Feedstock Mixture Research Articles

Co-pyrolysis of plastic waste and macroalgae Ulva lactuca, a sustainable valorization approach towards the production of bio-oil and biochar

To address the pressing demand for sustainable energy in light of environmental challenges, this study explored the synergetic effects of the co-pyrolysis of polyethylene terephthalate (PET) and Ulva lactuca macroalgae to yield bio-oil and biochar. The objective is to enhance the bio-oil quality for wider usability and to combat marine pollution. By employing co-pyrolysis, notable progress has been achieved in bio-oil yield and quality, particularly in hydrocarbon content, through the integration of PET. The highest bio-oil yield of 37.91 % was achieved under optimal conditions at 500 °C with a feedstock mixture consisting of 40 % U. lactuca and 60 % PET. Under these conditions, the bio-oil exhibited a significant increase in hydrocarbon content, reaching 57.16 %, which is essential for improving its energy potential. Biochar quality was also enhanced, with the biochar from a 70 % U. lactuca and 30 % PET blend showing a BET surface area of 20.18 m2/g, compared to the initial 1.38 m2/g of raw U. lactuca, indicating improved surface properties. This study presents a sustainable energy generation and environmental preservation approach, underscoring the potential of synergistically utilizing marine resources and plastic waste.

CO2 sequestration by indirect mineral carbonation of serpentine with (NH4)2SO4 as a recyclable extractant

Mineral carbonation with serpentine can offer a sustainable and safe process option for simultaneous CO2 emission reduction and utilization of nature mineral. In this study, a sustainable process for CO2 mineral sequestration was proposed by using serpentine and ammonium sulfate as feedstocks. The mixture of feedstocks was subjected to roasting with temperature ranging from 390°C to 480°C, converting magnesium into the corresponding sulfate. Then, water leaching was employed to dissolve the magnesium sulfate from the roasted samples. Finally, through a mineralization reaction, the corresponding magnesium bicarbonate was generated after sequestrating CO2. Under the optimal roasting-leaching conditions, i.e. roasting temperature of 420ºC, roasting time of 2 hours, and mass ratio of ammonium sulfate/serpentine of 3; leaching temperature of 80ºC, leaching time of 1 hour, and a liquid-to-solid ratio of 1, the magnesium extraction efficiency reached 76 %. Thermodynamics and experimental results demonstrated that during the sulfation roasting process, the products generated during roasting, magnesium sulfate and silicon dioxide, adhered to the surface of the serpentine, thus inhibiting the mass transfer process and impeding the progress of the reaction. However, the liquid-solid reaction facilitated by molten ammonium sulfate and the gas-solid reaction provided by the decomposition of ammonium salts into SO2 played a promoting role in the sulfation roasting reaction. The carbonation of sulfated serpentine results indicated that the optimal CO2 storage capacity can reach 204 kg/t serpentine.

Integrating Anaerobic Digestion With Struvite Production for Enhanced Nutrient Recovery, Pathogen Reduction, and Circularity in Manure Management

