The aim of this thesis is to investigate the degree of stabilization of waste in shallow landfills (simulated by test cells) with specific focus on biogas production and quality. The design of the test cells was found to be suitable for the dumping and stabilization of aerobically treated waste. After six months in the test cells, analysis of the waste from each cell showed that the waste was completely degraded.
Comparison of tests on solids Comparison of tests on eluates Biogas production: reading 1 Biogas production: reading 2.
Introduction
- Motivation of Work
- Objectives
- Overview of Investigation
- Structure of Dissertation
Municipal solid waste deposited at the Bisasar Road Landfill in Durban was composted in aerobic, open landfills for eight and sixteen weeks in a study presented in Simelane (2006). They were filled with untreated and pre-treated waste and were used to monitor the dynamics of long-term aeration and decomposition of the waste over a period of six months. Samples of leachate were collected weekly and analyzed to assess the rate of degradation of waste in the cells.
These results were then used to evaluate the effect of mechanical-biological pretreatment of municipal solid waste on the emission quality of sanitary landfills, the effect of separating the waste into fine and coarse fractions and its applicability to extend the aeration in shallow landfills, to determine.
Literature Survey
Introduction
Solid Waste Management
Sustainable Waste Management
- Sustainable Waste Management in South Africa
- Landfills
- The Sanitary Landfill
- The "Flushing Bioreactor"
- The PAF Model
The National Waste Summit held in Polokwane in 2001 agreed that there is an urgent need to reduce, reuse and recycle waste for the benefit of the environment (Wiechers, et. al., 2002). The first is to increase the decomposition rate of the organic material in the landfill by distributing the moisture more evenly, thereby increasing the moisture content above field capacity. Currently, efforts to reduce emissions from landfills use one of the following methods (Cossu et. al., 2003):
Operation of the landfill in a semi-aerobic mode by aeration of the waste through natural air inflow or forced aeration,.
Decomposition of Solid Waste in Landfills
- Physical Decomposition
- Chemical Decomposition
- Biological Decomposition
- Aerobic Decomposition
- Acid-phase Anaerobic Decomposition
It will also have a high COD due to the presence of partially decomposed organic materials (Ham, 1988). Because of these organic acids and because of the presence of dissolved CO2, the leachate produced has an acidic pH level. Because of the acidic pH, the leachate is more chemically reactive and therefore has a high inorganic content (Ham, 1988).
Organic acids begin to be consumed, effluent COD decreases and pH increases until it becomes near neutral.
Landfill Emissions
- Landfill Gas
- Landfill Leachate
Because of this increase in pH, the leachate is no longer as chemically reactive as before, and the concentration of inorganic materials (whose solubility is affected by pH) will decrease. This phase of decomposition in which methane is produced is important because it lasts longer than the other phases and because it is the phase in which most of the decomposable wastes are broken down (Ham, 1988). Liquid from external sources, such as surface drainage, precipitation, groundwater, water from underground sources and the liquid produced by the decomposition of the waste itself, seeps through the solid waste mass (Tchobanoglous, 1993).
For each degradation phase, there is a corresponding, characteristic leachate composition resulting from the degradation products, the moisture flow and the availability of organic material in the decomposing waste (Ham, 1998).
Environmental Impacts of Landfills
- Fire and Explosion Hazards
- Vegetation damage
- Unpleasant odours
- Landfill settlement
- Groundwater pollution
- Air pollution
- Global warming
Landfill gas displaces oxygen from the root zone of the soil at and near landfills, causing damage to vegetation in these facilities (El-Fadel et. al., 1997). Carbon dioxide found in landfill gas is very soluble and therefore can easily contaminate groundwater (El-Fadel et. al., 1997). Traces of toxic gases released into landfill gas are also a source of groundwater contamination (El-Fadel et. al., 1997).
The VOCs in landfill gas may have the potential to increase cancer risk in local communities (El-Fadel et. al., 1997).
Mechanical-Biological Pretreatment
- Mechanical Pretreatment
- Biological Pretreatment
- Anaerobic waste pretreatment
- Aerobic waste pretreatment
During MBP, the degradation of biodegradable substances contained in the waste occurs, resulting in the minimization of biological processes taking place in the landfill (Scheelhaase, 1997). Separation results in the recovery of useful waste components for industrial reuse (such as metals and plastics) as well as waste-to-energy (RDF) fuels (Soyez, 2002). Shredding results in a reduction in the waste volume and an increase in the specific surface area of the waste, which enables more efficient biological decomposition (Heerenklage, 1995).
When MSW is treated anaerobically, the organic part of the waste is converted into biogas and waste.
Dome Aeration Technology
A DAT window is constructed with vertical exhaust domes and horizontal inlet ducts manufactured from carbon steel. This allows gases to flow through the domes and channels without allowing the compost material to fall. The hot gases, created by the decaying material, collect in the dome creating a column of hot gas.
The mixture is then crushed, mixed and irrigated. iii) Aeration is provided by the domes and channels and the decomposition process takes place aerobically. iv).
CASE STUDY
Pretreatment of Waste
- Construction and Operation of Windrows
A thermocouple was used to monitor the temperature of the windows from the chimneys and between the domes. The positions in which the decomposition temperatures inside the chimney were checked were at the edge, at a depth of lm and 2m and in the center of the bulk material. Removing material that is slowly or non-biodegradable before the decomposition process improves the efficiency of the process.
