2-2 Municipal Solid Waste Generation Generation and Management of Solid Waste in the United States from 1960 to 2012 (in pounds per capita per day) 1960 1970 1980 1990 2000 2005 2010 2012 2.68 3.25 3.66 4.57 4.74 4.69 4.44 4.38 0.17 0.22 0.35 0.64 1.03 1.10 1.15 1.14 Negligible Negligible Negligible 0.09 0.32 0.38 0.36 0.37 0.17 0.22 0.35 0.73 1.35 1.48 1.51 1.51 0.00 0.01 0.07 0.65 0.66 0.58 0.58 0.57 0.00 0.01 0.07 0.65 0.66 0.58 0.52 0.51 2.51 3.02 3.24 3.19 2.73 2.63 2.41 2.36 179 203.984 227.255 249.907 281.422 296.410 309.051 313.914 _ ::;= yard trimmings, food scraps, and other MSW organic material. Does not include backyard composting. :=r; stion of MSW in mass burn or refuse-derived fuel form, and combustion with energy recovery of source -~_~ ...••..•.-z..erials in MSW (e.g., wood pallets, tire-derived fuel). - recovery minus combustion with energy recovery. Discards include combustion without energy recovery~ __ not add to totals due to roundinq. MSW Generation, kg/per capita, Kaunas, LT,2010 ~------------------~--------------~--- --- ~~-----------1r-:-------------; • Hazardous • Wood • Terrapaks Other inorganic • Yard waste • Glass • Other organic • Food waste • Other metals • Ferrous metals • Plastics Paper and cardboard ::xample for seasonal changes in household waste composition. Source: [32] III WI ,. I ctln om n ' ant 9 'f W dy bicm I~ s. In addition, in diff " II ~O%.47 discussed here make II (anaerobic digestion < II I ere the specific organi I" sd or isolated, and the pr« ::omposting and anaerohl -sed of only one chemi , .e processes are numerou as one would describe 'Iii ANAEROBIC ons (absence of free oxygen] ::::H 4 ), carbon dioxide (CO) (NHJ, and a few others. T, ~l prompted wastewater trC,l1 waste solids and capture Ihl inery in the treatment plant ewater treatment plant is nllt J the potential for producin .erit. on dioxide can be calculaiul II) 2 + dNH3 II If' (11 chemical compositioi f I III I II~ urln the anaerobic n ral formula for glucose is C6H,206; hence by the equation v , a = 6, b = 12, c = 6, and d = O. II ° (24 - 12 - 12)H ° (24 + 12 - 12)CH (24 - 12 + 12)CO h " 6+ 4 2 ~ 8 4+ 8 2 ,,""'12°6 ~ 3CH4 + 3C02 j(' that the equation balances. The molecular weights are 180 ~ (1 ) + 3(44); hence 1 kg of glucose produces 0.73 kg of CO2 and () I kg of CH4• Recalling that 1 gram molecular weight of a gas at , I indard temperature and pressure occupies 22.4 liters, the pro- dll cion of CO2 and CH4 from 1 kg of glucose is 746 liters each of III hane and carbon dioxide. 1111(' rtunately, the chemical composition of MSW is difficult, if not impos- ", (I d t rrnine, although some attempts have been made to do so. The best 11111 IIIW tion is that the organic fraction of refuse can be described by the "t/1 II rmula C99H1490S9N. With this formula, the previous equation esti- II Ih. L the production of methane from a landfill is 257 liters of methane , I II I ra m of wet refuse (total, ...

1. 2-2 Municipal Solid Waste Generation
Generation and Management of Solid Waste in the United States
from 1960
to 2012 (in pounds per capita per day)
1960 1970 1980 1990 2000 2005 2010 2012
2.68 3.25 3.66 4.57 4.74 4.69 4.44 4.38
0.17 0.22 0.35 0.64 1.03 1.10 1.15 1.14
Negligible Negligible Negligible 0.09 0.32 0.38 0.36 0.37
0.17 0.22 0.35 0.73 1.35 1.48 1.51 1.51
0.00 0.01 0.07 0.65 0.66 0.58 0.58 0.57
0.00 0.01 0.07 0.65 0.66 0.58 0.52 0.51
2.51 3.02 3.24 3.19 2.73 2.63 2.41 2.36
179 203.984 227.255 249.907 281.422 296.410 309.051 313.914
_ ::;= yard trimmings, food scraps, and other MSW organic
material. Does not include backyard composting.
:=r; stion of MSW in mass burn or refuse-derived fuel form, and
combustion with energy recovery of source
-~_~ ...••..•.-z..erials in MSW (e.g., wood pallets, tire-derived
fuel).
- recovery minus combustion with energy recovery. Discards
include combustion without energy recovery~
__ not add to totals due to roundinq.

2. MSW Generation, kg/per capita, Kaunas, LT,2010
~------------------~--------------~--- ---
~~-----------1r-:-------------;
• Hazardous • Wood • Terrapaks
Other inorganic • Yard waste • Glass
• Other organic • Food waste • Other metals
• Ferrous metals
• Plastics
Paper and cardboard
::xample for seasonal changes in household waste composition.
Source: [32]
III WI ,. I
ctln
om n '
ant 9 'f W dy bicm I~
s. In addition, in diff " II
~O%.47
discussed here make II
(anaerobic digestion < II I
ere the specific organi I"
sd or isolated, and the pr«

3. ::omposting and anaerohl
-sed of only one chemi ,
.e processes are numerou
as one would describe 'Iii
ANAEROBIC
ons (absence of free oxygen]
::::H
4
), carbon dioxide (CO)
(NHJ, and a few others. T,
~l prompted wastewater trC,l1
waste solids and capture Ihl
inery in the treatment plant
ewater treatment plant is nllt
J the potential for producin
.erit.
on dioxide can be calculaiul
II)
2 + dNH3
II If' (11 chemical compositioi
f I III I II~ urln the anaerobic
n ral formula for glucose is C6H,206; hence by the equation
v , a = 6, b = 12, c = 6, and d = O.
II ° (24 - 12 - 12)H ° (24 + 12 - 12)CH (24 - 12 + 12)CO

4. h " 6+ 4 2 ~ 8 4+ 8 2
,,""'12°6 ~ 3CH4 + 3C02
j(' that the equation balances. The molecular weights are 180 ~
(1 ) + 3(44); hence 1 kg of glucose produces 0.73 kg of CO2
and
() I kg of CH4• Recalling that 1 gram molecular weight of a gas
at
, I indard temperature and pressure occupies 22.4 liters, the pro-
dll cion of CO2 and CH4 from 1 kg of glucose is 746 liters each
of
III hane and carbon dioxide.
1111(' rtunately, the chemical composition of MSW is difficult,
if not impos-
", (I d t rrnine, although some attempts have been made to do
so. The best
11111 IIIW tion is that the organic fraction of refuse can be
described by the
"t/1 II rmula C99H1490S9N. With this formula, the previous
equation esti-
II Ih. L the production of methane from a landfill is 257 liters
of methane
, I II I ra m of wet refuse (total, organic plus inorganic,
assuming wet refuse is
, I, I I gradable organic). In using this equation, note that the
only carbon
I 1,111 I rticipate in the production of gas is from
decomposable materials,
It I () d waste and paper. Other organics, most importantly
plastics, do not
111" • to produce gas.

5. II,' two ways of generating methane are to capture the gases
produced in
11111 r to digest organics in an anaerobic digester using tanks
similar to those
I 11 W stewater treatment plants or another structure, such as a
horizontal orI" linder. Methane generation both in anaerobic
digesters and in landfills
II I II. d in this section, although a more complete presentation
of landfill gas
,,111I1 in is found in Chapter 8. Much of the following
anaerobic decomposition
111 liPI lies to both processes, however.
Anaerobic Decomposition in Mixed Digesters
I 'III a ic metabolic pathways for the decomposition or
degradation of wastes
"lfl(,/e (with oxygen) and anaerobic (in the absence of oxygen).
While an aerobic
( 111 ,iii ht be generally represented as
1"11111 organics] + oxygen ~ CO2 + Hp + NO; + SO~2 + other
products
MEE 5901, Advanced Solid Waste Management
Unit V Assignment
This assignment will allow you to demonstrate the following
objectives:
· Assess the fundamental science and engineering principles of
solid waste management.
· Examine the impact of solid waste on human populations.

6. Instructions: Biological treatment of municipal wastes are the
primary means for degrading organic matter and for stabilizing
the contents of the landfill. Both aerobic and anaerobic
processes are functioning in landfills and compost piles. The
majority of regulations are set up to protect these biological
populations from being killed off or limited in their ability to
complete the degradation cycle. The methane by-product can be
used as an energy source to help reduce operating costs and to
limit the release of a very strong greenhouse gas into the
environment. This assignment will allow you to further explore
these concepts.
Answer the questions directly on this document. When you are
finished, select “Save As,” and save the document using this
format: Student ID_Unit# (ex. 1234567_UnitI). Upload this
document to BlackBoard as a .doc, docx, or .rtf file. The
specified word count is given for each question. At a minimum,
you must use your textbook as a resource for these questions.
Other sources may be used as needed. All material from outside
sources (including your textbook) must be cited and referenced
in APA format. Please include a reference list after each
question.
1) Navigate to the CSU Online Library and review some articles
on landfills and on compost piles. This assignment is not about
summarizing these operations but about analyzing and
comparing the differences between these two fundamental
principles of solid waste management. Describe when and why
each of these fundamentals is appropriate for use to manage
municipal solid waste. Include in your discussion details about
the differences of microbial mechanisms, the end products of
degradation, and of factors that help and harm the performance
of these operations. How effective is each one? (Your total
response for all parts of this question should be at least 500
words.)

