Water Treatment ProcessesSlide 2Summary of Mainline Water Treatment ProcessesWater Treatment Processes: StorageWater Storage and Microbial ReductionsTypical Surface Water Treatment PlantChemical Coagulation-FlocculationCoagulation-Flocculation, ContinuedMicrobe Reductions by Chemical Coagulation-FlocculationSlide 10Granular Media FiltrationSlow Sand FiltersMicrobial Reductions by Slow Sand FiltrationSlide 14Slide 15Microbe Reductions by Rapid Granular Media FiltersMicrobe Reductions by Chemical Coagulation-Flocculation and Filtration of River Water by Three Rx Plants in The NetherlandsCryptosporidium Removals by Sand FiltrationCryptosporidium Removal by Coagulation and Direct FiltrationSlide 20Cryptosporidium Reductions by Coagulation and FiltrationMembrane FiltersCryptosporidium Reductions by Membrane FiltrationAdsorbers and Filter-AdsorbersSlide 25Slide 26Water Softening and Microbe ReductionsMicrobial Reductions by Softening TreatmentDisinfection of Microbes in Water: Conventional Methods used in the Developed WorldDisinfection KineticsSlide 31Factors Influencing Disinfection of MicrobesEffects of Water Quality on DisinfectionSlide 34Disinfection: A Key Barrier Against Microbes in WaterWater Treatment ProcessesENVR 890Mark D. SobseySpring, 2007Water Sources and Water Treatment•Drinking water should be essentially free of disease-causing microbes, but often this is not the case.–A large proportion of the world’s population drinks microbially contaminated water, especially in developing countries•Using the best possible source of water for potable water supply and protecting it from microbial and chemical contamination is the goal–In many places an adequate supply of pristine water or water that can be protected from contamination is not available•The burden of providing microbially safe drinking water supplies from contaminated natural waters rests upon water treatment processes–The efficiency of removal or inactivation of enteric microbes and other pathogenic microbes in specific water treatment processes has been determined for some microbes but not others.–The ability of water treatment processes and systems to reduce waterborne disease has been determined in epidemiological studiesSummary of Mainline Water Treatment Processes•Storage•Disinfection–Physical: UV radiation, heat, membrane filters–Chemical: Chlorine, ozone, chlorine dioxide, iodine, other antimicrobial chemicals•Filtration–Rapid granular media–Slow sand and other biological filters–Membrane filters: micro-, ultra-, nano- and reverse osmosis•Other physical-chemical removal processes–Chemical coagulation, precipitation and complexation–Adsorption: e.g., activated carbon, bone char, etc,–Ion exchange: synthetic ion exchange resins, zeolites, etc.Water Treatment Processes: StorageReservoirs, aquifers & other systems: –store water–protect it from contamination•Factors influencing microbe reductions (site-specific)–detention time–temperature–microbial activity–water quality: particulates, dissolved solids, salinity–sunlight–sedimentation–land use–precipitation–runoff or infiltrationWater Storage and Microbial Reductions•Microbe levels reduced over time by natural antimicrobial processes and microbial death/die-off•Human enteric viruses in surface water reduced 400-1,000-fold when stored 6‑7 months (The Netherlands) –Indicator bacteria reductions were less extensive, probably due to recontamination by waterfowl. •Protozoan cyst reductions (log10) by storage were 1.6 for Cryptosporidium and 1.9 for Giardia after about 5 months (The Netherlands; G.J Medema, Ph.D. diss.)–Recent ICR data indicates lower protozoan levels in reservoir or lake sources than in river sources; suggests declines in Giardia & Cryptosporidium by storageTypical Surface Water Treatment PlantChemical Coagulation-FlocculationRemoves suspended particulate and colloidal substances from water, including microorganisms. Coagulation: colloidal destabilization•Typically, add alum (aluminum sulfate) or ferric chloride or sulfate to the water with rapid mixing and controlled pH conditions•Insoluble aluminum or ferric hydroxide and aluminum or iron hydroxo complexes form•These complexes entrap and adsorb suspended particulate and colloidal material.Coagulation-Flocculation, ContinuedFlocculation:•Slow mixing (flocculation) that provides for for a period of time to promote the aggregation and growth of the insoluble particles (flocs). •The particles collide, stick together abd grow larger•The resulting large floc particles are subsequently removed by gravity sedimentation (or direct filtration)•Smaller floc particles are too small to settle and are removed by filtrationMicrobe Reductions by Chemical Coagulation-Flocculation•Considerable reductions of enteric microbe concentrations.•Reductions In laboratory and pilot scale field studies: –>99 percent using alum or ferric salts as coagulants–Some studies report much lower removal efficiencies (<90%)–Conflicting information may be related to process control•coagulant concentration, pH and mixing speed during flocculation. •Expected microbe reductions bof 90-99%, if critical process variables are adequately controlled•No microbe inactivation by alum or iron coagulation–Infectious microbes remain in the chemical floc–The floc removed by settling and/or filtration must be properly managed to prevent pathogen exposure. •Recycling back through the plant is undesirable•Filter backwash must be disinfected/disposed of properly.Cryptosporidium Removals by Coagulation (Jar Test Studies)Coagulant Dose (mg/L)Oocyst Removal, % (log10)Alum 5199.8 (2.7)87 (0.9) Iron 6599.5 (2.3)97 (1.5)Granular Media Filtration•Used to remove suspended particles (turbidity) incl. microbes. •Historically, two types of granular media filters:–Slow sand filters: uniform bed of sand; –low flow rate <0.1 GPM/ft2–biological process: 1-2 cm “slime” layer (schmutzdecke)–Rapid sand filters: 1, 2 or 3 layers of sand/other media; –>1 GPM/ft2–physical-chemical process; depth filtration•Diatomaceous earth filters–fossilized skeletons of diatoms (crystalline silicate); powdery deposit; few 10s of micrometers; porousSlow Sand Filters•Less widely used for large US municipal water supplies•Effective; widely used in Europe; small water supplies; developing countries•Filter through a 3‑ to 5‑foot
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