Bioreactor Landfills
Promoted By Leachate Recirculation:
A Full-Scale Study
Samuel T.S. Yuen B.E., M.Eng.Sc.
Thesis submitted in total fulfilment of the requirements of the degree of
Doctor of Philosophy
Department of Civil & Environmental Engineering
University of Melbourne
March 1999
Dedicated to Zona,
a wife of boundless patience
and
a mother of immense love
Abstract______
The concept of bioreactor landfills has certainly gained a lot of attention in the past decade. Its advantages over the conventional “dry tomb” landfills are well demonstrated by many laboratory tests and pilot-scale studies. However, there is still further full-scale research work required before we can truly translate this concept into everyday practical operations. Aiming to bridge this gap, an experiment has been conducted in the Lyndhurst Landfill, Victoria, Australia. This thesis covers:
(i) The experimental implementation of a full-scale bioreactor landfill cell (stimulated by leachate recirculation) to quantify the stabilisation of waste in terms of leachate quality, gas composition and production, waste temperature, and landfill settlement.
(ii) The evaluation of leachate recirculation system performance and moisture flow mechanism in municipal solid waste.
(iii) The study of water balance in the full-scale experimental cell to identify the significance of various water components for the purpose of leachate management.
(iv) The development of an in-situ technique for measurement of moisture in municipal solid waste for the hydrological investigations in (ii) and (iii) above.
As pointed out in a literature review, the research committed to hydrological aspects of bioreactor landfills has been very limited compared to the work that has been done in biodegradation enhancement. The hydrological component of this thesis helps to address this shortcoming.
The thesis demonstrates that there is no ideal method available for the in-situ moisture measurement of landfills. Nevertheless, with certain limitations, the use of a neutron probe combined with in-situ access tubes can offer acceptable indirect, non-destructive measurements. This technique has been successfully applied in this experiment to monitor seasonal moisture change and moisture variation caused by leachate injection.
The water balance study has identified the significance of various water components in the experimental cell. This information is important and useful in terms of leachate management for both dry and wet landfills, especially for those located in a similar climate region.
The numeral modelling and field measurements of a leachate recirculation trial demonstrated the limitation of the recirculation system, which failed to distribute leachate uniformly in the waste mass. This finding is significant in terms of exposing the inadequacy of recirculation devices and the urgent need for their improvement. Contradicting the suggestions by many studies, this thesis demonstrates that the classical theory based on saturated/ unsaturated flow through a homogeneous porous medium can at best be used to predict bulk leachate flow but is not useful in predicting moisture patterns.
An enhanced biodegradation has been achieved in some parts of the experimental cell by leachate recirculation. The biodegradation enhancement has not occurred in the entire waste mass due to a poor leachate distribution caused by heterogeneity. This implies that the use of limited sampling points in full-scale experiments is unlikely to be sufficient in delineating the extremely heterogeneous nature of landfills. This explains to some extent the rather confusing monitoring results that have been observed in this experiment and in other full-scale studies.
The most important finding of this thesis is that a full-scale landfill is extremely heterogeneous, a feature that tends to be misrepresented by small-scale experiments. It is for this important reason that small-scale results in many cases could not be reproduced in full-scale landfills. This vital point is clearly demonstrated by the thesis both in the hydrological investigation and in the stabilisation indicator monitoring.
According to the findings of this thesis, undoubtedly the most urgent need is to improve the current technique of leachate recirculation. Given the heterogeneous nature of landfills, it would be practically difficult to achieve a uniform moisture distribution throughout the waste mass. Nevertheless, this is the area that future research focus should be directed.
Declaration______
To the best of my knowledge and belief, this thesis comprises only my original work and contains no material previously written or published by another person except where due reference is made in the text. None of the work presented in this thesis, in whole or in part, has been accepted for the award of a degree or diploma at any other university or institution. The length of this thesis is less than 100,000 words excluding tables, figures, references and appendices.
