Dry Digestibility Research Articles

Machine Learning for Enhancing Prediction of Biogas Production and Building a VFA/ALK Soft Sensor in Full-Scale Dry Anaerobic Digestion of Kitchen Food Waste

Based on operational data collected over 1.5 years from four industrial-scale dry anaerobic digesters used for kitchen food waste treatment, this study adopted eight typical machine learning algorithms to distinguish the best methane prediction model and to develop a soft sensor based on the VFA/ALK ratio. Among all the eight tested models, the CatBoost (CB) algorithm demonstrated superior performance in terms of prediction accuracy and model fitting. Specifically, the CB model achieved a biogas production prediction accuracy (R2) ranging from 0.604 to 0.915, and a VFA/ALK R2 between 0.618 and 0.768 on the test dataset. Furthermore, the feature importance analysis revealed that biomass amount into the dry anaerobic digester was the primary factor influencing biogas production. Chemical oxygen demand (COD) and total ammonia nitrogen (TAN) were identified as the most significant factors impacting the VFA/ALK indicator during dry anaerobic digestion, collectively contributing to nearly 50% of the influence. Overall, this study verifies the feasibility of using machine learning to predict biogas production in industrial-scale dry anaerobic digestion and provides a crucial foundation for monitoring the stability of dry anaerobic digesters.

Recovery of Titanium from Red Mud Using Carbothermic Reduction and High Pressure Leaching of the Slag in an Autoclave

Red mud is a by-product of alumina production, which is largely stored in landfills that can endanger the environment. Red mud, or bauxite residue, is a mixture of inorganic compounds of iron, aluminum, sodium, titanium, calcium and silicon mostly, as well as a large number of rare earth elements in small quantities. Although certain methods of using red mud already exist, none of them have been widely implemented on a large scale. This paper proposes a combination of two methods for the utilization of red mud, first by carbothermic reduction and then, by leaching under high pressure in an autoclave in order to extract useful components from it with a focus on titanium. In the first part of the work, the red mud was reduced with carbon at 1600 °C in an electric arc furnace, with the aim of removing as much iron as possible using magnetic separation. After separation, the slag is leached in an autoclave at different parameters in order to obtain the highest possible yield of titanium, aiming for the formation of titanium oxysulfate and avoiding silica gel formation. A maximal leaching efficiency of titanium of 95% was reached at 150 °C using 5 mol/L sulfuric acid with 9 bar oxygen in 2 h. We found that high-pressure conditions enabled avoiding the formation of silica gel during leaching of the slag using 5 mol/L sulfuric acid, which is a big problem at atmospheric pressure. Previously silica gel formation was prevented using the dry digestion process with 12 mol/L sulfuric acid under atmospheric pressure.

Cobalt-modified digestate-derived biochar enhances kitchen waste anaerobic dry digestion: Performance, microbial mechanisms, and metabolic pathways

To achieve simultaneous in-situ high-value utilization of digestate and efficient resource recovery of kitchen waste (KW). In this work, Co-modified digestate-derived biochar (DDB-Co) was prepared for the first time, the effects of DDB-Co on KW mesophilic dry anaerobic digestion were investigated, and the underlying mechanisms were elucidated. The results showed that the specific surface area of DDB-Co increased to 98.7 m2/g, which was 37.4 % higher than that of the unmodified group (DDB). DDB-Co exhibited a dose-dependent effect on biogas production from the KW dry digestion, with the optimal dose of 4.0 g/L (calculated on a solid content) DDB-Co yielding 205.3 mL/(g·VS) of biogas, representing an 80.9 % increase compared to the CK group. However, higher doses, such as 8.0 g/L DDB-Co, reduced the cumulative biogas production. Mechanistic analysis indicated that 4.0 g/L DDB-Co facilitated the dissolution of particulate organic matter and accelerates the conversion process of volatile fatty acids (VFA) in KW, thereby preventing excessive acidification. Microbial community structure analysis revealed that DDB-Co reduced microbial richness and diversity but selectively enriched microorganisms such as Lactobacillus and Methanothrix, accelerating the direct interspecific electron transfer (DIET) reaction rate and increasing biogas production. Metagenomic analysis demonstrated that DDB-Co primarily upregulated the relative abundances of key enzymes in the acetate decarboxylation methanogenesis pathway, such as acetate kinase (ackA), phosphate acetyltransferase (pta), and acetyl-CoA synthetase (acs), enhancing biogas yield and maintaining system stability. The findings of this work expand the high-value utilization pathways for digestate and provide an alternative solution for the efficient resource recovery of KW.

