Results, Finding and Discussions

Transcription

1 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 1

2 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 years as shown in Figure 14. Figure 2- Age group based sample size of the survey About per cent of the people were students while other per cent were professionals in various fields. Of total sample size, per cent belonged to rural areas and 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. 2

3 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 3

4 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 4

5 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 Mean Median Mode 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. 5

6 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, 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. Content removed Figure 6- Cleanliness of Tripoli city is in terms of waste management 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 6

7 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. C 6 H 12 O 6 < > 2 CH 3 CH 2 OH + 2CO 2 C 6 H 12 O 6 + 2H 2 < > 2 CH 3 CH 2 COOH + 2H 2 O 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 7

8 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 8

9 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 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 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 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 9

10 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 C d Q w C w Equation 3- Calculating Solids Retention Time (SRT) V = digester volume (m 3 ) Cd = solid concentration in the digester Qw = volume washed each day (m 3 ) 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 V S V Equation 4- Calculating Organic Loading Rate (OLR) VS = concentration of volatile solid in the feedstock Digestion Process 10

11 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 preprocessing. 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 11

12 Figure 9- Solid Waste Conversion Unit (Source; 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. 12

13 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 Capital Cost Capital cost to establish an AD plant involves the cost of the following Content removed Operational and Maintenance Cost Table 10 gives a brief insight into the maintenance and operational cost of proposed plant. 13

14 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, ,007 Eight Managers 180, ,267 Fifteen Electricians 150, ,389 Ten Mechanics 120, ,511 Twenty-five Plant Operators 200, ,519 Forty General Workers 250, ,649 Maintenance 2per cent of the investment cost per year = 295, ,466 Contingency Plan 100, ,259 Total Cost 1,375,000 2,561, 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 (m 3 ) 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 20m 3 of biogas per ton for some digesters, while others produce as much as 98m 3 (Marika et al. 2013). 14

15 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 m 3 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 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 1 13,201, NPV of Benefit 2 13,201, ,343,273 8,517, ,517, ,343,273 8,517, ,343,273 8,517, ,343,273 8,517,

16 7 2,343,273 8,517, ,343,273 8,517, ,343,273 8,517, ,343,273 8,517, 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 16

17 Table 4- Correlation based statistical analysis of variables impacting environment of Tripoli Correlations How much food do you think you discard on average daily? Correlation Coefficient 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? ** N (No. of Observations) How much do you feel climate of Tripoli have been polluted in last 10 years? Correlation Coefficient N (No. of Observations) Is municipal waste a major reason of pollution in Tripoli? Correlation Coefficient Is there frequent burning happens near the waste collection bins? ** Correlation is significant. N (No. of Observations) Correlation Coefficient N (No. of Observations) ** 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, 17

18 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 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? Correlation Coefficient How much food do you think you discard on average daily? Do municipal authorities collect waste regularly? ** Do municipal authorities collect waste regularly? N (No. of Observations ) Correlation Coefficient ** N (No. of Observations ) ** 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 18

19 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 19