Solid Waste Principles Exam 2

processing

alters physical characteristics of the waste stream or removed particular things from waste/recycling

separation

permits more efficient processing and management of waste components

refuse physical characteristics

particle size (air separators)

bulk density

angle of repose (storage/stacking

material abrasiveness

moisture content (combustion)

storage and processing operations

storing

conveying

compaction

size reduction

pulping

roll crushing

granulating

how is waste stored

combustion facilities

material recovery facility

combustion facilities

continuously fired and require sufficient storage for at least 2 days

material recovery facility (MRF)

storage is important to even out fluctuation in supply

dirty MRF accepts solid waste

clean MRF only accepts recyclables

design considerations of storing waste

public health (odor/rats and rodents)

fire (spontaneous combustion)

what is the maximum storage time of MSW

2 days

ways of conveying waste

rubber belted conveyors

live bottom feeders

vibratory feeders

screw feeders

drag chains

pneumatic conveyors

compaction of waste

good, decreases volume and saves money

shredding waste

good, make everything the same size, fairly homogenous, increase compaction, decreases landfill volume, reduces odor, reduces insects, stuff doesn’t blow away, no large food particles for rats

why is shredding good for fuel

allows for more uniform heating value, requires less excess air, and saves cost on energy and air pollution control equipment

types of separation

hand picking, trommel screens, air classifiers, magnets, eddy current, optical (glass & plastic)

eddy current

electric currents change magnetic field in conductor by circulating

types of landfills

open dumps, reactor, bioreactor, mineral, monofill, mechanical biological pretreatment, construction and demolition debris

what is the difference between a conventional landfill and a bioreactor landfill? (exam q)

water,

water is intentionally added to bioreactor landfills (increases stabilization rates) and only shows up in conventional landfills from rain or waste

bioreactor landfills have accelerated decomposition, improved leachate quality, increased gas generation rates, and improved solid waste stability

bioreactor landfills

anaerobic is used in the US

ways landfill gas can be collected

gas wells, gas flares

why is it challenging for liquids to move through a landfill? (exam q)

waste is compacted, low permeability covers

leaching

a landfill process, dissolution of materials from solid phase of landfill

promoted by liquid movement through landfill

primary path for removal of non-degradable materials (metals, dissolved OM, ammonia)

physical and chemical landfill processes

precipitation

reduction

sorption

volatilization

geotechnical landfill processes

compaction

settlement

interfacial shear stresses

surface erosion

potential landfill failure modes

slope failures

excessive and uneven settlement

erosion

interfacial surface failure

what is landfill leachate? (exam q)

liquid that forms when water percolates through solid waste in a landfill picking up contaminants from MSW

what affects leachate generation? (exam q)

leachate minimization, waste composition, addition of liquids, landfill age, climate, cover type

leachate treatment

young: biological treatment

middle aged: combination of biological, physical, and chemical treatment

mature/stabilized: physical and chemical treatment

how is leachate usually treated

discharged to a POTW or wastewater treatment plant

pretreatment of leachate

depends on discharge location, size of treatment plant, and biosolids quality

treatment of leachate

(direct discharge) depends on discharge location and permit requirements

biological treatment of leachate

sequencing batch reactors

conventional activated sludge

membrane bioreactors

moving bed biofilm/biological reactor

chemical treatment of leachate

precipitation/sedimentation

breakpoint chlorination (ammonia removed)

physical treatment of leachate

membrane filtration

evaporation

issues with landfill gas generation

odor

explosive danger

methane is a greenhouse gas

health hazards

groundwater contamination

pressure head buildup in landfill

landfill gas regulation

RCRA subtitle D & Chapter 17-701

concentration of methane cant exceed 25% of lower explosive limit in on-site structures

emission guidelines

established by clean air act

require: well designed/operated collection system

control device capable of reducing NMOCs by 98%

new regulations

lower the emission threshold

shortening time allowed for gas collection system installation

shortening time allowed for well field expansion

lower or remove the landfill size threshold

gas composition-major gases

methane 45-60% by volume

carbon dioxide 40-60% by volume

nitrogen 2-5% by volume

oxygen .1-1% by volume

ammonia .1-1% by volume

hydrogen 0-.2% by volume

trace gases <.6% by volume

purpose of emission measurements

monitor waste degradation, modeling evaluation and validation, regulatory compliance, and working towards sustainability goals (reducing greenhouse gas emissions)

what scales can emissions be measured at

area/point, whole landfill, regional, statewide

how can emissions be measured

flux chambers, drones/aircraft, eddy covariance flux towers, etc.

top-down emission measurements approaches (exam q)

satellite, towers, aircraft

bottom-up emission measurements approaches (exam q)

individual source measurements, chambers

how can landfill gas be used? (exam q)

liquid fuel for rockets, auto engines, or distributed generation of power (hydrogen, solid oxide fuel cell, micro turbine generators)

what does BOD:COD ration indicate

relative biodegradability of leachate (usually declines when methane starts forming)

relative biodegradability of leachate

BOD/COD

low = <.5

medium = .5-.75

high = >.75

leachate treatment

biological, chemical, evaporative, physical

landfill liner types

single, composite, geocomposite, double

geomembrane liner

synthetic sheets, man made with NO natural clay (HDPE, PVC, EPDM)

geosynthetic clay liner

both synthetic AND natural, a natural sodium bentonite clay layer sandwiched between 2 geosynthetic layers

single liner

compacted clay liner, geomembrane, or geosynthetic clay liner

composite liner

clay liners and geomembranes, geomembrane over compacted clay, geosynthetic clay, or both

why do leachate collection systems fail

clogging from particulate transport or chemical precipitation, clogging from biological material buildup, or pipe breakage/slope change

what happens when leachate collection fails

extra head on liner, side seeps, reduced leachate output, landfill instability