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Abstract

Methane fermentation has been widely used to dispose sewage sludge at wastewater treatment plants (WWTPs), due to production of renewable energy in form of biogas. Antibiotics present in wastewater might accumulate in a sewage sludge. The aim of the present study was to investigate the impact of three antibiotics from different classes in three different doses on methane production from sewage sludge. For this purpose, metronidazole (MET), amoxicillin (AMO) and ciprofloxacin (CIP) were individually added to anaerobic reactors with sewage sludge collected from municipal WWTP. The antibiotics highest concentration (1024 mg/kg of AMO; 512 mg/kg of MET and CIP) lowered methane production and methane content in biogas. MET exerted the most marked effect and lowered methane production to 36.8 ± 3.7 mL CH4/kg volatile solids (VS). Tested antibiotics probably inhibited methanogenic Archaea, which resulted in volatile fatty acids (VFAs) accumulation. Addition of MET resulted in accumulation of many kinds of VFAs with the highest concentration of acetic acid (17.52 ± 1.85 g/L). Addition of AMO resulted in accumulation of butyric acid only (253.00 ± 15.89 g/L). However, addition of CIP resulted in accumulation mainly acetic acid (7.58 ± 0.82 g/L) and isovaleric acid (2.01 ± 0.41 g/L). Next, synergistic effect of these antibiotics in a low concentration of 16 mg/kg of AMO, 8 mg/kg of MET, and 2 mg/kg of CIP was measured in semi‐continuous conditions. These low concentrations of antibiotics individually slightly influenced methane fermentation, however synergistic effect of them caused inhibition of methane production and accumulation of VFAs. This article is protected by copyright. All rights reserved

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... For example, amoxicillin at a concentration of 0.76 mg/L significantly reduced methane production by 19.1 % (P < 0.05) in a sewage sludge anaerobic digestion system. However, although 48.44 mg/L amoxicillin did not further reduce methane production, it significantly reduced the content of methane in biogas (from 62.1 % to 43.9 %), this is because amoxicillin inhibited the activity of methanogenic archaea that convert volatile fatty acids into methane, resulting in a reduced methane content in the biogas (Rusanowska et al., 2020). Additionally, another study reported that amoxicillin at 48.44 mg/L reduced methane production in sewage sludge anaerobic digestion by 27.4 % and reduced methane content in biogas (reduced to 44 %) (Czatzkowska et al., 2021). ...
... To be more specific, the most common archaea were Methanosarcinales (0.4 %) and Methanomicrobiales (0.02 %), which are significant acetoclastic and hydrogenotrophic methanogens, respectively (Silva et al., 2020). In addition, ciprofloxacin at 0.012 and 0.095 mg/L only slightly reduced methane production, but a high concentration of 24.2 mg/L reduced methane production by 29.1 % (Rusanowska et al., 2020). The reason may be that the high concentration of ciprofloxacin inhibited the activity of methanogenic archaea (Rusanowska et al., 2020). ...
... In addition, ciprofloxacin at 0.012 and 0.095 mg/L only slightly reduced methane production, but a high concentration of 24.2 mg/L reduced methane production by 29.1 % (Rusanowska et al., 2020). The reason may be that the high concentration of ciprofloxacin inhibited the activity of methanogenic archaea (Rusanowska et al., 2020). Furthermore, biogas production during real/adapted sludge anaerobic digestion was strongly inhibited by 52 % when the concentration of ciprofloxacin was 0.5 mg/L (Environmentally relevant concentration) (Fáberová et al., 2019). ...
Article
As a common biological engineering technology, anaerobic digestion can stabilize sewage sludge and convert the carbon compounds into renewable energy (i.e., methane). However, anaerobic digestion of sewage sludge is severely affected by antibiotics. This review summarizes the effects of different antibiotics on anaerobic digestion of sewage sludge, including production of methane and volatile fatty acids (VFAs), and discusses the impact of antibiotics on biotransformation processes (solubilization, hydrolysis, acidification, acetogenesis and methanogenesis). Moreover, the effects of different antibiotics on microbial community structure (bacteria and archaea) were determined. Most of the research results showed that antibiotics at environmentally relevant concentrations can reduce biogas production mainly by inhibiting methanogenic processes, that is, methanogenic archaea activity, while a few antibiotics can improve biogas production. Moreover, the combination of multiple environmental concentrations of antibiotics inhibited the efficiency of methane production from sludge anaerobic digestion. In addition, some lab-scale pretreatment methods (e.g., ozone, ultrasonic combined ozone, zero-valent iron, Fe³⁺ and magnetite) can promote the performance of anaerobic digestion of sewage sludge inhibited by antibiotics.