7. 2) A community of 62,000 does not have a municipal recyclinge
program, and they it sends all of their its refuse to the
municipal landfill. Will the landfill generate enough natural gas
to meet the needs of the city if the municipality needs to
annually generate 10 million cubic meters of natural gas
(methane) and the city collects all of the methane that is
generated? How will this affect the population of the city?
Explain your answer. (Your total response for all parts of this
question should be at least 300 words.)
MEE 5901, Advanced Solid Waste Management 1
Course Learning Outcomes for Unit V
Upon completion of this unit, students should be able to:
1. Assess the fundamental science and engineering principles of
solid waste management.
7. Examine the impact of solid waste on human populations.
Reading Assignment
Chapter 6:
Biological Processes

8. Unit Lesson
The two key biological operations that are used in the treatment
of municipal solid waste are composting and
landfilling. Composting is an aerobic process. This is why
compost piles need to be periodically turned to
allow oxygen to diffuse into the microbes in the compost pile.
Compost piles are ideal for treating highly
organic wastes that include food wastes, garden wastes, yard
and park wastes, and dewatered sludges from
municipal wastewater treatment plants. The biggest advantage
of compost piles is their ability to stabilize
wastes, which results in the volume reduction of waste
materials. Depending on the rate that organic
materials are applied to the compost pile and on the health of
the microbial population in the pile, periodic
additions of new waste can be made to the pile. Treating readily
biodegradable organic wastes in compost
piles results in carbon dioxide being emitted. Besides reducing
waste volumes, compost piles are capable of
destroying pathogens that are contained in the waste.
Stabilized waste that is free of metals and hazardous wastes can
be packaged and sold as a fertilizer.
Municipalities that use compost as a revenue source must
control the chemical content of the waste going
into the pile and perform toxicity and metal testing on the
stabilized contents to confirm the safety of the
product. In the case where stabilized compost piles are not to be
placed into commerce, the compost can be
used as a soil additive to agricultural lands (which also requires
testing to confirm the absence of toxic
compounds and metals) and as a soil fill to reclaimed land.
The microbial population of municipal landfills operates by a

9. different biological mechanism. Landfills operate
by means of anaerobic processes that treat and stabilize waste
refuse. Anaerobic degradation processes
function in the absence of oxygen. This category of microbial
treatment is associated with the production of
methane that can be captured, compressed, and used as a fuel
source to support combustion processes
capable of producing energy and electricity. The methane
generated by landfills can have an adverse impact
on atmospheric conditions. Methane is 25 times more powerful
than carbon dioxide when their global
warming impact is considered (United States Environmental
Protection Agency, n.d.). This is one of the
reasons that methane is collected for energy conversion. Even
landfills that have a well designed methane
gas collection system will experience at least a 10% leakage
rate to the atmosphere.
In Europe, mechanical-biological treatment of municipal solid
waste is becoming popular. Mechanical
treatment utilizes separation processes like shredding and
crushing operations to prepare the waste for
composting or for landfilling. These combination operations
break down the refuse into particle fractions. With
a standardized particle size, municipalities in Europe have
experienced a 40 to 60% reduction in the amount
of waste going to landfills. The European Union (EU) also has
experienced that by using separation
processes as a pre-treatment, it changes the waste profile and
particle size of what goes into landfills. This
has resulted in pulling out readily degradable organic content
from the landfill that leads to a reduction of the
generation of methane by 95%.
UNIT V STUDY GUIDE

10. Role of Biological Processes in
Stabilizing Municipal Solid Waste
MEE 5901, Advanced Solid Waste Management 2
UNIT x STUDY GUIDE
Title
Europe is also developing advanced technologies for treating
municipal solid waste. These include in-vessel
treatment processes that can be located inside a building
structure. These include tunnels, vertical towers or
silos, rotating drums, and housed bays with forced mechanical
aeration and agitation.
Tunnel composting utilizes rectangular vessels that use push
walls for moving the refuse through the system.
Tunnels operate in a batch mode, but new continuous flow
systems are starting to be piloted. These units are
loaded from the top and aeration is through pipes and slats in
the floor. Cool air is used both as an oxygen
source and for keeping the temperature in the correct range.
Moisture is added to the compost by an
overhead spray system.
Vertical compositing operates as a plug flow reactor that
continuously moves the refuse through the system.
Waste enters the top of the tower and is removed from the
bottom. These tower systems mostly utilize a

11. passive aeration system, but where there are multiple chambers
that may be utilized, forced aeration systems
become necessary.
Rotating drums also operate in a continuous flow through
system. The refuse is mixed by the baffles during
the rotation of the drum. Aeration can be either passive or
forced depending on the amount of refuse being
treated. The drum is unique in that it can break open plastic
bags and release the contents. The energy of
rotation breaks the size of the larger materials, and, with a long
enough retention time, the unit can eliminate
the need for a shredding operation.
Long bays inside of buildings store waste in piles. Augers are
primarily used to turn over the waste piles to
allow oxygen to penetrate to the microbial populations. During
the turning process, the refuse is moved
towards the end of the pile. The floor is often fitted with a
forced air system to keep the piles aerobic and to
keep a high rate of refuse stabilization. Odors are captured and
prevented from escaping to the inside of the
building and to the outside by a negative pressure system and
high room air exchange rate. The air
containing the odor is scrubbed in a chemical bath that destroys
the odors.
Another interesting technology is to dry the refuse as a
pretreatment step referred to as bio-drying. The waste
is heated, and air is passed through the heated refuse, which
dries the waste and lowers the water content of
the mixture. The efficiencies of mechanical and separation
technologies are greatly improved when the waste
enters these unit operations in a dry condition.
Advanced treatment processes produce a superior compost

12. product for sale in commerce. The EU is
adopting manufacturing technologies and principles to treat
municipal solid wastes. The revenue that is
generated from the recycled materials pulled out of the waste
helps to offset the high capital and operational
costs of the equipment and staff needed to operate and maintain
these systems. Keeping readily degradable
organics out of the landfill greatly reduces the amount of
methane that is generated and that needs to be
captured and managed. The use of compost piles also treats
refuse that could go into the landfill, which
reduces the operating life of the facility for the community. By
keeping organics out of the landfill, obnoxious
odors are not generated and emitted into the atmosphere and
downwind communities.
In Europe, land is at a premium, and wastes are generally
handled on a regional basis rather than by each
individual community. The EU driver is a lack of available
space while the driver for municipalities in the U.S.
will be economics. For now, due to the high costs of using
advanced treatment technologies, technology
adoption in the U.S. will be low and limited to regions with a
high density population. However, this may
change as landfills built in the 1980s begin to fill up and new
facilities become very costly to design, build, and
permit. Municipalities will begin to look to privatize these
services, and it will be these service providers who
will begin to implement many of these technologies as they look
to regionalize solid waste treatment for the
communities in which they operate.
Reference

13. United States Environmental Protection Agency. (n.d.).
Overview of greenhouse gases. Retrieved from
https://www3.epa.gov/climatechange/ghgemissions/gases.html
MEE 5901, Advanced Solid Waste Management 3
UNIT x STUDY GUIDE
Title
Suggested Reading
The topic of treatment of organic wastes, which is covered in
this unit, is explored more in the article below.
Take a few minutes to read this article to gain a deeper
understanding of this topic.
Zupancic, G. D., & Grilc, V. (2012). Anaerobic treatment and
biogas production from organic waste. In S.
Kumar (Ed.), Management of organic waste (pp. 3-28).
Retrieved from
http://www.ewp.rpi.edu/hartford/~ernesto/S2014/SHWPCE/Pape
rs/SW-
BiochemicalTreat/Zupancic-OrganicWaste-AnaerobicTreat.pdf
http://www.ewp.rpi.edu/hartford/~ernesto/S2014/SHWPCE/Pape
rs/SW-BiochemicalTreat/Zupancic-OrganicWaste-
AnaerobicTreat.pdf

14. http://www.ewp.rpi.edu/hartford/~ernesto/S2014/SHWPCE/Pape
rs/SW-BiochemicalTreat/Zupancic-OrganicWaste-
AnaerobicTreat.pdf
I
CSU Math Center | 1-800-977-8449 x6538 | [email protected]
Math Center Requests: Math Center Request Form
Natural Gas Generation at a
Landfill
LINK:
http://columbiasouthern.adobeconnect.com/p8uq6mujllb/
Problem: A community of 50,000 people does not have a
municipal recycling program, and it sends
all of its refuse to the municipal landfill. Will the landfill
generate enough natural gas to meet the
needs of the city if the municipality needs to annually generate
15 million cubic meters of natural gas
(methane) and the city collects all of the methane that is
generated?

15. Additional information:
* Each resident generates 4.38 lbs. of refuse per day (see p. 43).
* Each pound of refuse generates 257 liters of methane (see p.
239).
Solution
:
To calculate the quantity of methane
4.38 ��
������ ∙ ���
× 50,000 ������ ×
257 � ���ℎ���
�� �� ������
×

16. 1 �3
1,000 �
×
365 ���
1 ����
= ��, ���, ��� ��
Therefore, 20.5 million m3 of natural gas is produced per year.
Yes, the landfill will
generate enough natural gas to meet the needs of the
municipality.
mailto:[email protected]
https://mycsu.columbiasouthern.edu/student/forms/courses/math
-center-request/
http://columbiasouthern.adobeconnect.com/p8uq6mujllb/?OWA
SP_CSRFTOKEN=6a590a2ccc5ebcb1e022d036045805ab0797e3

17. 59cb0d297096c9f4a96d9b7ee1
Okay, this problem discusses determining if a community of
50,000 people who do not have a municipal
recycle program and they send all of their refuse to the
municipal landfill. The question is, “Will the landfill
generate enough natural gas (methane) to meet the needs of the
city if the municipality needs to annually
generate 15 million cubic meters of natural gas and the city
collects all of the methane that is
generated?”.
Here’s additional information you need to know. Each resident
generates 4.38 pounds of refuse per day,
and the information came from page 43. Each pound of refuse
generates 257 liters of methane, and that
would be on page 239.
So we’re literally going to see how much methane can be
created with the waste adding 50,000 people.
You use literally what you read in here: 4.38 pounds of refuse
generated per person, per day times
50,000 people. So we’ve got that number. We’ve taken care of

18. this. And now, this is where you kind of
have to think about, “what else are we talking about?”. Here’s
our additional information. The 257 liters of
methane and that’s per pound of refuse—that’s what it says
here—per pound. So there’s that. And then,
we are going to convert that to cubic meters because here’s
what we’re looking for: will there be enough?
At least, you’ve got to have at least 15 million at the minimum.
So 1,000 liters is equivalent to one cubic meter, and then we
have 365 days in one year. So we have
pounds, and pounds are gone. And then we have our people, and
then our day, and then our liters, and
the year is part of this.
So we literally take the 4.38 and multiply by 50,000, and
multiply by 257, then multiply by 365 equals.
Then, divide it by 1,000, and you will get 20,543,295 cubic
meters per year. I didn’t write per year here, of
methane, which is plenty.
So as long as it at least generates 15 million, well it generates
20 million. So the answer is yes, the landfill
will generate enough gas to meet the needs of the municipality.

