Presentation on theme: "Drinking Water Treatment – Chapter 25 Class Objectives Be able to define the possible components of a water treatment train and their functions Be able."— Presentation transcript:
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
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
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
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
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 Removal efficiency is dependent on microbial type:
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
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
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 How do you determine biodegradable organic carbon in a water distribution system?
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) = (N max 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 10 6 CFU/μg acetate-carbon Thus, if the final yield of the test organism is 5 x 10 6 CFU/ml after 9 days of incubation: AOC = 5 x 10 6 CFU/ml x 1000 ml/L = 1.22 μg acetate-carbon equivalents/liter 4.1 x 10 6 CFU/μg acetate carbon AOC Test
Comparison of Concentrations of DOC and AOC in Various Water Samples Source of water Dissolved organic carbon (mg carbon/L) Assimilable organic carbon (mg carbon/L) River Lek6.80.062–0.085 River Meuse4.70.118–0.128 Brabantse Diesbosch4.00.08–0.103 Lake Yssel, after open storage5.60.48–0.53 River Lek, after bank filtration1.60.7–1.2 Aerobic groundwater0.3<0.15
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