... On the contrary, [61] reported that a mixture of OTC and CTC caused antagonism on volume of cumulative methane production, with their combined inhibition rate being lower than the sum of their individual inhibition rates. Conversely, [64] observed a synergistic effect in a mixture of 16 mg/kg of metronidazole, 8 mg/kg of amoxicillin, and 2 mg/kg of ciprofloxacin, causing notable inhibition on methane production and VFAs accumulation. [30] indicated that a possible antagonism effect might be generated internally between the antibiotics' functional groups in the mixed TC, OTC, SDZ, and Norf, greatly reducing methane production. ...
... On the other hand, mixed ENR and SMX showed non-significant effects on microbial activity [70]. Mixed AMO, MET, and CIP significantly reduced biogas production but did not inhibit the methanogenic activity [64]. However, it is hard to indicate the influence of mixed SAs compounds on the activity of microbes during AD process due to a lack of studies in this particular point. ...
Article
Veterinary antibiotics (VAs), extensively utilized in animal healthcare, are not present as a single compound in the environment and ultimately present as a mixtures. A significant research gap persists regarding the removal of mixed VAs (MVAs) and their influence on anaerobic digestion (AD) process. It is crucial to delve into the capabilities of AD in eliminating MVAs concern effectively. In this review, a state-of-art overview of MVAs removal and their impacts on AD process was provided for first time. Most of MVAs studies have concentrated on mixtures containing Tetracyclines (TCs), Fluoroquinolones (FQs), and Sulfonamides (SAs) with a leading interest by China. The collected data reveals that MVAs generated a competition on their biological degradation and their adsorption into sludge during AD process. These phenomena exhibited lower MVAs removal at approximately 60 ± 3.0 % compared to individual removal performances of antibiotics by AD. TCs tend to have a greater inhibitory impact on biogas production compared to other antibiotic groups, FQs could stimulate biogas production, while combining different antibiotic groups worsened the biogas production. The inoculum content appears to play a significant role in mitigating the effects of MVAs on biogas production. While MVAs effects on AD’s microbial activity were found to be contradictory depends mainly on the antibiotics group. Nevertheless, the above influences are riddled with uncertainties that require more extensive investigation. This review aims to broaden our understanding of MVAs interaction within the AD process, examines antibiotic mixtures' impact on AD-driven removal efficiency, and outlines future research directions.
... On the other hand, other studies showed contradictory results in term of methane production as a function of antibiotics levels. For example, increasing antibiotics concentrations leads to increase cumulative and daily methane production (Lallai et al. 2002;Lu et al. 2014;Rusanowska et al. 2020;Huang et al. 2023). The obtained results could be explained by using a different mixture of antibiotics and AD duration. ...
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The behavior and removal of roxithromycin (ROX), oxytetracycline (OTC), chlortetracycline (CTC), and enrofloxacin (ENR) were investigated during the steady state of sludge anaerobic digestion (AD) in semi-continuous mode (37 °C). Sludge was spiked at realistic concentrations (50 μg/L of each antibiotic) and then used to feed the bioreactor for 80 days. Antibiotics were extracted from the substrate and digested sludge samples by accelerated solvent extraction (ASE). Accurate determination of antibiotics was obtained by the standard addition method (SAM) associated with the liquid chromatography-tandem mass spectrometry (LC–MS/MS). The presence of antibiotics at a concentration of 2.5 μg/g TS had no inhibitory effects on methane (CH4) production, total and volatile solids (TS and VS) removal as well as chemical oxygen demand (COD) removal. During the steady-state, antibiotics were removed significantly by 50, 100, and 59% respectively for the ROX, OTC, and CTC. Furthermore, ENR removal was not statistically significant and was estimated at 36%. This study highlighted that AD process could partially remove parent compounds, but ROX, CTC, and ENR persisted in the digested sludge. Hence, AD could be considered as a sludge treatment for mitigating, but not suppressing, the release of antibiotics through sludge application.
... On the contrary, the relative abundances of CAT decreased in CIP_M and CIP_HP, which suggested that some archaeal genera of CAT were sensitive to higher concentrations and found it hard to recover. As for MT, CRAT, CRT, and RT, their relative abundances were stabilized during stress-and post-effect periods, which might be explained by the archaeal communities being resistant to the influences of a volatile environment [21]. Compared with known genera, the relative abundances of unknown taxa were more versatile ( Figure 3). ...
