Article

Influence of two-phase anaerobic digestion on fate of selected antibiotic resistance genes and class I integrons in municipal wastewater sludge

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Abstract

The response of representative antibiotic resistance genes (ARGs) to lab-scale two-phase (acidogenic/methanogenic phase) anaerobic digestion processes under thermophilic and mesophilic conditions was explored. The associated microbial communities and bacterial pathogens were characterized by 16S rRNA gene sequencing. A two-phase thermophilic digestion reduced the presence of tetA, tetG, tetX, sul1, ermB, dfrA1, dfrA12 and intI1 exhibiting 0.1-0.72 log unit removal; in contrast, tetO, tetW, sul3, ermF and blaTEM even increased relative to the feed, and sul2 showed no significant decrease. The acidogenic phase of thermophilic digestion was primarily responsible for reducing the quantity of these genes, while the subsequent methanogenic phase caused a rebound in their quantity. In contrast, a two-phase mesophilic digestion process did not result in reducing the quantity of all ARGs and intI1 except for ermB and blaTEM. ARGs patterns were correlated with Proteobacteria and Actinobacteria during the two-phase anaerobic digestion.

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... Like natural ecosystems, residual antibiotics in AD may increase ARG propagation by selection pressure (Yun et al., 2021). Several studies also confirmed the significance of HGT in ARG dissemination during AD (Fig. 1b), indicated by a positive correlation between ARGs and MGEs (Jang et al., 2020;Wu et al., 2016). Although AD can remove ARGs, HGT can be encouraged depending on specific operating conditions, leading to inadequate ARG removal . ...
... However, only a few studies looked into the effects of such twostage configuration on ARG removal (Table 1). Wu et al. (2016) studied ARG and MGE removal in two-stage digesters operated under thermophilic and mesophilic conditions. In general, thermophilic AD provided superior ARG removal than mesophilic AD. ...
... Moreover, ARGs were positively correlated with intI1, indicating the role of HGT on ARG propagation. (Wu et al., 2016) Two-stage AD Municipal waste activated sludge 35 and 55 • C/Semi-continuous/13 days (Two-stage: 5 and 10 days for first and second stage, respectively; Single stage: 15 days) ...
Article
The overuse and inappropriate disposal of antibiotics raised severe public health risks worldwide. Specifically, the incomplete antibiotics metabolism in human and animal bodies contributes to the significant release of antibiotics into the natural ecosystems and the proliferation of antibiotic-resistant bacteria carrying antibiotic-resistant genes. The organic feedstocks used for anaerobic digestion are often highly-rich in residual antibiotics and antibiotic-resistant genes. Hence, understanding their fate during anaerobic digestion has become a significant research focus recently. Previous studies demonstrated that various process parameters could considerably influence the propagation of the antibiotic-resistant genes during anaerobic digestion and their transmission via land application of digestate. This review article scrutinizes the influences of process parameters on antibiotic-resistant genes propagation in anaerobic digestion and the inherent fundamentals behind their effects. Based on the literature review, critical research gaps and challenges are summarized to guide the prospects for future studies.
... Previous researches have indeed confirmed these contradictory results. For example, Wu et al. (2016) investigated the effects of a two-phase anaerobic digestion process on the reduction of representative ARGs: the presence of tetA, tetG, tetX, sul1, ermB, dfrA1, and dfrA12 exhibited 0.1-0.72 log unit removal, while the abundance of tetO, tetW, sul3, ermF, and bla TEM even increased compared with the feed, and sul2 showed almost no change at all. ...
... In two-phase thermophilic digestion, the presence of tetA, tetG, tetX, sul1, and ermB exhibited slight removal, while the abundance of tetO, tetW, sul3, ermF, and bla TEM even increased compared with the feed, and sul2 showed almost no change at all, suggesting that the effects of sludge digestion on each type of ARGs may not be consistent (Wu et al. 2016). Some researchers speculate that it may be related to the different responses of microorganisms (such as the increase or decrease of specific bacteria at different temperatures) to anaerobic digestion (Jang et al. 2017;Xue et al. 2019). ...
... The release of ARGs from the hosts would help reduce their absolute abundance. Su et al. (2015) and Wu et al. (2016) both observed that ARG abundances and microbial diversity increased significantly at the same time. ...
Article
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Sewage sludge, a common by-product of wastewater treatment plants, is one important repository of antibiotic resistance genes (ARGs). The growing demands of sewage sludge reclamation, such as land application, increase the possibility of introducing ARGs into the environment and even the further dissemination of antibiotic resistance. Previous studies have paid much attention to the removal efficiencies of conventional pollutants such as heavy metals and pathogenic microorganisms during the sludge treatment processes. However, the effects on the abundance and diversity of ARGs got great concerns only recently. This paper mainly focuses on the enrichment and transmission modes of ARGs in sludge and the effects of representative sludge treatment technologies on ARG distributions in sludge. It seems that most physical and chemical techniques such as microwave, alkali treatment, and coagulation are ineffective in ARG reduction. The impacts of biological sludge treatment technologies on ARGs are varied, probably because of the diverse microbial community structures, operational parameters, and even environmental factors such as rainwater. Therefore, the sensitivities of potential hosts of specific ARG to the sludge treatments should determine the abundance of ARG before and after treatment. In addition, a reasonable combination of different sludge process techniques is usually a better choice than the single one for ARGs’ removal due to its better ability to efficiently damage the embedded cells and directly degrade the released ARGs. In summary, the appropriate treatment techniques should be applied on the excess sewage sludge to help mitigate the release of ARGs to the environment.
... Additionally, a significant decrease in the AA of the total ARGs in the final effluent samples from plant A (ranging from 5.98 × 10 3 to 6.49 × 10 3 copies/ mL) was observed, with a remarkable decrease in the acidogenic reactor. Similarly, Wu et al. (2016) reported a significant reduction in ARGs in a thermophilic acidogenic phase reactor during two-stage (acidogenic-methanogenic) AD of municipal wastewater sludge. Overall, a two-stage AD can effectively control ARG levels (p < 0.05), although it has a shorter HRT than a single-stage AD. ...
... In contrast, the data of Zhang et al. (2016) and He et al. (2019) mentioned that S-RGs were enriched after AD. A rebound in the AAs of sul1 and sul2 was also identified in a thermophilic methanogenic reactor during a two-stage (acidogenic-methanogenic) AD (Wu et al., 2016). Contrastively, no rebound in the AAs of sul1 and sul2 was observed in either plant. ...
... To reduce the binding affinity of macrolides to ribosomes, bacteria can modify a single 23S rRNA via the members of the Erm methyltransferase family (Wilson, 2014). Previous studies have demonstrated a high AA of the M-RGs encoding rRNAs, methyltransferase, in organic solid wastes, including sewage sludge, food waste leachate and manure (He et al., 2019;Jang et al., 2017;Lee et al., 2017;Ma et al., 2011;Wu et al., 2016). Recently, Tian et al. (2016) and Zhang et al. (2015) found a significant reduction in ermB after AD of sludge under mesophilic and thermophilic conditions. ...
Article
Efficiencies of removing antibiotic resistance genes (ARGs) and intI1 were explored using eight full-scale anaerobic digesters. The digesters demonstrated different characteristics on the basis of substrate types (food waste, manure or sludge); configuration (single or two-stage); temperature (psychrophilic, mesophilic or thermophilic); hydraulic retention time (HRT) (9.7-44 days); and operation mode (continuous stirred tank reactor or plug flow reactor). Digesters' configuration or operating parameters showed a greater effect on abundance of ARGs than the type of input substrate. Redundancy analysis (RDA) accounted for 85.2% of the total variancesand digesters with the same configuration and operational conditions showed similar performance for removal of ARGs. The highest efficiencies of removing ARGs (99.99%) were observed in two-stage thermophilic digesters with relatively long HRTs (32 days). The lowest removal efficiency (97.93%) was observed in single-stage mesophilic with relatively short HRTs (9.7 days), likely due to vertical and horizontal gene transfer.
... Microwave-based pretreatment is another effective pretreatment method in anaerobic digestion, which includes microwave pretreatment, microwave-heat pretreatment, and microwave-H 2 O 2 Table 2 Main findings of the ARGs in different sludge digestion methods. Wu et al., 2016;Wu et al., 2018) pretreatment. Microwave pretreatment uses 600 W microwave irradiation to heat the sludge from 20 ℃ to 100 ℃ for 5 min and showed promising results in increasing methane production by up to 84% (Tong et al., 2016(Tong et al., , 2018Zhang et al., 2017). ...
... TPAD includes two phases, where the first phase is for hydrolytic acidification, i.e. pretreatment stage, and the second phase is majorly operated for the methanogensis (Zhang et al., 2020a). TPAD not only improves the methane production of sludge in anaerobic digestion but also effectively reduces the abundance of pathogens in sludge (Wu et al., 2016;Zhang et al., 2020a). However, conflicting observations have been reported regarding the fate of ARGs during TPAD. ...
... However, conflicting observations have been reported regarding the fate of ARGs during TPAD. In a lab-scale continuous TPAD, negligible changes in the abundance of all targeted ARGs were observed due to the TPAD (Wu et al., 2016) using RT-qPCR analysis. In contrast, a recent lab-scale study found that TPAD increased the total abundance of ARGs in sludge from 229.1 ppm (ppm, 1 read in a million reads) to 355.7 ppm through metagenomics (Wu et al., 2018). ...
