Compostagem
- 1. Composting for Soil Remediation João Ricardo Sousa, UTAD
- 2. Overall Process Schematic Composting Rocks Excavated contaminated soil Rotary screen Amendment soil mix Treated soil to landfill Washed rocks to landfill Windrows Wash tank
- 3. Composting Amendment mix Windrows Screen Monitoring Rotavator
- 4. Process Description Composting Wet organic solids are oxidized to biologically stable forms such as humus Low moisture result in accumulation of heat Can be engineered to be aerobic or anaerobic process Since concentration of hazardous chemicals is often low, organic chemicals should be added to the contaminated soil to initiate process Hazardous chemicals can be broken down or biotransformed to innocuous end products
- 5. Process Application Composting Originally composting has been applied to agricultural, yard and kitchen wastes and biosolids Initial application to hazardous wastes in 1960s for treating biodegradable insecticides (e.g.. diazinon, parathion) Current applications cover petroleum hydrocarbons, explosives, and chlorinated compounds (e.g.. DDT, PCB, TNT) in soils and sediments
- 6. Design Considerations Composting High temperatures are desirable to enhance solubility and mass transfer rates Pile dimensions should be chosen to ensure microbial heat generation is greater than heat dissipated through the surface Since concentrations of contaminant is very small, the amendment materials must provide the necessary carbon, nitrogen and act as heat source as well
- 7. Design Considerations Composting Amendment materials should also include bulking agents to improve porosity Absorbent bulking materials are preferred to retain moisture (e.g.. straw, wood chips, rice hulls) Inert absorbent bulking materials are ideal (e.g.. inert synthetic chemicals) Bulking agents should be resistant to compaction and biodegradation
- 8. Design Considerations Composting Adequate acclimated microbial inoculum may be present in the contaminated soil Sewage sludge is often added to augment the microbial population Specially developed in the laboratory may be required for specific chemical groups Recycling composted soil can also provide additional viable microbial population
- 9. Design Considerations Composting Moisture is essential for microbial growth in transporting contaminants, nutrients, and oxygen across the cell membrane High moisture levels reduce porosity and therefore result in decrease microbial activity Optimum moisture level is ~ 50 to 80% of water- holding capacity
- 10. Types of Composting Systems Composting - Soil placed in closed reactor with mechanical mixing and forced aeration - Aeration by turning the pile manually or mechanically - Aeration by forced air injection Windrows Systems Static Mix Systems In-vessel System Open Systems Closed Systems
- 11. Windrows System Composting Pile Width = 3 to 4 m (10 to 12 ft) Pile Height = 1.2 to 1.5 m (4 to 5 ft) Overhead sprinkler system
- 12. Details of Windrow House Composting Overhead sprinkler system Aeration system Leachate collection system
- 13. Static Pile System Composting Pile height = 3 to 6 m (10 to 20 ft) Aeration system Leachate collection system
- 14. Static Pile System Composting Mechanical aeration by forced aeration or vacuum extraction Airflow controls temperature and provides oxygen Vacuum extraction minimizes emission of VOCs and off gases; but cools down the pile Forced aeration improves pile temperature by bringing in the heat of compression
- 15. In-vessel System Composting Better control of temperature and oxygen Emissions of VOCs and OH gases can be captured and treated if necessary Better treatment efficiency due to improved mixing and mass transfer Less affected by environmental and weather conditions Capital intensive