Water and wastewater treatment processes

1. 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

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

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

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

5. Sewer systems

6. Typical composition of untreated domestic wastewater

7. Microorganism concentrations in untreated wastewater

8. (Minimum) Goals of wastewater treatment processes • <30 mg/L BOD5 • <30 mg/L of suspended solids • <200 CFU/100ml fecal coliforms

9. Conventional Community (Centralized) Sewage Treatment Secondary Treatment Using Activated Sludge Process Sludge drying bed or mechanical dewatering process Pathogen Reductions Vary from: low (<90%) to Very High (>99.99+%)

10. Typical Municipal Wastewater Treatment System Preliminary or Pre-Treatment SecondaryTreatment PrimaryTreatment Disinfection Sludge Treatment& Disposal

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

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

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

14. Primary Wastewater Treatment PrimaryTreatment

15. Primary sedimentation • To remove settleable solids from wastewater

16. Primary Clarification Scum: Oil, Grease, Floatable Solids PrimaryEffluent PrimarySludge Influent from Preliminary Treatment Section through a Circular Primary Clarifier Primary Treatment

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

18. Primary sedimentation • To remove settleable solids from wastewater • Maximum flow: 30 - 40 m3 per day • Retention period: 1.5 - 2.0 hours (at maximum flow) • 50 - 70 % removal of suspended solids • 25 - 35 % removal of BOD5 • ~20 % removal of phosphate • ~50 % removal of viruses, bacteria, and protozoa • 90 % removal of helminth ova

19. Secondary Wastewater Treatment SecondaryTreatment

20. Secondary treatment processes • To remove suspended solids, nitrogen, and phosphate • 90 % removal of SS and BOD5 • Various technologies • Activated sludge process • Tricking filter • Aerated lagoons • Rotating biological contractors

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

22. 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 Simplified Activated Sludge Description The Activated Sludge Process Secondary Treatment

23. Activated sludge process • To remove suspended solids, nitrogen, and phosphate • Food to microorganism ratio (F:M ratio): 0.25 kg BOD5 per kg MLSS (mixed liquor suspended solids) per day at 10 oC or 0.4 kg BOD5 per kg MLSS per day at 20 oC • Residence time: 2 days for high F:M ratio, 10 days or more for low F:M ratio • Optimum nutrient ratio: BOD5:N:P =>100:5:1 • 90 % removal of BOD5 • ~20 % removal of phosphate • > 90 % removal of viruses and protozoa and 45 - 95 % removal of bacteria

24. Secondary Treatment Using Trickling Filter Process SecondaryTreatment TricklingFilter Secondary Treatment

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

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

27. Tricking filter process • To remove suspended solids, nitrogen, and phosphate • Organic loading (BOD5 X flow/volume of filter): 0.1 kg BOD5 per m3 per day • Hydraulic loading: 0.4 m3 per day per m3 of plan area • 90 % removal of BOD5 • ~20 % removal of phosphate • Variable removal levels of viruses, 20-80 % removal of bacteria and > 90 % removal of protozoa

28. Wastewater Disinfection Disinfection

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

30. 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

31. Breakpoint Reaction for Chlorine • Reaction of ammonium with free 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 Disinfection

32. Breakpoint Reaction for Chlorine Monochloramine, organochloramines Dichloramine, nitrogen trichloride, and organochloramines Cl2:N < 5:1 mass basis Ref: Metcalf & Eddy, Inc., 1979. Wastewater Engineering, Treatment and Disposal. McGraw-Hill, New York.

33. 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

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

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

36. UV disinfection in wastewater • To inactivate pathogens in wastewater • Low pressure, low pressure high-output, or medium pressure lamp • 40 mJ/cm2 • Similar level of reduction for total and fecal coliforms, and enteric viruses, but a lot higher level of reduction for Giardia and Cryptosporidium

37. Overall pathogen reduction in wastewater treatment

38. Water treatment processes

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

40. Water contaminants (I)

41. Water contaminants (II)

42. Water contaminants (III)

43. Water contaminants (IV)

44. Water contaminants (V)

45. Multiple barrier concept for public health protection

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

47. Water treatment processes

48. 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 → FeOx ↓(ferric oxides) + MnO2 ↓ (manganese dioxide) • Fe (HCO3)2 (Ferrous bicarbonate) + KMnO4 (Potassium permanganase) → Fe (OH)3 ↓(Ferric hydroxide) + MnO2 ↓(manganese dioxide) • Mn (HCO3)2 (Manganese bicarbonate) + KMnO4 (Potassuim permanganase) → MnO2 ↓(manganese dioxide)

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

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