Waste Streams Research Articles

A prototype system for the removal of 137Cs from liquid radioactive waste using reverse osmosis membrane.

Cesium removal from aqueous solutions of radioactive waste streams is a challenge in the field of radioactive waste management; this is due to the small atomic radii of Cs+ metal ions and their high migration ability. So, the development of a withstand system for the removal of Cs+ is crucial. In the current study, the removal of radioactive cesium from aqueous solutions using an RO-TLC membrane was studied. Two modifications were conducted; the first is to enlarge the cesium metal ion radii by interacting with mono- and dibasic acids, namely, stearic acid, tartaric acid, citric acid, and EDTA, and the second is the modification of the RO membrane pore size via reaction with the same acids. The modification was confirmed using SEM, FTIR, and EDX analysis techniques. The Cs+ and K+ rejection capacities and water permeability across the membrane at 1.5 bars were evaluated. Along with using the above-mentioned acids, the Cs+ metal ion retention index (RCs) was also obtained. It was found that employing EDTA as a chelating agent in an amount of 1.5g/L in conjunction with the variation of feed content since it provided the highest value of RCs ~ 98% when used. Moreover, the elution of Cs+ using water, EDTA, ammonia, and HCl is also investigated. The optimal value of the eluent concentration was (0.25M) HCl. Finally, Langmuir and Freundlich isotherm models were applied for a better understanding of the sorption process. The results of the present work more closely match the Langmuir isotherm model to determine the dominance of the chemical sorption mechanism.

Synergistic microwave and acidic deep eutectic solvent-based pretreatment of Theobroma cacao pod husk biomass for xylooligosaccharides production

The bioconversion of lignocellulosic biomass into novel bioproducts is crucial for sustainable biorefineries, providing an integrated solution for circular economy objectives. The current study investigated a novel microwave-assisted acidic deep eutectic solvent (DES) pretreatment of waste cocoa pod husk (CPH) biomass to extract xylooligosaccharides (XOS). The sequential DES (choline chloride/citric acid, molar ratio 1:1) and microwave (450W) pretreatment of CPH biomass was effective in 67.3% xylan removal with a 52% XOS yield from total xylan. Among different XOS of varying degrees of polymerization, a higher xylobiose content corresponding to 69.3% of the total XOS (68.22 mg/g CPH) from liquid fraction was observed. Enzymatic hydrolysis of residual xylan from pretreated CPH biomass with low commercial xylanase (10 IU/g) concentration yielded 24.2% XOS. The MW-ChCl/citric acid synergistic pretreatment approach holds great promise for developing a cost-effective and environmentally friendly method contributing to the sustainable production of XOS from agricultural waste streams.

Dynamic simulation and analysis of dichloromethane-acetone, dichloromethane-trichloromethane and dichloromethane-toluene VOC mixture abatement systems under transient feed conditions

Minimisation of environmental footprint in line with sustainability goals rests at the top of the agenda of the pharmaceutical industry. Volatile Organic Compounds (VOCs), while essential to primary pharmaceutical manufacturing, are solvents whose emissions pose a risk to human health and ecosystems. Adsorption on activated carbon beds is an established technology for end of pipe emissions control, which, however, faces efficiency limitations by quick and irregular bed saturation due to complex, transient feeds. This study employs a validated nonisothermal, multicomponent adsorption model to quantitatively assess the exact effect and potential value of waste stream feed sequencing towards activated carbon bed utilisation optimisation. Our results indicate that gradual increase of dichloromethane feed concentration in combination with a low, constant inlet concentration of the strongly adsorbing component leads to the latest breakthrough onset for the dichloromethane-acetone, dichloromethane-chloroform and dichloromethane-toluene mixtures, paving the way to industrial VOC emission abatement scheduling and process optimisation.

