Geotechnical properties of municipal solid waste at Laogang Landfill, China

Laboratory investigation and prediction of permeability of fresh to five-year-old municipal solid wastes of low and high food contents

The permeability of municipal solid wastes (MSWs) is important for the design and operation of landfills. This study presented the experimental investigation of the permeability of low food content- (LF-) and high food content- (HF-) MSWs prepared in laboratory-scale bioreactors for up to 5 years. The permeability of MSWs with diverse degrees of decomposition (DOBs), void ratios, and permeation liquids was measured (288 tests). The measured permeability was compared to that predicted from the (modified) Kozeny-Carman (K-C) equations in four different forms. The results indicated that the permeability of both LF- and HF-MSWs decreased significantly (p < 0.05) with decomposition under a given void ratio. The predicted permeability using the original K-C equation fitted well with that of fresh MSWs. The permeability of decomposed MSWs was closer to the predicted results using the modified K-C equation with the effective void ratio. This can be attributed to the increase in the fine fractions due to degradation. The reduction in the effective voids was more significant with HF-MSWs. The parameters required in the (modified) K-C equations showed a good correlation with DOB and effective particle size (d10). The predicted permeability based on the relationship between DOB (or d10) and equation parameters was within 3 times the difference compared to the measured values. The above results indicated that the modified K-C equation can be adopted to predict the permeability of fresh and degraded MSWs while more field-scale experiments should be conducted to further evaluate its feasibility.

Study on the water retention curve of shredded municipal solid waste considering the compressibility of specimens based on the centrifuge method

The water retention curve (WRC) of municipal solid waste (MSW) is the important hydraulic parameter for the study of unsaturated seepage analysis in landfills. Due to the compressibility and degradability of the waste, the search for a method to quickly and accurately test its water retention curve (WRC) is a current problem that needs to be solved. In this paper, considering the volume change of the waste specimens in test, the test principle of centrifuge testing of WRC is corrected to make it applicable to the testing of waste WRC. In addition, the WRCs of 20 MSW specimens with typical landfill compositions and porosities are measured using the corrected centrifuge test. The effects of compositions and porosities of waste specimens on WRC parameters were analyzed. The results are summarized as follows. Disregarding the height reduction of specimens resulted in overestimated matric suction values and underestimating volume water content values. By comparing uncorrected and corrected values, the maximum difference of the matric suction and volumetric water content reach 233 kPa and 11%, respectively. This study can provide a reference for accurately measuring the WRC of MSW using a centrifuge. For the waste specimen without kitchen and yard waste, composition had less of an effect on the WRC of waste compared to porosity. The effect of the content of the non-absorbable fraction on the residual volumetric water content θr and the parameter nv in the van Genuchten model was significant. The initial porosity n had a great effect on the parameter α.

A critical review of municipal solid waste hydraulic conductivity: A mini review

This study is a critical review of municipal solid waste (MSW) hydraulic conductivity that includes investigation of the influence of vertical stress, dry unit weight and degradation. A total of 56 studies were compiled that included laboratory-, pilot- and landfill-scale hydraulic conductivity experiments. Compacting waste and increasing vertical stress reduce MSW hydraulic conductivity via reshaping the pore networks throughout the waste matrix, reducing the void ratio and increasing tortuosity. However, the magnitude of reduction in hydraulic conductivity is dependent on stress, waste composition and decomposition. Solid waste decomposition can have opposing effects on hydraulic conductivity. Some studies have indicated that an increase in MSW decomposition results in particle size reduction and settlement that reduces the void ratio and decreases hydraulic conductivity. Conversely, some studies indicate that waste decomposition reduces the solid mass, which increases the void ratio and creates larger flow paths that increase hydraulic conductivity. The data compilation, observations and key findings from this study are beneficial for solid waste practitioners to improve design, analysis and operation of MSW landfills.

Experimental investigation of water retention curves of municipal solid wastes with different paper contents, dry unit weights and degrees of biodegradation

This paper investigates the drying and wetting water retention curves (WRCs) of municipal solid wastes (MSWs) with different paper contents, dry unit weights and degrees of biodegradation (DOBs). Fresh synthetic samples were prepared based on the field composition of the MSWs at Mugga Lane Landfill, the Australian Capital Territory (ACT), Australia. The degraded samples were prepared in simulators with MSWs of different initial dry unit weights and decomposition periods with leachate recirculation. The water retention curves (WRCs) of the MSWs were determined using pressure plate tests, in both drying and wetting phases. The outflow from MSWs was analysed using Gardner's method to obtain the unsaturated hydraulic conductivity. The results indicate that the WRCs of the MSWs are greatly affected by the DOB, paper content and dry unit weight. When DOB < 30 %, as DOB increases, the air-entry pressure of MSWs with paper increases, and the residual moisture content decreases regardless of paper content. With DOB > 30 %, the air entry pressure and residual water content depend on the balance between organic matter and highly decomposed organic constituents. The paper content affects the WRCs of MSWs due to its water retention capacity and change in the particle size distribution with decomposition. The increase in the dry unit weight of MSWs significantly increases the air entry pressure and residual moisture content, similar to the borehole samples with combined effects of biodegradation and increase in stress level from literature. Hysteresis effects have been observed during the drying and wetting of MSWs. The hysteresis of WRCs increases with the paper content and DOB.

