1. Bugs. Toxic materials Solids and color. 3. Solids and color 4. All above. 1. Water treatment overview:

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1 Lecture #1 Objectives: - Overview water treatment process - Understand water quality parameters 1. Water treatment overview: (1) Water sources:. - Deep wells - relatively clean maybe hard; - Shallow wells; rivers; lakes; reservoirs need more treatment. (2) Water quality concern: - Appearance - color; odor; turbidity; solids; - Pathogens: bacteria; protozoa; viruses; helminthes; - Organic pollutants pesticides; - Inorganic pollutants - heavy metals (Pb; As;...); - Disinfectants and disinfection by-products; - Radionuclides; What are major concerns of the drinking water quality? 1. Bugs 2. Toxic materials 3. Solids and color 4. All above (3) Treatment methods: - Microorganisms disinfection 0% 0% 0% 0% Bugs Toxic materials Solids and color All above - Debris screening - Heavy particles settling - Colloid and suspended solids and some soluble pollutants coagulation + flocculation + clarification - Small, non-settleable particles sand filtration - Hardness (mostly for groundwater) softening - Dissolved organic pollutants; odors Activated carbon adsorption; air stripping; biological treatment

2 Which method is used to remove small, non-settleable particles at the end of the treatment process? 1. Sand filtration 2. GAC adsorption 3. Air stripping 4. All above Sand filtration 0% 0% 0% 0% GAC adsorption Air stripping All above 2. Safe drinking water act: (1) Drinking water standards: - To make sure the drinking water is safe; -Only apply for public water systems = connections or >25 people for > 60 days/year; - Primary standards: for harmful substances; - The maximum contaminant level (MCL) Enforceable for regulated substances; Treatment technique (TT) requirements; - The maximum contaminant level goal (MCLG) = no adverse effect level; 0 for all carcinogenic chemicals - Secondary standards: for non-critical parameters such as color, odor; not enforceable; True or false: Federal drinking water standards apply to the water supply to every home 1. True 2. False 0% 0% True False (2) Primary MCLs: - For potentially toxic chemicals - 2 L per day consumption for lifetime + other sources 10-6 chance of effect - Organic chemicals, inorganic chemicals, microorganisms, disinfectants, disinfection byproducts, and radionuclides - For carcinogens: Normally the minimum detectable level; - Organic chemicals: mostly from human activity; Table 6.1 (page 2); ppm = parts per million = mg/l 1 ppm = 1000 ppb = 1000 µg/l Benzene cancer mg/l industrial chemicals.. TCE cancer mg/l dry cleaning

3 - Inorganic chemicals: from human activity and the natural world; Table 6.2 (page 3) Arsenic (As) nervous system effects 0.01 mg/l; groundwater; coal fly ash (leaching); pesticides; industrial wastes Nitrate blue-baby effect 10 mg/l fertilizers; wastewater; For water contaminants, 1 mg/l equals to 1. 1 ppm µg/l ppb 4. All above Cadmium kidney effects mg/l metal finishing; natural mineral deposits Lead/Copper action levels 0.0/1.3 mg/l 1 ppm 0% 0% 0% 0% 1000 µg/l 1000 ppb All above - Microorganisms: Total coliform; fecal coliform E. Coli O7:H7 is pathogenic to humans contaminated ground beef, raw milk, fruit juices Cryptosporidium; Giardia. Turbidity directly indicates the overall water quality; Nephelometric turbidity units (NTU) always <1 NTU; 95% of time < 0.3 NTU Mostly based on the technology used for treatment (TT) Cryptosporidium - Disinfectants: from disinfection activities; Chloramines MRDL=4.0 mg/l; Chlorine MRDL=4.0 mg/l; Chlorine dioxide MRDL=0.8 mg/l;

