Influence of zero-valent iron nanoparticles on anaerobic digestion of swine manure: effects on methane yield

This study evaluated the effect of zero-valent iron nanoparticles (NZVI) on the anaerobic digestion of swine manure. A wide range of doses of NZVI was evaluated (5, 10, 15, 20, 25, 50, and 100 mgFe°/gVS). The maximum methane yield of 0.4506 L/gVSremoved was obtained with the concentration of 10 mgFe°/gVS representing an increase of 58.99% than the control system with 0.2834 L/gVSremoved, indicating that Fe° improves the methanogenic activity. However, when using doses greater than 20 mgFe°/gVS, there were decreases in the methane yield of 34.4-47.98%. Also, to observe the effect of NZVI in anaerobes was evaluated the activity in the electron transport system (ETS), where the control reactor showed an activity of 31.91 μg INTred/gVS•h, while in reactors with NZVI showed values of 39.48 μg INTred/gVS•h (10 Fe°mg/gVS), observing a stimulation of Fe° in microbial activity. However, the dose of 100 mgFe°/gVS showed the greatest decrease in methane yield (0.1474 L/gVSremoved) and a reduction in ETS was observed by 8.5% compared to the control. The effect on the composition of the volatile fatty acids was observed, where the control system obtained a maximum production of acetic acid of 639 mg/L, which was exceeded with the dose of 10 mg Fe°/gVS by 215% and a decrease of 41.15% with the inhibitory concentration of 100 mg Fe°/gVS. As a result, higher doses of NZVI affect the metabolic activity of anaerobes as well as the acetoclastic pathway causing a decrease in the methane production.

Migration and Transformation of Cd in Pig Manure-Insect Frass (Hermetia illucens)-Soil-Maize System

Little is known about the fate of heavy metals in the recycling system of animal manure-black soldier fly larvae (BSFL) transformation-larval frass application. In this work, BSFL-transformed pig manure with different concentrations of exogenous cadmium (Cd) (0, 3, 15, 30 mg kg^-1), and the obtained BSFL frass fertilizer were further used in pot experiments of maize planting to explore Cd migration during the whole recycling system. Results showed that Cd addition to pig manure had no significant effects on BSFL growth or BSFL transformation performance. The Cd concentrations in BSFL frass were 10.9-19.8% lower than those in pig manure, while those in BSFL bodies were 2.3-4.0-times those of pig manure. For maize planting, only 30 mg kg^-1 of Cd treatment significantly inhibited maize growth. The BSFL frass application (under exogenous Cd treatment) enhanced Cd contents in the aboveground and underground parts of maize (3.3-57.6-times) and those in soil (0.5-1.7-times) compared with CK (no Cd addition). Additionally, 61.2-73.5% of pig manure-sourced Cd was transformed into BSFL frass and the rest entered BSFL bodies. Only a small part (0.31-1.34%) of manure-sourced Cd entered maize plants. BSFL transformation decreased the proportions of weak acid-dissolved Cd from 44.2-53.0% (manure) to 37.3-46.0% (frass). After frass application, the proportions of weak acid-dissolved Cd in soil were further decreased to 17.8-42.5%, while the residual fractions of Cd increased to 27.2-67.7%. The findings provided a theoretical basis for the rational application of BSFL frass fertilizers sourced from heavy-metal-contaminated manure.

Impact of Swine and Cattle Manure Treatment on the Microbial Composition and Resistome of Soil and Drainage Water

Evaluating potential environmental and clinical impacts of industrial antibiotic use is critical in mitigating the spread of antimicrobial resistance. Using soil columns to simulate field application of swine or cattle manure and subsequent rain events, and a targeted qPCR-based approach, we tracked resistance genes from source manures and identified important differences in antimicrobial resistance gene transport and enrichment over time in the soil and water of artificially drained cropland. The source manures had distinct microbial community and resistance gene profiles, and these differences were also reflected in the soil columns after manure application. Antibiotic resistance genes (ARGs) were only significantly enriched in effluent samples following the first rain event (day 11) for both soil types compared to the control columns, illustrating the high background level of resistance present in the control soils chosen. For swine, the genes tetQ, tet(36), tet44, tetM, sul2 and ant(6)-ib persisted in the soil columns, whereas tetO, strB and sul1 persisted in effluent samples. Conversely, for cattle manure sul2 and strB persisted in both soil and effluent. The distinct temporal dynamics of ARG distribution between soil and effluent water for each manure type can be used to inform potential mitigation strategies in the future.

