Effects of chlorine disinfectants on the microbial community structure and the performance of anaerobic digestion of swine manure

A relationship between body size and the gut microbiome suggests a conservation strategy

A key goal of conservation is to protect the biodiversity of wild species to support their continued evolution and survival. Conservation practice has long been guided by genetic, ecological, and demographic indicators of risk. Cope's rule suggests that species tend to evolve larger body sizes over time. Here, we provide strong evidence to support the inclusion of body size when formulating wildlife conservation strategies. The gut microbiome can mirror the physiological and environmental adaptation status of the host. This study established a connection between body size and the gut microbiome in the Felidae family using 70 fecal samples collected from 18 individuals through metagenomic data analysis and mining metagenome-assembled genomes (MAGs). Two enterotypes were identified in the Felidae gut: Bacteroides and Clostridium. Medium-sized felids predominantly harbored Clostridium, associated with pathogenicity, whereas large and small felids harbored both beneficial Bacteroides and pathogenic Clostridium. Species that evolved larger body sizes over time exhibited distinct changes in gut microbial communities, such as enhanced nutrient extraction and metabolic capabilities. Larger felids exhibited a more diverse, stable gut microbiome engaged in metabolic processes and extensive host interactions, indicating an evolved functional role in various biological processes. Conversely, that of smaller felids is less diverse, with more viruses and pathogenic elements primarily involved in chemical synthesis. These findings provide essential insights for developing conservation strategies that consider the nutritional needs of different-sized feline species, control the transmission of pathogens, and allocate resources based on their unique gut microbiome characteristics.IMPORTANCEBody size is a fundamental trait that varies greatly among taxa and has important implications for life history and ecology. Cope's rule suggests that species tend to evolve larger body sizes over time. However, its correlation to body size evolution remains unclear. This study aimed to establish a connection between body size and the gut microbiome in the Felidae family through metagenomic data analysis. Our results support Cope's rule, illustrating that increased body size correlates with shifts in the gut microbiome, enhancing survival and adaptability.

Impact of Phosphogypsum on Viability of Trichuris suis Eggs in Anaerobic Digestion of Swine Manure

Waste from livestock farms contains various pathogens, including eggs and larvae of helminths-pathogens of parasitic diseases harmful to animals and humans. One of the methods for their effective processing to obtain biofertilizer and biofuel is anaerobic digestion, which requires further improvement to completely suppress the viability of pathogenic microorganisms in mesophilic conditions. To this end, the use of anaerobic digestion under sulfate reduction conditions to suppress pathogens using biogenic hydrogen sulfide is promising. Consequently, this study aims to study the effect of a sulfur-containing additive such as phosphogypsum on the disinfection of pig manure during anaerobic digestion. Egg mortality was already found to increase significantly compared to the control (80% and more), even at a minimum concentration of phosphogypsum (5%), on the fifth day of the experiment. At the same time, the maximum effect (100% mortality of Trichuris suis eggs) was recorded at a 10% concentration of phosphogypsum, starting from the 10th day of the study. Our experiment showed that changes in anaerobic digestion conditions using phosphogypsum could positively affect digestate disinfection. However, further research is needed to optimize the conditions of the process for an effective combination of disinfection with the production of environmentally safe organic fertilizers and high-quality biogas with a high level of methane.