ABSTRACTIntroductionAnaerobic digestion (AD) is essential for manure management, generating biogas and nutrient‐rich digestate for organic fertilizer. However, improper digestate use can pose environmental risks. Recovering struvite, a magnesium ammonium phosphate (MAP) compound, from digestate provides a sustainable, controlled‐release fertilizer, supporting a circular economy in agriculture.Materials and MethodsThe study employed a two‐stage (liquid–solid) AD process using poultry, dairy, and swine manures, along with wasted corn silage. Digestates were sampled for physicochemical and biogas quality analyses, with feedstocks categorized into D1 and D2, and a composite (D3) formed for struvite characterization. Microbial populations were enumerated on selective media, and struvite mineral content was analysed via argon plasma emission spectrometry.ResultsThe digesters processing feedstock mixtures D1 and D2 achieved specific methane yields of 1.26 L/g CODs fed and 1.49 L/g CODs fed, with cumulative biogas production of 374 and 369 L, respectively, over four 77‐day cycles. The two‐stage AD process significantly reduced antibiotic‐resistant, Enterobacteriaceae and Enterococcus spp. Total ammoniacal nitrogen (TAN) recovery rates were high at 98%–99%, with a consistent struvite crystal mass of 0.67 g/10 mL, indicating the efficiency of this integrated process. The agronomic value of struvite was determined, indicating its potential utility as a fertilizer, and scanning electron microscopy analysis revealed diverse crystal structures, warranting further investigation into their implications for usage and storage.ConclusionThe results suggests that the two‐stage AD process efficiently transforms organic waste into high‐quality biogas, reduces antibiotic‐resistant bacteria, and facilitates nutrient recovery through struvite precipitation. This approach supports co‐digestion of multi‐substrates and promotes circular economy principles, with potassium or sodium phosphate enhancing struvite recovery for sustainable agriculture.

Ethanol production from the wood and fruit juice of paper mulberry via simultaneous saccharification and juice co-fermentation under normal and very high gravity conditions

A novel batch simultaneous saccharification and juice co-fermentation (SSJcF) process was investigated using mixtures of PHP (phosphoric acid plus hydrogen peroxide) pretreated wood and fruit juice of paper mulberry tree. All the different substrate mixture configurations evaluated under normal gravity SSJcF (total sugar titer of 180 g/L) significantly improved both ethanol concentration and yield compared to sole simultaneous saccharification and fermentation (SSF) of paper mulberry wood. Among the different mixing ratios, the feedstock mixture with equal sugar content from each substrate resulted in maximum ethanol concentration, yield and productivity of 77.1 g/L, 83.9 % and 1.1 g/L/h, respectively. The external additions of mineral nutrients also had no impact on fermentation performance of the mixture. Furthermore, SSJcF was evaluated under different levels of high gravity (HG) and very high gravity (VHG) conditions. The total sugar titer of 350 g/L at equal contributions from each substrate reached very high ethanol concentration of 147.0 g/L, with yield and productivity of 82.3 % and 1.5 g/L/h, respectively. By implication, the PM wood and fruit juice mixture could serve as suitable low-cost and non-food feedstock alternative to the typical use of sugary and/or starchy feedstocks for VHG fermentation.

Vigna mungo (L.) Hepper as Heterogeneous Catalyst for Generation of Biodiesel from a Mixture of Multiple Oil Feedstocks

A cost-effective catalyst is essential to reduce the expenses of producing biodiesel. This study is aimed at utilizing the waste of the black gram (Vigna mungo (L.) Hepper) plant as an efficient catalyst for producing biodiesel from a blend of different edible and inedible oils. The catalyst was developed by igniting the dried material and then subjecting it to calcination at 550°C for 2 h. The feedstock was prepared by mixing the oils in an equivalent ratio for the reaction. Various sophisticated techniques such as XRD, FT-IR, XPS, BET, FESEM-EDX, HRTEM, and SAED were employed to characterize the prepared catalyst. The catalyst’s catalytic activity was assessed by transesterification of the oil mixture. The optimized transesterification conditions were 10 wt% of catalyst loading, 9 : 1 of MTOR, 65°C of reaction temperature, and 1.6±0.14 h of reaction time producing 94.79±0.27% of biodiesel yield and 96.86% oil conversion. The calcined catalyst’s alkaline solubility was found to be 2.77 mmol/g, basicity as 0.13 mmol/g, and 14.57 per hour as the turnover frequency (TOF). Catalyst reusability was conducted and found that the catalyst could be reprocessed up to three successive cycles. The synthesized biodiesel’s physicochemical characteristics were assessed and found to conform to ASTM D6751 and EN 14214 requirements.

