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Avai lab le a t www.sc iencedi rec t .com

ht tp : / /www.e lsev ier . com/ loca te /b iombioe

Emergy analysis of cassava-based fuel ethanol in China

Hui Yang, Li Chen, Zongcheng Yan*, Honglin Wang

School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China

a r t i c l e i n f o

Article history:

Received 7 December 2009

Received in revised form

28 July 2010

Accepted 18 October 2010

Available online 8 December 2010

Keywords:

Emergy analysis

Fuel ethanol

Cassava

Emergy indices

Sustainability

Evaluation

* Corresponding author. Tel./fax: þ86 20 871E-mail address: zcyan@scut.edu.cn (Z. Ya

0961-9534/$ e see front matter ª 2010 Elsevdoi:10.1016/j.biombioe.2010.10.027

a b s t r a c t

Emergy analysis considers both energy quality and energy used in the past, and compensates

for the inabilityofmoneytovaluenon-market inputs inanobjectivemanner. Its commonunit

allows all resources to be compared on a fair basis. As feedstock for fuel ethanol, cassava has

someadvantages overother feedstocks. Theproductionsystemof cassava-based fuel ethanol

(CFE) was evaluated by emergy analysis. The emergy indices for the system of cassava-based

fuel ethanol (CFE) are as follows: transformity is 1.10 Eþ 5 sej/J, EYR is 1.07, ELR is 2.55, RER is

0.28, andESI is0.42.Comparedwith theemergy indicesofwheatethanolandcornethanol,CFE

is themost sustainable. CFE is a good alternative to substitute for oil in China. Non-renewable

purchased emergy accounts for 71.15% of the whole input emergy. The dependence on non-

renewable energy increases environmental degradation, making the system less sustainable

relative to systemsmoredependent on renewable energies. For sustainable development, it is

vital to reduce the consumption of non-renewable energy in the production of CFE.

ª 2010 Elsevier Ltd. All rights reserved.

1. Introduction how to evaluate sustainability of the production system of BFE

In recent decades, oil shortage and environmental deteriora-

tion have caused people to paymore andmore attention to the

biomass-based fuel ethanol (BFE). BFE can ease oil import

burden and lessen the greenhouse effect. What is more,

ethanol used in the form of blends in gasoline can improve the

quality of gasoline by increasing the octane level [1]. BFE is by

far themostwidely used biofuel for transportationworldwide.

China is currently the world’s third largest producer of BFE.

The yield of fuel ethanol of China had got to 1.7 million tons in

2009. So far it is mandatory to use E10 in nine provinces that

account for about one-sixth of the country’s vehicles.

When using an alternative source of energy, it is necessary

to evaluate the whole production chain to correctly evaluate

potential environmental benefits and disadvantages. BFE is an

alternative fuel for gasoline and diesel, it is usually considered

to be renewable and environmental friendly. But the produc-

tion of BFE consumesmuch non-renewable energy. Therefore,

11109.n).ier Ltd. All rights reserved

becomes a great concern of every country. Many methods

have been presented to evaluate BFE, such as energy analysis

[2e6], economic analysis [7e9], environmental evaluation

[3,10] and exergetic evaluation [11]. There is no generally

accepted evaluation method to assess sustainability of the

system, for each method mentioned above has its own

advantages which can help us understand sustainability of

the system from a special perspective. Emergy analysis is

considered as a valid approach to quantify both environ-

mental and economical costs.

Emergy, a measure of real wealth, is the sum of the avail-

able energy of one kind previously required, either directly or

indirectly, through input pathways to make a product or

service [12]. Because solar energy is the primary source which

feeds all processes and cycles on Earth. Inputs to a process are

therefore normalized to a unit, namely the solar emergy joule

or solar emjoule (sej). Emergy is not a state function, because it

considers the specific path from the initial to the present state

.

Fig. 1 e Inputs and outputs emergy flows of the system.

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9582

[13]. To derive the solar emergy of a resource or commodity, it

is necessary to trace back through all the resources and energy

flows that were used to produce it and express these input

flows in the amount of solar energy that went into their

production [14]. The emergy of each input to a system is

calculated in terms of solar emjoules (sej) bymeans of suitable

conversion factors called transformity or specific emergy

(expressed in sej/J, sej/g, or other units). “Transformity” is

defined as the amount of directly and indirectly emergy

required to generate a unit of energy [15]. For example, if

4000 sej are required to generate wood which contains 1 J of

energy, then the solar transformity of that wood is 4000 sej/J.

Emergy analysis has superiority compared with energy

analysis or economic analysis. Energy analysis can’t reflect

the quality of energy, and it calculates different kinds of

energy together on the common unit of joule. No differences

are among 1 J of electricity, nuclear energy, and solar energy

in energy analysis. Labor, information, and technological

devices contain relatively small energy flows, but high

emergy flows for their formation and maintenance. It is

Table 1 e Emergy-based indices.