19. 11111"11 1 III 'I III HIiIIl'1 ill
IIII I /10111 1111' II I ,Ill, I /11'
'I Willi WOldt! h' III(' II flIH' I 1'111 It
01 111111 1111/ uuu ('nil Iw III Iii I
I I,O'VtI I -cov 'I Y or 111,11,', ,II ,
III' , 1'''1('1, will I will I I' tlu 1'"11
0/ 111' , Il'a I with res] I'll tll
m.u ','I,tI /?
5-33_ A ordlng I Pig II' - 0, is II I'll
10 1111)1 t Iy s parat one 01 1111
m t rials from th oth 'I' Ihl"" I
your answer.
5-34_ Using Figure 5-27, what is IIH'
advantage of the susp nett' I I 111
magnet over the other two IYlh"
of magnets?
/

20. . /
gical Processes /
I 1 r fuse contains ab.o_ut~75%organic material, which can be
con-
I l us ful energy by combustion, as discussed in the next
chapter, or
lul products by biological processes, which is the topic of this
chapter.
I h three components of MSW of greatest interest in the
bioconver-
II I rocesses are qarbaqe (food waste), paper products, and yard
wastes.
III J ir age fraction of refuse varies with geographical location
and season.
I I Illy habits, of course, affect its composition and quantity, as
does the
I II lnrd of living. Kitchen garbage grinders in more affluent
communities

21. " II r r much of the putrescible waste from the refuse stream to
the sewer-
I' y tem, and the reduction of the garbage fraction is a
continuing trend
I" United States and in many other countries.'
rhe garbage fraction also has by far the highest moisture content
of
IIY nstituent in MSW, but the moisture is rapidly transferred to
absorbent
11,11 ials (such as newspapers) as soon as contact is made.
Garbage also
, 1 J to be well mixed in MSW, and therefore it is often
difficult to find
h 11 ifiable bits of garbage in mixed refuse other than the large
pieces, such
range peels or apple cores. Garbage is even better distributed in
MSW

22. 11111 waste is shredded.
The fraction of paper in MSW tends to remain fairly stable
throughout
IIII year. However, the total amount of paper discarded has
been decreasing.
Yard waste generation is seasonal." For example, in some
climate
I 11 s there is essentially no yard waste generated during the
winter months.
237
In 1'1 11, IiI m unt ci y. r I w, I
reflecting th w th ,An 1m I •
yard waste is the amount of lignin HI
decompose in biological processes, A th nt g
increases in yard waste, the lignin cont nt in r 5 5, In ad

23. tree species the lignin content varies from 15 to 40%,47
The two methods of biological conversion discussed h I C
of the organic fraction of refuse, The methods (anaerobic dl
composting) are broad-spectrum processes, where the spe in I II
I "
responsible for the bioconversion are not identified or isolated,
dill III,
cesses are described by empirical data, Because composting n ~
.III I ,
digestion do not begin with raw material composed of only 01 I"
,,,I
the specific biochemical reactions involved in these processes
ar 1111111,
and therefore it is not possible to approach them as one would d
',I II11
hydrolysis of cellulose,
()( Iy I t
i i 11, II lill

24. 6-1 METHANE GENERATION BY ANAEROBIC
DIGESTION
When organic matter decays under anaerobic conditions
(absence of free II I' I
the end products include gases such as methane (CH4), carbon
dioxide (I II
small ~~ounts of hydrogen sulfide (H2S), ammonia (NH3), and
a few 01""1 I
recognmon long ago that methane is an excellent fuel prompted
wastew.uei II
ment plant design engineers to digest (decompose) waste solids
and captuu II
gas for use in heating buildings and running machinery in the
treatment 1'1 I
While the quantity of methane generated in a wastewater
treatment plant I II
sufficient to consider its conversion to pipeline gas, the
potential for PI()dlllll
pipeline gas from decomposing refuse has a lot of merit.
Ideally, the production of methane and carbon dioxide can be
c.lI"tlIH
using the following equation:

25. C H ON + (4a - b - 2c + 3d)
a bed 4 H20 ~
(
4a + b - 2c + 3d) (4a - b + 2c + 3d)
8 CH4 + 8 CO2 + dNH3
Example 6-1 illustrates how this equation can be used ifthe
chemical compos 11111
of a material is known.
f C 1"111 (II, 111111111111
n ral formula for glucos i C611'2 6; h nc by the equation
= 6, b = 12, c = 6, and d 0,
H 0 (24-12-12)HO (24+12-12) (24-12+12)
~ '7 6 + 4 2 ~ 8 CH4 + 8 C
IIH,P6 -- 3CH4 + 3C02
N that the equation balances. The molecular weights are 180 ~
1(16) -I- 3(44); hence 1 kg of glucose produces 0.73 kg of CO2
and

26. () 27 kg of CH4. Recalling that 1 gram molecular weight of a
gas at
I ndard temperature and pressure occupies 22.4 liters, the pro-
luction of CO2 and CH4 from 1 kg of glucose is 746 liters each
of
III thane and carbon dioxide.
III) ~ rtunately, the chemical composition of MSW is difficult,
if not im pos
I hi 10 leterrnine, although some attempts have been made to do
so. Th best
1"11 Irna tion is that the organic fraction of refuse can be
described by th l'
III L I formula C99HJ490S9N. With this formula, the previous
equation 'sli
lit that the production of methane from a landfill is 257 liters of
methane
I I I) ram of wet refuse (total, organic plus inorganic, assuming
wet refus is
, I bl degradable organic). In using this equation, note that the
only carb n
II 1,111 participate in the production of gas is from

27. decomposable materials,
II II ,IS food waste and paper. Other organics, most importantly
plastics, do riot
1111111 ose to produce gas.
'I'h two ways of generating methane are to capture the gases
produced in
110111 or to digest organics in an anaerobic digester using
tanks similar to rhos
I" 11wastewater treatment plants or another structure, such as a
horizontal or
1I11.tIcylinder. Methane generation both in anaerobic digesters
and in landfills
"I u sed in this section, although a more complete presentation
of landfill gas
1,"111lion is found in Chapter 8. Much of the following
anaerobic decomposi tion
1111 applies to both processes, however.
1 Anaerobic Decomposition in Mixed Digesters
I IWO basic metabolic pathways for the decomposition or
degradation of wastes

28. aorobio (with oxygen) and anaerobic (in the absence of oxygen).
While an aerobic
111 n might be generally represented as
II implex organics] + oxygen ~ CO2 + H20 + NO; + SO~2 +
other products
the ana .rohk d '( OlliIH), rlun of' ()1l,1I III It' Ii ' II Iwd ,I
[cornpl x or), IIi 81 I water :OJ I :11.1I 11/ I Nil.:
The end products in aerobi d omp sil iOIl II '.111 Iill k, I
(}ss('ssilllJ,1I1l.ld.11I
energy to be used by decomposing org, ni!ltnll (tlwy :II" ,I th -
ir 1111,111'11I' hi
state). The products of anaerobic decorn] sition, on rh th r hand,
.1 III' I
energy. Ammonia and hydrogen sulfide could be slill furth r
oxidlzed, .111111
ane contains considerable energy.
The microorganisms responsible for anaerobic decomposition
(.111I" III

29. into two broad categories:
1. Acid formers that ferment the complex organic compound: III
II
simple organic forms, such as acetic and propionic a i Is. '1111I
II
organisms can be either facultative or strict anaerobes.
2. Methane formers that convert the organic acids to methan .
TlwsI' 11111111
are strict anaerobes and have very slow growth rates-two
('11.11.111111
that cause considerable problems in anaerobic processes ill W,I
II
treatment and will similarly plague anaerobic decomposition III
I. It
Methane formers arc very sensitive to various environmental
/.111111 I
are strict anaerobes and quite sensitive to temperature changes.
'('Wit .nu
ent groups of methane formers seem to exist: one group
(mesofJlli/, ) , IIIII
ing best around 30 to 38°C (85 to lOO°F) and a second group
(1/1('1 IlIfI/I/111
operating best around 50 to 5SoC (120 to 135°F). The metharu

30. IltllIl
also require stable and neutral pH. Sufficient alkalinity (resist.u
It. lit'
drop) should be present to prevent the pH from falling below
(1,/1 111111
methane formers are sensitive to the presence of toxic materia
I:,. 'III II
heavy metals and pesticides.
During the acid-forming stage, the first step in the process
involves I II ••
lular enzymes produced by acid formers, which break down the
large 11111111
organic molecules. For example, the enzymes cellobiase and
cellulase bl(',11 till
cellulose to glucose, and lipase breaks fat to shorter-chained
fatty acids. '1 "' pi
cess is energy consuming.
Other bacteria then metabolize the glucose and other products
into III
acids, mostly acetic and propionic acid. These simple organic
acids thcn : I I I
substrate for methanogens. This methane formation is performed
by a nun 1111I

31. organisms that have specific substrates and roles in the overall
reactio n. '11" 1
reactions
CH
3
COOH ~ CH4 + CO2
4CH
3
CH
2
COOH + 2Hp ~ 7CH4 + 5C02
for acetic and propionic acids, respectively, are actually the net
results oi " 1111
number of steps. The resulting gas varies in composition but
averages ,Iltllll
60% methane with a heating value between 500 and 700 Btu/ft"
(47()t) II
6500 kJ/m3) 3
The total amount of gas theoretically available from the
anaerobic dil',l'llllt I

32. of MSW is considerably more than has been captured to date in
pilot plant Lu III
ties. Aboul54% of th volatil solids have been found to pass
through the dil'.I'~hI
and have not been onvcrt d LO 1 and CH4·
Total gas 0.3
production
(m3/kg volatile 0 2
solids added) .
0.4
__ --6(fC
__ --5(fC
4O"C
__ -4S'C------//---
;'
;'
/

33. I
/
I
0.1
5 10 15 20 25
Digester detention time (days)
- ----------
6 1 Gas production from anaerobic digestion of MSW. Source:
Based on .
T d J C L
· bman "Energy from Refuse by Bioconverslon FermentatIon
an . . Ie / . 1 295Idu~ Disposal Processes/" Resource Recovery
and Conservation: .
Pinnll ,lOx 111:11('11111, ('1111 lit' d 'II 1111'/111111) ,1111
'I' Ihlt I H', 1011, IIIII! II
must be ntrolle II y 1'('111 lYIlIg poll'lIl .11 I I /I I '101'(' 111'

34. H'I lO 1111' 1111' II t
present in the dig st r th Y must l 'I '1IIOV('d II I I III lI011 01'
PI' '( (11111111111 III
latter method has b n su ssfully al'l I xl ln old '1'10 !'t'Il)( vc II)
'Ialll wlll: 111111
in wastewater treatment plant .7
MSW digestion might be des rib' I nil I he lc ny or 1" III uon I"
VI tI 1111
( organic) matter as
dS
-= -K5
dt d
where
S = concentration of the biodegradable material (measur d (S
vO!.11 II
suspended solids, or a specific material if the system f, d is
controlled), mg/liter at time t
Kd = decay constant, days "
t = time, days

35. This is simply a first-order decay equation, stating that the rate
of decay is pll '1"1/
tional to the organics remaining, a reasonable assumption if the
process 1';11(' I 11111
time dependent. After integration,
S
- = e-K,I
50
where 50 is the original organic solids concentration, at the
starting time I "
given in mg/liter.
The materials balance within a completely mixed continuous
digester wot III1 1t
[rate of input] - [rate of output] + [rate of positive or negative
accumulation] = [rate of net ch;lIl1~I'1
If the digester is operating at steady state, the net change is
zero, and
Q50 Q5----K5=0
V V d