Samuel T.S. Yuen
Acknowledgement______
First I have to express my sincere gratitude to my three very talented academic supervisors, Mr. John Styles, Prof. Tom McMahon and Dr. Q.J. Wang, for the enthusiasm they shared with me in this research project. Without their timely stimulus, encouragement and support throughout the prolonged study period, the completion of this thesis would still be a dream. The privilege of enjoying their fellowship while I was also working as their colleague is also much appreciated.
A substantial portion of the funding of this project was provided by SITA-BFI (formerly known as Browning-Ferris Industries, Australia). Their commitment in providing the funding and test site, their belief in research to achieve a better waste management concept, and their credit in allowing fully independent research of the project is gratefully acknowledged.
Energy Development Limited, the contractor responsible for the collection and utilisation of the gas at the Lyndhurst Landfill, provided most of the labour and plant in constructing the leachate recirculation system and gas collection system in the experimental cell. They also provided the required equipment and technical staff for the monthly landfill gas monitoring. I am grateful to their important contribution.
Many people have offered their expert advice and critical assistance to allow the development of this resource demanding full-scale experiment. It would be difficult for me to remember and to thank every individual but I try to list and acknowledge all of them below:
· Messrs. Max Spedding, Daniel Fyfe, Mark D’Amore, John Ellul, Adam Martin and Miss Justine Maher of SITA-BFI for their interest in this research project and for their patience in coping with the inconvenience caused to their everyday operations at the Lyndhurst Landfill.
· Messrs. Allen Hollier, Shane Cribbes and all the staff of EnvirEng for their work at the front face of the construction and maintenance of the full-scale experimental cell.
· Mr. Keith Knox of Keith Knox Associates Environmental Consultants, U.K., for his expert discussion related to the leachate, gas and settlement monitoring data.
· Messrs. Tony Lowe, Geoff Duke and all other technical staff members in my Department for their advice in keeping the instrumentation working in the laboratory and in the field.
· Dr. Andrew Western, Dr. Francis Chiew, Mr. Mark Wood and all other fellow staff members and postgraduates in my Department who offered stimulating discussion and provided information on relevant references.
· Miss Fiona Thiele and Miss Kynwynn Jones who assisted in the laboratory and in the field while they were working on their undergraduate work training/ research project.
Last but not least, I am indebted to my parents for their encouragement and for daring me to take on the challenge of this Ph.D. study which had been in my mind for the past decade.
Table of Contents______
Page
1. Introduction
1.1 Landfill Development and Significance 1-1
1.2 Objectives and Scope of Study 1-3
1.3 Time Constraint 1-4
1.4 Thesis Layout 1-4
2. Literature Review
2.1 Landfill Degradation and Behaviour 2.2
2.1.1 Decomposition of Municipal Solid Waste 2-2
2.1.2 Evolution Sequence 2-6
2.1.3 Influence Factors 2-7
2.2 Process-Based Landfill Enhancement Techniques 2-14
2.2.1 Control/ Selection of Waste 2-14
2.2.2 Shredding of Waste 2-15
