support bacterial communities.

Adaptation to low-nutrient conditions: Fungi thrive when nitrogen and phosphorus are limited, conditions that suppress bacterial growth.

Fungal prevalence

Fungi typically occur at lower concentrations than bacteria in wastewater treatment systems (1-5% of total microorganisms), but their presence becomes more significant under:

• Low pH conditions (pH < 5.0)

• Complex organic loadings

• Low macronutrient concentrations

Important fungal organisms

Ascomycota species are particularly important, promoting both denitrification and cellulose degradation in wastewater systems.

4. Archaea – Specialized Processors

Archaea were historically classified as unusual bacteria but are now recognized as a separate kingdom with unique cellular characteristics.

Archaeal functions

Methanogenesis: Methanogenic archaea produce methane from short-chain organic acids and hydrogen. This process is vital for:

• COD/BOD reduction in anaerobic digesters

• Biogas production as renewable energy

• Stabilization of waste sludges

Ammonia oxidation: Ammonia-oxidizing archaea (AOA) play roles in nitrogen transformation, particularly important during winter when bacterial activity declines.

Archaeal occurrence

Archaea represent a smaller proportion of wastewater treatment microorganisms but are

concentrated in anaerobic digesters where they're essential for complete waste stabilization.

5. Algae – Photosynthetic Contributors

While less commonly emphasized, algae contribute to wastewater treatment through photosynthetic processes.

Algal functions

Nutrient removal: Algae consume nitrogen and phosphorus, utilizing these nutrients for growth.

Oxygen production: Through photosynthesis, algae produce dissolved oxygen that supports bacterial aerobic respiration.

Wastewater lagoons: In natural treatment systems like lagoons and ponds, algae are essential components.

Advantages and challenges

Advantages: Energy-efficient (powered by sunlight), low operational costs, potential for biofuel production

Challenges: Seasonal variability, potential overgrowth causing clogging, low-temperature performance limitations

6. Other Microorganisms

Rotifers: Multicellular microscopic organisms that:

• Clarify effluent by consuming suspended bacteria

• Break apart activated sludge flocs

• Indicate advanced system maturation

Helminths (parasitic worms): Present in raw wastewater but their numbers are significantly reduced through treatment processes.

Viruses and bacteriophages: Phages (viruses that infect bacteria) naturally regulate bacterial populations within treatment systems.

Functions of Microorganisms in Wastewater Treatment

Microorganisms perform multiple critical functions that transform polluted wastewater into clean, reusable water.

1. Organic Matter Degradation

The most fundamental function is breaking down biodegradable organic compounds into simpler forms.

Process: Aerobic bacteria oxidize organic matter (represented as CH₂O) to produce energy:

CH₂O + O₂ → CO₂ + H₂O + Energy (ATP)

Products: Carbon dioxide, water, new bacterial biomass

Significance: Removes biochemical oxygen demand (BOD) by 85-95%, which is the primary indicator of wastewater organic content

2. Nitrogen Removal Through Nitrification-Denitrification

Nitrogen removal is critical to prevent eutrophication (algal blooms) in receiving waters.

Nitrification Process

Step 1 - Ammonia oxidation: Bacteria of the genus Nitrosomonas oxidize ammonia (NH₃) to nitrite (NO₂⁻):

2NH₄⁺ + 3O₂ → 2NO₂⁻ + 4H⁺ + 2H₂O

Step 2 - Nitrite oxidation: Bacteria of genus Nitrobacter oxidize nitrite to nitrate (NO₃⁻):

2NO₂⁻ + O₂ → 2NO₃⁻

Requirements: Aerobic conditions, adequate dissolved oxygen (DO > 2 mg/L), stable pH

Denitrification Process

Mechanism: Under anaerobic conditions, heterotrophic bacteria use nitrate as an electron acceptor, reducing it sequentially to nitrogen gas:

NO₃⁻ → NO₂⁻ → NO → N₂O → N₂

Key organisms: Pseudomonas species, Paracoccus denitrificans, other facultative anaerobes

Requirements: Anoxic conditions (DO < 0.5 mg/L), organic carbon source, presence of denitrifying bacteria

Result: Nitrogen is removed from wastewater and escapes to the atmosphere as harmless N₂ gas

3. Phosphorus Removal

Microorganisms can remove excess phosphorus through biological processes, preventing eutrophication.

