Heavy metals removal/stabilization from municipal solid waste incineration fly ash: a review and recent trends

Waste treatment using thermal technologies, such as incineration, leads to the production of pollutants and wastes, including fly ash (FA). Fly ash contains heavy metals (HMs) and other contaminants and can potentially pose high risks to the environment and negatively impact health and safety. Consequently, stabilizing fly ash prior to either use or landfilling is crucial. The toxicity of fly ash through heavy metal leaching can be assessed using leaching tests. The leaching rates of heavy metals primarily depend on the surrounding conditions as well as fly ash properties and metal speciation. Physical separation, leaching or extraction, thermal treatment and solidification/chemical stabilization are proposed as suitable approaches for fly ash treatment. Economic considerations, environmental concerns, energy consumption and processing times can define the efficiency and selection of the treatment approach. This review considers the latest findings and compares the advantages and shortcomings of different fly ash treatment methods with the aim of highlighting the recent advances in the field. The review concludes that the simultaneous implementation of various methods can lead to highly efficient heavy metals removal/stabilization while simultaneously taking economic and environmental considerations into account

Economic feasibility and sustainability assessment of residual municipal solid waste management scenarios in NSW, Australia

This study evaluates the economic cost and sustainability of treating residual municipal solid waste (MSW) through five waste management scenarios. In the baseline scenario (Bsc), all waste was managed through landfilling, while in scenario 1 (Sc1) all waste was treated by incineration. Sc2 employed anaerobic digestion (AD) for food waste and landfilling, and Sc3 treated the waste through AD for food waste, incineration of combustible and plastic wastes, and landfilling. Sc4 treated the waste using AD, incineration, landfilling, and recycling of the plastic waste. The economic cost of waste management scenarios was estimated by calculating different economic variables, such as gate fees, including capital and operating costs, governmental incentives and levies, and also the potential of employed waste treatment technologies for resource recovery. The results revealed that Sc3 has the lowest economic cost of 238.1 mAUD/year, followed by Sc1 (261.9 mAUD/year), while Bsc proved to be the highest cost at 476.1 mAUD/year for MSW treatment. It was noticed that scenarios employing incineration had lower economic costs compared to Bsc and Sc2, mainly because incineration resulted in higher electricity generation and reduced greenhouse gas emissions. The sustainability assessment results confirmed that Sc3 had the lowest and Bcs the highest total economic cost and environmental damage

Slow pyrolysis of metal(loid)-rich biomass from phytoextraction: characterisation of biomass, biochar and bio-oil

Plants have successfully been used for phytoextraction of metal contaminated soils, however the use of these plants for energy production has been a subject of debates due to the potential conversion of the metals in the plants into airborne respirable particles. The aim of this study was to investigate the deportment of metal(loid)s during pyrolysis of a biomass cultivated in a highly contaminated soil in order to engineer best practice environmental approach for utilization of this biomass. A heavy metal(loid) contaminated mangrove (Avicennia marina var. australasica) biomass was used as a feedstock in this study. The biomass was subjected to slow pyrolysis under the heating rate of 60 ℃/min and different pyrolysis temperatures. Inductively coupled plasma mass spectrometry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray fluorescence spectroscopy and gas chromatography–mass spectrometry were introduced to characterise the biomass, biochar and bio-oil samples. Results showed that biochar yield decreased from 57.4 % to 35.3 % with the increase in pyrolysis temperature from 300 to 700 ℃. Heavy metal(loid)s (chromium, manganese, iron, copper, zinc, arsenic and lead) were mainly bound in the biochar produced at 300 ℃, while the recovery decreased substantially with the increase of pyrolysis temperature. Phenols, carboxylic acids and alcohols were the dominant compounds in all bio-oil samples. This study suggested further requirements of biochar quality and environmental risk assessment to provide a safe and value-added way of phytoextraction residual applications

Life cycle analysis of energy production from food waste through anaerobic digestion, pyrolysis and integrated energy system

The environmental performance of industrial anaerobic digestion (AD), pyrolysis, and integrated system (AD sequence with pyrolysis) on food waste treatment were evaluated using life cycle assessment. The integrated treatment system indicated similar environmental benefits to AD with the highest benefits in climate change and water depletion in addition to the increased energy generation potential and the production of valuable products (biochar and bio-oil). Pyrolysis results illustrated higher impact across water, fossil fuel, and mineral depletion, although still providing a better option than conventional landfilling of food waste. The dewatering phase in the AD process accounted for 70% of the treatment impact while the pre-treatment of the food waste was responsible for the main burden in the pyrolysis process. The study indicated that the three treatment options of food waste management are environmentally more favorable than the conventional landfilling of the wastes

Investigating the effect of Cu/zeolite on deoxygenation of bio-oil from pyrolysis of pine wood

