Use of PCR-DGGE based molecular methods to assessment of microbial diversity during anaerobic treatment of antibiotic combinations

Improving antibiotic removal and anaerobic digestion performance of discarded cefradine pellets through thermo-alkaline pretreatment

Discarded cefradine pellets (DCP) as the hazardous wastes contain lots of bioavailable sucrose. Anaerobic digestion (AD) may be a promising technology for treating DCP, achieving dual goals of waste treatment and resource recovery. However, high concentration of cefradine will inhibit the AD process. This study applied thermo-alkaline pretreatment (TAP) to remove cefradine and improve the AD performance of DCP. Around 95% cefradine could be degraded to different intermediate degradation products (TPs) in TAP at optimal condition, and hydrolysis and hydrogenation were the main degradation pathways. Quantitative structure-activity relationship analysis indicated that the main TPs exhibited lower toxicity than cefradine, and DCP residues after TAP were almost not toxic to E. coli K12 and B. subtilis growth by antibacterial activity analysis. Therefore, TAP promoted the biomethane yield in AD of DCP residues (274.74 mL/g COD), which was 1.91 times that of control group. Besides, compared to control group, final cefradine concentrations in liquids and sludge were significantly decreased in AD system with TAP, lowering environmental risk and indicating stronger prospect for process application. Microbiological analysis revealed that acidogens (Macellibacteroides, Bacteroides), syntrophs (Syntrophobacter, Syntrophorhabdus), and acetoclastic Methanosaeta were enriched in AD system with TAP, which contributed to improving AD performance of DCP.

Fungal Diversity in Barley Under Different Storage Conditions

The diversity of fungi in barley in simulated storage environments was analyzed. Barley was stored at different temperatures (15, 25, 35°C) and relative humidity (55, 65, 75, 85 RH) for 180 and 360 days. Alpha diversity, beta diversity, species composition, and species differences were analyzed using Illumina HiSeq technology. The fungal communities in all barley samples before and after storage belonged to 3 phyla, 18 classes, 39 orders, 71 families, 103 genera, and 152 species. The relative abundance of the dominant phylum Ascomycota was 77.98–99.19%. The relative abundance of Basidiomycota was 0.77–21.96%. At the genus level, the dominant genera of fungi in barley initially included Fusarium, Aspergillus, Microdochium, Alternaria, and Epicoccum. After 360 days of storage, the dominant genera became Epicoccum, Alternaria, Bipolar, Cladosporium, Fusarium, and Aspergillus. According to Venn diagrams and principal coordinates analysis, the fungal community diversity in barley initially was much higher than in barley stored at different temperatures and humidity. The application of PLS-DA could accurately distinguish between barley stored for 180 and 360 days. Some high-temperature and high-humidity environments accelerated storage. The dominant genera differed in different storage conditions and constantly changed with increasing storage duration. Epicoccum was one of the dominant genera after longer storage periods. This study provides theoretical support for optimizing safe storage conditions in barley.

Microbial analysis for the ammonium removal from landfill leachate in an aerobic granular sludge sequencing batch reactor

In this study, a laboratory-scale sequencing batch reactor (SBR) equipped with aerobic granular sludge (AGS) technology was continuously operated for 220 days to remove ammonium from an existing landfill leachate. The ammonium removal was characterized by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) technology. This method helped to analyze the long-term community structural stability of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and denitrifying bacteria (DB) throughout the experiment. Simultaneously, 16S rRNA gene cloning and sequencing analysis identified the dominant species of different microbial species. Experimental results confirmed that ammonium removal was inhibited at the high nitrogen loading rate (NLR) stage while the low NLR stage achieved satisfactory ammonium removal. Moreover, the findings demonstrated that functionally stable wastewater treatment bioreactors facilitated the occurrence of stable microbial community structures.