Quantification of degree of interactions during co-pyrolysis of nine typical carbonaceous wastes

Organic municipal waste is a mixture of carbonaceous feedstock and cross-interaction of volatiles in their co-pyrolysis has been well documented, but quantifying their extent of interactions in co-pyrolysis is difficult. In this study, the ratio of char yield from co-pyrolysis to calculated average of pyrolysis of single feedstock was used as an indicator to probe the interaction in co-pyrolysis of every two typical carbonaceous wastes (sawdust, rice, spinach, chicken manure, office paper, corrugated paper, plastic bottles/films, fiber towel) at 550 °C. The results indicated that the co-pyrolysis of sawdust and corrugated paper had the highest degree of interaction (0.44). Sawdust and rice with ash-rich feedstock (spinach, chicken manure and office paper) resulted in dominance of gasification reactions to reduce char production in co-pyrolysis process. In comparison, the organics from the degradation of spinach and corrugated/office paper could react with the derivatives (mostly radicals) of plastic bottle (PET), plastic film (PE) or fiber towel (polyesters) via secondary condensation to generate more char. The chicken manure with high ash content hardly forms char of enhanced yield during its co-pyrolysis with other feedstocks. The enhancing char yield through secondary condensation generally resulted in additional oxygen-containing deposit on char and reduced thermal stability, which was the opposite to the formation of char with dominance of gasification. Co-pyrolysis of varied feedstock also led to change of morphologies of char via filling mechanism or formation of organics.

Larval Frass of Hermetia illucens as Organic Fertilizer: Composition and Beneficial Effects on Different Crops.

Hermetia illucens has received a lot of attention as its larval stage can grow on organic substrates, even those that are decomposing. Black soldier fly breeding provides a variety of valuable products, including frass, a mixture of larval excrements, larval exuviae, and leftover feedstock, that can be used as a fertilizer in agriculture. Organic fertilizers, such as frass, bringing beneficial bacteria and organic materials into the soil, improves its health and fertility. This comprehensive review delves into a comparative analysis of frass derived from larvae fed on different substrates. The composition of micro- and macro-nutrients, pH levels, organic matter content, electrical conductivity, moisture levels, and the proportion of dry matter are under consideration. The effect of different feeding substrates on the presence of potentially beneficial bacteria for plant growth within the frass is also reported. A critical feature examined in this review is the post-application beneficial impacts of frass on crops, highlighting the agricultural benefits and drawbacks of introducing Hermetia illucens frass into cultivation operations. One notable feature of this review is the categorization of the crops studied into distinct groups, which is useful to simplify comparisons in future research.

Factors influencing synergistic pyrolysis of biomass and polypropylene for alcohols and hydrocarbon production

Results are presented on the co-pyrolysis of different blends of rapeseed stalk and plastic polypropylene (100:0, 75:25, 50:50, 25:75 and 0:100) using thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and pyrolyzer-gas chromatography/mass spectrometry (Py-GC/MS), independently. The effect of temperature (450, 550 and 650 °C) on the synergistic effect between rapeseed stalk and polypropylene at different blend ratios as well as on the yield and amounts of alcohols and hydrocarbons produced are presented. The thermogravimetric analysis results showed that at the same temperature, increase of polypropylene in the mixture, gradually increased the intensity and rate of pyrolysis reaction. The weight loss data revealed improved pyrolysis during the process. The Fourier transform infrared spectroscopy results showed that the transmittance of ketones, esters and acids increased while the content of ketones, esters and acids decreased with increased polypropylene in the mixture. The pyrolyzer-gas chromatography/mass spectrometry results showed that temperature and feedstock mixture ratio had an impact on the yield and amounts of alcohols and hydrocarbons. The pyrolysis effect was most favorable at 550 °C temperature and rapeseed stalk/polypropylene mixture ratio of 1:3. These results provide some practical insights on clean energy recovery from mixtures of agricultural residues and waste plastics using thermochemical conversion.