Effect of Sample Presentation on the Classification of Black Soldier Fly Larvae Using Near-Infrared Spectroscopy

Black soldier fly larvae (BSFL) (Hermetia illucens) reared on food waste streams are considered a sustainable source of protein in feed livestock diets. Recently, portable near-infrared spectroscopy (NIR) instruments have been assessed to monitor the consistency and quality of food waste streams used to feed black soldier fly larvae. During the application of NIR spectroscopy, sample presentation (e.g., drying, processing, particle size) plays an important role in the accuracy of the models developed (quantitative or qualitative analysis). The objective of this study was to evaluate the effect of sample presentation (number of larvae used during the scanning of BSFL) on the accuracy of classification models developed to trace the food waste stream (e.g., supermarket of childcare) used to feed the larvae. BSFL samples were sourced from two waste streams and scanned as half, 1, 2, or 3 larvae using an NIR portable instrument (MicroNIR, Viavi, Milpitas, California, USA). Principal component analysis (PCA) and linear discriminant analysis (LDA) were used to analyze the NIR data and to classify the samples according to the waste stream. The main differences in the NIR spectra of the BSFL samples associated with the number of larvae scanned were observed around 1200 nm, mainly associated with the C-H overtones (lipids). The classification results showed that high classification rates (>93%) were obtained regardless of the number of larvae scanned, ranging from 93% (using 0.5 larvae) to 100% (using 1, 2, or 3 larvae samples). Overall, the number of larvae scanned had minimal to no effect on the accuracy of the LDA classification models. The present study demonstrated that a portable NIR instrument can be suitable for an initial rapid classification or determination of the origin of the waste stream used to feed the BSFL.

The Application of Microbially Induced Calcium Carbonate Precipitation (MICP) Technology in Building Materials and its Contribution to Waste Resource Utilization

Abstract: In many countries around the world, waste generation has become an increasingly pressing issue, particularly in urban areas experiencing rapid population growth and industrialization. The volume of waste produced by human activities continues to rise, posing significant challenges to the environment, economy, and public health. Improper waste management can lead to air and water pollution, soil degradation, and the spread of diseases. Additionally, waste generation consumes substantial natural resources and energy, exacerbating resource depletion and contributing to greenhouse gas emissions.To address these challenges, sustainable waste management practices are essential to reduce waste generation and promote resource recovery and recycling. In this context, the development of innovative technologies, such as Microbially Induced Calcium Carbonate Precipitation (MICP) in building materials, offers an effective means of converting waste into valuable and sustainable applications. MICP is an environmentally friendly biogeochemical technique that employs microorganisms and chemical agents in biological processes to produce carbonate minerals, providing an energy-efficient, cost-effective, and sustainable solution to environmental and engineering challenges.Recent research indicates that waste streams can substitute for several MICP chemical components in microbial and cementitious agent growth media. MICP technology has been found not only to be effective in handling hazardous waste streams but also to be a cost-effective and sustainable solution applicable to various waste media. This comprehensive review aims to provide insights into the environmental advantages and engineering applications of MICP technology, with a particular focus on the potential contributions of waste streams. It also offers guidance for researchers on identifying and overcoming challenges associated with using waste streams for MICP technology applications.

Distribution of Per- and Polyfluoroalkyl Substances (PFASs) in a Waste-to-Energy Plant─Tracking PFASs in Internal Residual Streams.

Per- and polyfluoroalkyl substances (PFASs) constitute a diverse group of man-made chemicals characterized by their water- and oil-repellent properties and persistency. Given their widespread use in consumer products, PFASs will inevitably be present in waste streams sent to Waste-to-Energy (WtE) plants. We have previously observed a subset of PFASs in residual streams (ashes, treated process water, and flue gas) from a WtE plant. However, the transport and distribution of PFASs inside the WtE plant have remained unaddressed. This study is part of a comprehensive investigation to create a synoptic overview of the distribution of PFASs in WtE residues. PFASs were found in all sample types except for boiler ash. The total levels of 18 individual PFASs (Σ18PFASs) in untreated flue gas ranged from 5.2 to 9.5 ng m-3, decreasing with 35% ± 10% after wet flue gas treatment. Σ18PFASs in the condensate ranged from 46 to 50 ng L-1, of which perfluorohexanoic acid (PFHxA) made up 90% on a ng L-1 basis. PFHxA was also dominant in filter ash, where Σ18PFASs ranged from 0.28 to 0.79 ng g-1. This study shows that flue gas treatment can capture some PFASs and transfer them into WtE residues.

