Solid urban wastes minimization and energy conservation – A challenge for the 21st century in Brazil

P.H. Kanayama, L.B. dos Reis, M.E.M. Udaeta

This work focuses on the minimization of urban solid wastes and energy conservation aimed at sustainable development. The minimization of urban solid wastes is related to efficient material resource utilization and helps to solve the problem of the shortage of available garbage disposal areas in great urban centers. On the other hand, energy conservation can be an alternative when the lack of investment in the electrical sector would otherwise restrict the continued economic growth of the country.

There are many ways of adequately dealing with urban solid wastes. For example, one can list the composting of organic wastes, recycling of materials, incineration of materials and the reduction in the amount of waste actually generated. In this paper, each of these options is evaluated and linked to energy conservation, in an attempt to show that it is necessary to consider all of these topics in order to construct a sustainable development model.

Use of waste generated by shoe counter scrap pieces in plaster of Paris composites

C.S. Kazmierczak, A.P. Kern, I.S. Santos, H.C. Silva, M.V. Ramires
The growing increase of industrial waste of difficult degradation is a major concern for industries due to environmental concerns and the strong action of environmental organizations. The ‘Centro Tecnológico do Couro, Calçados e Afins’ (CTCCA), in cooperation with a group of shoe companies, proposed a research project to the University Vale do Rio dos Sinos aiming at recycling counter scrap waste generated by shoe industries. The present paper describes the investigation undertaken by a research team at UNISINOS to develop a competitive alternative for recycling this waste material.

In this study a new composite material combining plaster of Paris (gypsum) and waste ground in a knife mill was used. The different types and amount of waste materials available for recycling were studied to select the most suitable. This was followed by a thorough chemical and physical characterization.

This work presents the mechanical properties of composites molded with plaster of Paris and counter scrap pieces, determined by compression, impact and flexure strength tests. Results so far indicate that the recycling of these materials in the production of a new construction material is a sound alternative. It was found that some admixtures significantly improve impact resistance properties. Additional characterization studies of these composites are currently under way, alongside with the determination of thermal, acoustic, and durability properties.

Testing of soil and inorganic residues prior to utilisation: Development of rational limit values and adaptation of test methods

O. Hjelmar, P.E. Holm, N.K.J. Lehmann

This paper describes a methodology for regulatory testing and evaluation of the environmental properties of soil and inorganic waste materials prior to utilisation. The methodology establishes a direct relationship between the risk posed to the groundwater by various utilisation scenarios for soil and granular mineral waste materials and the results of leaching tests performed on the waste. The concept is based on flux considerations and does not take attenuation mechanisms into consideration. Only impacts on the groundwater quality are considered in this model, and it must be supplemented with other relevant criteria. The application of the model is demonstrated for two utilisation scenarios with coal fly ash. Leaching data, which can be used as input to the model, are scarcer for soil than for waste materials. As part of the pursuit of soil leaching data, the paper also discusses how a batch leaching test developed for testing of granular mineral waste materials can be adjusted and applied to soil/contaminated soil. Among the recommended adjustments is to use a 0.001 M CaCl2 solution rather than pure demineralised water as the leachant, as this will prevent clogging of the filters with fine materials. It is further recommended always to use a contact time of 24 hours, since this is practical and appears to increase reproducibility compared to short contact times.

Further development of a process for treatment of APC residues from MSW incinerators

O. Hjelmar, H. Birch, J.B. Hansen

A process for treatment of semidry and dry APC system residues from MSW incinerators based on an initial aqueous extraction followed by re-suspension and stabilisation of the filter cake with carbon dioxide and/or phosphoric acid was developed in 1994 - 1997 and was shown to produce a material with vastly improved disposal properties. This paper summarises some of the earlier results and presents some preliminary results of a new ongoing R&D project aimed at optimising and preparing the process for full-scale implementation and extending the applicability of the process to include fly ash and wet scrubber sludge. The results of leaching tests performed on residues treated at a new large-scale pilot plant indicate that good results may be obtained for most contaminants using carbon dioxide and phosphoric acid, both for semidry residues and fly ash. Using CO2 alone also yields good results, but the leachability of Pb is higher at low pH values. Tests also indicate that it may be feasible to use another waste product, namely sewage sludge ash as the source of phosphorous. Further work has been initiated to improve the stabilised residues and reduce the leaching of SO42-, Hg and some oxyanions.

Recycled aggregate concrete sound barriers for urban freeways

Z.A. Krezel, K. McManus

An increased rate of construction and demolition (C&D) waste generation in the Melbourne metropolitan area has a two-way impact, viz., a rapidly disappearing available landfill space and depletion of natural resources. As a result, there is government and community pressure to reduce the volume of waste by recycling of the waste material and the reuse of its products. This paper focuses on the enhancement of concrete waste products to improve their use in the manufacture of new products. This approach has already resulted in the confirmation that Recycled Concrete Aggregate (RCAG) can be a suitable substitution for the coarse aggregate fraction in production of pre-mixed concrete. The current research focus is on understanding of two of the properties of RCAG and their impacts on strength, durability and the acoustic performance of new concrete. Firstly, the presence of any chemical impurities and their effect on microstructure development, and secondly, the porosity of the cement paste component of the aggregate and its effect on the acoustic performance of concrete, made from RCAG, are examined. The aim of the research is to develop structurally sound Recycled Aggregate Concrete (RAC) with a good sound absorbing characteristics, and to use it in the manufacture of sound barriers for urban freeways. Preliminary results clearly indicate that the porosity of RCAG is more than that of normal concrete aggregate and this has an advantageous impact on the sound absorption coefficient of RAC, and that the strength of such concrete is more than adequate for the intended application.

