Microorganisms and the Environment

Microorganisms are found almost everywhere on Earth.

They live in:

• soil
• water
• sediments
• oceans
• plants and animals
• decaying organic matter
• extreme environments

Although most microorganisms are invisible to the naked eye, their activities have enormous effects on:

ecosystems.

Without microorganisms, nutrients would not cycle efficiently, dead material would accumulate, and many ecosystems would be unable to function normally.

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Microbes as Ecosystem Workers

Microorganisms perform several essential environmental roles.

They:

• decompose dead organisms
• recycle nutrients
• participate in the carbon cycle
• participate in the nitrogen cycle
• break down wastes
• form relationships with plants
• help maintain soil fertility
• remove some pollutants
• contribute to wastewater treatment

Microorganisms therefore connect the living and nonliving parts of an:

ecosystem.

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Decomposition

Decomposition is the breakdown of dead organisms and organic waste into simpler substances.

Bacteria and fungi are important:

decomposers.

They secrete enzymes onto dead material.

These enzymes break large biological molecules into smaller substances that microorganisms can absorb and use.

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Why Is Decomposition Important?

Imagine an ecosystem without decomposers.

Dead:

• plants
• animals
• leaves
• microorganisms
• wastes

would continually accumulate.

More importantly, nutrients trapped inside this material would not be efficiently returned to the environment.

Decomposition releases nutrients that can be:

reused by other organisms.

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Nutrient Cycling

Matter does not simply flow through an ecosystem once and disappear.

Elements such as:

• carbon
• nitrogen
• phosphorus
• sulfur

are continually:

recycled.

Microorganisms carry out many of the chemical transformations that make this recycling possible.

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Microorganisms and the Carbon Cycle

Carbon is found in:

• carbon dioxide
• living organisms
• dead organic matter
• soil
• oceans
• fossil fuels

Microorganisms affect the movement of carbon between these reservoirs.

During decomposition, microbes break down organic compounds.

Through respiration, many release:

carbon dioxide.

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Microbial Respiration

Like other organisms, many microorganisms release energy through:

cellular respiration.

A simplified equation for aerobic respiration is:

glucose + oxygen → carbon dioxide + water + energy

The carbon dioxide can return to the atmosphere or water.

Plants and other photosynthetic organisms can then use carbon dioxide during:

photosynthesis.

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Microbes and the Nitrogen Cycle

Nitrogen is essential for producing:

• proteins
• DNA
• RNA

Although the atmosphere contains large amounts of nitrogen gas, most organisms cannot use atmospheric nitrogen directly.

Microorganisms perform several crucial transformations in the:

nitrogen cycle.

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Nitrogen Fixation

Nitrogen fixation converts atmospheric nitrogen gas into nitrogen-containing compounds that can enter biological systems.

Certain bacteria perform this process.

Some nitrogen-fixing bacteria live freely in soil.

Others form relationships with plants, particularly:

legumes.

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Root Nodules

Plants such as:

• peas
• beans
• clover

can contain structures called:

root nodules.

These nodules may contain nitrogen-fixing bacteria.

The bacteria receive nutrients from the plant.

The plant benefits from access to biologically useful nitrogen compounds.

This is an example of a:

mutualistic relationship.

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Nitrification

Other soil bacteria carry out:

nitrification.

During nitrification, nitrogen-containing compounds are converted through stages into forms such as:

nitrate ions.

Plants can absorb nitrate ions through their roots and use the nitrogen to manufacture:

• amino acids
• proteins
• nucleic acids

Microorganisms therefore strongly influence:

soil fertility.

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Denitrification

Some bacteria carry out:

denitrification.

They convert nitrate compounds into gaseous forms of nitrogen, returning nitrogen to the:

atmosphere.

Nitrogen fixation, nitrification, decomposition, and denitrification together help maintain the nitrogen cycle.

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Waste as an Environmental Problem

Human activities produce enormous quantities of:

waste.