Evaluation of the efficiency of dry anaerobic digester in the production of biogas and fertilizer using activated sludge and plant waste.

The process of dry anaerobic digestion (DAD) is an effective economic and environmentally friendly method due to its features such as reducing the volume of waste, destroying pathogens, consuming less energy, and producing biogas rich in energy and fertilizer. This study was conducted on a pilot scale with a reactor volume of 24L in 30 days for three ratios of C/N: 30, 25, and 20 separately using a mixture of activated sludge and plant waste. During the process, the temperature, pH, and ratio of C/N were measured at certain times, and the percentage of gases produced by the Gas chromatography (GC) device was also measured. The results were compared with the National standard of Iran (Compost, Physical, and Chemical Specifications) at the end of the process. The results showed that the average volume of biogas produced in ratios of C/N: 30, 25, 20 is 1.7, 2.5, and 1.5L. d-1, respectively. The results showed that in the C/N ratio of 20, and 25, the amount of, C/N ratio and NO3 are in the range the standard of class 1, and the amount of Phosphorus pentoxide (P2O5) is in the range the standard of class 2. The results showed that the average microbial parameters in ratios of C/N: 30, 25, and 20 are lower than the national standard of Iran. The dry digester is an efficient method in waste treatment, methane gas production, and quality fertilizer close to the national standard of Iran.

Selective Precipitation of REE-Rich Aluminum Phosphate with Low Lithium Losses from Lithium Enriched Slag Leachate.

Currently, recycling of spent lithium-ion batteries is carried out using mechanical, pyrometallurgical and hydrometallurgical methods and their combination. The aim of this article is to study a part of the pyro-hydrometallurgical processing of spent lithium-ion batteries which includes lithium slag hydrometallurgical treatment and refining of the obtained leachate. Leaching was realized via dry digestion, which is an effective method capable of transferring over 99% of the present metals, such as Li, Al, Co, Cu, and others, to the leachate. In this work, the influence of three types of precipitation agents (NaOH, NH4OH, Na3PO4) on the precipitation efficiency of Al and Li losses was investigated. It was found that the precipitation of aluminum with NaOH can result in the co-precipitation of lithium, causing total lithium losses up to 40%. As a suitable precipitating agent for complete Al removal from Li leachate with a minimal loss of lithium (less than 2%), crystalline Na3PO4 was determined under the following conditions: pH = 3, 400 rpm, 10 min, room temperature. Analysis confirmed that, in addition to aluminum, the precipitate also contains the REEs La (3.4%), Ce (2.5%), Y (1.3%), Nd (1%), and Pr (0.3%). The selective recovery of these elements will be the subject of further study.

A novel bio-coagulation/co-digestion/pyrolysis scheme for banana pseudostem waste management: techno‑economic and sustainability approaches.

While several studies have focused on utilizing banana pseudostem waste (BPW) for wastewater treatment via bio-coagulation, this process still suffers from secondary pollution caused by the disposal of generated sludge. To avoid this pollution transfer issue, this study is the first to focus on the recyclability of post-coagulation sludge (PCS) to recover added-value products. For this purpose, BPW was used as a model bio-coagulant for the decontamination of laundry wastewater (LWW), followed by anaerobic digestion and pyrolysis schemes to recover biogas and biochar, respectively. In the first experiment, BPW succeeded in removing 55.44 ± 1.21%, 90.40 ± 3.09%, and 78.13 ± 2.44% of chemical oxygen demand (COD), turbidity, and surfactant, respectively, at the optimized condition (pH = 3.5, dosage = 2.34 g/L, stirring speed = 160.6 rpm, and settling time = 55.5 min). Inoculating the spent bio-coagulant with cattle manure (CM), with a mixing ratio of 1:1 (w:w), showed a biogas yield of 110.33 ± 6.02 mL/g COD. The synergetic effect of spent coagulant and microbes of CM was further validated by performing a COD mass balance, showing that about 31.52 ± 1.63% of CODfeed was converted to bio-CH4 (as COD). Further, the thermal treatment of digestate was successfully employed for biochar recovery at a yield of 0.58 ± 0.05 g biochar/g dry digestate. The study also revealed that the triple LWW treatment/biogas/biochar strategy could gain economic benefits with a payback period of 4.4 years. Hence, BPW could be used as a promising feedstock for pollution reduction, energy generation, and gaining profits.