Article
Sludge from wastewater treatment plants can act as a repository and crucial environmental provider of antibiotic resistance genes (ARGs). Over the past few years, people’s knowledge regarding the occurrence and removal of ARGs in sludge has broadened remarkably with advancements in molecular biological techniques. Anaerobic and aerobic digestion were found to effectively achieve sludge reduction and ARGs removal. This review summarized advanced detection and removal techniques of ARGs, in the last decade, in the sludge digestion field. The fate of ARGs due to different sludge digestion strategies (i.e., anaerobic and aerobic digestion under mesophilic or thermophilic conditions, and in combination with relevant pretreatment technologies (e.g., thermal hydrolysis pretreatment, microwave pretreatment and alkaline pretreatment) and additives (e.g., ferric chloride and zero-valent iron) were systematically summarized and compared in this review. To date, this is the first review that provides a comprehensive assessment of the state-of-the-art technologies and future recommendations.
... In addition, mesophilic alkaline fermentation followed by mesophilic AD (MM) increased total energy recovery by 29% compared to M process. Although previous studies have explored the fate of representative ARGs through qPCR in two-stage AD, it was impossible to uncover the capacity of two-stage AD on the reduction of ARGs (Wu et al., 2016;Zhang et al., 2017). Therefore, it is necessary to comprehensively identify the occurrence and fate of ARGs in the two-stage process for hydrogen and methane production from WAS. ...
... The above results suggested that two-stage AD was more effective on the ARGs reduction than one-stage AD. This observation was consistent with the previous study, and the two-stage AD was the valuable facility for the reduction of ARGs (Wu et al., 2016;Zhang et al., 2017). ...
... The above results clearly showed that MLS could not be efficiently removed in AD process and they could be significantly enriched in alkaline fermentation. It should be noted that the dynamics of MLS resistance genes during AD process was rarely reported previously, possibility owning to the absence of primers of qPCR methods Tian et al., 2016;Wu et al., 2016;Zhang et al., 2017). ...
Article
Waste activated sludge (WAS) from wastewater treatment plants is an important reservoir of antibiotic resistance genes (ARGs). The fate of ARGs in this process was not revealed previously. The present study applied metagenomic approach to examine the occurrence and fate of ARGs in thermophilic alkaline fermentation followed by mesophilic anaerobic digestion (TM), by comparison with mesophilic alkaline fermentation followed by mesophilic anaerobic digestion (MM) and one-stage mesophilic anaerobic digestion (M) process. The removal efficiency of two-stage anaerobic digestion (AD) to total ARGs is higher than that of one-stage AD. The hydrogen and methane production stages of two-stage AD processes have dissimilar impact on the fate of ARGs. Macrolide, lincosamide, and streptogramin (MLS) resistance genes were enriched, especially in the hydrogen production reactors of TM and MM processes. Statistical analysis of metagenomic profiles analysis suggested that bacA may be the differential ARG subtype of two-stage AD process. ARG-like sequences encoding antibiotic efflux pump, antibiotic inactivation and antibiotic target alteration mechanisms were identified as the dominant ARGs resistance mechanisms in all samples. Procrustes analysis showed that microbial community composition structured the resistome. Co-occurrence patterns between ARGs and microbial phylogeny revealed that 26 bacterial species might be potential hosts of 94 ARG subtypes.
... The improved two-phases AD systems could have the attributes and may be useful for degrading VAs and other toxic substances (Schievano et al., 2012;Wu et al., 2016) without compromising biogas production potential. Unlike the traditional AD system that has only one phase, these have two separate reactors for acidogenesis and methanogenesis, which make them more effective in removing VAs and ARGs. ...
... In the AD process, temperature is regulated to obtain a favorable environment for a better microbial activity, and thereby enhancing methane production (Lin et al., 2016) and reducing ARGs or the carrier anaerobes (Sun et al., 2016;Tian et al., 2016;Wu et al., 2016). This condition improves heat energy and enzyme activity of thermophilic microbes in the system, which could improve the breakdown of antibiotic molecules. ...
... On top of this, in the AD systems with long retention time, high relative abundance of multidrug ARGs can be found in the digestate. Moreover, some groups of ARGs like, for instance, sul and tet could respond to temperature modification at a lower rate compared to other groups (Tian et al., 2016;Wu et al., 2016). This demonstrates the complexity of the problem and the need of further studies. ...
Article
This systematic review was aimed to summarize studies on removal of veterinary antibiotics (VAs), antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) with anaerobic digestion (AD) of manure and demonstrate areas of focus for improved removal efficiency. The environmental risks associated to the release of the same were also critically evaluated. The potential of AD and advanced AD of manure on removal rate of VAs, ARGs and MGEs was thoroughly assessed. In addition, the role of post and pre-AD treatments and their potential to support VAs and ARGs removal efficiency were evaluated. The overall review results show disparity among the different groups of VAs in terms of removal rate with relatively higher efficiency for β-lactams and tetracyclines compared to the other groups. Some of sulfonamides, fluoroquinolones and macrolides were reported to be highly persistent with removal rates as low as zero. Within group differences were also reported in many literatures. Moreover, removal of ARGs and MGEs by AD was widely reported although complete removal was hardly possible. Even in rare scenarios some AD conditions were reported to increase copies of specific groups of the genes. Temperature pretreatments and temperature phased advanced AD were also reported to improve removal efficiency of VAs while contributing to increased biogas production. Moreover, a few studies also showed the possibility of further removal by post-AD treatments such as liquid-solid separation, drying and composting. In conclusion, the various studies revealed that AD in its current technological level is not a guarantee for complete removal of VAs, ARGs and MGEs from manure, and this could threaten the healthcare and disturb the soil microbial ecology when released to soils with digestate use as fertilizer. Thus, intensive management strategies need to be designed to increase removal efficiency at the different manure management points along the anaerobic digestion process.
... The HTG can help spreading the ARGs from commensal and free-living species to pathogenic ones through three canonical modes of conjugation, transformation and transduction, making the ARGs difficult to be completely removed from the environment (Von Wintersdorff et al., 2016). Consequently, to control the ARB and ARGs in sludge, several studies have investigated their fates in different sludge treatment systems (Su et al. (2015;Yang et al., 2016;Zhang et al., 2016;Yang et al., 2014;Wu et al., 2016). Aerobic composting and anaerobic digestion are considered potential recycling methods for treating sludge. ...
... In addition, Su et al. (2015) found 156 unique ARGs and mobile genetic elements in composted sewage sludge. Compared to composting, thermophilic anaerobic digestion at temperatures between 50°C and 55°C appears to produce better results in terms of reducing the ARGs (Diehl and LaPara, 2010;Wu et al., 2016). However, only a small portion of certain types of ARGs can be limited by anaerobic digestion (Yang et al., 2014;Wu et al., 2016). ...
... Compared to composting, thermophilic anaerobic digestion at temperatures between 50°C and 55°C appears to produce better results in terms of reducing the ARGs (Diehl and LaPara, 2010;Wu et al., 2016). However, only a small portion of certain types of ARGs can be limited by anaerobic digestion (Yang et al., 2014;Wu et al., 2016). As a result, there is an ongoing search for a suitable approach to control the ARGs during sludge recycling. ...
Article
Diverse antibiotic resistance genes (ARGs) present in sewage sludge are difficult to be eliminated using conventional sludge treatment processes. To date, little remains known on the fate of the ARGs during vermi-composting of sludge. This study aimed to investigate the effect of earthworms on the fate of tetracycline and fluoroquinolone resistance genes, and integrons during vermicomposting of sewage sludge through contrasting two systems of sludge stabilization with and without earthworms. Compared to the control without earthworms, vermicomposting significantly (p < 0.05) decreased the abundances of tetracycline and fluoroquinolone resistance genes and int1, with complete removal for parC. Variations in ARGs were associated with environmental factors, horizontal gene transfer, bacterial community composition, and earthworms during vermicomposting. In addition, earthworms strongly affected the possible host bacteria encoding ARGs and Int1, abating the patho-genic bacteria in vermicomposting product. These results imply that vermicomposting could effectively reduce tetracycline and fluoroquinolone resistance genes in the sludge.
... It has also been estimated that the global consumption of antibiotics in agriculture will rise by 67% in the next decade due to a projected increase in the number of animals required for food production and intensive farming systems [5]. As a consequence, the development of antibiotic-resistant bacteria can be expected [6,7]. ...
... Several authors confirmed that ozonation is a suitable technique for pretreatment of waste biological sludge to enhance its solubilization and simultaneously remove adosorbed antibiotcs [25]. Furthermore, it was also found that anaerobic digestion is an effective treatment method for destruction of antibiotic resistance genes [7]. ...
Article
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The aim of the work was to assess the efficiency of ozonation and ozonation in combination with H2O2 in jet loop reactor to increase biotreatability of persistent veterinary antibiotic Tiamulin. The efficiency of oxidative processes was monitored by combined approach based on determination of efficiency of wastewater treatment and impact to waste sludge stabilization. Degradation of Tiamulin in model wastewater (100 mg L-1) during oxidation was followed by COD and DOC measurements while changes in biodegradability were determined by respirometric measurements. Biogas production potential was also determined to identify problems related to anaerobic digestion of waste sludge resulted in treatment of Tiamulin-contaminated wastewater. At ozone dose of 69 gozone gCOD-1 and 220 gozone gDOC-1removal for COD and DOC was 26% and 17%, respectively. Better biotreatability was confirmed by respirometric testing. H2O2 addition did not improve removal efficiency (11-13%). The second stage of nitrification was suppressed by the addition of Tiamulin and ozonation again recovered N - NO 3 - formation. O3/H2O2 treated sample reduced the nitrification, especially formation of N - NO 2 - in the first phase of the process. Simultaneously, quadratic model was developed to describe the relationship between oxygen uptake rate and changes in ammonium nitrogen concentration due to the oxidative treatment. The positive impact of ozone was also confirmed by ozonation of Tiamulin-contaminated (400 mg L-1) waste sludge where biogas production potential was increased for 6-times. Combination of approaches confirmed, that O3 effectively increase the treatability of Tiamulin in wastewater and sludge while addition of the hydrogen peroxide generally did not improve the performance of the processes.