2.2.3 Waste Compaction 2-15
2.2.4 Buffer Addition 2-16
2.2.5 Sewage Sludge Addition 2-16
2.2.6 Pre-composting Part of Landfill Waste 2-16
2.2.7 Enzymes Addition 2-17
2.2.8 Leachate Recirculation 2-18
2.3 Developments in Leachate Recirculation 2-19
2.3.1 Small-Scale Studies 2-19
2.3.2 Full-Scale Studies 2-29
2.3.3 Summary of Developments in Leachate Recirculation 2-40
2.4 Landfill Hydrology 2-44
2.4.1 Performance of Leachate Recirculation System 2-44
2.4.2 Water Balance of Landfill Cells 2-45
2.4.3 Hydraulic Properties of Municipal Solid Waste 2-46
2.4.4 Saturated/ Unsaturated Flow in Municipal Solid Waste Medium 2-47
2.5 Research Needs 2-47
3. Approach and Methodology
3.1 Bioreactor Landfill Stabilisation 3-2
3.2 In-situ Moisture Monitoring of Municipal Solid Waste 3-3
3.3 Water Balance of Experimental Cell 3-4
3.4 Performance of Recirculation System and Moisture Flow Mechanism 3-5
4. Experimental Set-up
4.1 Experimental Cell Design and Construction 4-2
4.1.1 General 4-2
4.1.2 Size of Experimental Cell 4-4
4.1.3 Waste Composition 4-6
4.1.4 Waste Moisture Content 4-8
4.1.5 Daily/ Interim Covers 4-11
4.1.6 Density and Porosity of Waste 4-12
4.1.7 Cell Containment System 4-13
4.1.8 Leachate Collection system 4-14
4.1.9 Gas Extraction System 4-15
4.1.10 Leachate Recirculation System 4-17
4.2 Instrumentation and Monitoring Program 4-20
4.2.1 In-situ Municipal Solid Waste Moisture Monitoring 4-21
4.2.2 Climatic Data 4-23
4.2.3 Surface Runoff 4-23
4.2.4 Landfill Settlement 4-25
4.2.5 In-situ Waste Temperature 4-25
4.2.6 Saturated Leachate Level/ Leachate Sampling 4-27
4.2.7 Volume of Leachate Collected and Recirculated 4-28
4.2.8 Landfill Gas Composition and Flow Rate 4-29
4.2.9 Groundwater Quality 4-29
4.2.10 Monitoring Program 4-30
4.3 Leachate Recirculation Strategy 4-32
5. In-situ Moisture Monitoring of Municipal Solid Waste
5.1 Previous Work 5-2
5.2 Feasibility Assessment 5-4
5.2.1 Electromagnetic Technique 5-5
5.2.2 Electrical or Thermal Conductivity 5-5
5.2.3 Tensiometric Technique 5-6
5.2.4 Neutron Scattering 5-7
5.2.5 Outcome of Feasibility Assessment 5-11
5.3 Laboratory Investigation 5-11
5.3.1 Quantity Potential Limitations of Neutron Scattering 5-11
5.3.2 Test Set-up 5-13
5.3.3 Results and Discussions 5-14
5.4 Field Trial 5-18
5.4.1 Set-up and Installation 5-18
5.4.2 Results and Discussions 5-19
5.5 Conclusions 5-24
6. Water Balance of Experimental Cell
6.1 As-Capped Moisture Content 6-2
6.2 Meteorological Records 6-2
6.3 Hydrological Data 6-5
6.3.1 Runoff Measurements 6-5
6.3.2 Evapotranspiration 6-6
6.3.3 Estimated Runoff, Lateral Drainage and Percolation 6-13
6.3.4 Volume of Leachate Recirculated 6-16
6.3.5 Basal Storage 6-17
6.3.6 Groundwater Ingress through Liner 6-21
6.4 Pre-capping Water Balance 6-22
6.5 Post-capping Water Balance 6-26
6.6 Conclusions 6-36
7. Moisture Flow in Municipal Solid Waste and
Performance of Leachate Recirculation Systems
7.1 Previous Work 7-2
7.1.1 Modelling Moisture Transport in MSW as Saturated/ Unsaturated Flow
Through Homogeneous Porous Media 7-2
7.1.2 Modelling Leachate Recirculation System 7-7
7.1.3 Measurements of Moisture Movement in MSW Media 7-9
7.2 Study of Leachate Recirculation System in Experimental Cell 7-13
7.2.1 Numerical Simulation of Experimental Recirculation System 7-14
7.2.2 Field Measurements 7-22
7.3 Discussion and Conclusions 7-28
7.3.1 Moisture Flow Mechanism in MSW Media 7-28