Phytoremediation potential of seedlings: comparing heavy metal accumulation in Ailanthus, Acer, and Fraxinus species.

This study investigates the phytoremediation potential of non-productive seedlings of Ailanthus altissima, Acer pseudoplatanus, and Fraxinus excelsior for lead, cadmium, and zinc accumulation in contaminated soils of Zanjan Province, an industrial area with significant pollution. The evaluation employed a completely randomized design, with three treatment levels for each element, alongside a control treatment, replicated three times over a two-year period. A total of 810 one-year-old seedlings from the three species were involved in the study. Soil contamination levels, ranging from 0 to 2000mg/kg for lead and zinc and from 0 to 200mg/kg for cadmium, were administered through soil pot irrigation. Sampling of seedling stems and pot soils was conducted in November of 2021 and 2022. The absorption levels of elements in the samples were determined using the dry acid digestion method and an ICP-OES atomic absorption spectrometer. Results indicate species-specific variations in metal absorption, with Ailanthus showing the highest accumulation rates. Findings suggest Ailanthus as a promising candidate for soil improvement in polluted environments, particularly in contaminated soils of Zanjan Province.

From Food Waste to Sustainable Agriculture: Nutritive Value of Potato By-Product in Total Mixed Ration for Angus Bulls.

Raw potato fries are a type of potato by-product (PBP), and they have great potential as a partial replacement of grain in animal feeds to improve the environmental sustainability of food production. This study aimed to investigate the effects of replacing corn with different levels of PBP (0%, 12.84%, 25.65%, and 38.44%) in the total mixed ration (TMR) of Angus bull. Sixty 16-month-old Angus bulls (548.5 ± 15.0 kg, mean ± SD) were randomly assigned to four treatments. The results indicated that with the increase in the substitution amount of PBP, the body weight decreased significantly. The dry matter apparent digestibility and starch apparent digestibility linearly decreased as PBP replacement increased. The feed ingredient composition in the TMR varied, leading to a corresponding change in the rumen microbiota, especially in cellulolytic bacteria and amylolytic bacteria. The abundance of Succiniclasticum in the 12.84% PBP and 38.44% PBP diets was significantly higher than that in the 0% PBP and 25.65% PBP diets. The abundance of Ruminococcus linearly increased. In conclusion, using PBP to replace corn for beef cattle had no negative impact on rumen fermentation, and the decrease in apparent digestibility explained the change in growth performance. Its application in practical production is highly cost-effective and a strategy to reduce food waste.

Determination Ca, Cu, Fe, Mn, and Zn release from food in simple gastrointestinal extraction test

In this study, by conducting simulated in vitro digestion experiments on samples, the extraction rates of several essential metal elements in some common food ingredients were determined to guide a rational and balanced diet. At the same time, taking vegetables as an example, the research investigated the impact of food preprocessing on the extraction rates of metal elements within them, demonstrating that the influence of heat treatment varies for different element extraction rates. A wet digestion system using nitric acid-hydrogen peroxide was established for seafood and vegetable samples, and an analytical method for determining Ca, Cu, Fe, Mn and Zn using inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The detection limits of the method ranged from 0.0003 mg L−1 to 0.1567 mg L−1, with RSDs between 0.004% and 7.161%. The measured contents of several important metal elements in standard substances were largely consistent with national standards, confirming the accuracy and precision of the method. Based on wet digestion, the contents of various metal elements in simulated digestive fluids were determined. The detection limits for the simulated digestion method ranged from 0.0005 mg L−1 to 0.0077 mg L−1, with RSDs between 0.001% and 8.839%, verifying the precision of the method. Consequently, the extraction rates of metal elements in the two types of samples were obtained, leading to the conclusion that vegetable samples are more easily digested compared to seafood, releasing their metal elements. Moreover, the extraction rates of different elements vary within the same type of sample, and the extraction rates of the same element also differ across different samples. For dried fruit samples, a dry ashing digestion system was established, and an analytical method for determining Ca, Cu, Fe, Mn and Zn using ICP was developed. The detection limits of this method ranged from 0.0003 mg L−1 to 0.0073 mg L−1, with RSDs between 0.001% and 1.076%, and the spiked recovery rates were between 85.43% and 105.96%, confirming the accuracy and precision of the method. Based on dry ashing digestion, the contents of various metal elements in simulated digestive fluids were measured, which led to the determination of the element extraction rates. Among these, the extraction rates for Ca, Cu, and Mn were relatively high.

Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach

While several researchers have investigated the anaerobic digestion (AD) of textile wastewater for dye degradation, their studies suffer from lower biogas productivity due to substrate inhibition and the occurrence of secondary pollution from digestate disposal. Hence, this study focuses on using the extract of wheat straw (WS) as a co-substrate to facilitate the dye AD process, followed by recycling the digestate sludge for biochar production. In the first study, the batch digesters were operated at different dye wastewater (DW)/WS ratios (0–50% v/v), substrate-to-inoculum ratio of 0.28–0.50 g/g, pH 7.0 ± 0.2, and 37 °C. The digester operated at a DW/WS fraction of 65/35% (v/v) showed the best chemical oxygen demand (COD) removal efficiency of 68.52 ± 3.40% with bio-CH4 of 270.52 ± 19.14 mL/g CODremoved. About 52.96 ± 3.61% of the initial COD mass was converted to CH4, avoiding inhibition caused by volatile fatty acid (VFA) accumulation. In the second experiment, the dry digestate was thermally treated at 550 °C for 2 h under an oxygen-deprived condition, yielding 0.613 ± 0.031 g biochar/g. This biochar exhibited multiple functional groups, mineral contents, and high stability (O/C = 0.193). The combined digestion/pyrolysis scenario treating 35 m3/d (106.75 kg COD/d) could maintain profits from pollution reduction, biogas, biochar, and carbon trading, obtaining a 6.5-year payback period.

Integrated aerobic-anaerobic digestion of highly solids-loaded corn stover and swine manure under dynamic aeration: Temperature rise, physicochemical characteristics, and methane production

This research aimed to design an integrated aerobic-anaerobic reactor with dynamic aeration that was automatically regulated based on real-time oxygen concentration and investigate the aerobic pretreatment and subsequent dry co-anaerobic digestion (co-AD) characteristics of highly solids-loaded corn stover and swine manure in terms of temperature rise, physiochemical characteristics, and methane production. The high-temperature feedstocks from the aerobic pretreatment phase rapidly entered the AD phase without transportation and effectively improved the start-up and methane production of the co-AD. Oxygen concentration range, aeration rate, and pretreatment time affected the cumulative aeration time, temperature rise, and organic matter removal interactively during aerobic pretreatment, and a low aeration rate was relatively preferable. Although the lignocellulose removal increased with the increase in pretreatment duration, the maximal lignin elimination efficiency only reached 1.30%. The inoculum injection in the transition phase from aerobic pretreatment to co-AD and the leachate reflux during co-AD were also critical for producing methane steadily apart from aerobic pretreatment. The cold air weakened the temperature rise of aerobic pretreatment, and the low-temperature leachate reduced the methane production in the co-AD process. An oxygen concentration range of 13%–17%, aeration rate of 0.10 m3/(min·m3), pretreatment time of 84 h, inoculum loading of 40%, leachate refluxing thrice per day, and double-layer inoculation were optimum for improving the integrated aerobic-anaerobic digestion system's ability to resist low temperatures and achieving high methane production. The maximal cumulative and volatile solids (VS) methane yields of corn stover and swine manure reached 444.58 L and 266.30 L/kg VS.

Comparison of Dry, Wet and Microwave Digestion Procedures for the Determination of Heavy Metal in Yoghurt Samples

Abstract: This work proposes a novel technique for utilizing the most suitable digestion process to determine concentrations of heavy metals such as Pb, Cd, Al, As, Zn, and Fe in Yoghurt samples using AAS. Conventional digestion techniques often involve time-consuming and tedious procedures, which leads to the loss of analyte and reduced accuracy. In this study, we propose the utilization of microwave-assisted digestion, a rapid and efficient technique that offers complete digestion of the samples and minimizes the risk of analyte loss. In order to get optimal efficiency and precision, this study outlines the optimization of the microwave-assisted digestion parameters, such as power, time, and reagent concentrations. The proposed method was validated by calculating the recovery % among dry, wet and microwave digestion methods. Results show that among all, the recovery percentage was found to be highest in the microwave digestion method.

