Utilization of municipal solid waste (MSW) ash in cement and mortar

Solid waste management is gaining significant importance with the ever-increasing quantities of waste materials generated these days. With increased environmental awareness and its potential hazardous effects, recycling/utilization of these materials have become an attractive alternative to disposal. Some of these waste and hazardous materials could possible be used in cement-based materials. One of such waste is municipal solid waste. Ash is obtained after incineration of MSW.This paper presents comprehensive details of the physical, chemical, and mineralogical composition, elemental analysis of ash obtained from MSW. It also covers the effect of MSW ash on the hydration characteristics, setting times, compressive strength, sulfate resistance and mass loss of cement and mortar. It also deals with the leachate analysis of MSW ash.     

The reuse of municipal solid waste incinerator fly ash slag as a cement substitute

The results of the treatment of fly ash from a municipal solid waste incinerator (MSWI) by melting are described, and the safety and the effectiveness of using the slag produced by this melting treatment are studied. The properties of the MSWI fly ash slag were analyzed, to evaluate the feasibility of its reuse as a substitute for part of the cement required in mortar preparation. This MSWI fly ash slag was found to be comprised mainly of SiO₂ and CaO, which can be substituted for up to 20% of the cement content in mortar, without sacrificing the quality of the resultant concrete. In fact, the concrete thus produced has greater compressive strength, 10% higher than that without the substitution. The setting time of the fresh mortar becomes lengthens as increasing amounts of cement are replaced; while the spread flow value increases with the increasing percentage of cement substitution. X-ray diffraction analysis reveals that when the W/C=0.38 and the curing AGE=28 days, the crystal patterns in the mortar samples, prepared with different amounts of cement having been replaced by MSWI fly ash slag are similar. According to the results of the toxic characteristic leaching procedure analysis, MSWI fly ash slag should be classified as general non-hazardous industrial waste, that meets the effluent standard. Therefore, the reuse of MSWI fly ash slag is feasible, and will not result in pollution due to the leaching of heavy metals.     

A review on the use of waste glasses in the production of cement and concrete

The use of recycled waste glasses in Portland cement and concrete has attracted a lot of interest worldwide due to the increased disposal costs and environmental concerns. Being amorphous and containing relatively large quantities of silicon and calcium, glass is, in theory, pozzolanic or even cementitious in nature when it is finely ground. Thus, it can be used as a cement replacement in Portland cement concrete. The use of crushed glasses as aggregates for Portland cement concrete does have some negative effect on properties of the concrete; however, practicle applicability can still be produced even using 100% crushed glass as aggregates. The main concerns for the use of crushed glasses as aggregates for Portland cement concrete is the expansion and cracking caused by the glass aggregates. This paper summarizes the progresses and points out the directions for the proper uses of waste glasses in Portland cement and concrete.     

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc.Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.     

Utilization of washed MSWI fly ash as partial cement substitute with the addition of dithiocarbamic chelate

The management of the big amount of fly ash as hazardous waste from the municipal solid waste incinerator (MSWI) has encountered many problems in China. In this study, a feasibility research on MSWI fly ash utilization as partial cement substitute in cement mortars was therefore carried out. MSWI fly ash was subjected to washing process to reduce its chlorine content (from 10.16% to 1.28%). Consequently, it was used in cement mortars. Ten percent and 20% replacement of cement by washed ash showed acceptable strength properties. In TCLP and 180-day monolithic tests, the mortars with washed ash presented a little stronger heavy metal leachability, but this fell to the blank level (mortar without washed ash) with the addition of 0.25% chelate. Therefore, this method is proposed as an environment-friendly technology to achieve a satisfactory solution for MSWI fly ash management.     