Indices Expression

EYR Y/F

¼ (N þ R þ F)/F

EYR (emery yield ratio) is a measure of the abili

investing in outside resources. The higher the v

invested. EYR measures the system’s net contri

dependency on purchased inputs, and to show

ELR (N þ FN)/

(R þ FR)

ELR (environmental loading ratio) is used to eva

system. The higher the proportion of non-renew

ELR reflect relatively small environmental loadi

indicate a relatively low impact on the environm

‘dilute the impact’); values between 2 and 10 me

of relatively concentrated environmental impac

a relatively small local environment, of very co

RER (R þ FR)/

(N þ R þ F)

¼ 1/(1 þ ELR)

RER (Renewable emergy ratio) is used to evaluate

reliance of the system on renewable resources.

ESI EYR/ELR ESI (Emergy sustainability index) is a sustainabi

a process or system must obtain the highest yie

less than 1 appear to be indicative of products o

ratios greater than 1 indicative of products and p

run sustainability seems to be characterized by E

sustainability have ESI accordingly greater [14].

inaccurate to express the value of different kinds of energy

(such as sunlight and fuels) in joules. Emergy (with unit

emjoule) analysis is totally different from conventional

energy (with unit joule) analysis which merely accounts for

the remaining available energy at present. Emergy analysis

considers both energy quality and energy used in the past, it

is a more feasible approach to evaluate the status and posi-

tion of different energy carriers in universal energy hierarchy

[16].

In economic analysis, price often fluctuates with the rela-

tion of supply and demand. Odum [17] argued that “money

cannot be used directly to measure environmental contribu-

tions to the public good, sincemoney is paid only to people for

their services, not to the environmental service generating

resources or assimilatingwastes.” Brown et al. [18] also argued

that price did not determine value, giving the example that “a

gallon of gasoline will power a car the same distance no

matterwhat its price, thus its value to the driver is the number

of miles (work) that can be driven.” Emergy analysis

compensates for the inability of money to value non-market

Signification

ty of the system to exploit and make local resources available by

alue of this index, the greater the return obtained per unit of emergy

bution to the economy beyond [15]. It was used to estimate process

the environmental contribution to the region’s economy.

luate how much “pressure” is placed on the environment by the

able emergy used, the higher the pressure on the environment. Low

ng, while high ELR suggest greater loading. ELR values less than 2

ent (or processes that could use a large area of a local environment to

an that the system caused a moderate impact; up to 10 are indicative

t [26]. Extremely high ELR is might result from the investment, in

ncentrated inputs derived from non-renewable energies [14].

the renewability of the system. It is linked to the ELR, and reflects the

lity function for a given process or economy [27]. To be sustainable,

ld ratio (EYR) at the lowest environmental loading ratio (ELR) [28]. ESI

r processes that are not sustainable in the long run and those with

rocesses that are sustainable contributions to the economy. Medium

SI between 1.0 and 5.0, while processes and products with long range

Fig. 2 e Energy flow diagram of bioethanol production from cassava chips.

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9 583

inputs in an objective manner. Its common unit allows all

resources to be compared on a fair basis.

Most existing methods, such as life cycle assessment and

exergy analysis, do expand the system boundary beyond the

scope of a single process, indirect effects of raw material

consumption, energy depletion and pollutant emissions can

be taken into account. However, these methods ignore the

crucial contribution of systems to human beings [19]. Emergy

analysis provides a more holistic alternative to many existing

methods for environmentally conscious decisionmaking. The

concept of critical natural capital and a framework to account

for have been suggested recently [20]. Emergy analysis can

quantify the contribution of natural capital for sustaining

economic activity [21]. Emergy aims at providing a sustain-

ability assessment of ecological & industrial products and

processes [22].

The production system of cassava-based fuel ethanol (CFE)

was evaluated by emergy analysis in this paper. Emergy

analysis considers the free environmental inputs, which are

usually not accounted in traditional energy analysis. And

Fig. 3 e Trend of emdollar ratio f

emergy analysis has many indices to evaluate the system. In

so doing, it is possible to provide insight into the present and

future performance and suitability of biofuel production

activities.

2. Emergy analysis of CFE

2.1. Cassava-based fuel ethanol

As feedstock for fuel ethanol, cassava has two advantages

over other feedstocks. First, cassava is a shrubby tropical

plant, widely grown for its large, tuberous, starchy roots,

especially on marginal land where rice, wheat, corn, sugar-

cane and other agricultural crops cannot grow well [23].

Second, cassava is not a staple food for the Chinese people.

Using cassava for ethanol production would not cause the

foodstuff crisis as would corn andwheat. Cassava is easy to be

comminuted, and has short cooking time and low gelatiniza-

tion temperature. Therefore, cassava is a suitable feedstock

or the world and China [35].

Table 2 e Emergy analysis of CFE.

