Fraction Of Municipal Solid Waste Research Articles

Microbial biomass production from enzymatically saccharified organic municipal waste and present microbial inhibitors

AbstractThe study investigated the potential of the organic fraction of municipal solid waste (OFMSW) for microbial biomass production. The compositional analysis of OFMSW showed richness in sugars, proteins, lipids, organic acids, and ethanol, suggesting promising cheap cultivation feedstock if inhibitory compounds are sustainably detoxified. The enzymatic hydrolysis with Cellic® CTec3 and AMG® 300 L BrewQ (Novozymes A/S) demonstrated excellent saccharification of sugar polymer, reaching 92% glucan hydrolysis and 70% xylan hydrolysis. However, higher enzymatic dosages led to a rise in the total organic acids content, potentially causing increased microbial inhibition. Full hydrolysate and hydrolysate after solids removal were cultivated with seven robust microbial strains. Cultivation on hydrolysate with solids showed consumption of sugars and organic acids solely by commercial backer yeast Saccharomyces cerevisiae. Removal of solids from hydrolysate resulted in increased performance of tested strains, showing consumption of measured organic acids and ethanol by S. cerevisiae, Yarrowia lipolytica DSM 8218, and Cutaneotrichosporon oleaginosus ATCC 20509. Remarkably, the investigation of biomass production revealed superior cell mass formation and detoxification by S. cerevisiae, resulting in 18.9 g of biomass/L hydrolysate with 50% of crude protein (w/w) in shake flasks and 13.2 g/L of hydrolase with 46% of crude protein (w/w) in a 5-L bioreactor. Furthermore, bioreactor cultivation confirmed organic acids and ethanol conversion into biomass, highlighting S. cerevisiae’s suitability for utilizing OFMSW for microbial biomass production. These findings contribute to advancements in biowaste-to-fodder conversion, promoting the development of a more sustainable circular economy. Graphical abstract

Organic Fraction Municipal Solid Waste Compost and Horse Bean Green Manure Improve Sustainability of a Top-Quality Tobacco Cropping System: The Beneficial Effects on Soil and Plants

Organic Fraction Municipal Solid Waste Compost and Horse Bean Green Manure Improve Sustainability of a Top-Quality Tobacco Cropping System: The Beneficial Effects on Soil and Plants

Black soldier fly larvae efficiently bioconvert the organic fraction of municipal solid waste thanks to the functional plasticity of their midgut

Abstract The saprophagous larvae of Hermetia illucens show promising potential as effective agents for bioconverting organic waste and by-products into valuable biomass. Their capability to efficiently transform organic substrates, varying in nutrient content, origin, texture, and moisture, is strictly correlated with the morphofunctional complexity of their digestive system and the associated microbiota. In addition, post-ingestion mechanisms are set in motion to regulate the midgut activity depending on the feeding substrate, thus ensuring the nutritional requirements of the larvae. This study aims to assess the capability of H. illucens larvae to grow and biotransform the organic fraction of municipal solid waste (OFMSW). In particular, the larvae were reared on substrates mimicking the OFMSW with different nutrient content, and their growth and bioconversion performance, as well as the quality of larval and pupal biomass were evaluated. Our results demonstrate that the nutritional composition of the rearing substrates had minimal impact on the efficiency of the bioconversion process and on the protein, lipid, and chitin content of the insect biomass. This was due to a fine transcriptional regulation of genes encoding enzymes involved in protein, polysaccharide, and lipid digestion in midgut cells. As a consequence, larvae reared on OFMSW with the lowest protein, starch, and lipid content exhibited a significant increase in protease, amylase, and lipase activities. Overall, this study highlights the value of H. illucens larvae in valorising the OFMSW, demonstrating that variations in its composition do not significantly affect the quality of the bioconversion process. These findings hold significant practical implications as current strategies for OFMSW treatment remain unsatisfactory and innovative approaches are needed to enhance bio-waste recycling and reduce the environmental impact of waste management.