Pyophage cocktail for the biocontrol of membrane fouling and its effect in aerobic microbial biofilm community during the treatment of antibiotics

Membrane bioreactor systems face an inevitable challenge that is biofouling, which not only hinders the operation of the system, but also poses an environmental and medical concern caused by the increased antibiotic resistance in bacterial biofilms. This study investigates the disruption of membrane fouling using bacteriophage cocktail (Pyophage) in an aerobic membrane bioreactor for treatment of wastewater containing high non-lethal concentration of erythromycin, tetracycline and sulfamethoxazole, while also considering the effect of the cocktail on performance. The results indicate that Pyophage cocktail contributes significantly to the decrease (45%) in transmembrane pressure while also suppressing biofilm-producing bacteria compared to the control reactors. It also reconstructed biodegradation mechanism of antibiotics especially increasing the relative abundance of gram-negative bacteria by enhancement the removal rate of erythromycin and sulfamethoxazole from the aerobic system to 99%.

Performance and Microbial Community of Different Biofilm Membrane Bioreactors Treating Antibiotic-Containing Synthetic Mariculture Wastewater

The performance of pollutant removals, tetracycline (TC) and norfloxacin (NOR) removals, membrane fouling mitigation and the microbial community of three Anoxic/Oxic membrane bioreactors (AO-MBRs), including a moving bed biofilm MBR (MBRa), a fixed biofilm MBR (MBRb) and an AO-MBR (MBRc) for control, were compared in treating antibiotic-containing synthetic mariculture wastewater. The results showed that MBRb had the best effect on antibiotic removal and membrane fouling mitigation compared to the other two bioreactors. The maximum removal rate of TC reached 91.65% and the maximum removal rate of NOR reached 45.46% in MBRb. The addition of antibiotics had little effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N)—both maintained more than 90% removal rate during the entire operation. High-throughput sequencing demonstrated that TC and NOR resulted in a significant decrease in the microbial diversity and the microbial richness MBRs. Flavobacteriia, Firmicutes and Azoarcus, regarded as drug-resistant bacteria, might play a crucial part in the removal of antibiotics. In addition, the dynamics of microbial community had a great change, which included the accumulation of resistant microorganisms and the gradual reduction or disappearance of other microorganisms under antibiotic pressure. The research provides an insight into the antibiotic-containing mariculture wastewater treatment and has certain reference value.

Activated Sludge Microbial Community and Treatment Performance of Wastewater Treatment Plants in Industrial and Municipal Zones

Controlling wastewater pollution from centralized industrial zones is important for reducing overall water pollution. Microbial community structure and diversity can adversely affect wastewater treatment plant (WWTP) performance and stability. Therefore, we studied microbial structure, diversity, and metabolic functions in WWTPs that treat industrial or municipal wastewater. Sludge microbial community diversity and richness were the lowest for the industrial WWTPs, indicating that industrial influents inhibited bacterial growth. The sludge of industrial WWTP had low Nitrospira populations, indicating that influent composition affected nitrification and denitrification. The sludge of industrial WWTPs had high metabolic functions associated with xenobiotic and amino acid metabolism. Furthermore, bacterial richness was positively correlated with conventional pollutants (e.g., carbon, nitrogen, and phosphorus), but negatively correlated with total dissolved solids. This study was expected to provide a more comprehensive understanding of activated sludge microbial communities in full-scale industrial and municipal WWTPs.

Metabolomics Study of Subsurface Wastewater Infiltration System Under Fluctuation of Organic Load

Subsurface Wastewater Infiltration System (SWIS) is a sewage ecological treatment technology with low investment, energy consumption, and operating cost. SWIS soil contains a large variety of microorganisms. The metabolic process and production of microorganisms are an important basis for qualitatively describing the process of pollutant removal. In order to discover the microbial decontamination pathways in SWIS, the metabolic profiles of soil microorganisms in SWIS were analyzed by UPLC-MS. Partial least squares-discriminant analysis (PLS-DA)and principal component analysis (PCA) pattern recognition methods were used to classify the samples. According to the model's variable importance factor (VIP value), potential biomarkers were screened and biological information contained in the metabolites was also analyzed. The correlation between metabolites and environmental factors was explored by RDA analysis. In total, 230 differential metabolites with VIP value greater than 1.5 were screened out when the influent organic load fluctuated at 250 mg L^-1, 400 mg L^-1, and 500 mg L^-1. After identifying and screening, 35 differential metabolites were identified and used to further analyze the metabolic pathway. It turns out that microbial metabolites in SWIS were mainly glycosides, fatty acids, amino acids, pigments, diterpenoids, and some polymers under medium and high organic loading conditions. At low organic load, the microbial metabolites in SWIS were mainly ketones, alcohols, and esters.