Harnessing Biogas in India: A Sustainable Pathway for Sustainable Energy Development

The review underscores the pivotal role of the Indian biogas sector in addressing the challenges posed by inadequate sanitation practices, exploring how the biogas sector is a potentially transformative force for waste management and energy production. Decentralized biogas facilities utilizing various organic materials, including agricultural waste, kitchen waste, organic industrial waste, sewage sludge, and floral waste, have reshaped rural landscapes. These facilities electrify remote villages, benefiting over 5 million residents and reducing energy expenses by 40%. Critically, these efforts preserve vital ecosystems, exemplified by the rejuvenation of 10,000 hectares of mangroves in the Sundarbans, sequestering an impressive 500,000 metric tons of CO2 annually. Innovative technologies, such as the anaerobic digestion process and advanced biogas production systems featuring improved gas purification techniques, two-stage digesters, and optimized feedstock mixtures, play a crucial role in this sustainability journey. These advancements boost biogas yields by 20%. Importantly, byproducts like digestate are efficiently upcycled into 500 Mt of high-quality biofertilizers annually, significantly enhancing crop yield, particularly wheat and maize, by 15%. Moreover, the transformative impact extends to environmental sustainability by converting digestate into 1,000 Mt of biodegradable plastics, leading to a 30% reduction in traditional plastics usage. Government support and well-crafted policies have been instrumental, with subsidies driving the adoption of biogas digesters in 50,000 households, creating 5,000 jobs, and reducing methane emissions by 2 MMt annually. Biogas catalyzes integrated sustainability, accompanying cleaner environments, improved livelihoods, and resilient ecosystems by harmonizing sanitation, energy, and ecosystem preservation.

Thermochemical Co-Liquefaction of Fruit Pomace’s Blends in a Binary Solvent System Toward Value-Added Bioproducts

Abstract Poland belongs to the most meaningful producers of fresh food products in the European Union, e.g., apples, cherries, carrots, as well as currants. A significant part of these products are subjected to further processing, which results in the generation of an abundant amount of wet residues, such as pomace. The present paper aims to investigate the possibility of co-processing various industrial residues in the form of fruit pomaces through thermochemical liquefaction toward high-energy-density biocrude and biochar. More specifically, industrial wastes received from commercial juice production, i.e., blackcurrant, apple, and cherry pomaces, were converted under subcritical conditions of the water-isopropyl alcohol solvent system at fixed conditions. Particular focus was put on testing binary and ternary mixture feedstock systems and the possibility of predicting the bioproduct yield. Furthermore, the quality of the resultant biocrudes was analyzed by means of FTIR, GC-MS, and elemental analysis. For all separately studied raw materials and their binary and ternary mixtures, the dominant group fraction was biocrude with its yield ranging between 45.8 and 54.5 wt%. Produced liquids exhibit high energy density (HHV between 30.1 and 32.4 MJ/kg); thus, all of them pose perspective alternative fuels for generating heat and electricity. Also, the solid biochars presented a high energy density (HHV around 24–26 MJ/kg) and can be considered as an alternative energy carrier. The postulated approach aims to increase the flexibility and profitability of future technology of processing useless waste toward value-added bioproducts for the chemical and energy sectors.

Manual wooden low-pressure briquetting press: An alternative technology of waste biomass utilisation in developing countries of Southeast Asia