Numerical modelling of settlement of municipal solid waste in landfills coupled with effects of biodegradation

This paper presents the development of a new settlement model to predict the long-term settlement of municipal solid wastes (MSWs). The total settlement of the MSWs results from the direct loss of solids due to decomposition and compression due to stress variation induced by loss of solids, flow of gas and liquid and mechanical creep. The geotechnical properties of MSWs are considered as functions of degrees of biodegradation (DOB). To validate the model, two settlement profilers (2.5 years) and three geodetic monitoring networks (2 years) were installed at Mugga Lane Landfill, ACT, Australia to monitor the settlement of an MSW lift and three closed landfill cells, respectively. The settlement rates of the landfill cells with the ages of 7, 8, 14, and 8, 9 and 15 years are 0.53, 0.35, 0.06 and 0.46, 0.36, 0.05 mm/day, respectively. In addition, 5 large scale and 3 small scale bioreactors were set up in the field and laboratory to address the long-term physical, mechanical and biochemical behaviours of the MSWs under different stress levels. The predicted settlement is compared to the test results from the bioreactors, in-situ monitoring data and the settlement predicted using an existing model, which has been improved by coupling the geotechnical properties of MSWs with DOBs. The predicted settlement using the proposed model well fits the test results and monitoring data. The settlement strain is predicted to be 28.2 % during the filling stage of the landfill and 5.9 % in 5 years after the closure.

Influence of oil and gas exploration and production waste on municipal solid waste hydraulic conductivity

This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) on hydraulic behavior of municipal solid waste (MSW). A series of laboratory experiments were conducted to assess the impacts of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods on hydraulic conductivity. Hydraulic conductivity (k) for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3 × 10^-5 m/s to 10^-7 m/s as vertical stress increased from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in k to 10^-8 m/s as vertical stress increased above 200 kPa. The addition of E&PW did not impact the available flow path, even though adding E&PW to MSW reduced the void spaces. This indicated that the waste matrix is capable of accepting E&PW while keeping the flow structure within the waste matrix. However, for vertical stress greater than 50 kPa, mixtures of MSW + 80% E&PW were observed to yield hydraulic conductivity < 10^-9 m/s.

Effects of moisture content and landfill age on the shear strength properties of municipal solid waste in Xi'an, China

With the continued expansion of waste landfills, accidents may occur if the landfills are not properly stabilized. In this study, samples of municipal solid waste (MSW) from a waste landfill in Xi'an, China were collected through on-site drilling. Considering the effects of nine landfill ages (1, 2, 3, 11, 12, 13, 21, 22, and 23 y) and six moisture contents (natural, 20, 40, 60, 80, and 100%), 324 groups of MSW were tested in the laboratory using a direct shear test apparatus. The results indicate the following: (1) with an increase in horizontal shear displacement, the shear stress of MSW gradually increases without a peak stress phenomenon, which is a displacement hardening curve; (2) with an increase in landfill age, the shear strength of MSW increases; (3) with an increase in moisture content, the shear strength of MSW increases; (4) with an increase in landfill age, the cohesion (c) decreases and the internal friction angle (φ) increases; and (5) with an increase in moisture content, the c and φ of MSW increases. The c range found in this study was 6.04-18.69 kPa, while the φ was 10.78-18.26°. The results of this study can provide a reference for stability calculations for MSW landfills.

An overview of in situ testing and geophysical methods to investigate municipal solid waste landfills

Municipal solid waste (MSW) management is challenging as a whole. Global waste generation is expected to continue to increase in the coming years, and landfills are currently the primary destination. Therefore, the stability of these structures must be carefully evaluated to prevent failures and associated health and pollution risks, which implies the determination of waste properties using more reliable approaches. This paper presents a scoping review of field data from MSW landfills and outlines suggestions for future work. Studies published in the past twenty years were selected following a systematic search process in databases. Aspects discussed include (1) strength parameters and soil behavior type from in situ testing, (2) elastic moduli from seismic wave propagation, and (3) moisture content from geoelectrical measurements. Although the values of geotechnical parameters have varied due to waste heterogeneity and applied methods, the trends observed with depth and age could be compared. Research opportunities involve the spatial analysis of mechanical properties at a given site, seismic response of landfills with high organic content and saturation degree, interpretation of long-term resistivity monitoring, and combination of electrical properties to assess the degradation stages within the waste mass.

Analysis of the existence form of landfill leachate water level and its development pattern under the condition of considering internal source water: a case study

In this paper, we study the existence form and development pattern of leachate level in the pile through a case of high water level landfill. The innovation of this paper is to consider not only the infiltration of rainfall, but also the internal source water of waste as the source of leachate. There is one main water level and multiple layers of stagnant water levels in this study area. The main water level of the pile first appears along the base slope of the landfill, and the trend of development is to connect from the bottom pile upwards layer by layer. The connection point of each layer gradually moves from the upstream side to the downstream side with time, and the main water level is formed by the gradual connection of the stagnant water level in each layer of the pile. Piles filled with slope as the base surface, and the stagnant water level in the pile first develops on the slope. And piles that are filled with a gentle base surface, and stagnant water level in the pile is uniformly developed on the base surface. At least one layer of stagnant water level exists in each layer of the pile, and multiple saturated zones occur in landfills with gentle base surfaces, and the saturation zone of the upper and lower waste pile will be penetrated. Depending on the form of leachate water level present in the pile, the location can be reasonably chosen for engineered precipitation of the landfill, and based on the development trend of each water level in the pile, it can provide a reference for the site selection and design of the landfill.