Enhanced Biological Phosphorus Removal (EBPR)

Specialized bacteria, particularly Acinetobacter species, accumulate excess phosphorus under alternating aerobic-anaerobic conditions.

Mechanism:

• Anaerobic zone: Microorganisms release stored phosphorus into the wastewater as a byproduct of fermentation

• Aerobic zone: The same microorganisms take up excessive phosphorus and store it intracellularly

• Net result: Phosphorus is removed from the wastewater when biomass is wasted

Removal efficiency: 80-90% phosphorus removal is achievable

4. Biosolids Production

During wastewater treatment, microorganisms convert dissolved organic matter into solid bacterial biomass (biosolids or activated sludge).

Significance:

• Biomass accumulation allows settling of solids from treated water

• Biosolids can be further processed and used as soil amendments (fertilizer)

• Nutrient recovery: Biosolids contain nitrogen, phosphorus, and organic matter

5. Pathogen Reduction

Microorganisms in treatment systems reduce pathogenic bacteria, viruses, and parasites through multiple mechanisms.

Mechanisms:

• Direct predation: Protozoa consume bacterial pathogens

• Competition: Commensal bacteria compete for nutrients with pathogens

• Hostile conditions: Extended retention time in hostile conditions inactivates pathogens

• Biofilm exclusion: Pathogenic organisms have difficulty colonizing established biofilms

Result: Pathogen log reduction of 1-3 orders of magnitude, meeting discharge and reuse standards

6. Transformation of Toxic Compounds

Specialized microorganisms can degrade or transform toxic organic compounds into less harmful substances.

Examples:

• Degradation of pesticides and herbicides

• Breakdown of industrial chemicals

• Transformation of pharmaceutical residues

• Removal of persistent organic pollutants

Importance of Microbial Wastewater Treatment

Understanding why microbial wastewater treatment is essential provides context for its widespread adoption and future development.

Environmental Protection

Untreated wastewater containing high concentrations of organic matter, nutrients, and pathogens severely degrades receiving waters through:

• Eutrophication causing algal blooms and dead zones

• Oxygen depletion (hypoxia) that kills aquatic life

• Pathogen contamination affecting human and animal health

Microbial treatment mitigates these impacts by removing pollutants before discharge.

Public Health

Wastewater contains disease-causing pathogens including:

• Bacteria (E. coli, Salmonella, Vibrio)

• Viruses (hepatitis A, rotavirus, norovirus)

• Parasites (Giardia, Cryptosporidium)

Microbial treatment processes reduce pathogen concentrations by 1-3 orders of magnitude, protecting downstream water users.

Water Scarcity Solutions

As freshwater becomes increasingly scarce in many regions, treated wastewater represents a critical water resource. Microbial treatment is essential for wastewater reclamation and reuse, enabling water recycling for:

• Irrigation of agricultural crops

• Industrial cooling water

• Groundwater recharge

• Non-potable urban reuse

Economic Benefits

Cost advantages: Biological treatment is significantly more economical than chemical treatment alone, reducing operational costs by 50-70%.

Resource recovery: Biosolids and biogas produced during treatment provide economic value, offsetting treatment costs.

Industrial symbiosis: Treated wastewater can be reused industrially, reducing both water consumption and treatment costs.

Regulatory Compliance

Most jurisdictions require biological wastewater treatment to meet:

• BOD discharge limits (typically 10-30 mg/L)

• Total suspended solids (TSS) limits (typically 10-30 mg/L)

• Nitrogen limits (varying by region, 5-15 mg/L)

• Phosphorus limits (varying by region, 0.5-2 mg/L)

• Pathogen/coliform limits for reuse applications

Microbial treatment efficiently meets these regulatory requirements.

How Microbes Help Reclaim Wastewater

Wastewater reclamation—the treatment of wastewater to standards suitable for specific reuse applications—heavily depends on optimized microbial processes.

