(4 2 3 )/8ab c d+− −
10.16 Return to Example 10.6 in this chapter. The overall greenhouse gas effect of a landfill is
sensitive to a number of parameters and assumptions. In Example 10.6, an assumption of 80%
gas recovery is used and leads to an overall greenhouse gas benefit of 0. 10 metric tons CO2e.
Leaving all parameters and assumptions in place used to solve Example 10.6, what is the
percentage of landfill gas collected that provides an overall benefit of reducing greenhouse gas
emissions.
10.17 What percentage reduction in yard waste would be required to reduce the NH4+ released in
landfill leachate by 1 kg per Mg of MSW? Assume only yard waste contributes to NH4+ in
leachate. Assume the waste composition provided in Figure 10.2 and Table 10.5. Assume all N
in yard waste is eventually released as NH4+.
Solution:
10.18 Daily cells for a landfill are operated so that the following conditions are maintained:
thickness of daily cover = 0.2 m; slope (horizontal:vertical) = 3:1; working face for refuse = 30
m; height of refuse = 3 m; and volume of daily refuse = 1,800 m3/day. The landfill is interested
in reducing requirements for daily cover soil over its 20 yr life and is considering three options.
Which option would be the best? Why?
Option 1: Increase height of refuse to 4 m.
Option 2: Increase daily refuse volume by 2000 m3/day.
Option 3: Decrease working face to 20 m.
Solution:
10.19 Estimate the landfill area required, in hectares, given the following specifications: daily
cover thickness = 0.2 m; total final cover = 1.0 m (in addition to daily cover); height above
ground before biodecay and settlement = 10 m; lift height = 3 to 5 m; depth below ground level
that waste can begin to be placed = 5 m; landfill site area is square; MSW generation rate =
100,000 Mg/yr; side slopes at 3 horizontal:1 vertical for daily cells and external slopes; working
face width = 8 m; open for disposal 360 days per year; 30 yr life; and in-place density of fresh
3
= 700 /MSW kg m
.
Solution:
( )( )( )
3
/
0.2 3 0.2 3 0.2
397 1 1 1
4.53 8
267.4
445.62
267.4 2,
30 (445.62 ) 365 30 4,879,539
daily cell
daily Cell
daily Cell
V = Vr 1 + T H 1 + G × T / L 1 + G × T / W
Vm L
VL
Total landfill volume for years L
××
= ×+ ×+ ×+ =
= +
= + × ×= +
{ }
( )
()
( )
( )
11 1 1 11 1 1 1 1
2 22 2
22
2
928,030
[ ( 2)( 2)] ( 2)( 2) :
3
2,928, 030 14
4,879,539 ( 2 3 14) ( 2 3 14)
3
2,928, 030 14
4,879,539 2 168 7,056 84
3
2,928, 030
4,879,539 14 1,176
L
h
V L W L Gh W Gh L W L Gh W Gh L W
LL LL
L
L L LL
L
L
L
=××+−−+××−− =
+ = × + −×× + × −××
+ =× − + +−
+=−
32
2
32,928
0 14 1,176 4,879,539 2,928,030
634.14
, 634.14 634.14 402,137
L
L L L solve for L
Lm
Since W L the area m m m
+
=−− −
=
= =×=
10.20 You need to budget for a new transfer station in your district. A similar transfer station
cost $1 million, but that station was 50 percent larger than yours. How much money should you
budget so that your local government will have enough money to pay for the new transfer
station? Assume that the economy of scale factor for transfer stations is 0.9.
Solution:
10.21 Go the World Health Organization Web site (www.who.org). Learn about a disease that is
transmitted through improper disposal of solid waste. What is the extent of the disease on a
global level?
Solution:
Students’ responses will vary.
10.23 Identify an engineering professional society that you could join as a student or after
graduation that deals with issues of solid-waste management. What are the dues for joining this
group? What benefits would you receive as a member while working in practice?
Solution:
Students’ responses will vary.
10.23 Determine the number of students currently enrolled full time at your university or college.
Then, using the information provided in Figure 10.2 and Tables 10.2 and 10.5, determine the
energy content associated with a day’s worth of solid waste that would be generated by this
population.