Positive Effects of Organic Substitution in Reduced-Fertilizer Regimes on Bacterial Diversity and N-Cycling Functionality in Greenhouse Ecosystem

Conventional fertilization in the greenhouses of North China used excessive amounts of chemical and organic fertilizer, resulting in soil degradation and severe agricultural non-point source pollution. A nine-year study was conducted on a loamy clay soil in Shijiazhuang, Hebei province, to investigate the effects of reduced-fertilizer input regimes on soil property, bacterial diversity, nitrogen (N) cycling and their interactions. There were four treatments, including high organic + chemical fertilizer application rate and three reduced-fertilizer treatments with swine manure, maize straw or no substitution of 50% chemical N. Treatments with reduced-fertilizer input prevented soil salinization and acidification as in local conventional fertilization after being treated for nine years. In comparison to chemical fertilizer only, swine manure or maize straw substitution maintained higher nutrient availability and soil organic C contents. Fertilizer input reduction significantly increased bacterial richness and shifted bacterial community after nine years, with decisive factors of EC, Olsen P and C/N ratio of applied fertilizer. Soil chemical characteristics (EC, pH and nutrients), aggregation and C/N ratio of applied fertilizer selected certain bacterial groups, as well as N-cycling functions. Reduced-fertilizer input decreased the potential nitrification and denitrification functioning of bacterial community, but only in organic substitution treatments. The results of this study suggested that fertilizer input reduction combined with organic C input has potential in reducing non-point source pollution and increasing N-use efficiency in greenhouse vegetable production in North China.

Distribution Patterns of Antibiotic Resistance Genes and Their Bacterial Hosts in a Manure Lagoon of a Large-Scale Swine Finishing Facility

The spread of antibiotic resistance genes (ARGs) that are present in livestock manures, which are discharged into the environment, is a severe threat to human and animal health. Here, we used 16S rRNA gene profiling and metagenomic analysis to characterize microbial community composition and antibiotic resistance in a manure storage lagoon from a large-scale swine finishing facility. Manure samples were collected at intervals of two years. Both the prokaryotic community and the resistome were dominated by the Firmicutes, Proteobacteria and Bacteroidota. Metagenomic analysis of two samples revealed 726 and 641 ARGs classified into 59 and 46 AMR gene families. Besides multidrug efflux pumps, the predominating ARGs potentially encoded resistance to tetracyclines, macrolide-lincosamide-streptogramin, aminoglycosides, peptide antibiotics, rifamycin, chloramphenicol, and beta-lactams. Genes from all predominant AMR gene families were found in both samples indicating overall long-term stability of the resistome. Antibiotic efflux pumps were the primary type of ARGs in the Proteobacteria, while antibiotic target alteration or protection was the main mechanism of resistance in the Firmicutes, Actinobacteriota and Bacteroidota. Metagenome-assembled genomes (MAG) of four multidrug-resistant strains were assembled. The first MAG, assigned to Escherichia flexneri, contained 46 ARGs, including multidrug efflux pumps, modified porins, beta-lactamases, and genes conferring resistance to peptide antibiotics. The second MAG, assigned to the family Alcaligenaceae, contained 18 ARGs encoding resistance to macrolide-lincosamide-streptogramin, tetracyclines, aminoglycosides and diaminopyrimidins. Two other MAGs representing the genera Atopostipes and Prevotella, contained four and seven ARGs, respectively. All these MAGs represented minor community members and accounted for less than 0.3% of the whole metagenome. Overall, a few lineages originated from the gut but relatively rare in the manure storage lagoon, are the main source of ARGs and some of them carry multiple resistance determinants.

Determination of Tetracycline, Oxytetracycline, Sulfadiazine, Norfloxacin, and Enrofloxacin in Swine Manure Using a Coupled Method of On-Line Solid-Phase Extraction with the UHPLC-DAD

The use of various veterinary antibiotics (VAs) in animal husbandry raises serious concerns about the development of antibiotic resistance. Antibiotics such as tetracycline, oxytetracycline, sulfadiazine, norfloxacin, and enrofloxacin are the most frequently used antimicrobial compounds in animal husbandry and generate large eco-toxicological effects; however, they are still difficult to determine in a complex matrix such as swine manure. This study has developed an effective method for detecting five VAs in swine manure using Ultra-High-Performance Liquid Chromatography-Diode Array Detector (UHPLC-DAD) coupled with on-line solid-phase extraction (SPE). The results show that the mobile phase of ACN/0.01 M oxalic acid was the optimum at pH 3.0. VAs in a swine manure matrix were extracted using solid extraction buffer solution (T3) with 97.36% recovery. Sensitivity, accuracy, and precision were also evaluated. The validity study showed good linearity (R2 > 0.99). Limit of detection (LOD) was found to be from 0.1 to 0.42 µg mL-1 in the liquid fraction and from 0.032 to 0.58 µg g-1 dw in the solid fraction. The corresponding values of the limit of quantification (LOQ) ranged from 0.32 to 1.27 µg mL-1 for the liquid fraction and from 0.096 to 1.77 µg g-1 dw for the solid fraction. Therefore, the proposed method showed the potential applicability for detecting different antibiotic compounds from swine manure samples.

