Topic 6 Water Quality

Water Quality Considerations

• Microbial Growth

  • viruses, bacteria, eukaryotic parasites

• other biological material

  • e.g., from food

• feces and urine contamination

• chemicals

  • industrial, agricultural runoff

  • chemicals excreted in urine

Harmful bacteria

• ecoli → pathogenic (transmitted from the fecal to oral route, found in the ruminance of cows)

• Cholera (vibrio cholerae) → food borne

• Typhoid fever → water-borne; food-borne category

• cyanobacteria blooms (prokaryotic) → overgrowth = compromises in water quality

E Coli

• Causes severe gastrointestinal illness

Vibrio Cholerae

• agent responsible for cholera, disease characterized by acute watery diarrhea and rapid dehydration

Salmonella enterica serovar Typhi

• causes typhoid fever and is typically associated with contaminated drinking water

Cyanobacterial Blooms

• occur in nutrient-rich waters, produce toxins that may affect both human and ecosystem health

Harmful Viruses

• norovirus

• polio virus

• hepatitis A

• Rotavirus

• adenovirus

• all of these viruses non-enveloped/ naked viruses

Norovirus

• common cause of acute gastroenteritis and is highly infectious even at low doses

Poliovirus

• transmitted through contaminated water and can lead to poliomyelitis, a disease that can cause paralysis

Hepatitis A

• spreads via fecal to oral route and can cause liver inflammation and illness

Rotavirus

• major cause of severe diarrhea in young children

Adenovirus

• present in water and is associated with a range of illnesses,
  including respiratory and gastrointestinal infections

Harmful eukaryotes

• Giardia

• Cyclospora

• Cryptosporidium

• Algal Blooms

Giardia

• protozoan parasite that can cause gastrointestinal illness following ingestion of contaminated water

Cyclospora

• protozoan pathogen associated with waterborne transmission and can lead to prolonged diarrheal disease

Cryptosporidium

• highly resistant protozoan parasite that can survive common disinfection processes and cause cryptosporidiosis, which is characterized by severe watery diarrhea

Algal blooms

• represent a hazard in water systems, as certain eukaryotic algae may proliferate rapidly under nutrient-rich conditions and contribute to water quality deterioration and toxin production

Main goals of waste water treatment?

The main goals of wastewater treatment are to:

• Lower total organic carbon (TOC) by:

  • Removing organic compounds

  • Oxidizing organic material into CO₂

• Remove, kill, or inactivate harmful microbes through:

  • Intrinsic mechanisms: Competitive exclusion by beneficial microbes

  • Extrinsic mechanisms: Physical, chemical, and biological treatment processes

• Reduce inorganic nutrients such as:

  • Ammonium (NH₄⁺), Nitrate (NO₃⁻), Phosphates (PO₄³⁻)

  • Recall: Carbon (C), nitrogen (N), and phosphorus (P) are essential nutrients for microbial growth.

• Remove persistent organic pollutants (POPs), including:

  • Pesticides

  • Pharmaceuticals

Why are carbon (C), nitrogen (N), and phosphorus (P) important in wastewater treatment?

• Nitrogen (N) and phosphorus (P) promote rapid phytoplankton growth, which can cause eutrophication.

• Some phytoplankton produce toxins that are harmful to humans and wildlife.

• When phytoplankton die, they become organic carbon (C).

• Organic carbon feeds heterotrophic microbes, which consume O₂ while decomposing it.

• This increases biological oxygen demand (BOD) and can deplete oxygen in aquatic environments, harming aquatic life.

What are the four main steps of wastewater treatment?

• Pre-treatment

  • Physically removes large debris (e.g., branches, stones).

• Primary treatment

  • Removes suspended particles by sedimentation and raking.

  • Removes grease, oils, and floating material by skimming.

  • Typically takes several hours.

• Secondary treatment

  • Microbes degrade organic matter, reducing biological oxygen demand (BOD).

