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CHAPTER 4

Results, Finding and Discussions

4.1 Background

The chapter provides the results of the questionnaire and semi-structured interview questions.

These results were further analysed to produce meaningful findings that are discussed in detail

throughout the chapter. It was essential to appropriately analyse these findings in order to

produce recommendations for the implementation of this technology in Libya. In order to

establish an AD plant in a specific locality, it needs to consider multiple factors so that

maximum benefits can be attained.

4.2 Demographic Analysis of Respondents

Figure 1- Gender based sample size of the survey

An online survey questionnaire was prepared and kept online for 20 days to gather as much

data as possible to make accurate estimations and derive statistics about food waste amount

and type of food waste. Sample size of the population was estimated to be 100 however, a

total of 112 people returned completed questionnaires. Based on a gender categorisation 76

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male and 36 females as shown in Figure 13 participated in the survey. Almost people of all

age groups gave their poll but mostly the survey questionnaire was filled by people in age

bracket of 26-34 years as shown in Figure 14.

Figure 2- Age group based sample size of the survey

About 69.90 per cent of the people were students while other 21.25 per cent were

professionals in various fields. Of total sample size, 28.43 per cent belonged to rural areas

and 71.57 per cent belonged to urban areas. Most of the people belonged to the Tripoli city

or nearby areas as shown in Figure 7. It verifies their familiarity about the city and its

requirements. The questionnaire contains 27 questions in total including many aspects of the

research in order to obtain qualitative type of data relevant to the research.

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Figure 3- Distance of the people undergoing survey from the Tripoli city

4.3 Waste to Energy: An Alternative Method of Electricity Generation in Tripoli

Figure 4- Source of electricity generation in Libya

Since Tripoli has been rich enough in oil reservoirs, fossil fuels are a primary source of

electricity generation here. According to the survey, oil is the most used source of electricity

generation in Libya as shown in Figure 16. Keeping in mind the expected exhaustion of

natural resources with the increasing population and electricity demands in Tripoli, which is

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the capital and one of the largest populated cities of Libya, there needs to be a shift from

national grids to renewable electricity generation methods. In the survey people were asked

how often do they undergo electricity outages and above 40 per cent answered with

‘frequently’, while above 29 per cent said they face problem of shortfalls every day. Hence,

the current scenario of the Tripoli city demands an alternative energy generation method to

be adopted along with the conventional energy generation plants in order avoid scarcity of

natural resources in the future.

Figure 5- How often Tripoli city undergo electricity outages?

4.4 Waste to Energy (WTE) Conversion

There are three main categories of WTE methods are; thermochemical extraction, biochemical

extraction and mechanical Content removed….

4.5 Current State of Food Waste Management in Tripoli

In order to access the current situation of wood waste treatment, habit of food waste among

people and municipal authorities are reviews via a survey. Statistical analysis is performed

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using data collected from the survey as shown in the Table 8. The data collected through

questionnaire contains Content removed…

Table 1- Statistical analysis of current state of food waste management in Tripoli

How much

food do you

think you

discard on

average daily?

How clean do

you think

Tripoli city is?

In terms of

waste

management?

What is

general food

waste habit of

people in

Tripoli?

Do you yourself

take care of

proper, hygienic

disposal of

household

waste?

Valid entries in

data

109 103 102 104

Mean 3.06 3.29 3.08 2.24

Median 3.00 3.00 3.00 3.00

Mode 4 3 3 1

Since the data is qualitative in nature, mean and median do not provide a reasonable average

for our study. Thus mode of the data presents most reliable form of average amount of food

waste collection/day/person. Hence as per the data obtained, majority of participants

suggested that;

The range of food waste most selected by the people of Tripoli is 1-2 kg/day per person

(option 4 from the questionnaire)

Total food waste collection is estimated by how much food waste people discard every day.

The average food waste calculated is 0.8 tones/person per year which is approximately

178,640 tones/year on average in Tripoli. The calculations are performed using following

equation.