Substance flow analysis of persistent toxic substances in the recycling process of municipal solid waste incineration residues

S. Sakai, S. Mizutani, T. Uchida, T. Yoshida

This study analyzes the substance flow such as heavy metals and dioxins in the process of recycling these residues containing slugs, and studies possible recycling of various residues, while making comparison with the standards for heavy metals and PCDDs/DFs regarding soil and water quality.

New trends on EAF slags management in the Basque Country

G. Ortiz de Urbina, A. Egizabal, R. San Martín
700,000 tonnes of primary slags are generated each year in the 13 steel plants located in the Basque Country, a small region of 20,664 Km2. Nowadays, as there is not Spanish regulation concerning environmental aspects related to the utilization of wastes, this great amount of waste is being landfilled.

In order to solve environmental problems due to this kind of waste management a two years project covering the environmental aspects related to steel slags reutilization as a construction material was carried out. Results derived from the project have lead to a final draft of a Decree about steel slags reutilization as a construction material.

The environmental quality of fly ashes from co-combustion

F.J.M. Lamers, M. Beerlage, J.W. van den Berg

In the Netherlands the government allows the co-combustion of maximum 10% of secondary fuels together with coal. To show whether the quality of fly ashes is affected by co-combustion, a broad research program was performed in which both the technical and the environmental quality of concrete with fly ashes from co-combustion were evaluated in comparison to the quality of concrete with reference fly ashes. In the research program fly ashes from co-combustion of sewage sludge, paper sludge, pet cokes, phosphorous gas, waste wood and a type of liquid hydrocarbon were evaluated. Both the technical and the environmental quality of most ashes from co combustion were shown to be comparable to that of regular fly ashes. This paper reports on the environmental quality of fly ashes from co-combustion; the technical quality is reported elsewhere (Lamers and Van den Berg, 1999). The leaching behaviour of concrete with fly ashes from co-combustion, is diffusion controlled. The components that were potentially introduced because of co-combustion did not lead to increase of leaching. As a result of the outcomes of the technical research program the Dutch regulations for fly ash as a filler or part of the binder were adjusted to make utilisation of fly ashes from co-combustion possible. Commercial operation of co combustion of several secondary fuels is running now at most of the Dutch coal fired power plants.

A dynamic approach to the assessment of leaching behaviour

K.H. Gardner, T.L. Theis

This paper describes a set of experiments that were used to investigate the mechanisms that control the rate of leaching from municipal solid waste incinerator ashes and a numerical approach to the estimation of mass transfer coefficients. A small column reactor was used for the experiments, and chemical equilibrium speciation software was used to assist in analyzing the leachate composition. It was found that certain major ions and trace metals were limited by the solubility of various solid phases, while other major ions were limited in concentration by physical transport processes. The numerical model was able to satisfactorily predict the influence of the controlling solid phases, and was able to estimate the governing mass transfer coefficients. For example, the model accurately predicts that the release of lead from the ash is controlled early on (the first approximately 50 pore volumes) by the solubility of PbSO4(s), and for the following approximately 3000 pore volumes was controlled by the solubility of Pb(OH)2(s). Effective diffusion coefficients were significantly lower for trace metals and reactive major ions than for salts, indicating sorptive retardation within the ash matrix may be occurring.

An initial investigation of the use of a rubber waste (EPDM) in asphalt concrete mixtures

J.B. Metcalf, K. Gopalakrishnan, M.D. Waters

The need to improve the performance of asphalt concrete mixes for heavier traffic loads has led to several developments which include the use of polymers to improve asphalt cement (AC) properties resulting in Hot Mix Asphalt Concrete (HMAC) mixes with decreased temperature susceptibility, and increased resistance to rutting and load-associated. Polymer additives can also improve adhesion and cohesion and resistance to moisture-induced damage. A large quantity (300 Kilotons) of Ethylene Propylene Diene Monomer (EPDM) is produced by several industries in Louisiana each year. Of this, 1 to 5 percent represent residual waste and is being landfilled at a cost of $50-$70 per ton. The residual may be slightly out of specification or slightly contaminated, but the bulk properties of the material remain unchanged.

This paper reports a laboratory study of the potential for residual EPDM as a modifier of asphalt cement (AC). The study evaluated the engineering properties and moisture susceptibility behavior of HMAC containing EPDM modified asphalt cements.

The results indicate that residual EPDM has potential as an asphalt modifier.