Performance and microbial community variations of anaerobic digesters under increasing tetracycline concentrations

An overview of the occurrence, impact of process parameters, and the fate of antibiotic resistance genes during anaerobic digestion processes

Antibiotic resistance genes (ARGs) have emerged as a significant global health threat, contributing to fatalities worldwide. Wastewater treatment plants (WWTPs) and livestock farms serve as primary reservoirs for these genes due to the limited efficacy of existing treatment methods and microbial adaptation to environmental stressors. Anaerobic digestion (AD) stands as a prevalent biological treatment for managing sewage sludge and manure in these settings. Given the agricultural utility of AD digestate as biofertilizers, understanding ARGs' fate within AD processes is essential to devise effective mitigation strategies. However, understanding the impact of various factors on ARGs occurrence, dissemination, and fate remains limited. This review article explores various AD treatment parameters and correlates to various resistance mechanisms and hotspots of ARGs in the environment. It further evaluates the dissemination and occurrence of ARGs in AD feedstocks and provides a comprehensive understanding of the fate of ARGs in AD systems. This review explores the influence of key AD parameters such as feedstock properties, pretreatments, additives, and operational strategies on ARGs. Results show that properties such as high solid content and optimum co-digestion ratios can enhance ARG removal, while the presence of heavy metals, microplastics, and antibiotics could elevate ARG abundance. Also, operational enhancements, such as employing two-stage digestion, have shown promise in improving ARG removal. However, certain pretreatment methods, like thermal hydrolysis, may exhibit a rebounding effect on ARG levels. Overall, this review systematically addresses current challenges and offers future perspectives associated with the fate of ARGs in AD systems.

Effects of bulk tank milk, waste milk, and pasteurized waste milk on the nutrient utilization, gastrointestinal tract development, and antimicrobial resistance to Escherichia coli in pre-weaned dairy calves

This study aimed to assess the impact of bulk tank milk (BTM), waste milk (WM), and pasteurized waste milk (PWM) on nutrient digestibility, ruminal and cecal fermentation, gastrointestinal tract (GIT) development, and antimicrobial resistance of fecal Escherichia coli from dairy calves at 2 periods (30 and 60 d of age). Calves were grouped according to body weight, serum protein levels, and breed composition. Three treatments were included: BTM (n = 21), WM from cows under antibiotic treatment (n = 21), and PWM (waste milk submitted to high-temperature, short-time pasteurization; n = 21). A total of 63 calves were used, of which: 18 animals (n = 6 per treatment) evaluated in the period of 4 - 30 d and 45 (n = 15 per treatment) from 4 - 60 d. During the experimental period, a daily intake of 6 L of milk was divided into 2 equal meals, with ad libitum access to water and starter. Milk and feed intakes were recorded daily. Apparent total-tract digestibility and nitrogen balance were conducted from 25 to 29 d of age (n = 6) and from 53 to 57 d of age (n = 15). Animals were euthanized at 30 ± 1 and 60 ± 1 d of age for the assessment of ruminal and cecal fermentation and GIT development. Antimicrobial susceptibility testing was conducted at 1, 30, and 60 d of age (n = 15/treatment). Statistical analysis utilized a linear mixed-effects model for continuous outcomes and generalized linear models for single measurements (R software). Treatments WM and PWM had lower rumen pH, higher ruminal acetate concentration, larger reticulorumen and liver, and a higher prevalence of fecal-resistant E. coli compared with BTM at both 30 and 60 d. Up to 60 d, both BTM and WM treatments exhibited higher digestibility of ether extract and gross energy compared with the PWM, whereas WM and PWM treatments showed increased nitrogen intake and retention compared with the BTM. These findings suggest that pasteurization of waste milk negatively affects nutrient digestibility and calf performance, while also impacting rumen development. Additionally, the use of milk containing antibiotic residue leads to the selection of resistant E. coli in the GIT over time.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

A review on the effects of discharging conventionally treated livestock waste to the environmental resistome

Globally, animal production has developed rapidly as a consequence of the ongoing population growth, to support food security. This has consequently led to an extensive use of antibiotics to promote growth and prevent diseases in animals. However, most antibiotics are not fully metabolized by these animals, leading to their excretion within urine and faeces, thus making these wastes a major reservoir of antibiotics residues, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the environment. Farmers normally depend on conventional treatment methods to mitigate the environmental impact of animal waste; however, these methods are not fully efficient to remove the environmental resistome. The present study reviewed the variability of residual antibiotics, ARB, as well as ARGs in the conventionally treated waste and assessed how discharging it could increase resistome in the receiving environments. Wherein, considering the efficiency and environmental safety, an addition of pre-treatments steps with these conventional treatment methods could enhance the removal of antibiotic resistance agents from livestock waste.