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𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑓𝑜𝑜𝑑 𝑤𝑎𝑠𝑡𝑒 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟 𝑖𝑛 𝑇𝑟𝑖𝑝𝑜𝑙𝑖 (𝑡𝑜𝑛𝑛𝑒𝑠) =

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑓𝑜𝑜𝑑 𝑤𝑎𝑠𝑡𝑒 𝑑𝑖𝑠𝑐𝑎𝑟𝑑𝑒𝑑 𝑝𝑒𝑟 𝑝𝑒𝑟𝑠𝑜𝑛 ( 𝑡𝑜𝑛𝑛𝑒𝑠) × 𝑆𝑐𝑎𝑙𝑖𝑛𝑔 𝐹𝑎𝑐𝑡𝑜𝑟

Equation 1- Calculating Amount of Food Waste per Year

People were asked about the cleanliness condition of Tripoli in terms of waste disposals

management and the mode in the table shows option 3 (as also confirmed from table 8) in the

questionnaire which is most selected option by the respondents. According to figure 18, 32.29

per cent respondents indicated that, one can see waste on the roads in Tripoli city. Which

indicates that the waste management system is in need of an update and if necessary, food

waste amount is adequate to run a WTE plant.

Figure 6- Cleanliness of Tripoli city is in terms of waste management

Content removed…

4.6 Technical Feasibility

Anaerobic digestion is a step wise process as shown in Figure 21. The process is consisted on

hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The process of converting food

waste into their basic units such as sugars, amino acids, and long-chain fatty acids from

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carbohydrates, proteins and fats respectively, is called as hydrolysis. The procedure can be

very odorous sometimes. Hydrolyzed products then undergo acidogenesis which converts

them into fatty acids or alcohols. The glucose in this process is either converted into ethanol

or propionate as described by (Mata-Alvarez, 2003) in the following chemical equations.

𝐶6𝐻12𝑂6 < − − > 2 𝐶𝐻3𝐶𝐻2𝑂𝐻 + 2𝐶𝑂2

𝐶6𝐻12𝑂6 + 2𝐻2 < − − > 2 𝐶𝐻3𝐶𝐻2𝐶𝑂𝑂𝐻 + 2𝐻2𝑂

Figure 7- Process flow diagram of anaerobic digestion (Serna, 2009)

The process of converting remaining fatty acids and alcohol in the process into acetic acid,

carbon dioxide and hydrogen for Content removed…

Technical plant Description; Valorga Anaerobic Digestion Technique

Valorga is a dry, continuous type technique which was initially developed in 1918 in France,

primarily for the treatment of organic part of municipal solid waste (MSW). The later version

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although was made adaptable to treat mixed MSW. While first pilot Valorga plant was

established in 1982 in Montpellier, France. While first industrial plant was established in 1988

in Amiens, France with the capacity of 50,000 tones/year (De Laclos et al., 1997).

Figure 22: Valorga anaerobic digestion reactor (Arsove, 2010)

Figure 22 above shows a typical Valorga AD reactor which typically is a one stage vertical,

plug-flow cylinder in Content removed…

Table 1: Installed capacity of commonly used AD technologies

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4.7 Factors Effecting the AD Process

The AD process is sensitive to external conditions thus it is important to maintain factors that

affect the process of AD plant. External conditions are important to maintain to get the

required results in anaerobic digester. Some of the factors effecting the AD process are

4.7.1 pH

The acceptable range for the bacteria to perform digestion is between 5.5 and 8.5 (Seadi et

al., 2008). And the methanogenic group work only with pH close to neutral levels as

methanogen population consume acids produced in the previous stages. If methanogenesis

cannot work properly, acid will be accumulated and pH becomes lower. pH can be used as

the indicator for overloading of feedstock.

4.7.2 Temperature

Temperature is another very critical parameter to control in anaerobic digestion. There are

three main temperature ranges where anaerobic digestion can occur: Thermophilic (50ºC –

60ºC), Mesophilic (35ºC – 40ºC) and Psycrophilic (15ºC – 25ºC) (De Bruyn & Hiborn, 2007).

Content removed….

4.7.3 Retention Time (RT)

Retention time means the time the feedstock spends in the digester. The retention time

depends on the feedstock and the operational parameters, especially temperature. Shorter

retention time will lead to higher biogas generation rate but lower overall degradation.

Retention time is greatly related to the size of the digester, as the longer the RT, the bigger

the digester should be. So, it is important to find a suitable RT for the design of digester. RT

can be divided into hydraulic retention time (HRT) and solids retention time (SRT). HRT is

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the number of days the materials stay in the tank which is equal to volume divided by the flow

of feedstock. SRT is the quantity of solids stayed in the digester divided by the quantity of

solid waste each day. Equations are listed below (Curry & Pillay, 2012):

𝐻𝑅𝑇 = 𝑉

𝑄

Equation 2- Calculating hydraulic Retention Time (HRT)

𝑆𝑅𝑇 = 𝑉 ∗ 𝐶𝑑

𝑄𝑤 ∗ 𝐶𝑤

Equation 3- Calculating Solids Retention Time (SRT)

V = digester volume (m3)

Cd = solid concentration in the digester

Qw = volume washed each day (m3)

Cw = solid concentration of the waste

Organic Loading Rate (OLR)

Organic Loading Rate is the amount of organic materials added to the digester in a given

amount of time.

