Waste to Carbon: Biocoal from Elephant Dung as New Cooking Fuel

Conserved core microbiota in managed and free-ranging Loxodonta africana elephants

The gut microbiota plays a crucial role in animal health and homeostasis, particularly in endangered species conservation. This study investigated the fecal microbiota composition of European captive-bred African savanna elephants (Loxodonta africana) housed in French zoos, and compared it with wild African savanna elephants. Fecal samples were collected and processed for DNA extraction and amplicon sequencing of the 16S rRNA gene. The analysis of α and β diversity revealed significant effects of factors such as diet, daily activity, and institution on microbiota composition. Specifically, provision of branches as part of the diet positively impacted microbiota diversity. Comparative analyses demonstrated distinct differences between captive and wild elephant microbiomes, characterized by lower bacterial diversity and altered co-occurrence patterns in the captive population. Notably, specific taxa were differentially abundant in captive and wild elephants, suggesting the influence of the environment on microbiota composition. Furthermore, the study identified a core association network shared by both captive and wild elephants, emphasizing the importance of certain taxa in maintaining microbial interactions. These findings underscore the impact of environment and husbandry factors on elephant gut microbiota, highlighting the benefits of dietary enrichment strategies in zoos to promote microbiome diversity and health. The study contributes to the broader understanding of host-microbiota interactions and provides insights applicable to conservation medicine and captive animal management.

Can Biochar Improve the Sustainability of Animal Production?

Animal production is a significant contributor of organic and inorganic contaminants in air, soil, and water systems. These pollutants are present beginning in animal houses and impacts continue through manure storage, treatment, and land application. As the industry is expected to expand, there is still a lack of affordable, sustainable solutions to many environmental concerns in animal production. Biochar is a low-cost, sustainable biomaterial with many environmental remediation applications. Its physicochemical properties have been proven to provide environmental benefits via the adsorption of organic and inorganic contaminants, promote plant growth, improve soil quality, and provide a form of carbon sequestration. For these reasons, biochar has been researched regarding biochar production, and application methods to biological systems have a significant influence on the moisture content, pH, microbial communities, and carbon and nitrogen retention. There remain unanswered questions about how we can manipulate biochar via physical and chemical activation methods to enhance the performance for specific applications. This review article addresses the positive and negative impacts of biochar addition at various stages in animal production from feed intake to manure land application.

Properties of Animal-Origin Ash—A Valuable Material for Circular Economy

In the presented paper, two types of animal-origin biomass, cow dung and chicken litter, are characterized in terms of combustion-related problems and ash properties. It was found that these parameters strongly depend on the farming style. Whether it is cow dung or chicken litter, free-range raw materials are characterized by higher ash contents than industrial farming ones. Free-range samples contain chlorine at lower levels, while industrial farming samples are chlorine rich. Free-range samples are characterized by the predominant content of silica in the ash: 75.60% in cow dung and 57.11% in chicken litter, while industrial farming samples contain more calcium. Samples were classified by 11 “slagging indices” based on the ash and fuel composition to evaluate their tendencies for slagging, fouling, ash deposition and bed agglomeration. Furthermore, an assessment was made against the current EU law regulations, whether the ashes can be component materials for fertilizers. The phosphorus concentration in the investigated ashes corresponds to 4.09–23.73 wt% P2O5 and is significantly higher in industrial chicken litter samples. The concentrations of Hg, Cu, As, Ni, Cd and Pb in all samples are below the limits of the UE regulations. However, concentrations of Cr in all samples and Zn in industrial chicken litter exceed these standards.

Lab-Scale Study of Temperature and Duration Effects on Carbonized Solid Fuels Properties Produced from Municipal Solid Waste Components

In work, data from carbonization of the eight main municipal solid waste components (carton, fabric, kitchen waste, paper, plastic, rubber, paper/aluminum/polyethylene (PAP/AL/PE) composite packaging pack, wood) carbonized at 300–500 °C for 20–60 min were used to build regression models to predict the biochar properties (proximate and ultimate analysis) for particular components. These models were then combined in general models that predict the properties of char made from mixed waste components depending on pyrolysis temperature, residence time, and share of municipal solid waste components. Next, the general models were compared with experimental data (two mixtures made from the above-mentioned components carbonized at the same conditions). The comparison showed that most of the proposed general models had a determination coefficient (R²) over 0.6, and the best prediction was found for the prediction of biochar mass yield (R² = 0.9). All models were implemented into a spreadsheet to provide a simple tool to determine the potential of carbonization of municipal solid waste/refuse solid fuel based on a local mix of major components.

