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.

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.