Plastic-containing food waste conversion to biomethane, syngas, and biochar via anaerobic digestion and gasification: Focusing on reactor performance, microbial community analysis, and energy balance assessment.

To manage the mixture of food waste and plastic waste, a hybrid biological and thermal system was investigated for converting plastic-containing food waste (PCFW) into renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results showed that anaerobic digestion (AD) of food waste, polyethylene (PE)-containing food waste, polystyrene (PS)-containing food waste, and polypropylene (PP)-containing food waste generated a methane yield of 520.8, 395.6, 504.2, and 479.8 mL CH4/gVS, respectively. CO2 gasification of all the plastic-containing digestate produced more syngas than pure digestate gasification. Syngas from PS-digestate reached the maximum yield of 20.78 mol/kg. During the digestate-derived-biochar-amended AD of PCFW, the methane yields in the biochars-amended digesters were 6-30% higher than those of the control digesters. Bioinformatic analysis of microbial communities confirmed the significant difference between control and biochar-amended digesters in terms of bacterial and methanogenic compositions. The enhanced methane yields in biochars-amended digesters could be partially ascribed to the selective enrichment of genus Methanosarcina, leading to an improved equilibrium between hydrogenotrophic and acetoclastic methanogenesis pathways. Moreover, energy balance assessment demonstrated that the hybrid biological and thermal conversion system can be a promising technical option for the treatment of PCFW and recovery of renewable biofuels (i.e., biogas and syngas) and bioresource (i.e., biochar) on an industrial scale.

Three-dimensional non-isothermal numerical model for predicting semi-volatile organic compound transport process in a room.

In this paper, a three-dimensional non-isothermal computational model for predicting indoor SVOC distribution is proposed, considering the effects of turbulence diffusion and suspended particles. The realizable k-ε model is introduced for turbulent flow simulation in a room. The Euler-Euler method is adopted to deal with the gas-particle two-phase flow coupled problem. Inertia slip velocity and irreversible first-order absorption boundary are employed for more accurate prediction of particle motion. The simulated curve of outlet gas-phase di-2-ethylhexyl phthalate (DEHP) concentration with emission time is verified by available experimental data. The emission process of DEHP in a 15 m2 room in Beijing during 100 days with or without air cleaner is simulated by the developed model considering air leak through window and door gaps. It is found that if the air cleaner keeps on all the time during 100 days the gas-phase DEHP concentration in the room will tend to be uniform, while the emission process is far from equilibrium without an air cleaner even the emission lasts 100 days. Results also suggest that floor heating, decrease of particle concentration, weaken of heat transfer, enhancement of mass transfer, and air infiltration in window gap contribute to decrease DEHP concentration.

Co-transesterification of waste cooking oil, algal oil and dimethyl carbonate over sustainable nanoparticle catalysts.

Key challenges for the application of biodiesel include their high acid value, high viscosity, and low ester content. It is essential to develop later-generation biodiesel from unexploited non-food resources for a more sustainable future. Reuse of biowaste is critically important to address these issues of food safety and sustainability. Thus, the co-transesterification of waste cooking oil (WCO), algal oil (AO) and dimethyl carbonate (DMC) for the synthesis of fatty acid methyl esters (FAMEs) was investigated over a series of nanoparticle catalysts containing calcium, magnesium, potassium or nickel under mild reaction conditions. Nanoparticle catalyst samples were prepared from biowaste sources of chicken manure (CM), water hyacinth (WH) and algal bloom (AB), and characterized using XRD, Raman and FESEM techniques for the heterogeneous production of biodiesel. The catalyst was initially prepared by calcination at 850 °C for 4 h in a major presence of CaxMgyCO3, KCl and K2CO3. The WCO and AO co-conversion of 98% and FAMEs co-selectivity of 95% were obtained over CM nanoparticle catalyst under the reaction conditions of 80 °C, 20 mins and DMC to oil molar ratio of 6:1 with 3% catalyst loading and 3% methanol addition. Under the optimum condition, the density, viscosity, and cetane number of the biodiesel were in the range of diesel standards. Nanoparticle catalysts have been proven as a promising sustainable material in the catalytic transesterification of WCO and AO with the major presence of calcium, magnesium and potassium. This study highlights a sustainable approach via biowaste utilization for the enhancement of biodiesel quality with high ester content, low acid value, high cetane number, and low viscosity.