Although briquetting is an appropriate technology for the production of renewable energy, its widespreadness in Southeast Asia is limited. Especially due to the high initial investments and energy consumption of a high-pressure briquetting press. However, manual low-pressure briquetting presses (operating pressure <5 MPa) can represent a relevant alternative, regarding to their ease of use and modest energy consumption. The aim of the present research was to develop and verify a manual wooden low pressure briquetting press with a square-shaped pressing chamber, piston and a single lever as a pressing unit. In practice, press was designed, manufactured, and verified by successful bio-briquette samples production. Four different feedstock mixtures were prepared from coconut mesocarp fibre (CF), bamboo skin (BS), pineapple leaves (PL), sugarcane bagasse (SB); each mixed with external binding agent (wastepaper) in biomass:binder ratios of 1:1 and 2:1. The achieved bulk density ρ ranged from 204.30 ± 15.73 kg m−3 for 1:1 feedstock mixtures and 199.31 ± 23.13 kg m−3 for 2:1 feedstock mixtures. The press efficiency, feasibility and practicability were positively evaluated within their possible utilisation in rural areas of developing countries. The importance of research increases constantly due to the worldwide need for a transition from fossil fuels to renewable energy sources, proper waste management, and reduction of environmental and health risks related to improper treatment of waste materials. The final idea of the article contributes to the development of the sector of clean green energy production, simultaneously with raising awareness about sustainable technologies for proper waste management within the wide public.

Optimization of Process Variables in the production of Biodiesel from Jatropha-Neem Hybrid Feed stock Mixture

In the search for suitable clean and renewable fuels to replace conventional diesel, alternatives such as biodieselsare being researched upon daily. Challenges of low biodiesel yield per hectare of vegetable oils have prompted the need for optimization. This research is aimed at optimizing process variables in the production of biodiesel from the mixture of Jatropha and Neem seed oils. A 31-run Central Composite Design was employed in a response surface optimization process; four independent process variables, namely temperature, time, catalyst concentration and mixing speed were optimized in an alkali based transesterification process of biodiesel synthesis. The result was a 97.05% biodiesel yield from Jatropha –Neem hybrid mixture.

Fused Filament Fabrication for Metallic Materials: A Brief Review.

Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technology mostly used to produce thermoplastic parts. However, producing metallic or ceramic parts by FFF is also a sintered-based AM process. FFF for metallic parts can be divided into five steps: (1) raw material selection and feedstock mixture (including palletization), (2) filament production (extrusion), (3) production of AM components using the filament extrusion process, (4) debinding, and (5) sintering. These steps are interrelated, where the parameters interact with the others and have a key role in the integrity and quality of the final metallic parts. FFF can produce high-accuracy and complex metallic parts, potentially revolutionizing the manufacturing industry and taking AM components to a new level. In the FFF technology for metallic materials, material compatibility, production quality, and cost-effectiveness are the challenges to overcome to make it more competitive compared to other AM technologies, like the laser processes. This review provides a comprehensive overview of the recent developments in FFF for metallic materials, including the metals and binders used, the challenges faced, potential applications, and the impact of FFF on the manufacturing (prototyping and end parts), design freedom, customization, sustainability, supply chain, among others.

Microstructural Modification of Cold-Sprayed Ti-Cr3C2 Composite Coating by Laser Remelting

Laser processing is an effective post-treatment method for modifying the structure and improving the properties of cold-sprayed coatings. In the present work, the possibility of fabricating a hard and wear-resistant Ti-based cermet coating by cold spray followed by laser remelting was studied. A mixture of titanium and chromium carbide powders in a ratio of 60/40 wt.% was deposited by cold spray onto a titanium alloy substrate, which ensured the formation of a composite coating with a residual chromium carbide content of about 12–13 wt.%. The optimal values of laser beam power (2 kW) and scanning speed (75 mm/s) leading to the qualitative fusion of the coating with the substrate with minimal porosity and absence of defects were revealed. The microstructure and phase composition of as-sprayed and remelted coatings were examined with SEM, EDS and XRD analysis. It was shown that the phase composition of the as-sprayed coating did not change compared to the feedstock mixture, while the remelted coating was transformed into a β-Ti(Cr) solid solution with uniformly distributed nonstoichiometric TiCx particles. Due to the change in microstructure and phase composition, the remelted coating was characterized by an attractive combination of higher microhardness (437 HV0.1) and lower specific wear rate (0.25 × 10−3 mm3/N × m) under dry sliding wear conditions compared to the as-sprayed coating and substrate. Laser remelting of the coating resulted in a change in the dominant wear mechanism from oxidative–abrasive to oxidative–adhesive with delamination.