Solution:
Students’ responses will vary based on the number of students enrolled at their university or
10.24 Assume the population of the United States will reach 420,000,000 in 2050. Estimate the
annual mass of municipal solid waste that will be generated in the United States in 2050 and the
annual amount that will require landfilling (both answers in metric tons). Use information
provided in Table 10.2. Justify your assumptions on changes in solid-waste generation per
person and landfill disposal per person from now until 2050. HINT: Graph waste generation
versus time and also the percent of waste land filled versus. time and observe the trends. Make
your own assumptions (e.g., waste generation will be the same in 2050 as 2010; waste generation
will decrease back to 1960 levels; and/or the percent of landfill waste will decrease as recycling
becomes more mainstream or it will remain the same).
Solution:
Graph table 10.2 as shown below:
Waste Generation vs. Time
Students’ answers may vary but two potential answers may be:
It appears that the waste generated over time is following somewhat of a bell curve. If we
continue this trend we can assume that by 2050 the waste generation per person reverts back to
1960 levels and the percent of waste generation landfilled follows the negative linear decline to
25%.
In the worst case scenario we may assume that the waste generation per person and percent of
waste generation landfill remains the same in 2050 as 2010 (0.74 Mg per person per year and
54% is landfilled).
y = –0.9443x + 99.949
R² = 0.9366
0
20
40
60
80
100
120
Percent of waste generation landfilled
10.25 Non legume vegetable wastes have a moisture content of 80% and are 4% N (on a dry
mass basis). The vegetable wastes are to be composted with readily available sawdust. The
sawdust has a moisture content of 50% and is 0.1% N (on a dry mass basis) The desired C:N for
the mixture is 20. The C:N ratio for vegetable wastes is 11, and the C:N ratio for sawdust is 500.
Determine the kg of sawdust required per kilogram of vegetable waste that results in an initial
C:N ratio of 20.
Solution:
10.26 A mixture of organic materials is to be composted. The mixture begins with 40% moisture
and 80% of the solids are VS. Assume that 50% of the VS are lost through composting along
with 70% of the moisture. What is the moisture content of the final compost?
Solution:
Solutions Manual prepared by: Colleen Naughton, Ziad Katirji, Heather E. Wright Wendel, and
James Mihelcic
Environmental Engineering: Fundamentals, Sustainability, Design, 2nd Edition
James R. Mihelcic and Julie Beth Zimmerman, John Wiley & Sons, New York, 2014.
10.27 EPA provides five methods of composting at this web site:
http://www.epa.gov/compost/types.htm Develop a table that lists the five methods in one
column, and brief description of the method in a second column.
Solution:
Type
Description
Backyard or
Onsite
Composting
This composting can be implemented right outside your home, apartment,
community or business for food scraps and yard trimmings. Little space or
equipment is required but education is critical.
Vermicomposting
This composting uses red worms or garden filed worms to compost typical
compost items (feed scraps, paper, plants, etc.) in bins. This type of compost is
ideal for and often utilized at apartments, small offices, and schools.
Aerated (Turned)
Windrow
Composting
This larger scale (e.g. communities and businesses) form of composting is laid out
in rows of long piles or “windrows“. These winrows must be aerated mechanically
or manual to aerate them. There are ideal dimensions for these piles. Different
types of waste can be composted using this method such as grease, liquids, and
animal byproducts in addition to the typical yard wastes and food scraps.
Aerated Static
Pile Composting
This compost is formed into large piles with layers of bulking agents such as wood
chips and shredded newspaper for better air circulation. This method is used for
more homogenous mixes of organic waste such as food scraps, paper products, and
yard trimmings often from larger communities, landscapers or farms. Air blowers
may be required to better aerate the piles. This compost can be read in as little as 3
months.
In–Vessel
Composting
In this method of composting, organic materials are stored in large vessels such as
drums, silos, or concrete lined trenches. This uses less space than winrow
composting. A diversity of wastes can be composted in these vessels including
meat and animal manure. Some of these vessels can fit into restaurant or school
kitchens or larger scale containers can be used by food processing plants.
10.28 Estimate the total landfill costs (in 2003 Euros) for a situation where you must landfill (a)
75,000 Mg of solid waste per year and (b) 1,000,000 Mg of solid waste per year.
Solution: