2. Water and wastewater treatment processes ENV H 452/ENV H 542 John Scott Meschke Office: Suite 2249, 4225 Roosevelt Phone: 206-221-5470 Email: jmeschke@u.washington.edu Gwy-Am Shin Office: Suite 2339, 4225 Roosevelt Phone: 206-543-9026 Email: gwyam@u.washington.edu

3. Key points Purpose of the individual unit processes The typical operating conditions The outcome of the processes Microbial reduction of the processes

4. How much wastewater do we produce each day? Wastewater Characteristics These values are rough estimates only and vary greatly by locale.

5. Wastewater treatment systems Decentralized –Septic tank –Waste stabilization ponds Facultative lagoon Maturation lagoon –Land treatment –Constructed wetland Centralized

6. Sewer systems

7. Typical composition of untreated domestic wastewater

8. Microorganism concentrations in untreated wastewater

9. (Minimum) Goals of wastewater treatment processes <30 mg/L BOD 5 <30 mg/L of suspended solids <200 CFU/100ml fecal coliforms

10. Conventional Community (Centralized) Sewage Treatment Pathogen Reductions Vary from: low ( 99.99+%) Secondary Treatment Using Activated Sludge Process Sludge drying bed or mechanical dewatering process

11. Typical Municipal Wastewater Treatment System Preliminary or Pre- Treatment Primary Treatment Secondary Treatment Disinfection Sludge Treatment & Disposal

12. Preliminary Wastewater Treatment System Preliminary or Pre- Treatment Solids to Landfill

13. Preliminary Treatment Facilities Preliminary Treatment - Bar Racks Bar Racks: are used to remove large objects that could potentially damage downstream treatment/pumping facilities. Ref: Metcalf & Eddy, 1991

14. Preliminary Treatment - Grit chamber Grit chamber: used to remove small to medium sized, dense objects such as sand, broken glass, bone fragments, pebbles, etc.

15. Primary Wastewater Treatment Primary Treatment

16. Primary sedimentation To remove settleable solids from wastewater

17. Primary Clarification Primary Sludge Primary Effluent Influent from Preliminary Treatment Section through a Circular Primary Clarifier Primary Treatment Scum: Oil, Grease, Floatable Solids

18. Clarification Theory - Circular Basins Particles that are removed have a settling trajectory such that the particle settles before reaching the outside wall or end of clarifier. Center of Clarifier Basin Horizontal velocity decreases with increasing distance from center of clarifier basin Outside Wall of Clarifier Basin Primary Treatment

19. Primary sedimentation To remove settleable solids from wastewater Maximum flow: 30 - 40 m 3 per day Retention period: 1.5 - 2.0 hours (at maximum flow) 50 - 70 % removal of suspended solids 25 - 35 % removal of BOD 5 ~20 % removal of phosphate ~50 % removal of viruses, bacteria, and protozoa 90 % removal of helminth ova

20. Secondary Wastewater Treatment Secondary Treatment

21. Secondary treatment processes To remove suspended solids, nitrogen, and phosphate 90 % removal of SS and BOD 5 Various technologies –Activated sludge process –Tricking filter –Aerated lagoons –Rotating biological contractors

22. Secondary Treatment Using Activated Sludge Process Secondary Treatment Sludge drying bed or mechanical dewatering process

23. The Activated Sludge Process Aerobic microbes utilities carbon and other nutrients to form a healthy activated sludge (AS) biomass (floc) The biomass floc is allowed to settle out in the next reactor; some of the AS is recycled Secondary Treatment Simplified Activated Sludge Description

24. Activated sludge process To remove suspended solids, nitrogen, and phosphate Food to microorganism ratio (F:M ratio): 0.25 kg BOD 5 per kg MLSS (mixed liquor suspended solids) per day at 10 o C or 0.4 kg BOD 5 per kg MLSS per day at 20 o C Residence time: 2 days for high F:M ratio, 10 days or more for low F:M ratio Optimum nutrient ratio: BOD 5 :N:P =>100:5:1 90 % removal of BOD 5 ~20 % removal of phosphate > 90 % removal of viruses and protozoa and 45 - 95 % removal of bacteria

