Maximizing RDF recovery potential through the integration of electrical resistivity tomography and frequency-domain electromagnetic surveys for waste characterization in open dump mining.

Open dumping is a widespread waste management technique used in developing countries. This approach is simple and economical but has numerous environmental and health impacts. Open dump mining (ODM) can reduce waste in both open and controlled dumpsites by converting waste into refuse-derived fuel (RDF) for energy generation; however, before ODM implementation, the waste's characteristics and composition must be assessed. Geophysical surveys are widely used to characterize waste. The electrical resistivity tomography (ERT) method is a particularly common technique for determining waste composition, but it has several limitations. Therefore, a frequency-domain electromagnetic (FDEM) survey was used in this study as a pre-screening tool to evaluate the waste composition and overcome the limitations of ERT surveys. This study aimed to determine the relationship between geophysical data types (i.e., ERT and FDEM) and the optimal waste composition for RDF production and assess the ability of FDEM surveys to identify areas with RDF recovery potential. This study combined ERT and FDEM surveys with waste sample analysis in old/new controlled dumpsites in Thailand. The quantitative and qualitative correlations between the geophysical data (i.e., resistivity, conductivity, waste composition, and moisture content (MC)) were then assessed using linear and multiple linear regression analysis. Integrating geophysical surveys was found to have the potential to locate optimal RDF recovery areas, with low conductivity (0-100 mS/m) and high resistivity (>55 Ω·m) characteristics associated with areas of high RDF content (>40 % by weight). An unexpected finding was that increased waste age resulted in increased resistivity and decreased conductivity. Additionally, the MC depended on factors affecting spatial variability (e.g., precipitation and biodegradation). Overall, this study demonstrates that integrating ERT and FDEM surveys is a suitable pre-screening tool to evaluate waste characteristics and composition, mitigate ERT survey limitations, and improve waste investigation before ODM.

Investigating the effect of waste age and soil covering on waste characteristics prior to landfill mining using an electrical resistivity tomography technique.

This study analyzed the potential of landfill mining for refuse-derived fuel (RDF) production based on waste electrical resistivity, including the influence of waste age and soil cover. Electrical resistivity tomography (ERT) was used to determine the resistivity value of landfilled waste in four active and inactive zones, with two to four ERT survey lines collected per zone. Waste samples were collected for composition analysis. Linear and multivariate regression analyses were used to constrain the data correlation based on the waste's physical characteristics. An unexpected finding was that soil cover, rather than the waste's age, influenced the characteristics of the waste. To evaluate the RDF recovery potential, multivariate regression analysis showed a significant correlation between electrical resistivity, conductive materials, and moisture content. However, the obtained correlation between electrical resistivity and RDF fraction using linear regression analysis can be more conveniently used to evaluate RDF production potential in practice.

Improvement of energy recovery potential of wet-refuse-derived fuel through bio-drying process.

This paper proposes novel wet-refuse-derived fuel (Wet-RDF) bio-drying process with the variation of initial organic substrate and moisture content. The bio-drying was carried out using 0.3 m3 lysimeter aerated continuously at different rates. Two conditions of Wet-RDF feedstock tested included: Experiment A ‒ 37% organic substrate and 58% moisture content with an initial heating value of 2,889 kcal/kg; and Experiment B ‒ 28% organic substrate and 35% moisture content with an initial heating value of 4,174 kcal/kg. The bio-drying was performed in both experiments under negative ventilation mode and non-ventilation mode, the ventilation mode was set at the aeration rates of 0.2 m3/kg/day and 0.4 m3/kg/day. The results suggest that the optimum aeration rate was 0.4 m3/kg/day, achieving a 30% moisture reduction and a 60% heating value increase from their initial values. As a result, the improved wet-RDF qualified for the local cement industry's standard in terms of heating value.

Optimization of multi-frequency electromagnetic surveying for investigating waste characteristics in an open dumpsite.

Implications: Open dump mining (ODM) is now applied as a sustainable approach to combat improper waste disposal and reduce municipal solid waste (MSW) in the open dumpsite. To implement ODM for producing RDF, business developers must know the amount and composition of waste that can be converted into RDF before mining. This study used multi-frequency EM surveys with frequencies of 5,000, 11,000, and 15,000 Hz. This multi-frequency method effectively determined the waste composition and identified potential excavation points in the open dumpsite prior to ODM. This method can mitigate the limitations of traditional surveying, due to its improved mobility, lower time consumption, and reduced labor needs.

Effects of operating parameters on co-gasification of coconut petioles and refuse-derived fuel.