Shear strength characterization of fresh MBT and MSWI wastes from a Spanish treatment facility

A laboratory shear strength characterization of the landfilled materials of the Municipal Solid Waste integral treatment plant from the Meruelo Environmental Complex in Cantabria (Spain) was performed. The materials tested come from the rejection of the Mechanical and Biological Treatment (MBT-MSW) and the slags produced in the energy recovery plant (MSWI). Laboratory characterization consisted of direct shear and consolidated drained triaxial testing. Mohr-Coulomb failure criterion parameter values were obtained and compared to reported values in the literature. In some tests, failure was not reached due to the reinforcement effect for fibrous particles; thus, the mobilized shear strength parameters for different values of axial strain were obtained. The triaxial test results showed strain-hardening in MSW-MBT but not in MSWI. Failure was reached on both materials in direct shear testing, with MSWI showing peak and ultimate strengths, whereas MBT-MSW exhibited only ultimate strength. Direct shear test obtained strength can be characterized by a cohesion of 20 kPa and a friction angle of 33° for MBT-MSW ultimate strength, while cohesion and friction angle varies from 13.4 to 29 kPa and from 38.5° to 42.3° for MSWI ultimate and peak strength, respectively. The mobilized cohesion and friction angle obtained for MBT-MSW in consolidated drained triaxial tests ranged from 15.1 to 62.7 kPa and 20° to 28.7°, corresponding to a strain level of 5% and 25%, respectively. In triaxial testing of MSWI specimens, failure was reached, and the material showed a cohesion of 51.3 kPa and a friction angle of 32.8°.

Geotechnical properties of fresh municipal solid wastes with different compositions under leachate exposure

This paper investigates the geotechnical properties of a type of synthetic municipal solid waste (MSW). The tests were conducted on five groups of synthetic MSW compositions, based on the field characterization of fresh MSW samples collected from Mugga Lane landfill site, ACT, Australia. Compaction, hydraulic conductivity, compression, drained and undrained shear properties of the MSWs with water and leachate addition to the field moisture content were studied. The study shows that adding leachate could increase the maximum dry density of the MSWs under given moisture contents and compaction energies. The hydraulic conductivity of the MSWs could decrease by 100-fold when the confining pressure increases from 15 kPa to 240 kPa. The shear behaviours of the MSW samples follow the strain hardening behaviours of loose sand. The cohesion of the MSWs decreases but the friction angle of the MSWs increases with leachate addition due to the change in the surface tension and viscosity of the pore liquids and the loss of cementitious components. The addition of leachate increases the compression ratios of the MSWs by around 10% to 30% due to the change in the pH of the pore liquids. The most significant components affecting the shear and compression behaviours of the MSW were paper and wood. The effects of leachate exposure on the geotechnical properties of the MSWs is not very significant. It is important to consider the variation of MSW properties to the leachate properties (viscosity, pH and surface tension) in the large body of MSWs in the landfills.

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.

Mapping the impact of a large municipal waste disposal area on surface water: 1993-2017, case of Laogang, Shanghai

In China, the impact of waste disposal facilities is always a cause of concern for the government and the public. Laogang Municipal Waste Disposal Area (LMDA), Shanghai, one of the largest municipal waste disposal areas in the world was selected as case in this study, and it was attempted to analyze the changes in the surface water quality, and map the impacted area by LMDA on surrounding streams from its operation period of 1993-2017. The results showed that, during the whole period, only biochemical oxygen demand (BOD₅) showed a continuous improvement with a percentage of 85.92%, however, chemical oxygen demand (COD_cr), ammonia (NH₄⁺-N) and total phosphorus (TP) significantly improved but BOD₅ slightly deteriorated began from 2013. Using spatial analysis tools and Kendall's concordance test, COD_cr and phenol at LMDA showed a significant impact on surrounding surface water; especially, the impacted area for COD_cr decreased from 106.30 km² to 22.86 km² from 1993 to 2017, which dropped from 4.3 to 0.9 times the area of LMDA. Surprisingly, NH₄⁺-N and TP at LMDA were affected by the surrounding streams, instead of having an impact on them. Interestingly, heavy metals and non-metals such as Hg, As, Zn, and Se in the surrounding streams were unlikely affected by LMDA. The driving forces for surface water quality improvement included the eco-remediation of closed unsanitary landfills, upgrade in waste shipping and terminals, operation of sanitary landfills and incineration plants for landfill diversion. Capsule: Impacted area of municipal waste disposal area is not so large.

Household waste management in Singapore and Shanghai: Experiences, challenges and opportunities from the perspective of emerging megacities

Due to rapid economic development and urbanisation, emerging megacities with dense populations have witnessed a significant increase in waste generation. Megacities face challenges in developing sustainable waste management systems. Considerable heterogeneity exists across megacities in management strategies. The two selected emerging megacities, Singapore (a city-state) and Shanghai, have similar developmental characteristics, but their waste management modes differ strikingly. This study assessed the two modes in terms of management strategies, environmental effects, economic costs, and social outcomes. Environmental footprint analysis and cost quantification were employed for the assessment based on public data. The research results would permit a deeper understanding of the long-term sustainability of each mode while considering the feasibility of implementation across different contexts. It was found that the waste management system in Singapore had a relatively lower environmental impact than Shanghai before Shanghai's new waste segregation and recycling policy in 2019. However, when the effect of fossil fuel substitution is taken into account, the environmental burden in Shanghai can be lowered more substantially than the one in Singapore. Although Shanghai had more economic burden for the waste segregation at source, it tended to implement the circular economy principles (e.g., reduce, reuse, and recycling) better and improve its sense of community significantly. Based on the practical experiences from the two representative megacities, suggestions for better waste management practices were provided for Singapore, Shanghai, and other emerging megacities with similar circumstances. In addition, challenges and opportunities related to household waste segregation and recycling were identified to guide future practices in emerging megacities.

