1、ENVR 890/296 Microbe/Pathogen Survival/Reduction in the Environment, Excreta and Excreta Treatment Processes,Mark D. Sobsey Dept. of Environmental Sciences and Engineering,Microbial Survival/Inactivation A Kinetic Phenomenon,Microbe inactivation is best described by the rate(s) or kinetic of inactiv
2、ation Survival depends on reduction rate and time (duration of exposure) Expressing survival in absolute terms based on time only such as days or weeks is misleading Depends on initial and final microbe concentrations Express extent of inactivation per unit of time at specified conditions of exposur
3、e,Concentration ,Time ,100,10,1.0,0.1,Microorganism survival periods in faeces, sludge and soil,Some Physical Factors Influencing Microbe Survival in the Environment,TEMPERATURE,Greater Inactivation/death rates at higher temperatures Lower survival rates at higher temperatures But, some microbes wil
4、l grow or grow better at higher temperatures Many microbes survive better at lower temperature Some bacteria experience “cold injury” or“cold shock” and cold inactivation Thermal inactivation differs between dry heat and moist heat Dry heat is much less efficient than moist heat in inactivating micr
5、obes Some microbes survive very long times when frozen Other microbes are destroyed by freezing Ice crystals impale them Increased environmental temperatures can promotes pathogen spread by insect vectors (mosquitoes, flies, etc.),pH,Relative acidity or alkalinity A measure of hydrogen ion (H+) conc
6、entration Scale: 1 (most acidic) to 14 (most alkaline or basic) pH 7 is neutral Moving toward pH 1 the substance is more acidic Moving toward pH 14, the substance is more alkaline. Extreme pH inactivates microbes Chemically alters macromolecules Disrupts enzyme and transport functions Some enteric p
7、athogens survive pH 3.0 (tolerate stomach acidity) Some pathogens survive pH 11 and fewer survive pH 12,Microbes are most stable in the environment and will grow in some media (e.g., foods) in the mid pH range,Moisture Content Drying and Dessiccation,Drying or low moisture inactivates/kills some mic
8、robes Survival depends on moisture content or “water activity”But, removing water content of some foods can preserve them Most viruses rapidly inactivated in soil at 90% reduction within hours at room temp.) Some helminth ova (Entamoeba hystolytica) are very persistent dry Bacteria persistence to dr
9、ying and desiccation is highly variable Most bacteria can survive for extended periods of time Days to weeks for 90% reduction Bacteria and fungi spores are very persistent when dry,Physical Factors Influencing Survival, Continued,Ultraviolet radiation: about 330 to 200 nm Primary effects nucleic ac
10、ids; absorbs the UV energy and is damaged Sunlight: Ultraviolet radiation in sunlight inactivates microbes Visible light is antimicrobial to some microbes Promotes growth of photosynthetic microbes Ionizing radiation X-rays, gamma rays, beta-rays, alpha rays Generally antimicrobial; bacterial spores
11、 relatively resistant Main target of activity is nucleic acid Effect is proportional to the size of the “target” Bigger targets easier to inactivate; a generalization; exceptions Environmental activity of ionizing radiation in the biosphere is not highly antimicrobial Ionizing radiation is used in f
12、ood preservation and sterilization,Atmospheric and Hydrostatic Pressure,Most microbes survive typical atmospheric pressure Some pathogens in the deep ocean are adapted to high pressure levels (hydrostatic pressures): barophiles Survive less well at low atmospheric pressures Spores and (oo)cysts surv
13、ive pressure extremes High hydrostatic pressure is being developed as a process to inactivate microbes in certain foods, such as shellfish Several 100s of MPa of pressure for several minutes inactivates viruses and bacteria in a time- and pressure-dependent manner,Role of Solids-Association in Micro
14、bial Survival,Microbes can be on or in other, usually larger particles or they can be aggregated (clumped together) Association of microbes with solids or particles and microbial aggregation is generally protective Microbes are shielded from environmental agents by association with solids Protection
15、 depends on type of solids-association See diagrams, right Protection varies with particle composition Organic particles: often highly protective Biofilms protect microbes in them React with/consume antimicrobial chemicals Inorganic particles vary in protection Opaque particles protect from UV/visib
16、le light Inorganic particles do not always protect well against chemical agents Some inorganic particles are antimicrobial Silver, copper, other heavy metals/their oxides,Dispersed:least protected,Embedded: most protected,Adsorbed: partially protected,Clumped: interior microbes protected,: Antimicro
17、bial agent,Some Chemical Factors Influencing Microbe Survival in the Environment,Effects,Chemicals and Nutrients Influence Microbial Survival,Antimicrobial chemicals Strong oxidants and acids Strong bases Ammonia: antimicrobial at higher pH (8.0) Sulfur dioxide and sulfites: used as food preservativ