  • Lowers intestinal pathogens through:

    • Competition

    • Predation

    • Settling with floc

  • Common methods:

    • Trickling filter

    • Conventional Activated Sludge (CAS) process

• Tertiary treatment (optional)

  • Additional treatment to:

    • Remove pathogens

    • Remove nutrients (N and/or P)

    • Provide other advanced treatment as needed

Visual of steps

Secondary Treatment Trickle Filter

1. Wastewater is sprayed over the surface of a trickling filter.

2. As water moves downward, it provides nutrients for biofilm microbes living on the filter surface.

• Oxygen (O₂) may be pumped into larger filter beds to support aerobic microbial activity and prevent oxygen limitation.

• Excess organic waste can cause excessive biofilm growth, which may:

  • Clog the filter

  • Reduce treatment efficiency

• The biofilm community includes:

  • Bacteria

  • Fungi

  • Protists

• Larger organisms may graze on the biofilm, contributing to microbial community dynamics.

How does secondary wastewater treatment using an activated sludge reactor work?

• Activated sludge reactors rely on flocs, which are clumps of:

  • Organic material

  • Biofilm-associated microbes

• Flocs contain diverse microbial communities that work together to:

  • Degrade organic matter in wastewater

  • Reduce biological oxygen demand (BOD)

• Zoogloea is an important bacterium because it:

  • Helps form and stabilize floc structures

  • Promotes aggregation and settling of biomass

  • Improves treatment efficiency

What are the main components of an activated sludge reactor in secondary wastewater treatment?

An activated sludge reactor contains two main tanks:

1. Aeration tank

   • Wastewater is held for approximately 5–10 hours (variable).

   • Oxygen is supplied to support microbial communities that degrade organic matter.

2. Settling tank

   • Flocs settle to the bottom.

   • Allows separation of:

     • Clarified treated water

     • Microbial biomass (sludge)

Purpose: Reduce organic matter and lower biological oxygen demand (BOD) through microbial activity.

What is the purpose of an anaerobic sludge digester in wastewater treatment?

• Uses anaerobic microbes to break down waste in sludge.

• Removes excess microbial biomass produced from the activated sludge reactor.

• Takes approximately 2–4 weeks.

• Produces less biomass because:

  • Anaerobic microbes obtain less energy from metabolism.

  • Less energy is available for microbial growth, so more organic material is converted into end products instead of new cells.

• Can operate as:

  • Mesophilic digesters (moderate temperatures)

  • Thermophilic digesters (higher temperatures)

• Produces methane (CH₄), which can be captured and burned for energy.

• Remaining sludge can be:

  • Dehydrated and burned

  • Sent to landfill

  • Processed into biosolids used as fertilizer

What are potential problems that can occur during wastewater treatment?

• Changes in environmental conditions (e.g., organic concentration or O₂ levels) can promote the growth of filamentous bacteria.

• Excess filamentous bacteria can interfere with normal floc formation.

• This produces less dense flocs that:

  • Do not settle properly in the settling tank

  • Reduce the efficiency of wastewater treatment.

What is an example of a filamentous bacterium involved in wastewater treatment problems, and what conditions does it favor?

• Example: Sphaerotilus natans (G-)

• Requires:

  • Dissolved simple sugars

  • Organic acids as carbon sources

• Can tolerate low oxygen (O₂) conditions.

• Low oxygen conditions can allow it to grow excessively, disrupting normal floc formation and reducing settling efficiency.

• not pathogenic

How is the reduction of organic carbon in wastewater treatment assessed?

• Measured using biological oxygen demand (BOD).

• BOD = the amount of O₂ required by microbes to decompose organic matter remaining in water.

• A high BOD indicates:

  • More organic material is present.

  • More oxygen will be consumed by microbial decomposition.

• If high-BOD wastewater is released into lakes or rivers:

  • Microbes consume dissolved O₂.

  • Oxygen levels can decrease, harming aquatic organisms.

How is biological oxygen demand (BOD) measured?

• water sample (e.g., wastewater) is:

  1. Incubated at 20°C for 5 days

  2. Dissolved O₂ is measured at the start and end

  3. The difference in O₂ levels = BOD

• The test is performed in the dark to:

  • Prevent photosynthesis from producing O₂

  • Ensure oxygen changes are due only to microbial consumption

One measurement method:

• CO₂ produced by microbes is absorbed by NaOH pellets

• Pressure changes are measured

• Pressure changes are converted into O₂ consumption, which represents BOD.

Why do carbon (C), nitrogen (N), and phosphorus (P) matter in aquatic environments and wastewater treatment?