Effects of Physico-Chemical Parameters on Actinomycetes Communities during Composting of Agricultural Waste

The objective of this study was to investigate the influence of physico-chemical parameters on Actinomycetes communities and to prioritize those parameters that contributed to Actinomycetes community composition during the composting of agricultural waste. Denaturing gradient gel electrophoresis of polymerase chain reaction (PCR-DGGE) and redundancy analysis (RDA) were used to determine the relationships between those parameters and Actinomycetes community composition. Quantitative PCR (qPCR) and regression analysis were used to monitor the 16S rDNA copy numbers of Actinomycetes and to analyse the correlations between physico-chemical parameters and Actinomyces 16S rDNA gene abundance, respectively. The RDA results showed that moisture content, water soluble carbon (WSC) and pH (p < 0.05) made the main contributions to the temporal variations of Actinomycetes community composition. The output of the regression analysis indicated that moisture content (R2 = 0.407, p < 0.01) showed a negative linear relationship with the Actinomyces 16S rDNA gene abundance.

Evaluating the impact of bamboo biochar on the fungal community succession during chicken manure composting

The objective of this study was to investigate the fungal community succession and variations in chicken manure (CM) compost with different concentration of bamboo biochar (BB) as additive via the using of metagenomics method. The consequent obviously revealed that Chytridiomycota, Mucoromycota, Ascomycota and Basidiomycota were the dominant phylum, while Batrachochytrium, Funneliformis, Mucor, Phizophagus and Pyronema were the pre-dominant genera in each treatment. Redundancy analyses indicated that higher dosage of biochar applied treatments has significant correlation between fungal communities and environmental factors. The diversity of fungal community was analogous but the relative abundance (RA) was inconsistent among the all treatments. In addition, the principal component analysis was also confirmed that T5 and T6 treatments have considerably correlation than other treatments. However, the mean value of RA remained maximum in higher dosage of biochar blended treatments. Ultimately, the RA of different fungal genus and species were influenced in CM compost by the BB amendment.

Responses and roles of roots, microbes, and degrading genes in rhizosphere during phytoremediation of petroleum hydrocarbons contaminated soil

Rhizodegradation performed by plant roots and the associated bacteria is one of the major mechanisms that contribute to removal of petroleum hydrocarbons (PHCs) during phytoremediation. In this study, the pot-culture experiment using wild ornamental Hylotelephium spectabile (Boreau) H. Ohba was designed to explore responses and roles of roots, microbes, and degrading genes in the rhizodegradation process. Results showed that PHCs degradation rate by phytoremediation was up to 37.6-53.3% while phytoaccumulation accounted for a low proportion, just at 0.3-13.3%. A total of 37 phyla were classified through the high throughput sequencing, among which Proteobacteria, Actinobacteria, and Acidobacteria were the three most dominant phyla, accounting for >60% of the phylum frequency. The selective enrichment of PHC degraders with high salt-tolerance, including Alcanivorax and Bacteroidetes, was induced. Generally, relative abundance of the PHC degrading genes increased significantly with an increase in PHCs concentrations, and the gene copy number in the phytoremediation group was 1.46-14.44 times as much as that in the unplanted controls. Overall, the presence of PHCs and plant roots showed a stimulating effect on the development of specific degraders containing PHC degrading genes, and correspondingly, a biodegradation-beneficial community structure had been constructed to contribute to PHCs degradation in the rhizosphere.