A Hybrid Energy System Based on Externally Fired Micro Gas Turbines, Waste Heat Recovery and Gasification Systems: An Energetic and Exergetic Performance Analysis

The opportunities related to the adoption of synthetic gaseous fuels derived from solid biomass are limited by the issues caused by the peculiarities of the syngas. The aim of this paper is to analyze several possible layouts of hybrid energy systems, in which the main thermal source is the organic fraction of municipal solid wastes. The case of a small community of about 1000 persons is analyzed in this paper. The examined layouts coupled an externally fired micro gas turbine with a waste heat recovery system based on both an Organic Rankine Cycle and supercritical CO2 gas turbines. A thermodynamic analysis has been carried out through the use of the commercial software Thermoflex 31, considering the losses of each component and the non-ideal behavior of the fluids. The results of the numerical analysis highlight that the introduction of a waste heat recovery system leads to an increase of at least 16% in the available net power, while a cascade hybrid energy grid can lead to a power enhancement of about 29%, with a considerable increase also in the energetic and exergetic global efficiencies.

Optimization of Liquid-State Anaerobic Digestion by Defining the Optimal Composition of a Complex Mixture of Substrates Using a Simplex Centroid Design

This study aimed to define the optimal composition of three heterogeneous substrates of the anaerobic digestion process to maximize methane production. The investigated substrates were sewage sludge (SS), the organic fraction of municipal solid waste (OFMSW), and horse waste (HW). The optimal composition of these substrates was defined using the mixture design and, more specifically, the simplex–centroid mixture design. Customized methods and materials were employed to study the complex mixture design of these substrates. The findings revealed that the optimal mixture involved all three substrates with the composition 0.17 HW, 0.66 SS, and 0.17 OFMSW, which demonstrated the highest methane yield at 269 NmL·gVS−1. In addition, a mathematical model was developed to predict methane production based on a specific composition of co-substrates. The results were validated at the small pilot scale.

Valorizing Combustible and Compostable Fractions of Municipal Solid Waste to Biochar and Compost as an Alternative to Chemical Fertilizer for Improving Soil Health and Sunflower Yield

Reduced reliance on synthetic chemical fertilizers necessarily requires using renewable biomaterial-derived soil organic amendments (SOAs) in agriculture for sustained retention of nutrients through improvement in the soil organic matter (SOM). SOM replenishment through SOAs derived from wasted materials could help in its valorization by furthering the sustainability prospects of agronomic crop production systems. In the current study, compost (CP) and biochar (BC) were derived as SOAs from combustible and compostable fractions of municipal solid waste (MSW) for their potential valorization by adding SOAs as potential sustainable sources of nutrients as a replacement of chemical fertilizers (CF) for sunflower crops cultivated in potted soils. The experimental design included quadruplicated soil application of MSW-derived BC and CP in discrete and combined forms, each in three doses (% w:w), viz., low (L), medium (M), and high (H), i.e., BC-L, BC-M, BC-H; CP-L, CP-M, CP-H; and BC + CP-L, BC + CP-M, BC-CP-H. The results showed that, compared to the control (soil only), the sunflower growth and harvestable yield were significantly greater in BC + CF with a medium dose and were comparable to the growth and yield obtained in soils with CF. Sunflower growth in the discrete SOAs remained less than in the combined SOAs (BC + CP) and was attributed to the comprehensive soil health improvement rendered by the applied SOAs. The soil health improvement factors included SOM, CEC, and concentrations of total and available NPK. The dose-effect comparison of the SOAs showed highly variable trends, i.e., the sunflower growth did not correspond with the increase in dose of the SOAs. It is concluded that the combined application of BC + CP derived from MSW components at a medium dose could act as a potential alternative to CF. The developed approach resulted in MSW valorization, which improved soil health and yielded a better sunflower crop.