Combined effects of oxytetracycline concentration and organic loading rate on semi-continuous anaerobic digestion of swine wastewater

High concentrations of antibiotics in swine wastewater raises concerns about the potential adverse effects of anaerobic digestion (AD). Current studies mainly focused on the effects of various antibiotic concentrations. However, these studies didn't take into account the fluctuation of swine wastewater quality and the change of reactor operating conditions in practical engineering applications. In this study, it was found that in the operating systems with COD of 3300 mg/L and hydraulic retention time (HRT) of 4.4 days, the continuous addition of oxytetracycline for 30 days had no effect on the AD performance. Nevertheless, when COD and HRT were changed to 4950 mg/L and 1.5 days respectively, oxytetracycline at 2 and 8 mg/L increased the cumulative methane yield by 27% and 38% at the cost of destroying cell membrane, respectively, while oxytetracycline at 0.3 mg/L improved the performance and stability of AD. These results could be referred for practical engineering applications.

Removal performance and inhibitory effects of combined tetracycline, oxytetracycline, sulfadiazine, and norfloxacin on anaerobic digestion process treating swine manure

Combined veterinary antibiotics (CVAs) belonging to different antibiotics classes could cause exacerbated impacts on the anaerobic digestion (AD) process of swine manure. Four different antibiotics "two tetracyclines: tetracycline (TC) and oxytetracycline (OTC), one fluoroquinolones: norfloxacin (Norf), and one sulfonamides: sulfadiazine (SDZ)" were combined to evaluate their removal performances and its inhibition effects on AD. Results indicated that CVAs removal decreased from 84.3 to 63.7 %, with an increase in the initial concentration from 12.5 to 50 mg L^-1, where the removal of CVAs occurring in the order OTC > TC > Norf > SDZ. An average of 9.5, 7.5, 9.5, and 32.1 % of the spiked TC, OTC, SDZ, and Norf were remained in the sludge, respectively. With 50 mg L^-1 of CVAs, a competitive adsorption phenomenon was found to have a notable impact on biodegradation microorganisms' activity leading a 73.1 % decrease in CH₄ production. CVAs caused a temporal inhibition to the acidogenic activity followed by partial inhibition to methanogenic by 66.8 %, and IC₅₀ was 38.5 mg L^-1. Moreover, CVAs resulted in acetate accumulation, while 26 % and 48 % lower in TS and COD removal, respectively, were observed. A significant reduction in the relative abundance of bacteria and archaeal genera was also mentioned. The findings of this research would provide a more in-depth understanding of AD's performance in treating swine manure contaminated with combined antibiotics.

Long-term inhibition of chlortetracycline antibiotics on anaerobic digestion of swine manure

This study aimed to identify whether chronic effects are present in the anaerobic digestion (AD) of swine manure (SM) containing chlortetracycline (CTC), which is one of the major broad-spectrum veterinary antibiotics, and to elucidate the long-term inhibitory effects and recovery from the inhibition based on AD performance and microbial community. Two continuous-stirred tank reactors treating SM with and without CTC spiking (3 mg/L) were operated for 900 days. Due to the degradation and transformation, the total concentration including CTC's epimer and isomer in the test reactor was 1.5 mg/L. The exposure level was determined according to probabilistically estimated concentrations with uncertainties in field conditions. Until the cessation of CTC exposure on day 585, the methane generation of test reactor continuously decreased to 55 ± 17 mL/g-VS/day, 53% that of control. The methane generation and organic removal were not recovered within 300 days after the CTC exposure was stopped. During the experiment, stability parameters such as pH, total ammonium nitrogen, the composition of methane and alkalinity were the same for both reactors. The concentration and composition of VFAs in the test reactor were different with those of control but not in inhibition level. Microbial profiles revealed that reduction in bacterial diversity and changed balance in microbial species resulted in the performance downgrade under the long-term antibiotic pressure. Since it is hard to recover from the inhibition and difficult to predict the inhibition using physicochemical indicators, continuous exposure to CTC needs to be avoided for the sustainable management of AD plants treating SM.