Biosorption of Copper in Swine Manure Using Aspergillus and Yeast: Characterization and Its Microbial Diversity Study

Dietary copper supplementation in the feed of piglets generally exceeds 250-800 mg/kg, where a higher quantity (>250 mg/kg) can promote growth and improve feed conversion. Despite the reported positive effects, 90% of copper is excreted and can accumulate and pollute the soil. Data indicate that fungi have a biosorptive capacity for copper. Thus, the objectives of the present experiment were to study the effects of adding different strains of fungi on the biosorptive capacity for copper in swine manure and to evaluate potential effects on microbiota profiles. Aspergillus niger (AN), Aspergillus oryzae (AO), and Saccharomyces cerevisiae (SC) were selected, and each added 0.4% into swine manure, which contain 250 mg/kg of copper. The incubations lasted for 29 days, and biosorption parameters were analyzed on the 8th (D8), 15th (D15), 22nd (D22), and 29th (D29) day. Results showed that after biosorption, temperature was 18.47-18.77°C; pH was 6.33-6.91; and content of aflatoxin B1, ochratoxin A, and deoxynivalenol were low. In addition, residual copper concentration with AN was the lowest on D15, D22, and D29. The copper biosorption rate was also highest with AN, averaging 84.85% on D29. Biosorption values for AO reached 81.12% and for SC were lower than 80%. Illumina sequencing of 16S and ITS rRNA gene revealed that fungal treatments reduced the diversity and richness of fungal abundance, but had no effect on bacterial abundance. Unknown_Marinilabiliaceae, Proteiniphilum, Tissierella, and Curvibacter were the dominant bacteria, while Aspergillus and Trichoderma were the dominant fungi. However, the added strain of S. cerevisiae was observed to be lower than the dominant fungi, which contained less than 0.05%. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment predicted via PICRUSt2 that there were bacterial genes potentially related to various aspects of metabolism and environmental information processing. Overall, data indicated that Aspergillus can provide microbial materials for adsorption of copper.

Speciation of Main Nutrients (N/P/K) in Hydrochars Produced from the Hydrothermal Carbonization of Swine Manure under Different Reaction Temperatures

Hydrothermal carbonization (HTC) has been proved to be a promising technology for swine manure (SM) treatment. Currently, there is a lack of systematic understanding of the transformation characteristics of nutrient speciation in the HTC of SM. In this study, the speciation of the main nutrients (N/P/K) in SM-derived hydrochar produced at different reaction temperatures (200-280 °C) was investigated. The recovery of P (61.0-67.1%) in hydrochars was significantly higher than that of N (23.0-39.8%) and K (25.5-30.0%), and the increase in reaction temperature promoted the recovery of P and reduced the recovery of N. After the HTC treatment, the percentage of soluble/available P was reduced from 61.6% in raw SM to 4.0-23.9% in hydrochars, while that of moderately labile/slow-release P was improved from 29.2% in raw SM feedstock to 65.5-82.7%. An obvious reduction was also found in the amounts of available N (from 51.3% in raw SM feedstock to 33.0-40.5% in hydrochars). The percentages of slow-release N and residual N in hydrochars produced at 240 °C reached the maximum and minimum values (46.4% and 18.9%), respectively. A total of 49.5-58.3% of K retained in hydrochars was residual (invalid) potassium. From the perspective of the mobility and availability of N, P and K only, it was suggested that the HTC of SM should be carried out at 220-240 °C. Compared with the original SM, it is safer and more effective to use the SM-derived hydrochar as an organic fertilizer.

Development of a Real-Time Controlled Bio-Liquor Circulation System for Swine Farms: A Lab-Scale Study

Simple Summary

Odor emission from swine production facilities can irritate the people living in surrounding areas, although the farmers consider odor emission as a part of farming practice. Despite the governmental and institutional efforts, odor-related complaints from the neighborhood communities around the swine farms are rapidly increasing and have been identified as a key concern to sustaining progress of the swine industry globally. Bio-liquor circulation systems (BCSs) in swine farms have become popular among the farmers as an odor reduction technology in Korea. However, due to the lack of appropriate operating strategies, the odor reduction capacity of BCSs is often depleted. In this lab-scale study, a real-time control strategy based on oxidation–reduction potential (ORP) and pH (mV) time profiles was developed and applied for BCS operation. This study shows the potential effectiveness of using ORP and pH (mV) time profiles as operational parameters for the BCS to improve swine manure properties in slurry pits and thus reduce odor emission.

Abstract

In this study, an attempt was made to develop a real-time control strategy using oxidation–reduction potential (ORP) and pH (mV) time profiles for the efficient operation of bio-liquor circulation system (BCS) in swine farms and its effectiveness in reducing odor emission through improving manure properties in the slurry pit was evaluated. The lab-scale BCS used in this study comprised a bioreactor and a slurry pit. The bioreactor was operated in a sequence of inflow of swine manure → anoxic phase → aerobic phase → circulation to the slurry pit. The improvement in swine manure properties was elucidated by comparing the results of the BCS slurry pit (circulation type, CT) and conventional slurry pit (non-circulation type, NCT). The results revealed that the ORP time profile successfully detected the nitrate knee point (NKP) in the anoxic phase. However, it was less stable in detecting the nitrogen break point (NBP) in the aerobic phase. The pH (mV) time profile showed a more efficient detection of NBP. Compared to the NCT slurry pit, concentrations of ammonium nitrogen (NH₄-N) and soluble total organic carbon (STOC) and other analyzed swine manure properties were much lower in the CT slurry pit. In the aspect of odor reduction, around 98.3% of NH₃ was removed in the CT slurry pit. The real-time controlled BCS can overcome the drawbacks of fixed time-based BCS operation and therefore can be considered as a useful tool to reduce odor emission from intensive swine farming operations. However, further studies and refinement in control algorithms might be required prior to its large-scale application.

