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

As the need for hazardous waste management facilities becomes critical, several strategies including public-private partnership have been suggested and adopted by states to diffuse public opposition, and facilitate the siting of these facilities. Public-private partnership involves state ownership of the facility, and its operation by a private company. Proponents of this strategy contend that state ownership of facility and therefore an assumption of long-term liability would reduce public concerns regarding site maintenance. Also, that state or public ownership of the land on which the facility is built would thwart any local land use regulation that may be enacted to derail the site selection process. This paper, through a case study provides an analysis of this strategy, and surmised that factors identified in past research-public trust in institutions of government, in the perceived competence and integrity of the developer, and in the waste treatment technology to pose minimal risks to public health and the environment, are necessary to enhance the efficacy of public-private partnership in the siting of hazardous waste management facilities.

This work was part of a major study that examined the policy and technology implications of alternatives for managing the municipal solid wastes (MSW) of New York City. At this time, of the 4.1 million metric tons of MSW collected by the City annually, 16.6% are recycled, 12.4% are combusted in Waste-to-Energy (WTE) plants, and the remaining 71% are landfilled. Despite the heterogeneity of organic materials in MSW, the composite molecular structure can be approximated by the organic compound C₆ H₁₀ O₄. A formula was derived that allows the prediction of the heating value of MSW as a function of moisture and glass/metal content and compares well with experimentally derived values. The performance of a leading Waste-to-Energy plant that utilises suspension firing of shredded MSW, processes one million tons of MSW per year, and generates a net of 610 kWh/metric ton was examined. The results of this study showed that WTE processing of the MSW reduces fossil fuel consumption and is environmentally superior to landfilling.

On the basis of earlier experimental studies of the aerobic bioconversion of organic wastes, the preferred values of operating parameters and the biochemical rate constants of oxidation to CO₂ and H₂O were identified. Energy and material balances were then constructed for a large, 3 m deep aerobic cell holding 1,440 tons of the ‘wet’ component of organic wastes (major organic constituent: [C₆H₁₀O₄]_n). It was found that conduction/convection and radiation losses to the surroundings amount to a relatively small fraction of the chemical heat released by oxidation. Therefore, the surplus chemical heat must be removed by means of an upward water-saturated air flow that is several-fold the stoichiometric requirement for biodegradation. This study has quantified a basic process difference between anaerobic and aerobic bioconversion of organic matter: In the former, most of the chemical energy in the converted organic matter is stored chemically in the generated methane gas. In the latter, this energy is released in the cell and must be carried out in a relatively large air/water vapour flow through the cell.

The presence of PCDDs/DFs, PCBs and PAHs in the adsorbed or dissolved phases (depending on the leachate treatment process) was investigated in two landfills in Japan (Landfill M and Landfill N). The results of the investigations showed that, in general, persistent organic pollutants (POPs) having high Kow such as PCDDs/DFs and PCBs tended to exist in the adsorbed phase in both Landfill M and Landfill N. Furthermore, it was confirmed that their presence depended on log Kow by the appearance of PAHs.

In this work, we apply the concept of a “sorption chemical barrier”, as a means of improving landfill liner effectiveness. The sorption barrier is formed by addition of the organoclay hexadecyltrimethylammoniummontmorillonite (HDTMA-montmorillonite) to a fine sand-bentonite liner. Using previously published experimental data and mathematical model simulations, we demonstrate that such a liner retards significantly the transport of landfill leachate components, thus, increasing the useful life of the liner by a factor of 5 to 10, for the cases calculated. The superior HDTMA-liner performance is maintained even when the sorption extent is significantly decreased, as in the case of leachate containing methanol, a cosolvent miscible with water, found in some industrial and hazardous waste sites. The increase of the useful life of the liner results in smaller liner thickness, required to provide equivalent protection, from the point of view of contaminant transport, as compared to the liner containing no organoclay. Clay liner design based on hydraulic conductivity alone neglects the early breakthrough due to hydrodynamic dispersion and, therefore, is not a conservative one.