System integration of hydrothermal liquefaction and anaerobic digestion for wet biomass valorization: Biodegradability and microbial syntrophy.

Sewage sludge treatment & disposal pose environmental challenges in populated-dense urban environments. Due to its poor digestibility and dewaterability, sewage sludge contains high water content and concentrated nutrients (carbon, nitrogen, and phosphorus) even after conditioning and mechanical thickening. Regarding this, a pretreatment step and downstream anaerobic digestion (AD) are often required. To meet our societal goal towards a circular economy, system integration of hydrothermal pretreatment and AD now present an attractive approach for recovering resources from the wet sewage sludge biomass. In this study, such system integration together with struvite precipitation was applied for valorizing sewage sludge. Firstly, hydrothermal conditions of different temperatures (160 °C-230 °C) and duration (2 h-12 h) were compared to their performance of nutrients solubilization. Subsequently, the hydrothermal condition of 220°C-3 h was selected for further investigations of struvite recovery and bioenergy production. Through AD comparisons, the integrated process improved the ultimate biomethane yield by 38%. Interestingly, a lag phase occurred in the midst of the AD, which indicated the need for microbial acclimatization after the hydrothermal process. The long-term microbial monitoring revealed the efficient biomethane re-generation was closely related to the late enrichment of Syntrophus for potential H2-syntrophy. Therefore, on one hand, this study investigated an efficient and integrated approach of sewage sludge valorization. On other hand, it uncovered the microbial bottlenecks and potential biotechnological means for further system improvement. Further research about nutrients speciation in the integrated system would be desired.

Vegetal fiber paper matrix impregnated with silica gel for benzene removal.

Removing benzene from indoor space plays an important role in indoor air purification. A novel filter with vegetal fiber paper (VFP) as matrix hosting silica gel is proposed in this paper for benzene removal. In order to investigate the feasibility and performance of this idea, firstly, three pieces of VFP samples impregnated with different amounts of silica gel are fabricated and their benzene adsorption quantities are tested. The results show that three times is recommended as the optimal number for impregnating. The VFP sample impregnated with silica gel after the third impregnating exhibits commendable coating stability and good benzene adsorption performance. Additionally, at low relative pressure (Pb /Ps  ≤ 0.05), the experimental data of benzene adsorption isotherms fit well with the Langmuir model with R2 greater than 0.97. Then, two actual filters made of VFP impregnated with silica gel after the third impregnating were fabricated. It is found that the pressure drop of the actual filter is only 1200 Pa/m when the air velocity is 2 m/s. Besides, the one-pass efficiency of the filter can reach to 19.44%. It is expected that the silica gel coated on the filter can be modified to improve the purification performance of the filter.

Comparison-based optical study on a point-line-coupling-focus system with linear Fresnel heliostats.

Concentrating the concept of a beam-down solar tower with linear Fresnel heliostat (PLCF) is one of the feasible choices and has great potential in reducing spot size and improving optical efficiency. Optical characteristics of a PLCF system with the hyperboloid reflector are introduced and investigated theoretically. Taking into account solar position and optical surface errors, a Monte Carlo ray-tracing (MCRT) analysis model for a PLCF system is developed and applied in a comparison-based study on the optical performance between the PLCF system and the conventional beam-down solar tower system with flat and spherical heliostats. The optimal square facet of linear Fresnel heliostat is also proposed for matching with the 3D-CPC receiver.

Potential application of gasification to recycle food waste and rehabilitate acidic soil from secondary forests on degraded land in Southeast Asia.