Synergism of floated paperboard sludge cake /sewage sludge for maximizing biomethane yield and biochar recovery from digestate: A step towards circular economy

Anaerobic digestion of floated paperboard sludge (PS) cake suffers from volatile fatty acids (VFAs) accumulation, nutrient unbalanced condition, and generation of digestate with a risk of secondary pollution. To overcome these drawbacks, sewage sludge (SS) was added to PS cake for biogas recovery improvement under a co-digestion process followed by the thermal treatment of solid fraction of digestate for biochar production. Batch experimental assays were conducted at different SS:PS mixing ratios of 70:30, 50:50, 30:70, and 20:80 (w/w), and their anaerobic co-digestion performances were compared to the mono-digestion systems at 35 ± 0.2 °C for 45 days. The highest methane yield (MY) of 241.68 ± 14.81 mL/g CODremoved was obtained at the optimum SS:PS ratio of 50:50 (w/w). This experimental condition was accompanied by protein, carbohydrate, and VFA conversion efficiencies of 47.3 ± 3.2%, 46.8 ± 3.2%, and 56.3 ± 3.8%, respectively. The synergistic effect of SS and PS cake encouraged the dominance of Bacteroidota (23.19%), Proteobacteria (49.65%), Patescibacteria (8.12%), and Acidovorax (12.60%) responsible for hydrolyzing the complex organic compounds and converting the VFAs into biomethane. Further, the solid fraction of digestate was subjected to thermal treatment at a temperature of 500 °C for 2.0 h, under an oxygen-limited condition. The obtained biochar had a yield of 0.48 g/g dry digestate, and its oxygen-to-carbon (O/C), carbon-to-nitrogen (C/N), and carbon-to-phosphorous (C/P) ratios were 0.55, 10.23, and 16.42, respectively. A combined anaerobic co-digestion/pyrolysis system (capacity 50 m3/d) was designed based on the COD mass balance experimental data and biogenic CO2 market price of 22 USD/ton. This project could earn profits from biogas (12,565 USD/yr), biochar (6641 USD/yr), carbon credit (8014 USD/yr), and COD shadow price (6932 USD/yr). The proposed project could maintain a payback period of 6.60 yr. However, further studies are required to determine the associated life cycle cost model that is useful to validate the batch experiment assumptions.

From grass to gas and beyond: Anaerobic digestion as a key enabling technology for a residual grass biorefinery

Roadside grass clippings hold potential as a sustainable source of bioenergy as they do not compete with crops for land use, and are only partially utilized for low-value applications. In this study, we proposed using roadside grass as a sole feedstock for anaerobic digestion (AD) in three different settings, and assessed the potential of producing biomaterials and fertilizers from grass-based digestate. Wet continuous digestion at pilot scale and dry batch digestion at pilot and large scales resulted in biogas yields up to 700 Nm3.t−1 DOM with a methane content of 49–55 %. Despite promising results, wet AD had operational problems such as clogging and poor mixing; once upscaled, the dry digestion initially also presented an operational problem with acidification, which was overcome by the second trial. Digested grass fibers from the pilot dry AD were processed into biomaterials and performed similarly or better than the undigested fibers, while around 20 % performance reduction was observed when compared to reference wood fibers. A mass balance indicated reduced fiber recovery when higher biogas production was obtained. The liquid fraction from the pilot dry AD was characterized for its nutrient content and used as a biofertilizer in another study. In contrast, the leachate collected from the large-scale dry AD had a low nitrogen content and high chloride content that could hinder its further use. Finally, a regional market analysis was conducted showing that the biocomposites produced with the available grass fibers could substitute at least half of the current European market based on our results.