Note Item (unit) Data/(unit/yr) Transformity/(sej/unit） Emergy/(sej/yr)

R

1 Sun radiation (J) 1.35 E þ 17 1 1.35 E þ 17

2 Rain chemical potential (J) 1.32 E þ 14 3.05 E þ 04 [31] 4.03 E þ 18

3 Rain geopotential (J) 5.27 E þ 13 4.70 E þ 04 [31] 2.48 E þ 18

4 Wind (J) 1.04 E þ 14 2.45 E þ 03 [31] 2.55 E þ 17

Sum of R 4.03 E þ 18a

N

5 Net topsoil loss (J) 6.63 E þ 12 7.40 E þ 04 [32] 4.90 E þ 17

FR6 Stem cuttings (kg) 3.76 E þ 06 2.10 E þ 11[33] 7.90 E þ 17

7 Labor (man*h) 1.10 E þ 07 1.10 E þ 12 [34] 1.21E þ 19

8 management and service ($) 5.25 E þ 05 4.45 E þ 12b 2.34 E þ 18

9 Hydroelectricity (J)c 5.61 E þ 12 6.23 E þ 04 [14] 3.50 E þ 17

10 Water (kg) 3.47 E þ 08 6.64 E þ 08 [36] 2.30 E þ 17

11 Liquefying amylase (J) 5.77 E þ 11 5.40 E þ 04 [37] 3.12 E þ 16

12 Glucoamylase (J) 2.64 E þ 12 5.40 E þ 04 [37] 1.42 E þ 17

Sum of FR 1.60 E þ 19

FN13 Nitrogenous fertilizer (kg) 7.53 E þ 05 2.41 E þ 13 [38] 1.81 E þ 19

14 Phosphate (kg) 3.76 E þ 05 2.02 E þ 13 [38] 7.60 E þ 18

15 Potash (kg) 1.13 E þ 06 1.74 E þ 12 [38] 1.97 E þ 18

16 Herbicides (kg) 7.53 E þ 04 1.48 E þ 13 [38] 1.11 E þ 18

17 H2SO4 (98%)(kg) 29,000 1.53 E þ 11 [38] 4.48 E þ 15

18 (NH4)2SO4 (kg) 29,000 2.40 E þ 13 [38] 7.03 E þ 17

19 Coal (J) 3.56 E þ 14 4.00 E þ 04 [36] 1.42 E þ 19

20 3A molecular sieve ($) 22,857 4.45 E þ 12b 1.02 E þ 17

21 Diesel (J) 1.30 E þ 13 6.60 E þ 04 [15] 8.58 E þ 17

22 Coal electricity (J)c 1.30 E þ 13 1.71 E þ 05 [38] 2.22 E þ 18

23 Buiding & machinery ($) 8.00 E þ 05 4.45 E þ 12b 3.56 E þ 18

Sum of FN 5.04 E þ 19

Sum of inputs 7.10 E þ 19

Y

Ethanol produced (J) 6.44 E þ 14 1.10 E þ 05 7.10 E þ 19

a Rain and wind are considered to be co-products of sunlight, to avoid double counting among the inputs of renewable environmental

resources, only the item with the highest value is added to the total amount of emergy [15].

b Trend of emergy/dollar ratio in China from 1978 to 2005 is shown in Fig. 3, which has been published by Yang et al. [35]. In Fig. 3, the emergy/

dollar ratio of China was 7.29 Eþ 12 sej/$ in 2000, 5.87 Eþ 12 sej/$ in 2005.According the trend of emdollar ratio, the emergy/dollar ratio of 2010 in

China was speculated to be 4.45 E þ 12 sej/$.

c The electricity used is recalculated to primary energy for an average south China electricity production system, which is based on 30%

hydropower and 70% coal fuels.

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9584

for fuel ethanol. Fresh cassava becomes to blet very easily, so

it is usually made into cassava chips to reserve and use. The

production system of cassava chips includes field preparation

and ploughing, sowing, fertilization, weeding, harvesting,

pilling and slicing, baking and packing.

In the process of fuel ethanol production, cassava chips

were smashed to destroy the cellular tissue first, then the

mixture of pretreated cassava dry chips, water and special

amylase were kept under certain temperature and are

liquidized and subsequently saccharificated, so that starch

contained in the cassava would be converted into monomeric

sugars. Next the sugars were fermented into ethanol by yeast.

After fermentation, low concentration ethanol was passed on

to distillation where it was concentrated to 95.6% v/v ethanol.

At last, 99.5% v/v ethanol was obtained through adsorption of

molecular sieves.

The total ethanol production of the factory studied in this

paper is 24300 t/yr. 2.8 t cassava chips are needed to produce

1 t of ethanol. So the consumption of cassava chips in this

factory is 68265 t/yr. The growth cycle of fresh cassava is 10

months. The average productivity of fresh cassava in Guangxi

province is 40 t/ha. And 0.034 t cassava chips can be produced

from 0.1 t fresh cassava. Therefore, in order to meet the

ethanol productivity in this factory, 5019 ha of cassava need to

be planted. 213 kWh electricity and 0.5 t coal are needed to

produce 1 t ethanol. The investment on the buildings and

machineries in this factory is 8 million dollars. Most data

about the cassava planting were obtained from the Chinese

academy of tropical agricultural sciences. And most input

data about the ethanol production were investigated in the

factory. The emergy analysis of CFE combines the agricultural

and industrial systems together.

2.2. Evaluation indices for the studied system

Emergy analysis has many evaluation indices, which can

provide a better insight into particular cases and distinguish

the renewable and non-renewable components of the total

emergy that drive the process, as well as the “natural” and

economic inputs. The sustainability, renewability and

Table 3 e Transformity of fuels.

Fuel Transformity/(sej/J)

CFE 1.10 E þ 05

Ethanol from wheat [39] 2.77 E þ 05

Ethanol from corn [40] 1.89 E þ 05

Biodiesel [41] 2.00 E þ 05

Gasoline [15] 6.60 E þ 04

Crude oil [15] 5.40 E þ 04

Natural gas [15] 4.80 E þ 04

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9 585

efficiency of the system can be clearly analyzed through

a series of emergy-based indices.