36. where
Q = flow rate through digester, m3/day
V = volume of digester, m"
The accumulation term is negative because the organic material
is being des: r<IYI'I 1
The hydraulic residence time is t = Q/ V or
_ So - 5
t=---
Kd5
Hence, if Ka is known, the required residence time for any
reduction in solids 1.111
be calculated. Batch laboratory experiments can be used to
obtain values of I,,, 1'1
plotting the values of log 5/50 versus time and measuring the
slope as (Ki2.:() ')
Values of Kd for refuse slurries have not been reported.
The process kinetics also may be described in terms of the gas
produ. 1'./
instead of the volatile matter destroyed. Using a similar mass
balance, Pfelll'l
found that it was possible to describe the reactor performance

37. by the model
Co - C _
--"--- = K tC g
, 11Itl>(IlHIIll , Il'Odu( ti011 ,111.1Ihd"", , III UI II II
0,1,11'/111'1' 101,11'II
""UI P 'I' W"'111 volatllc : 1111 1111111 I .111111
d: Ily gas I 1'0 III Ii 11, lill'l'lI/I volll! II' III I
I Y 11'<uli I' sid n [im', (ill,I'~ rat nsta nt. days 1
"III I) hav two di tinct valu s. 'l'h' Il1lll.lIl'ill' Is rapl I and lasts
b tw ·n 5
d III 1,'Ys f Ilow d by a significantly I 1W 'I' 1', I '. '1', bl -1 is
a listing of the
illl' , AI 4~o there is a substantial dl' pin 1(8 from 40°C,
indicating again th .
I I' II (' of In sophilic and thermopbilic regimes in anaerobic
digestion.
1'/1' [uantiry of gas generated can be estimated by entering a
plot (su h (IS
111111 (1 I) at th calculated t (hydraulic residence time) and
reading off th g, I'

38. I'"" 11 () n. 13 ca use of the heterogeneous nature of the waste
and the fact tha t no I
111111' )1' ni s decompose, any theoretical calculations
probably would be fruit-
I III I' ~ I' , laboratory studies to determine kinetic constants for
a particular
II' 'n essary.
Potential for the Application
naerobic Digesters
II" Ih 1973 and 1979 worldwide oil crises, when many
communities were
III d ring waste-to-energy plants, anaerobic digestion was
viewed as a lower-
I I III I' environmentally friendly alternative method of
generating energy. AL
1I1I I III , much of the research was focused on mixed waste
low-solids anaerobi
III I ('S. However, for a variety of reasons, no large anaerobic
digestion plants
I" built.

39. 'I'h process is plagued by potential problems. There is no way to
ensure the
lilt ival of toxic materials before the waste goes into the
digesters, and "sour"
II .! I' (such as those encountered in wastewater treatment
plants) are a definite
II jUty.
Th problem of mixing a paper slurry has continued. Even pilot
plant scale
11I1 ng with fairly dilute slurries has been found to be a
problem. The desired
"I I! ncentration for these digesters is at 10%, which is a highly
viscous an I
1,1 6-1 Rate Constants, K for Gas Production in Anaerobic
Digesters
9
Rate Constant (day:")
, '"f rature, DC Initial Final
35 0.055 0.003

40. 40 0.084 0.043
45 0.052 0.007
50 0.117 0.030
55 0.623 0.042
60 0.990 0.040
1111 : [8J
thixotroplr lUll ,.111 W,llIll'Wl1! '1'111'111111'111PIIIIII "
wll'I' olhl. ('(II' 1'1111I I
normally rang fr III :1 10 51},1h,lllixlJ'H 111 IIlwIIY I ('('11 I
I rohl 'III. '1'1111'1md
have shown that typi al primary lig'MH'1 11'11110 II IV' old
2517h 01 I1III1
ume mixed-the remaining being d 'cd /ojIHI( ',111,'u 11"rot
lcms will HIIII'I' III 'I
refuse-digestion facilities as well. A I mou tnu on l)Joje tin
IIlorid, (0111 1111
break shafts on mixers because of the high fibrQLltl 'Olll nt fth
wnlll',
Large land areas are required by the digest rs. ( minimum 12
aen's (", hll)

41. a 1000 ton/day (900 tonne/day) plant." This an b a problem wh
'1'(' 11,1111111
costs prohibit long-range refuse movement and if the treatment
fa .ilit 11111 I
located on expensive urban land. And finally, the problem of
what to d(l 1111II
effluent and residue has not been solved. The sludge does seem
to Ul'W,111I I
ily (as it should) with all the fiber in it, but its ultimate disposal
is all ,HltlllllIlI
problem in the application of this process.
In the last few years there has been more interest in low-solids
(I S/l 11'.111III
total solids) anaerobic digestion of organic material. Toronto,
Canada bill II ,I 1111t
plant and is constructing a second plant (Figure 6-2).
Sacramento, alif()IIt1,111
has a small facility. These plants are designed to process a
source separated 11'1III
waste that is suitable for a low-solids facility. For example,
food waste is a d."11 IIII
feed stock but yard waste is not.
To manage all organics, European companies are building h igil

42. 1111,1
(greater than 20% total solids) anaerobic digesters. While some
plants PJ'()( I' 'I I till
source separated organics (such as food waste and green waste),
others pll I
Figure 6-2 Low-solids anaerobic digester. (Courtesy William A.
Worrell)
" 6-3 Anaerobic digestion tunnel. (Courtesy William A.
Worrell)
IIIlUll S that include a significant fraction of nonorganic. A
high-solids digestion
Ii 111is designed to feed and process "dry" material. Unlike a
low-solids system,
II I h generates effluent, a high-solids system recycles the
effluent to inoculate th '
11111tin ing feed material. Some designs have no mixing after
feeding, and the organ-
I III" placed into long, air-tight tunnels (see Figure 6-3). Other
designs slowly
IIII p rt the material through a vertical or horizontal
fermentation drum; this

43. I 1I11S in some mixing. Figure 6-4 illustrates the process
schematics of three of the
11111'l European manufacturers.
Pigure 6-5 shows a Kompogas anaerobic digestion plant near
Zurich,
, l~ rland, This plant accepts source separated organics,
including food waste
I 1'111 '0 ) "11 (I
1111l)I
II()I 1
Feed
Innoculum
Loop
Digested __ ~
Paste Digested

44. Paste
Digested
Paste
. Schematic drawing of various dry-solids anaerobic digesters.
Source: AcI,q Ii II
avivere, P., L. De Baere, and W. Verstraete, "Types of
anaerobic digest I', i."
rs, in Biomethanization of the Organic Fraction of Municipal
Solid Wast
/arez, Editor. 2002, IWA Publishing: Barcelona. pp. 111-140, as
used In CUll I III
Digestion Technologies Used for Treatment of Municipal
Organic Solid WII I
ntegrated Waste Management Board, March 2008. © 2008, 2010
by the .11111,,"I
vt of Resources Recycling and Recovery (CaIRecycle). All
nghts reserved. U'II 1111.
ure 6-5 Kompogas anaerobic digestion plant in Switzerland.
(Courtesy Willl,1111
Vorrell)

45. « I ria
2 Advantages and Disadvantages of Various Anaerobic
Digestion Systems
Disadvantages
llIill I.d I, hlll', 'I'll • W.I, Ii' , .Il!l'dd Ii 11 I II I III I I 1 II
h 1I'Iy,OI1l,11
II IIht! Oil h um Ii I' two to 1111'" W('('1 IIII 1111 11111 I" It •
"'suIIS in the
1.11111 oj' 111'Illun' for us' • s n 111'1. 'I'll I IIII III Ii
11I111('did( ligestat ,) is
I 1I1I11JlOst' I a 'I' bi ally. '1'10' PI'Otil1t I 111'111'111,111'
I II 1111I ( d quality
I 11111'1 lm 'nt.
III 1 I liLi n I dig st rs being 'illll'1' W '101 lli , III 'y nls an be
single-stage,
hll', I' b l h (a ilities. Single-stage Ii 1 '$( 'I'S are sirn] I l
design, build, and
I tll' 1111I p rate as a continuous ~ d YSl m. A two-stage
digester separates
lilt .Ii hydr lysis and acid-producing fermentation from the

46. methanogenesis.
I I 'ITISare also continuous feed systems. In Europe, most of
the systems are
I It I.IH' ystems. Finally, there are also batch digesters that are
fed initially and
II ,Iii IW I to operate. The advantages and disadvantages of the
various systems
Ii IWI1 n Table 6-2.
I. hnical
II logical
I onomic and
I nvironmental
Advantages
Derived from well-developed
wastewater treatment technology
Simplified material handling and
mixing
Dilution of inhibitors with fresh

47. water
hnical
Less expensive material handling
equipment
llIological
conomic and
nvironmental
Technical
Biological
Economic and
Environmental
No moving parts inside reactor
Robust (insert material and
plastics need not be removed)
No short-circuiting
Less VS loss in pre-treatment
Larger OLR (high biomass)

48. Limited dispersion of transient
peak concentrations of inhibitors
Cheaper pre-treatment and
smaller reactors
Very small water usage
Smaller heat requirement
Operational flexibility
Higher loading rate
Can tolerate fluctuations in
loading rate and feed composition
Higher throughput, smaller
footprint
Short-circuiting
Sink and float phases
Abrasion with sand
Complicated pre-treatment
Sensitive to shock as inhibitors spr
immediately in reactor
VS lost with removal of insert fraction In
pre-treatment
High consumption of water and heat
Larger tanks required

49. Not appropriate for wet (TS < 5%)
waste streams
Low dilution of inhibitors with fresh
water
Less contact between microorganisms
and substrate (without inoculation loop)
Robust and expensive waste handling
equipment required
Complex design and material
handling
Can be difficult to achieve true
separation of hydrolysis from
methanogenesis
Larger capital investment
I
I
Dranco

50. Biogas
I 0111101-1 I
ni()gil,
Feed
Innoculum
Loop
Digested
Paste Digest d ~
Paste
Digested
Paste
Figure 6-4 Schematic drawing of various dry-solids anaerobic
digesters. Sourc-: 1( 1111,j
from Vandevivere, P., L. De Baere, and W. Verstraete, "Types
of anaerobic digest I', I, ,I
solid wastes, in Biomethanization of the Organic Fraction of
Municipal Solid Wast "/

51. J. Mata-Alvarez, Editor. 2002, IWA Publishing: Barcelona. pp.
111-140, as used in 11111111
Anaerobic Digestion Technologies Used for Treatment of
Municipal Organic Solid W,I I
California Integrated Waste Management Board, March 2008. ©
2008, 2010 by th (11111, ,"
Department of Resources Recycling and Recovery (CaIRecycle).
All rights reserv d. lJ'" I
permission.
Fiquro 6 5 K mp d Il,) r ic dlllP 111111111 1111111 w II dill l,
( 11I1 'yW11I11I1I
11 W"", "'
6
Advantages and Disadvantages of Varlou
III rl
, I" Ie I
III n mle and
Illvlr nmental

52. hnlc I
II n mle nd
l/lvlr nm nt I
It Ilnle I
Advantages
Derived from well-develop d
wastewater treatment technol y
Simplified material handling n
mixing
Dilution of inhibitors with fre h
water
Less expensive material handlh
equipment
No moving parts inside r act r
Robust (insert material and
plastics need not be remov d)
No short-circuiting
Less VS loss in pre-treatm nt
Larger OLR (high biomass)

