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

Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.

Municipal solid waste is a problem to developed and developing cities in the world. If municipal solid waste is not managed well, it can be a source of numerous contaminants to water, air, and soil. Although landfill is at the bottom in terms of priorities of municipal solid waste management techniques, its applicability cannot be neglected in developing economies. Landfill site selection is a hard puzzle comprised of political, social, economic, and environmental factors. Makkah, Saudi Arabia, is targeting 30 million pilgrims by 2030, putting the city in a difficult circumstance: More pilgrims, more municipal solid waste. The current dump site, Kakia, is expected to be full by 2020; thus, there is a need to locate a new landfill site. In 20 years, Makkah is expected to produce 44 million tonnes of municipal solid waste, which requires approximately a 7.5 m × 5,874,000 square meter landfill capacity. In this study, a geographic information system, analytical hierarchy process, vertical electrical sounding, and ground-penetrating radar are applied to select the best new landfill site for Makkah. By combining these techniques, there are three suitable site locations: (39°36 ́38.45 ́ ́E: 21°18 ́26.46 ́ ́N), (39°37 ́54.07 ́ ́E: 21°19 ́35.25 ́ ́N), and (39°44 ́04.45 ́ ́E: 21°13 ́08.93 ́ ́N). These sites have a considerable depth to water table of 12 m. Therefore, the city of Makkah should use these findings to establish a sanitary landfill.

This article presents an evaluation of the influence on the natural carbonation process of the use of granite cutting residue as a replacement for fine aggregate in mortars. The methodology adopted consisted of replacing the fine aggregate with granite cutting residue, analysing the carbonation depth with the aid of an experimental planning matrix of 2³ + 3 repetitions at the central point. The influence of the exposure time, the percentage of residue in the mixture, and the particle size of the residue used were evaluated. The exposure time variable was found to have the greatest influence on the carbonation process. Under the conditions analysed, granite residue was found to be beneficial, reducing the carbonation depth.

Spent lead paste is the main component in lead-acid batteries reaching end of life. It contains about 55% lead sulphate and 35% lead dioxide, as well as minor amounts of lead oxide. It is necessary to recycle spent lead paste with minimal pollution and low energy consumption instead of the conventional smelting method. In this study, a novel approach involving hydrometallurgical desulphurisation and thermal degradation is developed to recover lead as PbO products from spent lead acid batteries. First, the desulphurisation effects and phase compositions of products with different transforming agents were compared, and the optimum conditions using (NH₄)₂CO₃ as a transforming agent were determined. And then, the thermal degradation processes of both precursors lead carbonate and lead dioxide were investigated to prepare α-PbO, Pb₃O₄, and β-PbO products in argon and air atmospheres, respectively. Both the desulphurisation precursors and the calcination products were characterised by thermogravimetry and differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The results showed that the lead oxide products were prepared, including α-PbO at 450°C in argon, Pb₃O₄ and β-PbO at 480°C and 620°C in air, respectively.

Thermal treatment offers advantages of significant volume reduction and energy recovery for the polyurethane foam from waste refrigerators. In this work, the pyrolysis kinetics of polyurethane foam was investigated using the model-fitting, model-free and distributed activation energy model methods. The thermogravimetric analysis indicated that the polyurethane foam decomposition could be divided into three stages with temperatures of 38°C–400°C, 400°C–550°C and 550°C–1000°C. Peak temperatures for the major decomposition stage (<400°C) were determined as 324°C, 342°C and 344°C for heating rates of 5, 15 and 25 K min^-1, respectively. The activation energy (E _α ) from the Friedman, Flynn–Wall–Ozawa and Tang methods increased with degree of conversion (α) in the range of 0.05 to 0.5. The coefficients from the Flynn–Wall–Ozawa method were larger and the resulted Eα values fell into the range of 163.980–328.190 kJ mol^-1 with an average of 206.099 kJ mol^-1. For the Coats–Redfern method, the diffusion models offered higher coefficients, but the E values were smaller than that from the Flynn–Wall–Ozawa method. The Eα values derived from the distributed activation energy model method were determined as 163.536–334.231 kJ mol^-1, with an average of 206.799 kJ mol^-1. The peak of activation energy distribution curve was located at 205.929 kJ mol^-1, consistent with the thermogravimetric results. The Flynn–Wall–Ozawa and distributed activation energy model methods were more reliable for describing the polyurethane foam pyrolysis process.

In many countries, municipal solid waste management is considered a very important challenge, and the most relevant costs in this field are dedicated to the collection process. Therefore, this study aimed to propose a mathematical model with multiple depots and multiple intermediate facilities to minimize fixed and variable costs of waste collection. Intermediate facilities are used in the developed countries in their waste collection network, because these facilities reduce the long-term costs of waste management and increase the quality of the waste collection process. Also, in reality, the amount of waste generated per day is not deterministic, so, to cope with the issue of uncertainty in the amount of waste, a fuzzy optimization approach was considered. Furthermore, a system where vehicles that could collect the wastes in multiple tours, with a maximum number of tours for each vehicle, was also considered. Due to the high complexity of this model, a genetic algorithm was elaborated. Further, the efficiency of the proposed algorithm was confirmed by comparison with the exact solution in small dimensions. It should be noted that the initial solution of this algorithm was obtained by a proposed heuristic algorithm. Finally, a case study on the vehicle routing of municipal solid waste was conducted in a district of Tehran, Iran. Moreover, the solutions of the model were validated by comparing the results of the proposed model and the current real-life situation. The contractors could improve vehicle routes and reduce costs by implementing the results of the proposed model, without any additional cost.