Examples include:

• sewage
• food waste
• agricultural waste
• industrial wastewater
• animal waste
• household wastewater

Untreated waste can contain:

• organic matter
• nutrients
• pathogens
• chemicals
• suspended solids

Microorganisms can help treat many types of biological waste.

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Wastewater Treatment

Wastewater treatment uses physical, chemical, and biological processes to make wastewater safer before it is discharged or reused.

Microorganisms are particularly important during:

biological treatment.

They consume and break down biodegradable organic substances in the wastewater.

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A Simplified Wastewater Treatment Process

A wastewater-treatment system may include:

screening → settling → biological treatment → further clarification → disinfection → treated water

Different treatment facilities use different systems.

Microorganisms are particularly important in the:

biological treatment stage.

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Primary Treatment

During primary treatment, physical processes remove larger materials and suspended solids.

Processes may include:

• screening
• sedimentation
• removal of floating materials

Primary treatment removes some waste, but substantial dissolved and suspended organic material can remain.

Microorganisms help deal with this during:

secondary treatment.

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Secondary Treatment

Secondary treatment relies heavily on microorganisms.

Bacteria and other microorganisms consume:

biodegradable organic matter.

They use these substances as sources of:

• carbon
• nutrients
• energy

As microbes process the organic material, the amount of biodegradable waste in the water decreases.

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Activated Sludge

One common biological wastewater-treatment system is the:

activated sludge process.

Wastewater is mixed with a community of microorganisms.

Air is supplied to provide:

oxygen.

The microorganisms grow and consume organic substances in the wastewater.

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The Aeration Tank

An aeration tank contains wastewater and microorganisms.

Air or oxygen is introduced into the tank.

This supports aerobic microorganisms that use organic waste during:

respiration and growth.

A simplified process is:

organic waste + oxygen → microbial activity → simpler products + new microbial biomass

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Why Add Oxygen?

Aerobic microorganisms require oxygen for:

aerobic respiration.

Providing oxygen allows them to break down organic material efficiently.

Without sufficient oxygen, the microbial community and treatment process may change significantly.

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Settling the Microorganisms

After biological treatment, water may enter a settling tank.

Microbial cells and other particles form:

sludge.

This material settles toward the bottom.

Cleaner water can then be separated from the sludge.

Some activated sludge may be returned to the treatment system to maintain a healthy population of:

microorganisms.

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Biological Oxygen Demand

A useful measure of water pollution is:

biochemical oxygen demand (BOD).

BOD is related to the amount of oxygen microorganisms require while breaking down biodegradable organic matter in water under specified conditions.

Water containing large amounts of biodegradable organic material generally has:

higher BOD.

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Why Can High BOD Be Harmful?

If untreated organic waste enters a river:

microorganisms decompose waste → microbial respiration increases → dissolved oxygen decreases

Low dissolved oxygen can harm:

• fish
• aquatic invertebrates
• other aerobic organisms

Wastewater treatment reduces biodegradable organic material before water enters natural ecosystems.

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Anaerobic Digestion

Some waste is treated using:

anaerobic digestion.

This process occurs without oxygen.

Communities of microorganisms break down organic matter and produce gases including:

methane and carbon dioxide.

The resulting gas mixture is called:

biogas.

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What Can Be Treated by Anaerobic Digestion?

Materials can include:

• sewage sludge
• food waste
• animal manure
• agricultural waste
• some industrial organic wastes

Instead of simply disposing of these materials, microorganisms can convert part of their chemical energy into:

useful biogas.

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Biogas

Biogas contains a significant proportion of:

methane.

Methane can be burned as a fuel.

Depending on the system, biogas can be used to produce:

• heat
• electricity
• upgraded renewable gas

Anaerobic digestion therefore combines:

waste treatment + energy recovery.

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Digestate

After anaerobic digestion, material called:

digestate

remains.

Depending on its composition, treatment, and local regulations, digestate can sometimes be used as a source of nutrients for agriculture.

This illustrates how biotechnology can help turn some waste materials into:

useful resources.