4 - Disinfection byproducts: from disinfection activities; Bromate 0.01 mg/l; from ozone disinfection Chlorite 1.0 mg/l; from chlorine dioxide disinfection 1 Cl chloride +1 ClO hypochlorite +3 ClO 2 chlorite +5 ClO 3 chlorate +7 ClO 4 perchlorate - Radionuclides: from natural sources; Alpha particles - picocuries per Liter (pci/l) Beta particles and photon emitters; Radium 226 and Radium 228 (combined); Uranium; Haloacetic acids (HAA5) mg/l; Total Trihalomethanes (TTHMs) mg/l; Which of the following disinfection byproduct will be produced if ozone is used for disinfection? 1. Chlorite 2. Bromate 3. THMs 4. HAAs (3) Secondary guidelines: suggested levels (not MCL!) - Table 6.3 (page 5) - chloride, color, iron, odor, ph,. (4) Drinking Water Contaminant Candidate List (CCL): - Microorganisms and chemicals 0% 0% 0% 0% Chlorite Bromate THMs HAAs (5) Sampling, record keeping, and reporting: - Need to follow required procedures when taking samples; - Detailed information for the sample and the quality parameters; - Public notification within 48 hours if primary MCLs are not met; Review questions: What are the major water quality concerns? What is the conventional drinking water treatment process? Why is groundwater cleaner than surface water? How to remove heavy particles? What is MCL? What is MCLG? How are these parameters determined? What is the major difference between primary standards and secondary standards? What is turbidity? Why is it the most important parameter for the overall drinking water quality? What are side effects of disinfection?

5 Lecture #2 Objectives: - Design settling tank to remove heavy particles - Understand coagulation principles 3. Sedimentation: A process to remove heavy and large particles (1) Settling process: - Sedimentation tank = settling tank = clarifier - Settling velocity is related to the specific gravity and particle size - Setting types: Discrete settling (free settling); Flocculent settling; Zone settling (hindered settling); For two clay particles with different sizes, 1. The larger particle settles faster than the smaller particle 2. The larger particle settles at the same velocity as the smaller particle 3. The larger particle settles slower than the smaller particle The larger particle se... 0% 0% 0% The larger particle set... The larger particle se... (2) Detention time: = settling time - Longer settling time = better particle removal hours; T = V/Q - Example 6.1 (page 7) for detention time calculation - Example 6.2 (page 7) for tank dimension calculation

6 (3) Free settling of discrete particles: - Only the particles that have settling velocity greater than a specific value can be removed; - Overflow rate = surface loading = upflow velocity V 0 = Q/A S V 0 H t HQ LHW Q LW Q A (4) Settling tank design: -Overflow rate determine the tank area: to make sure particles with certain settling velocity can are removed; - Detention time determine the volume therefore the depth of water: to make sure water to receive certain period of treatment time (not to disturb the tank); - Example 6.4 (page 8): For average Q = 6 ML/d Determine: Diameter; SWD (water depth) What is the most critical design parameter defining the clarifier efficiency? 1. The detention time 2. The overflow rate 3. The water depth 0% 0% 0% Design criteria: HRT = 4 h (detention time) Overflow rate = 20 m 3 /m 2 -day The detention time The overflow rate The water depth (5) Inclined settling system (plate or tube settlers): - Increase settling area/reduce settling depth; - Handle 3 6 times more flow; - Not for secondary clarifier;

7 Adding inclined tubes/plates in clarifiers can enhance particle removal. Why? 1. It provides more settling area thus reduces the settling distance of particles 2. It increases particle settling velocity 3. It increases particle size It provides more settl... 0% 0% 0% It increases particle se... It increases particle size 4. Coagulation and flocculation: Remove turbidity, color, and bacteria (1) Colloid stability: - Colloid particles are very small; normally they are negatively charged repel each other - Coagulant: neutralize the surface charge when particles are in contact, they stick together form large settleable size - Too much coagulant reverse the charge restabilization Why do colloid materials not settle? 1. They are too small and the settling velocity caused by the gravity force is negligible 2. They carry the same type of surface charge therefore repel each other 3. All above They are too small an... 0% 0% 0% They carry the same... All above

8 (2) Coagulants: Usually aluminum and iron salts Aluminum sulfate (alum): Al 2 (SO 4 ) 3.14H 2 O Al 3+ + H 2 O Al(OH) x + H + Best ph range: ; higher ph creates larger flocs Ferric sulfate and ferric chloride: Fe 2 (SO 4 ) 3 and FeCl 3 Fe 3+ + H 2 O Fe(OH) 3 + H + Best ph range: 4 12 (wider than above) Which of the following process can help the coagulation process? 1. Adding clay 2. Adding polymers 3. Adjusting ph 4. All above Coagulant aids: - Activated silica, clay, return sludge, and polymers; - Alkalinity addition/ph adjustment: need alkalinity to neutralize the acidity Lime (slaked lime; hydrated lime) and soda ash Adding clay 0% 0% 0% 0% Adding polymers Adjusting ph All above (3) Rapid mix: - To quickly disperse the chemical to particle surface for surface charge neutralization; - Degree of mixing is measured by the velocity gradient: W - Mechanical mixers: G = s -1 ; retention time: sec; power requirement: horsepower per MGD; - In-line static mixers: mixing time 1 3 s, head loss 2 3 ft; need a screen to prevent clogging; G P V Which is the parameter that directly defines the mixing intensity? 1. The turbulence 2. The velocity gradient 3. The mixing power The turbulence 0% 0% 0% The velocity gradient The mixing power

