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

A case study and a literature review have been carried out to address the two questions: how can waste flow data from collection systems be interpreted and compared? and which factors are decisive in the results of recycling programmes in household waste collection systems? The aim is to contribute to the understanding of how recycling programmes affect the quantity of waste and sorting activities. It is shown how the results from various waste sorting systems can be interpreted and made comparable. A set of waste flow indicators is proposed, which together with generic system descriptions can facilitate comparisons of different collections systems. The evaluation of collection systems depends on the system boundaries and will always be site-specific to some degree. Various factors are relevant, e.g. environmental objectives, technical function, operating costs, types of recyclable materials collected separately, property-close collection or drop-off systems, economic incentives, information strategies, residential structure, social codes, etc. Kerbside collection of recyclables and weight-based billing led to increased waste sorting activities in the case study. Forty-three decisive factors are listed and discussed.

Environments in the vicinity of the lead (Pb) smelters are contaminated by emissions containing high concentrations of antimony (Sb) and arsenic (As). Air-pollution-control (APC) residues from bag-type filters from a secondary Pb smelter were subjected to leaching experiments to elucidate the controlling mechanisms of Sb and As release. Kinetic batch leaching tests at a liquid-to-solid (L/S) ratio of 10 L kg^{- 1} within the time frame of 720 hours and batch leaching at various L/S ratios (ranging from 1 to 1000 L kg^-1) were performed. In contrast to other inorganic contaminants (Pb, Cd, Zn), less than 1% of the total Sb and As content was leached from the residues. At a L/S ratio of 10, the As and Sb concentrations in the leachates exceeded the EU limit values for non-hazardous waste (0.2 and 0.07 mg L^-1 ). According to PHREEQC-2 calculations, the concentrations of As and Sb are controlled by the precipitation of complex arsenates and antimonates mainly at low L/S ratios. The washing and related chemical/mineralogical transformation of APC residues was suggested as a technological pre-treatment process before their re-smelting in a blast furnace. The Ferrox-like processing of the resulting contaminated process water/leachate was simulated using the PHREEQC-2 code. Significant reduction was obtained in the concentration of some key contaminants (As, Cu, Pb, Zn) related to sorption on newly formed hydrous ferric oxides, whereas Sb and Cd exhibited only limited attenuation.

This article reviews the results obtained from stack emissions analysis during the co-firing process of municipal solid waste (MSW) from the municipality of Tabio, Colombia, in a Hoffmann-type brick kiln. MSW (2 tonne) was incinerated and about 18.5 tonnes of clay were processed into brick using one and four kiln chambers, respectively. During the process, the following emissions were investigated: particulate emissions, emissions of SO₂, SO₃, NO _X, metals (Sb, As, Cd, Co, Sn, Cr, Cu, Mn, Ni, Hg), hydrofluoric and hydrochloric acid, hydrocarbons (such as methane) and emission of polychlorinated dioxins and furans. Also, CO emissions were monitored during each test to evaluate the influence of MSW co-firing on that parameter. The observed emissions concentrations proved to be below the threshold values issued by MAVDT, the environmental authority in Colombia, indicating that the emissions were under control during the proposed process. In addition, statistical analysis showed that the emissions were 10—40% below the regulation limit with a confidence of 95%.

Fluorescent lamps are widely used world-wide due to their long life and energy saving capability. These lamps contain mercury (Hg) as a source of fluorescent radiation. The object of this study is a new technology for physicochemical treatment of waste fluorescent lamps. The residuals of the technological process were evaluated for potential leaching of heavy metals into the environment. Evaluation was performed using standardized extraction tests. Additionally, X-ray diffractometry (XRD) analysis, as well as tests with complex-forming agents and under pH-stable conditions were performed aiming to predict stability of the residuals in various environmental conditions. According to the XRD analysis, the minerals fluorapatite and hydroxylapatite were dominant in analyzed samples. The results of total extraction by aqua regia revealed that residuals contain relatively high total concentrations of Hg, Mn, and Zn. Concentrations of heavy metals, leaching to aqueous solution, were compared to leaching limit values (according to EU legislation). The concentrations of available Hg in the waste fluorescent lamp treatment products, according to its solubility in the water, exceed the limit values. The measured water-leachable Hg concentration was 4.88 mg kg^-1, while the value for waste acceptable at hazardous waste landfill sites is 2 mg kg^-1. Concentrations of other measured heavy metals did not exceed the limit values. According to the results, Hg stabilization potential for presented technology exceeds 99%.