Mitigation of Gaseous Emissions from Stored Swine Manure with Biochar: Effect of Dose and Reapplication on a Pilot-Scale

Rural communities are affected by gaseous emissions from intensive livestock production. Practical mitigation technologies are needed to minimize emissions from stored manure and improve air quality inside barns. In our previous research, the one-time surficial application of biochar to swine manure significantly reduced emissions of NH3 and phenol. We observed that the mitigation effect decreased with time during the 30-day trials. In this research, we hypothesized that bi-weekly reapplication of biochar could improve the mitigation effect on a wider range of odorous compounds using a larger scale and longer trials. The objective was to evaluate the effectiveness of biochar dose and reapplication on mitigation of targeted gases (NH3, odorous, volatile organic compounds VOCs, odor, greenhouse gases (GHG)) from stored swine manure on a pilot-scale setup over 8-weeks. The bi-weekly reapplication of the lower biochar dose (2 kg/m2) showed much higher significant percentage reductions in emissions for NH3 (33% without and 53% with reapplication) and skatole (42% without and 80% with reapplication), respectively. In addition, the reapplication resulted in the emergence of a statistical significance to the mitigation effect for all other targeted VOCs. Specifically, for indole, the percentage reduction improved from 38% (p = 0.47, without reapplication) to 78% (p = 0.018, with reapplication). For phenol, the percentage reduction improved from 28% (p = 0.71, without reapplication) to 89% (p = 0.005, with reapplication). For p-cresol, the percentage reduction improved from 31% (p = 0.86, without reapplication) to 74% (p = 0.028, with reapplication). For 4-ethyl phenol, the percentage emissions reduction improved from 66% (p = 0.44, without reapplication) to 87% (p = 0.007, with reapplication). The one-time 2 kg/m2 and 4 kg/m2 treatments showed similar effectiveness in mitigating all targeted gases, and no statistical difference was found between the dosages. The one-time treatments showed significant percentage reductions of 33% and 42% and 25% and 48% for NH3 and skatole, respectively. The practical significance is that the higher (one-time) biochar dose may not necessarily result in improved performance over the 8-week manure storage, but the bi-weekly reapplication showed significant improvement in mitigating NH3 and odorous VOCs. The lower dosages and the frequency of reapplication on the larger-scale should be explored to optimize biochar treatment and bring it closer to on-farm trials.

Thermal Treatment of Biomass: A Bibliometric Analysis—The Torrefaction Case

The aim of the paper was to summarize and discuss current research trends in biomass thermal treatment (torrefaction process). Quantitative analyses were carried out, in which the main countries, research units and scientists were indicated. The analysis showed a clear upward trend in number of publications after 2010. Most scientists on selected topics come from China, USA, Canada, South Korea, Republic of China, Poland (Web od Science—Core Collection (WoS-CC) and Scopus databases). Quantitative analysis also showed that the most relevant WoS-CC categories in the summary are: Energy Fuels, Engineering Chemical, Agricultural Engineering, Biotechnology Applied Microbiology and Thermodynamics and Scopus Subject area: Energy, Chemical Engineering, Environmental Science, Engineering and Chemistry. Thematic analysis included research topics, process parameters and raw materials used. Thematic groups were separated: torrefaction process (temp.: 150–400 °C), hydrothermal carbonization process (HTC) (temp: 120–500 °C), pyrolysis process (temp.: 200–650 °C) and gasification and co-combustion process (temp.: 350–1600 °C). In the years 2015–2019, current research topics were: new torrefaction technologies (e.g., HTC), improvement of the physico-mechanical, chemical and energetic properties of produced fuel as well as the use of torrefied biomass in the process of pyrolysis, gasification and co-combustion. The raw materials used in all types of biomass thermal treatment were: energy crops, wood from fast-growing and exotic trees, waste from the agri-food industry, sewage sludge and microalgae.