Swine Manure Composting With Compound Microbial Inoculants: Removal of Antibiotic Resistance Genes and Their Associations With Microbial Community

In this study, compound microbial inoculants, including three Bacillus strains and one Yeast strain, were inoculated into swine manure composting to explore the effects on antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), microbial community structure, and pathogenic bacteria. The results indicated that the abundances of the detected ARGs ranged from 3.6 × 10³ to 1.13 × 10⁸ copies/g. The ARGs with the highest abundance was sul2, and the lowest was blaCTX. Composting removes most of the ARGs and MGEs by 22.8-99.7%. These ARGs were significantly reduced during the thermophilic phase of compost. The removal rate of ARGs at the different layers of compost pile was different as follows: middle layer > upper layer > lower layer. But some ARGs proliferated significantly in the maturation phase of compost, especially the sulfonamide resistance genes. Compound microbial inoculants increased the temperature of compost, accelerated water loss, nitrogen fixation, and increased the removal rate of β-lactamase resistance genes, the transposon gene tn916 and part of tetracycline resistance genes by 3.7-23.8% in compost. Compound microbial inoculants changed the community structure and increased the Bacillus abundance in the thermophilic phase of compost. And it was helpful for removing pathogens during composting. The addition of compound microbial inoculants causes the decrease of Firmicutes and the increase of Bacteroidetes, which may be related to the removal and proliferation of ARGs.

Pilot-Scale Demonstration of Membrane-Based Nitrogen Recovery from Swine Manure

Gas-permeable membranes technology presents a high potential for nitrogen (N) recovery from wastewaters rich in ammonia (NH₃). The EU project Ammonia Trapping (AT) is aimed at transferring knowledge from the lab-scale level to on-farm pilot-scale level, using this technology to recover NH₃ from livestock wastewaters. The goal of this study is to report the results of an on-farm pilot-scale demonstration plant using gas-permeable membranes to recover N from raw swine manure. After a setup optimization of the plant, stable, and continuous operation was achieved. The maximum NH₃ recovery rate obtained was 38.20 g NH₃-N m⁻² membrane day⁻¹. This recovery rate was greatly affected by the temperature of the process. In addition to its contribution to NH₃ emissions reduction, this technology contributes to the recovery of nutrients in the form of a concentrated stable ammonium sulphate solution. This solution contained 3.2% of N, which makes it suitable for fertigation. The economic approach revealed an economic feasibility of the technology, resulting in a cost of 2.07 € per kg N recovered.

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.

[Effects of microbial agents on bacterial community composition during swine manure composting]

The process of swine manure and wheat straw aerobic composting was examined, with exogenous microbial agents being added in treatment group. The physicochemical properties were measured by conventional methods, and bacterial community characteristics were investigated by high throughput sequencing analysis. Exogenous microbial agents increased high-temperature duration, reduced pH value at the end of fermentation stage, augmented total nitrogen content, reduced C/N ratio. Results from principal component analysis showed that microbial agents affected the stability of bacterial community during composting. At the phylum level, the relative abundance of Firmicutes, Proteobacteria, and Chloroflexi was higher in the treatment group. At the class level, the relative abundance of Clostridia, Alphaproteobacteria, and Gammaproteobacteria in the treatment group were higher at the mesophilic and thermophilic phases. At the family level, Peptostreptococcaceae, Clostridiaceae_1, and Halanaerobiaceae of the Clostridia and Micromonosporaceae in the treatment group were higher at the mesophilic and thermophilic phases. Halocella was significantly positively correlated with exogenous microbial agents, while Ammoniibacillus was significantly negatively correlated with it. It suggested that microbial agents significantly changed the physicochemical properties and bacterial community structure during swine composting.

Microbial community dynamics during anaerobic co-digestion of corn stover and swine manure at different solid content, carbon to nitrogen ratio and effluent volumetric percentages