25. Secondary Treatment Using Trickling Filter Process Secondary Treatment Trickling Filter

26. http://www.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/streem/trickfil.jpg Primary effluent drips onto rock or man-made media Rotating arm to distribute water evenly over filter Rock-bed with slimy (biofilm) bacterial growth Primary effluent pumped in Treated waste to secondary clarifier

27. Trickling Filter http://www.eng.uc.edu/friendsalumni/research/labsresearch/biofilmreslab/Tricklingfilter_big.jpg

28. Tricking filter process To remove suspended solids, nitrogen, and phosphate Organic loading (BOD 5 X flow/volume of filter): 0.1 kg BOD 5 per m 3 per day Hydraulic loading: 0.4 m 3 per day per m 3 of plan area 90 % removal of BOD 5 ~20 % removal of phosphate Variable removal levels of viruses, 20-80 % removal of bacteria and > 90 % removal of protozoa

29. Wastewater Disinfection Disinfection

30. Wastewater disinfection To inactivate pathogens in wastewater Several choices –Free chlorine and combined chlorine –UV –Ozone –Chlorine dioxide

31. Process Chemistry of Free Chlorine Chlorine does not inactivate microorganisms directly. Microorganisms are inactivated by the hypochlorous acid (HOCl) and the hypochlorite ion (OCl - ). Disinfection

32. Breakpoint Reaction for Chlorine Sum of chloramine residual concentrations called combined residual Process is very dependent on pH, temperature, contact time, and initial ratio of chlorine to ammonia Organic nitrogen compounds react rapidly with chlorine to form organochloramines Reaction of ammonium with free chlorine: Disinfection

33. Breakpoint Reaction for Chlorine Ref: Metcalf & Eddy, Inc., 1979. Wastewater Engineering, Treatment and Disposal. McGraw-Hill, New York. Cl 2 :N < 5:1 mass basis Dichloramine, nitrogen trichloride, and organochloramines Monochloramine, organochloramines

34. Wastewater chlorination To inactivate pathogens in wastewater Dynamic chloramination and breakpoint chlorination 5 - 20 mg/L for 30 minutes > 99.99 % reduction of total and fecal coliforms, ~90 % reduction of enteric viruses, ~50% reduction of Giardia, but < 10 % reduction of Cryptosporidium

35. Ultraviolet (UV) Disinfection Closed-channel, horizontal, parallel to flow Medium pressure, high-intensity lamps Automatic cleaning Disinfection

36. Ultraviolet (UV) Disinfection Closed-channel, horizontal, parallel to flow (Trojan) Raised UV Lamp Unit Disinfection

37. UV disinfection in wastewater To inactivate pathogens in wastewater Low pressure, low pressure high-output, or medium pressure lamp 40 mJ/cm 2 Similar level of reduction for total and fecal coliforms, and enteric viruses, but a lot higher level of reduction for Giardia and Cryptosporidium

38. Overall pathogen reduction in wastewater treatment

39. Water treatment processes

40. Water contaminants Chemicals –Inorganics –Organics Synthetic organic compounds Volatile organic compounds Microbes –Viruses –Bacteria –Protozoa parasites –Algae –Helminths

41. Water contaminants (I)

42. Water contaminants (II)

43. Water contaminants (III)

44. Water contaminants (IV)

45. Water contaminants (V)

46. Multiple barrier concept for public health protection

47. Barrier Approach to Protect Public Health in Drinking Water Source Water Protection Treatment Disinfection Disinfectant residual in distribution system