Optimization of alkaline hydrothermal treatment for humic acids production from corn straw digestate using the response surface methodology

Anaerobic digestion (AD) technology was widely used for treating waste biomass, during which a large amount of lignin-rich digestate would be produced, needing further treatment. In this study, corn straw digestate (CSD) was used as raw material for hydrothermal humic acids (HHA) producing through alkaline hydrothermal treatment (AHT). According to the response surface analysis, the optimal reaction conditions were determined to be 156°C, 2 hours, and 5% KOH (% of the dry digestate), resulting in a HHA yield of 40.3 wt%. Structural characterization analysis showed the produced HHA had abundant oxygen-containing functional groups (e.g., C-O and CO) in HHA and aromatic structures, which also showed good thermal stability. By AHT with hemicellulose and lignin, the HHA yields reached 79.2%. Hemicellulose and lignin proved to be important components for HHA formation. In addition, the protein content in the EPS extraction solution of HC was significantly reduced compared to CSD, indicating that the dewaterability of the digestate were improved after AHT. This technique provides a feasible approach for the further utilization of residual lignocellulosic materials after anaerobic digestion.

Prevention of Silica Gel Formation for Eudialyte Study Using New Digestion Reactor

This work includes a combined hydrometallurgical treatment of a eudialyte ore sample with a subsequent preparation of leaching residue using mechanical separation methods. Hydrometallurgical treatment contains dry digestion with sulphuric acid at room temperature and filtration of the obtained product. The objectives of adopting these procedures are to test a new digestion reactor in order to prevent silica gel formation from the eudialyte ore. The obtained results revealed that silica gel formation is prevented during dissolution with sulphuric acid. A high leaching efficiency of light rare earth elements (La, Ce, Nd, Y) was reached using the dry digestion process with sulphuric acid, where the starting molarity was 12 mol/L. After the filtration process, magnetic separation is studied as the main method to recover weakly magnetic minerals like amphiboles and pyroxenes from the leaching residue in the magnetic fraction and feldspars in the nonmagnetic fraction. A new combined research strategy was developed for the production of different concentrates such as the one bearing Zr, Hf, and Nb.

Methane emissions and rumen microbiome response during compensatory growth on either a forage or grain-based finishing diet in beef cattle.

The aim of this experiment was to evaluate the effect of the level of prior nutritional restriction during backgrounding in Angus steers on methane (CH4) emissions, diet digestibility, rumen fermentation, and ruminal microbiome under either a forage or grain-based finishing diet. Eighty steers (body weight [BW]: 444 ± 39kg, age: 18 ± 1 mo) were blocked and randomly assigned within the block to either an optimal (0.6 to 0.7kg/d) or suboptimal (0.3 to 0.4kg/d) growth rate to exploit compensatory growth (CG), during 97 d of backgrounding. Following, for 84 d, half of the steers in each group were finished on a forage diet while the other half were finished on a grain-based diet. During the backgrounding period, CH4 emissions tended (P ≤ 0.07) to be higher; however, CH4 intensity expressed by BW gain was 50% lower (P < 0.01) for optimal compared to suboptimal growth steers. BW gain, dry matter intake, diet digestibility, and ammonia nitrogen in the rumen were greater (P < 0.01) for optimal compared to suboptimal steers. During the finishing period, CH4 emissions in either forage or grain finishing diets were similar (P > 0.05) for both backgrounding treatments. However, due to greater BW gain in suboptimal steers (1.20 vs. 0.97kg/d), their CH4 intensity-related coefficient decreased (P < 0.05) during the finishing period. Diet digestibility or any fermentation parameter was unaffected (P > 0.05) by previous backgrounding during the finishing period. In fact, rumen microbial abundance measured during finishing was not modified (P > 0.05) by previous backgrounding. Steers finished under grain conditions, had lower (P < 0.01) daily CH4 emissions and CH4 intensity. Additionally, grain-fed steers increased (P < 0.05) BW gain, diet digestibility, propionic, lactic, and valeric acids, Succinivibrionaceae family and Succiniclasticum, Erysipelotrichaceae UCG-002, Sharpea, and Megasphaera bacteria genera, compared to forage-fed steers. In conclusion, ruminal microbiome and fermentation, diet digestibility, and CH4 emissions were unaffected during finishing between prior levels of backgrounding growth. However, given the higher BW gain in suboptimal steers in both finishing diets, CH4 intensity was reduced in comparison to the optimal backgrounded steers. Nevertheless, lifetime emissions of the steers need to be assessed with the different dietary regimens, since suboptimal steers reduced CH4 emissions during the backgrounding period but, additional days of finishing were required to achieve the same BW as their contemporaries.