The Prediction of Calorific Value of Carbonized Solid Fuel Produced from Refuse-Derived Fuel in the Low-Temperature Pyrolysis in CO2

The decrease in the calorific value of refuse-derived fuel (RDF) is an unintended outcome of the progress made toward more sustainable waste management. Plastics and paper separation and recycling leads to the overall decrease in waste’s calorific value, further limiting its applicability for thermal treatment. Pyrolysis has been proposed to densify energy in RDF and generate carbonized solid fuel (CSF). The challenge is that the feedstock composition of RDF is variable and site-specific. Therefore, the optimal pyrolysis conditions have to be established every time, depending on feedstock composition. In this research, we developed a model to predict the higher heating value (HHV) of the RDF composed of eight morphological refuse groups after low-temperature pyrolysis in CO₂ (300–500 °C and 60 min) into CSF. The model considers cardboard, fabric, kitchen waste, paper, plastic, rubber, PAP/AL/PE (paper/aluminum/polyethylene) composite packaging pack, and wood, pyrolysis temperature, and residence time. The determination coefficients (R²) and Akaike information criteria were used for selecting the best model among four mathematical functions: (I) linear, (II) second-order polynomial, (III) factorial regression, and (IV) quadratic regression. For each RDF waste component, among these four models, the one best fitted to the experimental data was chosen; then, these models were integrated into the general model that predicts the HHV of CSF from the blends of RDF. The general model was validated experimentally by the application to the RDF blends. The validation revealed that the model explains 70–75% CSF HHV data variability. The results show that the optimal pyrolysis conditions depend on the most abundant waste in the waste mixture. High-quality CSF can be obtained from wastes such as paper, carton, plastic, and rubber when processed at relatively low temperatures (300 °C), whereas wastes such as fabrics and wood require higher temperatures (500 °C). The developed model showed that it is possible to achieve the CSF with the highest HHV value by optimizing the pyrolysis of RDF with the process temperature, residence time, and feedstock blends pretreatment.

Mitigation of Gaseous Emissions from Swine Manure with the Surficial Application of Biochars

Environmental impact associated with odor and gaseous emissions from animal manure is one of the challenges for communities, farmers, and regulatory agencies. Microbe-based manure additives treatments are marketed and used by farmers for mitigation of emissions. However, their performance is difficult to assess objectively. Thus, comprehensive, practical, and low-cost treatments are still in demand. We have been advancing such treatments based on physicochemical principles. The objective of this research was to test the effect of the surficial application of a thin layer (¼ inches; 6.3 mm) of biochar on the mitigation of gaseous emissions (as the percent reduction, % R) from swine manure. Two types of biochar were tested: highly alkaline and porous (HAP) biochar made from corn stover and red oak (RO), both with different pH and morphology. Three 30-day trials were conducted with a layer of HAP and RO (2.0 & 1.65 kg∙m−2, respectively) applied on manure surface, and emissions of ammonia (NH3), hydrogen sulfide (H2S), greenhouse gases (GHG), and odorous volatile organic compounds (VOCs) were measured. The manure and biochar type and properties had an impact on the mitigation effect and its duration. RO significantly reduced NH3 (19–39%) and p-cresol (66–78%). H2S was mitigated (16~23%), but not significantly for all trials. The phenolic VOCs had relatively high % R in most trials but not significantly for all trials. HAP reduced NH3 (4~21%) and H2S (2~22%), but not significantly for all trials. Significant % R for p-cresol (91~97%) and skatole (74~95%) were observed for all trials. The % R for phenol and indole ranged from (60~99%) and (29~94%) but was not significant for all trials. The impact on GHGs, isobutyric acid, and the odor was mixed with some mitigation and generation effects. However, larger-scale experiments are needed to understand how biochar properties and the dose and frequency of application can be optimized to mitigate odor and gaseous emissions from swine manure. The lessons learned can also be applicable to surficial biochar treatment of gaseous emissions from other waste and area sources.

