The effect of temperature on the biodegradation properties of municipal solid waste

A review of existing methods for predicting leachate production from municipal solid waste landfills

Landfilling is one of the predominant methods of municipal solid waste (MSW) disposal worldwide, while the generation of leachate, a kind of toxic wastewater, is among the primary factors behind landfill instability and environmental contamination problems. Precise prediction of leachate production is crucial to landfill safety evaluation and design. This paper presents a comprehensive review of methods for predicting leachate production from MSW landfills. Firstly, compositional characteristics of MSW and leachate generation mechanism are analysed. Factors influencing leachate production are summarised based on the generation mechanism, including the components of MSW, climatic conditions, landfill structure, and environmental factors. Then, we classified the existing methods for predicting leachate production into four categories: water balance formula, water balance model, empirical formula, and artificial intelligence model methods. Advantages, disadvantages, and applicability of different leachate production prediction methods are compared and analysed. Furthermore, limitations in the existing leachate production prediction methods for MSW landfills and scope for future research are discussed.

Physical, geotechnical and biochemical behaviours of municipal solid waste in field and laboratory bioreactors

This paper investigates the effects of degrees of compaction (initial dry unit weights), recirculation liquid and rate, and environmental temperature on the long-term physical, geotechnical, and biochemical properties of municipal solid wastes (MSWs) biodegraded for approximately 800 days. Four field bioreactors were filled with fresh MSWs collected from a landfill site. Three laboratory bioreactors were filled with synthetic MSWs with the composition same as that used in the field bioreactors. The bioreactors were recirculated with water or leachate at different rates. Compared to water recirculation, leachate recirculation further promotes the settlement of the MSWs and methane generation. Increasing the recirculation rate does not significantly increase the settlement of the MSWs. The biocompression ratio increases with the environmental temperature. The MSWs with lower dry unit weights are more sensitive to the change in temperature, especially with leachate recirculation. However, opposite to common sense, the decomposition of MSWs may not significantly contribute to the settlement after analysing the relationship between the degrees of biodegradation and settlement of the MSWs. Over 90 % of the settlement during the test period was completed within 25 % degrees of biodegradation. The major change in the physical, geotechnical, and biochemical properties occurs at low (less than20 %) degrees of biodegradation. A new equation is proposed to describe the nonlinear variation in the methane generation rate. The modelled methane generation rate and accumulated volume of methane well match the test results from the laboratory scale bioreactors and other studies.

Coupled mechanical creep and bio-compression and residual settlement in a multi-stage municipal solid waste landfill, Korea

Based on a field monitored dataset measured at landfill #1 over 21 years, the characteristics of settlement coupling mechanical creep and biodegradation and the residual settlement were analyzed. Since landfill #1 is a multi-stage municipal solid waste (MSW) landfill where dykes are constructed after landfilling for subsequent waste fills, the waste decomposition between the lower and upper lifts was quite different and it is difficult to discern between the mechanical creep and bio-compression on the settlement curves. The compression ratio coupled with mechanical creep and bio-compression and the residual compression ratio were determined as 0.233 and 0.068, respectively. This implies that biodegradation was gradually and significantly reduced in the MSW settlement behavior after the residual settlement began. The starting date of residual settlement was distributed between 3821 and 5402 days from the initial date of landfilling. The settlement coupling mechanical creep and biodegradation (S_MB) was 2.9 times larger than the residual settlement (S_RS), and the duration of S_MB is determined to be 0.3 times that of S_RS. In addition, the remnant methane gas content existed in the landfill gas, and low-level biodegradation was still generated in the waste buried for more than 10 years after the residual settlement began.