Problematic effects of antibiotics on anaerobic treatment of swine wastewater

Swine wastewaters with high levels of organic pollutants and antibiotics have become serious environmental concerns. Anaerobic technology is a feasible option for swine wastewater treatment due to its advantage in low costs and bioenergy production. However, antibiotics in swine wastewater have problematic effects on micro-organisms, and the stability and performance of anaerobic processes. Thus, this paper critically reviews impacts of antibiotics on pH, COD removal efficiencies, biogas and methane productions as well as the accumulation of volatile fatty acids (VFAs) in the anaerobic processes. Meanwhile, impacts on the structure of bacteria and methanogens in anaerobic processes are also discussed comprehensively. Furthermore, to better understand the effect of antibiotics on anaerobic processes, detailed information about antimicrobial mechanisms of antibiotics and microbial functions in anaerobic processes is also summarized. Future research on deeper knowledge of the effect of antibiotics on anaerobic processes are suggested to reduce their adverse environmental impacts.

Long-term impact of a tetracycline concentration gradient on the bacterial resistance in anaerobic-aerobic sequential bioreactors

Wastewater treatment systems are considered as hotspots for release of antibiotic resistance genes (ARGs) into the environment. Anaerobic-aerobic sequential (AAS) bioreactors now are intensively used for wastewater treatment worldwide. However, the occurrence of ARGs in wastewater treatment systems exposed to low-level (i.e., sub-inhibitory) antibiotic is poorly known. Here, we studied the distribution patterns of seven tetracycline resistance genes (tet genes) including tet(A), tet(C), tet(G), tet(X), tet(M), tet(O), and tet(W), as well as one mobile element [class 1 integron (intI1)] in AAS bioreactors under exposure to tetracycline from 50 μg/L to 500 μg/L. Additionally, effect on the removal performance of nutrients and tetracycline in both anaerobic and aerobic units was also investigated. A tetracycline concentration gradient selected for bacterial resistance in the anaerobic reactor, with the exception of tet(A) and tet(W), and the tetracycline removal deteriorated by 47%. However, the abundance of tet and intI1 genes reduced in the subsequent aerobic unit, and the removal of tetracycline, soluble COD, and NH₄⁺-N maintained at average efficiencies of 91%, 90%, and 93%, respectively. The level of tet(X) was largely unaffected by AAS treatment. It is notable that intI1 genes probably played a crucial role on the horizontal dissemination of tet genes. The tetracycline levels and intI1 genes appear to be the primary factors influencing the occurrence of tet genes in AAS bioreactors. Nonetheless, AAS treatments still show promise for reducing antibiotics, ARGs and mobile elements without affecting nutrient removal, and need further research for practical applications.

PCR-DGGE Analysis on Microbial Community Structure of Rural Household Biogas Digesters in Qinghai Plateau

To investigate contribution of environmental factor(s) to microbial community structure(s) involved in rural household biogas fermentation at Qinghai Plateau, we collected slurry samples from 15 digesters, with low-temperature working conditions (11.1-15.7 °C) and evenly distributed at three counties (Datong, Huangyuan, and Ledu) with cold plateau climate, to perform polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and further sequencing. The bacterial communities in the total 15 digesters were classified into 38 genera with Mangroviflexus (12.1%) as the first dominant, and the archaeal communities into ten genera with Methanogenium (38.5%) as the most dominant. For each county, the digesters with higher biogas production, designated as HP digesters, exclusively had 1.6-3.1 °C higher fermentation temperature and the unique bacterial structure composition related, i.e., unclassified Clostridiales for all the HP digesters and unclassified Marinilabiliaceae and Proteiniclasticum for Ledu HP digesters. Regarding archaeal structure composition, Methanogenium exhibited significantly higher abundances at all the HP digesters and Thermogymnomonas was the unique species only identified at Ledu HP digesters with higher-temperature conditions. Redundancy analysis also confirmed the most important contribution of temperature to the microbial community structures investigated. This report emphasized the correlation between temperature and specific microbial community structure(s) that would benefit biogas production of rural household digesters at Qinghai Plateau.

Acclimatization of a mixed-animal manure inoculum to the anaerobic digestion of Axonopus compressus reveals the putative importance of Mesotoga infera and Methanosaeta concilii as elucidated by DGGE and Illumina MiSeq

In this study, a multifarious microbial mix from different sources is acclimatized over a period of three months to digesting cowgrass, and the changes in the community structure are examined with both a traditional denaturing gradient gel electrophoresis method as well as a next generation sequencing MiSeq method. It is shown that the much more in depth analysis by Illumina gives more information about the relative abundance and thus putative importance of the role of various microbes, in particular the bacterium Mesotoga infera and the archaeon Methanosaeta concilii.