Gasification is recognized as a green technology as it can harness energy from biomass in the form of syngas without causing severe environmental impacts, yet producing valuable solid residues that can be utilized in other applications. In this study, the feasibility of co-gasification of woody biomass and food waste in different proportions was investigated using a fixed-bed downdraft gasifier. Subsequently, the capability of biochar derived from gasification of woody biomass in the rehabilitation of soil from tropical secondary forests on degraded land (adinandra belukar) was also explored through a water spinach cultivation study using soil-biochar mixtures of different ratios. Gasification of a 60:40 wood waste-food waste mixture (w/w) produced syngas with the highest lower heating value (LHV) 5.29 MJ/m(3)-approximately 0.4-4.0% higher than gasification of 70:30 or 80:20 mixtures, or pure wood waste. Meanwhile, water spinach cultivated in a 2:1 soil-biochar mixture exhibited the best growth performance in terms of height (a 4-fold increment), weight (a 10-fold increment) and leaf surface area (a 5-fold increment) after 8 weeks of cultivation, owing to the high porosity, surface area, nutrient content and alkalinity of biochar. It is concluded that gasification may be an alternative technology to food waste disposal through co-gasification with woody biomass, and that gasification derived biochar is suitable for use as an amendment for the nutrient-poor, acidic soil of adinandra belukar.

Coupling effect of reaction conditions on the catalytic activity of Cu-Mn composite oxide catalysts for toluene.

Volatile organic compounds (VOCs) are one of the major components of air pollution. Catalytic combustion is a promising technology for the treatment of VOCs and at its center is the preparation of efficient and cheap catalysts. In this study, by loading copper (Cu) and manganese (Mn) on Santa Barbara Amorphous-15 (SBA-15) molecular sieve, the Cux-Mny/SBA-15 (x = 1, 2; y = 1, 2) composite metal oxide catalyst was prepared using the equal volume impregnation method. Their performance in the toluene catalytic combustion reaction was investigated by adjusting the molar ratio (x : y), and the loading of Cu and Mn. The results of the Brunner-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses show that the CuMnO spinel phase can be detected in the Cu-Mn composite metal oxide catalyst doped with a low concentration of Cu. The overall rod-like structure of the fibrous network structure provides a large specific surface area, and the particle crystallinity is low and the dispersion is good. Due to the synergistic effect of Cu and Mn, the greater the amount of Mn3+ and adsorbed oxygen species (Oads) that are available, and the higher the turnover frequency (TOF) value, the better and more superior catalytic performance and excellent stability is obtained, when compared with the single-component oxides used in toluene catalytic combustion. After a continuous catalytic reaction for 12 h, the toluene conversion rate remained above 95%. The coupling effect of the catalytic reaction temperature and concentration of oxygen on the catalytic combustion of toluene was also studied. At a low reaction temperature (<250 °C), the increase of the concentration of oxygen played a superior role in promoting the conversion of toluene. The kinetic analysis of the toluene catalytic combustion process showed that the catalytic combustion of toluene by Cu-Mn/SBA-15 followed both the Mars-Van Krevelen (MVK) and Langmuir-Hinshelwood (L-H) reaction mechanisms. With the increase of the Oads amount caused by the decrease of the Cu ratio, the proportion of the L-H reaction mechanism increases.

Machine learning and circular bioeconomy: Building new resource efficiency from diverse waste streams.

Biorefinery systems are playing pivotal roles in the technological support of resource efficiency for circular bioeconomy. Meanwhile, artificial intelligence presents great potential in handling scientific tasks of high-dimensional complexity. This review article scrutinizes the status of machine learning (ML) applications in four critical biorefinery systems (i.e. composting, fermentation, anaerobic digestion, and thermochemical conversions) as well as their advancements against traditional modeling techniques of mechanistic approach. The contents cover their algorithm selections, modeling challenges, and prospective improvements. Perspectives are sketched to further inform collective efforts on crucial aspects. The multidisciplinary interchange of modeling knowledge will enable a more progressive digital transformation of sustainability efforts in supporting sustainable development goals.

Advancing the bioconversion process of food waste into methane: A systematic review.