The ratio of the total emergy used to the mass or energy of

the product, gives a unit, namely specific emergy or trans-

formity (Tr), in unit of sej/g or sej/J, respectively. Moreover,

specific emergy can be conceived as an indicator which

represents the position that a given transformation process

(and its product) occupies in the hierarchical network of the

earth’s biosphere [15]. Through multiplying the inputs with

certain transformities, the emergy amount of each input

resource and service can be calculated. The transformity of

the product is calculated by dividing the total emergy of the

yield by the quantity of the output.

In addition to transformity, several other emergy-based

indices can be calculated. In Fig. 1, inputs emergy flows

represent three categories of resources: R as renewable envi-

ronmental resources, N as non-renewable environmental

resources and F as the purchased resources. The R andN flows

are provided by the environment and are economically free.

The economic inputs, F, are provided by the market and are

related to fluxes which are accounted by the economy. F can

also be divided into two categories, renewable purchased (FR)

and non-renewable purchased (FN). The outputs, Y, may

include products, services and also emissions which are

released to the environment [24]. As is shown in Table 1, there

are many emergy indices for better evaluation of the con-

cerned system and indication of various performances of the

system in terms of ecological efficiency and sustainability [25].

The emergy/dollar ratio is the ratio of total emergy use of

a state or country to gross national product (GNP) for the

national economy. It can be used to convert money payments

into emergy units. It varies in different countries and has been

shown to decrease each year, which is an index of inflation.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

%/desu

ygrem

E

rain

soil

loss

stem

cutt

ings

Nfe

rtil

izer

phos

phat

e

pota

sh

ehrb

icid

es

Fig. 4 e The emergy proportion of each flo

Generally speaking, developing countries have a higher

emergy/dollar ratio, because their economy involves more

direct use of environmental resources without money

exchange, thus a dollar from these countries can buy more

real wealth than in developed countries [29]. It is useful for

evaluating service inputs given in money units where an

average wage rate is appropriate.

2.3. Emergy evaluation procedure

The first step in the application of the emergy methodology is

to construct system diagrams to categorize all components

into renewable or non-renewable, environmental or

purchased. A system’s diagram is drawn using the symbols of

the energy language of systems ecology [15,30] to graphically

represent system components, emergy sources and flows and

the circulation of money through the system. The compo-

nents and subsystems are connected with arrows which

indicate energy, feedstock and information flows [15]. The

energy flow diagram of CFE production system is shown in

Fig. 2.

The second step for the emergy analysis is to make emergy

evaluation tabulation to place the numerical value and the

units of each flow mentioned in the diagram. To obtain the

emergy value of each input, the raw data of input such as

joules, grams or dollars are multiplied by their transformities.

Emergy analysis of CFE production system is shown in Table 2.

Finally, various emergy-based indicators are calculated.

The ecological efficiency, environmental impact and the

sustainability of the studied system are assessed.

3. Results and discussions

As is shown in Table 2, the transformity of CFE is

1.10 Eþ 05 sej/J. Transformity is path dependent, thatmeans it

is susceptible to the material and energy used at each step of

the production process. The transformity of different fuels are

compared in Table 3.

Results indicate that the transformities of biofuels are

greater than those of fossil fuels. This can be explained by the

fact that a larger amount of resources are required to produce

the biofuels. However, fossil fuels are far from being

elec

tric

ity

wat

er

chem

ical

s

coal

dies

el

mac

hin

ery

lab

or

w to the whole inputs of CFE system.

5.67 0.69

22.51

71.15

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

/desuygre

mE

%R N FR FN

Fig. 5 e The emergy proportion of four category flows to the whole inputs of CFE production system.

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9586

renewable resources, because the time needed for their

regeneration is extremely long compared to the time of their

exploitation. The transformity of CFE is the lowest in the three

kinds of biomass-based fuel ethanol. It is also lower than any

biodiesel shown in Table 3. It means that CFE consumes the

least emergy in the production process. In order to save

energy, the transformity of the same product should be

decreased as much as possible. In the process of cassava

cultivation, it is necessary to choose the better variety of stem

cuttings, improve the planting technology to increase the

yield, and use less N, P, K fertilizers and more farm manure

to decrease the emergy input. It is also very important to

improve the technology of fermentation and distillation to

save energy.

The emergy proportion of each flow to the whole inputs of

CFE system is shown in Fig. 4. Nitrogenous fertilizer, coal, and

labor are themain inputs of all emergy flows in the production

system of CFE. If the production technology of nitrogenous

fertilizer is improved to decrease its transformity, or farm

manuresubstitutes fornitrogenous fertilizerpartially, the total

emergy input will decrease. Moreover, farm manure is the

renewable resource, so using more farm manure is good for

sustainable development. Coal is used to produce steam in the

industrial process ofCFEproduction. It is important to improve

the technology and optimize the operation conditions of

the industrial process to reduce theconsumptionof steam.The

emergy of labor nearly accounts for 20% of all inputs. The

mechanization level of cassava cultivation in China is low,

which is decided by the national conditions. Appropriately

developing the mechanized farming of cassava is necessary.