18、es Nitrates and nitrites: used as food preservatives Enzymes: Proteases Nucleases Amylases (degrade carbohydrates) Ionic strength/dissolved solids/salts High (or low) ionic strength can be anti-microbial Many microbes survive less in seawater than in freshwater High salt (NaCl) and sugars are used t
19、o preserve foods Has a drying effect; cells shrink and die Heavy metals: Mercury, lead, silver, cadmium, etc. are antimicrobial Nutrients for growth and proliferation Carbon, nitrogen, sulfur and other essential nutrients,Some Biological Factors Influencing Microbe Survival in the Environment,Effect
20、s,Biological Factors Influence Microbial Survival,Chemical antagonistic activity by other microorganisms: Proteolytic enzymes/proteases Nucleases Amylases Antibiotics/antimicrobials: many produced naturally by microbes Oxidants/oxides Fatty acids and esters; organic acids (acetic, lactic, etc.) Pred
21、ation Vectors Reservoir animals,Factors Affecting Survival in Liquid,Temperature Ionic Strength Chemical Constituents/Composition of Medium Microbial Antagonism Sorption Status Type of Microbe,Factors Affecting Survival in Aerosols,Temperature Relative Humidity Moisture Content of Aerosol Particle C
22、omposition of Suspending Medium Sunlight Exposure Air Quality (esp. “open air” factor) Size of Aerosol Particle Type of Microbe,Factors Affecting Survival on Surfaces,Type of Microbe Type of Surface Relative Humidity Moisture Content (Water Activity) Temperature Composition of Suspending Medium Ligh
23、t Exposure Presence of Antiviral Chemical or Biological Agents,Microbe Survival in Liquid Media,Temperature Increased inactivation with increasing temperature Most are inactivated rapidly (minutes) above 50oC Some microbes are more thermotolerant than others (e.g. Hepatitis A virus, bacterial/fungal
24、 spores, some helminth ova (ascarids) Most are inactivation more at higher temperatures Chemical composition of media influences survival Protein/other organics & Mg&Ca ions protect Generally very stable at ultra-cold temperatures, Some loss of infectivity occurs with freezing and thawing,Survival i
25、n Liquid Media,pH Direct effects on conformation of proteins and other biomolecules Indirect effects on adsorption and elution from particles pH range of stability is microbe-dependent Polio: 3.8 to 8.5 for maximum stability Salt Content Variable effects on microbe survival Affects microbe physiolog
26、y (isotonic conditions), adsorption and stability of biomolecules Divalent cations (Mg2+) can increase thermo-stability of viruses and bacteria E,g., MHV, enteroviruses, HAV,Microbe Survival in Liquid Media,Microbial Antagonism Microflora influences microbe survival Metabolites: enzymes, VFAs, NH3 a
27、re antiviral Use of pathogen as a nutrient source Greater microbe survival documented in sterilized or pasteurized matrices, as compared to non-sterile matrices Phenomena demonstrated in sewage, fresh, estuarine, and marine waters, soils and sediments.,Microbe Survival in Liquid Media,Adsorption Sev
28、eral possible mechanisms: Ionic attractions and repulsions covalent reactions (with active chemicals) hydrogen bonding hydrophobic interactions double layer interactions van der Waals forces Adsorption status greatly influences survival adsorbed microbes generally survive longer than unadsorbed micr
29、obes Protection and accumulation in sediments and soils,MicrobeSurvival in Liquid Media,Organic Matter In liquid media, organic matter increases microbe survival Increased oxidant demand protects from oxidation If an enzyme substrate, protects from enzymatic attack Can coat to protect microbe partic
30、les In soils, organic matter has variable effects on microbes Possible competition for adsorption sites May coat or protect microbe particles Bacteria may grow of organics are nutrients,Microbe Survival in Liquid Media,Antimicrobial Chemicals Ionic and non-ionic detergents, particularly for envelope
31、d viruses and some bacteria Ammonia is virucidal; ammonium ion is not Germicides (chlorine, ozone, etc.) Light Direct microbicidal activity below wavelengths of 370 nm Indirect antimicrobial activity: stimulation of microflora growth triggering formation of reactive oxidants activation of photoreact
32、ive chemicals,Microbe (Virus) Survival in Aerosols,Relative Humidity and Moisture Content Viruses with lipid survive better at lower relative humidity Viruses with little or no lipid content survive better at higher relative humidity Viral inactivation or retention of infectivity may be a function o
33、f stabilization (drying of aerosol) and of rehumidification of aerosol particle upon collection Effect of relative humidity on virus survival may be influenced by temperature effects,Microbe Survival in Aerosols,Temperature Survival decreases with increased temperature Suspending Media composition i
