Waste Management & Research: The Journal for a Sustainable Circular Economy

This paper reports on the potential to apply the choice experiment method to understand the public’s preferences for solid waste management programmes in Macao. A random sample survey of 260 respondents in Macao was conducted during the summer in 2004. The survey data was analysed using conditional multinomial logit models. The study results indicate that Macao residents prefer: (1) waste segregation and recycling at source; (2) noise reduction during waste collection and transportation and (3) lower garbage fees. The study concludes that choice experiment is a reliable tool in the analysis of respondents’ preferences for developing a suitable solid waste management programme in Macao.

Cost estimation is a basic requirement for planning municipal solid waste management systems. The variety of organizational, financial and management schemes and the continuously developing technological advancements render the economic analysis a complex task, made more complex by the scarcity of real cost data. The objectives of this paper were: (1) to explore the problems arising in getting cost estimates from scattered and limited published data; (2) to suggest a procedure for generating cost functions relating initial set-up cost and operating cost with facility size; and (3) to present such cost functions, relevant to European states, for selected types of solid waste treatment and disposal facilities. Regarding the problems of available scarce data, one needs to deal with cost figures which correspond to facilities with variations in size, technology, year of construction, working conditions, level of technological automation, environmental impacts, social acceptance, capacity utilization rate, composition of inflowing waste, waste management policies, degree of compliance with quality standards, etc. The paper addresses this issue and discusses the proper use of statistical analyses in such cases of fragmented data; moreover, it points out some usual misuses of statistics by analysts and the danger of getting erroneous results. The suggested process for generating cost functions acceptable to the decision-makers is pivoted around the question of acceptable approximation level. Finally, approximate cost curves are suggested for waste-to-energy facilities, landfilling facilities, anaerobic digestion facilities and composting facilities.

During the last decade, systems analysis has become a more frequently used tool in municipal waste management. This paper investigates how one such analysis, carried out in a Swedish county, was perceived by local municipal officers and politicians as support in the decision-making process. A questionnaire was sent to municipal officers and politicians in local government committees and municipal councils. The respondents considered the most important aspects in evaluating scenarios to be: possibilities for municipal co-operation to minimize cost and negative environmental influence; sound working conditions for refuse disposal personnel; low emissions of greenhouse gases; keeping household economy in mind; and using technologies that are known and reliable. Aspects of relatively low importance were the number of locally generated job opportunities, and minimizing work efforts for the households. The study also showed differences between male and female respondents and between politicians and municipal officers, on how scenarios were valued and on which aspects of the systems analysis were of greatest importance for this valuation. Respondents, on average, were satisfied with the systems analysis, and its usefulness as a decision-support tool. However, more work should be carried out to explain and present the results of the systems analysis to further improve its usefulness.

The available expertise on managing and operating solid waste management (SWM) facilities varies among countries and among types of facilities. Few experts are willing to record their experience, while few researchers systematically investigate the chains of events that could trigger operational failures in a facility; expertise acquisition and dissemination, in SWM, is neither popular nor easy, despite the great need for it. This paper presents a knowledge acquisition process aimed at capturing, codifying and expanding reliable expertise and propagating it to non-experts. The knowledge engineer (KE), the person performing the acquisition, must identify the events (or causes) that could trigger a failure, determine whether a specific event could trigger more than one failure, and establish how various events are related among themselves and how they are linked to specific operational problems. The proposed process, which utilizes logic diagrams (fault trees) widely used in system safety and reliability analyses, was used for the analysis of 24 common landfill operational problems. The acquired knowledge led to the development of a web-based expert system (Landfill Operation Management Advisor, http://loma.civil.duth.gr), which estimates the occurrence possibility of operational problems, provides advice and suggests solutions.

This paper investigates the number of observed households setting out their containers for kerbside recyclable collection in two Welsh kerbside recycling programmes; namely, Rhondda Cynon Taf County Borough Council and Caerphilly County Borough Council. Analysed data from the monitoring of approximately 114 000 households in the two separate kerbside programmes are presented, making this the largest study of kerbside recycling behaviour in the UK. The average household set-out rates of individual households per electoral division and per street in each programme were compared. Average household set-out rate for a particular electoral division and street was then related to certain socio-economic indicators. The study was performed using the ‘ArcView’ geographical information systems (GIS) package. The model identified a moderate link between household set-out rate (%) and socio-economic status at electoral division level. However, there was no correlation between socio-economic status and average household set-out rate in a street. Household set-out rates for both programmes fluctuated significantly in streets with similar socio-economic status. Another significant factor affecting set-out rate, herein named the ‘Nant-y-Gwyddon effect’, is also described.

