The biodegradation of solid waste materials, the main cause of secondary settlement in landfills, has a significant impact on the post-closure performance of landfill capping systems. Excessive settlement may in turn lead to water ingress and enhanced leachate generation, significantly increasing the risk of harm to the environment. Largescale long-term laboratory experiments were conducted to identify the rate and magnitude of waste settlement using three purpose-designed test reactors (consolidating anaerobic reactors (CARs)). This paper presents a detailed characterisation of the waste, its associated chemical and physical properties, and the overall volume changes associated with degradation over time. The total magnitudes of settlement after 919 days were 27 . 6% in CAR 1 (under 150 kPa pressure) and 25 . 0% in CAR 2 (50 kPa). Long-term secondary settlement was found to be dependent on waste depth-that is, stress dependent. Increased stress (150 kPa) led to a 20% increase in the rates of long-term secondary compression in comparison with a stress level of 50 kPa. Secondary settlement due to biodegradation was found to be of comparable magnitude to the component of secondary settlement caused by mechanical creep (values of 11 . 1-13 . 7%). If the settlement behaviour in the CARs approximates to full-scale observations, this data set could be used for validation of quantitative landfill settlement models. NOTATIONK absolute zero temperature in Kelvin (273 . 2K) p 1 pressure at volume V 1 p 2 pressure at volume V 2 p a measured atmospheric pressure in the laboratory in kPa p 0 a atmospheric pressure at sea level in kPa (101 . 3 kPa) p w water vapour pressure in kPa T reference temperature in the laboratory in degrees Celsius V 1 volume of gas at pressure p 1 V 2 volume of gas at pressure p 2 V 0 a standardised V g to dry gas at standard temperature and pressure (STP) V g volume of biogas released at each venting event V h volume of headspace Áp limiting increase in pressure (1 . 0 kPa)
A series of laboratory tests was performed to characterise the anaerobic biodegradation potential of a fresh well-characterised sample of municipal solid waste (MSW). This characterisation included measurement of the quality and quantity of biogas produced, determination of the loss of cellulose and hemicellulose (as indicated by measurements of neutral detergent fibre (NDF) and acid detergent fibre (ADF)) and assessment of various leachate chemical characteristics at key phases during the biodegradation process. Twelve 1-litre high-density polyethylene reactors were filled with 100 g of prepared MSW together with a methanogenic mineral media and a bacterial seed derived from an anaerobic digester. Two other reactors, containing no MSW, were used as blanks. Relationships between the chemical composition of the waste and the capacity for predicting the biochemical methane potential (BMP) of fresh waste are discussed. The methane recovery is presented and discussed in the context of the theoretical yield expected from these reactors and from larger consolidating anaerobic reactors (CARs) used in a parallel study.
A numerical model is presented based on conceptual considerations of chemical and biological reaction processes in landfills. The model enables the details of mixed-culture population dynamics and locally based multiple reaction schemes to be described as functions of the chemical and physical environmental conditions. In its current stage of development, the model is primarily used as a research tool to analyze the influence and value of various model parameters on biodegradation and landfill gas formation processes. In order to test the accuracy of the model, simulation results have been compared with experimental data obtained from a 340-day experiment on the degradation of waste within a "consolidating anaerobic reactor (CAR)." A good match with simulated results was obtained to the measurement of methane and carbon dioxide formation, as well as to the measured concentrations of sulphate and ammonium ions in the liquid phase. In particular, the experimentally observed influence of sulphate on the methane formation could be modeled taking into account interactions between sulphate-reducing and methanogenic bacteria.
A modelling challenge made to international research groups with landfill modelling capabilities is described. The challenge invited participants to model and predict the performance of a well-constrained laboratory experiment on the settlement and biodegradation of municipal solid waste (MSW). Data on the set-up and operational procedures of two laboratory-scale waste reactors were provided, together with limited results on leachate chemistry in the first two months of a 2½-year experiment. Participants were then invited to submit their modelled predictions over time for any (or all) of: waste settlement; degradation and gas production; evolution of leachate chemistry. Results from the exercise were collated by an organising committee prior to presentation and discussion at HPM2, an international workshop on the hydrological, physical and mechanical behaviour of landfills.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.