An overview of waste materials recycling in the Sultanate of Oman

Various wastes and by-product materials are generated in the Sultanate of Oman including reclaimed asphalt pavement (RAP) aggregate, demolition concrete, cement by-pass dust (CBPD), copper slag, petroleum-contaminated soils (PCS), discarded tires, incinerator ash, and others. Recycling of such materials in construction is not practiced. Research data are also minimal into the potential use of selected materials in construction applications. This paper will present the results of several laboratory studies conducted into the use of PCS in asphalt concrete mixtures; on the use of CBPD in soil stabilization and flowable fill mixtures; on the utilization of copper slag and CBPD as cementitious materials; on the use of incinerator ash in cement mortars; and on the use of RAP aggregate in road bases and sub-bases. Laboratory data generally indicate that it is feasible to partially reuse some of these materials in construction provided that economic incentives and environmental concerns are taken into consideration.     

E‐waste in the world today: An overview of problems and a proposal for improvement in Brazil

Environmental issues have been at the center of society's concerns for a long time. Recently, this kind of concern is growing even more due to the damage caused to the environment by electrical and electronic product waste. Based on this same concern, this work aimed to analyze, through a literature review, the production and treatment of electronic waste in today's world, with an emphasis on Brazil and China. The articles reviewed point to an increase in the production of this type of waste, in both Brazil and China, and reveal that the current processes of treatment of electronic waste mostly aim to obtain profit through the recovery of precious metals such as copper. This paper concluded that although Brazil is one of the major producers of e‐waste, more than 90% of its e‐waste has not had a proper final destination. This deficiency in e‐waste treatment in Brazil is mainly due to financial factors and the lack of a robust educational policy focused on the environment. Thus, this work suggests the implementation of an effective educational policy aimed at environmental conservation, as well as investments in research on recycling methods in Brazil, especially on the use of e‐waste as an aggregate in the manufacture of concrete.     

Assessing determinants of industrial waste reuse: The case of coal ash in the United States

Devising effective strategies to facilitate waste reuse depends on the solid understanding of reuse behaviors. However, previous studies of reuse behavior have been limited in scope, focusing mostly on household recycling behaviors or very limited types of industrial wastes. To gain a better understanding of the business reuse behaviors, this study examined the impact of various factors in technical, economic, regulatory, and behavioral categories in the case of coal ash generated in the United States. The results of fixed effect models for fly ash and bottom ash particularly showed the significance role of the behavioral factor. In both models, a proxy variable, which represents knowledge sharing among the power plants or the utility's decision-making, turned out to be statistically significant and had the largest coefficient estimates among a group of variables. This finding may imply that the characteristics of waste reuse behavior are determined more by business decision-making behaviors than by market or institutional factors. However, the role of the behavioral variable was stronger in the bottom ash models than in the fly ash models. While the reuse of bottom ash was determined primarily by the behavioral variable, fly ash reuse was determined by more diverse factors including economic and regulatory variables. This could be explained by material characteristics in relation to competing resources and the nature of reuse applications.     

An analysis of the use of life cycle assessment for waste co-incineration in cement kilns

Life cycle assessment, LCA, has become a key methodology to evaluate the environmental performance of products, services and processes and it is considered a powerful tool for decision makers. Waste treatment options are frequently evaluated using LCA methodologies in order to determine the option with the lowest environmental impact. Due to the approximate nature of LCA, where results are highly influenced by the assumptions made in the definition of the system, this methodology has certain non-negligible limitations. Because of that, the use of LCA to assess waste co-incineration in cement kilns is reviewed in this paper, with a special attention to those key inventory results highly dependent on the initial assumptions made. Therefore, the main focus of this paper is the life cycle inventory, LCI, of carbon emissions, primary energy and air emissions. When the focus is made on cement production, a tonne of cement is usually the functional unit. In this case, waste co-incineration has a non-significant role on CO₂ emissions from the cement kiln and an important energy efficiency loss can be deduced from the industry performance data, which is rarely taken into account by LCA practitioners. If cement kilns are considered as another waste treatment option, the functional unit is usually 1 t of waste to be treated. In this case, it has been observed that contradictory results may arise depending on the initial assumptions, generating high uncertainty in the results. Air emissions, as heavy metals, are quite relevant when assessing waste co-incineration, as the amount of pollutants in the input are increased. Constant transfer factors are mainly used for heavy metals, but it may not be the correct approach for mercury emissions.     

The Indian perspective of utilizing fly ash in phytoremediation, phytomanagement and biomass production

Coal-based power generation is a principal source of electricity in India and many other countries. About 15–30% of the total amount of residue generated during coal combustion is fly ash (FA). FA is generally alkaline in nature and contains many toxic metals like Cr, Pb, Hg, As and Cd along with many essential elements like S, B, Ca, Na, Fe, Zn, Mn and P. Dumped FA contaminates the biosphere by mobilization of its fine particles and hazardous metals. Despite the negative environmental impact of FA, coal continues to be a major source of power production in India and therefore FA disposal is a major environmental issue. To overcome this problem, FA dumping sites have been started as a potential resource for biomass production of tree species. Phytoremediation is a strategy that uses plants to degrade, stabilize, and remove contaminants from soils, water and waste FA. Phytomanagement of FA is based on the plants' root systems, high biomass, woody nature, native nature, and resistance to pH, salinity, and toxic metals. Recently Indian researchers mostly from the National Botanical Research Institute have been working on phytoremediation and revegetation of FA dykes, inoculation of bacterial strains for reducing FA stress and biomass production from FA dykes. Many international researchers have worked on reclamation, revegetation and utilization of FA. FA utilization saves resources, mainly land (topsoil), water, coal, limestone and chemical fertilizer. Safe utilization of FA is a major concern around the world and regulatory bodies are enforcing stringent rules for the proper management of FA. This article summarizes various viable avenues in India for FA utilization and environmental management.     

Management and recycling of waste glass in concrete products: Current situations in Hong Kong

Disposal of more than 300 tonnes waste glass daily derived from post-consumer beverage bottles is one of the major environmental challenges for Hong Kong, and this challenge continues to escalate as limited recycling channels can be identified and the capacity of valuable landfill space is going to be saturated at an alarming rate. For this reason, in the past ten years, a major research effort has been carried out at The Hong Kong Polytechnic University to find practical ways to recycle waste glass for the production of different concrete products such as concrete blocks, self-compacting concrete and architectural mortar. Some of these specialty glass-concrete products have been successfully commercialized and are gaining wider acceptance. This paper gives an overview of the current management and recycling situation of waste glass and the experience of using recycled waste glass in concrete products in Hong Kong.     

Analysis of the implementation of effective waste management practices in construction projects and sites

In this paper, the implementation of effective waste management practices in construction projects and sites is analyzed, using data from a survey answered by 74 Spanish construction companies based in Catalonia. Most commonly implemented practices were found to be on-site cleanliness and order, correct storage of raw materials, and prioritization of the nearest authorized waste managers. The least widespread practices were the use of a mobile crusher on site, the creation of individualized drawings for each construction site, and the dissemination of the contents of the waste management plan to all workers, to help them to meet its requirements. Waste regulations for construction and demolition, and the corresponding construction waste management facilities, were designed before the recession in the Spanish construction sector. Current waste generation rates are still below predicted levels, and the infrastructure was designed for five times more waste generation. Even so, the percentage of reused and recycled waste currently amounts to 43%. Survey respondents highlighted various instruments and measures that would make the management of construction and demolition waste more sustainable. Most of the opportunities identified by construction firms are within the scope of government and related to a combined system of bonus and penalties and the establishment of environmental awareness and training programmes for all the stakeholders. Within the scope of authorized waste managers, firms suggested improvements such as the standardization of fees, a reduction of the time until the issue of waste management certificates, a higher number of inspections, and a change in the current model of a few large construction waste management facilities. This research is useful to better understand the current status of construction and demolition waste management in construction projects and sites. Thus, the results of this research will guide policy makers and relevant stakeholders such as contractors, clients, architects and engineers to achieve the EU target of recovering 70% of construction and demolition waste in 2020. In this sense, reliable information can help governments and professional associations to set future C&D waste management regulations, training programmes and dissemination tools, inspections, etc.     

Critical analysis of the waste management performance of two uranium production units in Brazil--part II: Caetite production center

This paper discusses the environmental waste management of the Heap-Leach Uranium Production Facility of Caetité located in a semi-arid region in Brazil. A comparison is made with the first uranium production site of the country located in Poços de Caldas. It is demonstrated that differences in the operational process along with different environmental conditions can lead to different impacts. In the present case groundwater is the potential most sensitive environmental medium despite the well-established consensus in the literature that radon and aerosol emissions may turn-out to be the most relevant environmental aspects of an installation located at this type of region. Most of the ²²⁶Ra content in the ore remains in the leached ore that is deposited with the waste rock. A lack in appropriate prediction of the hydrological balance has been causing unanticipated emissions of liquid effluents into the environment. Chemical treatment of this effluent may be needed. Contamination of groundwater in the short term by the waste ponds is not to be expected but it can be a relevant issue in the long term. As a consequence, careful closure schemes will need to be put in place. Finally, the overall costs with remediation in the Caetité production center are lower than those observed at the Poços de Caldas mining site.     

Cement and concrete flow analysis in a rapidly expanding economy: Ireland as a case study

A national material flow model for concrete, the most popular construction material in Ireland, was developed based on the framework of material flow analysis. Using this model the Irish concrete cycle for the year 2007 was constructed by analysing the material life cycle of concrete which consists of the three phases of: production (including extraction of raw materials and manufacture of cement), usage (ready-mix and other products) and waste management (disposal or recovery). In this year, approximately 35 million metric tonnes of raw materials were consumed to produce 5 million metric tonnes of cement and 33 million metric tonnes of concrete. Concrete production was approximately 8 metric tonnes per capita. By comparison, the concrete waste produced in that year was minimal at only 0.3 million metric tonnes. Irish building stock is young and there was little demolition of structures in the year of study. However this build up of construction stock will have implications for the future waste flows when the majority of stock built in the last decade (43% of residential stock was constructed in the last 15 years) reaches its end of life.     

The water vulnerability of metro and megacities: An investigation of structural determinants

Urban areas are becoming increasingly subject to and vulnerable to water‐related natural disasters. Urban areas are a kind of socio‐ecological system wherein the human development dynamics co‐evolve with the natural dynamics. Most of the literature is focused on the impact of natural disasters on human development; we evaluate the impacts of human development on natural disasters and present an analysis of this phenomenon in the context of megacities. The approach is exploratory and begins with the construction of a database on the 595 existing megacities in the world. Multifactor analysis is then used to determine the main characteristics of these megacities. Finally, three structural components (maturity, anthropization and centrality) are identified and then correlated with data on water‐related hazards, distinguishing groups of cities according to their structure and factors of vulnerability to water‐related risks.     

Environmental and economic aspects of production and utilization of RDF as alternative fuel in cement plants: A case study of Metro Vancouver Waste Management

Municipal solid waste (MSW) disposal and management is one of the most significant challenges faced by urban communities around the world. Municipal solid waste management (MSWM) over the years has utilized many sophisticated technologies and smart strategies. Municipalities worldwide have pursued numerous initiatives to reduce the environmental burden of the MSW treatment strategies. One of the most beneficial MSWM strategies is the thermal treatment or energy recovery to obtain cleaner renewable energy from waste. Among many waste-to-energy strategies, refuse-derived fuel (RDF) is a solid recovered fuel that can be used as a substitute for conventional fossil fuel. The scope of this study is to investigate the feasibility of RDF production with MSW generated in Metro Vancouver, for co-processing in two cement kilns in the region. This study investigates environmental impacts and benefits and economic costs and profits of RDF production. In addition, RDF utilization as an alternative fuel in cement kilns has been assessed. Cement manufacturing has been selected as one of the most environmentally challenged industries and as a potential destination for RDF to replace a portion of conventional fossil fuels with less energy-intensive fuel. A comprehensive environmental assessment is conducted using a life cycle assessment (LCA) approach. In addition, cost–benefit analysis (CBA) has been carried out to study the economic factors. This research confirmed that RDF production and use in cement kilns can be environmentally and economically viable solution for Metro Vancouver.     