... A previous study reported that Erm resistance genes, such as ermB and ermF, were prevalent in the ADS process . The enrichment of certain genes might be a result of host bacterial cells harboring such genes that are subject to amplification via cell growth or HGT or attenuation via differential survival with respect to the digester operating conditions (Wu et al., 2016;Zhang et al., 2016b). These results implied that anaerobic bacteria might carry more MLS resistance genes than aerobic bacteria, although further analysis is needed to verify the cause of the higher abundance of ARGs in ADS than AS. ...
... Different MGE patterns between the AS and ADS samples might be affected by different types of stressors, such as the temperature, nutrient load, HRT, SRT, and pH of the biological process, which will exert a selective effect on the types of ARB and ARGs in the bioreactor Guo et al., 2017). In particular, the ADS samples overall showed enhanced abundance of class 1 integrons and enhanced diversity of gene cassettes containing various ARGs, which may accelerate the mobility of some ARGs in the ADS samples (Ghosh et al., 2009;Gillings et al., 2014;Wu et al., 2016). The variations in the abundances of MGEs were not consistent in the aerobic treatment systems (Su et al., 2015;Zhang et al., 2016a). ...
Article
Full-text available
Antibiotic resistance genes (ARGs) are emerging contaminants that pose a potential threat to human health worldwide. Urban wastewater treatment plants (WWTPs) are a main source of both antibiotic-resistant bacteria and ARGs released into the environment. Nevertheless, the propagation of ARGs and their underlying mechanisms and the dynamics of mobile genetic elements (MGEs) in WWTPs have rarely been investigated in South Korea. In this study, shotgun metagenomic analysis was used to identify comprehensive ARGs and their mechanisms, bacterial communities, and MGEs from 4 configurations with 2 activated sludge (AS) and 2 anaerobic digestion sludge (ADS) samples. A total of 181 ARG subtypes belonging to 22 ARG types were broadly detected, and the ARG abundances in the AS samples were 1.3–2.0 orders of magnitude higher than in the ADS samples. Multidrug and bacitracin resistance genes were the predominant ARG types in AS samples, followed by ARGs against sulfonamide, tetracycline, and β-lactam. However, the composition of ARG types in ADS samples was significantly changed. The abundance of multidrug and β-lactam resistance genes was drastically reduced in the ADS samples. The resistance genes of MLS were the predominant, followed by ARGs against sulfonamide and tetracycline in the ADS samples. In addition, plasmids were the dominant MGEs in the AS samples, while integrons (intI1) were the dominant MGEs in the ADS samples. These results provide valuable information regarding the prevalence of ARG types and MGEs and the difference patterns between the AS and ADS systems.
... However, its composition was favorable in comparison to non-treated sludge due to a higher share of CH 4 (83%). Increased biogas production was expected due to the disintegration of sludge by ozone resulting in more soluble organics as a suitable substrate for biogas production (Wu et al. 2016). Ozonation of the contaminated sludge also enhanced biogas production significantly in comparison to contaminated sludge (180/80 hPa, Figure 5). ...
... As found in the past studies, florfenicol reduced biogas production by ≈5% at 6.4 mg L −1 , by 40% at 36 mg L −1 and by 75% at 210 mg L −1 (Mitchell et al. 2013). Furthermore, it was found that anaerobic digestion is an effective treatment method for destruction of antibiotic resistance genes (Wu et al. 2016). . Biogas production for sludge and ozonated sludge, sludge contaminated with 100 mg L −1 tiamulin and ozonated contaminated sludge. ...
Article
The capability of ozone to reduce the hazardous impact of environmentally persistent antibiotic tiamulin in term of toxicity reduction and enhancement of biodegradability was investigated. Different ozone doses were applied but ozonation was not effective enough to increase the biodegradability of tiamulin in the aqueous phase. The opposite effect was observed in anaerobic digestion experiments, where ozonation as a pretreatment step of antibiotic-contaminated sludge detoxify tiamulin and improves biogas production for 75%. As confirmed by ¹H NMR and HPLC-HRMS analyses, the tiamulin molecule completely reacts with ozone at low ozone/COD molar ratio of 0.03, primarily attacking the vinyl double bond with further oxidation of sulfur and nitrogen atom, and gradual decomposition of tiamulin skeleton.
... Anaerobic digestion (AD) is one of the established treatment processes used to stabilize and reduce the volume and mass of sewage sludge and animal manure [125]. Although AD is believed to inactivate pathogens and is preferable to direct sludge/manure land application, growing evidence indicates the conventional AD process is relatively inefficient for the attenuation of ARGs [131,63,78]. This has prompted the expression of valid concerns regarding the public health implication of recycling digestate to arable land. ...
Article
Full-text available
The urgent need to reduce the environmental burden of antibiotic resistance genes (ARGs) has become even more apparent as concerted efforts are made globally to tackle the dissemination of antimicrobial resistance. Concerning levels of ARGs abound in sewage sludge and animal manure, and their inadequate attenuation during conventional anaerobic digestion (AD) compromises the safety of the digestate, a nutrient-rich by-product of AD commonly recycled to agricultural land for improvement of soil quality. Exogenous ARGs introduced into the natural environment via the land application of digestate can be transferred from innocuous environmental bacteria to clinically relevant bacteria by horizontal gene transfer (HGT) and may eventually reach humans through food, water, and air. This review, therefore, discusses the prospects of using carbon- and iron-based conductive materials (CMs) as additives to mitigate the proliferation of ARGs during the AD of sewage sludge and animal manure. The review spotlights the core mechanisms underpinning the influence of CMs on the resistome profile, the steps to maximise ARG attenuation using CMs, and the current knowledge gaps. Data and information gathered indicate that CMs can profoundly reduce the abundance of ARGs in the digestate by easing selective pressure on ARGs, altering microbial community structure, and diminishing HGT.
... For example, Christgen et al. found that the removal rate of ARGs in wastewater by an anaerobic-aerobic sequence bioreactor was higher than that by the aerobic reactor (83%) and anaerobic reactor (62%), reaching 85% (Christgen et al., 2015). Wu et al. found that thermophilic anaerobic digestion significantly reduced tet, sul, ermB, dfrA1, and other ARGs in municipal wastewater sludge (Wu et al., 2016). ...
Article
Landfills are reservoir of antibiotics and antibiotic resistance. Antibiotic resistance would transport to the environment through landfill leachate, posing threaten to the environment. However, long term monitoring on antibiotic resistance genes in landfill leachate transportation is limited. Furthermore, antibiotic resistance gene hosts and their risk assessment are lacking. In this study, we investigated the seasonal variation of ARGs sulI, tetO and tetW in seven Chinese municipal solid waste landfill leachates over two years (2017–2018) by quantitative polymerase chain reaction. We also evaluated the associated bacterial hosts and their risk levels based on metagenomics and omics-based framework for assessing the health risk of antimicrobial resistance genes, respectively. Because sulI, tetO and tetW are abundant and the most frequently detected ARGs in global landfill system, they are selected as target ARGs. Results showed that the relative content of target ARGs in 2017 was 100 times higher than that in 2018, suggesting ARGs attenuation. The hosts of sulI were phyla of Lentisphaerae and Proteobacteria, whereas the hosts of tetO and tetW were Bacteroidetes and Firmicutes. Remarkably, the host species include pathogenic bacterium (Salmonella enterica, Labilibaculum filiforme, Bacteroidales bacterium, Anaeromassilibacillus senegalensis, and Pseudochrobactrum sp. B5). ARGs tetO and tetW belong to the Rank II level with characters of enrichment in the human-associated environment and gene mobility, and sulI ranked as Rank VI. In addition, among 1210 known ARGs in the landfill leachate, 78 ARGs belonged to risk Rank I (enrichment in human-associated environment, gene mobility and pathogenicity), demonstrating high health risk of landfill system. These results demonstrate that antibiotic resistance in landfill and landfill leachate have high health risk and the kind of ARGs with high abundance in human-associated environment, gene mobility and pathogenicity should be paid more attention.
... However, if the current trend of increasing sludge production continues, it will become increasingly urgent to speed up the overall reaction rates of AD performance to manage these greater amounts of sewage sludge while working within the challenges presented by current physical, spatial and budgetary constraints. To address the imminent need for greater digester capacity, considerable interest has been shown in the development of alternative options, such as twostage AD [7] or substrate pretreatment [8]. In addition, the concept of recuperative thickening (RT) has been introduced to improve digestion performance (volatile solid reduction [VSR] and biogas production) [9]. ...