Multi-Barrier Treatment Approach

Modern wastewater reclamation employs multiple sequential treatment stages, each utilizing specific microbial functions:

Stage 1 - Secondary biological treatment: Removes BOD, TSS, and initial pathogen reduction through conventional microbial processes (activated sludge or trickling filters)

Stage 2 - Advanced biological treatment: Additional biological treatment stages including:

• Nitrification/denitrification reactors for enhanced nitrogen removal

• Fixed biofilm reactors for phosphorus removal

• Lagoons or constructed wetlands for polishing

Stage 3 - Tertiary treatment: Physical/chemical polishing including membrane filtration, UV disinfection, or advanced oxidation

Stage 4 - Storage and distribution: Chlorination or other residual disinfection to maintain water quality during storage and distribution

Specific Reclamation Applications

Agricultural Irrigation Reuse

Microbial treatment must reduce:

• Pathogens (meet fecal coliform standards, typically <200 CFU/100mL for unrestricted crops)

• Nutrients (prevent excessive fertilization)

• Salts (prevent soil salinization)

Microbial technologies used: Activated sludge followed by lagoons or constructed wetlands, providing both treatment and natural filtration

Industrial Reuse

Industrial applications require:

• BOD reduction (typically <5-10 mg/L)

• Suspended solids removal

• Specific chemical removal depending on industrial application

Microbial technologies used: Optimized activated sludge, biofilm reactors, sometimes supplemented with advanced oxidation

Non-potable Urban Reuse

Toilet flushing, landscape irrigation, and other non-potable uses require:

• BOD < 5 mg/L

• TSS < 5 mg/L

• Pathogen reduction (1-3 log removal minimum)

• Color and turbidity removal

Microbial technologies used: High-rate biological reactors, membrane bioreactors (MBRs), followed by UV or advanced oxidation

Potable Reuse (Indirect)

The most stringent standard, typically requiring:

• Complete BOD removal

• Multiple pathogen log reductions (4-6 logs)

• Removal of pharmaceutical residues and micropollutants

Microbial technologies used: Advanced biological treatment combined with activated carbon, ozonation, reverse osmosis, and ultraviolet disinfection

What is a Microbial Culture for Wastewater Treatment?

A microbial culture in wastewater treatment refers to a controlled community of microorganisms specifically cultivated or selected to perform wastewater treatment functions.

Types of Microbial Cultures

Mixed (Consortium) Cultures

The most common type used in wastewater treatment plants, containing diverse microorganisms:

• Natural communities that develop spontaneously in treatment systems

• Composed of hundreds or thousands of species

• Self-balancing through competitive and predatory relationships

Advantages:

• Robust and resilient to input variations

• Can degrade diverse pollutant types

• Naturally stable

Disadvantages:

• Less predictable performance

• Difficult to optimize for specific pollutants

Pure Cultures

Single-species or limited-species cultures used for specific applications.

Applications:

• Research and development

• Treatment of specific industrial wastes

• Bioremediation of targeted pollutants

Advantages:

• Predictable performance

• Can optimize for specific compounds

Disadvantages:

• Requires continuous management

• More susceptible to contamination

• Limited versatility

Enriched Cultures

Mixed cultures enhanced or selected for specific functions, such as:

• Nitrifying cultures (enriched for ammonia and nitrite oxidizers)

• Denitrifying cultures (enriched for anoxic heterotrophs)

• Phosphorus-removing cultures (enriched for PAO bacteria)

Microbial Culture Maintenance

Maintaining viable microbial cultures requires:

Continuous feed: Supply of biodegradable substrate (food) to support growth

Environmental control:

• pH maintenance (typically 6.5-8.0)

• Temperature control (20-35°C for mesophilic systems)

• Dissolved oxygen (aerobic systems require >2 mg/L)

Solids retention time (SRT): Control of how long microorganisms remain in the system, typically 8-15 days for conventional treatment

Nutrient balance: Adequate nitrogen and phosphorus (approximately BOD:N:P = 100:5:1)

Washout prevention: Regular return of settled sludge to aeration tanks maintains microbial populations

What is Microbial Treatment?

Microbial treatment (also called biological treatment or bioremediation in broader contexts) is the use of microorganisms to degrade, transform, or remove contaminants from wastewater, soil, or water.