A review on settlement models of municipal solid waste landfills

Currently, landfill is the most common, economical, and convenient method for municipal solid waste (MSW) disposal in countries around the world. MSW has a complex composition and special engineering characteristics, which lead to a very complex settlement mechanism in MSW landfills. This article reviews the description of this settlement mechanism in the existing literature and classifies it into stress-related mechanisms, biodegradation processes of organic substances, water-related mechanisms and physical and chemical processes of inorganic components. Based on the settlement mechanism, the influencing factors of landfill settlement were analysed, including the composition of MSW, physical parameters, environmental factors, and the operation mode of the landfill. Some practical engineering suggestions are obtained by analysing the influencing factors of MSW landfill settlement. Four commonmethods for studying the settlement of MSW landfills are presented, including laboratory experiments, in-situ settlement monitoring, theoretical analysis, and numerical simulation. We classified the existing settlement models into six categories: a soil mechanics, rheological, empirical, biodegradation, constitutive, and multiphase coupling models. Advantages and disadvantages of the different models and their applicability are compared and analysed. Moreover, limitations in the modelling process of MSW landfill settlement and future research directions are discussed.

Pollution potential of dumping sites on surface water quality in Ethiopia using leachate and comprehensive pollution indices

Municipal solid waste disposed of in illegal dumpsites pollutes the surface and groundwater. However, accurately determining these pollution levels is typically challenging for practitioners and decision-makers in developing countries. The purpose of this study is to use the leachate pollution index (LPI) to assess the contamination potential of uncontrolled dumping sites along the course of the Kulfo River in Arba Minch, Ethiopia. The comprehensive pollution index (CPI) approach was also utilized to assess the suitability of Kulfo River water quality for aquatic species. Leachate samples were collected from four uncontrolled dumping sites along the Kulfo River's course and analyzed for fifteen leachate characteristics necessary to quantify the LPI sub-indices. Water samples were taken from three monitoring stations along the river and examined for aquatic species suitability. When the leachate parameters were compared to the Indian limit for discharge of treated leachate, it was found that dumping sites posed a considerable risk of pollution to adjacent water resources. The overall LPI ranged from 23.34 to 27.35, which is higher than the discharge standard LPI of 5.69, indicating that dumping sites can threaten the surrounding water resources and human health. Based on the rating scale of CPI, at all monitoring stations, the river resulted severely polluted. Finally, appropriate strategies to reduce the pollution and the related mismanagement of solid waste were discussed. Combining LPI and CPI methods can represent a crucial tool for experts and decision-makers in developing countries to evaluate the pollution potential of dumping sites and water resource monitoring.

A comparison between constitutive models for the municipal solid waste

This paper compares the behavioural models of municipal solid waste (MSW) using the corresponding experimental data. To do so, the proposed models are first reviewed and, then, the algorithms and codes of different models are written. After obtaining each model's algorithm, the same experimental data are considered as input, and the strain-stress curve is plotted for each model. In the first method, the total strain in the waste is obtained based on the summation of the elastic, plastic, biological, and creep strains. Afterward, the equivalent stress is obtained. In this method, using biological changes over time, the age of the waste is calculated as an effective parameter in MSW behaviour. Moreover, the effect of creep on the waste is considered independently. In the second algorithm, MSW is considered as fibre and paste material, and the strain-stress curve is obtained. In this method, the waste is considered as a soil model, and the effect of different parameters are calculated. Due to the complexity of the MSW behaviour and considering various parameters, such as the age of the waste, E changes over time, creep, and biological changes, the Krase model has less error than the other models. Using the soil behaviour model for the waste has a significant error, indicating the difference between the results for the behaviours of the two substances.

Comparison of waste settlement characteristics for two landfills disposed in long sequential periods

Changes in waste management policy affect the settlement characteristics of waste landfills in which the waste disposal is operated for decades. In this study, the waste settlements were calculated by using the data measured in two multi-staged landfills for 27 years. The relationship between the changes in waste management policies and settlement characteristics is analyzed. Sequentially launched waste management policies reduced the organic matters in municipal solid waste (MSW) of the landfill. This change in turn influenced the engineering properties of landfill waste, e.g. water content, unit weight, and initial void ratio, etc. Due to the reduction of food waste in landfills, the water content decreased and the unit weight increased. The initial void ratio declined by the decrease of water content and the increase of unit weight. The annual primary and secondary compression indices, C_c and C_α, of each lift also increased/decreased due to the change in waste composition. The C_c of Phase #1 increased from an average of 0.34 to an average of 0.51 because the percentage of coal ash in MSW drastically decreased and the percentage of food, paper, and plastic, which are highly compressible, increased. On the other hand, the C_c of Phase #2 declined from an average of 0.15 to an average of 0.025 due to the decrease of the waste compressibility from the reduction of organic matters. The C_α of Phase #1 and #2 decreased by the reduction of organic matter and moisture which are needed for biodegradation of wastes in the landfill.