Effect of Phanerochaete chrysosporium inoculation on bacterial community and metal stabilization in lead-contaminated agricultural waste composting

The effects of Phanerochaete chrysosporium inoculation on bacterial community and lead (Pb) stabilization in composting of Pb-contaminated agricultural waste were studied. It was found that the bioavailable Pb was transformed to stable Pb after composting with inoculum of P. chrysosporium. Pearson correlation analysis revealed that total organic carbon (TOC) and carbon/nitrogen (C/N) ratio significantly (P<0.05) influenced the distribution of Pb fractions. The richness and diversity of bacterial community were reduced under Pb stress and increased after inoculation with P. chrysosporium. Redundancy analysis indicated that C/N ratio, total organic matter, temperature and soluble-exchangeable Pb were the significant parameters to affect the bacterial community structure, solely explained 14.7%, 11.1%, 10.4% and 8.3% of the variation in bacterial community composition, respectively. In addition, the main bacterial species, being related to organic matter degradation and Pb stabilization, were found. These findings will provide useful information for composting of heavy metal-contaminated organic wastes.

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

Broad and increasing interest in sustainable wastewater treatment has led a paradigm shift towards more efficient means of treatment system operation. A key aspect of improving overall sustainability is the potential for direct wastewater effluent reuse. Anaerobic membrane bioreactors (AnMBRs) have been identified as an attractive option for producing high quality and nutrient-rich effluents during the treatment of municipal wastewaters. The introduction of direct effluent reuse does, however, raise several safety concerns related to its application. Among those concerns are the microbial threats associated with pathogenic bacteria as well as the emerging issues associated with antibiotic-resistant bacteria and the potential for proliferation of antibiotic resistance genes. Although there is substantial research evaluating these topics from the perspectives of anaerobic digestion and membrane bioreactors separately, little is known regarding how AnMBR systems can contribute to pathogen and antibiotic resistance removal and propagation in wastewater effluents. The aim of this review is to provide a current assessment of existing literature on anaerobic and membrane-based treatment systems as they relate to these microbial safety issues and utilize this assessment to identify areas of potential future research to evaluate the suitability of AnMBRs for direct effluent reuse.

Biofilm processes in treating mariculture wastewater may be a reservoir of antibiotic resistance genes

Antibiotics are heavily used in Chinese mariculture, but only a small portion of the added antibiotics are absorbed by living creatures. Biofilm processes are universally used in mariculture wastewater treatment. In this study, removal of antibiotics (norfloxacin, rifampicin, and oxytetracycline) from wastewater by moving bed biofilm reactors (MBBRs) and the influence of antibiotics on reactor biofilm were investigated. The results demonstrated that there was no significant effect of sub-μg/L-sub-mg/L concentrations of antibiotics on TOC removal. Moreover, the relative abundance of antibiotic resistance genes (ARGs) and antibiotic resistance bacteria (ARB) in MBBR biofilm increased because of selective pressure of antibiotics. In addition, antibiotics decreased the diversity of the biofilm bacterial community and altered bacterial community structure. These findings provide an empirical basis for the development of appropriate practices for mariculture, and suggest that disinfection and advanced oxidation should be applied to eliminate antibiotics, ARGs, and ARB from mariculture wastewater.