Effect of ethanol additive on bio-mix biodiesels from a raw mixture of various feedstocks

Effect of ethanol additive on bio-mix biodiesels from a raw mixture of various feedstocks

H2-rich gas production from co-gasification of biomass/plastics blends: A modeling approach

East Asia experiencing massive population growth, which will certainly challenge traditional waste management systems. In recent years, gasification has attracted much attention since it converts carbon-based residues into valuable gas and requires cheaper gas cleaning equipment compared to available technologies. This study presents an ASPEN plus model for simulation of steam co-gasification of polyethylene (PE) and pine (PI) using various temperatures (740–830 °C), steam/waste ratio, S/W (0.5–0.8) and PE content in the feedstock mixture (0–60 %). The predicted results were compared with the experimental data available in the literature, and a good agreement was achieved. In general, an increase in gasifier temperature and S/W led to higher H2 production and lower tar content in the syngas resulting from co-gasification process. Regarding tar conversion, increasing the gasifier temperature played a more important role compared to adding steam to the gasifier. H2 content and H2 yield gradually increased from 33.01 to 47.81 % and 48.09–57.76 g/kg, respectively, when PE increased from 0 to 60 %, which may be due to a greater amount of hydrogen present in PE. Over a PE content range from 0 to 60 %, tar concentration had a nearly linear increase, which can be attributed to lower oxygen content available in the mixture.

Simulation of co-pyrolysis of coffee ground and waste polystyrene foam in a tilted-slide reactor

Coffee ground is considered one of the promising biomass resources because it is one of the most popular beverages and has higher calorific value than other kinds of biomass. In the previous study on the fast pyrolysis of coffee ground, the viscosity of the pyrolysis oil was found to be very high and it was suggested to mix some amount of alcohol to reduce its viscosity. The quality of the pyrolysis oil also can be improved by mixing synthesis polymer such as polyethylene, polyethylene, or polystyrene as a feedstock. Recently, a tilted-slide reactor for fast pyrolysis was designed with a feeding capacity of 20 kg/h, in which no fluidizing gas is necessary for conveying hot sand. In the previous experiment, the co-pyrolysis of coffee ground and waste polystyrene foam was performed in the tilted-slide reactor. The ratio of waste polystyrene foam in the feedstock mixture was varied from 0% to 100% by weight, and fast pyrolysis was performed near the temperature of 550 °C. In this study, the co-pyrolysis was simulated by a commercial computational fluid dynamics code, and the results were compared with experimental results. A multistep kinetic mechanism was adopted for the pyrolysis of coffee ground and polystyrene. The volatile yields in the simulation approached the pyrolysis oil yields in the experiment by introducing a composite boundary condition to retain the unpyrolyzed polystyrene near the reactor bottom for longer residence time. The elemental composition and moisture contents became similar with measurement when increasing polystyrene blending ratio.

Assessing plastic and biomass-based biochar's potential for carbon sequestration: an energy-water-environment approach