Incentive policies in biomethane production toward circular economy

The transportation sector is marked by high emissions, and new sustainable solutions are required to solve this problem. Biomethane, also known as green gas, has the potential to regenerate certain wastes, promoting resource circularity. This study aimed at evaluating the profitability of small- and medium-sized plants using the organic fraction of municipal solid waste (OFMSW) and by-products, considering a new incentive decree within the mature biogas-biomethane market of Italy. Net present value (NPV) was used as a key indicator, and sensitivity, scenario, and risk analyses were proposed. The results showed that a high subsidy for by-products contributed to the profitability of by-products plants across multiple contexts. Conversely, stringent incentive values for the OFMSW led to diminished profitability for plants treating this substrate. Consequently, profitability was verified for 100 m3/h plants with by-products and 300 m3/h plants with the OFMSW. The break-even point analysis showed that the tariff value determining project profitability, contingent on size and substrate, ranged from 0.61 to 0.95 €/m3 for the OFMSW and 0.76–1.01 €/m3 for by-products. The results provide valuable policy and managerial insights, emphasizing the support needed for biomethane – a renewable and circular resource – to achieve the twin goals of energy independence and a low-carbon economy. Consequently, biomethane has the potential to contribute to the achievement of Sustainable Development Goals 7 and 12.

Advancing biorefinery technologies through transesterification and hydrothermal liquefaction for biodiesel and bioproducts production

BackgroundThe multicriteria assessment of advancing biorefinery to produce biodiesel (fatty acid methyl ester), glycerol, and torrefied pellets is a strategic approach towards sustainable development. MethodsA successive transesterification process was applied to separate lipids with alcohol, with a 1:7 mass-to-mass ratio in the presence of a heterogeneous catalyst of chitosan/polyvinyl alcohol-sodium hydroxide (CS/PVA-NaOH), to produce biodiesel and glycerol. Moreover, the remaining biomass is extracted to produce torrefied pellets by applying torrefaction through hydrothermal liquefication at 200–300 ℃ temperature. The biorefinery system using 613 kg organic fraction of municipal solid waste (OFMSW) produced 127.3 L of biodiesel, 14.5 kg of glycerol, and 387.5 kg of torrefied pellets. The whole systematic approach revealed two distinct areas with required characterized equipment such as dryer (A = 721.28m2), suspended in tank (V = 751.56m3), reactor (V = 721.56m3), cyclone (A = 743.48 m2), grinder (Q = 1352.31 m3/h), compactor (Q = 1367.31 m3/h), correspondingly. A gate-to-gate life cycle assessment (LCA) was performed for life cycle impact assessment (LCIA) through GaBi by using the ReCiPe 2016 Mid-point (H) and Endpoint (H) approach with a functional unit of 1000 kg municipal solid waste (MSW). Significant findingsThe economic assessment reveals the economic feasibility of the biorefinery project. The annual revenue determined the profitability index, which is $ 1.59 million annually, with a payback period of 1.8 years. The environmental analysis determined an eco-friendly production unit which can save 13.6% of carbon emissions by alternate use of photovoltaic energy. Conclusively, the calculated values and findings prove that biorefinery development using OFMSW is scientifically a win-win situation and notably assists in achieving circular bioeconomy and sustainable development goals (SDGs).

Kinetic Model Implementation of Fluidized Bed Devolatilization

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

New insight into the spatio-temporal patterns of functional groups of hotspot inside the composting aggregates by synchrotron-based FTIR in hyperthermophilic composting