Characteristics of Microbial Treatment

Enzymatic degradation: Microorganisms produce enzymes that break down complex molecules into simpler forms

Metabolic processes: Contaminants are consumed as food, generating energy for microbial growth

Bioaccumulation: Some microbes accumulate metals and other pollutants within their cells

Biotransformation: Some pollutants are chemically modified rather than completely mineralized

Conditions Necessary for Effective Microbial Treatment

1. Presence of degrading microorganisms: The necessary microbial species must be present or be introduced

2. Substrate availability: Microbes require degradable organic matter as an energy source (except for some autotrophic processes)

3. Appropriate oxygen regime: Either aerobic or anaerobic conditions matched to the treatment goal

4. Suitable pH: Most wastewater microbes function best at pH 6.5-8.0

5. Temperature: Optimal performance typically 20-35°C (mesophilic range)

6. Retention time: Sufficient time for microbial metabolism to occur (typically 4-24 hours)

7. Nutrient balance: Adequate nitrogen, phosphorus, and trace minerals

Common Microbes Used in Sewage Treatment

Specific bacterial species dominate different treatment processes and play distinct roles in sewage treatment.

Key Sewage Treatment Bacteria

Nitrifying Bacteria

Nitrosomonas europaea and related species:

• Oxidize ammonia to nitrite (Step 1 of nitrification)

• Chemolithotrophic (oxidize ammonia for energy)

• Slow-growing, long SRT required (8-15 days)

• Sensitive to environmental perturbations

Nitrobacter hamburgensis and related species:

• Oxidize nitrite to nitrate (Step 2 of nitrification)

• Also chemolithotrophic

• Sensitive to high nitrite concentrations

• Work in close association with Nitrosomonas

Denitrifying Bacteria

Pseudomonas species:

• Heterotrophic denitrifiers

• Fast-growing, versatile degraders

• Require anaerobic conditions and available organic carbon

• Most commonly encountered denitrifiers

Paracoccus denitrificans:

• Important heterotrophic denitrifier

• Can utilize various organic substrates

• Key player in low-nutrient conditions

Phosphorus-Accumulating Organisms (PAO)

Acinetobacter species:

• Accumulate and release phosphorus under alternating aerobic-anaerobic conditions

• Enable enhanced biological phosphorus removal (EBPR)

• Important in modern nutrient-removal plants

Tetrasphaera and Nostocoida species:

• Also accumulate phosphorus

• More tolerant of operational variations than Acinetobacter

Heterotrophic Organisms

Bacillus species:

• Degrade complex organics including proteins and polysaccharides

• Aerobic, forming endospores for survival during starvation

• Active throughout treatment train

Flavobacterium species:

• Degraders of complex biopolymers

• Biofilm-forming capability

• Important in attached-growth systems

Bacteria That Cause Operational Problems

Filamentous bacteria (e.g., Sphaerotilus, Nocardia):

• Excessive growth causes "sludge bulking"

• Results in poor settling and turbid effluent

• Triggered by low F/M ratio, low dissolved oxygen

• Requires operational adjustments to control

Foaming organisms (e.g., Gordonia, Mycobacterium):

• Produce surfactants causing persistent foam

• Difficult to control, sometimes requiring selective treatment

• Can be beneficial for degrading certain pollutants but problematic operationally

The Four Types of Wastewater Treatment

Comprehensive wastewater treatment typically involves four distinct stages, each serving specific purposes and utilizing microbial processes differently.

1. Preliminary Treatment

Objective: Remove large solids and debris that could damage equipment

Methods:

• Screening: Removes rags, plastics, sticks

• Grit removal: Settles sand and gravel

• Grease traps: Removes fats, oils, and grease (FOG)

Microbial involvement: Minimal—primarily physical removal

Outcome: Simplified wastewater entering primary treatment

2. Primary Treatment

Objective: Remove settable solids and some organic matter through gravity separation

Methods:

• Sedimentation tanks (primary clarifiers): Heavy particles settle

• Flotation systems: Light materials and grease rise for skimming

• Dissolved air flotation (DAF): Fine air bubbles carry light particles to surface

Microbial involvement: Minimal biological activity—primarily physical/chemical

Removal:

• Suspended solids: 40-60%

• BOD: 20-30%

Outcome: Primary effluent containing ~60-70% of original BOD

3. Secondary Treatment – Microbial Oxidation

Objective: Remove dissolved organic matter through biological oxidation

Primary microbial process: Aerobic biodegradation of organic compounds

Dominant microorganisms: Aerobic heterotrophic bacteria, protozoa

Common systems:

Activated Sludge Process

The most widely used secondary treatment system globally.

