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ENVR 430-1 Microbial Control Measures by Wastewater Processes - PowerPoint PPT Presentation

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ENVR 430-1 Microbial Control Measures by Wastewater Processes. Suggested Reading: Brock Chapter 28- Wastewater Treatment, Water Purification, and Waterborne Microbial Diseases pp. 934-942 (posted as .PDF file on website). Wastewater Impacts to Natural Receiving Waters.

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Wastewater impacts to natural receiving waters 1277825

ENVR 430-1Microbial Control Measures by Wastewater Processes

Suggested Reading:

Brock Chapter 28- Wastewater Treatment, Water Purification, and Waterborne Microbial Diseases pp. 934-942 (posted as .PDF file on website)

Wastewater impacts to natural receiving waters1
Wastewater Impacts to Natural Receiving Waters

  • Treated wastewater is often discharged to nearby natural waters

  • Biological oxygen demand (BOD)

  • Chemicals (nitrogen, phosphorus)

  • Synthetic Chemicals

  • Antibiotics

  • Microbial Pathogens

  • Metals

Water use cycle




Water Treatment


Water Source







to Receiving




Water Use Cycle

Wastewater impacts to natural receiving waters 1277825

Pathogen Concentrations in Raw Sewage

  • Influenced by many factors:

    • Types and prevalence of enteric infections in the population

    • Geographic, seasonal, and climate factors

    • Water use patterns

  • Pathogen concentrations in raw sewage

    • Enteric Viruses and Protozoan Cysts: ~ 104/L

    • Enteric Bacteria: ~105/Liter

Microbial reductions in wastewater treatment
Microbial Reductions in Wastewater Treatment

  • Treatment processes are designed for reduction of solids and organics

  • Targets are total suspended solids and BOD, not pathogens

  • Pathogens are removed by processes that reduce organic matter

  • Typical overall pathogen reductions ~90‑99%.

Primary treatment or primary sedimentation
Primary Treatment or Primary Sedimentation

  • Settle solids for 2‑3 hours in a static, unmixed tank or basin.

  • ~75-90% of particles and 50-75% of organics settle out as “primary sludge”

  • enteric microbe levels in primary sludge are ~10X higher than in raw sewage

  • Little removal of enteric microbes: typically ~50%

Secondary or biological treatment
Secondary or Biological Treatment

  • aerobic biological treatment

    • activated sludge or trickling filtration

  • Settle out the biological solids produced (secondary sludge)

    • ~90-99% enteric microbe/pathogen reductions from the liquid phase

    • enteric microbe retention by the biologically active solids

  • Biodegradation of enteric microbes

    • proteolytic enzymes and other degradative enzymes/chemical

    • Predation by treatment microbes/plankton (amoeba, ciliates, rotifers, etc.)

Waste solids sludge treatment
Waste Solids (Sludge) Treatment

  • Treatment of the settled solids from 1o and 2o sewage treatment

  • Biological “digestion” to biologically stabilize the sludge solids

    • Anaerobic digestion (anaerobic biodegradation)

    • Aerobic digestion (aerobic biodegradation)

    • Mesophilic digestion: ambient temp. to ~40oC; 3-6 weeks

    • Thermophilic digestion: 40-60oC; 2-3 weeks

  • Produce digested (biologically stabilized) sludge solids for further treatment and/or disposal

  • Waste liquids from sludge treatment are recycled through the sewage treatment plant

  • Waste gases from sludge treatment are released or burned if from anaerobic digestion: methane, hydrogen, etc.

Processes to further reduce pathogens pfrp class a sludge
Processes to Further Reduce Pathogens (PFRP)Class A Sludge

  • Class A sludge:

    • <1 virus per 4 grams dried sludge solids

    • <1 viable helminth ovum per 4 grams dried sludge solids

    • <3 Salmonella per 4 grams of dried sludge solids

    • <1,000 fecal coliforms per gram dry sludge solids

  • Class A sludge or “biosolids” can be disposed by a variety of options

    • marketed and distributed as soil conditioner for use on non-edible plants)

Processes for producing class a sludge
Processes for producing Class A sludge

  • thermal (high temperature) processes (incl. thermophilic digestion); hold sludge at 50oC or more for specified times

  • lime (alkaline) stabilization; raise pH 12 for 2 or more hours

  • composting: additional aerobic treatment at elevated temperature

Wastewater impacts to natural receiving waters 1277825

Land Application of Treated Wastewater:

Alternative Disposal Option

Modular wastewater treatment systems
Modular Wastewater Treatment Systems

electrochemical metals removal process, pH adjustment, coagulation, clarification, multi-media filtration, air stripping, activated carbon adsorption, final pH adjustment, sludge dewatering

Wastewater reuse
Wastewater Reuse

  • Wastewater is sometimes reused for beneficial, non-potable purposes in arid and other water-short regions