53. Limited dispersion of tran i I1t
peak concentrations of inhibit I'
Cheap r pre-treatm nt nd
sm II r r actors
V ry sm "W t r us
Sm " r h t r qulr m I1t
III 11
·dvantag of V rlou Annol',ohlll In f m
.al
Advantages
Simplified material handling
Reduced pre-sorting and treatment
Separation of hydrolysis and
methanogenesis
Higher rate and extent of
digestion than landfill bioreactors
Low cost
Appropriate for landfills

54. lie and
Tlental
111111111 I I
within 15-20 min t 60"
°C and within 15-20 mln
Less complete degradation I III ,11I1
(leach bed systems)
6-1-3 Methane Extraction from Landfills
Landfills are very large anaerobic digesters. However, unlike
the pn-vluu I,
cussed facilities, landfills are not optimized for gas production.
SOI11('«uunm
ties have tried to create a bioreactor landfill to increase the rate
of stabi I i:tull 1111 I
gas production. A bioreactor landfill is operated to rapidly
transform a II( I I II III '
organic waste. The increase in waste degradation and
stabilization is it colliI'll I
through the addition of liquid to enhance microbial processes,
Liquid IIIIi

55. added to almost the field capacity of the landfilL Field capacity
of the 1.111111111
the point at which the landfill is saturated with water prior to
any per 01.11"III I
can range from 35 to 60% moisture. To achieve field capacity in
wast . SI.11I Itl
10 to 20% moisture requires between 40 and 80 gallons per
cubic yard of WII 4
The extraction and use of gas from landfills is discussed in
detail in 1I,IPII" I
Composting differs from the previously discussed anaerobic
process in 111.11 II I
aerobic process, and the end product is the partially
decomposed organic 11.11 II!
Composting is often promoted as a "natural" process of solid
waste treauurut I
reason for this reputation is that compost piles can be readily
constru It'd II II
backyard, and the product is a useful soil conditioner. It is little
wonder, Ihi'll hi
that municipal engineers and city councils are besieged by
citizens grOllpN11111
that composting be initiated in their community in place of
alternative solu I I

56. disposal schemes such as landfilling and combustion, which
many people v
a waste of money and natural resources.
6-2-1 Fundamentals of Composting
Aerobic microorganisms extract energy from the organic matter
through a St'll
exothermic reactions that break down the material to simpler
materials. '1'111' " I
aerobic decay equation holds:
[complex organics) + oxygen ~ CO2 + Hp + NO~ + SO~-
+ [other less complex organics]
+ [heat)
6-2 COMPOSTING
Ihls decomposition, the temperature increases to.about 70°C
(160°F) ~n
,11. perated composting operations. As the reaction develops,
the ea.,~Y
III III H rs are mesophilic bacteria followed after about a week
by rhermophili
II I ,, In rinomycetes. and thermophilic fungi." Above 70°C,

57. spore-fon~lI1g
. d . t As the decomposition slows, the temperature drops.
1111, I! ormna e. d illi d
I 1111 ophilic bacteria and fungi reappear. Protozoa, nemato.
es. mi ipe es.
t 1111118 are also present during the later stages. The
concentratIOn of dead and
III I II nnisms in compost can be as high as 25%Y . .
I II' levated temperatures destroy most of the path?gemc.
bactena, eggs;
t f the more common pathogens and then survival at ele:ate~I I,
. orne 0 hili t g IS
h in Table 6-3 The product of thermop 1 lC compos in11" IIIIIIr
S are s own 1 . ....
III .illy free of pathogens. All potential pathogens, including
resistant parasrtes
.1 As aris eggs and cysts of Entamoeba hi5toly~ica, are
destroyed." . .
ritical variable in composting is the moisture co.ntent. If the
mlXt~lre IS

58. .1 ,Ih microorganisms cannot survive, and compostmg stops. If
there. IS to~
1 II w.u r, the oxygen from the air is not able to pe~etrate to
where the microor-
, I 1 are. and the mixture becomes anaerobic. TyplCally
compos~ should have a.
t fb tween 400/0 to 60% The right amount of moi sture.
whetherI 1111" onten 0 e ,I . I'd
I W t r sludge or other sources of water, that needs to be added
to the so 1 S
IIII v just the right moisture content can be calculated from a
simple mass
111111 :
M = moisture in the mixed pile ready to begin compo sting, as
percent
p .
moisture
M. = moisture in the solids, such as the shredded and screened
refuse, as
percent moisture

59. In'
and 01 dv nt
Criteria Advantages
Simplified material handling
Reduced pre-sorting and treatment
Separation of hydrolysis and
methanogenesis
Higher rate and extent of
digestion than landfill bioreactors
Low cost
Appropriate for landfills
Less complete degradation rOil/ ull
(leach bed systems)
Technical Comp ctlon prevents p r
leachate recycling
Variable gas production in
systems

60. ~ Biological
ti;:;-
u
"in
~ Economic and
Environmental
Source: [44]
6-1-3 Methane Extraction from Landfills
Landfills are very large anaerobic digesters. However, unlike
the prcviouvlv II
cussed facilities, landfills are not optimized for gas production.
Som 0 (011111111
ties have tried to create a bioreactorlandfill to increase the rate
of stabil iZ.1111I1II
gas production. A bioreactor landfill is operated to rapidly
transform and dl" I
organic waste. The increase in waste degradation and
stabilization is accorupll It
through the addition of liquid to enhance microbial processes.
Liquid 11111I

61. added to almost the field capacity of the landfill. Field capacity
of th 1.111111II
the point at which the landfill is saturated with water prior to
any percolnriuu II
can range from 35 to 60% moisture. To achieve field capacity in
waste SI.III "I
10 to 20% moisture requires between 40 and 80 gallons per
cubic yard of W,I I
The extraction and use of gas from landfills is discussed in
detail in Chapu-t /I
6-2 COMPOSTING
. . the temperature in r asl'~ 10 .Ihl
I 111 d composltIon, ,
I I .. d osting operations. As th 1"L°II(11011
I WI'II·op rate comp I
.., hilic bacteria followed aft 'I' ;1)OUI ,I
111111,IS are mesop d th hilic fungi.') 11 nv'
,I I . linomycetes, an ermop
I, • . As the decomposition slows, IIII'
, I ~ I r dommate. p' ,.. b . nd fungi reappear. I' ( :/,0., 11

62. 1111 (phlhc actena a '1'1
I nt during the later slag s. W DillIIIIns are a so prese b hi h
as 5(!/c1 Il
IItrflnisms in compost can e as 19 .
"I [1' d atures destroy most f the 1.111
IIII' levate temper
ome of the more common pathogens and 111'
I I . hown i Table 6-3 The produ ( of IlwlIlIt ur s are sown m·
.
11 I. f th ns All potential pathog ns, 11)(111
lit .11 free 0 pa oge . . I '. '. I
. d cysts of Entamoeba hlSto .yl IUI, .lIl (I I As ans eggs an .
. . I . bl in composting is the moisture ullritica vana e l
. isms cannot survive, and ornpos: I
I 111 mlCroorgalll, I , th .' ot able to p 'IWII',II,I w.u r, the
oxygen from e air IS n ..'
. and the mixture becomes anaerobIC: l'ypl all
I II are. fb tween 40% to 60%. The right t'lI1HlIlI

63. II 111' ontent 0 e h ' I
I d ther sources of water, t at n Cl S (11 w,I r s u ge or 0 I" I
. th . ht moisture content can be a (1 .1111II v )ust e ng
, 1111I :
Composting differs from the previously discussed anaerobic
process in thai II
aerobic process, and the end product is the partially
decomposed organic fl.1I lit I
Composting is often promoted as a "natural" process of solid
waste treatmrui I"
reason for this reputation is that compost piles can be readily
constructed II II,
backyard, and the product is a useful soil conditioner. It is little
wonder, 1III'Idill
that municipal engineers and city councils are besieged by
citizens grou ps 1111I
that composting be initiated in their community in place of
alternative solid WIII
disposal schemes such as landfilling and combustion, which
many people vn
a waste of money and natural resources.

64. 6-2-1 Fundamentals of Composting
Aerobic microorganisms extract energy from the organic matter
through a ~('I I
exothermic reactions that break down the material to simpler
materials. The IIi
aerobic decay equation holds:
[complex organics] + oxygen ---7 CO2 + Hp + NO; + SO~-
+ [other less complex organics I
+ [heat]
MX + lOaX,
Mp = a ~ + X
s a
. .n the mixed pile ready to bcgi I' I(M = moisture 1
P moisture
. in the solids such as the shrcdcl,'M = moisture 1 '
a percent moisture
X 111.1, (II oil I , wt'( 1111

65. x~= mHSS 01, III Ili' 01 (lIIWI 1)1111' 01 W,II 'I, lOll ('1'111.
,1. 111111' Iii I
s lids nt 'nl )1'the , 11Idl' I. Vi'l low, ,I goo I ," II III pi 1111
II
a tivat d slu Ig is LIS 'I, will hi, commonly li'ss 111,111 141;1
1;111
sn tons of a mixture of paper and other compostabl I t II iI. III
moisture content of 7%. The intent is to make a mixtur r 1I
111111
osting of 50% moisture. How many tons of water or Iu JI 11111
I
e added to the solids to achieve this moisture concentr ti II III
1111
ompost pile?
M X + 100X (10 X 7) + (100 X X)
M = a a s = s = 50
p X+X 10+X
s a 5
olving for Xs yields 8.6 tons of water or sludge.

66. : the water to be added is expressed in gallons instead of tons,
Ilw w,11I1
quation reads
MX+0.416W
M = a a s
p X + 0.00416 W
a s
Ws = water or sludge to be added in gallons. The other variable
,I
:l previously.
11 biochemical conversion processes (such as composting) are i
II I
ep operations. The first step is the decomposition of complex
moll'; lilt
materials into simpler entities. If there is no nitrogen available,
llil I I
lent of the process. If nitrogen is available, however, the second
sll'l' I I
sis of the breakdown products into new cells. These new
microuuuul I
Jute to the process, and the system operates in balance.