Environmental fate of antibiotic resistance genes in livestock farming

As emerging environmental pollutants, antibiotic resistance genes (ARGs) are prevalent in livestock farms and their surrounding environments. Although existing studies have focused on ARGs in specific environmental media, comprehensive research on ARGs within farming environments and their adjacent areas remains scarce. This review explores the sources, pollution status, and transmission pathways of ARGs from farms to the surrounding environment. Drawing on the "One Health" concept, it also discusses the potential risks of ARGs transmission from animals to human pathogens and the resulting impact on human health. Our findings suggest that the emergence of ARGs in livestock farming environments primarily results from intrinsic resistance and genetic mutations, while their spread is largely driven by horizontal gene transfer. The distribution of ARGs varies according to the type of resistance genes, seasonal changes, and the medium in which they are present. ARGs are disseminated into the surrounding environment via pathways such as manure application, wastewater discharge, and aerosol diffusion. They may be absorbed by humans, accumulating in the intestinal microbiota and subsequently affecting human health. The spread of ARGs is influenced by the interplay of microbial communities, antibiotics, heavy metals, emerging pollutants, and environmental factors. Additionally, we have outlined three control strategies: reducing the emergence of ARGs at the source, controlling their spread, and minimizing human exposure. This article provides a theoretical framework and scientific guidance for understanding the cross-media migration of microbial resistance in livestock farming environments.

From "resistance genes expression" to "horizontal migration" as well as over secretion of Extracellular Polymeric Substances: Sludge microorganism's response to the increasing of long-term disinfectant stress

Glutaraldehyde-Didecyldimethylammonium bromides (GDs) has been frequently and widely employed in livestock and poultry breeding farms to avoid epidemics such as African swine fever, but its long-term effect on the active sludge microorganisms of the receiving wastewater treatment plant was keep unclear. Four simulation systems were built here to explore the performance of aerobic activated sludge with the long-term exposure of GDs and its mechanism by analyzing water qualities, resistance genes, extracellular polymeric substances and microbial community structure. The results showed that the removal rates of CODCr and ammonia nitrogen decreased with the exposure concentration of GDs increasing. It is worth noting that long-term exposure to GDs can induce the horizontal transfer and coordinated expression of a large number of resistance genes, such as qacE, sul1, tetx, and int1, in drug-resistant microorganisms. Additionally, it promotes the secretion of more extracellular proteins, including arginine, forming a "barrier-like" protection. Therefore, long-term exposure to disinfectants can alter the treatment capacity of activated sludge receiving systems, and the abundance of resistance genes generated through horizontal transfer and coordinated expression by drug-resistant microorganisms does pose a significant threat to ecosystems and health. It is recommended to develop effective pretreatment methods to eliminate disinfectants.

Effect of biochar with various pore characteristics on heavy metal passivation and microbiota development during pig manure composting

Understanding the porosity of biochar (BC) that promotes the heavy metal (HM) passivation during composting can contribute to the sustainable management of pig manure (PM). The current work aimed to explore the influence of BC with varying pore sizes on the physicochemical properties and morphological changes of HMs (including Zn, Cu, Cr, As, and Hg), and microbiota development during PM composting. The various pore sizes of BC were generated by pyrolyzing pine wood at 400 (T1), 500 (T2), 600 (T3) and 700 (T4) °C, respectively. The results revealed a positive correlation between specific surface area of BC and pyrolysis temperature. BC addition contributed to a significantly extended compost warming rate and duration of high-temperature period, as well as HM passivation, reflected in the decrease in Exc-Zn (63-34%) and Red-Cu (28-13%) content, and the conversion of Oxi-Cr (29-21%) and Red-Hg (16-5%) to more stable forms. Moreover, BC at T4 exhibited the best effect on Zn and Cu passivation due to the highest specific surface area (380.03 m2/g). In addition to its impact on HM passivation, BC addition improved the microbial environment during PM composting, leading to enhanced microbial diversity and richness. Notably, Chloroflexi and Bacteroidota played key roles in promoting the transformation of Exc-Cu and Red-Hg into stable forms. This phenomenon further stimulated the enhanced decomposition of organic matter (OM) when BC prepared at 600-700 °C was added. Therefore, it can be concluded that the regulation of BC porosity is an effective strategy to improve HM passivation and the overall effectiveness of PM composting.

