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Chapter 6.3 Biological treatment

Chapter 6.3 Biological treatment. Application of biological treatment. Biological treatment of organic waste: optimises a natural process uses ubiquitous micro-organisms ( eg bacteria, fungi) requires control of temperature and nutrient balance may be aerobic or anaerobic

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Chapter 6.3 Biological treatment

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  1. Chapter 6.3Biological treatment TRP Chapter 6.3 1

  2. Application of biological treatment • Biological treatment of organic waste: • optimises a natural process • uses ubiquitous micro-organisms (eg bacteria, fungi) • requires control of temperature and nutrient balance • may be aerobic or anaerobic • For hazardous waste treatment, used for: • low contaminant-concentration organic wastes eg sludges TRP Chapter 6.3 2

  3. Factors influencing biological treatment • Suitability of the waste: • composition • physical form • pH • Biological treatment is only suitable for organic wastes with relatively low toxicity • It is not 100% efficient in destroying organic material TRP Chapter 6.3 3

  4. Process conditions • Biological treatment processes require control of: • temperature • moisture • pH • level of aeration • inhibitors such as metals • nutrients TRP Chapter 6.3 4

  5. Advantages of biological waste treatment • In the right conditions - ie temperature, humidity and pH - biological treatment is: • Effective • Tolerant to changes in waste composition - these may result in a short period of inactivity, but do not halt the process TRP Chapter 6.3 5

  6. Scope of treatment application • Wastewater treatment is the most widely used application of biological treatment eg for industries such as paper manufacture and recycling, food processing, tanneries and the pharmaceutical industry, and for landfill leachate • Also: • In-situ bio-remediation of contaminated soil • Slurry-phase treatment • Land treatment • Co-composting TRP Chapter 6.3 6

  7. On-site vs off-site treatment • For hazardous wastes, most processes suitable for on-site treatment • For wastewater, central treatment - but requires pre-segregation of toxic effluents TRP Chapter 6.3 7

  8. Typical wastewater treatment process Pre-treatment eg physical/chemical treatment, solids separation Treatment Biological treatment eg aerobic/ anaerobic suspended/attached batch/continuous Post-treatment eg filtration, adsorption Discharge of clean effluent BIOREACTOR TRP Chapter 6.3 8

  9. Wastewater treatment - liquid phase • Staged process • Must meet discharge limits • Data collection needed to prove compliance • Variations in composition must be expected • Use fixed or aqueous medium • May need complementary/finishing treatments eg lagoons, activated carbon TRP Chapter 6.3 9

  10. Wastewater treatment - example 1 Bacterial filter beds • Fixed media • Stable process • Good for high charges of effluent • Suitable for effluents with high organic loadings eg from canning industry, sugar industry TRP Chapter 6.3 10

  11. Wastewater treatment - example 2 Activated sludge • Widely used eg refineries, canneries, pharmaceuticals • Suitable for wastewater, aqueous hazardous wastes with < 1% suspended solids • Bacteria are aggregated in floating flocs • Recirculation ensures constant bacterial charge • Flexible but more sensitive process than bacterial filter beds • Bioreactor needs efficient mixing and high level of dissolved oxygen • Cleaner effluent than other biological processes • Needs a lot of energy TRP Chapter 6.3 11

  12. Wastewater treatment - example 3 Lagoons • Shallow impermeable water basins used for degradation of batches of effluent • Depends on action from bacteria, algae or aquatic vegetation • Low cost process • Suitable for wastewater with low organic contents • Not suitable for wastes with mainly chemical components • Often used as pretreatment stage TRP Chapter 6.3 12

  13. Slurry-phase treatment • Used for solid waste, sludge or contaminated soil • Needs mixing to: • homogenise slurry • break down solid particles • oxygenate • increase contact with microorganisms • Degrades waste at a faster rate, needs less land, than solid-phase treatment • Potential for use with additional waste streams eg wastes from wood preserving, petroleum refinery wastes TRP Chapter 6.3 13

  14. Land treatment - solid phase • involves applying wastes uniformly to prepared land at controlled rates • aimed at degradation of organic constituents • removes other waste constituents eg suspended solids, heavy metals • purely a treatment process - land NOT suitable for cultivation • Suitable for: • oily sludges and waste oils • organic sludges and liquids • widely used in the USA by petroleum industry • also possible to treat wastes from wood treatment eg preservatives such as creosote, pentachlorophenol TRP Chapter 6.3 14

  15. Co-composting - solid phase • Mixing of hazardous wastes with biodegradable solids to act as: • bulking agent - to create void spaces for passage of air • thermal source - by biological decomposition • Usually need two different materials as: • good bulking agent eg wood chips are poor thermal source • good thermal source eg dry molasses are poor bulking agent • Process takes place: • in windrows, turned to ensure adequate aeration • in static piles where air is forced or sucked through material • in vessel which offers greater process control/ VOC containment • Used for: • soils contaminated with coal tar • for TNT-contaminated sediments and soils TRP Chapter 6.3 15

  16. In-situ bio-remediation • Enables treatment without excavation and removal of contaminated material • An aerobic process • Enhances natural biodegradation • Influenced by hydrogeological factors • Can reduce contamination to acceptable levels in relatively short time eg 1-2 years TRP Chapter 6.3 16

  17. Soil heaping - solid phase • Combines land treatment and windrow composting • Effective for treating large volumes of contaminated soil and other wastes with low concentration of organics • Valuable where available land area is restricted TRP Chapter 6.3 17

  18. Emerging applications for biological treatment • For many waste types, biological treatment is still in early stage of development • New applications are being tested and developed eg • for treating additional hazardous waste streams • for integrating biological processes with physical-chemical treatment TRP Chapter 6.3 18

  19. Key considerations • Waste reduction and avoidance by generators should always be a priority • Role of on-site vs off-site technologies • Need to consider residues from treatment processes and their disposal • Transitional technologies may be used until final high-quality installations are available TRP Chapter 6.3 19

  20. Chapter 6.3 Summary • Biological treatment of hazardous waste • optimises a natural process • is suitable for low concentration organic wastes eg sludges • requires good control of process conditions • is relatively low cost, effective and tolerant to changes in waste • is most widely used for wastewater treatment • may be on-site or off-site • new applications being developed TRP Chapter 6.3 20

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