Material flow and environmental performance of the source segregated biowaste composting system.

Life cycle assessment (LCA) is performed to investigate the environmental impacts of two alternative approaches in a biowaste management system. The system inventory is based on actual data and on-site sampling for two consecutive years at the mechanical and biological treatment (MBT) facility at the prefecture of Chania (Greece). The facility pertains as MBT for household waste and material recycling (MR) for the recyclable fractions in two different process lines. The mass balances and environmental performance are assessed from waste generation to end-use. The LCA and ReCiPe 2016 methodology estimate the endpoint environmental impacts on human health, ecosystem quality and resource scarcity. The results show that biowaste source segregation in an integrated waste management system not only significantly benefits its recoverability potential it also improves its environmental performance. Impacts on human health (HH) have reduced by 4.6 times, on freshwater ecosystem quality (EQf) by 6.3 times and resource scarcity (RS) usage by 2.5 times when biowaste is combined with compost production and use, material recovery and reprocessing for fertilizer and raw material substitution.

Recent Biotechnology Advances in Bio-Conversion of Lignin to Lipids by Bacterial Cultures.

The complexity and recalcitrance of the lignin structure is a major barrier to its efficient utilization and commercial production of high-value products. In recent years, the "bio-funneling" transformation ability of microorganisms has provided a significant opportunity for lignin conversion and integrated biorefinery. Based on the chemical structure of lignin, this mini-review introduces the recent advances of lignin depolymerization by bacterial strains and the application of microbial lignin degradation in lipids production. Furthermore, the current challenges, future trends and perspectives for microbe-based lignin conversion to lipids are discussed.

Catalysing electrowinning of copper from E-waste: A critical review.

Smart technologies and digitalisation have increased the consumption of scarce metals that threaten the sustainability of intricated industries. Additionally, the growing streams of waste electrical and electronic equipment (e-waste) are significant hazards to public health and the environment. Thus, there is an escalating need to recover metals from e-waste for sustainable management of metal resources. Hydrometallurgical processing of e-waste, involving copper (Cu) leaching and its subsequent recovery from pregnant leach solution (PLS) via electrowinning, has emerged as an efficient strategy to close the recycling loop. Electrowinning from PLS demonstrated higher Cu recovery efficiency and operational feasibility with a lower reagent use and lesser waste generation. Nevertheless, multiple issues challenged its practical implementation, including selective recovery of Cu from PLS containing mixed metals and high energy consumption. This review (1) identifies the factors affecting Cu electrowinning from PLS; (2) evaluates the composition of lixiviants influencing Cu electrowinning; (3) appraises various catalysts developed for enhancing Cu electrodeposition; and (4) reviews coupled systems that minimised process energy consumption. From the literature review, electrocatalysts are prospective candidates for improving Cu electrowinning as they reduced the cathodic reduction overpotentials, enhanced surface reaction kinetics and increased current efficiency. Other catalysts, including bioelectrocatalysts and photoelectrocatalysts, are applicable for dilute electrolytes with further investigations required to validate their feasibility. The coupled systems, including slurry electrolysis, bioelectrochemical systems and coupled redox fuel cells, minimise process energy requirements by systematically coupling the cathodic reduction reaction with suitable anodic oxidation reactions having thermodynamically low overpotentials. Among these systems, slurry electrolysis utilising a single-step processing of e-waste is feasible for commericalisation though operational challenges must be addressed to improve its sustainability. The other systems require further studies to improve their scalability. It provides an important direction for energy-efficient Cu electrowinning from PLS, ultimately promoting a circular economy for the scarce metal resources.

Forecasting quantities of critical raw materials in obsolete feature and smart phones in Greece: A path to circular economy.