Effects of antibiotics on anaerobic digestion of sewage sludge: Performance of anaerobic digestion and structure of the microbial community

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.

Antibiotics in anaerobic digestion: Investigative studies on digester performance and microbial diversity

The ever-increasing consumption of antibiotics in both humans and animals has increased their load in municipal and pharmaceutical industry waste and may cause serious damage to the environment. Impact of antibiotics on the performance of commercially used anaerobic digesters in terms of bioenergy output, antibiotics' removal and COD removal have been compared critically with a few studies indicating >90% removal of antibiotics. AnMBR performed the best in terms of antibiotic removal, COD removal and methane yield. Most of the antibiotics investigated have adverse effects on microbiome associated with different stages and methane generation pathways of AD which has been assessed using high throughput technologies like metatranscriptomics, metaproteomics and flow cytometry. Perspectives have been given for understanding the fate and elimination of antibiotics from AD. The challenge of optimization and process improvement needs to be addressed to increase efficiency of the anaerobic digesters.

Antibiotics and antibiotic resistant bacteria/genes in urban wastewater: A comparison of their fate in conventional treatment systems and constructed wetlands

There is a growing concern that the use and misuse of antibiotics can increase the detection of antibiotic resistant genes (ARGs) in wastewater. Conventional wastewater treatment plants provide a pathway for ARGs and antibiotic resistant bacteria (ARB) to be released into natural water bodies. Research has indicated that conventional primary and secondary treatment systems can reduce ARGs/ARB to varying degrees. However, in developing/low-income countries, only 8-28% of wastewater is treated via conventional treatment processes, resulting in the environment being exposed to high levels of ARGs, ARB and pharmaceuticals in raw sewage. The use of constructed wetlands (CWs) has the potential to provide a low-cost solution for wastewater treatment, with respect to removal of nutrients, pathogens, ARB/ARGs either as a standalone treatment process or when integrated with conventional treatment systems. Recently, CWs have also been employed for the reduction of antibiotic residues, pharmaceuticals, and emerging contaminants. Given the benefits of ARG removal, low cost of construction, maintenance, energy requirement, and performance efficiencies, CWs offer a promising solution for developing/low-income countries. This review promotes a better understanding of the performance efficiency of treatment technologies (both conventional systems and CWs) for the reduction of antibiotics and ARGs/ARB from wastewater and explores workable alternatives.

A comprehensive review on biodegradation of tetracyclines: Current research progress and prospect

The release of tetracyclines (TCs) in the environment is of significant concern because the residual antibiotics may promote resistance in pathogenic microorganisms, and the transfer of antibiotic resistance genes poses a potential threat to ecosystems. Microbial biodegradation plays an important role in removing TCs in both natural and artificial systems. After long-term acclimation, microorganisms that can tolerate and degrade TCs are retained to achieve efficient removal of TCs under the optimum conditions (e.g. optimal operational parameters and moderate concentrations of TCs). To date, cultivation-based techniques have been used to isolate bacteria or fungi with potential degradation ability. Moreover, the biodegradation mechanism of TCs can be unveiled with the development of chemical analysis (e.g. UPLC-Q-TOF mass spectrometer) and molecular biology techniques (e.g. 16S rRNA gene sequencing, multi-omics sequencing, and whole genome sequencing). In this review, we made an overview of the biodegradation of TCs in different systems, refined functional microbial communities and pure isolates relevant to TCs biodegradation, and summarized the biodegradation products, pathways, and degradation genes of TCs. In addition, ecological risks of TCs biodegradation were considered from the perspectives of metabolic products toxicity and resistance genes. Overall, this article aimed to outline the research progress of TCs biodegradation and propose future research prospects.