Proof-of-Concept of High-Pressure Torrefaction for Improvement of Pelletized Biomass Fuel Properties and Process Cost Reduction

This paper provides a comprehensive description of the new approach to biomass torrefaction under high-pressure conditions. A new type of laboratory-scale high-pressure reactor was designed and built. The aim of the study was to compare the high-pressure torrefaction with conventional near atmospheric pressure torrefaction. Specifically, we investigated the torrefaction process influence on the fuel properties of wooden-pellet for two different pressure regimes up to 15 bar. All torrefaction processes were conducted at 300 °C, at 30 min of residence time. The initial analysis of the increased pressure impact on the torrefaction parameters: mass yields, energy densification ratio, energy yield, process energy consumption, the proximate analysis, high heating value, and energy needed to grind torrefied pellets was completed. The results show that high-pressure torrefaction needed up to six percent less energy, whereas energy densification in the pellet was ~12% higher compared to conventional torrefaction. The presence of pressure during torrefaction did not have an impact on the energy required for pellet grinding (p < 0.05).

The Impact of Surficial Biochar Treatment on Acute H2S Emissions during Swine Manure Agitation before Pump-Out: Proof-of-the-Concept

Acute releases of hydrogen sulfide (H2S) are of serious concern in agriculture, especially when farmers agitate manure to empty storage pits before land application. Agitation can cause the release of dangerously high H2S concentrations, resulting in human and animal fatalities. To date, there is no proven technology to mitigate these short-term releases of toxic gas from manure. In our previous research, we have shown that biochar, a highly porous carbonaceous material, can float on manure and mitigate gaseous emissions over extended periods (days–weeks). In this research, we aim to test the hypothesis that biochar can mitigate H2S emissions over short periods (minutes–hours) during and shortly after manure agitation. The objective was to conduct proof-of-the-concept experiments simulating the treatment of agitated manure. Two biochars, highly alkaline and porous (HAP, pH 9.2) made from corn stover and red oak (RO, pH 7.5), were tested. Three scenarios (setups): Control (no biochar), 6 mm, and 12 mm thick layers of biochar were surficially-applied to the manure. Each setup experienced 3 min of manure agitation. Real-time concentrations of H2S were measured immediately before, during, and after agitation until the concentration returned to the initial state. The results were compared with those of the Control using the following three metrics: (1) the maximum (peak) flux, (2) total emission from the start of agitation until the concentration stabilized, and (3) the total emission during the 3 min of agitation. The Gompertz’s model for determination of the cumulative H2S emission kinetics was developed. Here, 12 mm HAP biochar treatment reduced the peak (1) by 42.5% (p = 0.125), reduced overall total emission (2) by 17.9% (p = 0.290), and significantly reduced the total emission during 3 min agitation (3) by 70.4%. Further, 6 mm HAP treatment reduced the peak (1) by 60.6%, and significantly reduced overall (2) and 3 min agitation’s (3) total emission by 64.4% and 66.6%, respectively. Moreover, 12 mm RO biochar treatment reduced the peak (1) by 23.6%, and significantly reduced overall (2) and 3 min total (3) emission by 39.3% and 62.4%, respectively. Finally, 6 mm RO treatment significantly reduced the peak (1) by 63%, overall total emission (2) by 84.7%, and total emission during 3 min agitation (3) by 67.4%. Biochar treatments have the potential to reduce the risk of inhalation exposure to H2S. Both 6 and 12 mm biochar treatments reduced the peak H2S concentrations below the General Industrial Peak Limit (OSHA PEL, 50 ppm). The 6 mm biochar treatments reduced the H2S concentrations below the General Industry Ceiling Limit (OSHA PEL, 20 ppm). Research scaling up to larger manure volumes and longer agitation is warranted.