• Nitrogen (N) and phosphorus (P) promote faster phytoplankton growth.

• Excess phytoplankton growth can cause:

  • Eutrophication

  • Production of toxins that harm humans and wildlife

• When phytoplankton die, they provide organic carbon (C).

• Organic carbon feeds heterotrophic microbes, which consume O₂ during decomposition.

• Increased microbial oxygen consumption raises BOD and can lead to oxygen depletion in aquatic environments.

How is nitrogen removed during wastewater treatment?

Nitrogen removal occurs through nitrification and denitrification:

1. Nitrification (aerobic)

• Converts ammonia (NH₃/NH₄⁺) → nitrite (NO₂⁻) → nitrate (NO₃⁻).

• Reduces toxic ammonia and nitrite levels that can harm aquatic life.

• Requires oxygen (O₂).

2. Denitrification (anaerobic)

• Converts nitrate (NO₃⁻) → nitrogen gas (N₂).

• Often requires an input of organic carbon as an energy source for microbes.

Treatment design:

• Uses multiple reactors:

  • Aerobic reactor → nitrification

  • Anaerobic reactor → denitrification

Alternative: Anammox bacteria

• Convert ammonium + nitrite → N₂ gas directly.

• Ammonium: energy and electron source

• Nitrite: electron acceptor for respiration

• Are chemolithoautotrophs:

  • Use inorganic compounds for energy

  • Do not require organic carbon input.

What is the goal of drinking water treatment, and what types of water are treated?

Goal: Produce water that is safe to use and consume by removing contaminants and harmful microorganisms.

Types of water treated:

• Wastewater:

  • Domestic wastewater (from toilets and sinks)

  • Industrial wastewater

  • Storm water (urban runoff)

• Source water: Treated to make it safe for human use and consumption.

What are the main water sources for drinking water, and what is the purpose of reservoirs?

• Reservoirs: Natural or artificial storage systems that hold water for future use.

• Main water sources:

  • Mountain snowmelt

  • Streams

  • Rivers

  • Ponds

  • Lakes

What are the three particle removal steps in drinking water treatment, and what happens in each?

1. Coagulation: Chemical coagulants are added to neutralize charges and aggregate suspended particles.

2. Flocculation: Gentle mixing encourages particles to combine into larger flocs.

3. Sedimentation: Flocs settle to the bottom of the tank and are removed.

What are the pathogen removal steps in drinking water treatment, and what happens in each?

1. Filtration: Water passes through filter beds to remove any remaining particles.

2. Disinfection: Chemicals, UV light, or ozone are used to kill or inactivate harmful microorganisms, making the water safe to drink.

How did the introduction of chlorine impact public health?

• Chlorine was introduced for drinking water disinfection in the early 1900s.

• Chlorination greatly reduced waterborne diseases by killing harmful microorganisms.

• Its widespread use led to a decline in the crude death rate, improving overall public health.

What are the key concepts of disinfection in drinking water treatment?

• Chlorine is the most commonly used chemical disinfectant.

• Forms of chlorine used:

  • Chlorine gas

  • Sodium hypochlorite

  • Calcium hypochlorite

• Treatment plants must add disinfectants regardless of source water quality to ensure microbial safety.

• Non-chemical disinfection: Uses ultraviolet (UV) light to inactivate microorganisms.

• Effectiveness varies between disinfectants and target organisms.

• Disinfection works best when particle removal is sufficient because microbes can be protected inside particles.

How does chlorination affect bacteria?

Chlorine kills/inactivates bacteria by causing:

• Changes in cell membrane permeability → disrupts transport processes and damages cell integrity.

• Destruction of enzymes → interferes with essential metabolic functions.

• DNA destruction → prevents replication and normal cellular function.

• Disruption of lipid peroxidation → damages membrane lipids and weakens cell structure.

What are examples of harmful cyanobacterial toxins found in water, and how do they affect humans?

• Anatoxin:

  • A neurotoxin that affects the nervous system.

  • Not regulated in treated drinking water in Canada.

• Microcystin:

  • A hepatotoxin that damages the liver.

  • The only regulated cyanobacterial toxin in treated drinking water in Canada.

  • Maximum limit: 1.5 μg/L.