  • Often use advanced or additional treatment processes, sometimes referred to as “reclamation”

  • Biological treatment in “polishing” ponds and constructed wetlands

  • Physical-chemical treatment processes as used for drinking water:

    • Coagulation-flocculation and sedimentation

    • Filtration: granular medium filters; membrane filters

    • Granular Activated Carbon

    • Disinfection


  • Disinfection is any process to destroy or prevent the growth of microbes

  • Many disinfection processes are intended to inactivate microbes by physical, chemical or biological processes

  • Inactivation is achieved by altering or destroying essential structures or functions within the microbe

  • Inactivation processes include denaturation of proteins, nucleic acids, and lipids

When wastewater disinfection is recommended or required
When Wastewater Disinfection is Recommended or Required

  • Discharge to surface waters:

    • near water supply intakes

    • used for primary contact recreation

    • used for shellfish harvesting

    • used for irrigation of crops and greenspace

    • other direct and indirect reuse and reclamation purposes

  • Discharge to groundwaters:

    • used as a water supply source

    • used for irrigation of crops and greenspace

    • other direct and indirect reuse and reclamation purposes

Disinfection of wastewater
Disinfection of Wastewater

  • Intended to reduce microbes in 1o or 2o treated effluent

    • Typically chlorination

    • Alternatives: UV radiation, ozone, and chlorine dioxide

  • Good enteric bacterial reductions: typically, 99.99+%

    • Meet fecal coliform limits for effluent discharge

  • Less effective for viruses and parasites: typically, 90% reduction

  • Toxicity of chlorine and its by‑products to aquatic life now limits wastewater chlorination

    • Dechlorination

    • Alternative less toxic chemical disinfectants

    • Alternative treatment processes to reduce enteric microbes

    • granular medium filtration or membrane filtration

Calculating microbial reductions by treatment processes log 10 vs percent
Calculating Microbial Reductions by Treatment Processes: Log An Example10 vs. Percent

  • Microbial reductions are computed to normalize the raw data on treatment efficacy of different systems or at different sites

  • Reductions provide a uniform way to compare different treatment processes or systems


Disinfection kinetics
Disinfection Kinetics An Example

  • Disinfection is a kinetic process

  • increased inactivation with increased exposure or contact time

  • Chick's Law: disinfection is a first‑order reaction.

    (Nt/No = e-kT)

  • Assumptions of Chick’s Law

    • all organisms are identical

    • death (inactivation) results from a first-order or “single-hit” or exponential reaction

  • Seldom true in practice

Disinfection activity and the ct concept
Disinfection Activity and the CT Concept An Example

  • Disinfection activity can be expressed as the product of disinfection concentration (C) and contact time (T)

  • Assumes first order kinetics (Chick’s Law)

  • disinfectant concentration and contact time have the same “weight” or contribution in disinfection activity and in contributing to CT

  • Example: If CT = 100 mg/l-minutes, then

    • If C = 10 mg/l, T must = 10 min. for CT = 100 mg/l-min.

    • If C = 1 mg/l, then T must = 100 min. for CT = 100 mg/l-min.

    • If C = 50 mg/l, then T must = 2 min. for CT = 100 mg/l-min.

Disinfection activity and the ct concept1
Disinfection Activity and the CT Concept An Example

  • So, any combination of C and T giving a product of 100 is acceptable because C and T are interchangeable

  • The CT concept fails if disinfection kinetics do not follow Chick’s Law (are not first-order or exponential)

Wastewater impacts to natural receiving waters 1277825

Common Disinfectants in Water An Example

and Wastewater Treatment

  • Free Chlorine

  • Monochloramine

  • Ozone

  • Chlorine Dioxide

  • UV Light

    • Low pressure mercury lamp (monochromatic)

    • Medium pressure mercury lamp (polychromatic)

    • Pulsed broadband radiation

Wastewater impacts to natural receiving waters 1277825

First An Example



Log Survivors


Contact Time



  • Declining rate or “Shoulder” Curve Kinetics:

  • decline in disinfectant concentration over time;

  • multi-hit kinetics;

  • aggregation

  • Retardant Kinetics:

  • persistent fraction;

  • mixed populations;

  • different susceptibilities of microbes to inactivation;

  • aggregation


Wastewater impacts to natural receiving waters 1277825

Properties of an Ideal Disinfectant An Example

  • Broad spectrum: active against all microbes

  • Fast acting: produces rapid inactivation

  • Effective in the presence of organic matter, suspended solids and other matrix or sample constituents

  • Nontoxic; soluble; non-flammable; non-explosive

  • Compatible with various materials/surfaces

  • Stable or persistent for the intended exposure period

  • Provides a residual (sometimes this is undesirable)

  • Easy to generate and apply

  • Economical