Municipal solid waste management: Dynamics, risk assessment, ecological influence, advancements, constraints and perspectives

Global energy consumption has been increasing in tandem with economic growth, putting pressure on the world's supply of renewable energy sources. Municipal Solid waste (MSW) has been reported contributing immensely to the improvement of a secure environment and renewable sources. Energy scarcity and conventional MSW disposal methods in developing countries lead towards many environmental and economic issues. Scientists have been able to experiment with various waste-to-energy conversion technologies in light of this situation. This communication highlights and reviews WtE technologies to convert MSW and other feedstocks into electricity, hydrogen gas, bioethanol along with other value added products like fertilizer(s), platform chemicals as an environmentally friendly products. This review comprehensively summarized the dynamics, risk assessment, ecological influence, advancements, constraints and perspectives altogether in field of municipal solid waste management and treatment. Stare-of-the-art information on ecological influence and risk assessment in handling and transportation of municipal solid waste has been provided. Advanced trends involved in remediation of emerging pollutants and resources obtained from municipal solid wastes have been uncovered. Lastly, this paper comprises constraints and perspectives for uncovering MSW based circular bioeconomy aspects.

Geo-environmental and geotechnical characterization of municipal solid waste from the selective collection in São Paulo city, Brazil

This paper presents the characterization of municipal solid waste (MSW) randomly collected from two material recovery facilities in São Paulo city, before (input - recyclables) and after (output - rejects) the sorting processes. Geo-environmental and geotechnical tests were performed on shredded samples and a digestion method was applied to detect the metals As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations using an ICP OES. The objective was to assist future activities of integrated solid waste management and soil pollution. Results showed different particle sizes comparing the input (44.6%) and the output MSW (75.1%) passing through the 100-mm sieve. Organic matter and ash contents indicated the influence of inorganic carbon due to the plastics' presence, with values varying between 6 and 13%. The pH values obtained were neutral and the electrical conductivity of the MSW rejects suggested a higher amount of ions, with values above 1000 µS/cm. Metals analyses show that Cd, Cu, Ni, Pb, and Zn are present in high concentrations, depending on the types of the materials. Standard Proctor compaction curves yielded maximum dry unit weight varying from 6.6 to 10.0 kN/m³ and optimum moisture contents from 20 to 42%. Cohesion ranged from 1.3 to 31.3 kPa and friction angle from 3.2 to 42.9°. The results are comparable with those obtained for other countries using different MSW treatments and contribute to the data basis for MSW from the selective collection, aiming the integrated solid waste management, serving for other countries that adopt MSW sorting and recycling.

Extensive database of MSW shear strength parameters obtained from laboratorial direct shear tests: Proposal for data classification

For the design of Municipal Solid Waste (MSW) landfills, especially in the initial stages of the project, shear strength parameters are often selected from published results or literature recommendations and results of published tests. However, when adopting MSW shear strength parameters of MSW in the literature, a great variability is present, associated with testing procedures and intrinsic regional differences in the samples. Despite the lack of standardization of observations in the literature, statistical techniques results can help identify the main factors that affect this variability and categorize the observations for better inference of the results. This research gathered 313 observations of laboratory direct shear tests results presented in 30 international published researches, addressing results from different countries and testing configurations, in order to assess data statistical behavior and propose a classification. Results showed the factors that most contribute to the observational divergences, being the main factor associated with the mechanical-morphological behavior of waste components. A reorganization of data into classes (A, B and C) according to waste compressible, incompressible and reinforcement compositions was carried out in order to group shear strength parameters in a ternary diagram. The classification of shear strength envelopes for each proposed class and different strain levels enabled the verification of a hardening behavior of MSW and a prediction of mechanical parameters.

Physical, chemical, and mechanical properties of landfilled waste from Campina Grande, Brazil

The properties of municipal solid waste (MSW) in landfills vary considerably, depending on the waste's composition, time, and density. This variability in MSW properties leads to many uncertainties in the analysis of landfill performance. Therefore, this study aimed to evaluate landfilled waste's physical, chemical, and mechanical properties for 8 days. Throughout this study, it was possible to investigate the gravimetric composition, density of solid particles, moisture content, volatile solids, pH, total alkalinity, chemical oxygen demand (COD), ammoniacal nitrogen (N-NH₃), grain size distribution, compaction properties, and shear strength of the landfilled waste. It was found that 71% of the waste corresponds to the denominated "others" category, the content of fine materials is 65%, the optimum water content is 34%, the moisture content is 41%, and the volatile solids is 67%. The chemical parameters indicated that the MSW was in the initial phase of biodegradation (acidogenesis), as the pH, total alkalinity, COD, and N-NH₃ showed to be 5, 1575 mgCaCO3.L^-1, 13698.6 mgO2.L^-1, and 56 mgN-NH3.L^-1, respectively. On the mechanical aspect, the waste presented a cohesion of 17 kPa and an internal friction angle of 16°. In general, the results showed that the waste's physical, chemical, and mechanical properties altered during the landfilling process.

Research on direct shear strength characteristics of mechanically biologically treated waste

AbstractMechanically and biologically treated (MBT) waste has significant characteristics such as high stability and low moisture content, which can reduce water, soil, and gas pollution in subsequent treatments. This pre-treatment method is environmentally friendly and sustainable and has become a popular research topic in the field of environmental geotechnical engineering. Using a direct shear test apparatus and five shearing rates (0.25, 1, 5, 10, and 20 mm/min), the shear strength characteristics of MBT waste at the Hangzhou Tianziling Landfill were studied. The results indicate the following: (1) With the increase in horizontal shear displacement, the shear stress of MBT waste gradually increases without a peak stress phenomenon, which is a displacement hardening curve; (2) the shear strength increases with an increase in the shearing displacement rate, and the sensitivity coefficient is 0.64-2.66; (3) a shear strength, shearing rate, and normal stress correlation model is established, and the model has a high degree of fit with the overall experimental data; (4) cohesion (c), internal friction angle (φ), and the logarithm of the shearing rate are linear; (5) the range of c of MBT waste is 22.32-39.51 kPa, and φ is 64.24-68.52°. Meanwhile, the test data are compared with the test data in the literature. The ranges of c and φ of municipal solid waste determined via the shear test are found to be wider than those of MBT waste. The results of this study can provide a reference for the stability calculation of MBT landfills.

