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Drinking Water Treatment – Chapter 25 Class Objectives

Drinking Water Treatment – Chapter 25 Class Objectives. Be able to define the possible components of a water treatment train and their functions Be able to differentiate between rapid and slow filtration Identify the components of a water treatment train that are best for a virus. A protozoa.

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Drinking Water Treatment – Chapter 25 Class Objectives

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  1. Drinking Water Treatment – Chapter 25 Class Objectives • Be able to define the possible components of a water treatment train and their functions • Be able to differentiate between rapid and slow filtration • Identify the components of a water treatment train that are best for a virus. A protozoa. • List the possible detrimental effects of microbial biofilms in water distribution systems • Differentiate between dissolved organic carbon and assimable organic carbon • Describe the AOC test

  2. Where does drinking water come from? Rivers Streams Lakes Aquifers Drinking water treatment processes • Water treatment processes provide barriers between the consumer and waterborne disease • One or more of these treatment processes is called a treatment process train

  3. Typical Water Treatment Process Trains Chlorination Filtration (sand or coal) In-Line Filtration involves a coagulation step (additive that allows aggregation of suspended solids, e.g., alum, ferric sulfate, and ferric chloride, polyelectrolytes) Direct Filtration involves a flocculation step where the water is gently stirred to increase particle collision thereby forming larger particles Conventional Treatment involves a sedimentation step which is the gravitational settling of suspended particles

  4. Filtration Processes Used • Rapid filtration • used in United States • fast filtration rates through media (sand or anthracite) • backwashing needed • Slow sand filtration • common in United Kingdom and Europe • slow filtration rates through media (sand and gravel) • removal of biological layer needed • higher removal rates for all microorganisms

  5. Removal efficiency is dependent on microbial type: • Giardia and Cryptosporidium • filtration is best • large size • resistant cyst and oocyst • Enteric viruses • disinfection is ultimate barrier • filtration and coagulation also help via adsorption to particles • dependent on surface charge of virus

  6. Water Distribution Systems • Treated drinking water may go through miles of pipe to reach a consumer. The quality of the water is impacted by several things: • Dissolved organic compounds in finished drinking water is responsible for: • enhanced chlorine demand • trihalomethane production • bacterial colonization of water distribution systems • Increases resistance to disinfection, e.g., E. coli is 2400 X more resistant to chlorine when attached to surfaces • Increases frictional resistance of fluids • Increases taste and odor problems, e.g., H2S production • Can result in colored water (iron and manganese oxidizing bacteria) • Can cause regrowth of coliform bacteria • Can cause growth of pathogenic bacteria, e.g., Legionella

  7. Bacterial growth in distribution systems is influenced by: • Concentration of biodegradable organic matter • Water temperature • Nature of the pipes • Disinfectant residual • Detention time within distribution system

  8. How do you determine biodegradable organic carbon in a water distribution system? One way is to determine Assimilable Organic Carbon (AOC) • This test is used to determine amount of organic carbon capable of being oxidized by microbes • Measurements of bacterial activity in the test sample are determined over time by plate counts, ATP, turbidity, or direct cell counts

  9. AOC Test • Performed with a single bacterial species, Spirillum NOX or Pseudomonas fluorescens P-17 • A water sample is pasteurized by heat to kill the indigenous microflora and then inoculated with the test bacterium in stationary phase • Growth is monitored (7 to 9 days) until stationary phase is reached • Growth is determined and compared to standard growth on acetate (AOC concentrations are then reported as acetate-carbon equivalents) • AOC can be calculated as follows: • AOC (μg carbon/liter) = (Nmax x 1000)/Y where: • Nmax = CFU/ml • Y =yield coefficient in CFU/μg carbon • When using P. fluorescens strain P-17, Y = 4.1 x 106 CFU/μg acetate-carbon • Thus, if the final yield of the test organism is 5 x 106 CFU/ml after 9 days of incubation: • AOC = 5 x 106 CFU/ml x 1000 ml/L = 1.22 μg acetate-carbon equivalents/liter • 4.1 x 106 CFU/μg acetate carbon

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