Coconut agro-industry in the western region of Thailand generates a large amount of residues. This study investigated the energy production potential of discarded coconut petioles, with a focus on co-gasification with refuse-derived fuel (RDF). Gasification tests involving petioles, RDFs and their mixtures (25%, 50%, 75% or 100% by weight) were conducted in a laboratory-scale fixed bed reactor. Fuel samples of 5 g were gasified at 700°C-900°C for 60 minutes, using simulated air (79% N2 to 21% O2, by volume) as a gasifying agent. Gasification of petioles generated producer gas with lower heating values, estimated at 0.43-0.75 MJ Nm-3, while RDF produced 0.92-1.39 MJ Nm-3. Adding greater quantities of RDF to the fuel mixture resulted in an increase in the heating value of the producer gas and cold gas efficiency. The operating temperatures and gasifying-agent flow rates affected the efficiency of process differently, depending on the fuel composition. However, the maximum cold gas efficiency from both fuels was detected in tests conducted at 800°C. In co-gasification and pure refuse-derived-fuel tests, higher temperatures and gasifying-agent flow rates led to outputs with higher energy yields. Our findings suggested that co-gasification of petiole is a viable alternative waste-treatment technology for this region.

Methane and nitrous oxide emissions from shallow windrow piles for biostabilisation of municipal solid waste.

Shallow windrow piles were applied as a low-cost option for biostabilisation of municipal solid wastes (MSW) prior to their utilization as refuse-derived fuel (RDF). A considerable amount of greenhouse gas (GHG) emissions can be emitted during the biostabilisation of MSW, especially when in operation under high moisture conditions such as there are in tropical Asia. This study investigated the emission of methane (CH4) and nitrous oxide (N2O) from shallow windrow piles - with heights of 0.5-1.0 m - for the stabilization of MSW at a full-scale facility in Thailand. Measurements of CH4, CO2, and N2O emissions using the static-chamber method revealed high spatial heterogeneity characteristics in all zones with different waste ages. Peak methane emissions were observed after four months of biostabilisation. The average spatial methane emissions from the waste piles ranged from 7.33 to 26.88 g m-2 d-1 (14.86 g m-2 d-1, on average). The CH4 generation-rate constant was within the range of 3.3 to 4.0 yr-1, which is higher than that reported - about 2.20-3.50 yr-1 - from a deep windrow pile (3.5-4.0 m height). The spatial distribution of N2O emissions was in the range of 4.51-199.14 mg N2O t-1dry wt.d-1 (6.6-111.7 mg N2O m-2 d-1), similar to those previously studied from landfill operations. This shallow windrow pile technique can be applied as low-cost technology for biostabilisation of MSW in developing countries, where land area is available.Implications: Shallow windrow pile was applied as a low-cost option for biological treatment of municipal solid waste in developing countries where land area is available. This study evaluated the greenhouse gas emission characteristics during the operation of windrow pile. The findings suggest that the emission rates were varied spatially with waste ages in different zones. Higher methane generation rate constant was derived from shallow window pile as compared to deep windrow pile. The methane and nitrous oxide emission factors were derived.

The effectiveness of passive gas ventilation on methane emission reduction in a semi-aerobic test cell operated in the tropics.

Two landfill test cells, with and without gas vents, were used to investigate the effectiveness of passive aeration, through basal leachate pipes, in mitigating methane emissions from municipal solid waste disposal in the tropical climate of Thailand. Surface methane emission rate, as well as methane content in the landfill gas, were determined for a period of three years. The results indicate that the average methane emission rate from the test cell with passive gas vents (42.13 g/t dry wt./d) was about half of that from the test cell without gas vents (90.33 g/t dry wt./d). Methane emission rates from both test cells fluctuated and were influenced by precipitation. The emission rate during the wet period in the test cell with gas vents (61.67 g/t dry wt./d) was 3 times as much as that observed during the dry period (20.95 g/t dry wt./d). The emission rate during the wet period in the test cell without gas vents (120.33 g/t dry wt./d), was twice the value of that observed during the dry period (60.32 g/t dry wt./d). The measurements also revealed the formation of methane hotspots in the test cell with passive vents after rainfall events, leading to higher localized surface emissions. Introduction of gas vents helped reduce methane emissions from solid waste landfills in a tropical region. However, rainfall should be limited to avoid turning semi-aerobic conditions into anaerobic conditions.

Application of the IPCC Waste Model to solid waste disposal sites in tropical countries: case study of Thailand.

Measurements of landfill methane emission were performed at nine solid waste disposal sites in Thailand, including five managed sanitary landfills (four deep and one shallow landfills) and four unmanaged landfills (three deep and one shallow dumpsites). It was found that methane emissions during the rainy season were about five to six times higher than those during the winter and summer seasons in the case of managed landfills and two to five times higher in the case of unmanaged landfills. Methane emission estimate using the Intergovernmental Panel on Climate Change (IPCC) Waste Model was compared with the actual field measurement from the studied disposal sites with methane correction factors and methane oxidation factors that were obtained by error function analysis with default values of half-life parameters. The methane emissions from the first-order decay model from the IPCC Waste Model yielded fair results compared to field measurements. The best fitting values of methane correction factor were 0.65, 0.20, 0.15, and 0.1 for deep landfills, shallow landfills, deep dumpsites, and shallow dumpsites, respectively. Using these key parameters in the case of Thailand, it was estimated that 89.22 Gg of methane were released from solid waste disposal sites into the atmosphere in 2006.