Article
The effects of recuperative thickening (RT) and thermal hydrolysis during anaerobic digestion (AD) on AD performance, microbial communities and reduction of antibiotic resistance genes (ARGs) were investigated. Compared to the results in conventional AD (Phase I), biogas production increased slightly (10%) through RT (Phase II) but increased (63%) via RT with a digestate treatment system (DTS, thermal hydrolysis of thickened digestate) during AD (Phase III). Meanwhile, the three different operating conditions further influenced microbial community structures as well as efficiencies in reducing ARGs: The abundance of hydrolytic bacteria in Phase II and the abundance of acidogenic bacteria in Phase III increased, and 64.3% and 47.4% of the total sum of the relative abundance of ARGs in the substrate were removed in Phases II and III, respectively. Thus, RT-AD with DTS could represent a promising process for improved AD performance, but requires additional refinements to further reduce concentrations of residual ARGs in digestate.
... For example, Christgen et al. found that the removal rate of ARGs in wastewater by an anaerobic-aerobic sequence bioreactor was higher than that by the aerobic reactor (83%) and anaerobic reactor (62%), reaching 85% (Christgen et al., 2015). Wu et al. found that thermophilic anaerobic digestion significantly reduced tet, sul, ermB, dfrA1, and other ARGs in municipal wastewater sludge (Wu et al., 2016). ...
Article
Landfill are important reservoirs of antibiotics and antibiotic resistance genes (ARGs). They harbor diverse contaminants, such as heavy metals and persistent organic chemicals, complex microbial consortia, and anaerobic degradation processes, which facilitate the occurrence, development, and transfer of ARGs and antibiotic resistant bacteria (ARB). The main concern is that antibiotics and developed ARGs and ARB may transfer to the local environment via leachate and landfill leakage. In this paper, we provide an overview of established studies on antibiotics and ARGs in landfills, summarize the origins and distribution of antibiotics and ARGs, discuss the linkages among various antibiotics, ARGs, and bacterial communities as well as the influencing factors of ARGs, and evaluate the current treatment processes of antibiotics and ARGs. Finally, future research is proposed to fill the current knowledge gaps, which include mechanisms for the development and transmission of antibiotic resistance, as well as efficient treatment approaches for antibiotic resistance.
... Wu et al. [171] operated acidogenic and methanogenic reactors at mesophilic and thermophilic temperatures. Bacterial species including Bacteroidetes, Actinobacteria Chloroflexi, Firmicutes, and Proteobacteria were abundant in both reactors at two temperatures. ...
Article
Antibiotics are considered emerging contaminants that may cause substantial detrimental effects on the environment. The severe threat is the development of antibiotic resistance due to its frequent consumption. This review presents the feasibility of anaerobic digestion (AD) in eliminating antibiotics and antibiotic-resistant genes (ARGs) from the environment. This review concludes that anaerobic membrane bioreactor (AnMBR) is the most productive technology for antibiotics (sulfamethoxazole, sulfadiazine, trimethoprim, clarithromycin, erythromycin, ciprofloxacin, ofloxacin, cefalexin, cephradine) and ARGs removal (sul1, sul2, tetO, tetW, ermF, ermB, blaNDM-1, blaCTX-M-15, blaoxa-48, blaoxa-1). Inhibition to AD in terms of biogas or methane production upon antibiotics exposure has been observed for sulfamethoxazole (>25 mg/l), tetracycline (>1 mg/l), ofloxacin (>10 mg/l), ciprofloxacin (>80 mg/l), sulfamerazine (>90 mg/l), tylosin (>130 mg/l) and ceftiofur (>10 mg/l). This review also fortifies those microorganisms belonging to phylum Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Thermotogae, Euryarchaeota, Elusmicrobia, Chlorobi, Spirochaetes, Synergistetes, and Actinobacteria are important for stable performance of AD in terms of antibiotics removal and bioenergy production. However, the effects of antibiotics (individual and combined) on bioenergy production and microbial compositions have not been extensively investigated for AnMBR. Thus, further research must focus on these research gaps. In addition, AnMBR can be integrated with microbial fuel cells (MFCs) to enhance antibiotics and ARGs removal and mitigate membrane fouling issues while simultaneously producing bioelectricity and chemicals. Hence, future studies must examine their combined performance for antibiotic wastewater treatment. Additionally, mesophilic and thermophilic anaerobic digesters are exceptional in eliminating major ARGs (tetracyclines, sulfonamides, macrolides, fluoroquinolones, trimethoprim, beta-lactamase, aminoglycosides, florfenicol) from both biosolids (sludge) and manure. Nevertheless, forthcoming research must investigate their combined performance especially by using activated carbon and nano zero-valent iron (NZVI) in eliminating ARGs and enhancing bioenergy production.
... In Europe, almost half of the sludge generated in WWTPs and stabilized by AD processes is used in agriculture, either directly or after composting (Kelessidis and Stasinakis, 2012). The entry of PhACs into the environment through the application of stabilized sludge as soil fertilizer/conditioner implies a clear risk of contamination not only for environmental compartments (soil and water), but also for human health, particularly due to the spread and maintenance of antibiotic-resistant genes (ARG) and antibiotic resistant bacteria (aus der Beek et al., 2016;Bisognin et al., 2020;Urra et al., 2019;Wu et al., 2016). However, only few countries of the EU set in their national legislation limit values of concentrations for some target compounds in stabilized sludge as a requisite for land spreading, and to date no PhACs have been included among these (Christodoulou and Stamatelatou, 2016;Martín-Pozo et al., 2019). ...
Article
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The removal efficiencies (REs) of twenty-seven pharmaceutically active compounds (PhACs) (eight analgesic/anti-inflammatories, six antibiotics, four β-blockers, two antihypertensives/diuretics, three lipid regulators and four psychiatric drugs) were evaluated in a pilot-scale two-stage mesophilic anaerobic digestion (MAD) system treating thickened sewage sludge from a pilot-scale A²OTM wastewater treatment plant (WWTP) which was fed with wastewater from the pre-treatment of the full-scale WWTP Murcia Este (Murcia, Spain). The MAD system was long-term operated using two different sets of sludge retention times (SRTs) for the acidogenic (AcD) and methanogenic (MD) digesters (phase I, 2 and 12 days; and phase II, 5 and 24 days, in AcD and MD, respectively). Quantitative PCR (qPCR) and Illumina MiSeq sequencing were used to estimate the absolute abundance of Bacteria, Archaea, and Fungi and investigate the structure, diversity and population dynamics of their communities in the AcD and MD effluents. The extension of the SRT from 12 (phase I) to 24 days (phase II) in the MD was significantly linked with an improved removal of carbamazepine, clarithromycin, codeine, gemfibrozil, ibuprofen, lorazepam, and propranolol. The absolute abundances of total Bacteria and Archaea were higher in the MD regardless of the phase, while the diversity of bacterial and archaeal communities was lower in phase II, in both digesters. Non-metric multidimensional scaling (MDS) plots showed strong negative correlations among phyla Proteobacteria and Firmicutes and between genera Methanosaeta and Methanosarcina throughout the full experimental period. Strong positive correlations were revealed between the relative abundances of Methanospirillum and Methanoculleus and the methanogenesis performance parameters (volatile solids removal, CH4 recovery rate and %CH4 in the biogas), which were also related to longer SRT. The REs of several PhACs (naproxen, ketoprofen, ofloxacin, fenofibrate, and atenolol) correlated positively (r>0.75) with the relative abundances of specific bacterial and archaeal groups, suggesting their participation in biodegradation/biotransformation pathways.
... Notably, (nano) microplastics can also serve as carriers for antimicrobial resistance genes (ARGs) (Dong et al., 2021;Shi et al., 2020). The land application of digestate (i.e., biosolids) has been widely considered one of the major routes for transmitting ARGs to the environment (García et al., 2020;Wu et al., 2016;Zhang et al., 2019). Although current guidelines for land application of biosolids are primarily based on levels of pathogen and vector attraction reductions (Iranpour et al., 2004), future studies on the effects of (nano)microplastics should consider evaluating the digestate quality concerning these aspects. ...
Article
The presence of (nano)microplastics in domestic wastewater and their subsequent release to the aquatic environment via the discharge of treated sewage has raised significant concerns. Previous studies have also identified their excessive accumulation in sewage sludge. Anaerobic digestion is one of the most used sludge stabilization methods in wastewater treatment plants. Therefore, understanding the potential effects of (nano)microplastics on anaerobic digestion has been receiving increasing attention from researchers. This article provides a comprehensive review of mechanisms underlying the impacts of (nano)microplastics on anaerobic digestion. Notably, this review covers mechanisms of inhibition/enhancement of anaerobic digestion by (nano)microplastics and their potential impacts on biochemical pathways, key enzymes, functional genes, and microbial communities investigated to date. Moreover, potential environmental risks of biosolids contaminated with (nano)microplastics were highlighted. Finally, knowledge gaps and future research needs were outlined. This review will guide more standardized studies in the future, covering both fundamental and engineering aspects.
... AD decreases the abundance of most ARGs, but macrolide, lincosamide, streptogramin B (MLSB) resistance genes are consistently enriched, in both plants. An increase in MLSB resistance genes has also been reported during anaerobic digestion of sludge in other studies [8,35]. This apparent enrichment for MLSB resistance genes could be due to carriage in surviving gut bacteria, although this is unlikely as enrichment is also seen after TH, which appears to remove almost all gut bacteria from sludge. ...