67. -ecause of the high rate of microbial activity, a large supply of
nilllllllI
ed by the bacteria. If the reaction were slower, the nitrogen
could be 1;'1 II
ICemany reactions are occurring concurrently, a sufficient
nitrogen SIII'III
ary. The requirement for nitrogen can be expressed as the CjN
ratio, ,~III/I
•.CjN of 20: 1 is the ratio at which nitrogen is not limiting the
rate ()f dl'llll
on. Above a CjN of80:1, thermophilic composting cannot occur,
b« ,III~I I
::n severely limits the rate of decomposition. Most systems
operate Iwl
extremes. Some researchers recommend an optimal CjN ratio of
p, I I
uio higher than this can increase the time to maturity. Nitrogen
can il;'1 III
19 at a Cj N ratio greater than about 40: 115 At higher pH
levels, the 1111111
~lost into the atmosphere as ammonia gas ifthe CjN ratio
exceeds I'; I
11'('1'1'',I'. dill 111 1111 1111111"1 I "I 11'0 i1l as the

68. merit
< rbon concentration in the mixture prior to composting, as
percent
r total wet mass of mixture
rbon concentration in the refuse, as percent of total wet refuse
mass
rbon concentration in the sludge, as percent of total wet sludge
mass
l tal mass of sludge, wet tons per day
" total mass of refuse, wet tons per day
11I1 p II of the compost pile varies with time, showing an
initial drop, then
I "I l between 8.0 and 9.0, and finally leveling off between 7.0
and 8.9.16 If
, '"IIIIOSL heap becomes anaerobic, however, the pH continues
to drop due to
, rh III f the anaerobic acid formers. As long as the pile stays
aerobic, there is
I 111I uffering within the compost to allow the pH to stabilize
at an alkaline

69. U,
I'
I
Table 6-4 Carbon/Nitrogen Ratios for Various Materials
C/N
Food waste
Raleigh, NC
Louisville, KY
MSW (including garbage)
Berkeley, CA
Savannah, GA
Johnson City, TN
Raleigh, NC
Chandler, AZ
Sewage sludqe
Waste activated
Mixed digested

70. Wood (pine)
Paper
Grass
Leaves
Sawdust
15.4
14.9
33.8
38.5
80
57.5
65.8
6.3
15.7
723
173
20
40--80
511

71. Source: [15]
( :/1 arbon concentration in the mixture prior to composting, as
per nt
f total wet mass of mixture
( . arbon concentration in the refuse, as percent of total wet
refuse mass
'I
( • arbon concentration in the sludge, as percent oftotal wet
sludge
"
mass
" EO total mass of sludge, wet tons per day
= total mass of refuse, wet tons per day
I
III ' I I r of the compost pile varies with time, showing an initial
drop, then
" I Ill!) l between 8.0 and 9.0, and finally leveling off between

72. 7.0 and 8.9.1(, Ir
II 1111 )st heap becomes anaerobic, however, the pH continues
to drop due (
II I 1m f the anaerobic acid formers. As long as the pile stays
aerobic, there is
lilt 1'111 buffering within the compost to allow the pH to
stabilize at an alkalin
X" ())aSH tJl'solllHI W~'1 tun
x, = mass of slu lgc or other SOLI I' ~. oi WIIII'I', lOll. ('I'll
11.1ru 1I11H'H 1111 I
solids content f th sill lg iH WI low, n goo I nS8UII1III)1III I
I
activated sludge is used, wh i h is '0 III m Illy I 88 LI a n
IIVtI1111111 I
Ten tons of a mixture of paper and other compostable m t
ri(11111,
a moisture content of 7%. The intent is to make a m ixtur -f I
(1111'
posting of 50% moisture. How many tons of water or slud II111
I
be added to the solids to achieve this moisture concentration ill

73. IIII
compost pile?
M = MaX. + 100X, = (lOX 7) + (100 X X) _
p X + X 10 + X-50
s a s
Solving for Xs yields 8.6 tons of water or sludge.
If the water to be added is expressed in gallons instead of tons,
the W.lI,t h
ance equation reads
MX+0.416W
M = a a s
p X + 0.00416 W
a s
where Ws = water or sludge to be added in gallons. The other
variahk-. IIH
defined previously.
All biochemical conversion processes (such as composting) are

74. ill i' I~I,
two-step operations. The first step is the decomposition of
complex mohr nh
waste materials into simpler entities. If there is no nitrogen
available, 111I'1 I
full extent of the process. If nitrogen is available, however, the
second SII'PI
synthesis of the breakdown products into new cells. These new
microonuu 1
contribute to the process, and the system operates in balance.
Because of the high rate of microbial activity, a large supply of
nillll}llll
required by the bacteria. If the reaction were slower, the
nitrogen could be li'i,,1
but since many reactions are occurring concurrently, a sufficient
nitrogen S'IIII"
necessary. The requirement for nitrogen can be expressed as the
C/N ratio, ,,;.,111'1, II
A C/N of 20: 1 is the ratio at which nitrogen is not limiting the
rate 01 lil'I lit
position. Above a C/N of 80: 1, thermophilic composting cannot
occur, bCI.11I~III
nitrogen severely limits the rate of decomposition. Most

75. systems operate 111'11
these extremes. Some researchers recommend an optimal CjN
ratio of )'1 I "
C/N ratio higher than this can increase the time to maturity.
Nitrogen can IlI'l'''"
limiting at a C/N ratio greater than about 40: 1. I 5 At higher
pH levels, the I Ii11111 I
will be lost into the atmosphere as ammonia gas if the CjN ratio
exceeds 1'1 I
1('('ll'.1 l'
,
'/1
Table 6-4 Carbon/Nitrogen Ratios for Various Materials
C/N
----_._-------_._-------_ .._-_._----------_._-_._-_ .._-
Food waste
Raleigh, NC
Louisville, KY
MSW (including garbage)

76. Berkeley, CA
Savannah, GA
Johnson City, TN
Raleigh, NC
Chandler, AZ
Sewage sludge
Waste activated
Mixed digested
Wood (pine)
Paper
Grass
Leaves
Sawdust
15.4
14.9
33.8
38.5
80
57.5
65.8

77. 6.3
15.7
723
173
20
40-80
511
Source: [15]
fus and
lev I. POI' 'dllt-"II )11,11 I IIII)(). ,'., IIII' Pillf II 1111 III II
IIHII '111111'1.111111 II I
post pile an be I' -ndll I 'nH I1HII,lI('d il l.rl ( 111101 ,II •
,lpp.lI'tIlli ,II
The pH also t ('~ ts nil I' gcn Ii S , IWi,III (' 111111011111
(NIII) '(,IP' ,I 11111111
nium hydroxide is form d ab v a I II vnlue 01 7,(), will I k
lll1pO I' "I

78. and gaseous NH . Thus, ffi ient 011 p st IP 'l'tllloIlS,which (
lel'illi' ,101111.1 I3 _
of 8.0, cannot retain nitrogen at a great I' 01 -ntrnrion than C/N
01 .Ihl HII I I
The time required for a compost pil I rnatur , d I -nds 011
811I1111111111
the putrescence of the feed, the insulation and (CI'(lion I I'
vidcd, lire (/11 I
the particle size, and other conditions. Usually, tw w ks is onsid
'I'cd II" II I
mum time for the adequate composting of shredd d rnuni ipal
I"('IIM'ill II
rows. Mechanical compo sting plants, using inoculation of
previously (111111111 I
materials, can accomplish decomposition in 2 or 3 days. This
mat I'inl Is 'I 11111
active, however, and usually requires further stabilization. 12
The completion of composting is judged primarily on the b sis
01.1 II
drop in temperature and a dark brown color. A more accurate
111(':181111 I I
determination of starch concentration in the compost. Starch is
readily (('1111111

79. able, and thus, its disappearance is a good indicator of mature
compost. A "II
laboratory method for measuring starch in compost is available,
although II " I
nique yields only qualitative information.v" This technique also
can Iw ,IPI'III II
a composting demonstration project for the classroom." A more
rigorous 1111 I 1
of the end point is the drop in the C/N ratio to perhaps 12: l.
High I' C/N I III
will result in continued decomposition of the compost after it is
applied, .1111111
subsequent robbing of nitrogen from the soil.
Recognizing the difficulties involved in the processing of a
hetci (lf',1 III I
material such as municipal solid waste, Colueke" suggests that
the viabilirv III II
biochemical process be judged on the basis of the organisms
employed. 1{1'f1,lldl
of what biochemical process is used. the organisms should have
the 11111" I
characteristics:
Not Fastidious. They will work under adverse conditions (e.g.,

80. wid
temperature range) and be tolerant of environmental change.
Ubiquitous. They should exist in nature. since pure stock
cultures
degenerate with time and rarely stay pure.
Persistent. They must grow in the environment without special
assistant I'
Not Picky. They should be able to use a broad spectrum of
substrates
If these criteria are used to judge the efficacy of composting,
the [11111
would pass with flying colors. Composting is able to handle
many organii W I I
and seems to be insensitive to changes in flow rates and feed
characteristic s 1111
a purely fundamental and biochemical perspective, composting
makes a gt,,11 II
of sense. However, it is important not to forget the old saying:
"Garbage in. g,1I1 1 I
out." Thus what is being composted is very important.
6-2-2 Composting Organic Waste
The organic fraction of MSW can be composted, and the
products from II

81. facilities may have significant environmental and cash value.
Organic WII
are now composted in thousands of communities throughout the
Willi I
1111111(', 1 :,"1,111,1. (lYI'1 1,111 01 II(' 111111 .1"lId
I'HI lililll' 11, ()III(' /01111
IIII'll I III,''''
111111' )HIII~ Oil U mU111 lpnl /iud(' 1111 11111 flillpil
111'd PI') css. At ils /iill-
III vcly aerated ompost s ,1('11 (1111 I III III'tll'l ,11 II r s r 11
I
11.11,1'( I'g, ni wast pi cd 111 II "I P 111111'1 I II S, all d
windr ws.
,II I will Ir( ws ar laid in I 1115 lOWS 01 ,tI~()lIt II I) rt (1.2 to
2 m) high
1111 I (I), Moistur content is maintained 11 far 1:0% by adding
water and/ r
I, I ,I II'C I d. B cause the reaction is r bi , oxygen must be
made avail-
I II III' mi r rganisms, and this is done by turning the pile with

82. a specially
1111111, d agitator (Figure 6-7). While this is the least
expensive and simplest
t'" III 01 ornposting, it is not always used. Other factors such as
regulations,
I Jllllhl'rn. pace availability. organic waste composition. and
climate (rain.
III d's rl) may require different composting methods.
, 11101' sophisticated system uses an actively aerated system.
Windrows
fllllilt I 11 top of perforated rvc pipes (Figure 6-8) or concrete
floors
1111 ( () with an air distribution system and air blowers for
forced aeration.
1111 j- La and 6-11). Instead of turning the windrow
periodically to aerate the
"rlIIIW, c ir is forced through the windrows. The air blowers
supplying the air
Itl' rontinuous or intermittent. Enough air must be supplied to
support the
Ilrli mposting. Without enough oxygen. the pile will become

83. anaerobic and
I I 11101' problems. On the other hand. too much air will cool
the pile and stop
1I111l1 ting activity.
- - ------------
tire 6-6 Windrow composting system. (Courtesy William A.
Worrell)
I
~
••
~
•• •• •• ••
8 Perforated pipe for air distribution. (Courtesy William A.
Worrell)
6 9 Air distribution channels. (Courtesy William A. Worrell)