Micro- and mesoplastics release from the Indonesian municipal solid waste landfill leachate to the aquatic environment: Case study in Galuga Landfill Area, Indonesia

Small-sized plastic debris (micro- and mesoplastics) are emerging pollutants and widely detected in aquatic environments. However, micro- and mesoplastics pollution research with regard to landfills is limited. In this study, the occurrence, characteristics, and possible release of micro- and mesoplastic waste from the Galuga landfill leachate to the aquatic environment were studied. Micro- and mesoplastics were identified in all surface water samples from leachate influent and effluent of Galuga landfills. The average daily release to the aquatic environment was estimated at 80,640 ± 604.80 microplastic and 618,240 ± 1905.45 mesoplastic particles, respectively. The amount of microplastic increased three-fold and nine-fold for mesoplastics after input from the leachate drain. Micro- and mesoplastic main chemical compositions were polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polyester, and cellophane. This study implied that the leachate may cause micro and mesoplastic contamination to the aquatic environment. The results raised the knowledge of small-sized plastic debris in aquatic environments.

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.

Statistical modelling and assessment of landfill leachate emission from fresh municipal solid waste: A laboratory-scale anaerobic landfill simulation reactor study

Quantification, measurement of quality, post-treatment, and leachate control has been a significant problem due to the dumping of waste in an unscientific manner across the globe, and especially in developing countries like India. In this context, the objective of this study was to investigate the degradation of fresh mixed municipal solid waste (MSW) in an anaerobic landfill reactor operated with rainfall addition in laboratory conditions. Experiments were carried out in a landfill reactor of 1 m length × 1 m width × 1.1 m height. The reactor was simulated with 50 years weighted average actual rainfall rate of India. It contained the waste composition of 73% wet waste (food and kitchen) and 27% dry waste (paper, plastic, wood, textiles, and others). The leachate parameters were continually monitored for 39 weeks. In the fresh MSW landfill reactor it was evident that concentrations of leachate parameters were high initially, and there was a significant decrease in BOD₅ (7041-39310 mg L^-1), COD (15692-71630 mg L^-1) and TS (9077-33200 mg L^-1) in leachate. Therefore, rainfall had a direct influence on leachate quality. The developed first-order decay models were used for BOD₅, COD, and total solids with adjusted R² of 0.83, 0.92, and 0.96, respectively. Therefore, this model can be applied for leachate strength estimation at any given time from the period of deposition of waste under similar rainfall and waste compositions, and is largely applicable in India and tropical areas. This study is expected to be a good simulation for cities with the waste composition of high wet waste (>70%) as the estimations of important design parameters such as BOD₅, COD, VFA, and NH₄⁺-N were studied in this research. As the importance of moisture (precipitation) has been established in this study, some moisture additions can be designed in areas with low rainfall, such as arid zones.

Effect of waste compaction density on stabilization of aerobic bioreactor landfills

Landfill stabilization contributes to the safe operation and maintenance of landfills. This study used a simulated aerobic bioreactor landfill to investigate the impact of different compaction densities on its stabilization to provide a basis for optimal parameter selection during landfill design. Samples of municipal solid waste were tested with compaction densities of 450, 500, 550, 600, and 650 kg/m³ during the experiment. The optimum compaction density was obtained by periodically monitoring the temperature of the waste pile, the water quality of leachate, and the composition of the waste. The impacts of waste compaction density on waste pile temperature and leachate were investigated and coupled with the analysis of waste composition to discuss the possible reaction mechanism. Results showed that the most complete waste degradation occurred at 550 kg/m³ compaction density, which was effective at accelerating stabilization of the simulated aerobic bioreactor landfill. Limitations of the experiment are given to lay foundations for further study.