48. Water treatment processes

49. Oxidation To remove inorganics (Fe ++, Mn ++ ) and some synthetic organics –Cause unaesthetic conditions (brown color) –Promote the growth of autotrophic bacteria (iron bacteria): taste and order problem Free chlorine, chlorine dioxide, ozone, potassium permanganate –Fe ++ + Mn ++ + oxygen + free chlorine → FeO x ↓ (ferric oxides) + MnO 2 ↓ (manganese dioxide) –Fe (HCO 3 ) 2 (Ferrous bicarbonate) + KMnO 4 (Potassium permanganase) → Fe (OH) 3 ↓ (Ferric hydroxide) + MnO 2 ↓ (manganese dioxide) –Mn (HCO 3 ) 2 (Manganese bicarbonate) + KMnO 4 (Potassuim permanganase) → MnO 2 ↓ (manganese dioxide)

50. Physico-chemical processes To remove particles in water Coagulation/flocculation/sedimentation Filtration

51. Rapid Mix Intense mixing of coagulant and other chemicals with the water Generally performed with mechanical mixers Chemical Coagulant

52. Major Coagulants Hydrolyzing metal salts –Alum (Al 2 (SO 4 ) 3 ) –Ferric chloride (FeCl 3 ) Organic polymers (polyelectrolytes)

53. Coagulation with Metal Salts Al(OH) Al x (OH) y Colloid Al(OH) 3 Colloid Al(OH) 3 Colloid + + Soluble Hydrolysis Species (Low Alum Dose) Colloid Al(OH) 3 (High Alum Dose) Floc Sweep Coagulation Charge Neutralization

54. Horizontal Paddle Flocculator

55. Flocculation Example Water coming from rapid mix. rapid mix. Water goes to sedimentation basin. basin.

56. Sedimentation Basin

57. Sedimentation Basin Example Water coming from flocculation basin. Water goes to filter. Floc (sludge) collected in hopper Sludge to solids treatment

58. Coagulation/flocculation/and sedimentation To remove particulates, natural organic materials in water Coagulation –20 -50 mg/L of Alum at pH 5.5-6.5 (sweep coagulation) –rapid mixing: G values = 300-8000/second Flocculation: –Slow mixing: G values = 30-70/second –Residence time:10 -30 minutes Sedimentation –Surface loading: 0.3 -1.0 gpm/ft 2 –Residence time: 1 – 2 hours Removal of suspended solids and turbidity: 60-80 % Reduction of microbes –74-97 % Total coliform –76-83 % of fecal coliform –88-95 % of Enteric viruses –58-99 % of Giardia –90 % of Cryptosporidium

59. Filtration To remove particles and floc that do not settle by gravity in sedimentation process Types of granular media –Sand –Sand + anthracite –Granular activated carbon Media depth ranges from 24 to 72 inches

60. Filter Example Water coming from sedimentation basin. AnthraciteSand Gravel (support media) Water going to disinfection

61. Mechanisms Involved in Filtration Interception: hits & sticks Sedimentation: quiescent, settles, & attaches Flocculation: Floc gets larger within filter Entrapment: large floc gets trapped in space between particles Floc particles Granular media, e.g., grain of sand Removal of bacteria, viruses and protozoa by a granular media filter requires water to be coagulated

62. Rapid filtration To remove particulates in water Flow rate 2-4 gpm/ft 2 Turbidity: < 0.5 NTU (often times < 0.1 NTU) Reduction of microbes –50-98 % Total coliform –50-98 % of fecal coliform –10-99 % of Enteric viruses –97-99.9 % of Giardia –99 % of Cryptosporidium

63. Disinfection in water To inactivate pathogens in water Various types –Free chlorine –Chloramines –Chlorine dioxide –Ozone –UV

64. Trend in disinfectant use (USA, % values) Disinfectant197819891999 Chlorine gas918783.8 NaClO 2 (bulk)67.118.3 NaClO 2 (on- site) 002 Chlorine dioxide 04.58.1 Ozone00.46.6 Chloramines02028.4

65. Comparison of major disinfectants ConsiderationDisinfectants Cl 2 ClO 2 O3O3 NH 2 Cl Oxidation potential StrongStronger?StrongestWeak ResidualsYesNo Yes Mode of action Proteins/ NA Proteins Disinfecting efficacy GoodVery goodExcellentModerate By-productsYes Yes?No