Distribution patterns of functional microbial community in anaerobic digesters under different operational circumstances: A review

Anaerobic digestion (AD) processes are promising to effectively recover resources from organic wastes or wastewater. As a microbial-driven process, the functional anaerobic species played critical roles in AD. However, the lack of effective understanding of the correlations of varying microbial communities with different operational factors hinders the microbial regulation to improve the AD performance. In this paper, the main anaerobic functional microorganisms involved in different stages of AD processes were first demonstrated. Then, the response of anaerobic microbial community to different operating parameters, exogenous interfering substances and digestion substrates, as well as the digestion efficiency, were discussed. Finally, the research gaps and future directions on the understanding of functional microorganisms in AD were proposed. This review provides insightful knowledge of distribution patterns of functional microbial community in anaerobic digesters, and gives critical guidance to regulate and enrich specific functional microorganisms to accumulate certain AD products.

Inhibition of tetracycline on anaerobic digestion of swine wastewater

The inhibition of tetracycline on anaerobic digestion of synthetic swine wastewater was examined with a semi-continuous operation for 103 days at a dosage ranging 2-8 mg/L. COD concentrations, VFA compositions in effluents and methane production were measured. The negative effects of tetracycline on the four individual steps of anaerobic digestion and its toxicity on anaerobic microorganisms were also evaluated. Results showed that continuous addition of 8 mg/L tetracycline in the bioreactor resulted in 73.28% reduction of daily methane production and made anaerobic digestion upset. Besides, methanogenesis was particularly inhibited compared to other three steps and the corresponding enzyme activities decreased by 66%. Furthermore, the polysaccharide contents in EPS increased after exposure to tetracycline, which could inhibit direct connections among microorganism. At last, long-term exposure to tetracycline inhibit anaerobic microbial activities and caused liberation of lactate dehydrogenase. The results would provide novel insights for anaerobic digestion of swine wastewater.

Influence of lincomycin on anaerobic digestion: Sludge type, biogas generation, methanogenic pathway and resistance mechanism

This study investigated the tolerance, defensive response and methanogenic pathways of anaerobic granular slugde and anaerobic suspended sludge (AGS and ASS) exposed to different LCM concentrations. AGS presented a higher tolerance to LCM stress, accompanied with 20.8 ± 2.6% enhancement in methane production at 1000 mg/L LCM, which was likely attributed to the less cell deaths and extracellular polymeric substances (EPSs) protection. In the acidification stage, acetate accumulation was stimulated and the activity of acetate kinase was promoted by LCM. In the methanogenesis stage, propionate and butyrate utilization for methane production were impaired after LCM addition. LCM also improved the activity of pyruvate-ferredoxin oxidoreductase and strengthened the process of hydrogenotrophic methanogenesis, likely by accelerating interspecies electron transfer mediated by hydrogen. ErmB and ermF were the dominate LCM resistance genes in AGS under LCM pressure conferring the resistance mechanism of ribosomal protection.

Volatile fatty acid platform - a cornerstone for the circular bioeconomy

Annually, the EU produces more than 100 million tonnes of urban biowaste, which is largely under-valorized and in some cases even still landfilled without any energy or material recovery. If Europe wants to be ready for the future, it will need to make better use of this large biomass potential within a circular economy approach. The research project funded by the European Commission under the Horizon 2020 programme entitled 'VOLATILE-Biowaste derived volatile fatty acid platform for biopolymers, bioactive compounds and chemical building blocks' aimed to produce volatile fatty acids (VFAs) from biowaste for reprocessing into products, materials or substances to close the material loop. During the project, the partners were able to obtain average volatile fatty acid yields of 627 g COD/kg organic matter (OM) for food waste, 448 g COD/kg OM for separately collected vegetable, garden and fruit waste (VGF) and 384 g COD/kg OM for the organic fraction of municipal solid waste (OF-MSW) at concentrations ranging from 12 to 48 g/L, 6 to 40 g/L and 13 to 26 g/L, respectively. A membrane filtration cascade consisting of micro-, ultra- and nano-filtration followed by reverse osmosis was identified as a feasible way to purify and concentrate the VFA effluent, making them a suitable carbon source for further fermentation processes. Besides technical optimization, socio-economic and legal aspects associated with this platform technology were also studied and show that although this technology is still in development, it is providing an answer to changing societal and market expectations both regarding organic waste treatment and bio-based production strategies. Based on the current technological, economic and market evolutions, it is expected that the VFAP will play an important role in organic waste treatment in the coming years.

