Effect of increased temperature and leachate recirculation on biogas production and settlement of municipal solid waste.

This study evaluated the effects of increased temperature and leachate recirculation on volatile solids (VS), biogas, hydrogen sulphide (H2S) leachate quality (pH and chemical oxygen demand) and the settlement of municipal solid waste (MSW). Three large-scale tests were conducted with no leachate recirculation at 21°C, weekly leachate recirculation at 20°C and weekly leachate recirculation at 50°C. Leachate recirculation and increased temperature accelerated biodegradation and pushed forward the onset time (from 27 to 8 days). The increase of biodegradation activity was reflected in the change of biogas production, VS and settlement. Compressibility index Cc, increased from 0.71 and 0.77 at 21°C to 0.83 when the temperature was 50°C. In addition, leachate recirculation and high temperature reduced H2S concentration levels by inhibiting the growth of sulphate-reducing bacteria and leachate recirculation lowered H2S production by dissolving the high H2S presence. The results showed that MSW can have significantly changed mechanical and biochemical behaviour under different temperatures and saturations. The results help understand the processes in landfills for more effective short-term and long-term design and management.

Assessment of in situ properties of municipal solid waste with a large-diameter borehole method.

A Municipal Solid Waste Borehole Assessment (MBA) was developed to assess in situ geotechnical properties of municipal solid waste (MSW) during the boring of gas extraction well construction. A Large-Diameter Borehole Caliper (LDBC) was lowered into the borehole to measure the diameter and record the condition of the wall by time-lapse video photography. The results indicated that the borehole experienced significant radial compression with depth following completion. Radial compressions amounted to approximately 7.5% at 9.14 m, 10% at 21.3 m and 11% at 27.4 m below ground surface. The bulk modulus was estimated by using the captured volumetric strains and reported lateral earth coefficients, and the results showed that it increases with increasing depth. For MSW, the bulk modulus increased up to 13.4 MPa in a linear trend with depth. The unit weights of MSW were obtained using three diameter readings from LDBC, auger barrel outside diameter and outer cutting bit outside diameter. The results showed that the diameter based on outer cutting bit yielded realistic unit weights (5.08-9.68 kN m-3) due to unrealistic calculated saturations by other two assumed diameters. The borehole assessment with LDBC was shown to be an efficient and valuable means for characterising MSW and effectively designing gas extraction wells. The research provided a means to assess the waste mass with accuracy at great depths by directly observing and measuring borehole condition.

Assessment of gas dispersion near an operating landfill treated by different intermediate covers with soil alone, low-density polyethylene (LLDPE), or ethylene vinyl alcohol (EVOH) geomembrane.

This study evaluated the impact area of odiferous gas (i.e., H2S) dispersion near an operating landfill installed with three different intermediate covers, including soil alone, linear low-density polyethylene (LLDPE), or ethylene vinyl alcohol (EVOH) geomembrane (GM). By using the finite element method employing Reynolds-averaged Navier-Stokes and Fick's Law coupled equations, the performance of the different cover cases for reducing odor dispersion was comparatively evaluated considering environmental factors, including topographic, meteorology, and gas emission. The odor dispersion patterns and the size of affected residents were analyzed for the twelve different scenarios varied with the cover type and seasonal variation. According to the results, it was found that the wind speed affected the time of odor dispersions more with the relatively flat terrain conditions around the landfill but barely affected the size of the dispersion area. Moreover, it was found that the higher concentration (100 ppb) of odor gas is mainly located within a 5.0-km distance from the landfill. Among four seasons, the odor covers the largest area in summer, which is mainly due to the landfill producing more odor gas and giving a higher source concentration in summer. The gas dispersion simulation for different covers showed that the type of covering layer significantly affects the impact area boundary of gas odor. The results showed that the odor area of the LLDPE GM cover case is 1.3% of soil alone case, and the case of EVOH GM is 14.5% of LLDPE GM case. At the same time, the number of residents that may be affected by the odor of the LLDPE GM case and EVOH GM case is 4.81% and 0.63% of soil alone case, respectively.

Study on the Combined Effect of Municipal Solid Waste Incineration Bottom Ash and Waste Shingle in Hot Mix Asphalt.

This study investigated the positive effect of the combined use of recycled asphalt shingles (RASs) and municipal solid waste incineration (MSWI) bottom ash (B.A.) in asphalt concrete, which contributes to enhanced sustainability in pavement engineering. In addition, unlike traditional approaches that employ individual recycling material in hot mix asphalt (HMA), the combined use of the two waste materials maximizes the mechanical performance of the asphalt mixture. The addition of RAS (with 30-40% aged binder) as an additive generally enhances the strength/stiffness of the asphalt mixture. The high porosity/absorption of MSWI BA results in an additional amount of liquid asphalt binder in the mixture. As an admixture, RAS could supply the additional asphalt binder in the mixture when MSWI BA is used as an aggregate replacement. This research was conducted in two phases: (1) to examine the effect of MSWI BA alone and its optimal asphalt content (OAC), and (2) to assess the combined effect of B.A. and RAS in HMA. Multiple laboratory testing methods were employed for the mechanical performance investigation, including the Marshall stability test, rutting test, and indirect tensile test. The testing results show that the 20% B.A. replacement exhibits the best performance and that it requires an additional asphalt binder of 1.1%. For the combined use of MSWI BA and RAS, 5% RAS shows the best mechanical performance. All mixtures that contain the B.A. and RAS show greater strength than the control specimen (regular HMA).