Effects of Fe-N co-modified biochar on methanogenesis performance, microbial community, and metabolic pathway during anaerobic co-digestion of alternanthera philoxeroides and cow manure

The performance of anaerobic digestion (AD) is susceptible to disturbances in feedstock degradation, intermediates accumulation, and methanogenic archaea activity. To improve the methanogenesis performance of the AD system, Fe-N co-modified biochar was prepared under different pyrolysis temperatures (300,500, and 700 °C). Meanwhile, pristine and Fe-modified biochar were also derived from alternanthera philoxeroides (AP). The aim was to compare the effects of Fe-N co-modification, Fe modification, and pristine biochar on the methanogenic performance and explicit the responding mechanism of the microbial community in anaerobic co-digestion (coAD) of AP and cow manure (CM). The highest cumulative methane production was obtained with the addition of Fe-N-BC500 (260.38 mL/gVS), which was 42.37 % higher than the control, while the acetic acid, propionic acid, and butyric acid concentration of Fe-N-BC were increased by 147.58 %, 44.25 %, and 194.06 % compared with the control, respectively. The co-modified biochar enhanced the abundance of Chloroflexi and Methanosarcina in the AD system. Metabolic pathway analysis revealed that the increased methane production was related to the formation and metabolism of volatile fatty acids and that Fe-N-BC500 enhanced the biosynthesis of coenzyme A and the cell activity of microorganisms, accelerating the degradation of propionic acid and enhancing the hydrogenotrophic methanogenesis pathway. Overall, Fe-N co-modified biochar was proved to be an effective promoter for accelerated methane production during AD.

The long-term effect of glutaraldehyde on the bacterial community in anaerobic ammonium oxidation reactor

A 160-day incubation was performed with two anammox reactors (GA and CK) to investigate the effect of glutaraldehyde. The results indicated that anammox bacteria were very sensitive when glutaraldehyde in GA reactor increased to 40 mg/L, the nitrogen removal efficiency sharply decreased to 11%, only one-quarter of CK. Glutaraldehyde changed spatial distribution of exopolysaccharides, caused anammox bacteria (Brocadia CK_gra75) to disassociate from granules (24.70% of the reads in CK but only 14.09% in GA granules). Metagenome analysis indicated glutaraldehyde led to the denitrifier community succession from strains without nir (nitrite reductase) and nor (nitric oxide reductases) genes to those with them, and the rapid growth of denitrifiers with NodT (an outer membrane factor)-related efflux pumps replacing those with another TolC -related ones. Meanwhile, Brocadia CK_gra75 lacks the NodT proteins. This study provides important insight into community adaptation and potential resistance mechanism in an active anammox community after exposure to disinfectant.

Microbial electrosynthesis of acetate from CO2 in three-chamber cells with gas diffusion biocathode under moderate saline conditions

The industrial adoption of microbial electrosynthesis (MES) is hindered by high overpotentials deriving from low electrolyte conductivity and inefficient cell designs. In this study, a mixed microbial consortium originating from an anaerobic digester operated under saline conditions (∼13 g L^-1 NaCl) was adapted for acetate production from bicarbonate in galvanostatic (0.25 mA cm^-2) H-type cells at 5, 10, 15, or 20 g L^-1 NaCl concentration. The acetogenic communities were successfully enriched only at 5 and 10 g L^-1 NaCl, revealing an inhibitory threshold of about 6 g L^-1 Na⁺. The enriched planktonic communities were then used as inoculum for 3D printed, three-chamber cells equipped with a gas diffusion biocathode. The cells were fed with CO₂ gas and operated galvanostatically (0.25 or 1.00 mA cm^-2). The highest production rate of 55.4 g m^-2 d^-1 (0.89 g L^-1 d^-1), with 82.4% Coulombic efficiency, was obtained at 5 g L^-1 NaCl concentration and 1 mA cm^-2 applied current, achieving an average acetate production of 44.7 kg MWh^-1. Scanning electron microscopy and 16S rRNA sequencing analysis confirmed the formation of a cathodic biofilm dominated by Acetobacterium sp. Finally, three 3D printed cells were hydraulically connected in series to simulate an MES stack, achieving three-fold production rates than with the single cell at 0.25 mA cm^-2. This confirms that three-chamber MES cells are an efficient and scalable technology for CO₂ bio-electro recycling to acetate and that moderate saline conditions (5 g L^-1 NaCl) can help reduce their power demand while preserving the activity of acetogens.