Article
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Antibiotic resistant bacteria (ARB) and their genes (ARGs) have become recognised as significant emerging environmental pollutants. ARB and ARGs in sewage sludge can be transmitted back to humans via the food chain when sludge is recycled to agricultural land, making sludge treatment key to control the release of ARB and ARGs to the environment. This study investigated the fate of antibiotic resistant Escherichia coli and a large set of antibiotic resistance genes (ARGs) during full scale anaerobic digestion (AD) of sewage sludge at two U.K. wastewater treatment plants and evaluated the impact of thermal hydrolysis (TH) pre-treatment on their abundance and diversity. Absolute abundance of 13 ARGs and the Class I integron gene intI1 was calculated using single gene quantitative (q) PCR. High through-put qPCR analysis was also used to determine the relative abundance of 370 ARGs and mobile genetic elements (MGEs). Results revealed that TH reduced the absolute abundance of all ARGs tested and intI1 by 10–12 , 000 fold . After subsequent AD, a rebound effect was seen in many ARGs. The fate of ARGs during AD without pre-treatment was variable. Relative abundance of most ARGs and MGEs decreased or fluctuated, with the exception of macrolide resistance genes, which were enriched at both plants, and tetracyline and glycopeptide resistance genes which were enriched in the plant employing TH. Diversity of ARGs and MGEs decreased in both plants during sludge treatment. Principal coordinates analysis revealed that ARGs are clearly distinguished according to treatment step, whereas MGEs in digested sludge cluster according to site. This study provides a comprehensive within-digestor analysis of the fate of ARGs, MGEs and antibiotic resistant E . coli and highlights the effectiveness of AD, particularly when TH is used as a pre-treatment, at reducing the abundance of most ARGs and MGEs in sludgeand preventing their release into the environment.
... Any factor that affects this process would alter the fate of ARGs. Different factors reported to influence ARGs during composting and anaerobic digestion are summarized in Fig. 2. They are classified into four categories including substrate properties (microbial community composition, heavy metals, antibiotics, and solidity) (Miller et al., 2016;Yin et al., 2017;Xia et al., 2019;Carey et al. 2016;Sun et al., 2019;Zhang et al., 2016a), pretreatments (ozone, thermal hydrolysis, microwave treatment, and pH adjustment) Huang et al., 2017;Pei et al., 2016;Tong et al., 2018), additives (biochar, red mud, natural zeolite, zerovalent iron, and coal gasification slag) Sun et al., 2018;Wang et al., 2016;Zhang et al., 2018a), and operating parameters (sludge retention time-SRT, temperature, operation stage, and earthworm density) Diehl and LaPara, 2010;Huang et al., 2019;Liao et al., 2018;Ma et al., 2011;Sun et al., 2016;Wu et al., 2016). ...
Article
Antibiotic resistance genes (ARGs) in biowaste, such as livestock manure and excess activated sludge, pose potential threat to human and ecological health when applied to agricultural fields. Biological treatment approaches, such as thermophilic composting/vermicomposting and anaerobic digestion, widely adopted to stabilize biowaste have demonstrated significant effects on the fate of ARGs. However, the influence of these biological treatments on ARGs is not known. This review summarizes the occurrence of ARGs in biowaste and the impact of thermophilic composting, vermicomposting, and anaerobic digestion on the fate of ARGs with discussion on factors, including substrate properties, pretreatments, additives, and operational parameters, associated with ARGs during biological treatment of biowaste. Finally, this review explores the research implications and proposes new avenues in the field of biological treatment of organic waste.
... ✓ Generate higher energy due to the lack of oxygen in the process, producing a biogas rich in methane (a renewable energy source) (Zhang et al., 2014), ✓ Digested material that has potential to be used as fertilizer (Zhang et al., 2014), ✓ Final volume of the sludge reaches compost-like percentages (~54.3% in association with fungal pre-treatment of the sludge) (Yin et al., 2016), ✓ Contaminants and pathogens are efficiently removed (Wu et al., 2016). ...
Article
São Paulo is the most populous and industrialized state of Brazil, which strongly affect amounts and composition of the generated sewage sludges. Their use on agriculture sounds the most feasible disposal strategy since most Brazilian soils have low fertility, but the levels of hazardous substances must be low. This research examined the impacts of sewage source [domestic or mixed (domestic þ industrial)] and sewage processing (liming and redox conditions) on the chemical attributes of sludges from 19 waste-water treatment plants of São Paulo; as well as their suitability for agricultural use. Sewage source and liming were the main factors affecting sludges' chemical attributes, while redox conditions played a secondary role. Aerobically treated domestic sewage (C1) generated sludges most suitable for agriculture. Heavy liming in the processing of sewage of mixed origin (C2) produced sludges of much higher pH and Ca, with higher levels of certain hazardous elements (Fe, Zn, Mn, and Cr), but lower levels of OC, N-Kj, and K. Sludges from mixed sewers, not limed (C3) tended to have higher levels of S and hazardous elements (Ba, Mo, Cd, Pb, Ni, Al, and Cu). The inadequately regulated discharge of industrial wastewater into the municipal sewage network accounted for higher levels of hazardous elements in the sludges, but all of them are still suitable for agricultural use since only four sludges showed levels of either Zn (3) or Ni (1) that exceeded the thresholds permitted for direct application to agricultural fields, but both are nutrients to plants and Brazilian soils are often depleted on them. As raw materials for the manufacture of organic fertilizers, the levels of Cd, Cr, or Ni were unacceptable in about half (9) of the samples. It should be revised since hazardous element contents are diluted in the manufacture of the "new com-pound" and their application rates should be much lower than when sludge is directly applied. In conclusion, "low quality" sludges, such as C2 and mainly C3, have to be either composted or biodigested into "high quality" stabilized sludges; or used in the manufacture of organomineral fertilizers; or treated to remove pathogens and hazardous substances to be amended to agricultural soils, thus avoiding their non-sustainable disposal in landfills.
... Zhang et al. found that the abundances of ARGs in activated sludge in aerobic zone are higher than those in anoxic zone (Zhang et al., 2015). Wu et al. proposed that thermophilic two-phase digestion process has better ARGs removal efficiency than mesophilic digestion process (Wu et al., 2016). Sun et al. found that the predominant multiple antibiotic resistance gene clusters were different among ten MBRs plants (Sun et al., 2016). ...
Article
The prevalence and accumulation of antibiotic resistance genes (ARGs) were frequently detected in biological wastewater treatment processes, which might cause potential health crisis to human. In present study, the fates of ARGs during two different aerobic granular sludge (AGS) cultivation processes were investigated. The results showed that traditional AGS (T-AGS) cultivation process and enhanced AGS (E-AGS) cultivation process had significant differences (P < 0.005) in ARGs shift patterns. E-AGS process had higher average relative abundance (0.280 ± 0.079) of ARGs than T-AGS process (0.130 ± 0.041), while the intensity of ARGs enrichment during E-AGS (1.52-5.29 fold) was lower than T-AGS (3.79-75.31 fold) process. TnpA and intI1 as two different types of mobile genetic elements (MGEs) carrying ARGs, were observed to contribute significantly to the horizontal gene transfer (HGT) during T-AGS (r = 0.902, P < 0.050) and E-AGS (r = 0.823, P < 0.001) processes, respectively. Higher HGT level took place and more possible potential hosts (25 hosts) harboring ARGs were detected during E-AGS process comparing with T-AGS process (17 hosts). Meanwhile, over large AGS might increase the propagation of several antibiotic deactivation ARGs, so it was not advised. Overall, whether during T-AGS or during E-AGS process which was applied in a pilot-scale sequencing batch reactor treating municipal wastewater, the accumulation and spread of ARGs were inevitable. It should be valued that some suitable pre-treatments of seed sludge should be executed, meanwhile, advanced treatment for removing of ARGs in AGS should be conducted to maintain the relative abundances of ARGs at relatively low level.
... During thermal hydrolysis, the high temperature and pressure sterilized the sludge and destroyed cell walls, and it could reduce the abundance of ARGs that were susceptible to hydrolytic destruction (Ma et al., 2011;Pei et al., 2016). However, ARGs rebounded after subsequent AD processes (Ma et al., 2011;Wu et al., 2016). Nevertheless, AD with thermal hydrolysis pre-treatment showed better ARGs reduction in spite of the rebounding effect, the digesters receiving thermal hydrolyzed sewage sludge contained lower ARGs abundance than those receiving un-pretreated sewage sludge (Ma et al., 2011). ...
Article
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Sewage sludge from wastewater treatment plants (WWTPs) harbours large amounts of antibiotics, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs), the variation and fate of these emerging pollutants during sludge treatment processes must be thoroughly studied to reduce their potential risks to human health. In this study, 7 pilot-scale CSTR anaerobic digesters were established with the same seed sludge and fed with the same thermal hydrolysis pre-treated sewage sludge, while operating under different conditions. High-throughput quantitative PCR, UPLC-MS/MS and Illumina Hiseq-sequencing were used to systematically evaluate the responses of antibiotics, ARGs, and MGEs in sewage sludge to thermal hydrolysis pre-treatment and various anaerobic digestion (AD) conditions. The results showed that thermal hydrolysis effectively reduced the abundance (>94%) of almost all subtypes of ARGs and MGEs, and it was a powerful technology for reducing tetracyclines, macrolides, and lincosamides. Besides, the abundance of ARGs and MGEs in thermophilic digesters was lower than that in mesophilic digesters, suggesting that thermophilic digesters could be used to avoid the ARGs rebounding. In addition, the thermophilic system further reduced the concentrations of quinolones. For the digesters operated under the mesophilic conditions, a longer hydraulic retention time (HRT) facilitated the removal of antibiotics, ARGs, and MGEs. Furthermore, the microbial community and MGEs had important effects on the persistence and proliferation of ARGs in AD process. The findings of this study provide effective clues for controlling the spread of antibiotic resistance and suggest the optimal operating conditions of digesters.
