Water Lecture 3 A. Disinfection B. Water Safety PlansDrinking Water DisinfectionSlide 3Slide 4Summary Properties of Chemical DisinfectantsSummary Properties Physical DisinfectantsFactors Influencing Disinfection Efficacy and Microbial InactivationFactors Influencing Disinfection Efficacy and Microbial Inactivation (Continued)Factors Influencing Disinfection of MicrobesFactors Influencing Disinfection Efficacy and Microbial Inactivation, ContinuedSome Factors Influencing Disinfection Efficacy and Inactivation - VirusesFactors Influencing Disinfection Efficacy and Microbial Inactivation - ParasitesFactors Influencing Disinfection Efficacy and Microbial Inactivation - Water QualityFactors Influencing Disinfection Efficacy and Microbial Inactivation - Reactor Design, Mixing & Hydraulic ConditionsSlide 16Disinfection KineticsDisinfection Kinetics: Chick’s Law First-Order or Exponential KineticsSlide 19Disinfection Activity and the CT ConceptMicrobial Inactivation KineticsSlide 22Free Chlorine - Background and HistoryEffect of pH on Percentages of HOCl and OCl-Free Chlorine and Microbial InactivationMonochloramine - History and BackgroundMonochloramine: Chemistry and Generation)Reaction of Ammonia with Chlorine: Breakpoint ChlorinationOzoneChlorine DioxideSlide 31Slide 32Slide 33Slide 34UV Disinfection EffectivenessDrinking Water Supplies and Water Safety PlansSlide 37Water Safety PlansWater Safety Plans : System AssessmentWater Safety Plans : MonitoringWater Safety Plans : Management & CommunicationsApplying WSP to Your Water SystemExample – Your SystemFor each event consider:FrequencyWSPs: Risk Management Plans and PrioritiesSome ResourcesWater Lecture 3A. DisinfectionB. Water Safety PlansMark D. SobseyENVR 890-2Spring, 2009Drinking Water Disinfection•Any process to destroy or prevent the growth of microbes•Intended to inactivate (destroy the infectivity of) the 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 (structural proteins, enzymes, transport proteins)–nucleic acids (genomic DNA or RNA, mRNA, tRNA, etc)–lipids (lipid bilayer membranes, other lipids)Properties of an Ideal DisinfectantBroad spectrum: active against all microbesFast acting: produces rapid inactivationEffective in the presence of organic matter, suspended solids and other matrix or sample constituentsNontoxic; soluble; non-flammable; non-explosiveCompatible with various materials/surfacesStable or persistent for the intended exposure periodProvides a residual (sometimes this is undesirable)Easy to generate and applyEconomicalDisinfectants in Water Treatment•Free Chlorine•Monochloramine •Ozone •Chlorine Dioxide•UV Light•Low pressure mercury lamp (monochromatic) •Medium pressure mercury lamp (polychromatic)•Pulsed broadband radiation•Boiling•At household level in many countries and for emergencies in other countries (USA)•Iodine•Short-term use; long-term use a health concernSummary Properties of Chemical Disinfectants•Free chlorine: HOCl (hypochlorous) acid and OCl- (hypochlorite ion)–HOCl at low and pH OCl- at highpH; HOCl more potent germicide than OCl-–strong oxidant; relatively stable in water (provides a disinfectant residual)•Chloramines: mostly NH2Cl: weak oxidant; provides a stable residual•Ozone, O3: strong oxidant; provides no residual (too volatile, reactive)•Chlorine dioxide, ClO2,: strong oxidant; unstable (dissolved gas)•Concerns due to health risks of chemical disinfectants and their by‑products (DBPs), especially free chlorine and its DBPsSummary Properties Physical Disinfectants•UV radiation–low pressure mercury lamp: low intensity; monochromatic at 254 nm–medium pressure mercury lamp: higher intensity; polychromatic 220-280 nm)–reacts primarily with nucleic acids: pyrimidine dimers and other alterations•Boiling: efficient kill; no residual protection; fuel/environmental costsFactors Influencing Disinfection Efficacy and Microbial InactivationMicrobe type: Resistance to chemical disinfectants:•Vegetative bacteria: Salmonella, coliforms, etc.: low•Enteric viruses: coliphages, HAV, Noroviruses: Moderate•Bacterial Spores•Fungal Spores•Protozoan (oo)cysts, spores, helminth ova, etc.–Cryptosporidium parvum oocysts–Giardia lamblia cysts–Ascaris lumbricoides ova–Acid-fast bacteria: Mycobacterium spp.LeastMostHighResistance:Factors Influencing Disinfection Efficacyand Microbial Inactivation (Continued)Type of Disinfectant and Mode of ActionFree chlorine: strong oxidant; oxidizes various protein sulfhydryl groups; alters membrane permeability; also,oxidize/denature nucleic acid components, etc.Ozone: strong oxidant; ditto free chlorineChlorine dioxide: strong oxidant; ditto free chlorineElectrochemically generated mixed oxidants: strong oxidant; probably ditto free chlorineCombined chlorine/chloramines: weak oxidant;denatures sulfhydryl groups of proteinsUltraviolet radiation: nucleic acid damage:thymidine dimer formation, strand breaks, etc.Factors Influencing Disinfection of Microbes•Microbe type: disinfection resistance from least to most:vegetative bacteria viruses protozoan cysts, spores and eggs•Type of disinfectant: order of efficacy against Giardia from best to worst–O3 ClO2 iodine/free chlorine chloramines–BUT, order of effectiveness varies with type of microbe•Microbial aggregation: –protects microbes from inactivation–microbes within aggregates not be readily reached by the disinfectant•Particulates: protects from inactivation; shielded/embedded in particles•Dissolved organics: protects–consumes or absorbs (UV radiation) disinfectant; coats microbes•Inorganic compounds and ions: effects vary with disinfectant•pH: effects depend on disinfectant. –Free chlorine more biocidal at low pH where HOCl predominates. –Chlorine dioxide more microbiocidal at high pH•Reactor design, mixing and hydraulic conditions; better activity in "plug flow" than in "batch‑mixed" reactors.Factors Influencing Disinfection Efficacyand Microbial Inactivation, ContinuedMicrobial strain differences and microbial selection:•Disinfectant exposure may select for resistant strainsPhysical protection:•Aggregation•particle-association•protection within membranes and other solidsChemical
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