Hyperthermophilic composting (HTC) is a recently developed and highly promising organic fraction of municipal solid waste (OFMSW) treatment technology. Investigation of organic matter (OM) dynamics in compost particle is thus crucial for the understanding of humification of HTC process. Herein, this work aimed to study the chemical and structural changes of OM at the molecular level during HTC of OFMSW using EEM and SR-FTIR analyses. Additionally, two-dimensional correlation spectroscopy (2D-COS) was also utilized to probe and identify the changes in chemical constituents and functional groups of organic compounds on the surface of compost particles during different composting periods. Results show that SR-FTIR can detect fine-scale (~μm) changes in functional groups from the edges to the interior of compost particles during different composting periods by mapping the particles in situ. In the hyperthermophilic stage (day 9), the extracted μ-FTIR spectrum reveals a distinct boundary between anaerobic and aerobic regions within the compost particle, with a thickness of anaerobic zone (1460 cm−1) of approximately 30 μm inside the particle's core. This provides direct evidence of anaerobic trends at compost microscales level within compost particles. 2D-COS analysis indicated that organic functional groups gradually agglomerated in the order of 1330 > 2930 > 3320 > 1600 > 1030 > 895 cm−1 to the core skeleton of cellulose degradation residues, forming compost aggregates with well physicochemical properties. Overall, the first combination of SR-FTIR and EEM provides complementary explanations for the humification mechanism of HTC, potentially introducing a novel methodology for investigating the environmental behaviors and fates of various organic contaminants associated with OM during the in-situ composting biochemical process.

Development of a comprehensive environmental guidance and sustainability assessment for different organic fraction of municipal solid waste-to-biofuel scenarios based on life cycle analysis

The environmental impact assessment of organic fraction of municipal solid waste (OF/MSW)-to-biofuel structures is essential prior to scaling them up to identify worrisome impacts on ecosystems, resources, human health, and climate. The current article aims to address a sustainable and comprehensive guide for analyzing the environmental impacts (based on the life cycle analysis (LCA)) of different OF/MSW-to-biofuel structures. To analyze different structures, three pre-treatment procedures (namely, hot water/acetone organosolv/acid), two different hydrolysis treatment ways (acidic/enzymatic), and different fermentation alternative methods (ethanolic/acetone-ethanol-butanol fermentations) were considered. The findings of the research indicated that scenarios based on acetone-ethanol-butanol fermentation cannot address a favorable environmental performance (due to the insufficiency of the avoided effects of the output products to compensate the environmental burdens caused by acetone pre-treatment). In contrast, scenarios based on ethanolic fermentation integrated with hot water or acid-based pre-treatment process can address superior environmental performances compared to scenarios based on acetone-ethanol-butanol fermentation and ethanolic (with acetone pre-treatment). Comprehensively, Scenario S-4 (as most eco-friendly Scenario) yielded the greatest net environmental savings with reductions of −857.16 potentially disappeared fraction/m2 per year, −214.3 kg CO2 equivalent per ton of/MSW, and −3.33 GJ per ton of/MSW processed.

Enhanced thermophilic high-solids anaerobic digestion of organic fraction of municipal solid waste with spatial separation from conductive materials in a single reactor volume

Despite benefits such as lower water and working volume requirements, thermophilic high solids anaerobic digestion (THSAD) often fails due to the rapid build-up of volatile fatty acids (VFAs) and the associated drop in pH. Use of conductive materials (CM) can promote THSAD through stimulation of direct interspecies electron transfer (DIET), while the need for their constant dosing due to poor separation from effluent impairs economic feasibility. This study used an approach of spatially separating magnetite and granular activated carbon (GAC) from the organic fraction of municipal solid waste (OFMSW) in a single reactor for THSAD. GAC and magnetite addition could both mitigate the severe inhibition of methanogenesis after VFAs build-up to ∼28–30 g/L, while negligible methane production was observed in the control group. The highest methane yield (286 mL CH4/g volatile solids (VS)) was achieved in magnetite-added reactors, while the highest maximum CH4 production rates (26.38 mL CH4/g VS/d) and lowest lag-phase (2.83 days) were obtained in GAC-added reactors. The enrichment of GAC and magnetite biofilms with various syntrophic and potentially electroactive microbial groups (Ruminiclostridium 1, Clostridia MBA03, Defluviitoga, Lentimicrobiaceae) in different relative abundances indicates the existence of specific preferences of these groups for the nature of CM. According to predicted basic metabolic functions, CM can enhance cellular processes and signals, lipid transport and metabolism, and methane metabolism, resulting in improved methane production. Rearrangement of metabolic pathways, formation of pili-like structures, enrichment of biofilms with electroactive groups and a significant improvement in THSAD performance was attributed to the enhancement of the DIET pathway. Promising results obtained in this work due to the spatial separation of the bulk OFMSW and CM can be useful for modeling larger-scale THSAD systems with better recovery of CM and cost-effectiveness.