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Composting

Microorganisms are also responsible for:

composting.

Composting is the controlled biological decomposition of organic material.

Suitable materials can include:

• leaves
• grass
• plant waste
• food scraps
• agricultural residues

Bacteria and fungi break down this organic matter.

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Why Does Compost Become Warm?

Microorganisms release energy during:

respiration.

Some of this energy becomes heat.

In an active compost pile, rapid microbial metabolism can cause the temperature to rise substantially.

Temperature is therefore evidence of intense:

microbial activity.

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Conditions for Composting

Efficient composting depends on factors such as:

• moisture
• oxygen
• temperature
• particle size
• carbon-to-nitrogen balance
• microbial activity

Turning compost can increase:

aeration.

This supplies oxygen to aerobic decomposers.

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What Is Bioremediation?

Bioremediation is the use of living organisms to remove, transform, or reduce environmental pollutants.

Microorganisms are especially useful because some can metabolize pollutants.

In some cases, microbes can use a pollutant as a source of:

carbon or energy.

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How Does Bioremediation Work?

A simplified process is:

pollutant enters environment → suitable microorganisms encounter pollutant → microbial enzymes transform pollutant → less harmful products may form

The exact pathway depends on:

• pollutant
• microorganism
• oxygen availability
• temperature
• pH
• nutrients
• environmental conditions

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Oil Pollution

Petroleum contains many:

hydrocarbons.

Some microorganisms can break down certain hydrocarbons.

They may use components of petroleum as:

energy and carbon sources.

This natural microbial activity can contribute to the breakdown of some oil contamination.

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Bioremediation of Oil Spills

After an oil spill, naturally occurring hydrocarbon-degrading microorganisms may begin breaking down some oil components.

Environmental conditions may limit their activity.

Scientists may sometimes improve microbial degradation by supplying nutrients or optimizing conditions.

This approach is called:

biostimulation.

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Biostimulation

Biostimulation involves changing environmental conditions to encourage microorganisms already present to break down pollutants more effectively.

This might involve adding:

• nutrients
• oxygen
• electron acceptors

The aim is not necessarily to add new microorganisms.

Instead, it helps the existing microbial community perform:

more effectively.

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Bioaugmentation

Another approach is:

bioaugmentation.

Bioaugmentation involves introducing selected microorganisms into a contaminated environment.

These microorganisms are chosen because they can help degrade a particular:

pollutant.

Success depends strongly on whether the introduced organisms can survive and function under local environmental conditions.

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Biostimulation vs Bioaugmentation

These terms are easy to confuse.

Biostimulation

→ improve conditions for microorganisms already present.

Bioaugmentation

→ introduce selected microorganisms.

Both approaches may be used in:

bioremediation.

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Cleaning Contaminated Soil

Microorganisms can be used to treat soil contaminated with some:

• petroleum products
• solvents
• pesticides
• industrial chemicals

Treatment may occur:

in situ — directly at the contaminated location

or

ex situ — after contaminated material has been removed for treatment.

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In Situ Bioremediation

In situ means:

in the original location.

For example, contaminated groundwater might be treated by encouraging microorganisms underground to degrade pollutants.

Advantages may include:

• less excavation
• reduced transport of contaminated material
• potentially lower disturbance

However, conditions underground can be difficult to control.

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Ex Situ Bioremediation

Ex situ means that contaminated material is:

removed and treated elsewhere.

For example, contaminated soil could be excavated and placed in a controlled treatment system.

This can allow better control of:

• temperature
• moisture
• oxygen
• nutrients

However, excavation and transport can increase cost and disturbance.

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Microbes and Heavy Metals

Heavy metals present a different problem.

A microorganism cannot simply:

destroy a chemical element.

However, microorganisms can sometimes change the:

chemical form, mobility, or availability

of metals.

This can help immobilize, concentrate, or recover certain metals.

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Bioleaching

Bioleaching uses microorganisms to help release metals from minerals.

Certain microorganisms alter the chemical conditions surrounding ores.

This can help recover metals such as:

copper.