Enhancing physicochemical, rheological properties, and in vitro rumen fermentation of starch with Melastoma candidum D. Don fruit extract.

The utilization of polyphenol-modified starch in ruminants has not undergone extensive exploration. This study aimed to investigate the impact of the complex formed between starch and Melastoma candidum D. Don fruit extract on physicochemical properties, phenol release kinetics in various buffers simulating the gastrointestinal tract, methane production, and post-rumen digestibility. The interaction between starch and M. candidum D. Don fruit extract significantly (p < 0.001) increased resistant starch and particle size diameter. The maximum phenolic release from complex between starch and M. candidum D. Don fruit extract, due to gastrointestinal tract-simulated buffers, ranged from 22.96 to 34.60 mg/100 mg tannic acid equivalent. However, rumen and abomasum-simulated buffers released more phenolic content, whereas the intestine-simulated buffer showed higher antioxidant activity (ferric ion-reducing antioxidant power). Furthermore, complex between starch and M. candidum D. Don fruit extract significantly decreased dry matter rumen digestibility (p < 0.001) and maximum methane gas production (p < 0.001).

Phytochemical Screening, Antioxidant Capacity Measurement, and Mineral Content Determination of Thymus vulgaris L. Extracts

The aim of this study was to evaluate the chemical composition and antioxidant activity of Thymus vulgaris L. extracts. T. vulgaris L. is a medicinal plant that has various bioactive compounds. Four different solvents (ethanol, water, ethyl acetate, and chloroform) were used to extract these compounds from the plant. The phytochemical screening of the extracts showed that the ethanolic extract had the highest diversity of compounds, including coumarins, flavonoids, alkaloids, tannins, phenols, carbohydrates, and proteins. The total phenolic and total antioxidant contents of the ethanolic extract were measured by the Folin–Ciocalteu and phosphomolybdenum methods, respectively. The ethanolic extract had a high phenolic content of 77.7 mg gallic acid equivalent/g dry weight, which indicates its potential antioxidant capacity. The mineral content of T. vulgaris L. was also assessed by flame photometry and atomic absorption spectrophotometry after dry digestion. The plant contained five macroelements (K, Na, Ca, Mg, P) and three microelements (Fe, Cu, Zn) in different concentrations. The highest concentration was found for potassium (15259 mg/kg), followed by calcium (5118 mg/kg) and sodium (4793 mg/kg). The lowest concentration was found for phosphorus (1400 mg/kg), which was still higher than the microelements. Among the microelements, zinc had the highest concentration (24.82 mg/kg), followed by iron (17.44 mg/kg) and copper (14.98 mg/kg). The results of this study provide useful information for the users, collectors and practitioners of medicinal plants from polluted areas, as they can evaluate the quality and safety of T. vulgaris L. for human consumption.

Viscosity influence on kinetics parameters in dry anaerobic digestion

The viscosity that governs mass exchanges is a determining parameter of dry digestion kinetics. This observation leads to the measurement of viscosity influence on key kinetic parameters of digestion such as microbial growth, degradation of COD, biogas production and its CH4 quality. Thus, for limit viscosities at the beginning of digestion in batch mode at 37 °C and 55 °C of potato residues of 18–35 % TS content, the evolution of kinetic parameters is observed. The results show strong microbial growth for 4.39 × 10−2 Pa s and 7.5 × 10−2 Pa s in digestion at 37 °C and 4.12 × 10−2 Pa s in digestion at 55 °C. The reduction of COD is optimal for 7.50 × 10−2 Pa s at 37 °C and 6.57 × 10−2 Pa s at 55 °C. Biogas production is higher for 7.5 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. Finally, the CH4 content of biogas is higher for 4.39 × 10−2 Pa s and 4.12 × 10−2 Pa s at 37 °C and 55 °C, respectively. These results show that optimal conditions for microbial growth and CH4 production are obtained with the 22 % TS scenario giving a viscosity of 4.39 × 10−2 Pa s at 37 °C and 4.12 × 10−2 Pa s at 55 °C. These results confirm the importance of the viscosity in biochemical kinetics in dry digestion.