Assessing the Potential Climate Impacts and Benefits of Waste Prevention and Management: A Case Study of Sweden

This study employs a life cycle perspective to analyze the carbon footprints of various waste streams, evaluating 52 cases across 26 types of household waste in Sweden, with a focus on waste prevention and management. It demonstrates that while recycling can reduce carbon emissions, prevention could significantly enhance these benefits, with savings ranging from −36.5 to −0.01 kg-CO2-eq per kg of waste. Notably, Waste Electrical and Electronic Equipment (WEEE), textiles, tires, residual household, and plastic waste are the top five fractions most amenable to prevention on a per mass basis. Further analysis, considering waste volumes, shows that targeted recycling of materials like WEEE, metals, and paper could account for over 80% of potential carbon savings. However, the majority of potential climate impact is attributed to the energy recovery of unsorted (mixed) waste, contributing to more than 90% of total impacts. Redirecting all mixed waste to recycling could triple carbon savings, but focusing on prevention could potentially increase benefits twenty-sevenfold, particularly for waste like WEEE, food, and textiles. This research provides a valuable tool for identifying key areas in waste management to optimize climate benefits and enhance public awareness. However, it advises using local data for precise planning due to inherent uncertainties.

Phosphorus Release Dynamics from Ashes during a Soil Incubation Study: Effect of Feedstock Characteristics and Combustion Conditions

Recovering phosphorus (P) through combustion from waste streams, like wastewater sludge and animal manure, offers a promising solution. This research explores the P release patterns in different ashes derived from secondary raw materials, using a long-term soil incubation lasting 160 days. The study evaluated the P release dynamics in five types of ashes from enhanced biological phosphorus removal (EBPR) systems and pig slurry burned at different temperatures. According to the results, a primary effect was observed on P bioavailability during the initial incubation period. All tested ashes release more than 50% of the total P applied between days 5 and 10. Ashes from EBPR exhibited higher P release than those from pig manure, indicating ash origin as a key factor in P release. Additionally, combustion temperature was crucial, with higher temperatures resulting in increased P release rates. Furthermore, the Pearson correlation revealed a strong relationship between the characteristics of the ashes and the amount of P release. Overall, these findings suggest that ashes could be a valuable P-source for agriculture avoiding the process of wet chemical P extraction, thus reducing both economic and environmental costs.

Deep Learning Approaches for Automated Waste Classification and Sorting

Abstract: Effective waste management is critical for environmental sustainability in modern societies. Manual classification and sorting of waste streams is labour-intensive, error-prone, and poses health hazards. Recent advancements in deep neural networks provide new opportunities for automated waste characterization and segregation. This work develops a deep convolutional neural network architecture for classifying various materials commonly found in municipal solid waste. The model achieves over 93% accuracy in categorizing plastics, paper, metals, and glass items from images. The system is designed for edge deployment on low-cost hardware at waste sorting facilities. We implement a closed-loop simulation environment using robotic arms and conveyor belts to demonstrate automated segregation based on predicted waste categories. Results highlight viability for improved waste processing via integration of deep learning-enabled automation. Broader adoption could lead to reduced costs and environmental impact while increasing recycling rates

Improving waste management strategies in the food sector: case studies from Spain, Tunisia and Hong Kong