Article
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This study aimed to explore the response of archaeal communities and antibiotic-resistance genes (ARGs) to ciprofloxacin (CIP, 0.05–40 mg/L) and copper (Cu, 3 mg/L) combined pollution during stress- and post-effect periods in an activated sludge system. With the increase in the CIP concentration, the diversity of archaea decreased, but the richness increased under the stress of 10 mg/L CIP. Under stress and post effects, the change in unknown archaeal community structure was more significant than that of the known archaea. The relative abundance of unknown archaea was significantly reduced with the increase in CIP concentration. Meanwhile, there were certain archaea that belonged to abundant and rare taxa with different resistance and recovery characteristics. Among them, Methanosaeta (49.15–83.66%), Methanoculleus (0.11–0.45%), and Nitrososphaera (0.03–0.36%) were the typical resistant archaea to combined pollution. And the resistance of the abundant taxa to combined pollution was significantly higher than that of the rare taxa. Symbiotic and competitive relationships were observed between the known and the unknown archaea. The interactions of abundant known taxa were mainly symbiotic relationships. While the rare unknown taxa were mainly competitive relationships in the post-effect period. Rare archaea showed an important ecological niche under the stress-effect. Some archaea displayed positive correlation with ARGs and played important roles as potential hosts of ARGs during stress- and post-periods. Methanospirillum, Methanosphaerula, Nitrososphaera and some rare unknown archaea also significantly co-occurred with a large number of ARGs. Overall, this study points out the importance of interactions among known and unknown archaeal communities and ARGs in a wastewater treatment system under the stress of antibiotics and heavy metal combined pollution.
... Over and above that, methanogenesis was elevated although most studies investigating bioreactors reported reductions of CH 4 production as a consequence of antibiotic exposure (e.g. Aydin et al., 2015;Reyes-Contreras and Vidal, 2015;Rusanowska et al., 2020, but see: Lu et al., 2014). An additional mechanistic explanation of the increased productivity in this study might be provided by the fact that antibiotics can stimulate the release of extracellular polymeric substances in bacteria, which might represent an additional source of carbon utilized by methanogens (Lu et al., 2014). ...
Article
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Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2) and is inter alia produced in natural freshwater ecosystems. Given the rise in CH4 emissions from natural sources, researchers are investigating environmental factors and climate change feedbacks to explain this increment. Despite being omnipresent in freshwaters, knowledge on the influence of chemical stressors of anthropogenic origin (e.g., antibiotics) on methanogenesis is lacking. To address this knowledge gap, we incubated freshwater sediment under anaerobic conditions with a mixture of five antibiotics at four levels (from 0 to 5000 µg/L) for 42 days. Weekly measurements of CH4 and CO2 in the headspace, as well as their compound-specific δ13C, showed that the CH4 production rate was increased by up to 94% at 5000 µg/L and up to 29% at field-relevant concentrations (i.e., 50 µg/L). Metabarcoding of the archaeal and eubacterial 16S rRNA gene showed that effects of antibiotics on bacterial community level (i.e., species composition) may partially explain the observed differences in CH4 production rates. Despite the complications of transferring experimental CH4 production rates to realistic field conditions, the study indicated that chemical stressors contribute to the emissions of greenhouse gases by affecting the methanogenesis in freshwaters.
... The efficiency of anaerobic digestion is reduced by the presence of antibiotics and antibiotic residues, which inhibit the microbial community and activity, thus further limiting the efficiency of the entire anaerobic digestion system (Kovalakova et al., 2020;Rusanowska et al., 2020). Accordingly, existing pre-treatments are aimed to reduce levels of antibiotic residues (Gurmessa et al., 2020). ...
Article
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Recycling waste into new materials and energy is becoming a major challenge in the context of the future circular economy, calling for advanced methods of waste treatment. For instance, microbially-mediated anaerobic digestion is widely used for conversion of sewage sludge into biomethane, fertilizers and other products, yet the efficiency of microbial digestion is limited by the occurrence of antibiotics in sludges, originating from drug consumption for human and animal health. Here we present antibiotic levels in Chinese wastewater, then we review the effects of antibiotics on hydrolysis, acidogenesis and methanogenesis, with focus on macrolides, tetracyclines, β-lactams and antibiotic mixtures. We detail effects of antibiotics on fermentative bacteria and methanogenic archaea. Most results display adverse effects of antibiotics on anaerobic digestion, yet some antibiotics promote hydrolysis, acidogenesis and methanogenesis.
... The AD process settings were described in our previous study [34]. Anaerobic conditions were achieved by continuous flushing of pure nitrogen through sludge. ...
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This study showed the effect of amoxicillin (AMO), and oxytetracycline (OXY) at a concentration of 512 µg mL−1, and sulfamethoxazole (SMX), and metronidazole (MET) at a concentration of 1024 µg mL−1 on the efficiency of anaerobic digestion (AD) of sewage sludge (SS) and cattle slurry (CS). The production of biogas and methane (CH4) content, and the concentration of volatile fatty acids (VFAs) was analyzed in this study. Other determinations included the concentration of the mcrA gene, which catalyzes the methanogenesis, and analysis of MSC and MST gene concentration, characteristic of the families Methanosarcinaceae and Methanosaetaceae (Archaea). Both substrates differed in the composition of microbial communities, and in the sensitivity of these microor-ganisms to particular antimicrobial substances. Metronidazole inhibited SS fermentation to the greatest extent (sixfold decrease in biogas production and over 50% decrease in the content of CH4). The lowest concentrations of the mcrA gene (106 gD−1) were observed in CS and SS digestates with MET. A decline in the number of copies of the MSC and MST genes was noted in most of the digestate samples with antimicrobials supplementation. Due to selective pressure, antimicrobials led to a considerably lowered efficiency of the AD process and induced changes in the structure of methanogenic biodiversity.