Effects of micro-aeration on microbial niches and antimicrobial resistances in blackwater anaerobic digesters

Anaerobic digestion (AD) of source-diverted blackwater (toilet flush) at ambient room temperature presents challenges for fast hydrolysis of particulate matters. This study investigated the effect of different micro-aeration dosages for blackwater AD. Sequencing batch reactors were operated at ambient room temperature (22 ± 1°C) with micro-aeration (0, 5, 10, 50, and 150 mg O₂ g^-1 COD_feed per cycle) and gradually reduced hydraulic retention times from 5 d to 2 d. The methanogenesis efficiencies were greater at low oxygen dosages (i.e., 0, 5, 10) while the volatile fatty acids (VFAs) accumulated more at high oxygen dosages (i.e., 50, 150). Microbial communities were significantly different under different oxygen dosages (p<0.05), with segregation of microbial ecological niches in low and high oxygen dosage communities. The low-oxygen-dosage niche (0, 5, and 10 mg g^-1 COD_feed) was inhabited by fermenting and syntrophic bacteria (e.g., Cytophaga, Syntrophomonas) and methanogens (e.g., Methanobacterium, Methanolinea, Methanosaeta). The high-oxygen-dosage niche (50 and 150 mg g^-1 COD_feed) had significantly (p<0.05) more facultative anaerobic bacteria (Ignavibacteriales and Cloacamonales), and aerobic bacteria (Rhodocyclales). Moreover, blackwater can be a source of antimicrobial resistance genes (ARGs), which are affected by different oxygen dosages. The ARG variation correlated with the microbial community composition (p<0.05). Low-oxygen-dosage communities contained a higher prevalence of mobile gene elements (intI1 and korB) and tetM, ermB, sul1, sul2, and blaCTX-M than the high-oxygen-dosage communities, indicating that oxygen dosage influenced the prevalence of populations carrying ARGs. These findings suggest that application of micro-aeration to AD can be used to control ARG profiles.

Inhibition of norfloxacin on anaerobic digestion: Focusing on the recoverability and shifted microbial communities

Antibacterial properties of norfloxacin (NOR) could cause adverse impact on engineered biological process. In this study, the objective was to investigate the inhibitory effects of NOR on anaerobic digestion focusing on the recoverability and microbial community changes. The effects of different concentrations of NOR on anaerobic digestion were studied with three continuous feed cycles. Results showed that NOR seriously inhibited the methane production with an 50% inhibitory concentration (IC₅₀) of 0.41 mM. In addition, with extending of exposure time, inhibitory effect increasingly strengthened and the IC₅₀ values decreased to 0.16 mM and 0.07 mM in the second and third feeding cycle, respectively. However, when the inhibitor in supernatant was removed, the performance recovered and the relative methane yield increased by 9 times from 25.38 mL/g VS to 257.05 mL/g VS. The transformation of NOR showed that the degradation of NOR in the anaerobic digestion was difficult and the recovery was due to the removal of NOR. The microbial analysis revealed that the inhibition of NOR on bacteria of Candidatus_Cloacimonas, Petrimonas, Ercella, Sphaerochaeta and hydrogenotrophic methanogens of Methanoculleus and Methanobacterium was recoverable when NOR was removed. However, it was irreversible for acetoclastic methanogen of Methanosaeta. These findings provided comprehensive understanding on the characteristics of NOR inhibition and also provided feasible strategy to recover the NOR inhibited anaerobic digestion.

Antibiotic resistance genes are increased by combined exposure to sulfamethoxazole and naproxen but relieved by low-salinity