AbstractAppropriate waste generation and management is becoming increasingly important in making food systems more sustainable. It is, therefore, imperative to both reduce waste generation and sustainably manage the waste that cannot be reduced. However, this is challenging due to the heterogeneity of waste materials, the high economic costs of optimizing food systems and the low awareness of the issue in some societies. This article analyzes three case studies that explore improvements in waste management in the food sector in Europe, Africa and Asia. The case studies focus on a horticultural cooperative in Spain, a seafood company in Tunisia and municipal waste management in Hong Kong, highlighting different challenges and approaches. Key factors for horticultural waste management include a consistent regulatory framework, appropriate management systems and waste traceability. The article also highlights the potential for valorisation of waste products, such as blue crab by-products, which can be used to obtain polysaccharides, proteins, lipids, antioxidants, flavonoids, vitamins and minerals. A shift from landfill to anaerobic digestion is also recommended for a more sustainable waste management. By identifying and quantifying waste streams and problematic waste types, alternative solutions can be developed to improve the sustainability of the global food supply chain.

Plastic Packaging Waste Management: A Case in Implementation of Extended Producer Responsibility Policies in Minnesota

The plastic pollution crisis is a global challenge affecting governments, private citizens, and the environment. Plastic packaging, which makes up approximately 40% of all plastic material produced globally, accounts for less than 10% of recycled material. This discrepancy highlights the rapid growth of various plastic types and difficulty for local governments to implement needed waste management practices or meet required capacities. Extended producer responsibility (EPR) is a model for multiple waste streams that places the post-consumer responsibility of a product on the producer. As governments seek to develop legislation to better manage plastic waste, EPR is a policy tool that will promote circularity. This paper discusses the successes and challenges of EPR policies in the European Union (EU), and in states that have enacted them, particularly in California. Many states have introduced or are seeking to introduce legislation on EPR for plastic packaging in the next few years. The Packaging Waste and Cost Reduction Act, a bill for a product stewardship program for plastic and paper packaging materials was recently introduced in the Minnesota state legislature in 2024. This policy paper discusses several EPR policy options and recommendations to improve transparency and success of future EPR bills in states seeking to enact legislation, including Minnesota.

Industrial Waste Heat Utilization in the European Union—An Engineering-Centric Review

The efficient utilization of waste heat from industrial processes can provide a significant source of energy savings for production plants, as well as be a driver of sustainable operations and the abatement of emissions. Industrial waste heat usually is contained in liquid or gaseous outlet streams. Although the possible ways to utilize waste heat are discussed in a wide variety of papers, these either provide only a general overview of utilization options and opportunities or focus on a narrow range of industrial processes. The aim of the present paper is to discuss the practical aspects of waste heat utilization in the European Union so that the reader can gain perspective on (i) the thermal classification of waste heat, (ii) liquid and gaseous waste streams and their typical temperatures for industrial use cases, (iii) the technical, economic, physical, and environmental aspects barring full utilization of the available waste heat, (iv) waste heat sources in various industries, and (v) standardized equipment and technologies applicable to industrial waste heat utilization, including their advantages, disadvantages, and weak points.

Evaluation of Thermoplastic Starch Contamination in the Mechanical Recycling of High-Density Polyethylene

This research highlights the importance of addressing bioplastic contamination in recycling processes to ensure the quality of recycled material and move towards a more sustainable circular economy. Polyethylene (PE) is a conventional plastic commonly used in packaging for which large amounts of waste are produced; therefore, PE is generally recycled and has an established recycling process. However, the contamination of biodegradable polymers in the PE waste stream could impact recycling. This study, therefore, focuses on polyethylene (PE) that has been polluted with a commercial thermoplastic starch polymer (TPS), as both materials are used to produce plastic films and bags, so cross-contamination is very likely to occur in waste separation. To achieve this, recycled PE was blended with small quantities of the commercial TPS and processed through melt extrusion and injection molding, and it was further characterized. The results indicate that the PE-TPS blend lacks miscibility, evidenced by deteriorated microstructure and mechanical properties. In addition, the presence of the commercial TPS affects the thermal stability, oxidation, and color of the recycled PE.