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China is a major producer of antibiotics in the world, and the production process of antibiotics is accompanied by a large amount of wastewater containing high concentration of antibiotics. However, it is difficult to simultaneously remove conventional pollutants, antibiotics, and antibiotic resistance genes from antibiotic production wastewater by traditional anaerobic biological treatment technology. Anaerobic membrane bioreactor (AnMBR) combines the advantages of anaerobic treatment and membrane technology, and exhibits potential for treating antibiotics-containing wastewater. Based on the literature review, this paper summarized the current progress of antibiotics wastewater treatment using AnMBR, which showed the advantages on pollutant removal and reduction of antibiotic resistance genes. The impacts of antibiotics on microbial inhibition and enrichment of antibiotic resistance genes were focused. Moreover, this study proposed that technique integration of “enhanced hydrolysis pretreatment to remove antibiotic -AnMBR” was optimal short-flow treatment approach for antibiotic production wastewater. This technique integration could simultaneously improve wastewater treatment efficiency and antibiotic resistance control, which is the reference for green, efficient and safe treatment of pharmaceutical wastewater.
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A study was conducted to determine whether differences in the levels of volatile fatty acids (VFAs) in anaerobic digester plants could result in variations in the indigenous methanogenic communities. Two digesters (one operated under mesophilic conditions, the other under thermophilic conditions) were monitored, and sampled at points where VFA levels were high, as well as when VFA levels were low. Physical and chemical parameters were measured, and the methanogenic diversity was screened using the phylogenetic microarray ANAEROCHIP. In addition, real-time PCR was used to quantify the presence of the different methanogenic genera in the sludge samples. Array results indicated that the archaeal communities in the different reactors were stable, and that changes in the VFA levels of the anaerobic digesters did not greatly alter the dominating methanogenic organisms. In contrast, the two digesters were found to harbour different dominating methanogenic communities, which appeared to remain stable over time. Real-time PCR results were inline with those of microarray analysis indicating only minimal changes in methanogen numbers during periods of high VFAs, however, revealed a greater diversity in methanogens than found with the array.
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Antibiotic resistance genes have become highly mobile since the development of antibiotic chemotherapy. A considerable body of evidence exists proving the link between antibiotic use and the significant increase in drug-resistant human bacterial pathogens. The application of molecular detection and tracking techniques in microbial ecological studies has allowed the reservoirs of antibiotic resistance genes to be investigated. It is clear that the transfer of resistance genes has occurred on a global scale and in all natural environments. The considerable diversity of bacteria and mobile elements in soils has meant that the spread of resistance genes has occurred by all currently known mechanisms for bacterial gene transfer. Trans-kingdom transfers from plants to bacteria may occur in soil. Hot spots for gene transfer in the soil/plant environment have been described and colonized niches such as the rhizosphere and other nutrient-enriched sites, for example manured soil, have been identified as reservoirs of resistance genes. Although exposure and selection for tolerance of antibiotics is considerable in clinical environments there is increasing evidence that selection for resistant phenotypes is occurring in natural environments. Antibiotic-producing bacteria are abundant in soil and there is evidence that they are actively producing antibiotics in nutrient-enriched environments in soil. In addition there is clear evidence that the self-resistance genes found within antibiotic gene clusters of the producers have transferred to other non-producing bacteria. Perhaps most important of all is the use of antibiotics in agriculture as growth promotants and for treatment of disease in intensively reared farm animals. These treatments have resulted in gut commensal and pathogenic bacteria acquiring resistance genes under selection and then, due to the way in which farm slurries are disposed of, the spread of these genes to the soil bacterial community. Integrons with multiple resistance gene cassettes have been selected and disseminated in this way; many of these cassettes carry other genes such as those conferring heavy metal and disinfectant resistance which have been co-selected in bacteria surviving in effluents and contaminated soils, further maintaining and spreading the antibiotic resistance genes.