Combined pollution of antibiotic and non-antibiotic pharmaceutical residues is ubiquitous in realistic polluted environments, which is regarded as a complicated emerging pollution. Herein, high-throughput sequencing and high-throughput quantitative PCR were applied to profile the overall changes in microbial communities and antibiotic resistance genes (ARGs) of biofilms in response to a combination of naproxen and sulfamethoxazole pollution. After continuous operation for 120 days, naproxen or/and sulfamethoxazole were efficiently removed, and the salinity of 1.00% enhanced the removal rate of sulfamethoxazole. The high-throughput sequencing revealed that Eubacterium spp. with abundances of over 40.00% dominated in all samples, and combined pollution of naproxen and sulfamethoxazole more readily promoted the occurrence of multidrug-resistant microbes, including Pseudomonas and Methylophilus. The high-throughput quantitative PCR results showed that the combined pollution of naproxen and sulfamethoxazole increased the total abundance of ARGs to approximately 9 copies per cell. In contrast, increasing the salinity to 1.00% greatly reduced the overall abundance of ARGs to below 2 copies per bacterial cell. Mantel test and Procrustes analysis indicated that microbiomes from different treatments had tight links to their respective antibiotic resistomes. Furthermore, network analysis revealed that multidrug-resistant microbes were potential hosts for greatly enriched numbers of ARGs in the combined treatment. As increased salinity eliminated those multidrug-resistant but salt-sensitive microbes, the abundance of ARGs was significantly decreased. These results showed the high probability of the transmission of ARGs in biofilms exposed to combined pollution of naproxen and sulfamethoxazole, which could be relieved by increased salinity.

Contribution of antibiotics to the fate of antibiotic resistance genes in anaerobic treatment processes of swine wastewater: A review

Antibiotic resistance genes (ARGs) in water environment have become a global health concern. Swine wastewater is widely considered to be one of the major contributors for promoting the proliferation of ARGs in water environments. This paper comprehensively reviews and discusses the occurrence and removal of ARGs in anaerobic treatment of swine wastewater, and contributions of antibiotics to the fate of ARGs. The results reveal that ARGs' removal is unstable during anaerobic processes, which negatively associated with the presence of antibiotics. The abundance of bacteria carrying ARGs increases with the addition of antibiotics and results in the spread of ARGs. The positive relationship was found between antibiotics and the abundance and transfer of ARGs in this review. However, it is necessary to understand the correlation among antibiotics, ARGs and microbial communities, and obtain more knowledge about controlling the dissemination of ARGs in the environment.

Different inhibitory mechanisms of chlortetracycline and enrofloxacin on mesophilic anaerobic degradation of propionate

In anaerobic digestion, propionate is a key intermediate whose degradation is thermodynamically challenging and accumulation is detrimental to the process. Many wastewater streams contain antibiotics due to its globally increasing use, and these compounds can inhibit methane production. However, the effect of antibiotics on propionate degradation in anaerobic digestion remains unclear. In this study, the influence of two antibiotics (chlortetracycline [CTC] and enrofloxacin [EFX]) on biogas production and mesophilic propionate-degrading microbial community was investigated. CTC strongly repressed propionate oxidation, acetate utilization, and methane production, while EFX only inhibited propionate oxidation and methane production to a lesser extent. Microbial community analyses showed that syntrophic propionate-oxidizing bacteria (SPOB) Syntrophobacter had strong tolerance to both CTC and EFX. CTC inhibition mainly acted on the activity of acetate-oxidizing bacteria (Mesotoga, Geovibrio, Tepidanaerobacter, unclassified Bacteroidetes, and unclassified Clostridia) and acetoclastic methanogen, while EFX inhibition applied to the SPOB Smithella and acetoclastic methanogen. Network analysis further indicated that more complicated correlation among bacterial genera occurred in CTC treatments. These results suggested that CTC and EFX inhibited propionate degradation via different mechanisms, which was the result of joint action by antibiotics and microbial interactions.

Effectively remediating spiramycin from production wastewater through hydrolyzing its functional groups using solid superacid TiO2/SO4