The Proof-of-the Concept of Biochar Floating Cover Influence on Swine Manure pH: Implications for Mitigation of Gaseous Emissions From Area Sources

Mitigation of potentially hazardous and malodor compounds emitted from animal waste is needed to improve the sustainability of livestock agriculture. Bacteria control the generation of these compounds and also depend on the pH of manure. Influencing swine manure pH, especially on the liquid-air interface, may lead to a reduction of emission of odorous and hazardous compounds. The objective of this experiment was to test highly alkaline and porous (HAP) modified biochar with pH = 9.2 and red oak (RO) biochar with pH = 7.5 influence on swine manure pH acquired from the outdoor storage and deep pit storage under a barn. HAP and RO biochars were topically applied on the outdoor-stored (pH = 7.55), and pit (pH = 8.00) manures and spatial pH (every 1 mm of depth) were measured on days 0, 2, and 4. Results showed that HAP biochar increased outdoor-stored manure pH on day 4, particularly within the top 10 mm of depth, where pH ranged from 7.79 to 8.90, while in the case of RO pH ranged between 7.46 and 7.66, i.e., similar to control (7.57-7.64). Both biochars decreased pit-stored manure pH within the top 10 mm of depth (in comparison with the control pH of 8.36-8.47) to 8.19-8.30 (HAP), and 8.18-8.29 (RO) on day 4. However, differences were not considerable. The reason for the insignificant effect of biochars on pit manure was likely due to its higher buffer capacity in comparison with the outdoor-stored manure.

Waste to Energy: Solid Fuel Production from Biogas Plant Digestate and Sewage Sludge by Torrefaction-Process Kinetics, Fuel Properties, and Energy Balance

Sustainable solutions are needed to manage increased energy demand and waste generation. Renewable energy production from abundant sewage sludge (SS) and digestate (D) from biogas is feasible. Concerns about feedstock contamination (heavy metals, pharmaceuticals, antibiotics, and antibiotic-resistant bacteria) in SS and D limits the use (e.g., agricultural) of these carbon-rich resources. Low temperature thermal conversion that results in carbonized solid fuel (CSF) has been proposed as sustainable waste utilization. The aim of the research was to investigate the feasibility of CSF production from SS and D via torrefaction. The CSF was produced at 200~300 °C (interval of 20 °C) for 20~60 min (interval 20 min). The torrefaction kinetics and CSF fuel properties were determined. Next, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of SS and D torrefaction were used to build models of energy demand for torrefaction. Finally, the evaluation of the energy balance of CSF production from SS and D was completed. The results showed that torrefaction improved the D-derived CSF’s higher heating value (HHV) up to 11% (p < 0.05), whereas no significant HHV changes for SS were observed. The torrefied D had the highest HHV of 20 MJ∙kg−1 under 300 °C and 30 min, (the curve fitted value from the measured time periods) compared to HHV = 18 MJ∙kg−1 for unprocessed D. The torrefied SS had the highest HHV = 14.8 MJ∙kg−1 under 200 °C and 20 min, compared to HHV 14.6 MJ∙kg−1 for raw SS. An unwanted result of the torrefaction was an increase in ash content in CSF, up to 40% and 22% for SS and D, respectively. The developed model showed that the torrefaction of dry SS and D could be energetically self-sufficient. Generating CSF with the highest HHV requires raw feedstock containing ~15.4 and 45.9 MJ∙kg−1 for SS and D, respectively (assuming that part of feedstock is a source of energy for the process). The results suggest that there is a potential to convert biogas D to CSF to provide renewable fuel for, e.g., plants currently fed/co-fed with municipal solid waste.

Influence of Torrefaction and Pelletizing of Sawdust on the Design Parameters of a Fixed Bed Gasifier

Gasification of biomass in fixed bed gasifiers is a well-known technology, with its origins dating back to the beginning of 20th century. It is a technology with good prospects, in terms of small scale, decentralized power co-generation. However, the understanding of the process is still not fully developed. Therefore, assessment of the changes in the design of a gasifier is typically performed with extensive prototyping stage, thus introducing significant cost. This study presents experimental results of gasification of a single pellet and bed of particles of raw and torrefied wood. The procedure can be used for obtaining design parameters of a fixed bed gasifier. Results of two suits of experiments, namely pyrolysis and CO2 gasification are presented. Moreover, results of pyrolysis of pellets are compared against a numerical model, developed for thermally thick particles. Pyrolysis time, predicted by model, was in good agreement with experimental results, despite some differences in the time when half of the initial mass was converted. Conversion times for CO2 gasification were much longer, despite higher temperature of the process, indicating importance of the reduction reactions. Overall, the obtained results could be helpful in developing a complete model of gasification of thermally thick particles in a fixed bed.

