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 in the processes

4. Wastewater treatment processes

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

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

7. Sewer systems

8. Typical composition of untreated domestic wastewater

9. Microorganism concentrations in untreated wastewater

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

11. 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

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

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

14. 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

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

16. Primary Wastewater Treatment Primary Treatment

17. Primary sedimentation To remove settleable solids from wastewater

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

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 and SS ~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 and SS ~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. Overall pathogen reduction in wastewater treatment

32. Water treatment processes

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

34. Water contaminants (I)

35. Water contaminants (II)

36. Water contaminants (III)

37. Water contaminants (IV)

38. Water contaminants (V)

39. Multiple barrier concept for public health protection

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

41. Water treatment processes

42. 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)

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

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

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

46. 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

47. Horizontal Paddle Flocculator

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

49. Sedimentation Basin

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

51. Coagulation/flocculation/and sedimentation To remove particulates and natural organic materials in water Coagulation –20 -50 mg/L of Alum at pH 5.5-6.5 (sweep coagulation) –rapid mixing: G values = 300-800/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

52. 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

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

54. 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

55. 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

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

57. 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

58. 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