Pyrolysis is one of the significant technologies that can utilize lignocellulose biomass to produce different bioenergy fuels, such as bio-oil, pyrolytic gases and bio-char. The application of pyrolysis has been extensively studied to produce bio-oil, which is foreseen as the potential transportation fuel in the near future. However, the presence of oxygenated compounds, such as phenols and alcohols in bio-oil makes it highly acidic and unstable for a suitable transportation fuel. These oxygenated compounds can be converted to refinable hydrocarbons by using different catalysts. Therefore, this study aimed to prepare a catalyst that is Cu10%-zeolite and investigated its deoxygenation activity for bio-oil produced from pyrolysis of pine wood sawdust. The catalyst was prepared by a wet-impregnation method. Subsequently, the catalyst was characterized by X-ray diffraction and transmission electron microscopy. Furthermore, the catalyst was applied for in-situ (catalyst: biomass=5) and ex-situ catalytic pyrolysis (catalyst: biomass=3) and the results were compared with those from sole zeolite support. The pyrolysis process was carried out at a heating rate of 100 °C/min to a final temperature of 700 °C and the composition of bio-oil was examined by gas chromatography-mass spectroscopy. The results revealed that Cu-zeolite showed significant deoxygenation activity for bio-oil as compared to zeolite or without any catalyst. Evidently, Cu-zeolite after in-situ pyrolysis produced bio-oil with 20.9% aromatic hydrocarbons and 7.5% aliphatic hydrocarbons, which were approximately 80% and several times higher than with only zeolite, respectively. Meanwhile the concentration of alcohols was reduced from 47.5% to 5%. On the other hand, bio-oil produced from ex-situ catalytic pyrolysis was enriched with 41.6% aromatic hydrocarbons while only 1% alcohols were present in bio-oil. This promising deoxygenation activity can be ascribed to Cu-zeolite’s catalytic activity that converted phenol and alcohols to refinable hydrocarbons via various reactions, such as dehydration, decarboxylation and decarbonylation

Life cycle impact assessment of airborne metal pollution near selected iron and steelmaking industrial areas in China

Toxic metals in particulate matter pose a significant health risk to humans via inhalation and dermal exposure. Additionally, airborne pollution has negative impacts on terrestrial and aquatic quality as a result of atmospheric deposition. Iron and steelmaking industry is considered as a major contributor to airborne metal pollution. Given that China has been the largest steel producer and consumer since 1996, a detailed investigation of airborne metal pollution is required to assess the potential risks to both human health and ecosystem quality near iron and steelmaking areas in China. This study applied an environmental impact assessment approach to evaluate the freshwater ecotoxicity, terrestrial ecotoxicity, marine ecotoxicity and human toxicity caused by metal concentrations in PM1.1, PM1.1-2.1 and PM2.1-9.0 fractions. Results showed that heavy metals Cu and Zn associated with steelmaking activities were largely responsible for aquatic and terrestrial ecotoxicity. This study also found that As and Pb contamination presented the largest fraction of the impacts on human toxicity. Findings presented in this study showed that more stringent control measures are required to improve the environmental performance of the iron and steelmaking industries in China

Process and Techno-Economic Analysis for Fuel and Chemical Production by Hydrodeoxygenation of Bio-Oil

The catalytic hydrogenation of lignocellulosic derived bio-oil was assessed from the thermodynamic simulation perspective, in order to evaluate its economic potential for the production of added-value chemicals and drop-in fuels. A preliminary economic evaluation was first run to identify the conditions where the process is profitable, while a full economic analysis evaluated how the operating conditions affected the reaction in terms of yield. The results indicate that the bio-oil should be separated into water-soluble and insoluble fractions previous hydrogenation, since very different process conditions are required for the two portions. The maximum economic potential resulted in 38,234 MM$/y for a capacity of bio-oil processed of 10 Mt/y. In the simulated biorefinery, the insoluble bio-oil fraction (IBO) was processed to produce biofuels with a cost of 22.22 and 18.87$/GJ for light gasoline and diesel, respectively. The water-soluble bio-oil fraction (WBO) was instead processed to produce 51.43 ton/day of chemicals, such as sorbitol, propanediol, butanediol, etc., for a value equal to the market price. The economic feasibility of the biorefinery resulted in a return of investment (ROI) of 69.18%, a pay-out time of 2.48 years and a discounted cash flow rate of return (DCFROR) of 19.11%, considering a plant cycle life of 30 years

Preliminary screening for microplastic concentrations in the surface water of the Ob and Tom Rivers in Siberia, Russia

This study characterizes the abundance and morphology of microplastics in surface water of the Ob River and its large tributary, the Tom River, in western Siberia. The average number of particles for two rivers ranged from 44.2 to 51.2 items per m3 or from 79.4 to 87.5 μg per m3 in the Tom River and in the Ob River, correspondingly. 93.5% of recovered microplastics were less than 1 mm in their largest dimension, the largest group (45.5% of total counts) consisted of particles with sizes range 0.30-1.00 mm