The methane production and the microbial community dynamics of thermophilic anaerobic co-digestion (AD) of corn stover, swine manure and effluent were conducted at total solid (TS) content of 5%, 10% and 15%, the carbon to nitrogen ratio (C/N) of 20, 30 and 40 and the effluent volumetric percentage (EVP) of 20%, 40% and 60%. For batches with 5% TS, the highest methane yield of 238.5-283.1 mL g^-1 volatile solid (VS) and the specific methane productivity of 138.5-152.2 mL g^-1 initial VS were obtained at the C/N ratios of 20 and 30. For the mixtures with 10% and 15% TS, the highest methane yield was 341.9 mL g^-1 VS and 351.2 mL g^-1 VS, respectively, when the C/N ratio of 20% and 60% EVP conditions were maintained. Co-digestion of swine manure with corn stover caused an obvious shift in microbial population, in which the archaeal population changed from 0.3% to 2.8% and the bacterial community changed from 97.2% to 99.7%. The experimental batches with the highest relative abundance of the archaeal population (2.00% of total microbial population for 5% TS, 1.74% for 10% TS and 2.76% for 15% TS) had the highest rate of methanogenesis subsequently enhancing methane production (283.08 mL g^-1 VS for 5% TS, 341.91 mL g^-1 VS for 10% TS and 351.23 mL g^-1 VS for 15% TS). The results of microbiome analysis enabled understanding the key populations in biomethane generation.

Long-Term Mesophilic Anaerobic Co-Digestion of Swine Manure with Corn Stover and Microbial Community Analysis

Long-term anaerobic co-digestion of swine manure (SM) and corn stover (CS) was conducted using semi-continuously loaded digesters under mesophilic conditions. A preliminary test was first conducted to test the effects of loading rates, and results indicated the 3 g-VS L⁻¹ d⁻¹ was the optimal loading rate. Based on the preliminary results, a verification replicated test was conducted with 3 g-VS L⁻¹ d⁻¹ loading rate and different SM/CS ratios (1:1, 2:1 and 1:2). Results showed that a SM/CS ratio of 2/1 was optimal, based on maximum observed methane-VS_des generation and carbon conversion efficiency (72.56 ± 3.40 mL g⁻¹ and 40.59%, respectively). Amplicon sequencing analysis suggested that microbial diversity was increased with CS loading. Amino-acid-degrading bacteria were abundant in the treatment groups. Archaea Methanoculleus could enhance biogas and methane productions.

Higher Temperatures Do Not Always Achieve Better Antibiotic Resistance Gene Removal in Anaerobic Digestion of Swine Manure

This study employed high-throughput quantitative PCR and 16S rRNA sequencing to evaluate the effect of temperature and residual antibiotics on the dynamics of antibiotic resistance genes (ARGs) and microbial communities during anaerobic digestion of swine manure. The abundances of total ARGs and 16S rRNA genes significantly decreased in all of four treatments (25°C, 37°C, and 37°C with 50 mg of wet weight antibiotics of body weight, and 55°C). The abundances of most ARG types were significantly correlated with those of the 16S rRNA gene and transposase gene (P < 0.01). However, the abundances of total ARGs at 55°C were much higher than those of other treatments. Meanwhile, the microbial communities at 55°C, where the Streptococcus pathogen remained at a relatively high abundance and cellulose degraders and hydrogen producers, such as Ethanoligenens and Coprococcus bacteria, increased, were markedly different from those of other treatments. Redundancy analysis indicates that temperature, pH, and the genus Streptococcus had the highest explanation for ARG variation among experimental factors, chemical properties, and representative genera, respectively. Network analysis further showed that the genus Streptococcus contributed greatly to the higher ARG abundance at 55°C. The moderate antibiotic residue only caused a slight and transitory inhibition for microbially diverse populations and promotion for ARG abundance, probably due to the degradation of antibiotics and microbial adaptability. Our results clarify the cooperativity of gene transfer-related items on ARG variation and intensively prove that higher temperature cannot always achieve better ARG removal in anaerobic digestion unless pathogens and gene transfer elements are more efficiently inhibited.IMPORTANCE Antibiotic resistance genes (ARGs) are frequently detected with high abundance in manure-applied soils. Anaerobic digestion is one of widely used processes for animal waste treatment. Thus, it is critical to understand the potential of anaerobic digestion to attenuate ARGs. Although some previous studies recommended thermophilic digestion for ARG removal, they did not get sufficient evidence to support this view. The antibiotics applied to animals are mostly excreted through feces and urine because of incomplete metabolism. It is indispensable to know whether residual antibiotics in manure will hinder ARG attenuation in anaerobic digesters. The significance of our research is in comprehensively understanding the evolution and mechanism of ARGs in anaerobic digestion of swine manure affected by temperature and residual antibiotics, which will allow the development of an ARG elimination strategy before their release into the environment.

Temporal Dynamics of Bacterial Communities in Soil and Leachate Water After Swine Manure Application