The effects of leachate recirculation with supplemental water addition on methane production and waste decomposition in a simulated tropical landfill

In order to increase methane production efficiency, leachate recirculation is applied in landfills to increase moisture content and circulate organic matter back into the landfill cell. In the case of tropical landfills, where high temperature and evaporation occurs, leachate recirculation may not be enough to maintain the moisture content, therefore supplemental water addition into the cell is an option that could help stabilize moisture levels as well as stimulate biological activity. The objectives of this study were to determine the effects of leachate recirculation and supplemental water addition on municipal solid waste decomposition and methane production in three anaerobic digestion reactors. Anaerobic digestion with leachate recirculation and supplemental water addition showed the highest performance in terms of cumulative methane production and the stabilization period time required. It produced an accumulated methane production of 54.87 l/kg dry weight of MSW at an average rate of 0.58 l/kg dry weight/d and reached the stabilization phase on day 180. The leachate recirculation reactor provided 17.04 l/kg dry weight at a rate of 0.14l/kg dry weight/d and reached the stabilization phase on day 290. The control reactor provided 9.02 l/kg dry weight at a rate of 0.10 l/kg dry weight/d, and reached the stabilization phase on day 270. Increasing the organic loading rate (OLR) after the waste had reached the stabilization phase made it possible to increase the methane content of the gas, the methane production rate, and the COD removal. Comparison of the reactors' efficiencies at maximum OLR (5 kgCOD/m(3)/d) in terms of the methane production rate showed that the reactor using leachate recirculation with supplemental water addition still gave the highest performance (1.56 l/kg dry weight/d), whereas the leachate recirculation reactor and the control reactor provided 0.69 l/kg dry weight/d and 0.43 l/kg dry weight/d, respectively. However, when considering methane composition (average 63.09%) and COD removal (average 90.60%), slight differences were found among these three reactors.     

The effect of Na and Ca salts on MSWI bottom ash activation for reuse as a pozzolanic admixture

In this study the possibility of both chemical and combined chemical + thermal activation of municipal solid waste incinerator bottom ash was investigated. A number of chemical activators including Na₂SiO₃·9H₂O, NaOH, Na₂SO₄ and CaCl₂·2H₂O were individually added at varying concentrations to bottom ash/Portland cement mixtures having different bottom ash contents. The effect of the selected compounds was evaluated in terms of macroscopic properties including mechanical strength and composition of cementitious materials/water slurries. The results showed that Na-based activators were not capable of improving the characteristics of the cementitious products if compared to Portland cement under both normal and accelerated curing. Conversely, the use of calcium chloride at 40 °C-curing did promote the pozzolanic properties of bottom ash, leading to UCS values of 45.5 and 60.0 MPa after 10 and 20 days, respectively, as opposed to a value of 43.6 MPa obtained after 28 days for Portland cement under normal curing conditions.     

Combating desertification in Iran over the last 50 years: An overview of changing approaches

Desertification in Iran was recognized between the 1930s and 1960s. This paper traces Iran’s attempts to reclaim desertified areas, evaluates the anti-desertification approaches adopted, and identifies continuing challenges. Iran has areas vulnerable to desertification due to extensive areas of drylands and increasing population pressure on land and water resources. Over-grazing of rangelands is a particular problem. Initially desertification was combated mainly at the local level and involved dune stabilization measures, especially the use of oil mulch, re-vegetation and windbreaks. Insufficient technical planning in the early years has led to changed approaches to plant densities and species diversity in plantations, and increased on-going management of existing plantations. Since the late 1980s forage and crop production has increased in areas where runoff control techniques are practiced. The social and economic aspects of anti-desertification programs have assisted in poverty reduction by providing off-season employment in rural areas. In 2004 a national plan to combat desertification was ratified and this placed an emphasis on community participation. Continuing challenges include managing existing desertified areas as well as taking into account potential future problems associated with rapidly depleting groundwater supplies and a predicted reduction in the plant growth period accompanying climate change.