The effects of the aeration, seeding, and agitation on the composting of vegetable waste were studied in a laboratory-scale reactor. Experimental results showed that the final product at the end of a 4-day composting period met multiple maturity indices suggested by many researchers. The evolution of carbon dioxide during the composting process could be modelled with a modified Gompertz equation that described the bacteria growth successfully. Multivariate regression analysis was used to study the effects of operating parameters on the carbon conversion. The response surface contour plots were constructed using the regression equation for the examination of the dependence of carbon conversion on operating parameters. The maximum carbon conversion of 14.54% was obtained when the percentage of seeding was set at 14.5%, the air suction rate was set at 2.6 L kg^-1 dry-solid min^-1, and the agitator operated half of the time, alternating on and off for every 5 min. Future work will focus on the application of the data and the experience gained in this work to composters of pilot and semi-commercial scales.

This paper presents a model using fuzzy synthetic evaluation to estimate the methane generation rate constant, k, for landfills. Four major parameters, precipitation, temperature, waste composition and landfill depth were used as inputs to the model. Whereas, these parameters are known to impact the methane generation, mathematical relationships between them and the methane generation rate constant required to estimate methane generation in landfills, are not known. In addition, the spatial variations of k within a landfill combined with the necessity of site-specific information to estimate its value, makes k one of the most elusive parameters in the accurate prediction of methane generation within a landfill. In this paper, a fuzzy technique was used to develop a model to predict the methane generation rate constant. The model was calibrated and verified using k values from 42 locations. Data from 10 sites were used to calibrate the model and the rest were used to verify it. The model predictions are reasonably accurate. A sensitivity analysis was also conducted to investigate the effect of uncertainty in the input parameters on the generation rate constant.

Waste material in municipal landfills can be described as heterogeneous porous media, where flow and transport processes of gases and liquids are combined with local material degradation. This paper deals with the basic formulation of a multiphase flow and transport model applicable to the numerical analysis of coupled transport and reaction processes inside landfills. The transport model treats landfills within the framework of continuum mechanics, where flow and transport processes are described on a macroscopic level. The composition of organic and inorganic matter in the solid phase and its degradation are modelled on a microscopic scale. The degradation model captures the different reaction schemes of various microbial activities. Subsequently, transport and reaction processes have to be coupled, since emissions at the surface and from the drainage layer depend on the flow of leachate and gas, the transport of various substances and heat, and the biodegradation of organic matter. The theoretical considerations presented here are fundamental to the development of numerical models for the simulation of multiphase flow and transport processes inside landfills coupled with biochemical reactions and heat generation. The implicit modelling of leachate and gas flows including growth and decay of micro-organisms are innovative contributions to landfill modelling

The reduction of SO₂, HCl, and NO_x concentrations using calcium magnesium acetate (CMA) as a novel sorbent in a simulated municipal waste incinerator flue gas was investigated. The reduction of individual SO₂, HCl, and NO_x concentrations was tested at 850°C and it was found that CMA could reduce the SO₂ concentration by 74%, HCl concentration by 64%, or NO_x concentration by 94%. It was observed that individual SO₂ or HCl capture increased with increasing initial oxygen concentration in the reacting gas or increasing sorbent input. NO_x reduction decreased with increasing initial oxygen concentration in the reacting gas. The simultaneous reduction of SO₂, HCl, and NO_x concentrations by CMA was also investigated. It was found that CMA could simultaneously capture 60% SO₂ and 61% HCl and reduce NO_x concentrations by 26%, when the initial oxygen concentration in the reacting gas was 4%. During the simultaneous reduction of SO₂, HCl, and NO_x, it was noted that as the initial oxygen concentration in the reacting gas increased, the efficiency of SO₂ capture increased too, but the efficiency of HCl capture and the efficiency of NO_x destruction decreased.

Surveys of over 2000 households in Japan were conducted to investigate the characteristics of hazardous household waste (HHW) generation. In Japan, about 2.5 to 4.3 kg of HHW are produced per tonne of the residential waste stream. The percentage of used batteries in HHW was over 50%. Every household using spray (aerosol) cans had more than seven cans on average. The generation of HHW, in terms of both quantities and type of waste produced, appeared to vary with dwelling type. Detached dwelling residents tended to store HHW such as used batteries, whereas apartment residents tended not to store waste. The amounts of discarded HHW were larger at the end of the year in comparison with other months. The data accumulated were used to estimate the quantities of HHW disposed off annually, and the quantities and type of waste that might be received by a typical depot collection programme in Japan.