Mobile phones represent an ever-increasing waste stream due to the increasing ownership and short lifetime. In particular, smartphones are among the most valuable e-waste because of their extremely high content of numerous key metals, specifically in the printed circuit board and magnets. As feature and smart phones contain different key metals at different concentrations, it is important to distinguish between the two phone types to make reliable estimations. This study presents estimations of obsolete mobile phones quantities, generated in Greece in 1995-2035 and the Critical Raw Materials (CRMs) and Precious Metals (PMs) embedded in them, making a differentiation between feature and smart phones. The dynamic material flow analysis is adopted, the lifespan is evaluated by the Weibull distribution and future sales are predicted by the logistic model incorporating phases of growth, saturation and decline. Then, the future wastes are predicted by the Market Supply A model. According to the results, the generation of obsolete smartphones is constantly increasing, while the waste flows of feature phones are declining. Efficient recycling of obsolete phones (1995-2020) can cover the demand for key metals (Au, Pd, Co) in the new smartphones for more than a decade in Greece, while the demand for Ag, Sb, Si, Zn, Be, Ti will be covered for more than 15 years. In 2020-2035 the accumulated amounts of CRMs and PMs, only from the smartphone waste, will be 1292.02 and 14.11 tonnes, respectively. The findings can contribute to the management of a valuable e-waste category closing the loop between resources-products-wastes.

Technical and environmental assessment of laboratory scale approach for sustainable management of marine plastic litter.

Laboratory scale recycling of marine plastic litter consisting of polyethylene terephthalate (PET) bottle sorting, pyrolysis and chemical vapor deposition (CVD) was conducted to identify the technical and environmental implications of the technology when dealing with real waste streams. Collected seashore and underwater plastics (SP and UP, respectively) contained large quantities of PET bottles (33.2 wt% and 61.4 wt%, respectively), suggesting PET separation was necessary prior to pyrolysis. After PET sorting, marine litter was converted into pyrolysis oil and multi-walled carbon nanotubes (MWCNTs). Water-based washing of litter prior to pyrolysis did not significantly change the composition of pyrolysis products and could be avoided, eliminating freshwater consumption. However, distinct differences in oil and MWCNT properties were ascribed to the variations in feedstock composition. Maintaining consistent product quality would be one of challenges for thermochemical treatment of marine litter. As for the environmental implications, life cycle assessment (LCA) demonstrated positive benefits, including improved climate change and fossil depletion potentials. The highest positive environmental impacts were associated with MWCNT production followed by pyrolysis oil and PET recovery. The benefits of proposed approach combining PET sorting, pyrolysis and CVD allowed to close the waste loop by converting most of the marine litter into valuable products.

High temperature slagging gasification of municipal solid waste with biomass charcoal as a greener auxiliary fuel.

During high temperature slagging gasification of municipal solid waste (MSW), coal coke is typically used as an auxiliary fuel to maintain the high temperature in the gasifier and convert ashes into slag. Herein, biomass charcoal was utilized as a greener and more sustainable auxiliary fuel to replace the coal coke during stable and continuous gasification of MSW. Several monitoring characteristics were assessed, like operating conditions of the gasifier, influence of local MSW properties generated in Singapore, environmental impacts, and main by-products (slag, fly ash and metals). The performance data revealed that the replacement of coal coke with biomass charcoal provided significant environmental benefits. The use of biomass charcoal resulted in 78% less SO2 emissions, and 22% less generated fly ash because the lower sulfur content in biomass charcoal resulted in a 32% reduced use of sorbent for flue gas treatment. Furthermore, there was clear evidence of a 22% carbon footprint reduction due to replacing fossil fuel as auxiliary fuel. In addition, the slag characteristics demonstrated lower heavy metals leaching as compared to the incineration bottom ash generated from the conventional MSW incineration plant suggesting its great potential in the application as clean and green waste-derived material in the construction industry.

Dynamic estimation of future obsolete laptop flows and embedded critical raw materials: The case study of Greece.