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Antibiotics can disturb the production of biogas during anaerobic digestion. This study shows a systematic approach to understanding how the different bacterial populations involved in the final conversion of organic matter into methane are inhibited by 15 antimicrobial agents with different specificities and modes of action. The results obtained show the following trends: (i) some inhibitors, such as the macrolide erythromycin, lack any inhibitory effect on biogas production; (ii) some antibiotics, with different specificities, have partial inhibitory effects on anaerobic digestion and decrease methane production by interfering with the activity of propionic-acid- and butyric-acid-degrading bacteria, (e.g. antibiotics that interfere with cell wall synthesis, RNA polymerase activity and protein synthesis, especially the aminoglycosides); (iii) the protein synthesis inhibitors chlortetracycline (IC50 40 mg l-1) and chloramphenicol (IC50 15-20 mg l-1) are very powerful inhibitors of anaerobic digestion. The majority of the antibiotics tested lacked activity against acetoclastic methanogens, being active only on the acetogenic bacteria. However, chloramphenicol and chlortetracycline could cause the complete inhibition of the acetoclastic methanogenic archaea.
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This work investigated the individual and combined effects of zinc oxide, norfloxacin, and sulfamethazine on sludge anaerobic digestion-associated methane production, protein and carbohydrate metabolism, and microbial diversity. Norfloxacin and sulfamethazine (500 mg/kg) did not inhibit methane production, but inhibited its production rate. Zinc oxide nanoparticles with antibiotics inhibited hydrolysis, fermentation, and methanogenesis over varying digestion periods. Complex pollution had a greater impact on methane production than zinc oxide alone, with acute, synergistic toxicity to methanogenesis over short periods. Complex pollution also had varying effects on bacterial and archaeal communities during digestion. These results aid understanding of the toxicity of emerging contaminants in sludge digestion, with the potential to improve pollution removal and reduce associated risks.
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This study investigated the effects and fate of CIP on anaerobic sludge over a wide range of concentrations (0.05-50 mg/L), and 0.5-50 mg/L significantly inhibited organic removal and methanogenic activity, increased volatile fatty acids accumulation and low molecular weight soluble microbial products (SMPs), including p-cresol and nitrogen-containing compounds. Although microbial communities exposed to CIP did not differ significantly from the control in species diversity indices, Syntrophobacter and Methanothrix associated with acetogenesis and acetoclastic methanogenesis, respectively, were underrepresented in the CIP-exposed communities. Our study advances understanding of how environmentally relevant concentrations of CIP disrupts anaerobic digestion, which has important implications for anaerobic engineered systems treating CIP-bearing waste streams.
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We evaluated the chronic impact of oxytetracycline (OTC) on performance and antibiotic resistance development during the mesophilic anaerobic digestion (AD) of antibiotic-containing biomass. Mesophilic AD was conducted in a completely stirred tank reactor by constantly feeding municipal excess sludge spiked with increasing concentrations of OTC (0-1000 mg L-1) under a solid retention time of 20 days over a period of 265 days. Results showed that methane generation of mesophilic AD was inhibited when the OTC concentration in digested sludge was increased to around 18,000 mg kg-1(OTC dose, 1000 mg L-1), due to the inhibition of fermenting and acidogenic bacteria. Metagenomic sequencing and high-throughput quantitative PCR analysis demonstrated that tetracycline resistance genes were the most dominant type (38.47-43.76%) in the resistome, with tetG, tetX, tetM, tetR, tetQ, tetO, and tetL as the dominant resistant subtypes throughout the whole experimental period. The relative abundance of these tet genes increased from 2.10 × 10-1before spiking OTC (OTC concentration in digested sludge, 8.97 mg kg-1) to 2.83 × 10-1(p < 0.05) after spiking OTC at a dose of 40 mg L-1(OTC concentration in digested sludge, 528.52 mg kg-1). Furthermore, mobile genetic elements, including integrons, transposons, and plasmids, were also enriched with the increase in OTC dose. Based on partial canonical correspondence analysis, the contributions of horizontal (mobile element alteration) and vertical (bacterial community shift) gene transfer to antibiotic resistome variation were 29.35% and 21.51%, respectively. Thus, considering the inhibition of hydrolytic acidification and enrichment of antibiotic resistome, mesophilic AD is not suggested to directly treat the biomass containing OTC concentration higher than 200 mg L-1.
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The study focused on acute inhibition mechanism and effect of sulfamethoxazole (SMX) and tetracycline (TET) on the carboxylic acid utilization and the methanogenic activity. Duplicate batch reactors were operated in a range of 1–1000 mg/L for each antibiotic. Short chain fatty acid removal was determined in terms of soluble Chemical Oxygen Demand (COD) and specific fatty acid measurements together with methane generation. Additionally, seed sludge was characterized by Fluorescent in situ Hybridization (FISH). The inhibitory impacts of two antibiotics were variable with the initial dose. While in the lower sulfamethoxazole dosage, inhibition was observed in methanogenesis step. 35.8% and 46.8% inhibition in methane production were observed at 25 mg/L and 50 mg/L of SMX amended reactors. In higher SMX doses, short chain fatty acid utilization was inhibited even no acetate produced in the system. Inhibitory effect of tetracycline started at lower dose. 25% inhibition in methane production started at 1 mg/L of TET concentration. Additionally, it affected utilization of butyrate, propionate and acetate together. Tetracycline inhibited total microbial metabolism in terms of substrate utilization and methane generation between 500 mg/L and 1000 mg/L. FISH results showed that the dominant methanogenic group in the sludge was acetoclastic methanogens in term of Methanosarcina and Methanosaeta spp.
