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Water and wastewater treatment processes

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.

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Water and wastewater treatment processes

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  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 in the processes

  3. Wastewater treatment processes

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

  5. Wastewater treatment systems • Decentralized • Septic tank • Waste stabilization ponds • Facultative lagoon • Maturation lagoon • Land treatment • 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 BOD5 • <30 mg/L of suspended solids • <200 CFU/100ml fecal coliforms

  10. 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+%)

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

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

  13. 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

  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 PrimaryTreatment

  16. Primary sedimentation • To remove settleable solids from wastewater

  17. Primary Clarification Scum: Oil, Grease, Floatable Solids PrimaryEffluent PrimarySludge Influent from Preliminary Treatment Section through a Circular Primary 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 and SS • ~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 and SS • ~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. Overall pathogen reduction in wastewater treatment

  31. Water treatment processes

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

  33. Water contaminants (I)

  34. Water contaminants (II)

  35. Water contaminants (III)

  36. Water contaminants (IV)

  37. Water contaminants (V)

  38. Multiple barrier concept for public health protection

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

  40. Water treatment processes

  41. 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)

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

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

  44. Major Coagulants • Hydrolyzing metal salts • Alum (Al2(SO4)3) • Ferric chloride (FeCl3) • Organic polymers (polyelectrolytes)

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

  46. Horizontal Paddle Flocculator

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

  48. Sedimentation Basin

  49. Sedimentation Basin Example Water coming from flocculation basin. Water goes to filter. Floc (sludge) collectedin hopper Sludge to solidstreatment

  50. Coagulation/flocculation/and sedimentation • To remove particulates and natural organic materials in water • Coagulation • 20 -50 mg/L of Alumat 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/ft2 • 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

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