Experimental assessment of cement hydration and leaching characteristics for waste-to-energy bottom ash mixed with concrete.

To achieve a more sustainable waste-to-energy (WTE) process, the recycling of solid waste incineration (MSWI) bottom ash (BA) has received large attention nowadays. This study investigated how WTE BA form is changed after the hydration and the impacts of WTE BA hydration on its leaching characteristics by using geometrical and leaching tests when incorporated in cement matrix for the recycling. The material composition and characteristics of anhydrous BA, hydrated BA, cement paste, Portland cement concrete (PCC), and BA-combined PCC were evaluated through scanning electron microscopy, X-ray spectroscopy and X-ray diffraction analyses. The results confirmed that the WTE BA newly formed a complex phase of hydration products in a cement matrix. Synthetic precipitation leaching procedure (SPLP) test was also conducted to investigate the leaching behaviors of alkaline components and metals of BA in the crushed BA-PCC samples. Through the leaching study, the leachability of crushed BA-combined concrete was rigorously evaluated when recycled as construction materials (e.g. base, subbase, subdrainage, etc.), which is the worst-case scenario. The results revealed that the release of highly alkaline elements increases with increasing BA content. However, the release of trace metals was reduced by 20-30% significantly when mixed properly with Portland cement concrete (PCC), which is due to both physical and chemical binding in cement hydration products. In addition, the thresholds of water regulations, set by the World Health Organization (WHO) and the Environmental Protection Agency (EPA) of the United States, were assessed as the basis for evaluating the extent of the risk of the leaching of toxic materials.Implications: This study investigated how waste to energy (WTE) bottom ash (BA) form is changed after the hydration and the impacts of WTE BA hydration on its environmental leaching characteristics by using geometrical and leaching tests when incorporated in cement matrix for the recycling. Incorporating of WTE BA in cement mixture can form new mineralogical phases of hydration products in cement matrices such as Copper Hydrogen Arsenate Hydrate and Jahnsite. A significant reduction of alkaline elements (Si, Al, and K) from crushed PCC mixed with WTE BA due to the hydration. The lowest concentrations of major alkaline elements leached from the crushed PCC containing either 10% or 20% of BA contents. The averaged leaching concentration of detected elements is substantially below the water quality guidelines (provided by U.S. EPA and WHO) except Al.

Evaluation of depth-dependent properties of municipal solid waste using a large diameter-borehole sampling method.

This study is to analyze geotechnical properties and biological status of undisturbed municipal solid waste (MSW) associated with depth by using a large-diameter borehole sampling method. Through the method, a 28 m-borehole with 0.8 m of the diameter was drilled into the MSW body consisting of ten-lift layers of waste placed over 4000 days in an operating landfill. MSW sample cuttings were collected from the field site, weighted, and transferred to a laboratory for additional experiments to measure various properties such as moisture content, constituent characterization, unit weights, specific gravity, decomposition state, saturation, and compression rates with regard to waste depth. Also, the methane production obtained from MSW decomposition tests indicated that waste mass was relatively consistent throughout the depth of borehole and had not reached the accelerated production phase of methane. The wet and dry unit weights of the MSW sample with different depths produced excellent trends of the first-order rate with vertical stress. First Oder Rate Equation (FORE) analysis indicated that the maximum total and dry unit weight of MSW (γMSWw and γMSWd) achieved at depth in the waste mass were 12.9 kN/m3 and 10.6 kN/m3, respectively. Based on the waste shrinkage ratio (WSR) defined as the initial dry unit weight divided by succeeding dry unit weight, the height of the original MSW pile was estimated to be 40.5 m. Different compression parameters, including aggregated MSW compression index (Cc), modified compression index (CCE), and compression ratio parameter (Cc'), were comparably evaluated, which can be beneficial to understand compressibility and settlement processes in a landfill.Implications: Geotechnical properties and biological status of undisturbed municipal solid waste (MSW) associated with depth were analyzed by using a large-diameter borehole sampling method. The wet and dry unit weights of the MSW sample with different depths produced excellent trends of the first-order rate with vertical stress. Based on the waste shrinkage ratio (WSR) defined as the initial dry unit weight divided by succeeding dry unit weight, the height of the original MSW pile was estimated to be 40.5 m. Different compression parameters, including aggregated MSW compression index (Cc), modified compression index (CCE), and compression ratio parameter (Cc'), were comparably evaluated, which can be beneficial to understand compressibility and settlement processes in a landfill.