A Review of the Production of Hyaluronic Acid in the Context of Its Integration into GBAER-Type Biorefineries

Biorefineries (BRFs) that process the organic fraction of municipal solid waste and generate bioproducts and bioenergies have attracted attention because they can simultaneously address energy and environmental problems/needs. The objective of this article was to critically review the microbial production of hyaluronic acid (MPHA) and its production profile for its integration into a GBAER-type BRF (a type of BRF based on organic wastes) and to identify the environmental and economic sustainability aspects of the modified BRF that would confirm it as a sustainable option. It was found that the MPHA by selected strains of pathogenic Streptococci was moderate to high, although the trend to work with genetically transformed (GT) (innocuous) bacteria is gaining momentum. For instance, A GT strain of Corynebacterium glutamicum reached a maximum HA production of 71.4 g L−1. MPHA reports that use organic wastes as sources of carbon (C) and nitrogen (N) are scarce. When alternative sources of C and N were used simultaneously, HA production by S. zooepidemicus was lower than that with conventional sources. We identified several knowledge gaps that must be addressed regarding aspects of process scale-up, HA industrial production, economic feasibility and sustainability, and environmental sustainability of the MPHA.

Review of Municipal Organic Waste Management in Uttar Pradesh State, India

Organic waste is the main fraction of municipal solid waste in most developing countries. Despite various efforts, municipalities often fail to properly handle generated waste due to poor source segregation, inefficient collection system, insufficient financial resources, and a lack of proper treatment and disposal facilities. In India, organic waste mainly ends up in open dumpsites. The Government of India launched the Swachh Bharat Mission and enacted legislation to improve solid waste management. This notwithstanding, the most populous state of the country, Uttar Pradesh (UP), faces serious challenges in terms of achieving the national environmental policy goals. This study attempts to assess organic management practices in UP by analyzing the existing situation. The study reviewed the legal and financial frameworks governing the waste sector, the responsibility of stakeholders, waste segregation and collection mechanisms in place, and treatment and disposal methods. The identified gaps were analyzed to provide recommendations for the local conditions. The study recommends the control of incoming materials in centralized facilities compost facilities to enhance compost quality and enhance the management of organic waste via source segregation, animal feeding, and treatment in a decentralized manner.

Biomethane recovery and prokaryotic shifts in anaerobic co-digestion of food waste and paper waste in organic fraction of municipal solid waste: Effect of paper content

Biomethane recovery from paper waste (PW) was achieved by mesophilic co-digestion with food waste. The feeding material containing 0%, 20%, 40% and 50% of PW in total solids (TS) were investigated in the long-term continuous operation. The results showed that the biogas production, pH, alkalinity and biodegradation of volatile solids (79.8 ± 3.6%) were stable for PW contents no more than 50%. The PW = 50% condition was considered the critical limit for the reasons of pump clogging, sufficient alkalinity (2.0 ± 0.3 g-CaCO3/L) and depletion of ammonia. Prokaryotic diversity indices decreased with the increased PW contents. Great shifts were observed in the prokaryotic communities before and after the PW contents reaches 50% as TS (18.4% as total weights). Biomethane recovery yields were deceasing from 445 to 350 NL-CH4/kg-fed-volatile-solids. The PW contents as 40% as TS (13.1% as total weights) obtained the optimal performance among all the feeding conditions.