Bioleaching is an example of environmental biotechnology connected with:

mining and resource recovery.

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Microbes and Plastic Waste

Scientists are investigating microorganisms and microbial enzymes that can break down certain:

plastics.

Some enzymes can attack particular polymers and break them into smaller molecules.

This is an active area of biotechnology research.

However, microbes are not currently a simple solution to all plastic pollution.

Different plastics have very different:

chemical structures and biodegradability.

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Microbes and Pesticides

Some soil microorganisms can transform or degrade certain:

pesticides.

This may reduce the persistence of some chemicals in the environment.

However, degradation depends on:

• chemical structure
• microbial community
• temperature
• moisture
• pH
• oxygen

Some pollutants are much more resistant to microbial degradation than others.

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Environmental Biotechnology

Environmental biotechnology uses biological organisms or biological processes to help solve environmental problems.

Applications include:

• wastewater treatment
• composting
• anaerobic digestion
• bioremediation
• bioleaching
• resource recovery
• biofuel production
• environmental monitoring

Microorganisms are central to many of these technologies.

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Biosensors

Microorganisms or biological molecules can sometimes be used in:

biosensors.

A biosensor detects a biological or chemical substance and produces a measurable signal.

Environmental biosensors may help detect:

• pollutants
• toxins
• nutrients
• contaminants

This can help scientists monitor environmental:

quality.

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Microbes and Agriculture

Microorganisms can support more sustainable agriculture.

Examples include:

• nitrogen-fixing bacteria
• microbes involved in nutrient cycling
• microorganisms associated with plant roots
• biological control organisms
• decomposition of crop residues

These microbes can influence:

soil health and plant growth.

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Mycorrhizal Fungi

Mycorrhizae are associations between fungi and plant roots.

The fungus can increase the effective area available for absorbing:

• water
• mineral nutrients

The plant provides the fungus with:

organic carbon compounds.

These relationships can improve plant nutrient acquisition and contribute to healthy ecosystems.

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Microorganisms and Soil Fertility

Healthy soil contains enormous microbial communities.

These microorganisms contribute to:

• decomposition
• nutrient recycling
• soil structure
• nitrogen transformations
• interactions with plant roots

Soil is therefore not simply:

dirt.

It is a complex biological ecosystem.

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Microbes and the Carbon Cycle

Microorganisms can both release and store carbon.

For example:

decomposition and respiration → carbon dioxide released

while microbial growth can temporarily incorporate carbon into:

biomass.

Microorganisms therefore influence how carbon moves through ecosystems.

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Methane-Producing Microorganisms

Some microorganisms called:

methanogens

produce methane under anaerobic conditions.

Methanogens are actually members of the domain:

Archaea.

They occur in environments such as:

• wetlands
• sediments
• digestive systems
• anaerobic digesters

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Methane-Consuming Microorganisms

Other microorganisms can consume:

methane.

These are known as:

methanotrophs.

They can reduce the amount of methane reaching the atmosphere from some environments.

Microbial communities can therefore both produce and consume important:

greenhouse gases.

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Microorganisms and Sustainability

Environmental sustainability means meeting present needs while protecting the ecological systems and resources needed in the future.

Microorganisms can contribute by:

• recycling nutrients
• treating waste
• reducing some pollution
• producing renewable fuels
• recovering useful resources
• supporting soil fertility
• reducing reliance on some chemical processes

Their environmental importance extends far beyond their small size.

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Waste to Resource

A major principle of sustainability is finding ways to convert:

waste into useful resources.

Microorganisms can help achieve this.

For example:

food waste → anaerobic digestion → biogas

plant waste → composting → soil amendment

wastewater → microbial treatment → cleaner water

organic residues → microbial processing → useful chemicals

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The Circular Economy

A circular economy aims to keep materials in use for as long as practical and reduce waste.

Microbial biotechnology can contribute by:

• recycling nutrients
• recovering energy
• converting waste materials
• producing biodegradable materials
• recovering valuable compounds

Microorganisms can therefore connect:

waste management and resource production.