Low-Temperature Pyrolysis of Municipal Solid Waste Components and Refuse-Derived Fuel—Process Efficiency and Fuel Properties of Carbonized Solid Fuel

New technologies to valorize refuse-derived fuels (RDFs) will be required in the near future due to emerging trends of (1) the cement industry’s demands for high-quality alternative fuels and (2) the decreasing calorific value of the fuels derived from municipal solid waste (MSW) and currently used in cement/incineration plants. Low-temperature pyrolysis can increase the calorific value of processed material, leading to the production of value-added carbonized solid fuel (CSF). This dataset summarizes the key properties of MSW-derived CSF. Pyrolysis experiments were completed using eight types of organic waste and their two RDF mixtures. Organic waste represented common morphological groups of MSW, i.e., cartons, fabrics, kitchen waste, paper, plastic, rubber, PAP/AL/PE composite packaging (multi-material packaging also known as Tetra Pak cartons), and wood. The pyrolysis was conducted at temperatures ranging from 300 to 500 °C (20 °C intervals), with a retention (process) time of 20 to 60 min (20 min intervals). The mass yield, energy densification ratio, and energy yield were determined to characterize the pyrolysis process efficiency. The raw materials and produced CSF were tested with proximate analyses (moisture content, organic matter content, ash content, and combustible part content) and with ultimate analyses (elemental composition C, H, N, S) and high heating value (HHV). Additionally, differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA) of the pyrolysis process were performed. The dataset documents the changes in fuel properties of RDF resulting from low-temperature pyrolysis as a function of the pyrolysis conditions and feedstock type. The greatest HHV improvements were observed for fabrics (up to 65%), PAP/AL/PE composite packaging (up to 56%), and wood (up to 46%).

Waste-to-Carbon: Is the Torrefied Sewage Sludge with High Ash Content a Better Fuel or Fertilizer?

Sewage sludge (SS) recycling is an important part of the proposed ‘circular economy’ concept. SS can be valorized via torrefaction (also known as ‘low-temperature pyrolysis’ or ‘roasting’). SS can, therefore, be considered a low-quality fuel or a source of nutrients essential for plant growth. Biochar produced by torrefaction of SS is a form of carbonized fuel or fertilizer. In this research, for the first time, we tested the feasibility of torrefaction of SS with high ash content for either fuel or organic fertilizer production. The research was conducted in 18 variants (six torrefaction temperatures between 200~300 °C, and three process residence times of 20, 40, 60 min) in 5 repetitions. Fuel and fertilizer properties and multiple regression analysis of produced biochar were conducted. The higher heating value (HHV) of raw SS was 21.2 MJ·kg⁻¹. Produced biochar was characterized by HHV up to 12.85 MJ·kg⁻¹ and lower H/C and O/C molar ratio. Therefore, torrefaction of SS with high ash content should not be considered as a method for improving the fuel properties. Instead, the production of fertilizer appears to be favorable. The torrefaction increased C, N, Mg, Ca, K, Na concentration in relation to raw SS. No significant (p < 0.05) influence of the increase of temperature and residence time on the increase of biogenic elements in biochar was found, however the highest biogenic element content, were found in biochar produced for 60 min, under the temperature ranging from 200 to 240 °C. Obtained biochars met the Polish regulatory criteria for mineral-organic fertilizer. Therefore SS torrefaction may be considered a feasible waste recycling technology. The calculation of torrefaction energy and the mass balance shows energy demand <2.5 GJ∙Mg⁻¹ w.m., and the expected mass yield of the product, organic fertilizer, is ~178 kg∙Mg⁻¹ w.m of SS. Further investigation should consider the scaling-up of the SS torrefaction process, with the application of other types of SSs.