Results of life cycle energy consumption assessment by

Leng et al. show that coal is the main primary energy [6]. Coal

consumption accounts for 70% and N production accounts for

11% of the energy consumed in the whole life cycle. Results of

emergy analysis in this paper show that nitrogenous fertilizer,

coal, and labor are the main inputs of all emergy flows in the

production system of CFE. Nitrogenous fertilizer accounts for

Table 4 e Emergy indexes of CFE system.

Emergy indices EYR ELR RER ESI

Data 1.07 2.55 0.28 0.42

25%, coal accounts for nearly 20%, and labor also accounts for

nearly 20% of the whole input emergy. In life cycle energy

assessment, labor, environmental resources such as sun and

rain, and machinery were not considered. Different kinds of

energy such as coal and electricity were expressed in the

common unit of Btu. No differences are between 1 Btu of coal

and 1 Btu of electricity in energy analysis. But the labor, free

environmental resources, and machinery were accounted in

emergy analysis. All of the input flows were evaluated on the

same basis of sej. Therefore, emergy analysis is more accurate

than the life cycle energy assessment. And emergy analysis

has more indices to show sustainability of the system.

As is shown in Fig. 5, emergy from the environment only

accounts for less than 10% of the whole inputs. It indicates

that the system depends less on the environment. Non-

renewable purchased emergy accounts for 71.15% of the

whole input emergy. Because the process from cassava culti-

vation to ethanol production consumedmuch non-renewable

purchased resources, such as nitrogenous fertilizer, coal,

phosphate, coal electricity, and machinery. Renewable

purchased emergy accounts for 22.51% of the whole input

emergy. Labor is the main renewable purchased emergy.

Various emergy-based indicators of CFE are shown in

Table 4. EYR of CFE is 1.07, which shows the emergy from

environment is very little. The CFE systemmainly depends on

purchased emergy. EYR of extraction of minerals and fossil

resources are from 3 to 7 [15]. Minerals and fossil resources are

formed through long time of geological process. The social

inputs are only needed in exploitation. These result in the

high EYR of minerals and fossil resources.

The more non-renewable resources are consumed, the

heavier load is placed on the environment. Excessive loading

on environment by humanmight result in severe degradation

in ecological function of a system [42]. The ELR of CFE is 2.55,

wheat ethanol is 4.05 [39], and corn ethanol is 7.84 [40], so they

all have amoderate impact on the environment. However, the

CFE system has the lowest pressure on the environment

comparing the wheat ethanol and corn ethanol. Bioethanol is

not totally renewable, because it is produced by investing

large amounts of non-renewable resources. RER of CFE is 0.28,

wheat ethanol is 0.20 [39], and corn ethanol is 0.11 [40]. Thus

CFE system has the highest fraction of renewable emergy. ESI

is 0.42 for CFE, 0.31 for wheat ethanol [39], and 0.15 for corn

ethanol [40]. So the CFE system is the most sustainable.

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9 587

4. Conclusion

By quantifying natural and man-made, as well as renewable

and non-renewable inputs to CFE production system on

a common basis, emergy analysis facilitates comparisons

across the system and can identify manipulations to achieve

greater sustainability.

The transformity of CFE is 1.10 E þ 05 sej/J, which is lower

than biodiesel, corn ethanol and wheat ethanol. But the trans-

formity of biofuels are greater than thoseof fossil fuels, because

the production of biofuels need more inputs than fossil fuels.

However, the time needed for fossil fuels’ regeneration is

extremely long, and the fossil fuels are limited. Nitrogenous

fertilizer, coal, and labor are themain inputs of all emergyflows

in the production system of CFE. Non-renewable purchased

emergy accounts for 71.15% of the whole input emergy. The

dependenceonnon-renewableenergy increasesenvironmental

degradation, making the system less sustainable relative to

systemsmore dependent on renewable energies. It is necessary

to choose the better variety of stem cuttings, improve the

planting technology to increase the yield, and use less N, P, K

fertilizers andmore farmmanure to decrease the emergy input.

It is also very important to improve the technology of fermen-

tation and distillation to save energy. Emergy from the envi-

ronment only accounts for less than 10% of the whole inputs. It

indicates that the system depend less on the environment.

Emergy-based indicators of CFE were calculated. EYR of CFE is

only 1.07, which indicates that the CFE systemmainly depends

on purchased emergy. ELR of CFE is 2.55, so it has a moderate

impact on the environment. Non-renewable resources inputs

should be reduced to lighten the pressure on the environment.

RERofCFE is 0.28,wheatethanol is0.20, andcornethanol is0.11.

Thus CFE system has the higher renewability than wheat

ethanol or corn ethanol. ESI is 0.42 for CFE, 0.31 for wheat

ethanol, and0.15 for cornethanol. So theCFEsystemis themore

sustainable than the system of wheat ethanol or corn ethanol.

From the perspective of sustainability, CFE is a good

alternative to substitute for oil. But CFE is not totally renew-

able, and its production still consumes much non-renewable

resources. Therefore it is vital to reduce the non-renewable

energy used in production of CFE.