Application of swine manure to agricultural land allows recycling of plant nutrients, but excess nitrate, phosphorus and fecal bacteria impact surface and drainage water quality. While agronomic and water quality impacts are well studied, little is known about the impact of swine manure slurry on soil microbial communities. We applied swine manure to intact soil columns collected from plots maintained under chisel plow or no-till with corn and soybean rotation. Targeted 16S-rRNA gene sequencing was used to characterize and to identify shifts in bacterial communities in soil over 108 days after swine manure application. In addition, six simulated rainfalls were applied during this time. Drainage water from the columns and surface soil were sampled, and DNA was extracted and sequenced. Unique DNA sequences (OTU) associated with 12 orders of bacteria were responsible for the majority of OTUs stimulated by manure application. Proteobacteria were most prevalent, followed by Bacteroidetes, Firmicutes, Actinobacteria, and Spirochaetes. While the majority of the 12 orders decreased after day 59, relative abundances of genes associated with Rhizobiales and Actinomycetales in soil increased. Bacterial orders which were stimulated by manure application in soil had varied responses in drainage waters over the course of the experiment. We also identified a “manure-specific core” of five genera who comprised 13% of the manure community and were not significantly abundant in non-manured control soils. Of these five genera, Clostridium sensu stricto was the only genus which did not return to pre-manure relative abundance in soil by day 108. Our results show that enrichment responses after manure amendment could result from displacement of native soil bacteria by manure-borne bacteria during the application process or growth of native bacteria using manure-derived available nutrients.

Different Concentrations of Doxycycline in Swine Manure Affect the Microbiome and Degradation of Doxycycline Residue in Soil

Antibiotic residues that enter the soil through swine manure could disturb the number, community structure and functions of microbiota which could also degrade antibiotics in soil. Five different concentrations of doxycycline (DOX) incorporated into swine manure were added to soil to explore the effects of DOX on microbiota in soil and degradation itself. The results showed that the soil microbiome evolved an adaptation to the soil containing DOX by generating resistance genes. Moreover, some of the organisms within the soil microbiome played crucial roles in the degradation of DOX. The average degradation half-life of DOX in non-sterile groups was 13.85 ± 0.45 days, which was significantly shorter than the 29.26 ± 0.98 days in the group with sterilized soil (P < 0.01), indicating that the soil microbiome promoted DOX degradation. DOX addition affected the number of tetracycline resistance genes, depending on the type of gene and the DOX concentration. Among these genes, tetA, tetM, tetW, and tetX had significantly higher copy numbers when the concentration of DOX was higher. In contrast, a lower concentration of DOX had an inhibitory effect on tetG. At the same time, the microbial compositions were affected by the initial concentration of DOX and the different experimental periods. The soil chemical indicators also affected the microbial diversity changes, mainly because some microorganisms could survive in adversity and become dominant bacterial groups, such as the genera Vagococcus and Enterococcus (which were associated with electrical conductivity) and Caldicoprobacter spp. (which were positively correlated with pH). Our study mainly revealed soil microbiota and DOX degradation answered differently under variable concentrations of DOX mixed with swine manure in soil.

Recovery of Phosphorus From Swine Manure by Ultrasound/H2O2 Digestion, Struvite Crystallization, and Ferric Oxide Hydrate/Biochar Adsorption

Swine manure is potentially harmful to the environment but is also a readily accessible local source of phosphorus (P) for agricultural use. Decreasing the environmental impact of swine manure and recovering P from swine manure have been a challenge for a long time. In this study, an integrated process involving ultrasound/H₂O₂ digestion, struvite crystallization, and ferric oxide hydrate (HFO)/biochar adsorption was used to recover P from swine manure. The ultrasound/H₂O₂ treatment effectively solubilized the swine manure and converted organic P and other sparingly soluble P species into soluble phosphate. The struvite crystallization process allowed 85% of the available P to be recovered at pH 10.0 using a Mg:P molar ratio of 1.4 and a stirring rate of 150 rpm. HFO was loaded onto biochar synthesized by pyrolyzing ground corncob. The mechanism through which P was adsorbed was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The adsorption of P by the HFO/biochar followed pseudo-second-order kinetics and was primarily controlled by chemical processes. The maximum amounts of P adsorbed were 225.08–242.21 mg/g. Thermodynamic calculations indicated that the adsorption of P was endothermic and spontaneous and increased the degree of disorder in the overall system. P mass balance calculations indicated that 90.4% of the total P was recovered as struvite and P-saturated HFO/biochar.

Pre-digestion to enhance volatile fatty acids (VFAs) concentration as a carbon source for denitrification in treatment of liquid swine manure

Insufficient denitrification in biological treatment is often a result of the lack of a carbon source. In this study, use of the volatile fatty acids (VFAs) generated via pre-digestion as a carbon source to improve denitrification in sequencing batch reactor (SBR) treatment of liquid swine manure was investigated. The pre-digestion of swine manure was realized by storing the manure in a sealed container in room temperature and samples were taken periodically from the container to determine the VFA levels. The results showed that after 14 days of pre-digestion, the VFA level in the digested liquid was increased by 200%. A polynomial relationship for the VFA level in the digested manure with the digestion time was observed with a correlation coefficient being 0.9748. Two identical SBRs were built and operated on 8-h cycles in parallel, with one fed with pre-digested and the other raw swine manure. There were five phases included in each cycle, i.e., anaerobic (90 min), anoxic (150 min), anoxic/anaerobic (90 min), anoxic/aerobic (120 min), and settle/decant (30 min), and the feeding was split to 600 mL/200 mL and performed at the beginning of and 240 min into the cycle. The SBR fed on pre-digested swine manure achieved successful denitrification with only 0.35 mg/L nitrate left in the effluent, compared to 15.9 mg/L found in the effluent of the other SBR. Nitrite was not detected in the effluent from both SBRs. The results also indicated that there was no negative impact of feeding SBRs with the pre-digested liquid swine manure for treatment on the removal of other constituents such as total solids (TS), volatile solids (VS), suspended solids (SS), volatile suspended solids (VSS), and soluble chemical oxygen demand (COD). Therefore, anaerobic digestion as a pretreatment can be an effective way to condition liquid swine manure for SBR treatment to achieve sufficient nitrate removal.