With the continuous rise of food waste (FW) throughout the world, a research effort to reveal its potential for bioenergy production is surging. There is a lack of harmonized information and publications available that evaluate the state-of-advance for FW-derived methane production process, particularly from an engineering and sustainability point of view. Anaerobic digestion (AD) has shown remarkable efficiency in the bioconversion of FW to methane. This paper reviews the current research progress, gaps, and prospects in pre-AD, AD, and post-AD processes of FW-derived methane production. Briefly, the review highlights innovative FW collection and optimization routes such as AI that enable efficient FW valorization processes. As weather changes and the FW sources may affect the AD efficiency, it is important to assess the spatio-seasonal variations and microphysical properties of the FW to be valorized. In that case, developing weather-resistant bioreactors and cost-effective mechanisms to modify the raw substrate morphology is necessary. An AI-guided reactor could have high performance when the internal environment of the centralized operation is monitored in real-time and not susceptible to changes in FW variety. Monitoring solvent degradation and fugitive gases during biogas purification is a challenging task, especially for large-scale plants. Furthermore, this review links scientific evidence in the field with full-scale case studies from different countries. It also highlights the potential contribution of ADFW to carbon neutrality efforts. Regarding future research needs, in addition to the smart collection scheme, attention should be paid to the management and utilization of FW impurities, to ensure sustainable AD operations.

Meeting the heavy-metal safety requirements for food crops by using biochar: An investigation using sunflower as a representative plant under different atmospheric CO2 concentrations.

Global warming impacts on plant growth and food safety are emerging topics of concern, while biochar as a soil additive benefits plants. This study investigates (1) sunflower plant growth at various biochar concentrations in a soil-compost growing substrate under both ambient (420 ppm) and elevated (740 ppm) atmospheric CO2 concentrations, and (2) concentrations of heavy metals in the growing substrates and organs of the plants. The elevated CO2 concentration benefits the vegetative parts but harms the reproductive parts of the plants. Additionally, the elevated CO2 concentration inhibits the beneficial effects that biochar confers on the plants at the ambient concentration. The optimum biochar concentration at both CO2 levels was found to be 15%. At the time of harvest, most of the heavy-metal concentrations in the growing substrate increased. It was demonstrated that biochar can reduce the amount of heavy metals that accumulate in the roots and seeds whose heavy-metal concentrations complied with Singapore food safety regulations, while those for the biochar met the proposed Singapore biochar standard's thresholds. Our results show that the proposed Singapore biochar standard is practical and sound.

Research on Combustion Properties and Pollutant Emission Characteristics of Blends of Maltol Byproduct/Pine Sawdust.

In this paper, the combustion and pollutant emission characteristics of maltol byproduct, pine sawdust, and their blends were experimentally studied by thermogravimetry, tube furnace experiment, and scanning electron microscopy. The results show that the combustion process of maltol byproduct, pine sawdust, and their blends can be divided into three stages, in which the volatile release of the maltol byproduct includes two stages. The ignition temperature of the blended fuel is lower than that of sawdust. The NO x produced by combustion of the blended fuel is lower than that produced by sawdust combustion alone, and the SO2 emission is always at a low level. There is a certain synergy between maltol byproduct and pine sawdust mixed combustion. Comprehensively comparing the combustion characteristics and emission characteristics, the blended fuel made by adding less than 10% maltol byproduct into pine sawdust can improve the combustion characteristics and reduce emissions, and 10% is the best proportion of the blended fuel.

High-Efficiency, Mass-Producible, and Colored Solar Photovoltaics Enabled by Self-Assembled Photonic Glass.

Building-integrated photovoltaics is a crucial technology for developing zero-energy buildings and sustainable cities, while great efforts are required to make photovoltaic (PV) panels aesthetically pleasing. This places an urgent demand on PV colorization technology that has a low impact on power conversion efficiency (PCE) and is simultaneously mass-producible at a low cost. To address this challenge, this study contributes a colorization strategy for solar PVs based on short-range correlated dielectric microspheres, i.e., photonic glass. Through theoretical studies, first we demonstrate that the photonic glass self-assembled by high-index microspheres could enable both colored solar cells and modules, with easily variable colors and negligible parasitic absorption. By a fast spray coating process of colloidal monodisperse ZnS microspheres, we show the photonic glass layer could be easily deposited on silicon solar cells, enabling them to have structural colors. Through varying microsphere sizes, solar cells with different colors are achieved, showing low PCE loss compared to normal black cells. These colored solar cells are also encapsulated with a general lamination process to produce PV modules with various colors and patterns at a stunning PCE approaching 21%. Moreover, the long-term stability is subsequently verified by aging tests including an outdoor exposure for 10 days and a damp-heat test for 1000 h, and the mass producibility is demonstrated by presenting a colored PV panel with an output power over 108 W. These results confirm photonic glass as a promising strategy for colored PVs possessing high efficiency and practical applicability.