Low-temperature torrefaction assisted with solid-state KOH/urea pretreatment for accelerated methane production in wheat straw anaerobic digestion

Low-temperature torrefaction assisted with solid-state KOH/urea applied onto wheat straw was proposed to break down the lignocellulosic material to enhance biomethane production in anaerobic digestion (AD). The optimization of key parameters applying the Box-Behnken design and response surface methodology showed that an addition of 0.1 g/g_straw KOH/urea at 180 °C while torrefying for 30 min was the optimal condition for producing biomethane. Results indicate that co-applying KOH and urea in torrefaction synergistically enhanced the biodegradability of straw by effectively removing lignin and largely retaining cellulose, giving rise to a 41 % increase in the cumulative methane production compared to untreated straw (213 mL/g-volatile solids (VS_raw)) from batch AD. Additionally, the nitrogen- and potassium-rich digestates helped to improve soil fertility, thus achieving a zero-waste discharge. This study demonstrated the feasibility of using solid-state KOH/urea assisted low-temperature torrefaction as an effective pretreatment method to promote methane production during AD.

Knowledge and Practices of Cypriot Bovine Farmers towards Effective and Safe Manure Management

Manure from bovine farms is commonly used as an organic fertiliser. However, if not properly managed, it can spread significant biological and chemical hazards, threatening both human and animal health. The effectiveness of risk control hugely relies on farmers' knowledge regarding safe manure management and on the application of suitable management practices. This study aims to evaluate the knowledge and practices of Cypriot bovine farmers towards safer manure management, from its generation to its final use, in line with the One Health approach. Factors affecting farmers' knowledge and applied practices are also investigated through a questionnaire survey. The questionnaire was developed and sent to all eligible bovine farmers in Cyprus (n = 353), and 30% (n = 105) of them returned the completed questionnaire. Results revealed there are some gaps in farmers' knowledge. The use of manure for fertilising crops dominated. Only half of the farmers stored manure in appropriate facilities, with 28.5% of them using a dedicated area with cement floors and 21.5% utilising leakproof tanks. The majority (65.7%) stored manure for more than three months before its use as a fertiliser in a dried form. In multiple regression analysis, education level and farming purpose were significant determinants of farmer knowledge. In conclusion, Cypriot farmers' knowledge must be reinforced to ensure proper manure management. The results highlight the importance of providing relevant training to farmers. Although the current practices partially decrease manure pathogens, interventions to promote the use of more effective treatment methods, such as biogas transformation and composting, would be beneficial.

Promoting the overall energy profit through using the liquid hydrolysate during microwave hydrothermal pretreatment of wheat straw as co-substrate for anaerobic digestion

Liquid hydrolysate (LH) derived from the microwave hydrothermal pretreatment (MHP) of wheat straw (WS) was anaerobically digested together with the solid residual to promote the overall energy profit. Different MHP temperatures (90, 120, 150, 180 °C) and retention times (10, 20, 40 min) were investigated. Increased MHP intensity generated plenty of VFAs (mainly acetate) and phenols in the LH, implying the double-side effect of LH on AD. The highest methane production of 227.92 mL CH₄·gVS^-1 Raw was obtained with MHP at 120 °C for 10 min, 21.53 % higher than the control. While, MHP at 180 °C for 40 min exhibited 29.02 % lower methane production (113.13 mL CH₄·gVS^-1 Raw) and 115.86 % longer lag phase (3.13 days) than the control. Butyrate fermentation endowed the treatment groups of 180 °C with resilience from the overload and inhibition. Methanosarcina was largely enriched by the abundant acetate in LH on the early stage of anaerobic digestion (AD), especially when with high MHP intensity. Increased abundance of Methanosaeta and Methanobacterium played a crucial role in maintaining methane production at the middle and later stage. The high number of species and evenness in methanogens community were beneficial for the startup of batch AD. Although negative net energy was obtained, the lower ratio of energy input and output compared with the most researches using the solid residual after MHP as the sole substrate for AD demonstrated the contribution of LH to the overall energy profit.