Copper slag is a by-product obtained during matte smelting and refining of copper. The common management options for copper slag are recycling, recovery of metal and production of value-added products. In the present study using copper slag as a filler in glass-epoxy composites, the tensile modulus increased from 8.77 GPa to 9.64 GPa when using up to 10 wt% of copper slag but on further addition of copper slag (up to 20 wt%), the tensile modulus started to decrease down to 7.11 GPa. Similar trends were observed in the case of flexural strength and interlaminar shear strength. With the incorporation of copper slag particles, the impact strength increased about 10—15%. This work includes the processing, characterization and study of the erosion behaviour of a class of such copper slag filled glass-epoxy composites based on Taguchi’s experimental approach to characterise erosion behaviour. The results show that peak erosion takes place at an impingement angle of 60° for the unfilled composites whereas for the copper slag filled glass-epoxy composites it occurs at a 45° impingement angle. This paper considers the possible utilisation of copper slag as filler material for the preparation of composite materials and preparation of added-value products such as abrasive tools, cutting tools and railroad ballast.

Utilization of by-products or waste materials in concrete production are important subjects for sustainable development and industrial ecology concepts. The usages as mineral admixtures or fine aggregates improve the durability properties of concrete and thus increase the economic and environmental advantages for the concrete industry. The effect of clay waste (CW) containing boron on the mechanical properties of concrete was investigated. CW was added in different proportions as cement additive in concrete. The effect of CW on workability and strength of concrete were analysed by fresh and hardened concrete tests. The results obtained were compared with control concrete properties and Turkish standard values. The results showed that the addition of CW had a small effect upon the workability of the concrete but an important effect on the reduction of its strength. It was observed that strength values were quite near to that of control concrete when not more than 10% CW was used in place of cement. In addition to concrete specimens, replacing cement with CW produced mortar specimens, which were investigated for their strength and durability properties. The tests of SO ₄ ^2- and Cl^— effect as well as freeze—thaw behaviour related to the durability of mortar were performed. Consequently, it can be said that some improvements were obtained in durability properties even if mechanical properties had decreased with increasing CW content.

A method to obtain processed residue from mixed construction and demolition waste (mixed C&D-W) — free from environmental pollutants — for deposition in landfill is discussed. In particular, additional sieving, the presence of gypsum board in mixed C&D-W at the first stage of manual presorting, and the color of processed residue were studied for the basic characterization of the different fractions. Considerable precautions should be taken to prevent leaching of hazardous substances, such as T-Hg, Pb, Cr⁶⁺, As, and fluoride and its compounds, when processed residue, particularly in crushed fraction at an intermediate treatment facility, is used as construction material. A relatively high content of gypsum was noted in processed residue generated at demolition work compared to that generated at construction work in processed residue from mixed C&D-W in which the presence of gypsum board was observed at the first stage of manual presorting, and in white processed residue. Additional sieving for removal was ineffective because gypsum and wood have wide particle size distributions. To obtain processed residue having low gypsum and wood contents, white processed residue should be removed to eliminate gypsum (content, 59% of initial sample), and brown or brown and yellow processed residue should be removed to eliminate wood (content, 32% of initial sample) without mixing with processed residue containing other colors at stockyards. The removed residue should be deposited in a controlled-type landfill site.