Processes and prospects on valorizing solid waste for the production of valuable products employing bio-routes: A systematic review

Humanity is struggling against a major problem for a proper management of generated municipal solid waste. The collected waste causes natural issues like uncontrollable emission of greenhouse gases and others. Even though, escalation of waste results in minimizing the areas accessible for disposing the waste. Creating awareness in the society to use organic products like biofuels, biofertilizers and biogas is a need of an hour. Biochemical processes such as composting, vermicomposting, anaerobic digestion, and landfilling play important role in valorizing biomass and solid waste for production of biofuels, biosurfactants and biopolymer. This paper covers the details of biomass and solid waste characteristics and its composition. It is also focused to provide updated information about reutilization of biomass for value creation. Technologies and products obtained through bio-routes are discussed in current review paper together with the integrated system of solid waste management. It also covers challenges, innovations and perspectives in this field.

Demand gap analysis of municipal solid waste landfill in Beijing: Based on the municipal solid waste generation

Achieving accurate prediction of the Municipal Solid Waste (MSW) generation is essential for the sustainable development of the city. This paper selects Beijing as the research object, building a neural network model based on Grey Relational Analysis and Long and Short-Term Memory (GRA-LSTM), and choosing 14 influencing factors of MSW generation as the input indicators, to realize the effective prediction of MSW generation. Then this study obtains the landfill area in Beijing by using the aforementioned prediction results and the calculation formula of the landfill. Firstly, the GRA method is used to sort the influencing factors of the MSW generation for obtain the key influencing indexes. Secondly, the LSTM model is used to learn features of the key influencing indexes. Finally, the area of Beijing landfill is estimated by the calculation formula of landfill area. The results show that, first of all, the MAPE value of the GRA-LSTM combined model established in this paper is 7.3, and the prediction performance of this model is better than the other seven structural methods. Secondly, the area demand for landfills in Beijing shows an upward trend. At last, this paper put forward relevant suggestions to achieve sustainable urban development and deal with the increase in the MSW generation and the demand for landfills.

Simulation of gas transport in a landfill with layered new and old municipal solid waste

Average biodegradation rate of newly filled municipal solid waste (MSW) in landfills is relatively fast, and the landfill gas produced by the new MSW biodegradation can cause great variations in gas pressure. To predict the gas pressure distribution in the MSW layer, a one-dimensional gas transport model is established in this study. The following factors are considered in this model: (1) the variation of gas permeability with depth; (2) the anisotropy ratio of gas permeability; (3) the settlement caused by waste biodegradation. Furthermore, a single peak model for gas production is applied as the source term of gas production. The equation for settlement caused by waste biodegradation is presented, and the time of peak gas production rate is obtained by fitting the settlement of the newly filled layer. The stratification of the unsaturated and saturated regions is taken into account by distinguishing the difference in gas saturation. The layering of the new and old waste layers is considered by distinguishing the difference in the length of time that waste has been degraded to produce gas. Based on the method of numerical calculation, the gas pressure distribution in the landfill with layered new and old MSW is well simulated. The position where the maximum gas pressure occurs is found. The sensitivity analysis shows that the influence of the anisotropy ratio on gas pressure distribution is more significant.

Evaluation of geotechnical parameters of reclaimed land from near-surface seismic refraction method

Correct execution of civil engineering structures depends largely on the adequate and detailed mapping of the subsurface. This can be achieved by the application of appropriate geophysical or geotechnical methods in association with a detailed information on the geological sequence of the subsurface structure. In this study, a combination of near surface seismic refraction method, cone penetration test and borehole logs were used to obtain 2-dimensional (2D) information of the subsurface geological features. These methods were used to characterize the subsurface condition of a reclaimed land in Ajah area of Lagos for the purpose of construction. The seismic refraction method revealed three geologic layers with seismic velocities ranging between 258 and 3544 m/s. Additionally, the cone penetration test revealed that the geologic formation from the topsoil to a depth of 6 m was an alluvium of soft and highly compressible property. Furthermore, the percussion drilling test also confirmed the geologic formation from the topsoil to a depth of about 6 m to be highly compressible. However, a geologic formation with good geotechnical characteristics, such as a low compressibility potential, was encountered at a depth between 7 and 16 m, which coincides with the third layer of the seismic refraction method. The results of the three methods confirmed that the depth to most competent layer must be located before the foundations of engineering constructions are sited.

The influence of moisture enhancement on solid waste biodegradation

The objective of this study was to assess the influence of moisture enhancement strategies on biodegradation of municipal solid waste (MSW) in laboratory-scale reactors. Moisture enhancement strategies were varied with respect to dose volume (40, 80, 160, and 320 L/Mg-MSW) and dose frequency (dosing every ½, 1, 2, and 4 weeks). Biodegradation was evaluated based on methane generation to assess (i) the lag-time between the start of liquid dosing and onset of methane generation and (ii) the first-order decay rate for methane generation. In general, the decay rate increased with an increase in dose volume for a given dose frequency. In addition, trends of increasing decay rate and decreasing lag-time were observed for an increase in dose frequency for reactors operated with dose volumes of 40, 80, and 160 L/Mg-MSW. A key conclusion from this study was that reactors with more aggressive moisture enhancement attained more rapid methane generation that initiated at shorter elapsed times following the onset of dosing. An assessment of liquid dosing per month indicated that there were more pronounced impacts of increasing decay rate and decreasing lag-time as moisture enhancement increased from 40 L/Mg-MSW/month to 320 L/Mg-MSW/month as compared to the impact on both variables for an increase in liquid dosing above 320 L/Mg-MSW/month.