Process:

1. Aeration tank: Primary effluent mixed with returned activated sludge and aerated for 4-8 hours

2. Microorganism contact: Aerobic bacteria consume organic matter as substrate

3. Flocculation: Bacteria produce biofilm and settle together (activated sludge floc)

4. Secondary clarifier: Mixed liquor flows to clarifier where sludge settles

5. Sludge return: 50-80% of settled sludge recycled to aeration tank

6. Wasting: Excess sludge removed for further treatment

Performance: Removes 85-95% of BOD and 80-90% of TSS

Trickling Filter Process

Fixed biofilm system used especially in smaller facilities.

Process:

1. Primary effluent distributed over filter bed

2. Water trickles through carrier media (stone, plastic, etc.)

3. Biofilm of microorganisms grows on media surfaces

4. As wastewater trickles down, bacteria consume organic matter

5. Upper zones: primarily organic degradation

6. Lower zones: primarily nitrification (ammonia oxidation)

7. Sloughed biofilm settles in secondary clarifier

Advantages: Lower energy requirements, more compact, good for nutrient removal

Aerated Lagoons

Shallow basins with mechanical aeration, commonly used in small municipalities.

Process: Wastewater retained 5-7 days with continuous or intermittent aeration; aerobic bacteria degrade organics

Advantages: Simple operation, low energy use

Membrane Bioreactors (MBR)

Modern advanced secondary treatment combining activated sludge with membrane filtration.

Unique features:

• Membrane module (microfiltration or ultrafiltration) integrated into or external to aeration tank

• Maintains very high biomass concentrations

• Produces very high quality effluent

Advantages:

• Superior BOD and TSS removal (>99%)

• Pathogen removal

• Smaller footprint

Removal: 85-95% BOD, high TSS removal, initial pathogen reduction

4. Tertiary Treatment – Advanced Polishing

Objective: Further remove remaining impurities for specific reuse applications or discharge to sensitive waters

Processes involved:

Nitrification/Denitrification Reactors

Specialized reactors designed specifically for nitrogen removal.

Nitrification reactor: Aerobic conditions promoting ammonia-oxidizing bacteria

Denitrification reactor: Anoxic conditions promoting nitrate-reducing bacteria

Achievement: 80-95% nitrogen removal

Biological Phosphorus Removal

Specialized reactors exploiting Enhanced Biological Phosphorus Removal (EBPR) mechanisms.

Design: Alternating anaerobic and aerobic zones

Achievement: 80-90% phosphorus removal

Constructed Wetlands

Natural treatment systems using wetland plants and diverse microorganisms.

Processes:

• Physical filtration by sediments

• Chemical precipitation

• Microbial degradation (both aerobic and anaerobic)

• Plant uptake

Achievement: Additional BOD, nutrient, and pathogen removal; used for polishing and pretreatment

Sand Filtration and Media Filtration

Physical filtration enhanced by biofilm development on filter media.

Additional benefits: Biological polishing through biofilm

Advanced Oxidation Processes (AOP)

Chemical treatment (not primarily microbial) using ozonation, UV, hydrogen peroxide, or their combinations to further degrade resistant compounds.

Membrane Filtration

Ultra/nanofiltration for removal of:

• Colloidal particles

• Remaining suspended solids

• Some microorganisms

UV Disinfection

Ultraviolet light inactivates remaining pathogens.

Chlorination/Advanced Disinfection

Chemical disinfection ensuring pathogen elimination before reuse or discharge.

Applications of Microbial Technology in Wastewater Treatment

Practical applications of microbial wastewater treatment span numerous industries and treatment scenarios.

Municipal Wastewater Treatment

The largest application, treating domestic sewage from homes and communities.