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Advantages of Environmental Biotechnology

Using microorganisms can offer several advantages.

Microbial processes may:

• operate at moderate temperatures
• use naturally occurring organisms
• break down certain pollutants
• reduce waste
• recover resources
• require less energy than some alternatives
• treat contamination directly at some sites

However, these advantages depend on the particular:

application.

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Limitations of Bioremediation

Bioremediation is useful, but it is not a universal solution.

Limitations include:

• some pollutants cannot be biodegraded
• some processes are slow
• temperature may limit microbial activity
• incorrect pH may inhibit microbes
• nutrients may be limited
• oxygen may be unavailable
• toxic pollutant concentrations may kill microbes
• intermediate products may also require treatment

Bioremediation must therefore be carefully:

monitored.

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Not Every Pollutant Can Be Destroyed

Microorganisms can transform many organic compounds.

However, they cannot destroy:

elements.

For example, a microbe cannot make lead atoms disappear.

Instead, biotechnology might help:

• immobilize the metal
• change its chemical form
• concentrate it
• assist in recovery

Understanding this distinction is important when evaluating environmental biotechnology.

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Natural Processes vs Biotechnology

Microorganisms naturally:

• decompose waste
• cycle nutrients
• transform chemicals

Environmental biotechnology takes advantage of these natural abilities by:

controlling, enhancing, or applying them to specific problems.

Humans are therefore often using biological processes that already occur in ecosystems.

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Monitoring Environmental Biotechnology

Environmental applications must be monitored carefully.

Scientists may measure:

• pollutant concentration
• microbial activity
• oxygen concentration
• pH
• temperature
• nutrient concentrations
• breakdown products

The goal is to determine whether treatment is actually:

working.

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Evaluating Environmental Impact

A technology should not be considered sustainable simply because it uses:

microorganisms.

A complete evaluation should consider:

• energy use
• water use
• materials required
• waste generated
• effectiveness
• cost
• ecosystem effects
• long-term outcomes

Environmental sustainability requires looking at the:

whole system.

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Worked Example 1

Dead leaves fall onto forest soil.

What happens to them?

Bacteria, fungi, and other decomposers break down the organic material.

Nutrients are eventually returned to the:

ecosystem.

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Worked Example 2

Untreated sewage containing large amounts of organic material enters a river.

What may happen to dissolved oxygen?

Microorganisms rapidly decompose the organic matter.

Their respiration consumes oxygen.

Therefore:

dissolved oxygen may decrease.

This can harm aquatic organisms.

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Worked Example 3

A wastewater-treatment plant pumps air into a tank containing sewage and microorganisms.

Why?

The oxygen supports:

aerobic respiration.

This allows microorganisms to break down biodegradable organic matter efficiently.

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Worked Example 4

Food waste is placed inside an oxygen-free digester.

What useful product can microbial activity produce?

Biogas, containing methane.

The methane can be used as an energy source.

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Worked Example 5

Oil contaminates coastal soil.

Scientists add nutrients to encourage naturally occurring oil-degrading bacteria.

What technique is being used?

Biostimulation.

The existing microbial population is being encouraged to degrade the pollutant.

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Worked Example 6

Scientists introduce selected pollutant-degrading bacteria to contaminated soil.

What technique is being used?

Bioaugmentation.

Additional microorganisms are being introduced.

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Worked Example 7

A student suggests using bacteria to completely destroy mercury contamination.

What is wrong with this idea?

Mercury is an:

element.

Microorganisms cannot destroy mercury atoms.

They may be able to change the mercury's chemical form, mobility, or availability.

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Worked Example 8

Why can turning a compost pile increase decomposition?

Turning introduces more:

oxygen.

This can increase aerobic microbial activity.

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Worked Example 9

Why might bioremediation work slowly during winter?

Low temperatures generally reduce:

enzyme activity and microbial metabolism.

Pollutant degradation may therefore occur more slowly.