𝑂𝐿𝑅 = 𝑄 ∗ 𝑉𝑆

𝑉

Equation 4- Calculating Organic Loading Rate (OLR)

VS = concentration of volatile solid in the feedstock

4.7.4 Digestion Process

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The process of food waste digestion can be divided into four steps namely, pre-treatment,

waste digestion using an AD plant, gas recovery and residue treatment as shown in Figure 7.

In order to achieve homogeneity of the feedstock before the digestion process pre-treatment

is used. Separation of non-biodegradable material and shredding are the part of pre-

processing. Source separation is the step where items like glass, metal and stones are

separated. These objects are called undesirable recycling material . Recyclable materials are

separated in the phase of source separation. Mechanical separation can be employed if source

separation is not available. However, the resultant fraction is then more contaminated leading

to lower compost quality. The waste ultimately is shredded before sending into the digester.

Figure 8- Pretreatment process in anaerobic digestion (Braun, 2007)

Once the feedstock is inside the digester, Content removed…

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Figure 9- Solid Waste Conversion Unit (Source; http://www.soton.ac.uk/~sunrise/anaerobicdig.htm#ADsolidwaste)

4.8 Proposed Geographical Location

In order to establish a Valorga AD plant in Tripoli, there are various factors that need to be

considered for the specified choice and establishment of the plant to meet the objectives. Since

the food waste generation in Tripoli is about 178,640 tones/year on average, capacity of the

plant would depend directly on the amount of food waste available. Content removed….

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Figure 10- 3-Ring road, proposed location to establish an AD plant in Tripoli

4.9 Financial Analysis of AD Plant in Tripoli

Economic viability of the proposed food waste to energy conversion plant is estimated based

on the amount of food waste generation and capacity of proposed plant. This section help

estimating the investment cost, maintenance and transportation cost. The biogas yield on the

basis of quantity of the collected food waste and electricity generation capacity are also

estimated.

4.9.1 Capital Cost

Capital cost to establish an AD plant involves the cost of the following Content removed….

4.9.2 Operational and Maintenance Cost

Table 10 gives a brief insight into the maintenance and operational cost of proposed plant.

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Table 2- Operational and maintenance cost estimate for food waste to electricity conversion plant in Tripoli

Operational and Maintenance

Cost Type

Cost in British Pounds (£) Cost in Libyan Dinar

(LYD)

One General Manager 80,000 £ 149,007

Eight Managers 180,000 £ 335,267

Fifteen Electricians 150,000 £ 279,389

Ten Mechanics 120,000 £ 223,511

Twenty-five Plant Operators 200,000 £ 372,519

Forty General Workers 250,000 £ 465,649

Maintenance 2per cent of the investment

cost per year = 295,000 £

549,466

Contingency Plan 100,000 £ 186,259

Total Cost 1,375,000 £ 2,561,072

4.9.3 Biogas Yield and Electricity Benefit

Since the one of the objective is to meet the demand of electricity by using household waste,

so output of electricity generation is an important factor to access the efficiency of the plant.

Electricity generation depends directly on the quantity of biogas (m3) that can be extracted

from food waste. The type of waste, and design of the digester system, are primary factors in

determining the yield of methane gas. However generic output estimated by researcher is

20m3 of biogas per ton for some digesters, while others produce as much as 98m3 (Marika et

al. 2013).

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The assumptions made for this study suggest that the plant process approximately 450 tons of

food waste to generate 6 MW of electricity to be sold commercially. An AD plant of proposed

capacity would produce,

27 million m3 of biogas

52per cent is methane = 138 million kWh of total energy

40per cent of energy is converted to electricity = 55 million kWh electricity

Which is equivalent to 6 MW of electricity generation

Therefore, 55,000,000 kW of electricity a year at the rate of (15 LYD per K/W) will

yield an income of 1,412,500,000 Billion LYD every year.

4.9.4 Efficiency based on IRR and NPV

The IRR estimated for this investment using equation 2 is 8per cent. However, the (NPV) is

greater than 0, means the total discount value of the benefit is greater than the total discount

of the cost.

