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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

Distribution

System

Water Treatment

Plant

Water Source

Wastewater

Collection

Wastewater

Treatment

Plant

Discharge

to Receiving

Water

Water

Use

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
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

    Examples:


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

Order

Multihit

Log Survivors

Retardant

Contact Time

DISINFECTION AND MICROBIAL

INACTIVATION KINETICS

  • 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

Nt/N0


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