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Worked Example 10

A company claims its microbial treatment is environmentally sustainable because it uses bacteria.

Is this enough evidence?

No.

Scientists should also evaluate:

• energy consumption
• waste products
• effectiveness
• resources required
• environmental impacts

Sustainability must be evaluated across the whole process.

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Comparing Environmental Applications

Wastewater treatment

Purpose: Remove biodegradable organic waste and other contaminants.

Microbial role: Consume and transform waste materials.

Composting

Purpose: Convert organic waste into useful material.

Microbial role: Decompose plant and food material.

Anaerobic digestion

Purpose: Treat organic waste and recover energy.

Microbial role: Break down organic matter without oxygen and ultimately produce methane-rich biogas.

Bioremediation

Purpose: Reduce environmental contamination.

Microbial role: Transform or degrade pollutants.

Bioleaching

Purpose: Recover metals.

Microbial role: Alter minerals and help release metals.

Nutrient cycling

Purpose: Maintain ecosystem function.

Microbial role: Transform and recycle essential elements.

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Common Mistake: All Microorganisms Cause Pollution or Disease

Many microorganisms perform environmentally beneficial roles.

Without microbes:

• decomposition would be severely disrupted
• nutrient cycles would be altered
• wastewater treatment would be much more difficult
• many plants would lose important microbial partners

Microorganisms are essential components of healthy:

ecosystems.

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Common Mistake: Bioremediation Means Microbes Eat Everything

Microorganisms can degrade only substances for which they have suitable:

metabolic pathways.

Some pollutants are easily degraded.

Others are extremely resistant or cannot be destroyed biologically.

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Common Mistake: Bioremediation Removes All Pollution Immediately

Bioremediation can take:

weeks, months, or longer.

Its speed depends on the pollutant and environmental conditions.

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Common Mistake: Anaerobic Digestion and Composting Are the Same

They differ significantly.

Composting

usually relies heavily on aerobic decomposition.

Anaerobic digestion

occurs without oxygen and can produce methane-rich biogas.

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Common Mistake: Wastewater Treatment Simply Filters Sewage

Physical filtration and settling are important, but microorganisms perform much of the:

biological treatment.

They break down biodegradable organic material that cannot simply be removed by screens.

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Common Mistake: Microbes Can Destroy Heavy Metals

Heavy metals are elements.

Microorganisms cannot destroy the atoms.

They can sometimes alter their:

chemical form, mobility, or concentration.

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Check Your Understanding

1. Why are microorganisms important in ecosystems?

2. Define decomposition.

3. Name two major groups of microbial decomposers.

4. Why is decomposition important for nutrient cycling?

5. How do microorganisms contribute to the carbon cycle?

6. How do microorganisms contribute to the nitrogen cycle?

7. What is nitrogen fixation?

8. Explain the relationship between nitrogen-fixing bacteria and some plants.

9. What is nitrification?

10. What is denitrification?

11. How do microorganisms contribute to soil fertility?

12. Explain the role of microorganisms in wastewater treatment.

13. What happens during secondary wastewater treatment?

14. What is activated sludge?

15. Why is oxygen supplied to an aeration tank?

16. What is BOD?

17. Explain why high BOD can be harmful to aquatic ecosystems.

18. What is anaerobic digestion?

19. What useful fuel can be produced during anaerobic digestion?

20. How can anaerobic digestion contribute to sustainability?

21. Explain the role of microorganisms in composting.

22. Why can a compost pile become warm?

23. Define bioremediation.

24. How can microorganisms help clean petroleum contamination?

25. What is biostimulation?

26. What is bioaugmentation?

27. Compare in situ and ex situ bioremediation.

28. Why can microorganisms not completely destroy heavy metals?

29. What is bioleaching?

30. How might microbial biotechnology contribute to dealing with some plastic wastes?

31. Give four examples of environmental biotechnology.

32. What is a biosensor?

33. Explain how microorganisms support sustainable agriculture.

34. What is a mycorrhizal relationship?

35. How can microorganisms contribute to a circular economy?

36. Give three advantages of using microorganisms for environmental applications.

37. Give three limitations of bioremediation.

38. Why must environmental biotechnology be monitored?

39. Explain why a process is not automatically sustainable simply because it uses microorganisms.

40. Evaluate the importance of microorganisms to environmental sustainability using examples from nutrient cycling, waste treatment, bioremediation, and resource recovery.