Methodological framework for wastewater treatment plants delivering expanded service: Economic tradeoffs and technological decisions.

With emerging decarbonization to deploy more integrated waste management, there is a burgeoning need for re-managing waste-related infrastructures in urban environments. Wastewater treatment plants are key contributors to expanded environmental services, but relevant technological decisions and economic tradeoffs have to be assessed from a systems perspective. This study provides a methodological framework that consolidates the multiple technological and economic aspects of system retrofitting for such an evaluation purpose. Complex leachate from refuse transfer stations has been recently identified as the decarbonization roadblock of urban waste management, and it was chosen for investigations by this new methodological approach. The system impacts by complex leachate on the existing facilities were validated by experimental trials. To derive the financial outlooks for decision making, the evaluation matrix includes the quantitative impacts of bioenergy profiles, energy balance analysis of biogas utilization methods, needs of system retrofitting, economic factors, and their uncertainties. Due to the detected inefficiency of bioenergy recovery, bioinformatic analysis was proceeded for understanding the underlying mechanism to propose a mitigation solution. Overall, the methodological framework can provide a quantitative assessment of the centralized capability of wastewater treatment plants for systems planning in the new policy agenda of urban decarbonization, where the methodological potentials of expanded framework applications are also highlighted.

Viability of a practical multicyclic sorption-based water harvester with improved water yield.

Sorption-based atmospheric water harvesting (SAWH) has emerged as an attractive way to relieve water scarcity. However, the daily water yield of currently reported SAWH devices remains low to satisfy the rising demand for drinking water. The sorption and desorption kinetics, long-term stability and especially facile scaling-fabrication of adsorbents and scaled-up device implementation have become the bottleneck to such large-scale SAWH application. To overcome these challenges, an air-cooled SAWH device was fabricated to investigate its atmospheric water harvesting (AWH) performance under real island climate and its feasibility of multicyclic operation. Under monocyclic operation, the device demonstrated the superior water productivity as much as 3.9 kg day-1, or 0.39 kgwater kgadsorbent-1 day-1, at 31 °C and 70% RH, with a thermal efficiency of 25.4% (desorption at 94 °C). The SAWH device demonstrated successful water production through 2 adsorption-desorption cycles within one day, with increased thermal efficiency to as high as 32.2% and increased water harvesting performance up to 0.42 kgwater kgadsorbent-1 day-1 by 20-90%. This is the first demonstration in multicyclic SAWH at large scales, holding the promise of large-scale and practical water supply in island areas while opening up new applications such as indoor dehumidification.

Enhancing microbial lipids yield for biodiesel production by oleaginous yeast Lipomyces starkeyi fermentation: A review.

The enhanced production of microbial lipids suitable for manufacturing biodiesel from oleaginous yeast Lipomyces starkeyi is critically reviewed. Recent advances in several aspects involving the biosynthetic pathways of lipids, current conversion efficiencies using various carbon sources, intensification strategies for improving lipid yield and productivity in L. starkeyi fermentation, and lipid extraction approaches are analyzed from about 100 papers for the past decade. Key findings on strategies are summarized, including (1) optimization of parameters, (2) cascading two-stage systems, (3) metabolic engineering strategies, (4) mutagenesis followed by selection, and (5) co-cultivation of yeast and algae. The current technical limitations are analyzed. Research suggestions like examination of more gene targets via metabolic engineering are proposed. This is the first comprehensive review on the latest technical advances in strategies from the perspective of process and metabolic engineering to further increase the lipid yield and productivity from L. starkeyi fermentation.

A Review on Enhancing Cupriavidus necator Fermentation for Poly(3-hydroxybutyrate) (PHB) Production From Low-Cost Carbon Sources.