Acknowledgements

This study has been supported by Guangdong Provincial

Laboratory of Green Chemical Technology, China and

Thailand International Cooperation Program (Grant No.

18509J)，and Guangdong Provincial Science and Technology

Development Program (Grant No. 2006A50102002).

Appendix.

Notes to Table 2:

1. Sun radiation ¼ A � Ic � absorbed percentage

A(surface area) ¼ 5.02 E þ 07 m2

I (average yearly solar radiation) ¼ 110 kcal/

(cm2 a) ¼ 4.6 E þ 09 J/(m2 a)

Ic(solar radiation per the growth cycle of cassava) ¼I � 10/12 (a/c) ¼ 3.83 E þ 09 J/(m2 c)

Absorbed percentage ¼ 70%

Sun radiation ¼ 5.02 E þ 07 m2 � 3.83 E þ 09

J/(m2 c) � 0.7 ¼ 1.35 E þ 17 J/c.

2. Rain chemical potential energy ¼ A � Pc � D � DG

DG(Gibbs free energy) ¼ 4.94 J/g.

P ¼ yearly precipitation � (1-evapotranspiration rate

60%) ¼ 1600 mm/yr � (1 � 0.6) ¼ 0.64 m/yr.

Pc(precipitation per the growth cycle of cassava) ¼ P � 10/

12 yr/c ¼ 0.533 m/c

D(water density) ¼ 1 E6 g/m3

Rain chemical potential energy ¼ 5.02 E þ 07 m2 � 0.533

m/yr � 1 E6 g/m3 � 4.94 J/g ¼ 1.32 E þ 14 J/c.

3. Rain geopotential ¼ A � E � pc � D � g

E(average elevation) ¼ 80 m.

pc(precipitation) ¼ 1600 mm/yr � 10/12 yr/c ¼ 1.333 m/c

g(Gravity) ¼ 9.8 N/kg.

Rain geopotential ¼ 5.02 E þ 07 m2 � 80 m/yr � 1.333

m/c � 1 E þ 03 kg/m3 � 9.8 N/kg ¼ 5.27 E þ 13J /c

4. Wind kinetic ¼ r � c(vg)3G � A

r(air density) ¼ 1.23 kg/m3

c(drag coefficient) ¼ 1 E � 3

v(average annual wind velocity) ¼ 2.4 m/s

vg(geostropic wind) ¼ 10/6 v

G(Wind Gradient) ¼ 3.154 E þ 7 s/yr

Wind kinetic¼ 1.23 kg/m3 � 1E � 3� (2.4 m/s�10/6)3 � 3.154 E þ 7 s/yr � 10/12 yr/c � 5.02 E þ 07 m2 ¼1.04 E þ 14 J/c

5. Net topsoil loss ¼ A � E � O � Energy of organic soil

E(erosion rate) ¼ 350 g/(m2 yr)

O(organic soil percentage) ¼ 2%

Energy of organic soil ¼ 5.4 E þ 6 kcal/t � 4186

J/kcal ¼ 2.26 E þ 10 J/t

Net topsoil loss ¼ 5.02 E þ 7 m2 � 350 g/(m2 yr) � 10/12

yr/c � 2% � 2.26 E þ 10 J/t ¼ 6.63 E þ 12 J/c

6. Stem cuttings

750 kg stem cuttings were needed to plant 1 ha of cassava.

The plant area is 5019 ha.

Stem cuttings ¼ 750 kg/ha � 5019 ha ¼ 3.76 E þ 6 kg.

7. Labor

2200 men*h are needed to plant 1 ha cassava and produce

cassava chips. The plant area is 5019 ha.

Labor ¼ 2200 men*h/ha � 5019 ha ¼ 1.10 E þ 7 men*h.

9. 22 Hydroelectricity and coal electricity

Electricity consumed inproducing1 tof ethanolwas213kWh.

24300 t ethanol are produced in this factory every year.

Electricity¼213kWh/t�24300t¼5175900kWh¼1.86Eþ13 J.

Hydroelectricity consumed in producing ethanol ¼ 30% �Electricity ¼ 5.59 E þ 12 J.

Electricity consumed in cassava chips production ¼5.50 E þ 07 kJ.

Hydroelectricity consumed in producing cassava chips ¼30% � 5.50 E þ 07 kJ ¼ 1.65 E þ 10 J.

Hydroelectricity ¼ 5.59 E þ 12J þ 1.65 E þ 10 J ¼ 5.61 E þ 12 J.

Coal electricity ¼ 70% � (1.86 E þ 13 J þ 5.50 E þ 10 J)

¼ 1.30 E þ 13 J

b i om a s s an d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9588

11. Liquefying amylase

The consumption of liquefying amylase in this factory is

91 t/yr, and the energy per kg of enzymes is 6.32 E þ 6 J/kg.

So the energy of liquefying amylase consumed was

5.77 E þ 11 J/yr.

12. Glucoamylase

The consumption of liquefying amylase in this factory is

417 t/yr, and the energy per kg of enzymes is 6.32 E þ 6 J/kg.

So the energy of liquefying amylase consumed is

2.64 E þ 12 J/yr.

13e16. N, P, K fertilizers & Herbicides

N, P, K fertilizers & herbicides used in planting cassava

were respectively 150 kg/ha, 75 kg/ha, 225 kg/ha, and 15

kg/ha. And the planting area of cassava is 5019 ha.