84. Mobile aerator for windrows. (Courtesy William A. Worrell)
Figure 6-10 Air blowers for an aerated static pile. (Courtesy
William A Worr II)
Figure 6-11 Air blowers for a covered indoor aerated static pile.
(Courtesy Willidlll
A Worrell)
It 111'IH'I.ltl'd, I,ll t'l k I o III 110, I "1- III 111,111111 1111 I
II Il' l lnto III 'will I
1111' 1'111Is '''I' II" 110 ,IS 11 n '1"1 VI'.t II 1I1I1 , utu, lilli'
all' is blown lnro
IlIdlOW, III 'I) it Is, I sitivc aer.ulun 1111 P. I" III 'Ib I h S
advanu g s
II Ililv,lllllg'S, with 11 ativc 11'1,1111111 11'111, Ill' ,11'
passing through Ill'
I I lit Il' I int 111 pip at th bouom 01 till' II I 'by T '< Linga
vacuum. This air
11111111 1 'dis harg d into an air tr '(1111 'Ill sy L'In, su b as

85. a biofilter or scrub-
I 1IIIItlilimiz dors. However, a n I( rive t 'r Lionsystem uses
more power and
I 1IIIomi t the compost pile. Th bigg st disadvantage of a
positive aeration
It iii I III l the air is blown through the pile and exits into the
atmospher .
I IIIIolSe r not controlled. To control odors a layer of finished
compost or a
utili II v r can be placed on top of the pile. Thus the air must
pass through
111'1'1, whi h will remove some odors (see Figure 6-12).
I Hll'r ptions provide even more control of the compost process.
I I .uupl , the aerated composting may be done under a
permanent roof (see
III (I I ), which prevents run-off from rain during the compo
sting operation.
1111 IIII option is to compost inside a building (see Figure 6-
14) so that there will
1111 11111- ff and air can be collected and treated. Finally,
aerated composting

86. II III d)11 inside fully enclosed tunnels (see Figure 6-15) for
the highest level of
1 11111 or t mperature, moisture, and odor.
1'1' bic decomposition results in a dark brown earthy-smelling
material that
IIIWnutrient value but is an excellent soil conditioner.
I, ure 6-12 Plastic cover on a windrow compost pile. (Courtesy
William A Worrell)
• /s ill (OlIljlo, I 1ll,1I1lilil't'IIIII'd /111111~/ W / '
11t sign iII n III I LI bIi h(."1/ ill ')1 ' I (Ill( I d N I, (,111/ (' ,II
II
J ( , « (JII( 1'111. 1,(',1 /, 0" 'xt1mpl', I, I II
00 I J m 111 mp SI mil / ' 1'10111MSW J WI /
gned, however, the econon in' I '/ ,':, '. n 1111( sl/nll I" I 1
of compost. ( 11.1ys. IIIVAII,bly lJl lud s : / 101 I II II
Whil.e there may be some advantage to usin mixed

87. mdfilhng or incineration it will big. wast OlllpCl 1111
. For example, if regulati~ns p~eve~tc:; ia~~~l~~ mos; like.'y
I,.iv('11hI I I
- be necessary to compost the waste be .. 1 lmg 0 unn <II' /
WoIlli I
Th erore It IS andfilled
e ~econd problem, the limited reduction in the v .
techlllcal sOlutions because th olum (W,II"I II
e process can be cha d /
IS such as glass metals and I f nge I a Ill" I I II"
, r so on n act com ti
;:>lyanother process within a com Iete '. pos Ing may b' '1111 iii
~ process has been run to prod p mat~nals recovery planr, ()111
/"1
.iesh) of the light fraction of ~cela p~fitresCIble material from
IllI' II, 1/1
air-c aSSI led refuse 20 Thi .
% of the raw refuse and contained 740 . . .IS mal 1'1.1111111I
-y the material was digested for methane Yo v~latI.le s~hds.

88. Allho(IH/' III I
.posted. pro ucuon, It also all III III I II
The fraction of putrescible material in refu h .
~ears and will no doubt conti d se as been s~eadJ/y (/('(
/111/111
:ompostable fraction Similarlyn~e to 0 ~o: ~s the organic
fracliOIl i,,1III/II
3e could ever be recovered as co;::P~s an It IS un!j~ely that
more liI,III 'llIll
~ normal means, and this cost mu; b t. ~~e ~emalhlllng 50%
must Iw iii ",,
.aciliry e a e to t e total cost of 1111'~111111"
The last problem is mostly one of odor d .
ot that the odor from compost '1 . 1pro ucuon. Although
1>01111/'1,1
: minority. Compost plants do pi eSllls Pheasa.nt, these people
arc ill Ihl
sme -t ere IS no do bt f h
;:>lants must be located fairly far fr identi u .0 t a!- ,lIld 1111
:her cost-transportation. om resi entia I areas. ThIS
requir~'I1I1'''' "'

89. MSW composting plants are id . .
lot sell the compost '1'( must pal. a tipping fee to accept MSW.
II 1111/"
r contmue to accept . .
sh flow. This results in an ever l' . '1 mcommg MSW I() Ilid/IlI
. - ncreasmg pI e of c .
ds, It eventually is too big to be turn d . ompost on-SIte. ;, II1I
/'
:-problems. e , and It becomes anaerobl(, I d" I
In conclusion, it seems unlike! that . d
ge scale, at least in more developYed mIXe. waste composting
willIX'II I Ii
. . countnes Wheneve .
mUlllCIpal scale is suggested the d " 'k r <omposung II/ " '"
1ismal record of past mixed ~ t ecisron ~a ers should always
bea: "' 111111
: under an aura of optimism anadse ctohm~ostmg efforts. All of
these pl.uu-
. en usrasrn and all f th .nised Success The engineer and d " ' 0

90. e economt. 0111.11,
ae proposed new com ost la eCISlOn maker should ask what is
so dll/III
.rs have failed. p p nt that would allow it to succeed whih- .tI/11
While composting MSW presents man r bl .
{Shas real benefit Bioremedl'au'o b Y Pdo ems, compostmg of
SOliII "
. n can e use to tre t .I d
nated with oil and other petroleum roducts 1 a SOl an
~~undWoll.'I' ""
as bacteria, use contaminants as p f ~so vents, and pesticide- M
IIIII"
. . a source 0 rood and e Th dposting in cleaning up the cont . .
nergy. e a V<lIlLIIlI~I
ammatlOn seems well established.28
'II 1111 Iypl' 01 IHIiI I, .11 .111(1,III I H/IIII I I II
1111II rl, A (0 IIII l'lIlllo11 1111h n, 1l.lwdllll Ilild I/Ili 1111
11/11 ,I III ('riOI' C )111110111,high 1111111'011'11
/11"1{" I'OIll II 'w~g II' atrnc nt p/IIIII /11 I' 1"111 II 1'1 I' I'
I11fny y ('S is

91. I 1I/II11tl'j 'l1iS in OJ I osting." '1'111'pI(IIII"111will
«(11111osting slud always
111111Iilat lh s liels. ornpa I 100 ligitll , '(..-Iv"B II() sl ( s for
air to en! r
I'll. 'I'/Iis pr bl In can be solved h ml III! tll{' sill Ig with wood
chips and
1'1 I Ilf the mixture. The woo I hi] II fin.' ornp S d f poorly
decomposable
III., I ,11(/ lignin and can be readily I' rn v eI from the
stabilized material
11111'11,(,I' ning and then can be reused. Raw sludges can be
composted to a
(I I oil nditioner or a high-grade topsoil.
I ',ld I
,111I I I,
INAL THOUGHTS
II11II W rking for municipalities-either directly or indirectly-
must have
•• ill'! I' f autonomy. Professionals correctly believe that
professional auton-

92. , 11'11.f ial to the welfare of the public. If the government
starts telling phy-
III/lOW L treat people, telling preachers what to preach, or
telling engineers
II /Ilil I things, then the public loses. Accordingly, these
professions have
"III 1 gll rded their autonomy in the name of the public good.
The engineering
II (III r ognizes that, if engineering is to maintain its
professional autonomy,
1'11111/has to trust engineers, and it is very much to the
advantage of engineer-
Ilid Ih public at large to maintain this trust.
lilt" autonomy can be taken away by the state, of course, as
witnessed in
111 that have totalitarian governments (such as the former
Soviet Union) in
"IJII -proud and independent engineers became tools of the
communist
, HlIlI( ru and had little say in technical decisions. The inability
of those engi-

93. I Ii vie their concerns about projects that were
counterproductive, wasteful
II 11111's. and harmful to the public was in great part
responsible for the even-
I d"wn(alJ of the Soviet empire."
1111ln ers, as all other professionals, must work to maintain
public trust.
III11m te trust in the engineering profession, professional
engineering
II I, h ve all drafted statements that express the values and
aspirations of the
II (n-statements commonly referred to as a "Code of Ethics."
),, of the earliest codes of ethics in the United States was
adopted in 1914
1111AI11 rican Society of Civil Engineers (ASCE). Based in
spirit on the original
It III Harnmurabi."? the 1914 ASCE Code addressed the
interactions between
lilli'S and their clients and among engineers themselves. Only in
the 1963

94. I '11h did the ASCE Code include statements about the
engineer's responsibility
Ilu I .neral public, stating as a fundamental canon the engineer's
responsibility
,1111 health, safety, and welfare of the public.
11 I 97, ASCE modified its code to include the commitment of
engineers to
11111.11Ie development. The term sustainable development was
first popularized
llil W rld Commission on Environment and Development (also
known as the
111111111,nd Commission), which is sponsored by the United
Nations. Within this
1"111,. ustainable development is defined as /I development
that meets the needs
M rals ill «)lllpO ( 1",IIIIIr.(1111('1I110111~L W, h
1011(1,1(,1,1111)(' ,I( It
present signif ant I nbl: "l'nlill (' jlH 1'111,I I. ',Id, I(}t •
111111', I 1" III
level of 800 pprn in mp Sl!TIt I' /'10111M,'W,i~ WIl('11 (

95. )mjlo, 11111,.1
designed, however, th onomi analyslr Inv,III,11 I in lu I •. a
plnl I II
sale of compost.
While there may be some advantag l using mix xl WeSI' 011'1"1
III
to landfilling or incineration, it will be costly nd i !TI st lik ly
ddYl''' "
tion. For example, if regulations prevent the landfilling r UJ u •
I '<I WII h
may be necessary to compost the waste before it is landfill d.
The second problem, the limited reduction in the velum of' W.I
II
has technical solutions because the process can be changed I iH
IlI,d I
items such as glass, metals, and so on. In fact, composting may
Ill' 11111
simply another process within a complete materials recovery
pl;1111 (It I
scale process has been run to produce a putrescible material Ir
111(III I
(7-mesh) of the light fraction of air-classified refuse." This rnt t
'11.1111111

