Recycling Of Bottom Ash Research Articles

Rice Germination as a Bioassay to Test the Phytotoxicity of MSWI Bottom Ash Recycling Wastewater

This experiment assessed the phytotoxicity effect of untreated wastewater and treated wastewater from a municipal solid waste incineration (MSWI) bottom ash recycling facility on the germination rate and root elongation of two rice varieties (Var139 and Var9) in Taiwan. The results show that undiluted (treated and untreated) MSWI bottom ash recycling wastewater had more adverse effect on rice seed development than the 50% diluted wastewater. Between the two varieties, Var139 showed a higher performance than rice Var9 in diluted wastewaters. A short exposure (5 days) of 50% MSWI bottom ash wastewater presented no environmental risk for root development of both crops. However, short exposure of this wastewater at higher concentration (100%) significantly affected seed germination and root elongation. DOI: 10.1061/(ASCE)HZ.2153-5515.0000162. © 2013 American Society of Civil Engineers. CE Database subject headings: Bottom ash; Crops; Wastewater management; Water reclamation; Tests. Author keywords: MSWI; Bottom ash; Germination; Root elongation; Rice; Wastewater.

Speciation of Cu in MSWI bottom ash and its relation to Cu leaching

Abstract In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching). The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation.

Chemical activation in view of MSWI bottom ash recycling in cement-based systems

In the present study, the feasibility of recycling incinerator bottom ash in cementitious systems by means of chemical activation was investigated. Different Na-, K- and Ca-based hydroxides and salts were selected for the experiments on the basis of their recognized effects on activation of typical pozzolanic materials. The evolution of mechanical properties of bottom ash/Portland cement mixtures and the leaching of trace metals from the materials were a matter of major concern. The experiments were arranged according to a full factorial design, which also allowed to derive a predictive model for unconfined compressive strength as affected by bottom ash content as well as activator type and dosage. Among the activators tested, calcium chloride was found to affect mechanical strength far more positively than the other species used, at the same time ensuring low metal release from the material. On the other hand, the use of potassium sulfate was observed to cause a significant increase in metal leaching at pH < 12, which was probably associated to the release of contaminants initially immobilized within the structure of ettringite as soon as it converted into monosulfate over time.

Enhancing performance and durability of slag made from incinerator bottom ash and fly ash

This work presents a method capable of melting the incinerator bottom ash and fly ash in a plasma furnace. The performance of slag and the strategies for recycling of bottom ash and fly ash are improved by adjusting chemical components of bottom ash and fly ash. Ashes are separated by a magnetic process to improve the performance of slag. Analytical results indicate that the air-cooled slag (ACS) and magnetic-separated slag (MSS) have hardness levels below 590 MPa, indicating fragility. Additionally, the hardness of crystallized slag (RTS) is between 655 and 686 MPa, indicating toughness. The leached concentrations of heavy metals for these three slags are all below the regulatory limits. ACS appears to have better chemical stability than MSS, and is not significantly different from RTS. In the potential alkali-silica reactivity of slag, MSS falls on the border between the harmless zone and the potentially harmful zone. ACS and RTS fall in the harmless zone. Hence, the magnetic separation procedure of ashes does not significantly improve the quality of slag. However, RTS appears to improve its quality.

Life cycle assessment of disposal of residues from municipal solid waste incineration: Recycling of bottom ash in road construction or landfilling in Denmark evaluated in the ROAD-RES model

Two disposal methods for MSWI bottom ash were assessed in a new life cycle assessment (LCA) model for road construction and disposal of residues. The two scenarios evaluated in the model were: (i) landfilling of bottom ash in a coastal landfill in Denmark and (ii) recycling of bottom ash as subbase layer in an asphalted secondary road. The LCA included resource and energy consumption, and emissions associated with upgrading of bottom ash, transport, landfilling processes, incorporation of bottom ash in road, substitution of natural gravel as road construction material and leaching of heavy metals and salts from bottom ash in road as well as in landfill. Environmental impacts associated with emissions to air, fresh surface water, marine surface water, groundwater and soil were aggregated into 12 environmental impact categories: Global Warming, Photochemical Ozone Formation, Nutrient Enrichment, Acidification, Stratospheric Ozone Depletion, Human Toxicity via air/water/soil, Ecotoxicity in water/soil, and a new impact category, Stored Ecotoxicity to water/soil that accounts for the presence of heavy metals and very persistent organic compounds that in the long-term might leach. Leaching of heavy metals and salts from bottom ash was estimated from a series of laboratory leaching tests. For both scenarios, Ecotoxicity water was, when evaluated for the first 100 yr, the most important among the twelve impact categories involved in the assessment. Human Toxicity soil was also important, especially for the Road scenario. When the long-term leaching of heavy metals from bottom ash was evaluated, based on the total content of heavy metals in bottom ash, all impact categories became negligible compared to the potential Stored Ecotoxicity, which was two orders of magnitudes greater than Ecotoxicity water. Copper was the constituent that gave the strongest contributions to the ecotoxicities. The most important resources consumed were clay as liner in landfill and the groundwater resource which was potentially spoiled due to leaching of salts from bottom ash in road. The difference in environmental impacts between landfilling and utilization of bottom ash in road was marginal when these alternatives were assessed in a life cycle perspective.

Removal of Chloride in Bottom Ash from the Industrial and Municipal Solid Waste Incinerators

In the present work, recycling of bottom ash from both industrial waste and municipal solid waste incinerators (MSWI) was investigated. In order to recycle bottom ash as raw materials for cement production, it is necessary to remove chloride, which causes metal erosion in reinforced concrete. Therefore, experiments for removing chloride were carried out by washing bottom ash in order to obtain efficient washing conditions. The following conditions were investigated: pH, type of solution, particle size, bubbling and temperature. Although pH is the most effective parameter for reducing Cl content in ash, using acid to lower pH is not an environmental friendly treatment considering wastewater treatment. It was found that CO2, bubbling in the form of microbubble is a proper treatment to decompose insoluble chloride as an environmental friendly treatment.

Analysis of technical and environmental parameters for waste-to-energy and recycling: household waste case study

This paper focuses on the treatment of household waste by waste-to-energy conversion. It assesses, in particular, both technical and environmental implications of a waste pre-sorting that may affect the treatment process. To this end, a life cycle assessment study has been undertaken. The scope of the study encompassed material recycling, incineration of household waste, treatment of flue gases, energy recovery, recycling of bottom ash, treatment of fly ash and final disposal of waste. The study showed that material recycling leads to an improvement of the working conditions with respect to the incinerator. However, material recycling leads to a decrease of the energy recovery so that it is necessary to use additional boilers to meet the initial energy demand. The related impacts tend to offset the environmental benefits derived by the waste recycling itself. The study also demonstrated that the life cycle approach is a useful tool for the study of technical and environmental aspects of an energy system. Moreover, those aspects in the process that are open to improvement have been identified.