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ANAEROBIC SLUDGE DIGESTION PROCESS

ANAEROBIC SLUDGE DIGESTION PROCESS. Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit. WASTEWATER. Water used to carry waste products away from homes, schools, commercial establishments, and industrial enterprises. Sources of Wastewater.

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ANAEROBIC SLUDGE DIGESTION PROCESS

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  1. ANAEROBIC SLUDGE DIGESTION PROCESS Prepared By Michigan Department of Environmental Quality Operator Training and Certification Unit

  2. WASTEWATER Water used to carry waste products away from homes, schools, commercial establishments, and industrial enterprises.

  3. Sources of Wastewater Domestic Industrial Infiltration

  4. CHARACTERISTICS OF WASTEWATER Materials Toxic to Biota Metals Ammonia Pesticides Herbicides Chlorine Acids/Bases Human Health Hazards Pathogens Nitrate Toxic Materials

  5. GOAL – PURPOSE – RESPONSIBILITY Of “Treating” or Stabilizing Wastewater PROTECTION OF NATURAL RESOURCES PROTECTION OF PUBLIC HEALTH

  6. CHARACTERISTICS OF WASTEWATER Treatment Concerns Solids Oxygen Demand Nutrients Microorganisms

  7. Wastewater “Treatment” Removes These “Pollutants”

  8. Wastewater Treatment Processes • Physical / Chemical • screening • sedimentation • filtration • precipitation • chemical destruct • Biological • waste stabilization lagoon • trickling filter • rotating biological contactor • activated sludge

  9. Treatment Efficiencies Primary (Physical) Treatment 40 - 60 % Suspended Solids 30 - 40 % BOD Secondary (Biological) Treatment 90+ % Suspended Solids 90+ % BOD

  10. Removal of These “Pollutants” Produces “Residuals” Often called “Sludge” Settleable Suspended Dissolved Wastewater Pre Treatment Suspended Dissolved Organic Inorganic Effluent Secondary Primary Clarifier Rock Grit Plastic Etc. Secondary Clarifier Sludge Sludge Note: These residuals are sometimes called “Biosolids”, however that term is usually reserved for sludge that has been “stabilized” and meets specific requirements (pathogen reduction, vector attractions, metals concentration)

  11. SLUDGE The SETTLEABLE solids separated from liquids during processing.

  12. SLUDGECHARACTERISTICS • Organic /Inorganic • Oxygen Demand • Odors • Nutrients • Pathogens • Mostly Water

  13. Purpose of ‘Treatment” • Stabilize Organics • Eliminate Odors • Destroy Pathogens • Reduce Amount of Solids • Enhance De-watering

  14. Settleable Suspended Dissolved Wastewater Suspended Dissolved Pre Treatment Organic Inorganic Effluent Secondary Primary Clarifier Rock Grit Plastic Etc. Secondary Clarifier Gas Sludge Sludge Digester Recycled Water (Supernatant) Digested Sludge (Stabilized)

  15. TYPES of “TREATMENT” • Heat and Pressure • Heat and Chemical • Lime Stabilization • Biological Digestion

  16. Types of Digestion Biological Bacteria Aerobic Use “Free” Oxygen Anaerobic No “Free” Oxygen

  17. AEROBIC DIGESTION

  18. AEROBIC DIGESTION Advantages Effective for “secondary” sludge Simple operation No hazardous gas production Disadvantages Higher operating costs High energy demands No burnable gas Higher organic content

  19. ANAEROBIC DIGESTION

  20. ANAEROBIC DIGESTION Advantages Low operating costs Proven effectiveness Burnable gas produced Disadvantages Long start-up time Affected by changes in loading and conditions Explosive gas produced

  21. ANAEROBIC SLUDGE DIGESTION DIGESTION PROCESS

  22. Anaerobic Digestion Process “TWO-STAGE” Process OR “Two Phase” Process

  23. Anaerobic Digestion Process “TWO-STAGE” Process This Does Not Mean Two Tanks Process

  24. Anaerobic Digestion Process First Stage Second Stage “TWO-STAGE” Process OR “Two Phase” Process Two Types of Bacteria Each Relying On The Other

  25. Anaerobic Digestion Process First Organic MaterialChanged ByAcid Forming Bacteria ToSimple Organic Material + Organic Matter Organic Acids Bacteria First Stage

  26. Anaerobic Digestion Process Organic Acids First Organic MaterialChanged ByAcid Forming Bacteria ToSimple Organic Material Also Called Volatile Acids

  27. Anaerobic Digestion Process Organic Acids Second Methane-Forming Bacteria UseOrganic Acids ProduceCarbon Dioxide andMethane CH4 + CO2 + Bacteria Second Stage

  28. Anaerobic Digestion Process Continuous Process “TWO-STAGE” Process Methane Forming Acid Forming CH4 + CO2 Organic Acids Bacteria Organic Matter Bacteria Second Stage First Stage Stabilization

  29. Anaerobic Digestion Process Type of Food OrganicInorganic SolubleInsoluble

  30. Liquid Acids Cell Membrane Enzymes (Absorption) Adsorbed Particle Soluble Organics Typical Acid Forming Bacteria

  31. Type of Food Not All Organic Material Broken Down - Not Readily Degradable Poor Food - Plastics, etc. Inert Solids 40 to 60 % of Organics are Reduced

  32. Anaerobic Digestion Process “TWO-STAGE” Process OR “Two Phase” Process Two Types of Bacteria Each Relying On The Other Must Be In Balance !

  33. Anaerobic Digestion Process Methane Forming Acid Forming CH4 + CO2 Organic Acids Bacteria Organic Matter Bacteria Second Stage First Stage Volatile Acids Acid Phase Acids Used at Rate Produced

  34. Anaerobic Digestion Process Acids Used at Rate Produced - Drop in pH If Not Used Start-up Upset “Sour” “Stuck” Methane Formers Must Be Active

  35. Anaerobic Digestion Process Methane Formers: Slow Growers Very Sensitive to Changes Loading pH Temperature Digester Operation Depends On Maintaining Proper Environment for METHANE FORMERS BALANCE !

  36. Anaerobic Digestion Process Products of Digestion 1. Gases 7 to 12 cubic feet per pound of volatile destroyed Methane (CH4) Carbon Dioxide (CO2) 65 to 70 % 30 to 35 % 500 to 600 BTU per cubic foot Can Be Utilized: Heating Digester Heating Buildings Running Engines Electrical Power

  37. Anaerobic Digestion Process Products of Digestion 2. Scum Lighter Solids Floating from Gas Entrapment Builds Up If MIXING Is Inadequate Not Digested ( Separated from Bacteria) Reduces Digester Capacity Plugs Piping Plugs Vents and Flame Traps

  38. Anaerobic Digestion Process Products of Digestion 3. Supernatant Liquid That Leaves Digester Two Sources of Water In Digester: Water Pumped In Water Formed During Digestion Recycled Through Treatment Plant High In: Solids BOD Ammonia

  39. Anaerobic Digestion Process Products of Digestion 3. Supernatant Liquid That Leaves Digester Should Be Removed Frequently in Small Quantities

  40. Anaerobic Digestion Process Products of Digestion 4. Digested Sludge Final Product Inorganic Solids Volatile (Organic) Solids - Not Easily Digested “Stabilized”

  41. Well Digested Sludge Characteristics 1. Less Solids 2. Lumpy Appearance 3.Black 4. Less Objectionable Odor 5. Volatile Content Reduced

  42. Anaerobic Digestion Process Products of Digestion 1. Gases Methane (CH4) Carbon Dioxide (CO2) 2. Scum Lighter Solids 3. Supernatant Liquid Removed 4. Digested Sludge “Stabilized”

  43. TYPICAL “Two-Stage” ANAEROBIC DIGESTER SYSTEM Gas Gas Heat Exchanger Hot Water Recirculation Pump Transfer Pump Note: Two-Stage System here refers to two separate tanks (One for the treatment process and one for water-solids separation)

  44. Digestion Factors • Bacteria 2. Food 3. Loading 4. Contact 5. Environment

  45. Digestion Factors 1. BACTERIA Naturally Occurring Must Have Enough Living Organisms Two Different Types BALANCE The Other Factors –Important Because They Affect the Bacteria

  46. Digestion Factors 1. BACTERIA Balance 2. FOOD Volatile Solids

  47. Type of Food Not All Organic Material Broken Down - Not Readily Degradable Poor Food - Plastics, etc. Inert Solids 40 to 60 % of Organics are Reduced

  48. Digestion Factors 1. BACTERIA Balance 2. FOOD Volatile Solids Not All Volatile Material None of the Inorganic

  49. Digestion Factors 1. BACTERIA Balance 2. FOOD Volatile Solids 3. LOADING

  50. Digestion Factors 3. LOADING AMOUNT Applied to the Treatment Process Related to the SIZE of the System

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