Scale: Thousands of facilities globally, treating billions of gallons daily

Key microbes: Mixed consortia with emphasis on heterotrophs and nitrifiers

Challenge: Balancing pathogen elimination with biosolids management

Outcome: Clean effluent suitable for river discharge; biosolids for land application

Industrial Wastewater Treatment

Diverse industrial wastewaters requiring specialized biological treatment:

Food Processing

Challenges: High-strength organic wastewater, variable composition

Microbial treatment: Anaerobic treatment for initial COD reduction, followed by aerobic polishing

Brewery and Distillery

Challenges: High organic content, varying pH

Solution: Multi-stage anaerobic/aerobic treatment, energy recovery from biogas

Pharmaceutical Manufacturing

Challenges: Toxic organic compounds, antibiotics

Solution: Specialized bioreactors with selected microbial cultures

Pulp and Paper Mills

Challenges: Recalcitrant lignin and cellulose components

Solution: Multi-stage treatment, sometimes including fungal degradation

Wastewater Reclamation and Reuse

Direct treatment of wastewater for reuse applications.

Target reuse applications:

• Irrigation of landscapes and crops

• Industrial cooling water

• Toilet flushing in buildings

• Groundwater recharge (indirect potable reuse)

Technologies: Advanced biological treatment combined with tertiary treatment

Scale: Growing rapidly in water-scarce regions

Examples: California, Australia, Singapore leading indirect potable reuse programs

Biosolids and Nutrient Recovery

Treatment and beneficial reuse of waste sludges produced during biological wastewater treatment.

Anaerobic Digestion

Process: Anaerobic microbes convert sludge organic matter to biogas and stabilized solids

Products:

• Biogas (60-70% methane) for energy production

• Stabilized biosolids for agricultural use

Recovery: ~50% reduction in solids mass, valuable nutrients (nitrogen, phosphorus) recovered

Composting

Process: Aerobic microbes decompose sludge mixed with carbon source (woodchips, etc.)

Product: Stabilized compost suitable for soil amendment

Biochar and Hydrothermal Liquefaction

Emerging technologies: Thermochemical conversion of sludge producing bio-oil and biochar

Advantage: Faster processing (100x faster than anaerobic digestion), higher energy recovery

How Are Nitrates Removed from Wastewater?

Nitrate (NO₃⁻) removal is critical for preventing eutrophication in receiving waters and is essential for most wastewater reuse applications. Microbial processes provide the most cost-effective method for nitrate removal.

Denitrification: The Primary Nitrate Removal Process

Denitrification is the microbial reduction of nitrate to nitrogen gas, which escapes to the atmosphere.

The Denitrification Pathway

Denitrifying bacteria reduce nitrate through a series of enzymatic steps:

Step 1: Nitrate to NitriteNO₃⁻ → NO₂⁻ (catalyzed by nitrate reductase enzyme)

Step 2: Nitrite to Nitric OxideNO₂⁻ → NO (catalyzed by nitrite reductase enzyme)

Step 3: Nitric Oxide to Nitrous OxideNO → N₂O (catalyzed by nitric oxide reductase enzyme)

Step 4: Nitrous Oxide to Nitrogen GasN₂O → N₂ (catalyzed by nitrous oxide reductase enzyme)

Overall reaction: NO₃⁻ + 1.25 CH₃COO⁻ → 0.5 N₂ + 2 HCO₃⁻ + 0.25 H⁺

Conditions Necessary for Denitrification

1. Anaerobic conditions: Dissolved oxygen must be <0.5 mg/L (preferably <0.1 mg/L)

Reason: Bacteria preferentially use oxygen; only when oxygen is depleted do they use nitrate as electron acceptor

2. Available organic carbon: Denitrifying bacteria require organic compounds as electron donors for energy

Carbon sources: Wastewater's residual BOD, supplemental methanol or acetate, or external organic additions

Carbon requirement: Approximately 1.25 mg BOD needed per mg of NO₃⁻-N removed

3. Presence of denitrifying bacteria: While many bacteria possess denitrification capability, sufficient populations must be present or enriched

4. Adequate residence time: Sufficient time for denitrification reaction to complete (typically 2-4 hours in anoxic zones)

5. Appropriate pH: Optimal pH range 6.5-8.0; enzyme activity declines outside this range

6. Temperature: Enzyme activity increases with temperature (20-35°C optimal for most systems)

Denitrification System Configurations

Traditional Nitrification-Denitrification

Sequential process in separate reactors or zones:

1. Nitrification stage: Aerobic zone converts ammonia to nitrate

2. Denitrification stage: Anoxic zone reduces nitrate to nitrogen gas

Advantage: Separated processes can be optimized individually

Disadvantage: Requires two separate zones, higher carbon requirement

Single Reactor with Alternating Aeration

Process: Single aeration tank with alternating periods of aeration and no-aeration