Identification and evaluation of a dominant alga from municipal wastewater in removal of nutrients

To access better removal of nutrients with algae-based techniques, a dominant alga from real municipal wastewater was identified and its capacity in removing low concentrations of nitrogen (NH⁺₄ or NO^-₃) and phosphorus (PO^3-₄) was evaluated. Results showed that Oedogonium brevicingulatum, a filamentous green alga, was confirmed as the dominant alga in the secondary effluent of a municipal wastewater treatment plant by polymerase chain reaction-denaturing gradient gel electrophoresis. Low concentrations of NH⁺₄ or NO^-₃ (≤5 mg N L^-1) and PO^3-₄ (≤0.5 mg P L^-1) were 100% removed by the algae in a 7-d test. The maximum nutrient removal rate (V_max) and the half-saturation constant (K_m) for NH⁺₄ (10.03 ± 0.95 mg g^-1d^-1 and 0.19 ± 0.03 mg L^-1) and NO^-₃ (8.43 ± 0.21 mg g^-1 d^-1 and 0.27 ± 0.11 mg L^-1) indicated the uptake capability for NH⁺₄ is higher than that for NO^-₃. Meanwhile, it showed higher affinity for PO^3-₄ (V_max: 1.42 ± 0.02 mg g^-1 d^-1; K_m: 0.02 ± 0.00 mg L^-1) with NH⁺₄ as nitrogen source than that (V_max: 1.24 ± 0.15 mg g^-1 d^-1; K_m: 0.06 ± 0.03 mg L^-1) with NO^-₃ as nitrogen source. Moreover, nutrient removal efficiencies were observed steady when nitrogen/phosphorus ratio ranged from 5:1 to 20:1. These results suggest that the dominant algae from municipal wastewater have potentials to be applied in nutrient removal.

Immobilization of Cd in river sediments by sodium alginate modified nanoscale zero-valent iron: Impact on enzyme activities and microbial community diversity

This paper investigated how sodium alginate (SA)-modified nanoscale zero-valent iron (NZVI), play a constructive role in the remediation of cadmium (Cd) contaminated river sediments. The changes of the fraction of Cd, enzyme activities (urease, catalase, dehydrogenase) and bacterial community structures with the treatment by SNZVI were observed. The sequential extraction experiments demonstrated that most mobile fractions of Cd were transformed into residues (the maximum residual percentage of Cd increases from 15.49% to 57.28% after 30 days of incubation at 0.1 wt% SA), with the decrease of bioavailability of Cd. Exclusive of dehydrogenase, the activities of the other two enzymes tested were enhanced with the increase of incubation time, which indicated that dehydrogenase might be inhibited by ferric ions formed from SNZVI whereas no obvious inhibition was found for other enzymes. Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analyses were used for the detection of microbial community changes, and the results showed that SNZVI and NZVI could increase bacterial taxa and improve bacterial abundance. All the experimental findings of this study provide new insights into the potential consequences of SNZVI treatments on the metal Cd immobilization in contaminated river sediments.

Evaluation of A Novel Split-Feeding Anaerobic/Oxic Baffled Reactor (A/OBR) For Foodwaste Anaerobic Digestate: Performance, Modeling and Bacterial Community

To enhance the treatment efficiency from an anaerobic digester, a novel six-compartment anaerobic/oxic baffled reactor (A/OBR) was employed. Two kinds of split-feeding A/OBRs R2 and R3, with influent fed in the 1^st, 3^rd and 5^th compartment of the reactor simultaneously at the respective ratios of 6:3:1 and 6:2:2, were compared with the regular-feeding reactor R1 when all influent was fed in the 1^st compartment (control). Three aspects, the COD removal, the hydraulic characteristics and the bacterial community, were systematically investigated, compared and evaluated. The results indicated that R2 and R3 had similar tolerance to loading shock, but the R2 had the highest COD removal of 91.6% with a final effluent of 345 mg/L. The mixing patterns in both split-feeding reactors were intermediate between plug-flow and completely-mixed, with dead spaces between 8.17% and 8.35% compared with a 31.9% dead space in R1. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that the split-feeding strategy provided a higher bacterial diversity and more stable bacterial community than that in the regular-feeding strategy. Further analysis indicated that Firmicutes, Bacteroidetes, and Proteobacteria were the dominant bacteria, among which Firmicutes and Bacteroidetes might be responsible for organic matter degradation and Proteobacteria for nitrification and denitrification.