Single mixed refrigerant biomethane liquefaction plant integrated with solar energy: Dynamic simulation for the decarbonization of the heavy road transport sector

This works proposes a dynamic thermoeconomic analysis of a liquefied biomethane production plant to meet the fuel demand of a fleet of heavy duty trucks in the south of Italy. The biomethane is obtained from the upgrading of the biogas produced by means of anaerobic digestion through a plug flow reactor fed by organic fraction of municipal solid waste. The upgrading of the biogas is realized using a three-stage membrane compression process, producing a 96 % pure biomethane. The biomethane liquefaction is realized using a single-mixed refrigerant process and compared to a Linde cycle process. The whole system is assisted by solar energy to reduce the fossil energy consumption of the process and feed-in tariffs are considered as funding policy. The models for the anaerobic digestion, the biogas upgrading, and the biomethane liquefaction are in detail developed in MatLab. The anaerobic digestion model is based on the ADM1 biological model, integrated with a suitable heat transfer model. The biogas upgrading model is based on a simplified Fick model. The liquefaction model is based on an equivalent two heat-exchangers model, taking into account the transient heat transfer. All the components are then integrated in TRNSYS to perform the dynamic simulation for one operating year of the whole system. Results from the thermoeconomic analysis are outstanding in terms of profitability, showing a payback period of less than 2 years and a Net Present Value of the system of 402 M€. The great environmental impact is also confirmed by a Primary Energy Saving of 91 % and a dramatic reduction of 86 % of the CO2 equivalent emissions.

Syngas Purpose Pyrolysis-Gasification of Organic Fractions of MSW over Metal-Loaded Y-Zeolite Catalysts

The increasing environmental consideration and the growth of instability of the energy market call for methods that can process the organic fraction of municipal solid waste (OFMSW) into fuel instead of disposal. Due to the pyrolysis and gasification that are efficient procedures to achieve valuable products, gasification of OFMSW with different particle sizes and compositions was carried out in the presence of Ni and Ni-Ce-loaded Y-zeolite in a multizone tubular kiln reactor. During the experiments, 500°C was applied in the first reactor zone, while the 2nd zone was at an elevated temperature of 600°C or 900°C in the presence of steam. The combined pyrolysis and gasification experiments were also carried out without a catalyst with the same operating conditions. The feedstock was collected from the organic fraction of a Hungarian mechanical-biological treatment (MBT) plant and was separated into four different fractions based on particle size: <1 cm dry biomass and fine particles, 1-2 cm paper-rich, 2-6 cm paper and plastic-rich feedstocks, and <6 cm mixture of these fractions. During the experimental work, product yields; gaseous product composition; the ratio of H2/CO, CO2/CO, and CH4/CO; and lower heating value were determined in the function of feedstock composition, the applied temperature, and catalysts. It was found that the hydrogen content and H2/CO ratio of gaseous products were increased due to catalyst application and temperature elevation in the 2nd reactor zone. The addition of Ce to the Ni/Y-zeolite catalyst was advantageous in the case of hydrogen formation at a lower temperature (600°C). The hydrogen and methane content of products obtained from the catalytic pyrolysis-gasification of paper and plastic-rich OFMSWs on elevated temperatures were higher, which increased the lower heating value of those products. Based on the elemental analysis of the obtained solid residues, it was found that paper/plastic-rich feedstock released hydrogen and carbon with a higher extent. 1-2 cm feedstock-related solid residues had the highest H/C ratio which caused a 12.5-12.8 MJ/kg gross heating value. As a result, combined pyrolysis and gasification appear to be an efficient method to attain valuable outputs from OFMSW not only in gas but also in solid products.

Anaerobic digestion or composting? Small-scale plants design and holistic evaluations in a Sub-Saharan African context

