Safe Drinking Water Act A Regulates drinking water quality B Regulates the quality of wastewater discharged effluent and of the receiving water body C None of the above D A and B CEE 330 Water Treatment Text book 10 5 10 9 1 2 Chicago water treatment 3 What chemicals are mixed with water 4 What does alum do A Chlorine to disinfect B Fluoride to prevent teeth cavity C Aluminum sulfate D All of the above E None of the above A Make microscopic particles sticky B To form floc C To destroy bacteria D A and B E All of the above 5 6 1 Coagulation Flocculation Alum as coagulant Coagulation flocculation are important clarification processes that cause particles to aggregate so that they can be removed from water more easily by settling and or filtration Al2 SO4 3 18H2O 2Al3 3SO42 18H2O 7 Mixing and Flocculation Alum as coagulant Chemicals Added If water has sufficient bicarbonate HCO3Al2 SO4 3 18H2O 6HCO3 2Al OH 3 3SO42 6CO2 18H2O Here aluminum hydroxide precipitate Al OH 3 is a light fluffy floc that adsorbs colloidal particles on its surface as it settles 9 Fast Mixing Increasingly Slow Mixing Why the floculator mix the water slowly A Destroy the bacteria B Allow the flocs to form C Avoid floc breaking D B and C 10 E None of the above What does sedimentation process do Mixing intensity Rapid mix to disperse coagulant Slow mix to let the flocs grow Too much mixing will break the flocs Mixing intensity G 8 P wVb P is mixing power input Vb is volume of the basin w is viscosity of water 11 A Add approved chemical e g alum to help particles to clump together B Allow big aggregates sink to the bottom C Remove toxic chemicals D None of the above E A and B 12 2 FG FD FB Sedimentation V p g V p p g 3 vs d p drag force FD 3 sdp viscosity of water s particles settling velocity dp particle diameter gravitational force FG mg Vp pg m particle mass g 9 8 m s2 Vp particle volume d3p 6 p particle density buoyancy force FB mwg Vp g mw mass of water displaced by particles density of water substitute V p d3p g d3p 6 d3p pg 6 6 g p d 2 p vs 18 3 vs d p Stoke s law g 980cm s 2 d p vs Re 1 13 14 If the particles are assumed to be spheres with diameter dp 0 1mm and density p 2 65g cm3 what would be their settling velocity in cm s Viscosity of water 0 01185 g cm2s and density of water 1 00g cm3 A 7 6 cm s B 0 76 cm s C 0 076 cm s D None of the above 15 16 Water flow direction Water flow direction fig 10 11 fig 10 11 Particles moves in two direction Horizontally with the flow Vertically by sedimentation 17 Which of the following is NOT correct A Particle 3 sinks faster than is being carried by the flow vs3 vf B Particle 2 settles right before it flows out vs2 vf C Particle 1 sinks too slow vs1 vf but it can 18 still be removed 3 Particles in a clarifier Particles in a clarifier v Vc h If we want to remove all particles vs vc Design equation to find the size and flow rate of the sedimentation basin The critical settling velocity vc is the velocity needed for the particles to remove particles with d p to reach the bottom of the basin The vertical travel distance for particles is h h hQ hQ Q vc Vb hAb Ab vs g p d p2 18 vc Q Qh Qh h Ab Ab h V where Ab surface area of the clarifier hydraulic retention time of the clarifier Vb clarifier volume Q flow rate of water through the clarifier 19 Circular sedimentation basin has flow rate Q depth h and diameter db Silt particles to be removed with diameter dp and density p Given information include water temperature water density and viscosity Will the clarifier remove silt particles Performance of a clarifier 20 If the overflow velocity vc is too high water flows too fast particles don t have enough time to settle Typical overflow velocity vc 1 2 5 m h If the retention time is too short i e the depth of the clarifier is too small particles don t have enough time to settle Typical retention time is from 1 to 4 hours 21 22 Circular sedimentation basin has flow rate 3 MGD million gallons a day 1MGD 0 0438m3 s Depth h 3 5 m diameter db 21 m Silt particles to be removed dp 0 01mm and p 2200 kg m3 T 15oC w 999 1kg m3 w 0 00114 kg m s Will the clarifier remove silt particles A Yes B No C Cannot do this problem Calculate settling velocity Calculate hydraulic retention time Calculate critical velocity Compare settling velocity with critical velocity 23 24 4 Granular Filtration A B C D E Is used to remove micro size particles Requires backwash Should follow sedimentation A and B and C A and B but not C 25 26 Oocyst attachment on clean collectors Flow fig 10 12 IS 100 mM NaCl pH 7 0 25 C 27 28 Oocyst attachment on ripened collectors Flow IS 100 mM NaCl pH 7 0 25 C fig 10 01 29 30 5 Disinfection Water Treatment Summary Step 1 Screen out the big contaminants Screening A Is the process right before filtration B Is the process right before water is piped to homes C Uses chlorine or UV or ozone to inactivate pathogens D A and B E B and C Step 2 Make small contaminants stick together so that they become big flocs Coagulation Floculation Step 3 Give some time for the flocs to settle out Sedimentation Step 4 Filter out some additional contaminants Filtration Step 5 Kill the microorganisms Disinfection 31 Disinfection 32 Surface Water Treatment Disinfection of drinking water is defined as the removal and or inactivation of waterborne pathogens in a manner that does not harm the consumer Step 4 Disinfection Removal means that the pathogen is physically separated from the water Inactivation means that the pathogen is altered such that it is no longer infective http www trojanuv com Cl2 Storage UV light Distribution 33 Downside of Chlorination for water disinfection Chlorination for water disinfection Abel Wolman 1892 1989 34 Chlorine absorption and chlorination of water J Ind Eng Chem 11 206 13 1919 Chlorine saves countless lives The formation of disinfection byproducts DBP by the reaction of chlorine with natural organic matter in water Cl2 carbonaceous natural organic matter trichloromethane e g chloroform Cl2 nitrogenous natural organic matter NDMA 35 36 6 Disinfectant Degree of disinfection Disinfectant Solubility Residual Germicidal Cost Harmful DBP Chlorine gas or bleach High Yes Very good pH 7 Low 1 Yes Chloramine High Yes Fair 2 Yes Ozone Limited No Best 3 Yes but limited No Fair High …