N, P, K fertilizers & herbicides used were respectively

7.53 Eþ 5 kg, 3.76 Eþ 05 kg, 1.13 Eþ 06 kg, and 7.53 Eþ 04 kg.

19. Coal

Coal consumed in this factory is 12,150 t/yr, and the heat

value of coal is 29.308 MJ/kg.

Coal ¼ 12,150 t/yr � 29,308,000 J/kg ¼ 3.56 E þ 14 J/yr.

20. 3A molecular sieve

The investment on 3A molecular sieve in this factory is

137,142$. And the life of 3A molecular sieve is 6 years.

3A molecular sieve ¼ 137,142$/6yr ¼ 22,857$/yr.

21. Diesel

Diesel consumed in production system of cassava chips

were 7.53 E þ 12 J/yr.

Average distance from cassava chips production site to

factory is 50 km.

Energy density of truck transport is 1713Btu/(ton mile).

68265 t cassava chips are needed every year in this factory.

Diesel consumed in transporting cassava chips ¼ 68265 t/

yr � 50 km � 0.621 mile/km � 1056 J/Btu � 1713

Btu/(ton mile) ¼ 3.83 E þ 12 J/yr.

Average distance from factory to market place is 100 km.

Energy density of tank truck transport is 1028

Btu/(tonmile). 24300 t fuel ethanol are produced every year

in this factory.

Diesel consumed in transporting fuel ethanol ¼ 24300

t/yr � 100 km � 0.621 mile/km � 1056 J/Btu � 1028

Btu/(ton mile) ¼ 1.64 E þ 12 J/yr.

Diesel ¼ 7.53 E þ 12 J/yr þ 3.83 E þ 12 J/yr þ 1.64 E þ 12

J/yr ¼ 1.30 E þ 13 J/yr.

23. Building & machinery

The investment on the buildings and machineries in this

factory is 8.0 E þ 6$. And the operating life of the buildings

and machineries is considered to be 10 years.

Building & machinery ¼ 8.0 E þ 6$/10 year ¼ 8.0 E þ 5$/yr.

r e f e r e n c e s

[1] Nguyen Thu Lan T, Gheewala Shabbir H. Fossil energy,environmental and cost performance of ethanol in Thailand.J Clean Prod 2008;16(16):1814e21.

[2] Yu Suiran, Tao Jing. Energy efficiency assessment by lifecycle simulation of cassava-based fuel ethanol forautomotive use in Chinese Guangxi context. Energy 2009;34(1):22e31.

[3] Nguyen Thu Lan Thi, Gheewala Shabbir H, Garivait Savitri.Energy balance and GHG-abatement cost of cassavautilization for fuel ethanol in Thailand. Energy Policy 2007;35(9):4585e96.

[4] Nguyen Thu Lan T, Gheewala Shabbir H, Garivait Savitri. Fullchain energy analysis of fuel ethanol from cane molasses inThailand. Appl Energy 2008;85(8):722e34.

[5] Cardona Alzate CA, Sanchez Toro OJ. Energy consumptionanalysis of integrated flowsheets for production of fuelethanol from lignocellulosic biomass. Energy 2006;31(13):2447e59.

[6] Leng Rubo, Wang Chengtao, Zhang Cheng, Dai Du,Pu Gengqiang. Life cycle inventory and energy analysis ofcassava-based Fuel ethanol in China. J Clean Prod 2008;16(3):374e84.

[7] Yu Suiran, Tao Jing. Life cycle simulation-based economicand risk assessment of biomass-based fuel ethanol (BFE)projects in different feedstock planting areas. Energy 2008;33(3):375e84.

[8] Zhang Cheng, Han Weijian, Jing Xuedong, Pu Gengqiang,Wang Chengtao. Life cycle economic analysis of fuel ethanolderived from cassava in southwest China. Renew SustainEnergy Rev 2003;7(4):353e66.

[9] Krishnan MS, Taylor F, Davison BH, Nghiem NP. Economicanalysis of fuel ethanol production from corn starch usingfluidized-bed bioreactors. Bioresour Technol 2000;75(2):99e105.

[10] Beer Tom, Grant Tim. Life-cycle analysis of emissions fromfuel ethanol and blends in Australian heavy and lightvehicles. J Clean Prod 2007;15(8e9):833e7.

[11] Yang Q, Chen B, Ji Xi, He YF, Chen GQ. Exergetic evaluation ofcorn-ethanol production in China. Commum Nonlinear SciNumer Simulat 2009;14(5):2450e61.

[12] Lan Sh F, Qin P, Lu HF. Emergy evaluation of eco-economicsystem. Beijing: Chemical Industrial Press; 2002. p. 167e193.

[13] Pulselli RM, Simoncini E, Ridolfi R, Bastianoni S. Specificemergy of cement and concrete: an energy-based appraisalof building materials and their transport. Ecol Indic 2008;8(5):647e56.

[14] Brown MT, Ulgiati S. Emergy evaluations and environmentalloading of electricity production systems. J Clean Prod 2002;10(4):321e34.

[15] Odum HT. Environmental accounting: emergy andenvironmental decision making. New York: John Wiley &Sons; 1996.