In small developing settings, is it worth building anaerobic digestion (AD) or composting plants? This study explores the economic, management, and environmental dimensions of two small-scale alternatives for organic fraction municipal solid waste (OFMSW) treatment within the context of Lacor Hospital (Uganda): aerated static pile composting (S1) and AD with digestate composting (S2), both designed to manage approximately 347.5 tOFMSW annually. In the optimistic scenario, S1 achieves a cost savings of about −2.9 USD tOFMSW−1, while S2 incurs costs of 2.1 USD tOFMSW−1. In the pessimistic scenario, S1's costs rise to 3.9 USD tOFMSW−1, while S2 becomes more expensive at 9.5 USD tOFMSW−1. Management analysis underlines S2's complexity due to AD operations and digestate drying. Total normalized environmental impacts of S1 can be quantified with about 0.125 mPt tOFMSW−1, whereas S2 is equal to about −6.163 mPt tOFMSW−1. However, in an optimistic scenario, climate change endpoint category results are similar. On balance, the LCA analysis indicates that AD can be better than standalone composting. However, in developing settings serving approximately 3000 inhabitants, it is crucial to prioritize economic and management sustainability that can be obtained only by small-scale composting plants. These findings provide definite insights for small-scale waste management projects in low-income regions, offering valuable data and references for plant design and their replicability. The study sets the ultimate definition of the most feasible option to treat OFMSW in low-income settings: community composting. Unfortunately, economic barriers remain the main challenge: citizens should pay for the service and landfill management fees should be set by local governments.

Rheological insights into the degradation behavior of PP/HDPE blends

The (re-)processing and degradation behavior of polypropylene (PP) blends with high-density polyethylene (HDPE) is a crucial topic in mechanical recycling due to the prevalence of PP/HDPE mixtures. In particular, small amounts of cross-contamination (below 10.0 wt.%) between these polyolefins are quite common. While much empirical data is available, systematic studies on such blends are scarce and rarely account for the polymers’ chain structure. This study employs time-resolved rheology, atomic force microscopy (AFM), differential scanning calorimetry (DSC) and chemiluminescence techniques to study the degradation of different PP types containing 0.5 to 10.0 wt.% of HDPE. It is observed that the addition of small amounts of HDPE can result in a prominent change in the viscoelastic properties of PP during the thermo-oxidative degradation. The substantial evolution of elasticity in the blends is mainly related to the gelation of fine PE particles dispersed within the PP matrix. It is also shown that a smaller viscosity ratio between the blend components can lead to a more significant degradation through morphology alterations. Remarkably, time-resolved rheology studies revealed that even a small amount of HDPE (2.5 wt.%) can lead to a reduction in the thermo-oxidative stability of the PP/HDPE blend through excessive branching/crosslinking of the HDPE phase. This effect was particularly more pronounced when the PP contained an ethylene comonomer in its backbone. The finer morphology of PE particles in PP copolymer can exacerbate the thermo-oxidative stability of the blend. These insights are essential in designing new life cycles for recycled PP cross-contaminated with HDPE, typically found in the light fraction of municipal solid plastic waste.

Anaerobic sludge from a full-scale biodigester: physico-chemical and organic characterization, and principal component analysis (PCA)

The biological transformation of the organic fraction of municipal solid waste into bioenergy yields a solid digested material known as anaerobic sludge, comprising a mixture of organic and inorganic substances. This sludge holds significant potential as a renewable resource for agricultural reuse. However, there is also the potential risk of contamination from this material in receiving environments. Therefore, it is crucial to assess the characteristics of this material to ensure compliance with local regulations regarding its soil application, aiming to avoid adverse environmental impacts and ensure proper and viable disposal. In this study, conducted to explore the characteristics of bottom sludge collected from a pilot-scale anaerobic biodigester, various parameters were analyzed. The biodigester in question had a capacity of 1300 liters and a useful volume of 1000 liters, digesting food waste and water hyacinth (Eichhornia crassipes) in a ratio of 20% in terms of volatile solids from the macrophyte to the volatile solids of the food waste. A multivariate analysis was conducted on the following parameters: metals (Al, Ba, Cd, Cr, Cu, Fe, Mn, Mo, Pb, Se, V, Zn, Na, and K); total, fixed, and volatile solids; alkalinity; volatile fatty acids; ammonia; Kjeldahl nitrogen (NTK); and organic, inorganic, and total carbon (COT), to observe possible correlations among these parameters. Additionally, the sludge underwent nuclear magnetic resonance (NMR) analysis for detection and characterization of organic compounds. This approach provided a deeper understanding of the properties of anaerobic sludge produced strictly under the aforementioned conditions, contributing to further research in the field.