Assessment of chromite ore wastes for methylene blue adsorption: Isotherm, kinetic, thermodynamic studies, ANN, and statistical physics modeling

This research investigates the adsorption potential of chrysotile and lizardite, two minerals derived from chromite ore wastes, for the uptake of Methylene Blue (MB) dye from waste streams. The characterization of these minerals involves XRD, XRF, FTIR, and SEM. Results confirm the dominance of polymorphic magnesium silicate minerals, specifically chrysotile and lizardite, in the samples. The FTIR spectra reveal characteristic vibration bands confirming the presence of these minerals. The SEM analysis depicts irregular surfaces with broken and bent edges, suggesting favorable morphologies for adsorption. N2 adsorption-desorption isotherms indicate mesoporous structures with Type IV pores in both adsorbents. The Central Composite Design approach is employed to optimize MB adsorption conditions, revealing the significance of contact time, adsorbent mass, and initial MB concentration. The proposed models exhibit high significance, with F-values and low p-values indicating the importance of the studied factors. Experimental validation confirms the accuracy of the models, and the optimum conditions for MB adsorption are determined. The influence of solution acidity on MB uptake is investigated, showing a significant enhancement at higher pH values. Isothermal studies indicate Langmuir and Freundlich models as suitable descriptions for MB adsorption onto chrysotile and lizardite. The maximum adsorption capacities of MB for chrysotile and lizardite were found to be 352.97 and 254.85, respectively. Kinetic studies reveal that the pseudo-first-order model best describes the adsorption process. Thermodynamic analysis suggests an exothermic and spontaneous process. Statistical physics models further elucidate the monolayer nature of adsorption. Additionally, an artificial neural network is developed, exhibiting high predictive capability during training and testing stages. The reusability of chrysotile and lizardite is demonstrated through multiple regeneration cycles, maintaining substantial adsorption potential. Therefore, this research provides comprehensive insights into the adsorption characteristics of chrysotile and lizardite, emphasizing their potential as effiective and reusable sorbents for MB uptake from wastewater.

High-Temperature Hydrothermal Extraction of Phenolic Compounds from Brewer’s Spent Grain and Malt Dust Biomass Using Natural Deep Eutectic Solvents

Aligned with the EU Sustainable Development Goals 2030 (EU SDG2030), extensive research is dedicated to enhancing the sustainable use of biomass waste for the extraction of pharmaceutical and nutritional compounds, such as (poly-)phenolic compounds (PC). This study proposes an innovative one-step hydrothermal extraction (HTE) at a high temperature (120 °C), utilizing environmentally friendly acidic natural deep eutectic solvents (NADESs) to replace conventional harmful pre-treatment chemicals and organic solvents. Brewer’s spent grain (BSG) and novel malt dust (MD) biomass sources, both obtained from beer production, were characterized and studied for their potential as PC sources. HTE, paired with mild acidic malic acid/choline chloride (MA) NADES, was compared against conventional (heated and stirred maceration) and modern (microwave-assisted extraction; MAE) state-of-the-art extraction methods. The quantification of key PC in BSG and MD using liquid chromatography (HPLC) indicated that the combination of elevated temperatures and acidic NADES could provide significant improvements in PC extraction yields ranging from 251% (MD-MAC-MA: 29.3 µg/g; MD-HTE-MA: 103 µg/g) to 381% (BSG-MAC-MA: 78 µg/g; BSG-HTE-MA: 375 µg/g). The superior extraction capacity of MA NADES over non-acidic NADES (glycerol/choline chloride) and a traditional organic solvent mixture (acetone/H2O) could be attributed to in situ acid-catalysed pre-treatment facilitating the release of bound PC from lignin–hemicellulose structures. Qualitative 13C-NMR and pyro-GC-MS analysis was used to verify lignin–hemicellulose breakdown during extraction and the impact of high-temperature MA NADES extraction on the lignin–hemicellulose structure. This in situ acid NADES-catalysed high-temperature pre-treatment during PC extraction offers a potential green pre-treatment for use in cascade valorisation strategies (e.g., lignin valorisation), enabling more intensive usage of available biomass waste stream resources.