Real-time measurements of landfill atmospheric ammonia using mobile white cell differential optical absorption spectroscopy system and engineering applications

The real-time measurement of atmospheric ammonia at municipal solid waste (MSW) landfills and adjacent areas is necessary for landfill management and the health of nearby residence. Continuous, fast, and real-time monitoring of landfill odor gases is a challenge, especially for ammonia. To our knowledge, this was the first study for the characteristics and seasonal variabilities of atmospheric ammonia at a whole landfill using a Mobile White cell Differential Optical Absorption Spectroscopy (MW-DOAS) system, which also simultaneously offers high sensitivity and fast response. Results show that atmospheric ammonia levels at various landfill areas were significantly dependent on the characteristics of areas, such as municipal solid waste-related areas, leachate-related areas, sludge-related areas, and fly ash-related area, the atmospheric ammonia peak or average level at the active leachate pool of the active MSW site was the highest among all areas of the whole landfill, and the ammonia concentrations at the closed MSW landfill sites were low and dependent on the ages. Moreover, it was found that the seasonal variabilities of ammonia concentrations at most of those areas were significantly dependent on the ambient temperature, and ambient temperature variation caused the atmospheric ammonia level at the active leachate pool and active MSW landfill site in the summer survey to raise 3.5 times and 5.58 times than in the winter survey, respectively. Implications: Continuous, fast, and real-time monitoring ambient ammonia at or nearby a landfill is critical for landfill operators and local EPAs. This study demonstrates that the mobile White cell Differential Optical Absorption Spectroscopy (MW-DOAS) system is an effective tool for real-time monitoring ambient ammonia of a whole landfill. The results in this article provided a guideline to the characteristics and seasonal changes of ambient ammonia at various types of areas of a whole landfill as well as the impact of age to ambient ammonia at the closed landfill areas.

Impact of temperature on immediate and secondary compression of MSW with high and low food contents

Landfills in developing countries usually show municipal solid wastes (MSW) with large amount of food wastes, extraordinarily high moisture contents, and high internal temperatures. Because of these specific characteristics, significant post-closure settlements in landfills with high food waste are expected over time. This paper focused on the assessment of temperature impact on immediate and secondary compression behaviors of MSW with large contents of food, water, and plastic, comparatively to an aged low food content waste. A compression test was developed having a temperature-control system. The immediate compression index (C'_c) of HFWC samples was found to be higher than those of low food waste content (LFWC) owing to the soft behavior of food content, although immediate compression was 15-30% of total strains for HFWC wastes, while for LFWC samples it was 80% of total strains. Mechanical creep was also greater in HFWC owing to the soft behavior of the wet food components intensified by temperature increases. Mechanical creep of LFWC samples was attributed to the deformation of large parcel of soft plastics, also accelerated by temperature. The HFWC waste showed a first dominant phase of biocompression with an intense and rapid biological degradation, and a second phase characterized by reduced biological activity. Temperatures higher and high compression stresses are required to provide significant impact on biocompression index magnitudes. Overall, the compressibility of high food content wastes has shown to be significantly higher and the temperature impact led to twice total settlements of the MSW with low organic content.

Analytical Modelling of MSW Landfill Surface Displacement Based on GNSS Monitoring

Displacements of landfills play an important role in the reclamation process and geotechnical safety improvement of such sites. Landfill settlements are defined as a vertical displacement of waste body due to compression, degradable nature of the waste, and creep phenomenon of the waste particles. Waste composition is more diverse than natural soil. Thus, it has to be properly placed and compacted since the landfill body will continuously settle down. Several models of the landfill displacement estimation have already been developed. The aim of the present study was: (i) to review the methods of landfill settlements computation and (ii) to propose the model allowing landfill body displacements simulation based on monitoring datasets applying a Global Navigation Satellite Systems (GNSS) measurement. The new model employs Gauss-Newton iteration and Runge-Kutta methods to estimate landfill surface displacements. The objectives were to analyse and mathematically describe the landfill body displacements. The GNSS geodetic survey and computations allowed concluding that the landfill body has been transformed over the years. The results revealed that the curves of waste displacement are in agreement with the measured total displacement of the landfill, and all curves corresponding to waste displacement are perpendicular to the active edge of the landfill. In the period of a maximum of 4.5 years after the waste deposition with a layer of up to 16.2 m thickness, the phenomenon of expansion was observed, which then disappears, and more settlement occurs due to the gravity of upper layers. The analysed landfill as a whole does not experience significant displacements. Neither of the slope failures are observed, even for large inclination.

Hydraulic and mechanical behavior of municipal solid waste and high-moisture waste mixtures

The objective of this study was to investigate how addition of high-moisture waste (HMW) affects the hydraulic and mechanical behavior of municipal solid waste (MSW). Direct shear and hydraulic conductivity tests were conducted on MSW, HMW, and MSW-HMW mixtures prepared with HMW contents ranging from 20% to 80% (by total mass). Direct shear tests were conducted at normal stress between 22 and 168 kPa and hydraulic conductivity tests were conducted at vertical effective stresses of approximately 50, 100, and 200 kPa. A threshold HMW content of 40% was identified corresponding to substantial change in friction angle and hydraulic conductivity of the mixtures. Municipal solid waste and MSW-HMW mixtures with less than 40% HMW had friction angles between 29° and 32° and hydraulic conductivities greater than or equal to 1.3 × 10^-6 m/s. At HMW contents above 40%, the friction angle and hydraulic conductivity decreased with increasing HMW content. At 80% HMW, the hydraulic and mechanical behavior of the MSW-HMW mixture was comparable to HMW. The HMW had a friction angle of approximately 2° and hydraulic conductivity of 1.1 × 10^-11 m/s at a vertical effective stress of 50 kPa. Additional direct shear tests conducted on MSW and MSW-HMW mixtures soaked in water to simulate subsequent wetting post disposal revealed a decrease in friction angle from approximately 29° to 24° for MSW mixed with 40% HMW.

