Protecting people and livestock through pathogen treatment Microbiology Environmental microbiology water, wastewater, soil, air Medical microbiology, pathology, epidemiology

Human pathogens of concern Bacteria Viruses Protozoa Worms

Diseases caused by improper water / wastewater treatment

Indicator organisms Pathogen lab analyses  difficult to perform  poorly reproducible Fecal and total coliform analysis  E. coli

Quantifying cell concentration Plate count Multiple tube fermentation test (MPN) Membrane filter test Particle counters (electrical resistance) Dry weight Packed cell volume (centrifuge and dry) Optical density

Microbial growth pattern Lag phase = cells adapt to new environment Exponential phase = cells multiply rapidly Deceleration phase = depletion of a nutrient or accumulation of waste Stationary phase = zero net growth rate Death phase = cell death rate exceeds cell growth rate

Definitions Disinfection = Selective destruction of disease-causing organisms (pathogens). Sterilization = Destruction of all organisms.

Disinfection approaches Chemical agents Physical agents Mechanical means Radiation

Chemical agents Chlorine, Bromine, Iodine (halogens) Ozone Phenol, etc. Alcohols Heavy metals Soaps and detergents Hydrogen peroxide Alkalis and acids (pH>11 or pH<3)

Chemical agents: Characteristics “The ideal chemical agent” etc.

Physical agents Heat  Boiling (not effective for spores)  Pasteurization  Autoclaving Cold (freezing) Light  Sunlight  UV

Mechanical means Filtration Often a by-product of primary function

Mechanisms of disinfection Damage to cell wall Alteration of cell permeability Alteration of colloidal nature of protoplasm Inhibition of enzyme activity

Influencing factors Contact time Concentration Type of agent Temperature Number and type of organisms Nature of suspending liquid (pH, extraneous organics, turbidity)

Disinfection goals USEPA: Surface water treatment rule: 99.9% removal of Giardia l. (3-log) 99.99% removal of enteric viruses (4-log) Fecal coliform <200 organisms/100 ml (for Drinking Water: 0 organisms/100 ml)

Common pathogen treatments for small systems Filtration through soil Chlorination Lime stabilization (pH adjustment) UV

Soil filtration soil as microfilter pathogens die off outside of host predation by native microbes time lag before reaches receptor approximately 1-log kill (reduces bacterial load by an order of magnitude)

Chlorination Constraints: simple, safe, reliable, economical Common forms for onsite systems:  Sodium Hypochlorite (liquid)  Calcium Hypochlorite (tablet)  alternative halogen: Iodine crystals Reacts with ammonia, organics, and microorganisms

Breakpoint chlorination Goal: to provide residual protection Concern: trihalomethanes

Dechlorination Reduce problem of disinfection by- products (ex: trihalomethanes) Reducing agent (dechlor)  Sodium dioxide  Sodium bisulfate Aeration Activated charcoal

Lime stabilization raises pH (12 to 12.5 preferably) coagulation and clarification  physically removes protozoal cysts and worm eggs  reduces density of viruses

Lime stabilization Add to untreated (undigested) high strength organic wastes  Sludge  Septage  Manure Disinfects so that waste will not:  Putrefy (still high organic content)  Create odors  Cause health hazard

Lime stabilization background Low cost, simple technology Goal: maintain pH>12 for 30 minutes Dosage is adjusted based on  waste characteristics  required period of stability Temporary stabilization  Enables further handling and disposal  Delays onset of destabilization

Lime stabilization method Sources of lime  Hydrated lime: Ca(OH) 2  Quicklime: CaO  NOT agricultural limestone: CaCO 3 Forms  Dry (smaller facilities)  Slurry (larger facilities) Good mixing very important

Lime bactericidal effect (USEPA, 1984, p. 186)

Ultraviolet light (UV) low-pressure mercury arc lamp suspended above or submerged turbidity and UV transmittance lamp fouling and maintenance no residual no halogenated by-products