Greenhouse gas reduction and nitrogen conservation during manure composting by combining biochar with wood vinegar

The constant greenhouse gases (GHGs) and ammonia emissions during pig manure (PM) composting have made large contributions to air pollution and global temperature rise. This study aimed to evaluate the addition of biochar (B) and wood vinegar (WV) to reduce GHGs emissions and improve nitrogen retention and microbial activities during PM composting. Different treatments, carried out under a 1:2 ratio (dry weight) of PM and sawdust mixture with the addition of B (5%) and various proportions of WV, include a control treatment (CT) without the addition of B and WV and, B, B+0.5%WV, B+1.0%WV, B+1.5%WV, and B+2.0%WV treatments. The results indicated that the addition of B could accelerate the composting process in contrast to CT. In addition, various amounts of WV with B decreased NH₃, CO₂, CH₄ and N₂O emissions by 18.82-35.88%, 1.38-15.39%, 16.98-62.73%, and 4.47-19.91%, respectively. Furthermore, in contrast to the B treatment, WV addition was more effective in decreasing GHGs and NH₃ emissions, and the B+1.0% WV treatment displayed the lowest nitrogen loss (2.12%) and GHGs emissions (11.62 g/kg). The bacterial community analysis demonstrated that synergistic application of WV and B can increase the relative abundance of Proteobacteria which can contribute to nitrogen fixation and reduction of nitrogen loss. The results proved that combining B with WV can be a feasible strategy to effectively reduce GHGs emissions and improve nitrogen conservation in the composting industry.

Zero-valent iron is not always effective in enhancing anaerobic digestion performance

Liquid nitrogen was employed as a low-temperature medium to activate zero-valent iron (ZVI) powder in an attempt to strengthen its enhancement effect on anaerobic digestion (AD) of swine manure (SM). Surprisingly, it was found that both pristine ZVI and liquid nitrogen-pretreated ZVI (LZVI) did not significantly improve the AD performance or change the archaeal community structure. It was hypothesized that ZVI might not be effective at stress-free environment like in these digesters. To confirm this, an additional set of AD experiments were performed at high ammonia stress (about 4000 mg/L), results showed that ZVI and LZVI greatly alleviated ammonia inhibition and increased the CH₄ yield by 11.6% and 28.2%, respectively. Apparently, ZVI mainly affected AD systems by changing the metabolism pathways and enhancing the microbial activity to overcome process inhibition, and pretreatment of liquid nitrogen could significantly accelerate the dissolution of ZVI and improve its utilization efficiency, contributing to a greater extend of process recovery and improvement.

Combined effects of liquid digestate recirculation and biochar on methane yield, enzyme activity, and microbial community during semi-continuous anaerobic digestion

The combined effects of liquid digestate recirculation (LDR) and biochar on methanogenesis and microbial communities were studied in semi-continuous anaerobic reactors fed with wheat straw and swine manure. The tolerated organic loading rate (OLR) was expanded from 5 g- volatile solids (VS)∙L-1∙d-1 in the control to higher than 6 g-VS∙L-1∙d-1 in the LDR. At the OLR of 5.0 g-VS∙L-1∙d-1, average special methane yield in LDR with biochar was 0.234 L∙g-VS-1, which was 5.4 % higher than that of the LDR alone. Moreover, enzyme activity and microbial community analysis indicated that LDR with biochar enhanced the processes of hydrolysis and methanogenesis, and balanced the pathway between hydrogenotrophic and acetoclastic methanogenesis. The co-application of LDR and biochar synergistically enhanced the degradation pathways of substrates and the loading shock resistance of anaerobic digestion system. This study could offer strategies for developing sustainable applications of full and continuous LDR in industrial biogas projects.