This study investigated the pozzolanic reactions and engineering properties of waste brick-blended cements in relation to various replacement ratios (0—50%). The waste brick consisted of SiO₂ (63.21%), Al₂O₃ (16.41%), Fe₂O₃ (6.05%), Na₂O (1.19%), K₂O (2.83%) and MgO (1.11%), and had a pozzolanic activity index of 107%. The toxic characteristic leaching procedure (TCLP) results demonstrate that the heavy-metal content in waste bricks met the Environmental Protection Agency regulatory limits. Experimental results indicate that 10, 20, 30, 40 and 50% of cement can be replaced by waste brick, which causes the initial and final setting times to increase. Compressive strength development was slower in waste brick-blended cement (WBBC) pastes in the early ages; however, strength at the later ages increased significantly. Species analyses demonstrate that the hydrates in WBBC pastes primarily consisted of Ca(OH)₂ and calcium silicate hydrate (C—S—H) gel, like those found in ordinary Portland cement (OPC) paste. Pozzolanic reaction products formed in the WBBC pastes, in particular, various reaction products, including hydrates of calcium silicates (CSH), aluminates (CAH) and aluminosilicates (CASH), formed as expected, resulting in consumption of Ca(OH)₂ during the late ages of curing. The changes in the properties of WBBC pastes were significant as blend ratio increased, due to the pores of C—S—H gels and CAH filling via pozzolanic reactions. This filling of gel pores resulted in densification and subsequently enhanced the gel/space ratio and degree of hydration. Experimental results demonstrate waste brick can be supplementary cementitious material.

This investigation elucidates the pozzolic characteristics of pastes that contain waste brick from building construction and demolition wastes. The TCLP leaching concentrations of waste brick for the target cations or heavy metals were all lower than the current regulatory thresholds of the Taiwan EPA. Waste brick had a pozzolanic strength activity index of 107% after 28 days. It can be regarded as a strong pozzolanic material. The compressive strengths of waste brick blended cement (WBBC) that contain 10% waste brick increased from 71.2 MPa at 28 days to 75.1 MPa at 60 days, an increase of approximately 5% over that period. At 28 days, the pozzolanic reaction began, reducing the amount of Ca(OH)₂ and increasing the densification. The intensity of the peak at 3640 cm^{— 1} associated with Ca(OH)₂ is approximately the same for ordinary Portland cement (OPC) pastes. The hydration products of all the samples yield characteristics peaks at 978 cm^—1 associated with C—S—H, and at ~3011 cm^—1 and 1640 cm^—1 associated with water. The samples yield peaks at 1112 cm^—1, revealing the formation of ettringite. In WBBC pastes, the ratio Q²/Q¹ increases with curing time. These results demonstrate that increasing the curing time increases the number of linear polysilicate anions in C—S—H. Experimental results reveal that waste brick has potential as a pozzolanic material in the partial replacement of cement.

Fly ash is a solid waste generated in huge quantities from coal-fired thermal power stations during the combustion of coal. Rich in metal oxides, it has tremendous potential as a coating material on structural and engineering components. This work aims at developing and characterizing a new class of such coatings made of fly ash by a novel technique — plasma spraying. Plasma spray technology has the advantage of being able to process various low-grade ore minerals to obtain value-added products and also to deposit ceramics, metals and a combination of these, generating near-homogeneous coatings with the desired microstructure on a range of substrates. In the present investigation, coatings are developed on aluminium substrates using fly ash premixed with aluminium powder in different weight proportions at various plasma torch input power levels ranging from 9— 18 kW DC. The coatings are characterized in terms of interface adhesion strength and deposition efficiency. Maximum adhesion strength of about 35 MPa is recorded with coatings deposited at 12 kW power level. It was noticed that the quality and properties are significantly affected by the operating power level of the plasma sprayer. This work identifies fly ash as a potential coating material, suitable for possible tribological applications.