Solid Wastes
A. Solid waste: EPA defines
it as "a discarded material"
·
Solid waste is best measured by weight,
because its volume can change due to compaction.
·
Solid waste includes: solids,
liquids, and contained gases (i.e., not just solid materials)
·
Solid waste excludes:
o
agricultural wastes returned to soil
o
mining and milling wastes returned
to mine
o
domestic sewage, and nuclear
materials (all are covered under other
laws)
There are two major categories
of municipal solid waste as given below:
1. garbage:
relatively decomposable wastes
(kitchen, food wastes)
2. rubbish:
relatively non-decomposable wastes
(paper,cloth, glass, metal)
B. Integrated Solid Waste
Management:
During its life cycle, solid wastes
are first generated, transferred, and then disposed, sometimes leading to
various environmental and health effects. This life cycle is illustrated below.
|
A
|
B
|
C
|
D
|
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|
generation |
> |
transfer |
> |
disposal |
> |
effects |
> |
Each of the above capitalized
letters (A-D) represents techniques used to manage solid wastes:
·
A = source reduction
·
B = resource recovery
·
C = remediation and treatment
·
D = compensation
Generally
speaking, the earlier in this life cycle that we can manage the solid waste,
the more problems that we can prevent.
For example, consider source reduction below:
1. source
reduction: to
re-evaluate and eliminate waste generation
Once the waste is generated, we must
collect it for transfer and disposal. We can also reduce the load by resource
recovery and treatment. If final disposal is problematic, we may need
remediation. Finally. if
unfortunate effects do occur, we must provide compensation (a highly
undesirable outcome!)
2. collection: the greatest cost of solid waste
management
e.g., garbage
trucks
4. transfer: temporary holding facilities
(for
collection, storage, some treatment)
5. treatment: to reduce volume, mass, or risk of
waste
6. incineration:
controlled combustion of waste
7. RDF: refuse derived fuel (i.e., waste is
incinerated)
8. mass
burn: where nothing is sorted before
incineration
9. controls: temperature (ideally 1400-1800 degrees
F.)
turbulence
(oxygen) -- grates:
rectangular,
vertical circular,
rotary
kiln, others
time
(continuous preferred over batch)
10.ash: solid residue that remains after
burning
(bottom
ash = ash at bottom of incinerator)
(fly
ash = ash from smaller airborne particles)
11.pyrolysis: burning
wastes with no added oxygen (i.e., "roasting")
12. composting: controlled biodegradation of
plant
and animal matter
13. humus: decomposed plant and animal matter
a
good soil conditioner (but a poor fertilizer)
14. windrows: long rows of compost (a composting method)
15. procedure: shred wastes (allows faster
decomposition)
spread
waste in thin layers (2"-6"):
carbon
layers: paper, leaves, sawdust
nitrogen
layers: grass, kitchen scraps,
fruit
activator
layers: manure (dog droppings, etc.)
soil
fertilizer
sprinkle
with water to maintain moistness
ventilate
periodically
16. problems: AVOID:
meat, grease, bones, and weeds
odors:
if ammonia smell, add carbon
if rotting smell, add carbon,
ventilate,
stop watering
if
breakdown is too slow:
add nitrogen, activator
maintain water and oxygen
17.
resource
any process where materials are recovered
recovery: rather than discarded
18. reuse: use
again in same way
(e.g., a coke bottle
reused in exactly the same way)
19. reclamation: (also
called "utilization") use in new ways
(e.g., coke bottles
mixed with asphault to form
"glasphault")
20. recycling: use raw
material in various ways
(e.g., cullet = ground
glass
thus,
a coke bottle could be recast, but
the
glass could be used in various ways)
22.
tipping fees:
charge to dump garbage at a disposal site
(i.e., $/ton)
as
tipping fees rise,
the
use of other methods becomes more feasible.
Figure
1.
A.
Features: A sanitary landfill is NOT an
open dump.
It has at least three design
features given below:
1. protective clay soils or
lining: synthetic liners (e.g., PVC, PE)
2. layers layers of
waste 8-10 ft. deep (after compaction)
(or
"lifts"): with intermediate
settling (preferably for 1 year)
before
adding the next layer
3. cover daily: 6 inches
material: intermediate: 12 inches
final
cover: 24 inches
2-4 % grade
(for proper drainage)
less than 30 degrees on side slopes
B.
Methods:
4. area: uses natural slope: valley or ravine
methods
low
area method
ramp method
5. trench: man-made
C.
Processes:
6. LFG: landfill gas
aerobic: a. lasts several days to several
months
anaerobic: b. mostly CO2 formation (acid formers)
c.
increased methane formation (methane producers)
d.
stabilized (roughly equal % of methane and CO2)
(lesser levels of NH3 and H2S)
rates: depend on temperature, pH (acid
inhibits growth),
moisture,
type of wastes
methane: explosive limit of 5%
7. Leachate: from waste itself,
or water entering landfill
high in
organics, heavy metals
D.
Daily concerns:
8. records: type and amount of waste received
(measure
by weight, because volume changes),
# and
type of personnel, equipment
monitoring
leachate and gas production
9. procedures: standby equipment
exposed
waste area is minimized
work
with prevailing wind
portable
fencing (prevent wind blown waste)
compact to 12-18
inch layers (4-5 passes of tractor)
E.
Long-term concerns:
10. space: land area needed
11. access: fences, signs
12. time: 20-40 years operation
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