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This study evaluated the long-term effects of erythromycin-tetracycline-sulfamethoxazole (ETS) and sulfamethoxazole-tetracycline (ST) antibiotic combinations on the microbial community and examined the ways in which these antimicrobials impact the performance of anaerobic reactors. Quantitative real-time PCR was used to determine the effect that different antibiotic combinations had on the total and active Bacteria, Archae and Methanogenic Archae. Three primer sets that targeted metabolic genes encoding formylterahydrofolate synthetase, methyl-coenzyme M reductase and acetyl-coA synthetase were also used to determine the inhibition level on the mRNA expression of the homoacetogens, methanogens and specifically acetoclastic methanogens, respectively. These microorganisms play a vital role in the anaerobic degradation of organic waste and targeting these gene expressions offers operators or someone at a treatment plant the potential to control and the improve the anaerobic system. The results of the investigation revealed that acetogens have a competitive advantage over Archaea in the presence of ETS and ST combinations. Although the efficiency with which methane production takes place and the quantification of microbial populations in both the ETS and ST reactors decreased as antibiotic concentrations increased, the ETS batch reactor performed better than the ST batch reactor. According to the expression of genes results, the syntrophic interaction of acetogens and methanogens is critical to the performance of the ETS and ST reactors. Failure to maintain the stability of these microorganisms resulted in a decrease in the performance and stability of the anaerobic reactors. Copyright © 2015 Elsevier Ltd. All rights reserved.
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Antibiotic resistance has become a serious threat to human health. Sewage treatment plant (STP) is one of the major sources of antibiotic resistance genes (ARGs) in natural environment. High-throughput sequencing-based metagenomic approach was applied to investigate the broad-spectrum profiles and fate of ARGs in a full scale STP. Totally, 271 ARGs subtypes belonging to 18 ARGs types were identified by the broad scanning of metagenomic analysis. Influent had the highest ARGs abundance, followed by effluent, anaerobic digestion sludge and activated sludge. 78 ARGs subtypes persisted through the biological wastewater and sludge treatment process. The high removal efficiency of 99.82% for total ARGs in wastewater suggested that sewage treatment process is effective in reducing ARGs. But the removal efficiency of ARGs in sludge treatment was not as good as that in sewage treatment. Furthermore, the composition of microbial communities was examined and the correlation between microbial community and ARGs was investigated using redundancy analysis. Significant correlation between 6 genera and the distribution of ARGs were found and 5 of the 6 genera included potential pathogens. This is the first study on the fate of ARGs in STP using metagenomic analysis with high-throughput sequencing and hopefully would enhance our knowledge on fate of ARGs in STP.
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The impacts of four common animal husbandry antibiotics (ampicillin, florfenicol, sulfamethazine, and tylosin) on anaerobic digestion (AD) treatment efficiency and the potential for antibiotic degradation during digestion were evaluated. Sulfamethazine and ampicillin exhibited no impact on total biogas production up to 280 and 350mg/L, respectively, although ampicillin inhibited biogas production rates during early stages of AD. Tylosin reduced biogas production by 10-38% between 130 and 913mg/L. Florfenicol reduced biogas by ∼5%, 40% and 75% at 6.4, 36 and 210mg/L, respectively. These antibiotic concentrations are higher than commonly seen for mixed feedlot manure, so impacts on full scale AD should be minimal. Antibiotic degradation products were found, confirming AD effectively degraded ampicillin, florfenicol, and tylosin, although some products were persistent throughout the process. Contamination of AD solid and liquid effluents with sulfamethazine and antibiotic transformation products from florfenicol and tylosin could present an environmental concern.
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The individual and combined effect of cefazolin (CFZ) and oxytetracycline (OTC) on thermophilic anaerobic digestion (55°C) of dairy manure in batch digesters was investigated. Methane productions from the concentrations tested (30, 60 and 90mgL(-1)) were compared with no-antibiotic control. CFZ concentrations showed no inhibition (P>0.05) for methane production. The individual OTC and combined CFZ and OTC at concentrations of 30, 60 and 90mgL(-1) represented 79.1%, 70.3%, 68.6% (P<0.05) and 88.5%, 82.7%, 70.3% (P<0.05) respectively, of the control values. The high CH(4) production, optimal pH and VFA data during digestion indicated the process stability and treatment efficiency.