96. of 6% of the raw refuse and contained 74% volatile solids.
AIIIH)II}," I"
study the material was digested for methane production, it also
ould III I
composted.
The fraction of putrescible material in refuse has been steadily
t(o,llllill
the years and will no doubt continue to do so. As the organic fra
tiou I I I
the compostable fraction similarly drops, and it is unlikely that
more 111.111II
refuse could ever be recovered as compost. The remaining 50%
must III' "I I
of by normal means, and this cost must be added to the total
cost of"II,.' 1111I
ing facility.
The last problem is mostly one of odor production. Although
SPIIiI I'
insist that the odor from compost piles is pleasant, these people
are III III
tinct minority. Compost plants do smell-there is no doubt of that
,11111
the plants must be located fairly far from residential areas. This

97. requiu-uuut
another cost-transportation.
MSW composting plants are paid a tipping fee to accept MSW.
II Iii II
cannot sell the compost, it must continue to accept incoming
MSW 10 III III
a cash flow. This results in an ever-increasing pile of compost
on-site. i III
builds, it eventually is too big to be turned, and it becomes
anaerohn , I II
odor problems.
In conclusion, it seems unlikely that mixed waste composting
will ls- II
a large scale, at least in more developed countries. Whenever
compostinj; 1111
on a municipal scale is suggested, the decision makers should
always 1)(,,11II I
the dismal record of past mixed waste composting efforts. All of
these pili III
built under an aura of optimism and enthusiasm, and all of the
econorn i. 1111I
promised success. The engineer and decision maker should ask
what is so II "

98. in the proposed new compost plant that would allow it to
succeed wlul. 1111
others have failed.
While composting MSW presents many problems, composting of
Sill"
stocks has real benefit. Bioremediation can be used to treat soil
and groundw.tu i
taminated with oil and other petroleum products, solvents, and
pesticides. tvl I II
such as bacteria, use contaminants as a source of food and
energy. The adv.inhu
composting in cleaning up the contamination seems well
established."
11111 (II' III ,,1111111.110111I III ill 1111111II 1 I
" II d, A tOlllhllltllloll ,~I(h II ,.Iwdll II .llId 111111'11
III 1 Iii '1'101(OlliPOSI,hlgh III 1111°11'11
lutlll /'1'0111scwngc 1"'<11111'111plill" 1111• 1)'1'11 II' Ili)l'
many years as
1!lIIIIII'1'I1(S in ornp sling.i"'I'Ile Pllll,II'11 Wilt (Oml ostlng
sludg always
1111III 11 the s lids mpa I 10 I Ii ilil , k,wlnll 110 spa s ~ r air l

99. nt r
,,,. III, problem an b solved by nilx 11/(Ill' sludg with wood hi]
S (In I
1IIIIIf III' m ixtur . The wood hi] s arc ornp s d of poorly
decomposabl
I,I I ,iiI I lignin and can be readily I" IT) V d from the
stabilized mat rial
IIjilt 'I' 'ning and then can be r us d. Raw sludges can be
composte I l a
I" () I onditioner or a high-grade topsoil.
1'0111
.Ill,! I',
INAL THOUGHTS
"'1 W rking for municipalities-either directly or indirectly-must
hay
". II " f autonomy. Professionals correctly believe that
professional auton-
, 111'11fI ial to the welfare of the public. If the government
starts telling phy-
I I uw l treat people, telling preachers what to preach, or telling

100. engine rs
ItI III j lei things, then the public loses. Accordingly, these
professions hay
II I f II, rdeel their autonomy in the name of the public good.
The engineering
1111r ognizes that, if engineering is to maintain its professional
autonomy,
ulrl hs to trust engineers, and it is very much to the advantage
of engineer-
lid (ill public at large to maintain this trust.
III" c U tonomy can be taken away by the state, of course, as
witnessed in
III III l have totalitarian governments (such as the former Soviet
Union) in
II 1111 -proud and independent engineers became tools of the
communist
1I1I1!Pllland had little say in technical decisions. The inability
of those engi-
III v ice their concerns about projects that were
counterproductive, wasteful
11111 ,and harmful to the public was in great part responsible
for the even-
IIIIV 11 rail of the Soviet empire."

101. 11Iflneers, as all other professionals, must work to maintain
public trust.
1111111te trust in the engineering profession, professional
engineering
I It' h, ve all drafted statements that express the values and
aspirations of the
on-statements commonly referred to as a "Code of Ethics."
I "Il' of the earliest codes of ethics in the United States was
adopted in 1914
1 merican Society of Civil Engineers (ASCE). Based in spirit on
the original
III l lammurabi,"? the 1914 ASCE Code addressed the
interactions between
II liS and their clients and among engineers themselves. Only in
the 1963
ItIII did the ASCE Code include statements about the engineer's
responsibility
-neral public, stating as a fundamental canon the engineer's
responsibility
III II alth, safety, and welfare of the public.
III (997, ASCE modified its code to include the commitment of

102. engineers to
111,11Ie development. The term sustainable development was
first popularized
World Commission on Environment and Development (also
known as the
1II.Ind Commission), which is sponsored by the United Nations.
Within this
II, sustainable development is defined as "development that
meets the needs
o lh I I' 'S '111with Lit 01111'1' mislllK 1I1t'.1I I ( (f' futur ('11
'1',Hlt)!!. II) 11111
own needs. II/It ustainable cI v J I J)I 'Ill ( 111II,' I, r II xl in tI
11uI1lb'I' or W,I /
indeed the Brundtland Report itself in lud .. I'll IIf 'I' nt I
1I1ilioil III
report for the United Kingdom Departrn nt 111' Envir nrn nt
111.1II II1I
pages of definitions."
Although the original purpose of introducing the idea of susrn i

103. 11,11d d
opment was to recognize the rights of the developing nations ill
11'1111 I
resources, sustainable development has gained a wider meaning
and 11I)W111II
educational needs and cultural activities, as well as health, justi
c. I" 1,1
security." All of these are possible if the global ecosystem is to
nli)llI, II!
port the human species. We owe it to future generations,
therefor, 1101III Ii
the earth they will occupy. Using biological processes to
produce usclul I'HIII
such as methane and recovery nutrients is increasing. We
recogniz Ih,11III II
non renewable fossil fuels for our energy use is not in keeping
wi th IIII' I" It I
of sustainable development and contributes to the impact of
gl'<:('1I11I11I
Composting also contributes to nutrient recovery. For example,
ph splu n III
valuable limited resource and should be reused for agricultural
appl h ,II lilt
not lost in landfills.

104. References
l. Alter, H. 1989. "The Origins of Municipal
Solid Waste: The Relationship Between
Residues from Packaging Materials and
Food." Waste Management and Research
7:lO3-114.
2. Bell, 1. M. 1964. "Characteristics of
Municipal Refuse." Proceedings National
Conference on Solid Waste Research,
American Public Works Association,
February.
3. Pfeffer, J. T. 1974. Reclamation of Energy
from Organic Refuse. 670/2-74-016.
Cincinnati, Ohio.
4. Pfeffer, 1. T. and J. C. Liebman. 1976.
"Energy from Refuse by Bioconversion
Fermentation and Residue Disposal
Processes." Resource Recovery and
Conservation 1:295.
5. Hagerty, D. J., 1. L. Pavoni, and 1. E. Heer.

105. 1973. Solid Waste Management.
New York: Van Nostrand Reinhold Co.
6. Vesilind, P. A. 1979. Treatment and
Disposal of Wastewater Sludge. Ann
Arbor, Michigan: Ann Arbor Science
Publishers.
7. Lawrence, A. W. and P. L. M (,.111 I I
"The Role of Sulfide in Pl'eV('11111I1
Heavy Metal Toxicity in An,H'lIIhli
Treatment." Journal of the WIII"1
Pollution Control Federation ~'I I I I
8. Pfeffer, J. T. 1974. "Temperature I 1111
on Anaerobic Fermentation (,f
Domestic Refuse." Biotech1/()lu,~,'111I/
Bioengineering 16:77.
9. Hille, S. J. 1975. Anaerobic D(,('/IPI/
of Solid Waste and Sewage SIIit/S"
to Methane. EPA OSWMP SW I 'I
Washington, D.C.
io. Monteith, H. D. and J. P. Steplu-n II,

106. 1997. "Mixing Efficiencies ill
Full-scale Anaerobic Digesters I,,
Tracer Methods." Proceedings
Symposium on Sludge Trearuu III
Waste-water Technology Ccnru-,
Burlington, Ontario/ Canada
11. Bowerman, F. 1979. "Methane (,1'1111
from Deep Landfills." Proceedlll,"
Engineering Foundation COllk11 III
on Resource Recovery, Hennikr-r,
New Hampshire (July).
I I ,. I()'I ('IlI/IIIII~'I/I, 1i.11I111,11II• ,It • / II It (I J ,
1'1111/IVIIiI I: I{(i I 11'1'11' I III ,
III I ' II (I ,"jl,llil 11l'll SIIV v.il ln
" , I II /
11111111)till Munl II 11Wa,I", /01111111
111'1 I'ollutlon ;onll')1 P' I'mll n
I I(), I 1)1) I
11/1111 W an I It A. Nc rdSl' l. I ,II I'" , /I

107. /1,1'(.11'II ~ r Vi r I W st '011"11)Sllllg.
11/" 'I1I'1c' ,n. : 0-61:.
t , It 1t'1', " I 7 ." te t f th Art.o
II Iunv 'rsi n I I' ess ." vroce d".,p,s
I1II uc ring Ii undati n nf I' n '
111Ill'H UI' R v ry, Rindg r
'W II, mpshir (July).
" /It/lysis oj omposti~g as an. I
I II 11//011mental Remeduuion Technoiog) .
II I 1-. 1;1A 530-R-98-008.
I II I, P. A. 1973. "A Laboratory
I I' Is in Composting." Compost
1,11111e (September-October). . "
1 1 R 0 1971. "Compost Studies.II I, . . .
I tllllpOt Science (March-Apnl).
I I nd, P. A. 1973. Solid Waste
IIl,qineering Laboratory Manual. DU.r1:arn,
Nt rth Carolina: Department of CIVil
III ineering, Duke University.
I, L F F Kurz and G. J. Trezek. 1976.II ,II'., . .,. , f

108. /1M thane Gas Production as Part or
,I It fuse Recycling System. II Compost
, ('/ nce.
I ' I( H 1991. "Risk Assessment:1111 , . .
I mparing Composting ~nd
II ineration Alternauves. MSW
Management I, no. 3:29-32, 36-39.
V,llt r, R. 1971. "How to Compost
I. aves." American City (June): .p. 116.
Iml rique, J. O. and D. s: Rodenq~e.
I 95. Quoted in Decision Maker s
,uide to Solid Waste Management.
I;PA 530-r-95-023. Washington, D.C.
.I • 1987() sthnoek. J. and J. P. N. Smit. .
"Future of Composting in the
Netherlands." BioCycle (July).
ltlchard. T. L. and P. Woodbury. 1?93.
trategies for Separating Contammants

109. from Municipal Solid Waste. Cornell.
University Waste Management Institute.
I,
H,
, I).
I(),
1,
I I
1