Effects of anaerobic digestion on chlortetracycline and oxytetracycline degradation efficiency for swine manure

Manure containing antibiotics is considered a hazardous substance that poses a serious health risk to the environment and to human health. Anaerobic digestion (AD) could not only treatment animal waste but also generate valuable biogas. However, the interaction between antibiotics in manure and the AD process has not been clearly understood. In this study, experiments on biochemical methane potential (BMP) were conducted to determine the inhibition of the AD process from antibiotics and the threshold of complete antibiotic removal. The thresholds of the complete antibiotic removal were 60 and 40mg/kg·TS for CTC and OTC, respectively. CTC and OTC with concentrations below thresholds could increase the BMP of manure. When the CTC and OTC concentrations exceeded the thresholds, they inhibited manure fermentation, and the CTC removal rate declined exponentially with concentration (60-500mg/kg·TS). The relationship between OTC antibiotic concentration and its removal rate in AD treatment was described with exponential (40-100mg/kg·TS) and linear equations (100-500mg/kg·TS).

Mechanism and Effect of Temperature on Variations in Antibiotic Resistance Genes during Anaerobic Digestion of Dairy Manure

Animal manure comprises an important reservoir for antibiotic resistance genes (ARGs), but the variation in ARGs during anaerobic digestion at various temperatures and its underlying mechanism remain unclear. Thus, we performed anaerobic digestion using dairy manure at three temperature levels (moderate: 20 °C, mesophilic: 35 °C, and thermophilic: 55 °C), to analyze the dynamics of ARGs and bacterial communities by quantitative PCR and 16S rRNA gene sequencing. We found that 8/10 detected ARGs declined and 5/10 decreased more than 1.0 log during thermophilic digestion, whereas only four and five ARGs decreased during moderate and mesophilic digestion, respectively. The changes in ARGs and bacterial communities were similar under the moderate and mesophilic treatments, but distinct from those in the thermophilic system. Potential pathogens such as Bacteroidetes, Proteobacteria, and Corynebacterium were removed by thermophilic digestion but not by moderate and mesophilic digestion. The bacterial community succession was the dominant mechanism that influenced the variation in ARGs and integrons during anaerobic digestion. Thermophilic digestion decreased the amount of mesophilic bacteria (Bacteroidetes and Proteobacteria) carrying ARGs. Anaerobic digestion generally decreased the abundance of integrons by eliminating the aerobic hosts of integrons (Actinomycetales and Bacilli). Thermophilic anaerobic digestion is recommended for the treatment and reuse of animal manure.

Characterization of extracellular polymeric substances and microbial diversity in anaerobic co-digestion reactor treated sewage sludge with fat, oil, grease

Performance of co-digesters, treated of sewage sludge (SS) with fat, oil and grease (FOG), were conducted semi-continuously in two mesophilic reactors over 180days. Compared with SS mono-digestion, biogas production and TS removal efficiency of co-digestion were significantly enhanced up to 35% and 26% by adding upper limit FOG (60% on VS). Enhancement in co-digestion performance was also stimulated by the release of extracellular polymeric substances (EPS), which was increased 40% in both loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) than that of mono-digester. Based on high-throughput sequencing (HTS), analysis of microbial 16S rRNA gene comprehensively revealed the dynamic change of microbial community. Results showed that both bacterial and archaeal undergone an apparent succession with FOG addition, and large amount of consortium like Methanosaeta and N09 were involved in the process. Redundancy analysis showed the acetoclastic genera Methanosaeta distinctly related with biogas production and EPS degradation.

Biogas generation in anaerobic wastewater treatment under tetracycline antibiotic pressure

The effect of tetracycline (TC) antibiotic on biogas generation in anaerobic wastewater treatment was studied. A lab-scale Anaerobic Baffled Reactor (ABR) with three compartments was used. The reactor was operated with synthetic wastewater in the absence of TC and in the presence of 250 μg/L TC for 90 days, respectively. The removal rate of TC, volatile fatty acids (VFAs), biogas compositions (hydrogen (H₂), methane (CH₄), carbon dioxide (CO₂)), and total biogas production in each compartment were monitored in the two operational conditions. Results showed that the removal rate of TC was 14.97–67.97% in the reactor. The presence of TC had a large negative effect on CH₄ and CO₂ generation, but appeared to have a positive effect on H₂ production and VFAs accumulation. This response indicated that the methanogenesis process was sensitive to TC presence, but the acidogenesis process was insensitive. This suggested that the presence of TC had less influence on the degradation of organic matter but had a strong influence on biogas generation. Additionally, the decrease of CH₄ and CO₂ generation and the increase of H₂ and VFAs accumulation suggest a promising strategy to help alleviate global warming and improve resource recovery in an environmentally friendly approach.