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The effect of antibiotics on the psychrophilic anaerobic digestion (PAD) of swine manure slurry in sequencing batch reactors (SBRs) was investigated. Six antibiotics, tylosin, lyncomycin, tetracycline, sulphamethazine, penicillin and carbadox, were individually added to the pig diet at their maximum prescribed level. Manure slurries collected from pigs receiving control and medicated diets were individually fed to pairs of SBRs at organic loading rates (OLRs) ranging from 2.2 to 3.5 g total chemical oxygen demand (TCOD) per litre of bioreactor initial sludge volume per day. Three mixtures of slurries from pigs fed on individual antibiotics were also tested at OLRs varying between 2.5 and 3.2 g TCOD/l/d. The presence of penicillin and tetracycline in manure slurries reduced methane production by 35% and 25%, respectively. However, the slurries from pigs receiving the other antibiotics and the slurry mixtures did not significantly affect (P>0.05) methane production. In addition, the presence of individual and combined antibiotics did not have noticeable adverse effects on process stability and treatment efficiency. Total and soluble COD (TCOD and SCOD) reduction, total and volatile solids (TS and VS) removal, pH and volatile fatty acid (VFA) concentrations in experimental units were not statistically different (P>0.05) than in the controls. In all bioreactors, the TCOD, SCOD, TS and VS removal exceeded 62%, 76%, 65% and 75%, respectively.
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Volatile fatty acids (VFAs) are important mid-products in the production of methane, and their concentrations affect the efficiency of fermentation. However, their effects on methane yield and methanogenic bacteria growth have been less extensively studied. To address these effects, acetic acid, propionic acid, butyric acid and ethanol were used as substrates and an L9(34) orthogonal table was adopted to design anaerobic digestion tests. When the highest concentrations of ethanol, acetic acid and butyric acid were 2400, 2400 and 1800 mg L−1, respectively, there was no significant inhibition of the activity of methanogenic bacteria. However, when the propionic acid concentration was increased to 900 mg L−1, significant inhibition appeared, the bacteria concentration decreased from 6 × 107 to 0.6–1 × 107 ml−1 and their activity would not reconvert. These effects resulted in the accumulation of ethanol and VFAs, and the total methane yield consequently became very low (<321 ml). The original propionic acid concentration had a significant inhibitory effect on methanogenic bacteria growth (P < 0.01). An optimization analysis showed that ethanol, acetic acid, propionic acid and butyric acid at concentrations of 1600, 1600, 300 and 1800 mg L−1, respectively, led to the maximum accumulative methane yield of 1620 ml and the maximum methanogenic bacteria concentration of 7.3 × 108 ml−1.
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Upflow Anaerobic Sludge Bed (UASB) wastewater (pre-)treatment systems represent a proven sustainable technology for a wide range of very different industrial effluents, including those containing toxic/inhibitory compounds. The process is also feasible for treatment of domestic wastewater with temperatures as low as 14–16° C and likely even lower. Compared to conventional aerobic treatment systems the anaerobic treatment process merely offers advantages. This especially is true for the rate of start-up. The available insight in anaerobic sludge immobilization (i.e. granulation) and growth of granular anaerobic sludge in many respects suffices for practice. In anaerobic treatment the immobilization of balanced microbial communities is essential, because the concentration of intermediates then can be kept sufficiently low. So far ignored factors like the death and decay rate of organisms are of eminent importance for the quality of immobilized anaerobic sludge. Taking these factors into account, it can be shown that there does not exist any need for ‘phase separation’ when treating non- or slightly acidified wastewaters. Phase separation even is detrimental in case the acidogenic organisms are not removed from the effluent of the acidogenic reactor, because they deteriorate the settleability of granular sludge and also negatively affect the formation and growth of granular sludge. The growing insight in the role of factors like nutrients and trace elements, the effect of metabolic intermediates and end products opens excellent prospects for process control, e.g. for the anaerobic treatment of wastewaters containing mainly methanol. Anaerobic wastewater treatment can also profitably be applied in the thermophilic and psychrophilic temperature range. Moreover, thermophilic anaerobic sludge can be used under mesophilic conditions. The Expanded Granular Sludge Bed (EGSB) system particularly offers big practical potentials, e.g. for very low strength wastewaters (COD ≪ 1 g/l) and at temperatures as low as 10° C. In EGSB-systems virtually all the retained sludge is employed, while compared to UASB-systems also a substantially bigger fraction of the immobilized organisms (inside the granules) participates in the process, because an extraordinary high substrate affinity prevails in these systems. It looks necessary to reconsider theories for mass transfer in immobilized anaerobic biomass. Instead of phasing the digestion process, staging of the anaerobic reactors should be applied. In this way mixing up of the sludge can be significantly reduced and a plug flow is promoted. A staged process will provide a higher treatment efficiency and a higher process stability. This especially applies for thermophilic systems.