Developing an anaerobic digester with external Zeolite filled column for enhancing methane production from swine manure - A feasibility study

Development of digesters with an external zeolite column facilitates the convenient removal of the zeolite with TAN, without disturbing the continuous anaerobic digestion process. A digester with an inside zeolite bed (In-Zeo) and digester without adding zeolite (No-Zeo) were employed to compare the process performance with digester with external zeolite column (EX-Zeo). The cumulative, CH₄ yields were 5% and 15% greater in the EX-Zeo, and the In-Zeo digesters respectively compared to the No-Zeo digesters. Also, the % VS reduction was 49%, 55% and 41%, respectively in the Ex-Zeo, In-Zeo and No-Zeo digesters. The results indicated that treatment with 7% zeolite during anaerobic digestion has the potential to improve biodegradation of swine manure. The addition of zeolite appeared to reduce TAN from the digestate, thereby enhancing the CH₄ yield. Zeolite could be used either internally or externally to enhance CH₄ production through anaerobic digestion of swine manure.

Aerobic treatment of swine manure to enhance anaerobic digestion and microalgal cultivation

Aerobic treatment of swine manure was coupled with anaerobic digestion and microalgal cultivation. A 14-day aerobic treatment reduced the total solid content of swine manure by >15%. Ammonia and carbon dioxide were stripped by the air supplied, and this off-gas was further used to aerate the culture of Chlorella vulgaris. The microalgal growth rates in Bristol medium and the wastewater with the off-gas increased from 0.08 to 0.22 g/L/d and from 0.15 to 0.24 g/L/d, respectively. Meanwhile, the aerobically treated swine manure showed a higher methane yield during anaerobic digestion. The experimental results were used to establish a demonstration unit consisting of a 100 L composter, a 200 L anaerobic digester, a 60 L tubular photobioreactor, and a 300 L micro-open raceway pond.

[Removal of Chlortetracycline and Morphological Changes in Heavy Metals in Swine Manure Using the Composting Process]

The widespread use of antibiotics and heavy metals in livestock farms results in large residues of antibiotics and heavy metals in the livestock manure. Composting technology can biodegrade residual antibiotics and solidify heavy metals. A pilot composting reactor was used to analyze the characteristics of chlortetracycline (CTC) removal at different antibiotic concentrations[0 mg·kg^-1 (CK), 10 mg·kg^-1 (T1), and 50 mg·kg^-1 (T2)]. Moreover, the morphological changes in heavy metals during the composting process were analyzed. After composting, no chlortetracycline was detected in the CK group and the antibiotics degradation rates of T1 and T2 groups reached 96.31% and 97.32%, respectively. The chlortetracycline degradation fits the pseudo-first-order kinetics model. Heavy metals can be solidified during the composting; thus, the bioavailable state of Cu and Zn (exchangeable state, reducible state) changed into the oxidation state and residues with apparent passivation formed. The correlation analysis showed that the removal of CTC showed strong positive correlations with the biological available Cu and Zn.

Increased agronomic and environmental value provided by biochars with varied physiochemical properties derived from swine manure blended with rice straw

To compensate for the shortcomings of manure biochar, an lignocellulose-based feedstock (rice straw) was added into manure-based feedstock (swine manure) at 3:1, 1:1, and 1:3 (w/w) manure/straw ratios during biochar production within the pyrolysis temperature ranging from 300 to 700 °C. The results showed that the pyrolysis temperatures and the proportions of straw added both influenced the biochar properties. The overall properties of biochars at 300, 400, and 500 °C were thoroughly different from those at 600 and 700 °C by principal components analysis (PCA). The XRD, FTIR, and SEM spectra suggested that the addition of straw considerably changed the mineral crystals, functional groups, and porous structures in manure biochar, respectively. The Zn(II) adsorption batch experiments showed that the biochars with more proportions of manure had the largest Zn(II) adsorption capacity than other biochars at 300 °C, which was attributed to the mineral components, oxygen functional groups, and surface areas. To meet varied agronomic and environmental requirements, the different conditions including pyrolysis temperatures and proportions of straw added should be quantitated.