Construction of Cells
The leachate pipe allowed for the collection and discharge of leachate into the leachate tank. A 1000 L plastic leachate collection tank was placed at the edge of each test cell to which a leachate tube was attached. The gas vents were made from 50 mm pipes placed in each corner of the cell, along the slope of the cell bottom, totaling approximately 2 m each.
A drip irrigation system, consisting of a lateral pipe network system with a nozzle spacing of lm X lm, was installed on top of the stone layer.
Characterisation of Pretreated Waste
The moisture content of the solid that was deposited in the cells is shown in Table 3.9. The characterization of MBP waste eluates that were deposited in the test cells are shown in Figure 3.10. In order to fulfill the objectives of the study, it was necessary to carry out a case study for the construction of test cells and the characterization of the input material to the cells, as described in this chapter.
Comparison of the rate of degradation can then be made with samples removed from the cells after six months.
Materials and Methods
- Gas Analysis
- Leachate Characterisation
- Solids (TS and VS)
- Nitrogen
- Conductivity
- BOD (biochemical oxygen demand)
- COD (chemical oxygen demand)
- Characterisation of Eluates
- Characterisation of Solid Matter
- Moisture Content
- Field Capacity
- Respiration Index
- Measuring Biogas Production with the Liquid Displacement Method
- Accuracy of Results
- Nitrogen
- Conductivity
- Thermometer
The quantity and quality of the leachate produced by the cells were measured and recorded. Leachate characteristics (COD, BOD5, NH3, NOx, TS, VS, pH and conductivity) were then plotted against time (in days). The characteristics of the leachate and the methods used for their analysis are presented and discussed below.
The volatile solids test provides a rough estimate of the amount of organic matter in the waste. The pH of leachate is an indicator of the state of its biological activity (Majosi, 2005). The conductivity of a sample solution indicates the amount of dissolved ionic compounds and total dissolved solids.
The difference between the masses is a measure of the amount of water retained by the sample at field capacity. The amount of 200 - 250 ml of distillate to be collected also makes it possible to remove all traces of the sample from the apparatus. The resulting errors are reduced by analyzing each sample in duplicate. i) The pH meter is regularly calibrated with buffer solutions.
The gas analyzer is regularly tested against a known standard gas mixture to ensure the instrument's accuracy. ii). A filter in the instrument that filters pollutants from the air before sampling is replaced at regular intervals. i) The thermometer and thermocouple are regularly tested by measuring the temperature in a bath of boiling water and comparing with the expected result. ii).
RESULTS AND DISCUSSION
- Characterisation of Waste After Six Months Aeration in Cells
- Comparison of Characteristics
- Comparison of Tests on Solid Matter
- Comparison of Tests on Eluates
- Initial Flushing Events: Leachate Analysis
- Biogas Production
- Diagrammatic representation of biogas production in Cell 1
- Diagrammatic representation of biogas production in Cell 2
This section shows a comparison of the properties of the input material with the cells and material removed after six months of treatment in the cells. All samples show an increase in VS values, which is expected due to the continued aerobic activity. The conductivity of the eluate after 6 months of stabilization in the cells shows a marked increase.
As explained in Chapters 3 and 4, flush events were performed immediately after commissioning the cells. BOD concentrations give an indication of the biodegradable fractions leached from the cells during irrigation. The concentration of nitrates in the 16-week pretreated waste (cells 2 and 5) is much higher than the other cells.
The initial COD concentration in the control cell (cell 4) was high, as expected. The conductivity of the leachate decreases with time as a result of the initial oxygen consumption and the reduction of total leachable solids. This proved impossible, possibly due to the shifting and tearing of the plastic lining covering the cells during routine maintenance, which allowed air to penetrate the mass of debris.
In the vents of cell 1, 02 decreases and C02 increases as the initial oxygen trapped in the cells is consumed. In the cell 1 probes, O2 decreases and C02 increases as the initial oxygen trapped in the cells is consumed.
Diagrammatic representation of biogas production in Cell 3
At cell openings 3, 02 decreases and C02 increases as the initial oxygen trapped in the cells is consumed.
Diagrammatic representation of biogas production in Cell 4
AJw It /
Diagrammatic representation of biogas production in Cell 5
Sffli^Si
1 .'LfcWJ
Biogas Comparison with Liquid Displacement Experiment
This section presents the C02, O2, and CH4 evolution of MBP waste samples deposited in cells analyzed using liquid displacement anaerobic reactors. In an attempt to displace the liquid, the oxygen is quickly used up and the waste reaches the methanogenic stage in about 5 weeks. The cells, on the other hand, do not produce methane, which confirms the effectiveness of passive ventilation.
The results of this experiment show that the volume percentage of gas produced for 8 weeks and 16 weeks of pretreated waste is very similar, suggesting that it is not necessary to extend the aerobic treatment beyond 8 weeks.
Biogas Production After 6 Months Aeration (Liquid Displacement Method)
This experiment shows that there is a drastic reduction in methane production after 6 months of extended treatment in shallow landfills. There is very little gasifiable carbon left as most of it was converted to CO2 and O2 during the previous stage.
CONCLUSIONS
Leachate Data
![[IJDNE] Submission Acknowledgement](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==)