Article
Antibiotics commonly used in the treatment of pigs - amoxicillin trihydrate, oxytetracycline hydrochloride and thiamphenicol were added at different concentrations to aliquots of pig waste slurry plus anaerobic sludge in serum bottles. The biogas production and methane concentration in the headspace were monitored to determine the effect of the antibiotics on the anaerobic process. With thiamphenicol significant differences in methane production were found for concentrations of 80 and 160 mg l(-1) slurry. Compared to the control, only minor differences in methane production were noted in the bottles to which amoxicillin (60 and 120 mg l(-1)) had been added. Methane production was about the same for the bottles with different oxytetracycline concentrations (125 and 250 mg l(-1)) and for the control.
Article
Methane-forming microbes of the phylogenetic domain Archaea are part of the strictly anaerobic microflora of the human intestine. In bone marrow transplant (BMT) recipients, the regimen of intestinal decontamination with metronidazole is targeted to anaerobic bacteria. The effect on the anaerobic methanoarchaea, however, is unknown. Therefore, the faeces of patients undergoing BMT were investigated for methane production. The anoxic Hungate technique and an archaeal growth medium were used to culture faecal specimens. Methane production was measured in the head space of the culture bottles by gas chromatography using a thermal conductivity detector. In a testing serial specimen of 100 patients, 13 patients were found to bear methanogens, and 11 of these patients received metronidazole. The methane-producing faecal specimens occurred before metronidazole use in three patients, during the first week in five patients, and after cessation in three patients. No specimen of the 11 patients that was obtained during the 2nd-5th week of gut decontamination showed methane production. It is concluded that use of metronidazole directed against faecal anaerobic bacteria also suppresses or eliminates faecal methanogenic Archaea.
Article
The industrial production of beta-lactam antibiotics by fermentation over the past 50 years is one of the outstanding examples of biotechnology. Today, the beta-lactam antibiotics, particularly penicillins and cephalosporins, represent the world's major biotechnology products with worldwide dosage form sales of approximately 15 billion US dollars or approximately 65% of the total world market for antibiotics. Over the past five decades, major improvements in the productivity of the producer organisms, Penicillium chrysogenum and Acremonium chrysogenum (syn. Cephalosporium acremonium) and improved fermentation technology have culminated in enhanced productivity and substantial cost reduction. Major fermentation producers are now estimated to record harvest titers of 40-50 g/l for penicillin and 20-25 g/l for cephalosporin C. Recovery yields for penicillin G or penicillin V are now >90%. Chemical and enzymatic hydrolysis process technology for 6-aminopenicillanic acid or 7-aminocephalosporanic acid is also highly efficient (approximately 80-90%) with new enzyme technology leading to major cost reductions over the past decade. Europe remains the dominant manufacturing area for both penicillins and cephalosporins. However, due to ever increasing labor, energy and raw material costs, more bulk manufacturing is moving to the Far East, with China, Korea and India becoming major production countries with dosage form filling becoming more dominant in Puerto Rico and in Ireland.
Article
Degradation rates and removal efficiencies of Metronidazole using UV, UV/H2O2, H2O2/Fe2+, and UV/H2O2/Fe2+ were studied in de-ionized water. The four different oxidation processes were compared for the removal kinetics of the antimicrobial pharmaceutical Metronidazole. It was found that the degradation of Metronidazole by UV and UV/H2O2 exhibited pseudo-first order reaction kinetics. By applying H2O2/Fe2+, and UV/H2O2/Fe2+ the degradation kinetics followed a second order behavior. The quantum yields for direct photolysis, measured at 254 nm and 200-400 nm, were 0.0033 and 0.0080 mol E(-1), respectively. Increasing the concentrations of hydrogen peroxide promoted the oxidation rate by UV/ H2O2. Adding more ferrous ions enhanced the oxidation rate for the H2O2/Fe2+ and UV/H2O2/Fe2+ processes. The major advantages and disadvantages of each process and the complexity of comparing the various advanced oxidation processes on an equal basis are discussed.
Article
The potential risks associated with antibiotics present in the Swedish environment were assessed using concentrations found in hospital effluent, and sewage treatment waters and sludge, in combination with data on their environmental effects obtained from the literature. For the aqueous environment, measured environmental concentrations and effect/no observed effect concentration ratios were much lower than one in most cases. The only exceptions, where concentrations of the investigated substances were high enough to pose potential risks, were the concentrations of the two fluoroquinolones, ofloxacin and ciprofloxacin, in the hospital effluent. Treating digested dewatered sludge by heat did not fully eliminate norfloxacin or ciprofloxacin, thus pellets may still contain high amounts of these substances (sub to low mgkg(-1)dw). In leaching tests less than 1% of the amounts of these fluoroquinolones in the sludge or pellets reached the aqueous phase, indicating that their mobility is limited if sludge is used to fertilize soil.
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