Assessment of anaerobic bacterial diversity and its effects on anaerobic system stability and the occurrence of antibiotic resistance genes

This study evaluated the link between anaerobic bacterial diversity and, the biodegradation of antibiotic combinations and assessed how amending antibiotic combination and increasing concentration of antibiotics in a stepwise fashion influences the development of resistance genes in anaerobic reactors. The biodegradation, sorption and occurrence of the known antibiotic resistance genes (ARGs) of erythromycin and tetracycline were investigated using the processes of UV-HPLC and qPCR analysis respectively. Ion Torrent sequencing was used to detect microbial community changes in response to the addition of antibiotics. The overall results indicated that changes in the structure of a microbial community lead to changes in biodegradation capacity, sorption of antibiotics combinations and occurrence of ARGs. The enhanced biodegradation efficiency appeared to generate variations in the structure of the bacterial community. The results suggested that controlling the ultimate Gram-negative bacterial community, especially Acinetobacter-related populations, may promote the successful biodegradation of antibiotic combinations and reduce the occurrence of ARGs.

The shift of the microbial community in activated sludge with calcium treatment and its implication to sludge settleability

The sludge settleability is of prime importance for the activated sludge process. The effect of calcium ion on the biological performance of sludge was investigated in a lab-scale activated sludge system with varying Ca(2+) concentration. Results indicated that addition of 150mg/L Ca(2+) to the influent significantly improved the settling characteristics and metabolic reactivity of activated sludge in the bioreactors. Analyses using denaturing gradient gel electrophoresis (DGGE) and 16S rRNA sequencing showed that a significant difference in the presence of certain bacterial groups between the sludge systems with 150mg/L Ca(2+) and those with 0-100mg/L Ca(2+) addition. Ca(2+) also increased the production of the extracellular polymeric substance (EPS) and facilitated the development of microbial cluster in the bioreactor. Study showed that an addition of 150mg/L Ca(2+) to the influent provides a simple approach to improve the settling properties of activated sludge and maintain high pollutant removal efficiency.

Evaluation of microbial population and functional genes during the bioremediation of petroleum-contaminated soil as an effective monitoring approach

This study investigated the abundance and diversity of soil n-alkane and polycyclic aromatic hydrocarbon (PAH)-degrading bacterial communities. It also investigated the quantity of the functional genes, the occurrence of horizontal gene transfer (HGT) in the identified bacterial communities and the effect that such HGT can have on biostimulation process. Illumina sequencing was used to detect the microbial diversity of petroleum-polluted soil prior to the biostimulation process, and quantitative real-time PCR was used to determine changes in the bacterial community and functional genes (alkB, phnAc and nah) expressions throughout the biostimulation of petroleum-contaminated soil. The illumine results revealed that γ-proteobacteria, Chloroflexi, Firmicutes, and δ-proteobacteria were the most dominant bacterial phyla in the contaminated site, and that most of the strains were Gram-negative. The results of the gene expression results revealed that gram-negative bacteria and alkB are critical to successful bioremediation. Failure to maintain the stability of hydrocarbon-degrading bacteria and functional gene will reduce the extend to which alkanes and PAHs are degraded. According to the results of the study, the application of a C:N:P ratio of was 100:15:1 in the biodegradation experiment resulted in the highest rate at which petroleum hydrocarbons were biodegraded. The diversity of pollutant-degrading bacteria and the effective transfer of degrading genes among resident microorganisms are essential factors for the successful biostimulation of petroleum hydrocarbons. As such, screening these factors throughout the biostimulation process represents an effective monitoring approach by which the success of the biostimulation can be assessed.