Biochar from waste has emerged as a vital solution for multiple contemporary issues. While the organic content and porous structure of biochar have granted it multiple benefits. Where the use of biochar is proven to be beneficial for enhancing the soil structure and water and nutrients retention ability, therefore, saving water and boosting yields in arid regions. Moreover, biochar is capable to sequester carbon from the atmosphere and permanently store it within the soil. As such, this study evaluates the potential for carbon sequestration through biochar obtained from the pyrolysis of feedstock mixtures including camel manure, date pits, high-density polyethylene (HDPE) and low-density polyethylene (LDPE), and how it can enhance water and food security. Multiple energy and water supplying sources have been considered for different project scenarios to provide a broader understanding of biochar potentials. The lifecycle analysis (LCA) approach is utilized for the assessment of net emissions, while an economic study is conducted in Aspen Process Economic Analyser (APEA) to evaluate the feasibility of the different scenarios. Finally, single-objective optimization and multi-objective optimizations were carried out using excel and MATLAB genetic algorithm respectively to select optimal biomass blending and utilities options to fulfill the low cost and negative emissions targets. The assessment conducted for a Qatar case study indicates that the best waste blending scenario for maximum carbon sequestration potential was obtained at a mixing ratio of 20.4% Camel manure: 27% date pits: 26.3% LDPE: 26.4% HDPE. Furthermore, the optimum char blend for maximum carbon sequestration corresponding to the minimum cost of char mix was computed. The optimal biochar mixing percentage for highest net emission was obtained at a feedstock mixing ratio of 96.8% of date pits, 1.5% of LDPE, and 1.7% of HDPE with 0% of camel manure with an optimal cost of 313.55 $/kg biochar. Solar PV was selected as the best energy source in this pyrolysis study due to its reduced carbon emissions in comparison to other sources studied such as natural gas, coal and diesel. However, natural gas is selected to fulfill the economic objective. Moreover, the optimal water source was investigated including wastewater treatment, multi-stage flash and reverse osmosis desalination, where treated wastewater is selected as the optimal supply to fulfill both, economic and environmental objectives.

Supercritical water Co-gasification of biomass and plastic wastes for hydrogen-rich gas production using Ni-Cu/AC-CaO catalyst

Supercritical water gasification (SCWG) of sugar beet pulp (SBP) as lignocellulosic biomass and high-density polyethylene (HDPE) as plastic waste to produce hydrogen-rich gas is investigated. Factors affecting SCWG of SBP were investigated by experimental design method. The variable parameters included temperature (385–460 °C), reaction time (10–30 min) and feedstock concentration (0.25–3.25 wt%). 460 °C, 30 min and 1.04 wt% were identified as optimal points for the highest hydrogen yield. SCWG of SBP and HDPE blend with different ratios were carried out to investigate the synergetic effect of blending on the efficiency of total gas and hydrogen yields. Hydrogen production increased with increasing the ratio of HDPE in the feedstock mixture and reached its maximum of 8.95 mmol/g at the ratio of 40 wt% and then started to decrease. Using a low-cost catalyst (Ni–Cu/AC-CaO) for SCWG of blended feedstock enhanced the total gas and hydrogen yields by factors of 2.4 and 3.8, respectively.

Boosting butyrate and hydrogen production in acidogenic fermentation of food waste and sewage sludge mixture: a pilot scale demonstration

Within the urban scenario, the application of a biorefinery technology value chain can foster the conversion of different organic substrates into marketable and added-value products. In this work, a pilot-scale dark fermentation (DF) process has been carried out as a key step for volatile fatty acids (VFA) and hydrogen production from the liquid fraction of sewage sludge and food waste mixture. Six operating conditions have been monitored in terms of yield and process stability, by changing the hydraulic retention time (HRT) from 4 to 6 days and applying a short-term hyper-thermophilic hydrolysis (70 °C, 8 h) on the same feedstock mixture. A tubular centrifugation was utilized to remove part of the biosolids (driven to biogas production) before the DF step, which was applied on the soluble and/or colloidal organic matter only. The hydrolysis step favored the following acidification process, in which a fermentation yield up to 0.42 g CODVFA/g VS0 was achieved at 5 days as HRT. Hydrogen production (up to 34.4% v/v and 0.046 m3 H2/kg VS0) was positively affected by the hydrolysis application and by the decrease of the HRT, highlighting the possibility to produce biohythane in the modeled two-phases anaerobic bioprocess. On the other hand, without the application of the hydrolysis, a selective production of butyric acid (up to 75% COD basin) was achieved, furnishing a different valorization route for the chosen urban organic feedstock. Changes in operating conditions and performances were also reflected by the adaptation of the microbial community, whose characterization highlighted the occurrence of several fermentative microorganisms (e.g., Clostridiaceae, Ruminococcaceae).