9 (4) Flocculation: Slow mixing, allow particles to form large flocs - Paddle flocculators: Gt = ; G = s -1 ; t = 45 min; - Baffled channels: Velocity in channels m/s; Detention time: 20 min; Compared to the coagulation, a smaller G is used for flocculation. Why? (5) Upflow solids contact clarifier: Mixing, flocculation, and clarification in the same tank 1. To destabilize particles 2. To prevent breaking up flocs 0% 0% To destabilize particles To prevent breaking u...

10 (6) Jar test: simulate water treatment process; determine the optimum coagulants, dosage, ph; mixing intensity, reaction time; (7) Sedimentation in water treatment: Pre-sedimentation: - Used when surface contains high turbidity; - HRT > 3 h; - Chemical addition may be required; Sedimentation after flocculation: - HRT = 2-4 h; - Overflow rate = gpd/ft 2 (20 41 m/day); - Horizontal velocity < 0.5 m/min; - Max weir loading: 20,000 gpd/ft. Example: Design one water treatment clarifier to handle a flow rate of 1.5 MGD maximum daily flow at the design year. Design criteria: average overflow rate = 800 gpd/ft 2 ; minimum side-water depth = 10 ft; peak weir loading < 20,000 gpd/ft. Solution: (a) Calculate diameter: The max daily flow rate to each unit is 1.5 MGD; Choose surface overflow rate = 800 gpd/ft 2 ; A = 1.5 x 10 6 /800 = 1875 ft 2 ; D = 2 (1875/3.14) 0.5 = ft Choose design 50 ft; (b) Choose side water depth 10 ft; (c) Check peak weir loading: Total length of the weir = 3.14 x 50 = 7 ft Weir loading = 1.5 x 10 6 /7 = 9,554 gpd/ft < 20,000 gpd/ft OK (d) Check HRT: Total tank volume: 3.14 x 252 x 10 = 19,625 ft 3 = 146,795 gallon HRT = 146,795/(1.5 x 10 6 ) = day = 2.3 h Ok Review questions: Why is the settling velocity related to the particle size? What is the overflow rate? Why is it the most important parameter for clarifier design? Why can adding inclined tubes and plates enhance the clarifier performance for water treatment? Why do colloid particles not settle in water? How to destabilize them? What are major coagulants for water treatment? What are coagulant aids? Why do we need to rapidly mix the coagulant with water? What is the parameter of the mixing intensity? What is flocculation? Why should we reduce the mixing intensity during flocculation? Homework #5: Due Thursday 1. Please tell the differences between the US drinking water standards and Chinese drinking water standards, and offer some explanations. 2. Practice problems #5 (page 181)

11 Lecture #3 Objectives: - Design sand filters - Understand disinfection and its side effects 5. Filtration: Remove small nonsettleable solids mandatory for surface water and shallow groundwater (1) Sand filtration principle: - Straining: particles are too large to pass through the sand medium; - Interception: particles are attached to the medium; - Flocculation: particles attached to each other when contact; Straining Flocculation Straining - Settling; Interception Sedimentation Sand filter can remove very small particles. Why? Typical gravity filter system 1. Particles can be retained by the sand surface 2. Particles can flocculate and grow larger 3. Particles can stuck between sand medium 4. All above Particles can be retain.. 0% 0% 0% 0% Particles can floccula.. Particles can stuck b... All above