Breaking down the structural bonds and eliminating the functional groups are more efficient than destroying the whole molecule in antibiotic production wastewater (APW) pretreatment before further biotreatment. Two sulfated titania (TiO₂/SO₄) solid superacids, SSA1 and SSA2 were synthesized, characterized and used for hydrolytic pretreatment of spiramycin in APW. Spiramycin removal followed an order of SSA2>SSA1>TiO₂≈pH = 3>control. The hydrolytic efficiencies increased at elevated temperature from 25 °C to 65 °C. The hydrolytic kinetics followed a first-order model and SSA2 performed the fastest. The performances were positively correlated with both the total acidity determined by n-butylamine titration and the strength of acid sites measured by NH₃-temperature-programmed desorption (TPD). The residual solution for SSA2 presented the least antibacterial potency and anaerobic inhibition among all treatments. The hydrolyzed product was identified as the m/z 699.4321 fragment using UPLC-Q/TOF-MS, which was formed after losing a functional mycarose moiety from the parent molecular. The solid superacids were effective in selectively eliminating 433 mg/L of spiramycin and the antibacterial potencies of the spiramycin production wastewater, which contained very high concentrations of COD (33,000 mg/L). This hydrolytic method avoids using and handling hazardous and corrosive mineral acids on site. It is attractive as a selective catalytic pretreatment method to cleave antibiotics' functional groups and to reduce its inhibitory effects before sequential biotreatments.

Insights into the Fate and Removal of Antibiotics in Engineered Biological Treatment Systems: A Critical Review

Antibiotics, the most frequently prescribed drugs of modern medicine, are extensively used for both human and veterinary applications. Antibiotics from different wastewater sources (e.g., municipal, hospitals, animal production, and pharmaceutical industries) ultimately are discharged into wastewater treatment plants. Sorption and biodegradation are the two major removal pathways of antibiotics during biological wastewater treatment processes. This review provides the fundamental insights into sorption mechanisms and biodegradation pathways of different classes of antibiotics with diverse physical-chemical attributes. Important factors affecting sorption and biodegradation behavior of antibiotics are also highlighted. Furthermore, this review also sheds light on the critical role of extracellular polymeric substances on antibiotics adsorption and their removal in engineered biological wastewater treatment systems. Despite major advancements, engineered biological wastewater treatment systems are only moderately effective (48-77%) in the removal of antibiotics. In this review, we systematically summarize the behavior and removal of different antibiotics in various biological treatment systems with discussion on their removal efficiency, removal mechanisms, critical bioreactor operating conditions affecting antibiotics removal, and recent innovative advancements. Besides, relevant background information including antibiotics classification, physical-chemical properties, and their occurrence in the environment from different sources is also briefly covered. This review aims to advance our understanding of the fate of various classes of antibiotics in engineered biological wastewater treatment systems and outlines future research directions.

Impacts of sulfanilamide and oxytetracycline on methane oxidation and methanotrophic community in freshwater sediment

Methanotrophs are of great significance for the abatement of methane emission from anoxic environments. Antibiotics are ubiquitous in the environment and can affect microbial activity and community density and composition. However, information about the effect of antibiotics on methanotrophs is still lacking. The current study explored the influences of sulfonamides and tetracyclines on methane oxidation potential (MOP) and methanotrophic density and community structure in freshwater sediment microcosms. The addition of both sulfanilamide (SA) and oxytetracycline (OTC) could increase MOP and particulate methane monooxygenase subunit A (pmoA) gene density but decrease the number of pmoA transcripts. Both SA and OTC could also have impacts on sediment methanotrophic community structure. The antibiotic effects on MOP and methanotrophs were found to depend on the dosage and type of antibiotics. This work could provide some new insights towards the links between methane oxidation and antibiotics.

Evaluating Antibiotic Resistance Gene Correlations with Antibiotic Exposure Conditions in Anaerobic Membrane Bioreactors

Anaerobic membrane bioreactors (AnMBRs) are an emerging technology with potential to improve energy efficiency and effluent reuse in mainstream wastewater treatment. However, their contribution to the proliferation of contaminants of emerging concern, such as antibiotic resistance genes (ARGs), remains largely unknown. The purpose of this study was to determine the effect of select influent antibiotics at varying concentrations on the presence and abundance of ARGs in an AnMBR system and its effluent. Quantification of targeted ARGs revealed distinct profiles in biomass and effluent, with genes conferring resistance to different antibiotic classes dominating in biomass (macrolides) and effluent (sulfonamides). Effluent sul1 gene abundance was strongly correlated with abundance of intl1, signifying the potential importance of mobile genetic elements in ARG release from AnMBR systems. The addition of specific antibiotics also affected normalized abundances of their related ARGs, exemplifying the potential impact of selective pressures at both low (10 μg/L) and high (250 μg/L) influent antibiotic concentrations.

