Freshwater Microbiology

No. of drinking water microorganisms per litre

 Ranging from 10⁶ to 10⁹ microbial cells per litre

When is water considered microbiologically safe to drink?

Faecal contamination limited with regulations and monitoring

What opportunistic pathogen is harboured in some drinking water distribution systems?

Mycobacterium avium

Legionella pneumophila

Pseudomonas aeruginosa

Prevalence of waterborne illness

Not highly prevalent in Europe but An estimated 1 million lost working days per year

What type of antibiotic-related things are in water?

Antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) can be present and transferred between organisms

Why are strict regulations implemented for drinking water?

• To regulate the occurrence of potential pathogens in drinking water

• Only permit the occurrence of harmless microorganisms

What are the sources and factors affecting microbial populations in drinking water?

Bacterial phyla commonly prevalent in rivers?

•Cyanobacteria

•Proteobacteria

•Actinobacteriota

•Bacteriodota

What situations cause differences in microbial community structure?

Under strong seasonal effects - esp Rivers close to urban areas

• relative proportions of the occurring microorganisms change

Natural seasonal factors that influence microbial communities in surface water

• Temperature

• Rainfall

• Sunlight duration/intensity

• Evaporation

• Snowmelt

Etc.

What anthropogenic influence on microbial communities in freshwater systems

• Agricultural runoff

• Irrigation

• Wastewater treatment plant

What are groundwater complex microbial communities subject to?

Compositional and structural dynamics

• different factors involved in shaping groundwater comm. compared to surface water

Microbial community composition shaped by what processes: Surface water v.s. Groundwater

Surface - shaped by stochastic processes

Ground - shaped by deterministic processes

Overview of a typical wastewater treatment plant

Primary treatment steps of sewage treatment

• Non-biological treatment

• Removes solids

• Wastewater has still high nutrient load (e.g., C, N, S, and P)

Secondary treatment steps of sewage treatment

• Uses biological treatment

• Decreases dissolved organic carbon (DOC)

• Aerobic and anaerobic secondary treatment

3 types of important microbes in sewage treatment plants

Methanogens (Gen. methane from acetate/ use H2 + CO2) [mostly archaea]

Nitrifying bacteria (Nitrogenous waste → nitrate) [aerobes]

Denitrifying bacteria (nitrate → N2) [anaerobes]

Anoxic secondary treatment used for? and done in?

Used for breaking down solid waste

Done in an anoxic sludge digester

Anoxic secondary treatment: Solid waste involved of? and broken down by?

Complex polymers, e.g., cellulose and fiber

Break down by: Microbes that secrete lipases, proteases, amylases, etc.

Anoxic secondary treatment: What’s the major metabolic form in the treatment?

Fermentation

Anoxic secondary treatment: What’s the final product? and produced by? + Usage

Methane is produced by methanogenic archaea (methanogenesis)

→ be collected and used to generate electricity

Aerobic secondary waste treatments: Steps to produce activated sludge

• Air bubbled through wastewater

• Bacteria form large flocs during this process

• After the flocs form, they are allowed to settle out

Aerobic secondary waste treatments: Key species for forming large flocs

Zoogloea ramigera

→ forms a biofilm + is the base of the floc

Aerobic secondary waste treatments: What causes sludge bulking problems?

Filamentous bacteria → thickens sludge

Aerobic secondary waste treatments: Where does much of the organic material go?

• Binds to the floc

• eventually taken up by the microbial biofilm

Aerobic secondary waste treatments: % of biochemical oxygen demand (BOD) is used in this stage?

95%

How is activated sludge floc observed with a microscope?

• Microbes labelled with different fluorescent dyes

• Visualized with a laser-scanning microscope

What does Activated sludge floc consist of?

Mixed-species communities often containing:

Pseudomonas,

Achromobacter,

Flavobacterium,

Alcaligenes,

Arthrobacter,

Citromonas, B

acillus, etc.

What is key during sewage treatment?

Removal nitrogen

What do nitrifying bacteria do in sewage treatment?

• Ammonia → nitrate

(Ammonia has a high BOD as oxidation requires O2)

Which 2 groups of microbes are involved in sewage treatment nitrification?

• Ammonia oxidizing bacteria (AOB)

• Nitrite oxidizing bacteria (NOB)

Ammonia-oxidizing bacteria (AOB): What they do and 2 enzymes needed?

Oxidize NH₃  (ammonia) to NO₂^-  (nitrite)

• Ammonia monooxygenase (AMO)

• Hydroxylamine oxidoreductase (HAO)

Nitrite-oxidizing bacteria (NOB): What they do and the enzymes needed?

Oxidize NO₂^- (nitrite) to NO₃^- (nitrate)

• Uses the Nor enzyme complex

Similarity of Ammonia-oxidizing bacteria (AOB) and Nitrite-oxidizing bacteria (NOB)

Both respire OXYGEN

What does bacterial denitrification do?

Converts NO₃^- (nitrate) into N₂ (nitrogen)

What enzymes involved in nitrification?

AMO = ammonia → hydroxylamine (toxic)

HOA = hydroxylamine (toxic) → nitrite NOR (nitrite oxidoreductase)

How to remove phosphorus in wastewater treatment plants generally?

By mostly chemical precipitation

→ controlled by pH and presence of cations such as Ca, Fe and Al

How to remove phosphorus in wastewater treatment plants additionally with pH levels?

Microorganism-mediated chemical precipitation in aeration tank of activated sludge process by:

• low pH => soluble phosphate compounds

• increase in pH => phosphate precipitation and incorporation into sludge

How does enhanced biological phosphorus removal (EBPR) work?

Energy derived from the metabolism of stored (e.g., polyhydroxybutyrate - PHB) / external carbon sources in the presence of O₂ or NO₃

• used for accumulation of polyphosphates (inorganic phosphorus taken up by cells) inside cells

What is at the end of the sewage treatment process?

Secondary clarifiers

What additional treatments before release into water systems (mostly rivers)?

Chlorine disinfection

Dual media filtration etc.

What does additional treatments before releasing treated water aimed at doing?

Removing/reducing potential pathogens

influence what can potentially end up in drinking water, among other factors

What widespread method can be used to reduce microbial load in drinking water?

Chlorination of drinking water

What chlorine-containing compounds to treat water?

Sodium hypochlorite and chloramines, etc.

What Chlorine or chloramine levels is considered safe in drinking water?

Levels up to 4 milligrams per litre (mg/L), or 4 parts per million (ppm)