MSW landfill settlement characteristics are peculiar because a considerable amount of settlement occurs due to the decomposition of waste organic solids for very long duration. The total amount of settlement that occurs due to this decomposition in a MSW landfill is mainly dependent upon the amount of biodegradable solid waste and hence the fill age of the MSW landfill. The settlement stabilisation period is also dependent upon the decomposition condition. In order to investigate the settlement characteristics of MSW landfills, a mathematical model was proposed and applied to settlement data of MSW landfills which have various fill ages. A data bank of model parameters were obtained and the trends were analysed. The long-term settlement behaviour of MSW landfills can be fairly well estimated by the proposed model. It is supposed that the total remaining amount of settlement might be predicted on the basis of the fill age with two appropriate design parameters.

The aim of this study is the development of a procedure for the recycling of the ferrous-nickel slag that is widely used in open dry blast cleaning operations in Greek shipyards thus annually generating thousands of tons of blast cleaning waste. Laboratory tests were carried out, based on the reclamation of the material fraction with size a distribution within the range -1400+150 μm, in order to determine the number of the effective uses (life cycles) of the abrasive material. It is demonstrated that the reclamation yield in the first three life cycles is more than 80%. Laboratory tests also proved that the recycled ferrous-nickel slag has properties comparable to the fresh material’s ones in terms of particle size distribution, consumption and other physical-chemical properties.

A semi-industrial recycling unit of used ferrous-nickel slag was also designed and installed in a Greek shipyard (Neorion New SA of Syros Shipyards). The operation of the semi-industrial recycling unit verified the conclusions resulting from the laboratory tests, and most important, it was proved profitable for the shipyard.

The large volumes of wastes generated by industrialised society has led to efforts to find practical uses for these wastes, whilst also offsetting the consumption of natural resources. This paper describes the use of an innovative rotary kiln to produce synthetic aggregates from a variety of waste streams. The main waste used was a quarry fines which was blended with either paper sludge, clay, or a dredged harbour sediment. The different combinations were extruded and fired in the kiln to produce a material suitable for natural aggregate replacement. Two of the synthetic aggregates produced were tested by incorporation in to concrete as coarse aggregate replacement. The concrete 28-day compressive strengths achieved were above 40 N mm^-2 and compared favourably with control concretes made with natural aggregates and a commercially available lightweight aggregate (Lytag). Leaching tests have also been carried out to assess the potential environmental impact of utilisation. Although not finalised, these tests have also given favourable results.

Two sorting technologies including a chemical stain method and an x-ray fluorescence technique were investigated for separating chromated copper arsenate (CCA) treated wood from other wood types in the wood waste stream. Stains were investigated in both laboratory and field settings. Studies included specially mixed solutions with chrome azurol, 1-(2-pyridylazo)-2-naphthol (PAN) and rubeanic acid chemicals. X-ray fluorescence was tested in the laboratory using a commercially available x-ray fluorescence spectrometer. Laboratory scale experiments showed that both technologies were able to detect CCA treated wood in mixtures of treated wood and untreated wood, with detection limits on the order of 3 to 5% CCA. Results from field experiments at construction and demolition facilities indicate that although the chemical stains can be effectively used to identify CCA treated wood waste in field settings, their use will be limited to sorting relatively small wood waste piles due to increased labor and time needed for processing the wood waste. Operational parameters for sorting using x-ray fluorescence technology were established. These parameters concluded that arsenic was the most sensitive metal for analysis, analysis time was less than 2 seconds per wood sample, and the maximum separation distance between the sample and the x-ray probe was 2.5 cm. X-ray technology shows considerable promise for separating large quantities of CCA-treated wood from other wood types in the field using an on-line sorting system.

An analytical procedure, oxygen bomb combustion-ion chromatography (IC), has been developed for the determination of total chlorine in Automotive Shredder Residues (ASR). Samples of these residues are fired under elevated oxygen pressure (30 atm) and the combustion products are transferred into a Na₂ CO₃/NaHCO₃ absorbent solution containing 1% of H₂ O₂; the chlorine contents are then evaluated by ion chromatography. The use of the non-suppressed IC determination with a conductivity detector provides a rapid, sensitive and selective method for chlorine determination in ASR, allowing determinations of this heteroatom at levels below 1% in the presence of bromine and sulfur. Moreover, the proposed method allows the simultaneous determination of chlorine, bromine and sulfur which are potential environmental hazards.