Oscillation rheology, calorimetry and computed tomography: A practical toolkit combination of qualification for real poly(ethylene terephthalate) waste

The conventional qualification methodologies, such as internal viscosity measurement and Melt Flow Index (MFI) tests, which are routinely applied to pristine materials and homogenous waste, are not directly transferrable to the qualification process of plastic mixtures. The current investigation is oriented towards the development of a pragmatic suite of measurements techniques aimed at facilitating the qualification of diverse real polyethylene terephthalate (PET) waste streams. This is primarily achieved through the integration of oscillatory rheology, calorimetry and computed tomography (CT). Samples derived from both selective income (SI) and sorting residue (SR) of a manual selective waste sorting plant are included, along with an examination of PET material originating from refuse-derived fuel (RDF). To establish references for comparison, manually collected bottles with (BCL) and without (B) caps and labels are employed, leveraging their known composition and purity. Calorimetry reveals that the glass transition temperature (Tg) is the most sensitive parameter for tracking the structural and compositional changes in waste PET-based streams. The utilization of temperature sweep test in rheology for determining the melting temperature (Tm) proves advantageous, offering a significantly shorter measurement time (∼1:24) compared to calorimetry. Importantly, this approach yields the Tm of the genuine composition rather than individual components. Detection of metal content contaminations in PET waste streams is made possible through CT, while frequency tests in rheological measurements demonstrate effectiveness in discerning their effects.

Bioproduction of cerium-bearing magnetite and application to improve carbon-black supported platinum catalysts

BackgroundBiogeochemical processing of metals including the fabrication of novel nanomaterials from metal contaminated waste streams by microbial cells is an area of intense interest in the environmental sciences.ResultsHere we focus on the fate of Ce during the microbial reduction of a suite of Ce-bearing ferrihydrites with between 0.2 and 4.2 mol% Ce. Cerium K-edge X-ray absorption near edge structure (XANES) analyses showed that trivalent and tetravalent cerium co-existed, with a higher proportion of tetravalent cerium observed with increasing Ce-bearing of the ferrihydrite. The subsurface metal-reducing bacterium Geobacter sulfurreducens was used to bioreduce Ce-bearing ferrihydrite, and with 0.2 mol% and 0.5 mol% Ce, an Fe(II)-bearing mineral, magnetite (Fe(II)(III)2O4), formed alongside a small amount of goethite (FeOOH). At higher Ce-doping (1.4 mol% and 4.2 mol%) Fe(III) bioreduction was inhibited and goethite dominated the final products. During microbial Fe(III) reduction Ce was not released to solution, suggesting Ce remained associated with the Fe minerals during redox cycling, even at high Ce loadings. In addition, Fe L2,3 X-ray magnetic circular dichroism (XMCD) analyses suggested that Ce partially incorporated into the Fe(III) crystallographic sites in the magnetite. The use of Ce-bearing biomagnetite prepared in this study was tested for hydrogen fuel cell catalyst applications. Platinum/carbon black electrodes were fabricated, containing 10% biomagnetite with 0.2 mol% Ce in the catalyst. The addition of bioreduced Ce-magnetite improved the electrode durability when compared to a normal Pt/CB catalyst.ConclusionDifferent concentrations of Ce can inhibit the bioreduction of Fe(III) minerals, resulting in the formation of different bioreduction products. Bioprocessing of Fe-minerals to form Ce-containing magnetite (potentially from waste sources) offers a sustainable route to the production of fuel cell catalysts with improved performance.Graphical

Waste Prediction Approach Using Hybrid Long Short-Term Memory with Support Vector Machine