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Key Terms

• Environmental microbiology: Study of microorganisms and their activities in natural and human-managed environments.
• Decomposer: Organism that breaks down dead organic material.
• Decomposition: Breakdown of organic matter into simpler substances.
• Nutrient cycle: Movement and recycling of elements through ecosystems.
• Nitrogen fixation: Conversion of atmospheric nitrogen into biologically usable nitrogen compounds.
• Nitrification: Microbial conversion of reduced nitrogen compounds into nitrite and then nitrate.
• Denitrification: Microbial conversion of nitrate into gaseous forms of nitrogen.
• Wastewater treatment: Processes used to remove contaminants from wastewater.
• Activated sludge: Microbial biomass used in aerobic wastewater treatment.
• Aeration: Addition of air or oxygen to a system.
• Biochemical oxygen demand (BOD): Measure related to the oxygen microorganisms require to break down biodegradable organic matter under specified conditions.
• Anaerobic digestion: Microbial breakdown of organic material without oxygen.
• Biogas: Methane-rich gas produced during anaerobic digestion.
• Composting: Controlled biological decomposition of organic material.
• Bioremediation: Use of organisms to remove, transform, or reduce pollutants.
• Biostimulation: Modification of environmental conditions to encourage existing microorganisms to degrade pollutants.
• Bioaugmentation: Addition of selected microorganisms to assist pollutant degradation.
• In situ: Treatment performed at the original contaminated location.
• Ex situ: Treatment performed after contaminated material has been removed.
• Bioleaching: Use of microorganisms to help release metals from ores.
• Biosensor: System using a biological component to detect a substance and produce a measurable signal.
• Mycorrhiza: Association between a fungus and plant roots.
• Sustainability: Use of resources and processes in ways that protect long-term environmental and ecological functioning.
• Circular economy: Approach designed to reduce waste by keeping materials and resources in use.

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Key Takeaways

• Microorganisms are essential components of healthy ecosystems.
• Bacteria and fungi decompose dead material and recycle nutrients.
• Microorganisms play major roles in the carbon and nitrogen cycles.
• Nitrogen-fixing bacteria convert atmospheric nitrogen into forms that can enter biological systems.
• Other microorganisms carry out nitrification and denitrification.
• Soil microorganisms contribute strongly to soil fertility and plant growth.
• Microorganisms are essential to many forms of wastewater treatment.
• During biological wastewater treatment, microbes consume biodegradable organic material.
• High levels of organic pollution can increase microbial oxygen demand and reduce dissolved oxygen in natural waters.
• Anaerobic microorganisms can help convert organic waste into biogas.
• Composting relies on microorganisms to recycle organic wastes into useful material.
• Bioremediation uses organisms to remove, transform, or reduce environmental pollutants.
• Microorganisms can help break down some petroleum hydrocarbons and other organic contaminants.
• Biostimulation encourages microorganisms already present, while bioaugmentation introduces selected microorganisms.
• Microorganisms cannot destroy elements such as heavy metals, but they can sometimes change their chemical form or mobility.
• Bioleaching uses microorganisms to help recover metals from ores.
• Environmental biotechnology includes wastewater treatment, bioremediation, composting, anaerobic digestion, resource recovery, and environmental monitoring.
• Microorganisms can contribute to more sustainable agriculture and healthier soils.
• Microbial biotechnology can help transform some wastes into useful resources.
• Biological treatment is not automatically environmentally sustainable; its complete environmental impact must still be evaluated.
• Microorganisms are important to sustainability because they connect waste treatment, nutrient recycling, pollution control, energy recovery, agriculture, and ecosystem health.