Molecular insight into variations of dissolved organic matters in leachates along China's largest A/O-MBR-NF process to improve the removal efficiency

Dissolved organic matter (DOM) is a critical component of high-strength organic wastewater, and the study of them from molecular perspective could improve the removal efficiency. Leachate samples were collected from China's largest two stage anaerobic/aerobic membrane bioreactor and nanofiltration (A/O-MBR-NF) process, with the treatment capacity of 5000 t/d, and characterized by electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) from molecular perspective. High molecular weight (m/z > 500) compounds with 40-50 carbon atoms and 15-20 double bond equivalence (DBE) were biodegraded into medium molecular weight compounds with 10-20 carbon atoms and ∼10 DBE. Contribution of lipids and unsaturated hydrocarbons compounds in DOM turned into 42.1% and 2.5%, respectively, while contribution of condensed aromatics in DOM dramatically increased to 15.4% in leachates along the A/O-MBR process. Most of DOM was converted into higher polymerization degree and accumulated in concentrated leachate (CL). Sulfur-containing compounds, whose relative peak ratio accounted for 56.4%, were regarded as recalcitrant DOM in CL. Increase of retention time in anaerobic unit for raw leachate might be useful for decomposing the long-chain organic compounds, which could also reduce loadings for the following A/O-MBR process. Well-focus techniques such as sulfur-oxidation bacteria could be introduced into the MBR unit for better removing organo-sulfur compounds. Advanced oxidation processes for CL degradation would be efficiency for the removal of recalcitrant DOM. Thus, leachate could be disposed in a zero-discharge way based on the practical experience of such a typical working treatment process.

Landfill Slope Stability Improvement Incorporating Reinforcements in Reclamation Process Applying Observational Method

This paper concerns a case study presenting one of the biggest landfills in Poland that required application of complex engineering works to extend the deposing capacity of the structure. The shear strength parameters of the subsoil and waste material used for analyses were based on geotechnical investigation and were then applied in slope stability analyses of the landfill. For the purpose of safety management of the new development and reclamation plan for the landfill, an observational method was applied to increase the geotechnical safety of the structure. The slope reinforcement methods mainly included the geogrid, geocomposite, and berms construction. However, much of the uncertainty associated with the stability of the geogrid-reinforced slope is related to the time-dependent deformation of geosynthetic materials. For the purpose of changes in the geogrid parameters with time, the samples were excavated from the landfill slope after 20 years of exploitation and analyzed in the laboratory. The tests allowed precise determination of the material properties, changing geometry, and mechanical properties like tensile strength and strain. Obtained results were compared to parameters of the brand-new geogrid samples. The tests indicated only insignificant changes in geosynthetics, physical, or mechanical performance properties, and the slope has not been compromised in its stability or performance.

A coupled hydro-mechanical-biodegradation model for municipal solid waste in leachate recirculation

The weight of Municipal solid waste (MSW) leads to a decrease of void ratio in landfill with depth and the biodegradation of MSW also results in decrease of void ratio with time. The spatial and temporal changes of void ratio of MSW have significant effects on its hydraulic properties and consequently influence the leachate recirculation process. In this paper, an advanced coupled hydro-mechanical-biodegradation (H-M-B) model is proposed to analyze the full coupling process for leachate recirculation taking into account the effect of initial density profile and its change due to biodegradation. A new solver is presented using the finite volume method based on the OpenFOAM platform to implement the coupled H-M-B model. The volume change caused by effective stress, degree of saturation and degradation, and the effect of void ratio change on hydraulic properties, can be taken into account in the coupled H-M-B model. The results calculated by the coupled H-M-B model illustrate the effect of void ratio on hydraulic properties, and the effect of compressibility, initial density and biodegradation on leachate recirculation. This study will contribute to the understanding of the leachate recirculation process and enhance the design of MSW landfills.

Numerical model of aerobic bioreactor landfill considering aerobic-anaerobic condition and bio-stable zone development

Aeration by airflow technology is a reliable method to accelerate waste biodegradation and stabilization and hence shorten the aftercare period of a landfill. To simulate hydro-biochemical behaviors in this type of landfills, this study develops a model coupling multi-phase flow, multi-component transport and aerobic-anaerobic biodegradation using a computational fluid dynamics (CFD) method. The uniqueness of the model is that it can well describe the evolution of aerobic zone, anaerobic zone, and temperature during aeration and evaluate aeration efficiency considering aerobic and anaerobic biodegradation processes. After being verified using existing in situ and laboratory test results, the model is then employed to reveal the bio-stable zone development, aerobic biochemical reactions around vertical well (VW), and anaerobic reactions away from VW. With an increase in the initial organic matter content (0.1 to 0.4), the bio-stable zone expands at a decreasing speed but with all the horizontal ranges larger than 17 m after an intermittent aeration for 1000 days. When waste intrinsic permeability is equal or greater than 10^-11 m², aeration using a low pressure between 4 and 8 kPa is appropriate. The aeration efficiency would be underestimated if anaerobic biodegradation is neglected because products of anaerobic biodegradation would be oxidized more easily. A horizontal spacing of 17 m is suggested for aeration VWs with a vertical spacing of 10 m for screens. Since a lower aeration frequency can give greater aeration efficiency, a 20-day aeration/20-day leachate recirculation scenario is recommended considering the maximum temperature over a reasonable range. For wet landfills with low temperature, the proportion of aeration can be increased to 0.67 (20-day aeration/10-day leachate recirculation) or an even higher value.