The coronavirus pandemic has turned school and university learning system from classroom-based to exclusively online all over the world. As this change is accompanied by a spike in demand of laptops, an excessive amount of obsolete devices will be witnessed in the near future. Laptops are the most valuable e-waste category containing a high content of numerous critical raw materials, thus their waste management is crucial. Considering the impact of the coronavirus pandemic on the laptop lifespan, the future quantities and pieces of obsolete laptops in Greece are estimated (2016-2040), as well as the critical raw materials (CRMs) and precious metals (PMs) embedded in them, to illustrate the potential of recovering useful resources, thus contributing to a circular economy. To this end, dynamic material flow analysis is adopted, lifespan distribution is evaluated and future sales are predicted by the logistic model utilizing a bounding analysis. Then the future End-of-Life (EoL) laptop quantities are estimated taking time-varying parameters into consideration such as penetration rate, population, laptop weight and lifespan. This study is a dynamic estimation that avoids using average values adopted from literature that are not country specific. The provided information is useful for implementing national plans, improving the management of the most valuable category, EoL laptops, enhancing resources efficiency and contributing to a circular economy. The coronavirus pandemic has a similar impact on laptop sales in other countries, affecting their future laptop waste as well.

Transformation behaviors and environmental risk assessment of heavy metals during resource recovery from Sedum plumbizincicola via hydrothermal liquefaction.

Environmentally sound disposal of hyperaccumulator harvests is of critical importance to industrialization of phytoremediation. Herein, transformation behaviors and environmental risk of heavy metals were comprehensively examined during subcritical hydrothermal liquefaction of Sedum plumbizincicola. It is concluded that low temperature liquefaction favored resource recovery of heavy oil and hydrochars in terms of higher energy density, improved carbon sequestration and less energy consumption. Heavy metals were mainly distributed into hydrochars and water soluble phase with less than 10% in heavy oil. All metal elements except As could be accumulated in hydrochars by extending reaction time, whereas more than 96% of As was redistributed into water soluble phase. Prolonged liquefaction time facilitated immobilization of Cd, Cr and As in hydrochars, but fast liquefaction favored Pb stabilization. Liquefaction significantly reduced environmental risk level of Cd, Zn and As, but may mobilize Pb and Mn, especially for Mn to very high risk level at 240 ºC. High temperature with long reaction time tended to inhibit leaching rate of Mn, whereas low liquefaction temperature with short reaction time prevented the leaching of Zn and As from hydrochars. Overall, these findings are essential for downstream upgrading of heavy oil and metals recovery from hydrochars.

Processing of flexible plastic packaging waste into pyrolysis oil and multi-walled carbon nanotubes for electrocatalytic oxygen reduction.

Flexible plastic packaging waste causes serious environmental issues due to challenges in recycling. This study investigated the conversion of flexible plastic packaging waste with 11.8 and 27.5 wt.% polyethylene terephthalate (PET) (denoted as PET-12 and PET-28, respectively) into oil and multi-walled carbon nanotubes (MWCNTs). The mixtures were initially pyrolyzed and the produced volatiles were processed over 9.0 wt.% Fe2O3 supported on ZSM-5 (400 °C) to remove oxygenated hydrocarbons (catalytic cracking of terephthalic and benzoic acids) that deteriorate oil quality. The contents of oxygenated hydrocarbons were decreased in oil from 4.6 and 9.4 wt.% per mass of PET-12 and PET-28, respectively, to undetectable levels. After catalytic cracking, the oil samples had similar contents of gasoline, diesel and heavy oil/wax fractions. The non-condensable gas was converted into MWCNTs over 0.9 wt.% Ni supported on CaCO3 (700 °C). The type of plastic packaging influenced the yields (2.4 and 1.5 wt.% per mass of PET-12 and PET-28, respectively) and the properties of MWCNTs due to the differences in gas composition. Regarding the electrocatalytic application, both MWCNTs from PET-12 and PET-28 outperformed commercial MWCNTs and Pt-based electrodes during oxygen evolution reaction, suggesting that MWCNTs from flexible plastic packaging can potentially replace conventional electrode materials.

Environmental impact assessment of converting flexible packaging plastic waste to pyrolysis oil and multi-walled carbon nanotubes.