The study was conducted in Ludhiana District of Punjab (India) to understand the organic waste management practices followed by dairy farmers of the area. To investigate the practices pertaining to organic waste management, an ex-post facto research design was used and a total of 80 dairy farmers were selected randomly for the study, grouped as small and large dairy farmers. Results revealed that the majority of the farmers were using paddy straw as animal bedding followed by in situ burning. As far as paddy stubbles were concerned, most of the farmers were mulching them followed by in situ burning. All farmers were found to be using wheat straw as livestock feed and mulching wheat stubbles. For household waste, the majority of the farmers were found to be feeding kitchen waste to their livestock, preparing farmyard manure from garden waste and paper waste. For dairy waste management, all the farmers were preparing farmyard manure from dung and discarding livestock urine in drains. A little more than half of the farmers were producing biogas from the dairy waste. The majority of the dairy farmers of the research area were found to have low organic waste utilization scores. Relational analysis was carried out and social participation and knowledge level were found to be highly significant (p < 0.01) with a positive effect on the organic waste utilization score. Therefore, the study was concluded with the impression that the knowledge level of the farmers needs to be enhanced for better and effective utilization of organic waste.

The impacts of price and sustainability on municipal waste disposal demand have largely been ignored by waste management researchers. This paper considers a waste disposal supply chain that includes a disposal facility and a contractor. Both parties try to improve source sorting for waste collection to reduce the recycling cost at the disposal facility. Improving source sorting requires investment that would increase the price of the waste disposal service, thereby affecting the price-sensitive demand. The relationship between the service price and investments in waste sorting motives is analyzed in this paper via studying the trade-off between the optimal source sorting and the waste disposal service prices. Different scenarios based on the various players’ power structures are developed. Nash and Stackelberg games have been applied in order to find the optimal decision values in each scenario. The impact of cost sharing on optimal supply chain decisions is also studied. The numerical results show that the waste supply chain is more profitable when it is working under an integrated management structure. Moreover, reducing the required investment motivates supply chain players to select higher levels of waste sorting at the source. A numerical example is provided, followed by some managerial insights.

The recycling of polyvinyl chloride (PVC) recovered from the plastic insulations in wires and cables is a rising concern in the current situation due to its hazardous behaviour during recycling. Similarly, high-impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) used in the structural components of electrical and electronic equipment are also generated in large quantities. In the current work, three agendas were fixed: (a) to determine the effect of recycled polymeric material (HIPS and ABS) recovered from different sources on the mechanical property of the polymeric blends; (b) to formulate a high-impact strength blend; and (c) to deduce a mechanism for improved impact strength. The mechanical characterizations were conducted on the entire blends formulated. Among them, the recycled blend composed of recycled PVC (r-PVC) and recycled ABS (r-ABS) (segregated from uninterrupted power supply housing) and recycled HIPS (r-HIPS; collected from television housing) was confined for further physio-mechanical and thermal analysis. Besides, the r-PVC/r-ABS systems had shown better mechanical properties than r-PVC/r-HIPS systems in similar composition. The impact strength of blend r-PVC/r-ABS (70:30) was found to be 250 J/m, which was 200% more than the blend r-PVC/r-ABS (0:100). The compatibility and non-compatibility in PVC/ABS and PVC/HIPS blends respectively were explained with thermal, mechanical and morphological characterizations. Furthermore, a plausible cross-linking mechanism is developed between ABS and PVC, which controls the release of chlorine atoms into the environment.

The aim of this study is to present the optimum operating conditions for reducing energy consumption in the process of obtaining bio-oil from the mixture of sawdust, waste lubricating oil, lime, and commercial catalyst. In the study where the catalytic pressureless depolymerisation (also called Katalytische Drucklose Verölung – KDV) was applied, the operating conditions were analysed with response surface methodology. According to the analysis of variance results, a mathematical model was obtained for specific product yield (bio-oil amount/energy consumption g kW_e⁻¹). Effects of temperature (260°C–290°C), catalyst rate (1–2 wt.%) and reaction time (0.5–1 h) were investigated. The optimum conditions for the three independent variables (temperature, catalyst rate, reaction time) were 279 ± 2°C, 2 wt.% and 0.5 h, respectively. Maximum specific product yield was obtained as 970.17 g kW_e⁻¹. While the reaction time was the most effective regarding the amount of bio-oil obtained at 1 kW_e energy consumption, the temperature was found to be the least effective. In addition to these, bio-oil obtained under optimum conditions were characterised and compared with standard diesel specifications.