12 (2) Single media rapid sand filters: - Sand is graded for easy backwashing; Single media filter filtration mode - Effective size (10 percentile diameter) = mm; bed depth = 2 3 ft (~0.75 m); - Backwashing process: pump water back through the media; sand bed expends; particles are removed; - Loading rate: Q/A = 120 m 3 /day.m 2 or above; - At least 2 units; size of each unit up to 100 m 2 ; - Backwash: use 2 4% of treated water; Preferred filtration mode (3) Multimedia filter: - Several media including sand, anthracite, and/or garnet; media are graded largest and lightest on top; - Similar effluent quality; - Anthracite size mm; - Reduced the resistance and increase the capacity due to the use of large anthracite medium; - Loading rate up to 300 m 3 /day.m 2 ; - Backwash: use air and water mixture; Why are multimedia filters more frequently used than single media filters? 1. The multimedia filter has larger capacity thus longer filter run 2. The multimedia filter is cheaper to build 3. The multimedia filter produces better effluent quality 4. All above The multimedia filter... 0% 0% 0% 0% The multimedia filter.. The multimedia filter... All above (4) Filter design: - The total filter depth is about 3 m, but the medium thickness is about 0.75 m; - The area is calculated based on the filtration rate, or loading rate (similar to the overflow rate of the clarifier); - Multimedia filters can handle 2 3 times of the flow per unit filter area; 1.4 L/m 2.s vs. 3.5 L/m 2.s

13 (5) Filter operation: Initially particles are retained on the top layers of the medium; after a while the water velocity increase (due to the particle collection), break the particle, and force the particles move down to deep layers of the medium; when penetrate the medium, the effluent turbidity increase back washing (6) Slow sand filter: - Use very small sand medium; flow rate is very low; - Can effectively remove all particles especially biological particles (Giardia cysts and Cryptosporidium oocysts) due to the formation of biologically active layer on top; - Manual cleaning; once every several months; - Need large area; suitable for small communities; - Flow rate of water applied per unit area of the filter, or loading rate (Q/A) = m 3 /day.m 2. Slow sand filters produce better effluent than rapid filters because 1. The filtration medium is finer than rapid filters 2. The biological layer on top of the filter can break down pollutants and remove pathogens 3. All above The filtration medium i... 0% 0% 0% The biological layer o... All above

14 (7) Deep filter: - Larger medium size = mm diameter; - Thick filter bed: m deep; - Loading rate up to 8000 m 3 /day.m Disinfection: Kill pathogens (1) Pathogens: Microorganisms that cause the waterborne disease - bacteria, viruses, protozoa, and helminthes; Coliform bacteria as indicator organisms: - Easy to detect; - Their presence indicates the pollution by feces the presence of pathogens; Limitations: Coliform bacteria die off rate is faster than viruses and protozoa without coliform does not mean that there is no other pathogens. Why do we use coliform bacteria as an indicator for water biological quality? 1. Coliform bacteria can indicate the presence of other pathogens 2. Coliform bacteria are easy to detect 3. All above Coliform bacteria ca... 0% 0% 0% Coliform bacteria are... All above

15 (2) Chlorine disinfection: strong oxidant Breakpoint chlorination process: -Cl 2 (g) + H 2 O = HOCl + H + + Cl - -HOCl = H + + OCl - (hypochlorite); pk a = Chlorine react with ammonia form chloramines a weaker disinfectant; also called combined chlorine; - Free chlorine: HOCl + OCl - ; ph < 7.54 is more effective; - Residue chlorine: ~ 2 mg/l before entering the distribution system; - > 0.2 mg/l in distribution system; (3) Disinfection by products (DBPs): - Formed between chlorine and organic matter in water; - Trihalomethanes (THMs): chloroform; bromodichlorimethane; dibromochloromethane, and bromoform; - Haloacetic acids (HAA5): monochloroacetic acid; dichloroacetic acid; trichloroacetic acid; monobromoacetic acid, and dibromoacetic acid; (4) Chlorine dioxide (ClO 2 ): - Weaker, not forming THMs/HAAs; - Form chlorate and chlorite toxic; (5) Ozonation: - Kills everything instantly; - Not stable (half life minutes); - Form bromate toxic; (6) UV: - Kills pathogen on a specific location; Why is chlorine a commonly used disinfectant for drinking water disinfection? 1. Chlorine is strong and kills all pathogens quickly 2. Chlorine is stable and maintains the effect for a long time 3. Chlorine does not form disinfection by-products Chlorine is strong and... 0% 0% 0% Chlorine is stable an... Chlorine does not fo.. Review questions: Why can a sand filter remove very small particles? What are the differences between single-mediia sand filter, multi-media filtration system, deep bed filter, and slow filter? Why is sand graded when used in the filter? How do we clean up the above filters? What are pathogens? Why are coliform bacteria used as indicator organisms? What are their limitations? Why is Cl 2 commonly used to disinfect drinking water? Why is chlorine disinfection more effective when ph is less than 7.54? What are the major disinfection by-products?