A solution to low recycling rates of plastic waste is the conversion into multi-walled carbon nanotubes (MWCNTs) that have high value and can create additional revenue for plant operators. The purpose of this study was to perform a life cycle assessment (LCA) of an integrated system that involves flexible packaging plastic waste (FPPW) pyrolysis, oil upgrading, and MWCNTs production. The objectives were to determine the environmental impact of MWCNTs synthesis from non-condensable pyrolysis gases, and to assess the environmental impact of MWCNTs synthesis from different plastic fractions. Integrating MWCNTs synthesis to the plastic pyrolysis process provides various environmental benefits including, reduction of contribution towards climate change, fossil depletion, human toxicity (cancer), and ionizing radiation potentials. Sensitivity analysis of MWCNTs yields provided the range of impacts on the environment and a critical yield of >2% for most impact categories was determined. Comparison of different plastic fractions indicated that using low PET content feedstock had lesser impact on the environment, and demonstrated comparable performance to mixed virgin plastics for most impact categories. The results highlighted the versatility of the integrated pyrolysis process for treating diverse plastic waste fractions with negligible effects from the impurities present in the actual FPPW during thermal processing.

Insights into the speciation of heavy metals during pyrolysis of industrial sludge.

The purpose of this study was to determine the mechanisms in heavy metals immobilisation during pyrolysis of industrial sludge (IS). Pyrolysis was conducted in a fixed-bed unit at the temperature range between 400 and 800°C. Conventional and advanced analytical techniques were employed to assess the influencing parameters on the transformation of heavy metals during pyrolysis process. The examined heavy metals (i.e. Mn, Ni, Cu, Zn, Cd, and Pb) were effectively immobilised in the char derived at ≤600°C. In contrast, for the char derived at ≥700°C, Mn, Cu, and Zn leaching efficiencies were significantly increased. According to BCR sequential extraction procedure (SEP) results, pyrolysis of IS conducted at ≤600°C transformed heavy metals into stable fractions (i.e. associated with Fe-Mn nodules, and organics and sulphides), while Mn, Cu, and Zn bound in these fractions decomposed into easily soluble forms at higher temperatures. Advanced analytical characterisation (XRD, EDX, XPS, and FTIR) of the derived char and anion concentrations in the leachate have demonstrated that the increase in metal leaching was probably due to the formation of metal halides.

Characteristics of incineration ash for sustainable treatment and reutilization.

Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO2, and Al2O3. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials.

A novel real-time monitoring and control system for waste-to-energy gasification process employing differential temperature profiling of a downdraft gasifier.

A novel, cost-effective and real-time process monitoring and control system was developed to maintain stable operation of waste-to-energy gasification process. It comprised a feedback loop control that utilized the differential temperatures of the oxidation and reduction zones in the gasifier to determine the regional heat-flow (endothermic or exothermic), to assess the availability of oxidizing agent (for instance, air or O2) at the char bed and to calculate the fuel feeding rate. Based on the correlations developed, the air-to-fuel ratio or the equivalence air ratio (ER) for air gasification could be instantaneously adjusted to maintain stable operation of the gasifier. This study demonstrated a simplification of complex reaction dynamics in the gasification process to differential temperature profiling of the gasifier. The monitoring and control system was tested for more than 70 h of continuous operation in a downdraft fixed-bed gasifier with refuse-derived fuel (RDF) prepared from municipal solid wastes (MSW). With the system, fuel feeding rate could be adjusted accurately to stabilize the operating temperature and ER in the gasifier and generate syngas with consistent properties. Significant reductions in the fluctuations of temperature profiles at oxidation and reduction zones (from higher than 100 °C to lower than 50 °C), differential temperatures (from ±200 to ±50 °C) in gasifier and the flow rate (from 16 ±â€¯6.5 to 12 ±â€¯1.8 L/min), composition of main gas components, LHV (from 6.2 ±â€¯3.1 to 5.7 ±â€¯1.6 MJ/Nm3) and tar content (from 8.0 ±â€¯9.7 to 7.5 ±â€¯4.2 g/Nm3) of syngas were demonstrated. The developed gasifier monitoring and control system is adaptable to various types (updraft, downdraft, and fluidized-bed) and scales (lab, pilot, large scale) of gasifiers with different types of fuel.

Pyrolysis derived char from municipal and industrial sludge: Impact of organic decomposition and inorganic accumulation on the fuel characteristics of char.