[16] Chen GQ, Jiang MM, Chen B, Yang ZF, Lin C. Emergy analysisof Chinese agriculture. Agric Ecosyst Environ 2006;115:161e73.

[17] Odum HT. Self-organization, transformity, and information.Science 1988;242:1132e9.

[18] Brown MT, Odum HT, Murphy RC, Christianson RA,Doherty SJ, McClanahan TR, et al. Maximum powerdtheideas and applications of H.T. Odum. Niwot: University Pressof Colorado; 1995. p. 393.

[19] Hau Jorge L, Bakshi Bhavik R. Promise and problems ofemergy analysis. Ecol Modell 2004;178(1e2):215e25.

[20] Ekins P, Simon S, Deutch L, Folke C, De Groot R. A frameworkfor the practical application of the concepts of critical naturalcapital and strong sustainability. Ecol Econ 2003;44:165e85.

[21] Bakshi BR. A thermodynamic framework for ecologicallyconscious process systems engineering. Comput Chem Eng2002;24:1767e73.

[22] Hau JL, Bakshi RB. Promise and problems of emergy analysis.Ecol Modell 2004;178:215e25.

[23] Hu Zhiyuan, Fang Fang, Ben DaoFeng, Pu Gengqiang,Wang Chengtao. Net energy, CO2 emission, and life-cyclecost assessment of cassava-based ethanol as an alternativeautomotive fuel in China. Appl Energy 2004;78(3):247e56.

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 5 8 1e5 8 9 589

[24] Giannetti BF, Barrella FA, Almeida CMVB. A combined toolfor environmental scientists and decision makers: ternarydiagrams and emergy accounting. J Clean Prod 2006;14(2):201e10.

[25] Zhou JB, JiangMM, Chen B, Chen GQ. Emergy evaluations forconstructed wetland and conventional wastewater treatments.Commun Nonlinear Sci Numer Simulat 2009;14(4):1781e9.

[26] Brown MT, Ulgiati S. Emergy analysis and environmentalaccounting. Encycl Energy 2004;2:329e54.

[27] La Rosa AD, Siracusa G, Cavallaro R. Emergy evaluation ofSicilian red orange production- A comparison betweenorganic and conventional farming. J Clean Prod 2008;16(17):1907e14.

[28] Ulgiati Sergio. Mark T. Brown. Monitoring patterns ofsustainability in natural and man-made ecosystems. EcolModell 1998;108(1e3):23e36.

[29] Brown MT, Ulgiati S. Energy quality, emergy, andtransformity: H.T. Odum’s contributions to quantifying andunderstanding systems. Ecol Modell 2004;178(1e2):201e13.

[30] Odum HT. Ecological and general systems: an introduction tosystems ecology. Boulder: University of Colorado Press; 1994.

[31] Odum HT, Brown MT, Williams SB. Folio #1: introduction andglobal budget, Handbook of emergy evaluation:a compendium of data for emergy computation issued ina series of folios. Gainesville, USA: Center for EnvironmentalPolicy, University of Florida; 2000.

[32] BrownMT, Bardi E. Folio #3: emergy of global processes,Handbook of emergy evaluation: a compendium of data foremergycomputationissuedinaseriesof folios.Gainesville,USA:Center for Environmental Policy, University of Florida; 2001.

[33] Yang Hui, Chen Li, Yan Zongcheng, Wang Honglin.Emergy analysis of cassava chips-suitable feedstock for fuel

ethanol in China. Ecological Engineering 2010;10(36):1348e54.

[34] Ortega E. Handbook of emergy calculations. Sao Paulo, Brazil:Laborato’rio de Engenharia Ecolo’gica e Informa’ticaAplicada; 2000.

[35] Yang ZF, Jiang MM, Chen B, Zhou JB, Chen GQ, Li SC. Solaremergy evaluation for Chinese economy. Energy Policy 2010;38(2):875e86.

[36] Lingmei Wang. Zhang Jintun. Emergy evaluation of powerplant eco-industrial park. Chin J Appl Ecol 2004;15(6):1047e50.

[37] Coppola F, Bastianoni S, Østergard H. Sustainability ofbioethanol production from wheat with recycled residuesas evaluated by Emergy assessment. Biomass Bioenergy2009;33(11):1626e42.

[38] Brandt-Williams S. Emergy of Florida agriculture. folio #4,handbook of emergy evaluation. Gainesville, USA: Center forEnvironmental Policy, University of Florida; 2002.

[39] Dong Xiaobin, Ulgiati Sergio, Yan Maochao, Zhang Xinshi,Gao Wangsheng. Energy and emergy evaluation ofbioethanol production fromwheat in Henan Province, China.Energy Policy 2008;36(10):3882e92.

[40] Giampietro M, Ulgiati S. Integrated assessment of large-scale biofuel production. CRC Crit Rev Plant Sci 2005;24:365e84.

[41] Ulgiati SA. Comprehensive energy and economic assessmentof biofuels: when “Green” is not enough. CRC Crit Rev PlantSci 2001;20(1):71e106.

[42] Brown MT, Ulgiati S. Emergy-based indices and ratios toevaluate sustainability: monitoring economies andtechnology toward environmentally sound innovation. EcolEng 1997;9:51e69.