Temperature monitoring during a water-injection test using a vertical well in a newly filled MSW layer of a landfill

High temperature may adversely affect municipal solid waste (MSW) biodegradation and lead to an increase in the deformation of high-density polyethylene (HDPE) pipes used for the collection of leachate and landfill gas in landfills. The test in this study was to change the waste temperature around the vertical injection well by water injection using a vertical well. The test was conducted intermittently with two different flowrates in a newly filled MSW layer of a landfill. The temperature, gas pressure and leachate level in the test area were simultaneously monitored during this study. The results showed that the waste temperature around the vertical injection well was effectively changed by water injection, which did not result in a significant rise in the leachate level. During water injection, the waste temperature influence distance in the horizontal direction increased with depth from the leachate level to the bottom of the injection well. The bottom temperature of the injection well decreased to near the water-injection temperature. The range of influence of the waste temperature caused by intermittent water injections slightly increased in this test. After water injection was stopped, the waste temperature near the vertical injection well increased quickly initially, and then the increments became more gradual with time. When the leachate level recovered stably, there was still a temperature gradient around the injection well within the range of influence. The temperature and gas pressure in the waste above the leachate level and far away from the injection well were slightly influenced by water injection.

Risk assessment and rehabilitation potential of a millennium city dumpsite in Sub-Saharan Africa

Management of the ever-increasing generated solid waste had been a difficulty for state governments in Nigeria. The high costs connected to this waste management which had encumbered the state budget, ignorance or lack of understanding of resourceful waste management and insensitivity to environmental concerns may have led to partial neglect of this sector. This research paper is aimed at evaluating the rehabilitation potential and the risk level of Igbatoro dumpsite, an Ondo state-managed waste dumpsite which predominantly receives the waste of Akure and its environs. In determining rehabilitation/reconstruction potentials and assessing the risk of the dumpsite, an Integrated Risk Based Approach (IRBA) was considered. The Risk Index (RI) was calculated from the addition of the sensitivity index output with the attribute weightage of the twenty-seven (27) parameters studied. A total risk index of 571.58 was obtained for Igbatoro dumpsite indicating moderate hazard evaluation. Questionnaires distributed to dwellers around the dumpsite also showed that 83.6% of those interviewed agreed that the present management of the dumpsite is poor while 81.8% supported rehabilitation of the dumpsite. Hence, reconstruction of the Igbatoro dumpsite to an endurable and controlled landfill is hereby recommended.

Characterization of the constitutive behavior of municipal solid waste considering particle compressibility

This paper presents a characterization of the mechanical behavior of municipal solid waste (MSW) under consolidated drained and undrained triaxial conditions. The constitutive model was established based on a deviatoric hardening plasticity model. A power form function and incremental hyperbolic form function were proposed to describe the shear strength and the hardening role of MSW. The stress ratio that corresponds to the zero dilatancy was not fixed but depended on mean stress, making the Rowe's rule be able to describe the stress-dilatancy of MSW. A pore water pressure reduction coefficient, which attributed to the compressibility of a particle and the solid matrix, was introduced to the effective stress formulation to modify the Terzaghi's principle. The effects of particle compressibility and solid matrix compressibility on the undrained behavior of MSW were analyzed by parametric analysis, and the changing characteristic of stress-path, stress-strain, and pore-water pressure were obtained. The applicability of the proposed model on MSW under drained and undrained conditions was verified by model predictions of three triaxial tests. The comparison between model simulations and experiments indicated that the proposed model can capture the observed different characteristics of MSW response from normal soil, such as nonlinear shear strength, pressure dependent stress dilatancy, and the reduced value of pore water pressure.

The use of electrical resistivity tomography and borehole to characterize leachate distribution in Laogang landfill, China

Leachate is a polluting liquid which may cause harmful effects on human health or the environment without a tightly control manner. The leachate management is an important part of the design and operation of bioreactor landfills. To detect the leachate distribution in Laogang Landfill, China, the measurement of electrical resistivity tomography (ERT) was carried out in three areas with different ages. ERT method proved to be an effective non-invasive geophysical method in bioreactor landfills, and the physical properties of waste samples obtained by boreholes were tested in a laboratory. The correlation between the resistivity and the moisture content was described by Archie's law. The result shows that the moisture content of fresh waste is inhomogeneous, while that of aged waste increases with depth. A pseudo 3D model of the moisture content was proposed to improve the understanding of leachate distribution and exhibit the accuracy of the ERT method.

Study of stress-strain and volume change behavior of emplaced municipal solid waste using large-scale triaxial testing

The article presents the stress-strain and volume change behavior, shear strength and stiffness parameters of landfilled municipal solid waste (MSW) collected from two dump sites located in Delhi, India. Over 30 drained triaxial compression (TXC) tests were conducted on reconstituted large-scale specimens of 150mm diameter to study the influence of fiber content, age, density and confining pressure on the shear strength of MSW. In addition, a few TXC tests were also conducted on 70mm diameter specimen to examine the effect of specimen size on the mobilized shear strength. It is observed that the fibrous materials such as textiles and plastics, and their percentage by weight have a significant effect on the stress-strain-volume change behavior, shear strength and stiffness of solid waste. The stress-strain-volume change behavior of MSW at Delhi is qualitatively in agreement with the behavior reported for MSW from different countries. Results of large-scale direct shear tests conducted on MSW with an identical composition used for TXC tests revealed the cross-anisotropic behavior as reported by previous researchers. Effective shear strength parameters of solid waste evaluated from this study is best characterized by ϕ'=39° and c'=0kPa for the limiting strain-based failure criteria of K₀=0.3+5% axial strain and are in the range of the data reported for MSW from different countries. Data presented in this article is useful for the stress-deformation and stability analysis of the dump sites during their operation as well as closure plans.