A comprehensive study was conducted to evaluate the fuel properties of the char produced from pyrolysis of municipal sludge (MS) and industrial sludge (IS) at different pyrolysis temperatures (500-700 °C). A detailed characterisation of the char was performed to investigate the impact of the decomposition and the accumulation of organic and inorganic compounds during pyrolysis on the fuel properties of the derived char. Increase in pyrolysis temperature increased the fuel ratios especially in the MS-derived char. On the other hand, ash accumulation resulted in decreased higher heating values (HHVs). Dehydration and decarboxylation were the main reactions, which caused the decomposition of the organic compounds in raw sludge during pyrolysis. Thermogravimetric analysis results showed that high temperature pyrolysis could improve the thermal stability of the derived char. The accumulation of catalytic inorganic compounds improved the combustion reactivity of both the IS and MS-derived char. The MS-derived char showed higher slagging and ash fouling indices compared to the IS-derived char despite the lower ash content. However, slagging and ash fouling indices of the char were comparable to that of raw sludge samples. The results indicate that the accumulation and physicochemical transformations of heavy metals during pyrolysis process would not be significantly affected during combustion of the char. For practical application in combustion, the MS-derived char has a greater potential due to considerable HHVs, improved thermal stability, efficient combustion characteristics, lower heavy metals leaching and comparable ash related issues.

Evaluation of Lighting Systems, Carbon Sources, and Bacteria Cultures on Photofermentative Hydrogen Production.

Fluorescent and incandescent lighting systems were applied for batch photofermentative hydrogen production by four purple non-sulfur photosynthetic bacteria (PNSB). The hydrogen production efficiency of Rhodopseudomonas palustris, Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodospirillum rubrum was evaluated using different carbon sources (acetate, butyrate, lactate, and malate). Incandescent light was found to be more effective for bacteria cell growth and hydrogen production. It was observed that PNSB followed substrate selection criteria for hydrogen production. Only R. palustris was able to produce hydrogen using most carbon sources. Cell density was almost constant, but cell growth rate and hydrogen production were significantly varied under the different lighting systems. The kinetics study suggested that initial substrate concentration had a positive correlation with lag phase duration. Among the PNSB, R. palustris grew faster and had higher hydrogen yields of 1.58, 4.92, and 2.57 mol H2/mol using acetate, butyrate, and lactate, respectively. In the integrative approach with dark fermentation effluents rich in organic acids, R. palustris should be enriched in the phototrophic microbial consortium of the continuous hydrogen production system.

High-quality fuel from food waste - investigation of a stepwise process from the perspective of technology development.

A stepwise process (SP) was developed for sustainable energy production from food waste (FW). The process comprised of hydrothermal treatment followed by oil upgrading. Synthetic food waste was primarily used as feedstock in the hydrothermal reactor under subcritical water conditions. The produced hydrochars were analyzed for calorific value (17.0-33.7 MJ/kg) and elemental composition indicating high-quality fuel comparable to coal. Hydrothermal carbonization (e.g. 180°C) would be efficient for oil recovery (>90%) from FW, as compared to hydrothermal liquefaction (320°C) whereby lipid degradation may take place. The recovered oil was upgraded to biodiesel in a catalytic refinery process. Selected biodiesels, that is, B3 and B4 were characterized for density (872.7 and 895.5 kg/m3), kinematic viscosity (3.115 and 8.243 cSt), flash and pour point (30°C and >126°C), micro carbon (0.03% and 0.04%), sulfur (both <0.0016%), and calorific value (38,917 and 39,584 J/g), suggesting similar quality to commercial biodiesel. Fatty acid methyl ethers content was further analyzed to assess the influence of hydrothermal treatment in biodiesel quality, indicating the limited impacts. Overall, the SP provides a promising alternative for sustainable energy recovery through high-quality biofuel and hydrochar production.

Determination of urine-derived odorous compounds in a source separation sanitation system.