7.3.2 Performance of Leachate Recirculation System 7-29
7.3.3 Conclusions 7-30
8. Bioreactor Landfill Behaviour Simulated By
Leachate Recirculation
8.1 Leachate Composition 8-2
8.1.1 Sampling and Testing 8-2
8.1.2 Physical Indicators – pH, Alkalinity and Oxidation-Reduction Potential 8-3
8.1.3 Leachate Strength – Total Solids and Conductivity 8-7
8.1.4 Dilution Indicator – Chloride 8-9
8.1.5 Organics – BOD, COD, TOC and VFAs 8-10
8.1.6 Nitrogens – Organic Nitrogen, Ammonia, Nitrite and Nitrate 8-14
8.1.7 Sulphate/ Sulphide 8-17
8.1.8 Metals – Iron, Calcium, Magnesium, Sodium and Potassium 8-18
8.1.9 Trace Metals – Lead, Zinc, Manganese, Copper, Chromium, Arsenic, 8-20
Cadmium and Nickel
8.1.10 Summary of Leachate Composition Analysis 8-23
8.2 Gas Quality and Quantity 8-26
8.2.1 Implications of Collection System on Gas Measurement 8-26
8.2.2 Results of Monitoring 8-27
8.2.3 Quantifying Well Leakages 8-32
8.2.4 Using Methane Flow as a Biodegradation Indicator 8-34
8.2.5 Summary of Landfill Gas Analysis 8-37
8.3 Landfill Settlement 8-39
8.3.1 Mechanisms and Stages of Landfill Settlement 8-39
8.3.2 Quantify the Effects of Settlement due to Biodegradation 8-41
8.3.3 Summary of Settlement Analysis 8-50
8.4 In-situ Waste Temperature 8-51
8.4.1 Temperature as a Biodegradation Activity Indicator 8-51
8.4.2 Monitoring Results 8-51
8.4.3 Summary of Temperature Analysis 8-55
8.5 Conclusions 8-57
9. Summary and Conclusions
9.1 Summary 9-2
9.1.1 In-situ MSW Moisture Measurement Technique 9-2
9.1.2 Water Balance Study 9-2
9.1.3 Moisture Flow Mechanism and Recirculation System Performance 9-3
9.1.4 Monitoring of Stabilisation Indicators 9-4
9.2 Conclusions 9-6
9.2.1 Contributions from this Thesis 9-6
9.2.2 Shortcomings of this Thesis 9-8
9.2.3 The Way Ahead for Bioreactor Landfills 9-8
9.3 Recommendations for Future Work 9-10
9.3.1 The Lyndhurst Experimental Cell 9-10
9.3.2 Other Work 9-11
References R-1 to R-13
Appendix A: Plates A-1 to A-15
Appendix B: Daily Meteorological Measurement B-1 to B-11
(January 1995 to December 1997)
Appendix C: Daily Runoff Measurements C1
(November 1996 to December 1997)
Appendix D: Daily Potential Evapotranspiration Estimated by D-1 to D-7
Penman-Monteith Method
Appendix E: HELP Model Output (Modelling of Final Cap) E-1 to E-21
Appendix F: Output of Jensen Model Estimating Actual F-1 to F-6
Evapotranspiration
Appendix G: Leachate Composition Analysis Results G-1 to G-4
Appendix H: Landfill Gas Monitoring Data H1 to H3
Appendix I: Landfill Settlement Monitoring Data I-1
Appendix J: In-situ Waste Temperature Monitoring Data J-1
Appendix K: Groundwater Monitoring Data K-1 to K-10
Appendix L: Volumetric Moisture Content Isoclines L-1 to L-32
Predicted by Numerical Modelling
Appendix M: Publications Related to This Thesis M-1 to M-42
List of Figures______
Figure 2.1 – Simplified Anaerobic Degradation Processes Involving Various Bacteria Groups in a Landfill Ecosystem / 2-3
Figure 2.2 - Typical landfill Evolution Sequence in Terms of Gas and Leachate Composition (after Christensen & Kjeldsen, 1989; Farquhar & Rovers, 1973) / 2-5
Figure 4.1 – Location Plan of Lyndhurst Sanitary Landfill / 4-3
Figure 4.2 – As Constructed Survey Plan of Experimental cell / 4-5
Figure 4.3 – Record of Waste Disposed According to Waste Streams / 4-6
Figure 4.4 – Waste Composition Based on Waste Stream & WMC 1995 Data (By Wet Mass) / 4-7