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15 Cards in this Set
- Front
- Back
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What is sludge volume measured as?
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% solids; weight of dry solids in total wet weight
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processes used to concentrate sludge
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thickening and dewatering
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two specific methods of thickening sludge
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picket fence thickener and DAF
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name the two methods for de-watering sludge
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centrifuge (spins to remove liquid) and belt press ( presses to force liquid out)
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what are sludge drying beds?
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porous medium lets liquid drain out and sludge is scraped off (cheap and can yield high solids but are better suited to drier climate)
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considerations when applying sludge to land
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needs to be treated (pathogens and odour) must not overload soil ( can leach) -NZ guidelines for safe application of biosolids to land
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considerations when designing a landfill
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waste generation rate (incl pop. growth), design life (10yr minimum) , cover/seal material (some need clay) , allowing for buffer zones and access roads
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what are landfill liners and why are they used?
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seal landfill from soil to prevent gas and leachate loss; two types, impermeable soil eg clay or synthetic membrane. synthetics occupy less volume.
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what are the restrictions on the speed of degradation in a landfill (also relates to gas generation)
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no mixing; may have limited moisture, some organics are sealed in bags/containers, varying degrees of biodegradability.
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what are the four stages of gas and leachate generation?
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I - initial adjustment; II - transition phase; III - acid phase, IV - methane fermentation, V - maturation
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why does gas production need to be controlled?
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- odour prevention
- prevent methane release (greenhouse gas) - energy recovery - public safety (flammable and explosive) |
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what are the two broad approaches for collecting gas from landfills?
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- passive (rely on natural gas movement to vent gas)
- active ( blower or compressor to suck air out) , must avoid sucking air into landfill |
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what are the issues concerning leachate production from landfills?
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- moisture collects contaminants
- landfills often in valleys (naturally collects water) - use of run-off drains to divert water - rainfall must be handled also |
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what are the issues with collecting leachate from landfills?
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- want to avoid ponding on liner as pressure will build up causing a leak
- leachare needs to drain to a central pipe - if site is flat put terraces or perforated pipes to minimise distance for leachate to travel |
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How can leachate from landfills be treated?
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- disposed of as industrial effluent
- recycled through mature section to allow excess VFA's to be consumed (reduces cod and increases pH that can aide heavy metal removal) |