... And mobile integrons such as intI1, were the key to HGT. intI1 was reported to contribute to the transfer and integration of ARGs, which leading to an increased antibiotic resistance of bacterial in the environment (Didier, 2006). Ying also found that many ARGs such as ermB had a positive correlation with the intI1 ( Wu et al., 2016). As can be seen in Fig. 5, although the abundance of intI1 had a slight increase on 40th day and then peaked at 6.25 × 10 −2 copies/16S rRNA copies on 60th day, it still decreased by 51.8% on average after 100-day anaerobic digestion. ...
Article
Sludge is among the most important reservoirs of antibiotic resistance genes (ARGs), which would cause potential environmental risks with the sludge utilization. Currently, anaerobic digestion (AD) is effective to simultaneously realize the resource recovery and pollutants removal, including antibiotic resistance genes (ARGs), and various pretreatments are used to enhance the performance. Recently, plentiful publications have focused on the effects of pretreatment on ARGs removal, but the contradictory results are often obtained, and a comprehensive understanding of the research progress and mechanisms is essential. This study summarizes various pretreatment techniques for improving AD efficiency and ARGs reduction, investigates promising performance in ARGs removal when pretreatments combined with AD, and analyzes the potential mechanisms accounting for ARGs fates. The results showed that although thermal hydrolysis pretreatment showed the best performance in ARGs reduction during the pretreatment process, the significant rebound of ARGs would occur in the subsequent AD process. Conversely, ozone pretreatment and alkali pretreatment had no significant effect on ARGs abundance in the pretreatment stage, but could enhance ARGs removal by 15.6-24.3 % in the subsequent AD. Considering the efficiency and economic effectiveness, free nitrous acid pretreatment would be a promising and feasible option, which could enhance methane yield and ARGs removal by up to 27 % and 74.5 %, respectively. Currently, the factors determining ARGs fates during pretreatment and AD processes included the shift of microbial community, mobile genetic elements (MGEs), and environmental factors. A comprehensive understanding of the relationship between the fate of ARGs and pretreatment technologies could be helpful for systematically evaluating various pretreatments and facilitating the development of emerging and effective pretreatment techniques. Moreover, given the effectiveness, economic efficiency and environmental safety, we called for the applications of modern analysis approaches such as metagenomic and machine learning on the optimization of pretreatment conditions and revealing underlying mechanisms.
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In this study, the effect of different phenol disinfectant concentration on wastewater anaerobic digestion was indicated. The results indicated that the cumulative methane production decreased with the increase in the concentration of phenol disinfectant. The difference in the cumulative methane yield from disinfectants at concentrations of 0.04 mL/L, 0.2 mL/L, 0.4 mL/L and 0.8 mL/L was not significant (P≥0.05). However, the disinfectant concentration of 1.6 mL/L and 2.4 mL/L caused a decrease in methane yield by 69.98% (P<0.05) and 100% (P<0.05), respectively. The addition of phenol disinfectant led to the accumulation of volatile fatty acids (VFA), affected the secretion of extracellular polymeric substances (EPS) and the construction of anaerobic sludge. With the increase in disinfectant concentration, the activity of acetate kinase and coenzyme F420 were decreased. Furthermore, microbial community analysis indicated that the dominant bacteria were Firmicutes, Chloroflexi, Actinobacteria and Proteobacteria. The addition of disinfectant inhibited the growth of Methanosaeta and Methanobacterium. In addition, the high concentration of the disinfectant inhibited acidification and methanation process during the anaerobic digestion (AD) process and the inhibition was stronger in the methanation stage than in the acidification stage.
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In this paper, the hydrogen (H2) supply to trickle-bed reactor (TBR) in endogenous and exogenous ways by nano-zero-valent iron (nZVI) corrosion was indicated, in order to increase the biogas generation and methane (CH4) content from wastewater. The results showed that the nZVI corrosion H2 supply method increased the biogas generation in TBR. The daily average CH4 yields of TBR in stages 1–4 increased by 23.99 %, 35.76 %, 49.40 % and 56.13 % compared with control stage, respectively, and the highest CH4 content of 90.72 % was achieved in stage 3. The changes of enzyme concentration indicated that iron from nZVI enhanced the activities of acetate kinase and dehydrogenase, however, the activity of coenzyme F420 was lower due to the presence of homoacetogenic acetate formation that enhanced the acetoclastic methanogenesis pathway. Changes in the structure of the microbial community played an important role in the mechanism of CH4 enhancement, and the analysis of microbial abundance showed that the additions of nZVI and ferrous iron (Fe²⁺) changed the microbial communities, with increased abundances of hydrogenotrophic methanogens and homoacetogen.
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Leachate is a critical reservoir of antibiotic resistance genes (ARGs) and its proper treatment is closely related to human health and ecosystem safety. Here, we used high-throughput qPCR to explore the removal behavior of ARGs in two full-scale leachate treatment plants (LTPs) where biological treatment and membrane filtration processes were integrated. A total of 286 ARGs and 55 mobile genetic elements (MGEs) were detected, with aminoglycoside, multidrug and MLSB resistance genes being the most prevalent and abundant. Anaerobic digestion was found to be an important pretreatment process for leachate, while anoxic/aerobic tanks in membrane bioreactor (MBR) acted as incubators for ARGs due to their significant proliferation effect on ARGs. Integrated membrane filtration (UF-NF-RO) excelled in ARGs removal with absolute abundances reduced by 3 to 6 orders of magnitude, from about 10⁹ copies/mL in raw leachate to 10³-10⁵ copies/mL in effluents. Our results also showed that leachate treatment processes significantly altered the composition of ARGs and bacterial communities. Procrustes analysis and network analysis revealed strong associations between microbes and ARGs, with several hub genes and bacterial genera identified. Structural equation models (SEMs) indicated that bacterial composition, MGEs and basic water properties were the key drivers shaping ARGs dynamics in the raw leachate, biological system and filtration system, respectively. Notably, several pathogens (e.g., Klebsiella, Vibrio, Aeromonas) were closely correlated with ARGs in raw leachate and may amplify the dissemination risks of ARGs. Moreover, insertion sequences in biological systems would accelerate the horizontal gene transfer of ARGs. In short, this study provides new insights into the mechanisms of ARGs removal and dissemination behavior in industrial-scale LTPs.
Article
Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L–1) were fully investigated. The TC of 0 to 1 mg L–1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L–1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L–1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L–1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment.
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The co-existence of antibiotics and heavy metals in soil with manure application poses high risk to both environment and human health, and thus effective remediation methods are in urgent need. This study investigated the synergistic effects of electrokinetic remediation (EKR) on antibiotic resistance and arsenic (As) in co-contaminated paddy soils. EKR treatments in soil amended with pig manure (EKR-PD) showed better remediation efficiency compared with that without pig manure. In detail, the content of available As and the abundance of antibiotic-resistant bacteria (ARB) decreased by 25.2%−41.4% and 9.5%−21.1% after 7-d remediation, respectively, due to a relatively higher current density for EKR-PD. The role of the electric field contributed to 33.9% of antibiotic degradation. Antibiotic resistance genes (ARGs) with ribosomal-protection and enzymatic-deactivation types were easier to remove, with the removal ratio of 37.8%−41.6% in EKR-PD. Brevundimonas was the most significantly different species during remediation. Bacillus and Clostridium_ sensu_stricto_1 were potential host bacteria of ARGs in the electric field. Membrane transport might be an effective strategy for microorganisms to respond to the stress of both electric field and co-contaminated environments. This study supports the potential role of EKR in the co-contamination of heavy metals and antibiotic resistance under manure application.
Article
Anaerobic digestion (AD) is a key technology for the utilization of swine manure, but the complex pollution of heavy metals and antibiotics in manure is catching more attentions. In this study, AD of swine manure loading with four types of biochar was performed in a 1 L-frosted jar with the total fresh weight of 840 g, in which the effects of biochar on the AD stability and methane yields were focused, and the removal of antibiotics and migration of heavy metals were investigated as well. The results showed that the removal efficiencies of sulfadimidine and tylosin were remarkable, which were up to around 70% and 100%, respectively. The maximum methane yield of 146.98 mL/ (g VS) was noted in the digester added with the biochar derived from paper mill sludge (BPMS) which contained 87.35% of ash, having a high pHPZC of 8.95 and more mesopores and macropores. In this reactor, 12.40% of Cu was moved to the solid phase, and 70.26% of Zn and 82.80% of As were migrated to the solid digestate. Compared to the control, the content of the acid soluble Cu in the digester loaded with BPMS was decreased to 7.99%, and no acid soluble Zn was found along with a drop of 29.20% for the reducible Zn, and the residual As content was increased by 16.60%. It revealed that BPMS had a great potentiality to remove As and Zn in wastewater and synchronously mitigate the bioavailability of Cu/Zn/As in the digestate. Herein, applying BPMS in the AD of swine manure could reduce the complex pollution of heavy metals and antibiotics, and obtain a higher methane yield simultaneously.