Anaerobic digestion of Chinese cabbage waste silage with swine manure for biogas production: batch and continuous study

The aim of this study was to investigate the potential for anaerobic co-digestion of Chinese cabbage waste silage (CCWS) with swine manure (SM). Batch and continuous experiments were carried out under mesophilic anaerobic conditions (36-38°C). The batch test evaluated the effect of CCWS co-digestion with SM (SM: CCWS=100:0; 25:75; 33:67; 0:100, % volatile solids (VS) basis). The continuous test evaluated the performance of a single stage completely stirred tank reactor with SM alone and with a mixture of SM and CCWS. Batch test results showed no significant difference in biogas yield up to 25-33% of CCWS; however, biogas yield was significantly decreased when CCWS contents in feed increased to 67% and 100%. When testing continuous digestion, the biogas yield at organic loading rate (OLR) of 2.0 g VSL⁻¹ d⁻¹ increased by 17% with a mixture of SM and CCWS (SM:CCWS=75:25) (423 mL g⁻¹ VS) than with SM alone (361 mL g⁻¹ VS). The continuous anaerobic digestion process (biogas production, pH, total volatile fatty acids (TVFA) and TVFA/total alkalinity ratios) was stable when co-digesting SM and CCWS (75:25) at OLR of 2.0 g VSL⁻¹ d⁻¹ and hydraulic retention time of 20 days under mesophilic conditions.

Soybean Yield and Heterodera glycines Responses to Liquid Swine Manure in Nematode Suppressive Soil and Conducive Soil

The soybean cyst nematode (SCN), Heterodera glycines, is a major factor limiting soybean yield. Experiments were conducted in 2009 and 2010 to determine the effects of liquid swine manure and chemical fertilizer PK on soybean and corn yields, and on SCN population in an SCN-suppressive field (S-Site) and an SCN-conducive field (C-Site) in Minnesota. The experiment was a split-plot design with crop sequences as main plots and fertilizer treatments as subplots. The 2-yr crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus was SCN-susceptible soybean, and Res was SCN-resistant soybean. The fertilizer treatments were manure, PK, and a nonfertilizer as control. Manure did not reduce SCN egg population density but resulted in 31% lower SCN second-stage juvenile (J2) population density at the S-Site at 45 d after planting (DAP) in 2009. Manure also reduced spiral nematode (Helicotylenchus spp.) population density by 52% compared with PK and nonfertilizer treatments at S-Site at 45 DAP in 2009. The crop sequence of Corn-Sus and Res-Sus reduced the SCN egg and J2 but increased spiral nematode population density at both sites. An increase of 1.4 Mg/ha and 0.5 Mg/ha in yield of susceptible soybean was observed in manure and PK treatments, respectively, at the C-Site in 2009. Corn yield was 2.8 Mg/ha and 5.0 Mg/ha greater when treated with manure than nonfertilizer at the S-Site and C-Site, respectively. This study suggests that soil fertility management may be a useful strategy to alleviate the SCN damage to soybean.

Fate and Survival of Campylobacter coli in Swine Manure at Various Temperatures

Campylobacter coli is the most common Campylobacter species found in pig (95%), but the ability of this bacterium to survive in swine manure as well as the potential for causing human illness are poorly understood. We present here laboratory-scale experiments to investigate the effect of temperature on the survival of C. coli in spiked swine manure samples at temperatures from 4 to 52°C. The survival of C. coli during storage for 30 days was studied by three different methods: bacterial culture (plate counting), DNA qPCR, and mRNA RT-qPCR. The results indicate that C. coli could survive in swine manure up to 24 days at 4°C. At higher temperatures, this bacterium survived only 7 days (15°C) or 6 days (22°C) of storage. The survival of C. coli was extremely short (few hours) in samples incubated at 42 and 52°C. The results from the RT-qPCR method were consistent with the data from the bacterial culture method, indicating that it detected only viable C. coli cells, thus eliminating false-positive resulting from DNA from dead C. coli cells.

Effect of Liquid Swine Manure on Hatch and Viability of Heterodera glycines

Experiments were conducted in the laboratory and greenhouse to determine the effect of raw and anaerobically digested liquid swine manures on the hatch and viability of Heterodera glycines, the soybean cyst nematode. Anaerobic digestion was performed for 15 and 35 days to enrich volatile fatty acids (VFA) and ammonium (NH(4) (+)), respectively. All filtrates of the raw, VFA-enriched, and NH(4) (+)-enriched manures at 10(-1) to 250(-1) dilutions inhibited H. glycines hatch, and the reduction of hatch was increased with increasing concentration of the manure. Cumulative hatch at day 21 was only 2.1% to 3.7% in the 10(-1) dilution manures, while the hatch in water was 21% to 27.3%. The high concentrations appeared to be lethal to some eggs. Most second-stage juveniles (J2) of H. glycines were killed when incubated for 8 hours in the manure filtrate at the original concentration (>90% mortality) or for 48 hours at the 64(-1) dilution (> 82% mortality). When J2 were treated with the manures at 10(-1) to 250(-1) dilutions for 4 hours, only the 10(-1) dilution of VFA-enriched and raw manures resulted in a lower number of J2 that penetrated soybean roots as compared with lower concentrations. The VFA-enriched manure was the best, raw manure intermediate, and NH(4) (+)-enriched manure the least effective in inhibiting H. glycines hatch and killing eggs and J2.