In the context of a circular economy, bioplastic production using biodegradable materials such as poly(3-hydroxybutyrate) (PHB) has been proposed as a promising solution to fundamentally solve the disposal issue of plastic waste. PHB production techniques through fermentation of PHB-accumulating microbes such as Cupriavidus necator have been revolutionized over the past several years with the development of new strategies such as metabolic engineering. This review comprehensively summarizes the latest PHB production technologies via Cupriavidus necator fermentation. The mechanism of the biosynthesis pathway for PHB production was first assessed. PHB production efficiencies of common carbon sources, including food waste, lignocellulosic materials, glycerol, and carbon dioxide, were then summarized and critically analyzed. The key findings in enhancing strategies for PHB production in recent years, including pre-treatment methods, nutrient limitations, feeding optimization strategies, and metabolism engineering strategies, were summarized. Furthermore, technical challenges and future prospects of strategies for enhanced production efficiencies of PHB were also highlighted. Based on the overview of the current enhancing technologies, more pilot-scale and larger-scale tests are essential for future implementation of enhancing strategies in full-scale biogas plants. Critical analyses of various enhancing strategies would facilitate the establishment of more sustainable microbial fermentation systems for better waste management and greater efficiency of PHB production.

Microbial succession analysis reveals the significance of restoring functional microorganisms during rescue of failed anaerobic digesters by bioaugmentation of nano-biochar-amended digestate.

Nano-biochar application was investigated for anaerobic digestion of orange peel waste. The application for methane production focused on the optimization of biochar feedstock, rescue of failed digesters, and microbial succession analysis. It showed that sewage sludge (SS) derived biochar had the highest performance enhancement among the different feedstocks, which could be ascribed to the improvement of electron transfer, interspecies hydrogen transfer, and supply of trace elements. Subsequently, nano SS biochar-amended digestate was evaluated for rescuing failed digesters, and the experimental results indicated its positive roles through gradual bioaugmentation operation. The dynamic analysis of microbial succession indicated the successful application was through the mechanism of restoring partially the functional microbial communities. The major reconstruction of functional microorganisms included bacteria phyla Hydrogenispora (24.5%) and Defluviitoga (18.8%) as well as methanogenic genera of Methanosarcina (41.5%) and Methanobacterium (27.3%). These findings would contribute to rescuing failed anaerobic digesters by bioaugmentation with biochar-amended digestate.

Quantifying techno-economic indicators' impact on isolated renewable energy systems.

Addressing climate change with the rising global energy usage necessitates electricity sector decarbonization by rapidly moving toward flexible and efficient off-grid renewable energy systems (RESs). This paper analyzes the wind and solar micro-grids, with batteries and pumped hydro storage for a robust off-grid RES techno-economic operation, while considering diverse multi-objective optimization cases. This research has considered the RES variable operational losses in the developed methodology and relations between different indicators are evaluated, revealing a basic understanding between them. The results reveal that the reliability index is inversely related to the oversupply index, while directly related to the system self-sufficiency index. The cost of energy is more sensitive to technical indicators rather than the storage cost and so can be used as a primary monetary index. Energy and cost balance analysis showed that 16%-20% of the used energy was drained in RES operational losses, which were usually ignored in previous studies.

Effects of plastics on reactor performance and microbial communities during acidogenic fermentation of food waste for production of volatile fatty acids.

The aim of this work was to study the effects of plastics (high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET)) on reactor performance and microbial communities during acidogenic fermentation of food waste for the production of volatile fatty acids (VFA). The addition of HDPE and PS increased total VFA yields by 28% and 47%, respectively, whereas the addition of PP and PET decreased total VFA yields by 6% and 2%, respectively. The highest enhancing performance of PS could be ascribed to its highly porous structure that could provide immobilization effects for microbial growth. Degradation of various plastics was confirmed by FESEM results, but the degrees were limited (i.e., 3.9-8.7%). Bacterial analysis showed that the addition of various plastics altered the community diversity. Phylum Thermotogae and genus Defluviitoga dominated all the reactors. Potential HDPE- and PS-degrading microbes could belong to genus Clostridium_sensu_stricto_8, while Tepidanaerobacter_syntrophicus could be PET-degrading microbes.