Benefits: Integrated nitrification/denitrification, reduced space requirement

Technology: Sequencing batch reactors (SBRs), oxidation ditches

A/O Process (Anaerobic/Oxic)

Configuration:

• Initial anaerobic zone (no oxygen, no added carbon – just from wastewater)

• Followed by aerobic nitrification zone

Benefit: Combines phosphorus removal in anaerobic zone with nitrification in oxic zone

Anoxic/Oxic Process (Pre-Anoxic)

Configuration:

• Anoxic zone receives return sludge (containing nitrate from aerobic zone)

• Followed by aerobic nitrification zone

Benefit: Uses internally recycled nitrate, reduces external carbon requirement

Nitrogen Removal Efficiency

Target removal: Typically 80-95% nitrogen removal in engineered systems

Residual nitrate: 5-10 mg NO₃⁻-N/L in treated effluent

Complete denitrification rates: Up to 1.5 kg N removed per 1000 m³ per day in optimized systems

Challenges in Nitrate Removal

Incomplete denitrification: Sometimes produces N₂O instead of N₂, creating greenhouse gas emissions

Carbon limitation: Low-strength wastewater may lack sufficient carbon for complete denitrification

Temperature effects: Cold weather reduces denitrification rates

Filamentous microorganism growth: Can interfere with nitrification/denitrification balance

Alternative Nitrogen Removal Methods

Anammox (Anaerobic Ammonia Oxidation)

Anaerobic oxidation of ammonia to nitrogen gas directly, bypassing nitrate formation.

Advantages: Requires 50% less oxygen than nitrification/denitrification, produces less sludge, no external carbon required

Emerging technology: Successfully applied at some full-scale facilities

Partial Nitrification-Anammox

Combines partial nitrification (oxidizing ammonia to nitrite, not nitrate) with anammox.

Advantages: 25% lower oxygen requirement, 40% less carbon requirement than traditional nitrification/denitrification

Status: Commercial implementation increasing

Autotrophic Denitrification

Nitrogen removal using inorganic electron donors instead of organic carbon.

Electron donors: Hydrogen gas, elemental sulfur, metallic iron

Advantage: No organic carbon consumption

Disadvantage: Complex process control, potential harmful byproducts

Conclusion

Microbial wastewater treatment represents one of humanity's most effective and sustainable solutions for managing wastewater and protecting environmental and human health. By understanding the diverse microorganisms involved, their specific functions, and how to optimize treatment systems, we can achieve superior wastewater treatment outcomes while recovering valuable resources including energy and nutrients.

The future of wastewater treatment will increasingly involve:

• Advanced biological processes incorporating microbial engineering and selective enrichment

• Decentralized treatment systems enabling water reclamation and reuse at local scales

• Resource recovery focus transforming treatment plants into biorefinery facilities

• Climate-resilient systems designed to handle variable and extreme conditions

• Integration of emerging technologies combining biological processes with advanced treatments

IndoGulf BioAg recognizes the critical importance of optimized microbial consortia and specialized biological cultures in achieving sustainable wastewater treatment and water reclamation. Through development of bioaugmentation products, specialized microbial cultures, and optimization strategies, the future of wastewater treatment will increasingly harness the full potential of microbial technology for environmental protection and resource sustainability.

Key Takeaways

• Microbial treatment is cost-effective: 50-70% cheaper than purely chemical treatment methods

• Multiple microorganisms work synergistically: Bacteria, protozoa, fungi, and archaea each perform specialized functions

• BOD removal: 85-95% achieved through aerobic bacterial degradation

• Nitrogen removal: Accomplished through nitrification (88-95% efficiency) followed by denitrification

• Four treatment stages: Preliminary → Primary → Secondary (microbial) → Tertiary (advanced polishing)

• Nitrate removal: Achieved primarily through denitrification under anaerobic conditions with organic carbon source

• Resource recovery: Biogas and biosolids produced during treatment provide economic value

• Water reclamation: Microbial treatment is essential enabling technology for wastewater reuse applications

• Operational success depends on: Proper environmental conditions (aeration, pH, temperature, SRT, nutrient balance)

• Emerging alternatives: Anammox, partial nitrification, and autotrophic denitrification offer improved efficiency