Article
Antibiotic resistance genes (ARGs) encode resistance against antibiotic drugs in bacteria. Carbapenem antibiotics are one of the last lines of defence against bacterial infections and carbapenem resistance genes (CRGs) accumulate in sludge during wastewater treatment. Anaerobic digestion is the most used method for sludge treatment, and it is important to know the abundance and removal of CRGs in anaerobically digested sludge before land application due to their public health relevance. However, gene quantification is time-consuming, costly, and sensitive to contamination. Previous research indicates a nexus between ARGs, solids, and nutrients in sludge. This study aimed to develop multiple regression models to estimate the abundance of CRGs from solids and nutrient concentrations in sludge, which are routinely measured for the monitoring and design of anaerobic digesters. Batch and continuous reactors were operated at mesophilic and thermophilic temperatures. Sludge samples were taken during digestion. CRGs (blaGES, blaOXA-48 and blaIMP-27), 16S rRNA and integron class 1 were quantified. Solids, chemical oxygen demand, orthophosphate and ammonia were measured as well. Anaerobic digestion reduced the quantity of the genes. First and second-order Kinetic rate constants (K1 and K2) were affected by temperature, and K1 followed the order blaOXA-48 > blaGES > Int 1 > 16S rRNA. Multiple regression modelling was conducted in linear (LM) and non-linear (NLM) modes. This study presents the first NLM models to simulate the quantities of CRGs during anaerobic digestion of wastewater sludge. Adjusted R² ranged 0.352-0.988 and 0.916-0.996 for the LM and NLM models, respectively. NLM models estimated the gene abundance more accurately than LM models and may provide a useful tool for researchers and practitioners to estimate the removal rate of target genes under different operational conditions.
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The land application of digestate from anaerobic digestion (AD) is considered a significant route for transmitting antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) to ecosystems. To date, efforts towards understanding complex non-linear interactions between AD operating parameters with ARG/MGE abundances rely on experimental investigations due to a lack of mechanistic models. Herein, three different machine learning (ML) algorithms, Random Forest (RF), eXtreme Gradient Boosting (XGBoost), and Artificial Neural Network (ANN), were compared for their predictive capacities in simulating ARG/MGE abundance changes during AD. The models were trained and cross-validated using experimental data collected from 33 published literature. The comparison of model performance using coefficients of determination (R²) and root mean squared errors (RMSE) indicated that ANN was more reliable than RF and XGBoost. The mode of operation (batch/semi-continuous), co-digestion of food waste and sewage sludge, and residence time were identified as the three most critical features in predicting ARG/MGE abundance changes. Moreover, the trained ANN model could simulate non-linear interactions between operational parameters and ARG/MGE abundance changes that could be interpreted intuitively based on existing knowledge. Overall, this study demonstrates that machine learning can enable a reliable predictive model that can provide a holistic optimization tool for mitigating the ARG/MGE transmission potential of AD.
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The fate of intracellular antibiotic resistance genes (iARGs), extracellular ARGs (eARGs) and bacteriophage ARGs (bARGs) during anaerobic digestion (AD) of cow manure is unclear. Thus, the characteristics of iARGs, eARGs and bARGs during mesophilic AD (MAD) and thermophilic AD (TAD) of cow manure were investigated. The absolute abundances of iARGs decreased by 69.82% after TAD. After MAD and TAD, the total absolute abundances of eARGs increased by 63.5 times and 67.6 times, respectively, whereas those of the bARGs increased by 47.60% and 59.22%. eARGs were mainly derived from the non-specific lysis of Firmicutes, Bacteroidetes, while bacteriophages had a wide range of hosts. The variations in iARGs, eARGs and bARGs were affected by the microbial hosts but also directly driven by physicochemical factors (e.g., pH). Overall, the findings of this study revealed that there may be a risk of eARGs and bARGs disseminating during the AD of cow manure.
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This work investigated the metagenomics-based behavior of antibiotic resistance genes (ARGs) during cattle manure anaerobic digestion with zinc oxide nanoparticles (ZnO NPs) that are commonly used as animal feed additives. The 6.6% decrease in total ARGs abundance while remained unchanged ARGs diversity with ZnO NPs (5 mg/g total solid), suggested ZnO NPs may mitigate ARGs risk by abundance. Also, ZnO NPs affected ARGs with mechanisms specifically of antibiotic inactivation and antibiotic target change, and declined potential hosts’ abundance (bacterial genus Ruminiclostridium, Riminococcus, and Paenibacillus) which mainly contributed to the decreased ARGs’ abundance. Besides, microbial chemotaxis decreased by 17% with ZnO NPs compared to that without nanoparticles indicated a depression on potential hosts, who could develop the mechanism to adapt to altered digestion conditions, which probably inhibited the ARGs’ propagation. These findings are important to promote understanding of the potential ARGs risks in treatments of livestock wastes containing animal feed additives.
Chapter
The untreated water may lead to an excessive disposal of wastes which may reduce the water quality of water bodies and damage water ecosystems. Wastewater treatment systems are widely implemented in industries and municipalities to decrease toxic wastewater release into aquatic ecosystems. Wastewater recycling, reclamation, recovery, and reuse can be used as tools for the control of water resources and can attract researchers and stakeholders. Currently microbial fuel cells and microalgae are intensively studied as a cost-effective technology to complete sustainable wastewater treatment. These technologies have potential benefits for energy, and environmental and economic sustainability. This chapter will review the challenges, barriers, and opportunities associated with improving wastewater treatment systems.
Chapter
The increased population and water demands have forced the human community to search for new paradigms for supplying and managing water. The water reuse or potable and nonpotable application of reclaimed wastewater is attracting attention. The increased popularity of reclaimed water has raised safety concerns regarding the quality. With suitable treatment techniques (process redundancy, high-level disinfection), technical controls (regular inspections, alarm shutdowns), online monitoring control (residual chlorine concentration, turbidity in effluent), and operational controls (for deviation and variability), a reliable quality of reclaimed water can be accomplished. Monitoring and operational response plans are used to provide quality control in potable reclaimed water projects. Quality is assured by establishing multiple barriers and assessing the reliability of treatment. This chapter discusses the design principles and the important guidelines in water reclamation for better water quality.
Chapter
Mathematical modeling and optimization of wastewater treatment processes have become a powerful tool for process designing in engineering firms throughout the world. The wastewater treatment processes are complex, and their operations pose many challenges. The modeling and optimization of wastewater treatment processes facilitate in predicting the behavior of wastewater treatment processes, the fluctuations in the influent concentrations, flow rate, and concentration of pollutants without disturbing the real system. The mathematical models are extensively used at operating facilities for everyday operating decisions. The increased computer processing power, along with the user-friendly simulation software, has made it easier to model the complexities. This chapter provides a complete and detailed overview of the application of mathematical modeling in the field of wastewater treatment. The modeling approach, implementing the circular economy principles, is also discussed, highlighting the potential of wastewater treatment plants to be more sustainable waste resource recovery facilities.
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Anaerobic digestion (AD) processes of food waste (FW) have potential risk on environments due to the prevalence and dissemination of antibiotic resistance genes (ARGs). This study investigated the effect of bentonite on methane production and the abundance of ARGs in biogas slurry and residue during AD of FW. Results showed that methane production increased by 68.52% and 56.79% with 3 g/L and 5 g/L of bentonite in mesophilic and thermophilic digestion, respectively. Adding 5 g/L of bentonite effectively reduced the genes of ermB, ermF, tetQ, tetX, sul1, sul2 and intI1 with a range of 80.82% - 100.00% in biogas residue under mesophilic reactor. The abundance of ARGs and intI1 in biogas residue were lower than in slurry under both temperatures with 5 g/L of bentonite. Statistical analysis indicated that bentonite and temperature were main driver factors which could impact ARGs by influencing the abundance and structure of microbial communities.
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Currently, anaerobic sludge digestion (ASD) is considered not only for treating residual sewage sludge and energy recovery but also for the reduction of antibiotic resistance genes (ARGs). The current review highlights the reasons why antibiotic resistant bacteria (ARB) and ARGs exist in ASD and how ASD performs in the reduction of ARB and ARGs. ARGs and ARB have been detected in ASD with some reports indicating some of the ARGs can be completely removed during the ASD process, while other studies reported the enrichment of ARB and ARGs after ASD. This paper reviews the performance of ASD based on operational parameters as well as environmental chemistry. More studies are needed to improve the performance of ASD in reducing ARGs that are difficult to handle and also differentiate between extracellular (eARGs) and intracellular ARGs (iARGs) to achieve more accurate quantification of the ARGs.
Article
Antibiotics contamination of the environment is a growing public health concern, due to their persistency, possible chronic effects and spread of antibiotics resistance genes. The aim of the study was to determine efficiency of ozonation of waste biological sludge, contaminated by various antibiotics (400 mg L⁻¹ of Tiamulin, Amoxicillin and Levofloxacin) in terms of inreased biogas production potential. It was confirmed that contaminated waste sludge inhibits overall biogas production in further anaerobic stabilization for 10 - 30% resulting also in lower methane yield in the gas mixture (14 to 45%). Ozonation of waste biological sludge was accomplished in batch system for 10 (22 - 24 mgO3 gvss⁻¹) or 20 (36 - 69 mgO3 gvss⁻¹) minutes. The impact to biogas production potential was measured for untreated, contaminated, ozonated untreated and ozonated contaminated sludge after its addition to anaerobic sludge in closed system at 37 °C. Ozone at applied doses simultaneously removed antibiotics related inhibition of biogas production and in some cases enhances biogas production (13 - 18%) with improved methane yield (22 - 32%). The highest improvement in biogas production potential was determined for Tiamulin while ozonation of Levofloxacin contaminated sludge was less efficient. It was concluded, that proposed ozone doses resulted in removal of inhibition due to the antibiotics but did not lead to economically feasible increase of biogas production and methane yield.