16 Lecture #4 Objective: - Know softening and other water treatment methods 7. Other treatment processes (1) Water softening: Hardness: = Sum of all polyvalent cations especially Ca 2+ and Mg 2+ ; TH = Ca 2+ + Mg 2+ ; unit: mg/l as CaCO : moderately hard What is the problem associated with hard water? 1. It can form scale inside the boiler tube 2. It can hurt people when drinking it It can form scale insid... 0% 0% It can hurt people wh.. Example: Water has 20 mg/l Ca 2+ and 10 mg/l Mg 2+ ; what is the hardness (in mg/l as CaCO 3 )? Solution: change everything in meq/l, then add up and convert to mg/l as CaCO 3 : g 3 For Ca 2+ : atomic weight = 40 g/mole; equivalent weight = 20 g/eq.; calcium hardness = 20/20 = 1 meq./l; For Mg 2+ : atomic weight = 24 g/mole; equivalent = 12 g/eq; magnesium hardness = 10/12 = 0.83 meq./l; Total hardness: = 1.83 meq./l = 1.83 x 50 = 91.5 mg/l as CaCO 3

17 Hardness composition: - Carbonate hardness: Ca(HCO 3 ) 2 ; Mg(HCO 3 ) 2 ; This hardness decreases with the increase of temperature temporary hardness; - Noncarbonate hardness (NCH), or permanent hardness: calcium/magnesium sulfate, chloride, nitrate,... - TH = CH + NCH Lime-soda ash softening: (1) Lime neutralize CO 2 in water: CO 2 + Ca(OH) 2 = CaCO 3 (s) + H 2 O (2) Lime remove all carbonate hardness (CH): Ca(HCO 3 ) 2 + Ca(OH) 2 = 2CaCO 3 (s) + 2H 2 O Mg(HCO 3 ) 2 + Ca(OH) 2 = CaCO 3 (s) + MgCO 3 + 2H 2 O MgCO 3 + Ca(OH) 2 = Mg(OH) 2 (s) + CaCO 3 (s) (3) Lime convert Mg 2+ NCH to Ca 2+ NCH: MgSO 4 + Ca(OH) 2 = Mg(OH) 2 (s) + CaSO 4 (4) Soda ash remove calcium NCH: CaSO 4 + Na 2 CO 3 = Na 2 SO 4 + CaCO 3 (s) Cation exchange softening: - 2R-Na + Ca 2+ R 2 -Ca + 2Na + - Regeneration: R 2 -Ca + 2Na + (High Concentration) 2R-Na + Ca 2+ What softening method is used in our homes? 1. Lime-soda ash softening method 2. Ion exchange method 0% 0% (2) Aeration: Remove gas (CO 2 and H 2 S), oxidize iron and manganese to insoluble forms Lime-soda ash softe... Ion exchange method

18 (3) Carbon adsorption: Remove taste and odor; soluble organic matter; heavy metals; dechlorination; Breakthrough curve: In drinking water treatment, what method is used to remove colloid materials? 1. Filtration 2. Coagulation-flocculationclarification 3. Adsorption 0% 0% 0% Filtration Coagulation-flocculat... Adsorption

19 (4) Membrane filtration: RO: pore size: 0.1 nm; remove salts and synthetic organic compounds (SOCs); size exclusion and charge repulsion; NF: pore size: 1 nm; soften fresh water and remove DBP precursors; size exclusion and charge repulsion; UF and MF: pore size: 0.01 and 0.1 m; remove turbidity, pathogens, and particles from fresh waters; size exclusion only; Uncharged small organic molecules such as THMs and dissolved gases can not be removed. Filtration Spectrum Reverses osmosis (RO) Residential unit: RO equipment

20 Electrodialysis (ED) RO membrane removes contaminants through 1. Size exclusion 2. Charge repulsion 3. All above 0% 0% 0% Size exclusion Charge repulsion All above (5) Corrosion control: Add chemicals to water to control pipe corrosion; Sodium silicate; sodium phosphate (6) Fluoridation: Add fluoride to some water that lacks it (7) Desalination: Using evaporation methods or membrane methods Review questions: What is the temporary hardness? What is the permanent hardness? What is the unit of hardness? Why can lime remove temporary hardness? What is the principle p of the ion exchange softening? What are the purposes of carbon adsorption and aeration in drinking water treatment? What is the principle of the RO processes? Homework #6: Due Thursday 1. Explain why the multimedia filter is more commonly used than the mono-media filter for water treatment. 2. Why is chlorine more commonly used for drinking water y y g disinfection than other disinfectants? What are their side effects?