Effects of antibiotic residues in milk on growth, ruminal fermentation, and microbial community of preweaning dairy calves

The aim of this study was to evaluate the effects of antibiotic residues in milk on growth, ruminal fermentation, and microbial community of dairy calves in their first 35 d of age. Twenty newborn Holstein bull calves were assigned to 1 of 2 treatments equally: milk replacer without antibiotics (control) and milk replacer plus 4 antibiotics: 0.024 mg/L of penicillin, 0.025 mg/L of streptomycin, 0.1 mg/L of tetracycline, and 0.33 mg/L of ceftiofur (ANT). Starter intake and fecal consistency scores of each calf were recorded on a daily basis. Body weight, withers height, body length, and heart girth were measured on d 1, 7, 14, 21, 28, and 35 before feeding in the morning. Rumen fluid was collected on d 15, 25, and 35 to determine ruminal pH, volatile fatty acids (VFA), and NH₃-N concentrations. A total of 10 (5 per treatment) samples of rumen fluid taken on d 35 were analyzed for microbial community. Rumen tissues from the cranial ventral sac and cranial dorsal sac were collected from 8 calves of each group for morphology analysis on d 35 after being harvested. The results showed that calves in 2 treatments had similar starter intake, body weight, withers height, body length, heart girth, and average daily gain. The ANT group showed a lower diarrhea frequency in wk 4, and no differences were found for other weeks. Calves in the ANT group exhibited a greater concentration of acetic acid in the rumen and no differences for other VFA, total VFA, rumen pH, or NH₃-N. As for rumen morphology, the length of papillae from cranial ventral sac of the ANT group was longer than that of the control group. The results of ruminal microbial community showed that antibiotic residues had minor effects on bacteria phyla and bacteria diversity. At the genus level, calves in the ANT group showed lower richness of Prevotella and higher richness of Acetitomaculum. In conclusion, antibiotic residues stimulated the development of ruminal papillae and increased the production of acetic acid in rumen, which might be caused by the influence of antibiotics on the ruminal microbial community.

Anaerobic membrane bioreactors for antibiotic wastewater treatment: Performance and membrane fouling issues

Antibiotic wastewater has become a major concern due to the toxicity and recalcitrance of antibiotics. Anaerobic membrane bioreactors (AnMBRs) are considered alternative technology for treating antibiotic wastewater because of their advantages over the conventional anaerobic processes and aerobic MBRs. However, membrane fouling remains the most challenging issue in the AnMBRs' operation and this limits their application. This review critically discusses: (i) antibiotics removal and antibiotic resistance genes (ARGs) in different types of AnMBRs and the impact of antibiotics on membrane fouling and (ii) the integrated AnMBRs systems for fouling control and removal of antibiotics. The presence of antibiotics in AnMBRs could aggravate membrane fouling by influencing fouling-related factors (i.e., sludge particle size, extracellular polymeric substances (EPS), soluble microbial products (SMP), and fouling-related microbial communities). Conclusively, integrated AnMBR systems can be a practical technology for antibiotic wastewater treatment.

A historical legacy of antibiotic utilization on bacterial seed banks in sediments

The introduction of antibiotics for both medical and non-medical purposes has had a positive effect on human welfare and agricultural output in the past century. However, there is also an important ecological legacy regarding the use of antibiotics and the consequences of increased levels of these compounds in the environment as a consequence of their use and disposal. This legacy was investigated by quantifying two antibiotic resistance genes (ARG) conferring resistance to tetracycline (tet(W)) and sulfonamide (sul1) in bacterial seed bank DNA in sediments. The industrial introduction of antibiotics caused an abrupt increase in the total abundance of tet(W) and a steady increase in sul1. The abrupt change in tet(W) corresponded to an increase in relative abundance from ca. 1960 that peaked around 1976. This pattern of accumulation was highly correlated with the abundance of specific members of the seed bank community belonging to the phylum Firmicutes. In contrast, the relative abundance of sul1 increased after 1976. This correlated with a taxonomically broad spectrum of bacteria, reflecting sul1 dissemination through horizontal gene transfer. The accumulation patterns of both ARGs correspond broadly to the temporal scale of medical antibiotic use. Our results show that the bacterial seed bank can be used to look back at the historical usage of antibiotics and resistance prevalence.

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.