Table 3- Calculated IRR and NPV

Year Cost (LYD) Benefit

(LYD)

Discount

Factor for

8%

NPV of Cost NPV of

Benefit

1 13,201,250 - 0.925 12223380

2 13,201,250 - 0.857 11317944

3 2,343,273 8,517,471 0.793 1860165 8,517,471

4 2,343,273 8,517,471 0.735 1722376 6260595

5 2,343,273 8,517,471 0.680 1594792 5796848

6 2,343,273 8,517,471 0.630 1476659 5367452

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7 2,343,273 8,517,471 0.583 1367277 4969863

8 2,343,273 8,517,471 0.540 1265997 4601725

9 2,343,273 8,517,471 0.500 1172220 4260856

10 2,343,273 8,517,471 0.463 1085389 3945237

4.10 Impact of the AD Plant on Environment of Tripoli

Since electricity generation with fossil fuels involves burning, it causes the emission of CO2,

CO and other harmonious gases which pollute the environment and damage the ozone layer

gradually. A correlational study given in Table 12 represents Content removed…

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Table 4- Correlation based statistical analysis of variables impacting environment of Tripoli

Correlations

How much

food do you

think you

discard on

average

daily?

How much

do you feel

climate of

Tripoli

have been

polluted in

last 10

years?

Is

municipal

waste a

major

reason of

pollution

in Tripoli?

Is there

frequent

burning

happens near

the waste

collection

bins?

How much food do you

think you discard on

average daily?

Correlation

Coefficient

1.000 -0.042 0.208 -0.338**

N (No. of

Observations)

109

81

81

83

How much do you feel

climate of Tripoli have

been polluted in last 10

years?

Correlation

Coefficient

-0.042 1.000 0.195 -0.026

N (No. of

Observations)

81

81

80

80

Is municipal waste a

major reason of

pollution in Tripoli?

Correlation

Coefficient

0.208 0.195 1.000 -0.131

N (No. of

Observations)

81 80 81 80

Is there frequent

burning happens near

the waste collection

bins?

Correlation

Coefficient

-0.338** -0.026 -0.131 1.000

N (No. of

Observations)

83 80 80 83

** Correlation is significant.

Life cycle assessment of the proposed plant is an environmental tool that is proven effective

for the analysis of the product to study its interaction with environment. (Kim, 2010) has

explained it in detail which covers from waste generation to final disposal. The process of

digestion, as discussed above, undergoes various steps such as collection, transportation,

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treatment and disposal of waste material extracted from the plant. Emission of generated gases

goes into environment and water discharge is mixed with the water resources.

4.11 Impact of AD Plant on Public Health in Tripoli

Open dumping of waste not only generates bad odor, but also fumigate gases which pollute

environment and cause bad health impacts on the health of residents. It can invite mosquitos

and can be a reason of prevailing Diarrhea, Malaria and other viral infections in the locality.

Degrading food has microorganisms, decomposing the food in open environment, thus by

products can’t be discarded properly and can cause viral diseases. Content removed….

Table 5- Correlational based statistical analysis of variables influencing health of people

How much

food do you

think you

discard on

average daily?

Do municipal

authorities

collect waste

regularly?

How much food do you think you

discard on average daily?

Correlation

Coefficient

1.000 0.289**

N (No. of

Observations )

109 84

Do municipal authorities collect

waste regularly?

Correlation

Coefficient

0.289** 1.000

N (No. of

Observations )

84 84

** Correlation is significant.

Noise pollution can be an outcome of the plant if established near residential area as it will

generate considerable noise and can cause disturbance to the people. Also with aging of the

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plant the noise increases. Also the generators other than the food processing units have their

noise. Hygiene is the second major concern of the people who undergone survey about the

AD plant. Content removed…

4.12 Interview Questions Analysis

The five respondents chosen and accepted the invitation for an interview were associates of

the General Authority for Environmental Protection and were linked with the department

designated for environmental research and policy making. Three of the interviewees had

experience working with United Nations Development Programme. The officials interviewed

were all designated in a managerial position in their departments. Of the five participants only

one (participant C) strongly believed in recommending the idea of establishing an AD plant

in Tripoli. The respondent indicated;

“Having an AD plant in the country can help a lot with its waste management issue

and the proposition that establishing such a plant can contribute to the production of

electricity in a sustainable way is something that will be very new and very beneficial

to the country.”

The remaining participants believed that the development and implementation of an AD plant

will be unable to relieve the key environmental issues facing Libya, primarily indicated as

water pollution, desertification, lack of water supply, Content removed…