Abstract:
Landfilling of Municipal solid waste (MSW) is considered as a significant part of the integrated solid waste management in most of the megacities around the world. Since renewable energy technologies have gained attention, landfill gas (LFG) became one of the relevant sources of renewable energy in the biomass energy road map. However, both anaerobic digester and landfill sites generate methane, but landfill gas management is much more complicated than anaerobic digesters for two reasons. First, the MSW sent to the landfill site are mostly heteroses; therefore, considering the scale of the landfill the LFG generation would not be stable. Second, it isn't easy to have access to the MSW after it was put in place; however, there are plenty of ways to control the input material during the digestion process for most of the digesters. Based on the mentioned explanation, if it was possible to change the chemical properties of landfilled MSW in favour of LFG generation, not only the landfill gas capturing efficiency will improve, but the adverse effects of the organic fraction on the environment will significantly reduce.
The study described in the thesis details the processes adopted for developing and implementing a technically and financially viable method to enhance biogas generation in Hampton Downs landfill site. This involved detailed investigation to MSW properties of the landfill and comprehensive laboratory and field studies on the impact of different additives on biogas generation. The research undertaken focused on five key research areas; (ⅰ) physical and chemical properties of fresh and aged MSW put in place since 2013. (ⅱ) Current and future potential of LFG generation in the landfill site with existing and modified practice. (ⅲ) The effect of carbonaceous additives on biogas generation from MSW. (ⅳ) the influence of neutral red on biogas generation. And finally (ⅴ) the effects of all additives analysed in the laboratory scale in the field scale to investigate the role of additives in a real landfill condition.
The research was conducted with detailed investigations on the physical, chemical, and biological processes involved in the anaerobic digestion of fresh and aged MSW. This includes extensive field monitoring, sampling, laboratory testing, and data analysis before implementing the field test. In addition, to investigate the role of additives on anaerobic digestion, physical analysis has been
conducted. A new method for analysis of the electrical conductivity of the solid carbonaceous additives was developed.
The preliminary research objective for this research was investigated through a series of scientific papers centred on these key research disciplines. The most critical challenges of anaerobic digestion and the key role of additives to mitigate the adverse effects on biogas generation was reviewed. According to some of the studies, carbonaceous additives proved to be useful to improve the quality and quantity of biogas generation. However, the role of neutral red on biogas generation was reported only in one study. Studies explained many reasons why additives are influential in improving the efficiency of biogas generation. But according to the studies undertaken in chapter 1, promoting the Direct interspecies electron transfer that occurred during the application of carbonaceous and neutral red additives is the critical factor for boosting biogas generation.
In the next step, the laboratory studied started exploring the effect of different types of biochar and activated carbon on anaerobic digestion performance and biogas generation. revious studies have reported the positive impact of carbonaceous additives on anaerobic digestion; However, the detailed influence of these additives remained unclear. Through extensive analysis, especially thermogravimetric analysis, the critical features of both biochar and activated carbon during the anaerobic digestion were revealed. Chapter 2 of the thesis explains the critical impacts of biochar and activated carbon on MSW digestion on the laboratory scale.
As explained earlier, only one study reported the positive impact of using neutral red on biogas generation in a mine. Due to the low concentration of neutral red additive needed to add to anaerobic media compared to others and that neutral red can be easily diluted in leachate, further investigation was an excellent choice. Chapter 3 of the thesis outlines the role of neutral red on biogas generation, suggesting the optimum concentrations of neutral red according to the composition and age of the MSW. Finally, in the last chapter of this thesis, the influence of additives was investigated in the field. The results explained in chapters 2 and 3 introduced the most effective additive and optimum concentrations of various additives. Both biochar and neutral red were used in a landfill through leachate addition to adjusting the moisture content. In this study, both the quality and quantity of LFG affected
by the additives were explored. Also, the influence of each additive on organic fractions degradation through quantifying the landfill settlement has been investigated.