Article
Electrokinetic remediation is an effective technology for soil contaminated with heavy metals. However, little is known about the fate of antibiotic resistance in the process under heavy metal stress, since antibiotic resistance genes (ARGs) are widely distributed and can be co-selected with heavy metals. This study focused on antibiotic resistant bacteria and ARGs over different remediation periods (1, 2, and 5 days), voltages (0.4 and 0.8 V cm⁻¹), and initial concentrations (250–1,000 mg kg⁻¹ for Cu, and 1,000–3,000 mg kg⁻¹ for Zn). The application of polarity-reversal maintained a suitable pH, eliminating possible negative effects on soil quality. In addition to a decrease in total metals, the speciation was modified as residual forms decreased while reactive forms increased. Compared with anti-oxytetracycline bacteria, anti-sulfamethoxazole bacteria were more resistant to the electric field, which might be ascribed to greater constraints on their resistance enzymes. The presence of heavy metals accelerated the spread of ARGs, with a 2.67-fold increase for tetG, and a 3.86-fold increase for sul1. Among the ARGs studied, tetM and tetW, as well as sul genes were more easily removed than tetC and tetG genes. Finally, a significant correlation was found between ARGs and Cu, consistent with the relatively stronger toxicity of Cu and its high potential to induce the SOS response. This study advances the understanding of how electrokinetics influences antibiotic resistance in soil with heavy metals, which has important implications for the simultaneous control of these pollutants in soil.
Article
This study focus on the fate of ARGs in the full-scale AD of food wastewater (FWW). Residue was collected from two different full-scale thermophilic AD treating FWW. Ten selected ARGs, including tetracycline resistance genes (tetM, tetX, tetQ, tetH and tetG), sulfonamide resistance genes (sul1 and sul2), quinolone resistance genes (qnrD) and macrolide resistance genes (ermB and ermC), were amplified using quantitative polymerase chain reaction (qPCR). Furthermore, the class 1 integron-integrase gene (intI1) was selected as a representative mobile gene element. Remarkable reduction in the ARGs and intI1 was observed in two-stage (acidogenic–methanogenic) AD, particularly, tetG, tetH, tetM, tetQ, tetX and intI1 not detected. Additionally, significant positive correlation (p < 0.01) between ARGs and intI1 suggested a strong likelihood of horizontal gene transfer (HGT). Furthermore, stepwise multiple linear regression analysis revealed significant factors related to the fate of individual ARGs and intI1 during AD.
Article
In this study, the effects of different temperature transitions on the dynamics of antibiotic resistance genes (ARGs) and bacterial community were investigated during start-up of thermophilic anaerobic digestion (AD) of sewage sludge. Although two thermophilic reactors showed dissimilar removal efficiencies of ARGs in batch mode, both the removal efficiency and reduction patterns of ARGs were similar in continuous stirred tank reactor (CSTR) mode, resulting in significant reduction of the total sum of the relative abundance of ARGs. Using network analysis to explore the correlation between bacterial community and some specific ARGs revealed that composition of the bacterial community played a vital role in the fluctuations in the relative abundance of the antibiotic resistome, demonstrating that shaping the development of ARGs was facilitated by vertical gene transfer. To facilitate eliminating ARGs, minimizing their hosts which persist even under long-term operations is vital in thermophilic AD.
Article
Recent studies have consistently demonstrated increasing abundances of antibiotic resistance genes (ARGs) in the absence of antibiotic use. There is a large amount of quantitative data that has correlated the elevated ARGs levels with the concentrations of heavy metals in environments with anthropogenic impact. However, the mechanisms by which heavy metals facilitate the proliferation and horizontal gene transfer of ARGs among environmental bacteria were still unknown. This study validated effects of four typical heavy metals (Cu, Cd, Pb, Zn) on the plasmid RP4 mediated conjugative transfer of ARGs in freshwater microcosms. The results suggested that the typical heavy metals including Cu, Pb and Zn would promote conjugative transfer of the plasmid RP4, and Cu (5.0 μg/L) had the greatest ability to increase conjugative transfer by 16-fold higher than the control groups. In conjugative transfer microcosms, the species of each cultivable transconjugant were isolated, and their minimum inhibitory concentrations (MICs) were assessed via antibiotic susceptibility testing. The mechanism of the increased conjugative transfer of Cu was that Cu induced cell damage and the reduced conjugative transfer of Cd was that Cd increased the content of extracellular polymers substances (EPS). This study confirms that heavy metal Cu facilitates the conjugative transfer of environmental-mediated plasmid RP4 by cell damage effect, therefore accelerating the transmission and proliferation of ARGs.
Article
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.
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Global expectation for sustainability has prompted the transition of practices in wastewater treatment plants toward not only waste management, but also the energy and nutrient recovery. It has been shown that low temperature hydrotherm (HT) treatments can enhance downstream biogas production via anaerobic digestion (AD). Yet, because the application of combined HT and AD is still at its early stage, systematic understanding on the dynamic speciation evolution of critical elements is still lacking. This study investigated the energy and nutrient recovery from sewage sludge and swine manure via combined HT-AD treatment. Bench-scale investigation was conducted for evaluating biogas production and understanding the dynamic evolution of organics and P speciation. C and P speciation were characterized using complementary chemical and spectroscopic techniques, including 13C nuclear magnetic resonance (NMR) spectroscopy, P X-ray absorption near edge structure (XANES) spectroscopy, and sequential chemical extraction. Results from this study suggest that low-temperature HT pretreatment can achieve enhanced biogas production for sludge, as compared to the minimal effect on the biogas production from manure. It also provides guidance for P recovery from liquid digestate and solid residue after the AD process.
Article
The effects of nanoscale zero-valent iron (nZVI) on the performance of food waste anaerobic digestion and the fate of antibiotic resistance genes (ARGs) were investigated in thermophilic (TR) and mesophilic (MR) reactors. Results showed that nZVI enhanced biogas production and facilitated ARGs reduction. The maximum CH4 production was 212.00 ± 4.77 ml/gVS with 5 g/L of nZVI in MR. The highest ARGs removal ratio was 86.64 ± 0.72% obtained in TR at nZVI of 2 g/L. nZVI corrosion products and their contribution on AD performance were analyzed. The abundance of tetracycline genes reduced significantly in nZVI amended digesters. Firmicutes, Chloroflexi, Proteobacteria and Spirochaetes showed significant positive correlations with various ARGs (p < 0.05) in MR and TR. Redundancy analysis indicated that microbial community was the main factor that influenced the fate of ARGs. nZVI changed microbial communities, with decreasing the abundance bacteria belonging to Firmicutes and resulting in the reduction of ARGs.
Article
Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.
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This study aimed to assess the antibiogram of Aeromonas strains recovered from cattle faeces and the potential pathogenic status of the isolates. The antibiogram of the Aeromonas isolates demonstrated total resistance to clindamycin oxacillin, trimethoprim, novobiocin and ticarcillin. However, Aeromonas strains were sensitive to cefotaxime, oxytetracycline and tobramycin. The Aeromonas strains from Lovedale and Fort Cox farms were found to possess some virulence genes. The percentage distribution was aer 71.4 %, ast 35.7 %, fla 60.7 %, lip 35.7 % and hlyA 25 % for Lovedale farm and aer 63.1 %, alt 10.5 %, ast 55.2 %, fla 78.9 %, lip 21 % and hlyA 35.9 % for Fort Cox farm. Class 1 integron was present in 27 % of Aeromonas isolates; the bla TEM gene was present in 34.8 %, while the blaP1 class A β-lactamase gene was detected in 12.1 % of the isolates. Approximately 86 % of the isolates formed a biofilm on microtitre plates. The presence of multiple antibiotic resistance and virulence genes in Aeromonas isolates from cattle faeces reveals the pathogenic and infectious importance of these isolates and is of great significance to public health. The possession of a biofilm-forming capability by such isolates may lead to difficulty during the management of infection related to Aeromonas species.
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Ancient and diverse antibiotic resistance genes (ARGs) have previously been identified from soil, including genes identical to those in human pathogens. Despite the apparent overlap between soil and clinical resistomes, factors influencing ARG composition in soil and their movement between genomes and habitats remain largely unknown. General metagenome functions often correlate with the underlying structure of bacterial communities. However, ARGs are proposed to be highly mobile, prompting speculation that resistomes may not correlate with phylogenetic signatures or ecological divisions. To investigate these relationships, we performed functional metagenomic selections for resistance to 18 antibiotics from 18 agricultural and grassland soils. The 2,895 ARGs we discovered were mostly new, and represent all major resistance mechanisms. We demonstrate that distinct soil types harbour distinct resistomes, and that the addition of nitrogen fertilizer strongly influenced soil ARG content. Resistome composition also correlated with microbial phylogenetic and taxonomic structure, both across and within soil types. Consistent with this strong correlation, mobility elements (genes responsible for horizontal gene transfer between bacteria such as transposases and integrases) syntenic with ARGs were rare in soil by comparison with sequenced pathogens, suggesting that ARGs may not transfer between soil bacteria as readily as is observed between human pathogens. Together, our results indicate that bacterial community composition is the primary determinant of soil ARG content, challenging previous hypotheses that horizontal gene transfer effectively decouples resistomes from phylogeny.
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This review provides a detailed comparative summary of the recent and current research activities in the area of two-phase anaerobic digestion processes. The acid phase and the methane phase are first evaluated, individually, from microbiological, kinetic and modelling, process optimization, operation and control, inhibition, and toxicity points of view. The overall process performance is subsequently evaluated as a whole. