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Biolog ical Treatment Processes

Biolog ical Treatment Processes. Outline. Overview 3.1 Criteria for Successful Biological Treatment 3.2 Principles of Biological Reactions 3. 3 Wastewater Treatment Ponds 3. 4 Anaerobic Treatment Processes. Wastewater Treatment. 2.1 Overview of Treatment Processes.

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Biolog ical Treatment Processes

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  1. Biological TreatmentProcesses

  2. Outline • Overview • 3.1 Criteria for Successful Biological Treatment • 3.2 Principles of Biological Reactions • 3.3Wastewater Treatment Ponds • 3.4 Anaerobic Treatment Processes

  3. Wastewater Treatment

  4. 2.1 Overview of Treatment Processes • Preliminary & Primary Treatment • Physical / chemical processes to prepare wastewater for biological treatment • Removal of solids mainly • Usually cheaper/ easier than secondary processes • Examples: a. equalisation (flow and load), b. neutralisation, c. settling of solids, d. flotation of oil and grease, e. filtration etc

  5. 2.1 Overview of Treatment Processes • Secondary Treatment • Biological removal of biodegradable, mostly soluble organic compounds (carbon removal) • Aerobically • activated sludge plants, • aerated ponds • trickling filters etc. • Anaerobically • non-aerated ponds, • high rate anaerobic (biogas) plants

  6. Tertiary Treatment • Removal of specific pollutants with physical, chemical and/or biological methods • Examples: a. adsorption of organics by activated carbon b. precipitation or flocculation of phosphate etc. c. biological nitrogen removal d. disinfection • In general, costs increase with increasing degree of treatment

  7. Wastewater Treatment

  8. Outline • Overview • 3.1 Criteria for Successful Biological Treatment • 3.2 Principles of Biological Reactions • 3.3Wastewater Treatment Ponds • 3.4 Anaerobic Treatment Processes

  9. 3.1 Criteria for Successful Biological Treatment • Produce biological catalyst (biomass) • source of energy • source of cellular components (C, H, N, O, P, S etc.) • Maintain biomass • adequate environment (T, pH, toxics) • adequate retention time (rate of treatment) • Separation of biomass • grow suitable types of organisms ie. floc forming bacteria

  10. Outline • Overview • 3.1 Criteria for Successful Biological Treatment • 3.2 Principles of Biological Reactions • 3.3 Wastewater Treatment Ponds • 3.4 Anaerobic Treatment Processes

  11. 3.2 Principles of Biological Reactions A. Three Important Biological Reactions • Aerobic CHO + O2biomass + CO2 + H2O ≈ 50 % ≈ 50 % respiratory metabolism • Anaerobic CHO biomass + CO2 + CH4 + H20 10 - 20 % 80 - 90 % fermentative metabolism • Photosynthesis CO2 + H2O biomass + O2 energy supplied externally (light)

  12. 100 Anaerobic digestion Aerobic treatment Low Rate Anaerobic Treatment 10 Hydraulic Retention Time (days) 1 High Rate Anaerobic Treatment 0.1 100 1000 10000 100000 Wastewater COD (mg/L) B. Aerobic or Anaerobic ?

  13. 3.2 Principles of Biological Reactions C. Nutrient Requirements • "Major" elements: C, H, O, N • "Minor" elements: • P  DNA/RNA, phospholipids, ATP • S  for proteins, amino acids • K  in RNA, coenzymes • Mg  in RNA, coenzymes, as cation • Trace elements • Often essential: Ca, Mn, Fe, Co, Cu, Zn • Rarely essential: B, Na, Al, Si, Cl, V, Cr, Ni, As, Se, Mo, Sn, I

  14. Outline • Overview • 3.1 Criteria for Successful Biological Treatment • 3.2 Principles of Biological Reactions • 3.3 Wastewater Treatment Ponds • 3.4 Anaerobic Treatment Processes

  15. 3.4 Wastewater Treatment Ponds • Applied mostly in rural industries and small communities • Main benefits are low construction and operating cost • Classification based on biological activity, form of aeration and influent composition

  16. 1. Anaerobic Ponds Characteristics: • High organic load; • Deep (3-6m); • Biomass formation small (5-15% of C in feed)

  17. Anaerobic Pond Design & Operation Operational Considerations: • BOD removal 60-80% • Scum formation to contain odour emissions • Monitor pH (should be 6.4 - 7.8)

  18. 2. Facultative Ponds Characteristics: • “two zone” environment, depth 1.5 - 4 m; large • microbial diversity; medium organic load; odour free

  19. Facultative Pond Design & Operation • Design: Area Loading Rate • 40 - 140 kg BOD5/ha/d T>15oC • 20 - 40 kg BOD5/ha/d T<15oC • HRT 5 - 30 days • Operational Considerations: • Maintain aerobic conditions. Beware of over-loading causing the pond to turn anaerobic - odour problems

  20. 3. Aerated Ponds • Characteristics: • Mode is determined by the mixing intensity • Completely mixed: P/V = 2.3 - 4 W/m3 • Facultative: P/V ≈ 0.8 W/m3

  21. Aerated Pond Design & Operation • Design: • HRT 0.5 - 3 days • Aeration capacity ≈ 2*BOD load • Aerators: 1 - 1.5 kg O2/kWh • ΔBOD: 50 - 70% • Operational Considerations: • Can be very efficient for soluble BOD/ COD removal but solids concentrations too high for discharge (irrigation ok).

  22. 4. Aerobic (Oxidation) Ponds Characteristics: • Natural oxygenation (wind, photosynthesis); large surface area; shallow (1 - 1.5m); low organic loading. • Suitable for treating effluent from anaerobic ponds

  23. Aerobic Pond Design & Operation • Design: 40 - 120 kg BOD5/ha/d • Operational Considerations: • Maintain aerobic conditions. Beware of over-loading causing the pond to turn anaerobic.

  24. Outline • Overview • 3.1 Criteria for Successful Biological Treatment • 3.2 Principles of Biological Reactions • 3.3Wastewater Treatment Ponds • 3.4 Anaerobic Treatment Processes

  25. 3.4 Anaerobic Treatment Processes • Treatment under exclusion of oxygen • Carbon mainly converted to methane (CH4) and carbon dioxide (CO2) • Used for high organic loadings • Efficient and economic COD/BOD removal • Low rate systems use very long HRT eg. Anaerobic ponds • High rate systems use low HRT but need biomass retention mechanism eg. UASB • Increase rate of biological action by increasing temperature.

  26. Slow growing, pH sensitive archaea Fast growing, robust bacteria Anaerobic Process Principles Pathways of organics in anaerobic treatment

  27. Process types A. Single-stage processes • Long solids & hydraulic retention times (HRT) • Eg. Anaerobic digesters (20-30 d HRT) Anaerobic ponds (10-30 d HRT) B. Two-stage (high rate) processes • Short HRT in first stage, no biomass retention • Short HRT but with biomass retention in second stage, usually pH controlled • Eg. UASB, Hybrid, fluidised bed reactors etc.

  28. Biogas SLUDGE DIGESTER Treated effluent Wastewater Mixing mechanically or often by biogas recirculation A. Single Stage Process

  29. Gas collection below water level to reduce turbulence at overflow Biogas Treated effluent Gas collector Uniform flow distribution essential Sludge blanket From Pre-acidification Tank Granular biomass 1. Upflow Anaerobic Sludge Blanket (UASB)

  30. Packed bed (plastic material) for biofilm growth Biogas Treated effluent Uniform flow distribution essential Sludge blanket From Pre-acidification Tank Granular biomass 2. Hybrid Reactor

  31. B. Two-Stage Reactor Performance • COD removal 60 - 95% • BOD removal 80 - 95% • Gas production 0.3-0.6 m3/kg CODremoved • Methane production 0.2-0.35 m3/kg CODremoved • Methane conc. 55 - 75% • Sludge production 0.05-0.1 kg VSS/kgCODremoved

  32. Two-stage high-rate hybrid reactor for abattoir & industrial wastewater

  33. Anaerobic Reactor Design 1. Pre-acidification tank • Often on the basis of an equalisation tank (also variable volume operation) • Typical HRT 12-24 h • pH 5-6 if controlled, 4-5 if uncontrolled • Mixing usually only by inflow 􀃎 importance to minimise solids in influent • Covered tank, gas vented and treated or incinerated (with biogas in boiler or flare)

  34. Anaerobic Reactor Design 2. Methanogenic (2nd stage) reactor • Volume-based organic loading rate (OLR) Cin  biodegradable COD conc. in influent mg/L Q  wastewater flow rate m3/d VR methanogenic bioreactor volume m3 • Typical HRT 12-24 h, Solids RT 10-150 days • Usually heated to operate at 30 - 40°C

  35. Recycle and mix tank reduce pH control dosing Biogas CSTR-type tank usually not heated Methanogenesis Sludge blanket Acidif. Tank Mix Tank Acidogenesis Biomass retention as granules High Rate Anaerobic Treatment • Typical process flowsheet using Upflow Anaerobic Sludge Blanket (UASB) reactor

  36. Anaerobic Reactor Design • OLR designs for various reactor types: • UASB  6-12 kg COD/m3/d • Internal Circulation  15-25 kg COD/m3/d • Fluidised/expanded bed 12-20 kg COD/m3/d • Hybrid Reactor  6-12 kg COD/m3/d • OLR varies with degradability, temp., pH… • Hydraulic loading up to 24 m3/(m2reactor area d) • Gas loading 70 - 200 m3 gas /(m2reactor area d)

  37. Questions?

  38. Documentation

  39. Terima Kasih

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