Source separation sanitation systems have attracted more and more attention recently. However, separate urine collection and treatment could induce odor issues, especially in large scale application. In order to avoid such issues, it is necessary to monitor the odor related compounds that might be generated during urine storage. This study investigated the odorous compounds that emitted from source-separated human urine under different hydrolysis conditions. Batch experiments were conducted to investigate the effect of temperature, stale/fresh urine ratio and urine dilution on odor emissions. It was found that ammonia, dimethyl disulfide, allyl methyl sulfide and 4-heptanone were the main odorous compounds generated from human urine, with headspace concentrations hundreds of times higher than their respective odor thresholds. Furthermore, the high temperature accelerated urine hydrolysis and liquid-gas mass transfer, resulting a remarkable increase of odor emissions from the urine solution. The addition of stale urine enhanced urine hydrolysis and expedited odor emissions. On the contrary, diluted urine emitted less odorous compounds ascribed to reduced concentrations of odorant precursors. In addition, this study quantified the odor emissions and revealed the constraints of urine source separation in real-world applications. To address the odor issue, several control strategies are recommended for odor mitigation or elimination from an engineering perspective.

Multiple geophysical surveys for old landfill monitoring in Singapore.

One-dimensional boring presents limitations on mapping the refuse profile in old landfills owning to waste heterogeneity. Electrical imaging (EI) and multiple-analysis of surface wave (MASW) were hereby deployed at an old dumping ground in Singapore to explore the subsurface in relation to geotechnical analysis. MASW estimated the refuse boundary with a higher precision as compared to EI, due to its endurance for moisture variation. EI and MASW transection profiles suggested spots of interest, e.g., refuse pockets and leachate mounds. 3D inversion of EI and MASW data further illustrated the transformation dynamics derived by natural attenuation, for instance the preferential infiltration pathway. Comparison of geophysical surveys at different years uncovered the subterranean landfill conditions, indicating strong impacts induced by aging, precipitation, and settlement. This study may shed light on a characterization framework of old landfills via combined geophysical models, thriving landfill knowledge with a higher creditability.

Optimization of micronutrient supplement for enhancing biogas production from food waste in two-phase thermophilic anaerobic digestion.

The aim of this study was to enhance the biogas productivity of two-phase thermophilic anaerobic digestion (AD) using food waste (FW) as the primary substrate. The influence of adding four trace metals (Ca, Mg, Co, and Ni) as micronutrient supplement in the methanogenic phase of the thermophilic system was investigated. Initially, Response Surface Methodology (RSM) was applied to determine the optimal concentration of micronutrients in batch experiments. The results showed that optimal concentrations of 303, 777, 7 and 3mg/L of Ca, Mg, Co and Ni, respectively, increased the biogas productivity as much as 50% and significantly reduced the processing time. The formulated supplement was tested in continuous two-phase thermophilic AD system with regard to process stability and productivity. It was found that a destabilized thermophilic AD process encountering high VFA accumulation recovered in less than two weeks, while the biogas production was improved by 40% yielding 0.46L CH4/gVSadded/day. There was also a major increase in soluble COD utilization upon the addition of micronutrient supplement. The results of this study indicate that a micronutrient supplement containing Ca, Mg, Co and Ni could probably remedy any type of thermophilic AD process.

Insights for transformation of contaminants in leachate at a tropical landfill dominated by natural attenuation.

The purpose of this study was to track the long-term trends of contaminants distribution in the old landfill of Singapore through monitored natural attenuation and to explore the main parameters that rule such transition. Contaminants distribution, including dissolved organic matter (DOM), inorganic species, heavy metals, and organic compounds, was investigated via monitoring wells in the years 1997, 2004 and 2011. The data revealed that the distribution of contaminants possessed selective attention of spots associated with leachate movement. The hydrogeology of the landfill governed the fate and transportation of contaminants. More specifically, strong statistical correlations were identified between DOM and certain constituents in the leachate, suggesting enhanced mobilization potential. However, the leachate composition exhibited limited correspondence to the nearby solid waste, indicating the minor effect induced by the partitioning coefficient. The presence of sulphate unveiled air intrusion, suggesting increased stability of the landfill, where enhanced biodegradation occurred at earlier period responsible for higher BOD removal. Afterwards other parameters continued to facilitate the compounds removal resulting in overall low concentrations of the contaminants.