34、nfluences microbe stability effect is microbe dependent Salts stabilize some viruses (e.g. Poliovirus) Removal of salts stabilize other viruses (e.g. Langat, Semiliki Forest virus) Proteinacious material and organic matter may have similar mixed effects, depending on microbe type Polyhydroxy compoun
35、ds stabilize some virus types (e.g. Influenza) but have no effect on other viruses,Microbes Survival in Aerosols,Oxygen and Air Ions Oxygen has little direct effect on most viruses but may influence bacteria But, oxygenation may be synergistic with higher temperature and sunlight to inactivate micro
36、bes The “Open Air Factor” has been shown to have virucidal activity Poorly characterized chemical agents in open air that reduce virus survival compared to clean laboratory air May be reaction products of ozone and olefins,Microbe Survival in Aerosols,Light Virucidal activity of UV light is a greate
37、r in air than in liquid media Photosensitivity is virus type-dependent and may be related to the envelope Non-enveloped viruses (Poliovirus, Adenoviruses and FMDV) are more resistant to UV light than enveloped viruses (vaccinia, herpes simplex, influenza, and Newcastle disease virus) (Jenson, 1964;
38、Donaldson 1975; Applyard, 1967),Microbe Survival in Aerosols,Aerosol Particle Size Airborne microbes may be more rapidly inactivated in smaller aerosol particles than larger ones (some studies) Other studies observed no effect of particle size on virus survival Aerosol Collection Method Abrupt rehyd
39、ration of virus particles and other microbes upon collection may lead to their inactivation Prehumidification may improve recovery of infectious virus Effect is virus type-dependent,Microbe Survival on Surfaces,Adsorption State Air Water Interface Triple Phase Boundary Physical State Dispersed Aggre
40、gation Solids associated,Microbe Survival on Surfaces,Relative humidity Similar effects as seen in aerosols; effects are microbe type dependent Moisture Content In soils moisture content directly related to microbe survival Dessication Enhanced predation,Microbe Survival on Surfaces,Temperature Effe
41、cts as observed in liquid media and aerosols Interaction between relative humidity and temperature pronounced on surfaces for certain virus types (e.g. Polio, Herpes Simplex), less important for others (e.g. Vaccinia) (Edward, 1941),Microbe Survival on Surfaces,Suspending Media Effects similar to ef
42、fects on survival in aerosols Presence of fecal material Presence of salts Type of Surface Little effect by non-porous surfaces on most viruses important for some virus types (Herpes simplex) Effects more pronounce for porous surfaces (e.g. fabrics: cotton, synthetics and wool Light Effects similar
43、to those in aerosols and liquids,Microbe 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 ooc
44、ysts Giardia lamblia cysts Ascaris lumbricoides ova Acid-fast bacteria: Mycobacterium spp.,High,Factors Influencing Microbial Reductions by Wastewater Treatment Processes,Solids association: microbes embedded in larger particles or aggregated are: more likely to sediment (settle) protected from disi
45、nfection and other antagonists possibly different in their surface properties due to the other material present,Factors Influencing Microbial Reductions by Wastewater Treatment Processes,Temperature produces more microbial rapid inactivation: at higher temp. by thermal effects (denaturation) in biol
46、ogical processes by more rapid biological metabolism and enzymatic activity in chemical processes by faster reaction rates,Factors Influencing Microbial Reductions by Wastewater Treatment Processes,Temperature elevation for some pathogens may promote growth: Naegleria fowlerii and other amebas Legio
47、nella species Mycobacteria species Aeromonas species Vibrio species,Factors Influencing Microbial Reductions by Wastewater Treatment Processes,Biological activity can decrease pathogens by: Grazing, phagocytosis and other predation mechanisms Increased enzymatic activity by bacteria and other treatm
48、ent microbes: proteases, amylases, nucleases, etc. Increased adsorption to and accumulation in microbial biomass complexes: floc particles, biofilms, etc.,Primary Treatment or Primary Sedimentation,Settle solids for 23 hours in a static, unmixed tank or basin. 75-90% of particles and 50-75% of organ
49、ics settle out as “primary sludge” enteric microbe levels in 1o sludge are sometimes 10X higher than in raw sewage enriched by solids accumulation Overall, little removal of many enteric microbes: typically 50% for viruses and bacteria 50% for parasites, depending on their size,Enteric Microbe/Patho
50、gen Reductions in Secondary or Biological Treatment,Aerobic biological treatment: typically, activated sludge (AS) or trickling filtration (TF) Then, settle out the biological solids produced (2o sludge) 90-99% enteric microbe/pathogen reductions from the liquid phase Enteric microbe retention by the biologically active solids: accumulation in AS flocs or TF biofilms Biodegradation of enteric microbes by proteolytic enzymes and other degradative enzymes/chemicals Predation by treatment microbes/plankton (amoeba, ciliates, rotifers, etc.,