As climate change increases the risk of extreme rainfall events, concerns over flood management have also increased. To recover quickly from flood damage and prevent further consequential damage, flood waste prediction is of utmost importance. Therefore, developing a rapid and accurate prediction of flood waste generation is important in order to reduce disaster. Several approaches of flood waste classification have been proposed by various researchers, however only a few focus on prediction of flood waste. In this study, a Long Short-Term Memory (LSTM) and Support Vector Machine (SVM) approach is adapted to address these challenges. Two different raw datasets were obtained from the “Advancing Sustainable Materials Management: Facts and Figures 2015” source. The datasets were for 9 years (1960, 1970, 1980, 1990, 2000, 2005, 2010, 2014, 2015), and are labelled as the materials generated in the Municipal Waste Stream from 1960 to 2015 and the materials Recycled and Composted in Municipal Solid Waste from 1960 to 2015. The waste types were grouped as paper and paperboard (PP), glass (GI), metals (Mt), plastics (PI), rubber and leather (RL), textiles (Tt), wood (Wd), food (Fd), yard trimmings (YT) and miscellaneous inorganic wastes (IW).

Sustainability assessment of orange peel waste valorization pathways from juice industries

AbstractA wide variety of products such as high value-added bioactive materials, biofuels, biochemicals and bioplastics can be obtained by the valorization of waste streams in a comprehensive and holistic biorefinery concept. In this study a meta-analysis of the available technologies utilizing organic waste derived from the juice industry is conducted. Initially, a mass flow analysis is performed to quantitatively illustrate the available orange peel waste volumes in the EU followed by a geographic distribution. The overall sustainability of the available valorization scenarios is then analyzed by considering critical environmental, economic and energy indicators and comparing innovative and conventional valorization technologies. Innovative technologies are better in terms of energy requirements and extraction time and also, in product yield and environmental performance than the conventional ones (85.1%, 9.5% and 47.9% lower CO2 eq values for the extraction of essential oils, pectin and phenolic compounds respectively). In terms of orange peel waste valorization scenarios, landfilling shares the largest environmental impact, followed by thermochemical and biological conversion alternatives. Complex biorefinery schemes are proportionate to environmental performance and energy consumption, but inversely proportionate to production cost. Finally, a trade-off analysis illustrates a positive correlation between environmental indicators of the most under study valorization scenarios.

Effects of carbon-based conductive materials on semi-continuous anaerobic co-digestion of organic fraction of municipal solid waste and waste activated sludge

Organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS) are the most produced organic waste streams in urban centres. Their anaerobic co-digestion (AcoD) allows to generate methane (CH4) and digestate employable as renewable energy source and soil amendment, respectively, fully in accordance with circular bioeconomy principles. However, the widespread adoption of such technology is limited by relatively low CH4 yields that fail to bridge the gap between benefits and costs. Among strategies to boost AcoD of OFMSW and WAS, use of conductive materials (CMs) to promote interspecies electron transfer has gained increasing attention. This paper presents one of the few experimental attempts of investigating the effects of four different carbon(C)-based CMs (i.e., granular activated carbon – GAC, graphite – GR, graphene oxide – GO, and carbon nanotubes – CNTs) separately added in semi-continuous AcoD of OFMSW and thickened WAS. The presence of C-based CMs has been observed to improve CH4 yield of the control process. Specifically, after 63 days of operation (concentrations of GAC and GR of 10.0 g/L and of GO and CNTs of 0.2 g/L), 0.186 NL/gVS, 0.191 NL/gVS, 0.203 NL/gVS, and 0.195 NL/gVS of CH4 were produced in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.177 NL/gVS produced in the control process. Likewise, at the end of the test (i.e., after 105 days at concentrations of C-based CMs half of the initial ones), CH4 yields were 0.193 NL/gVS, 0.201 NL/gVS, 0.211 NL/gVS, and 0.206 NL/gVS in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.186 NL/gVS of the control process. Especially with regard to GR, GO, and CNTs, results obtained in the present study represent a significant advance of the knowledge on the effects of such C-based CMs to realistic and scalable AD process conditions respect to previous literature.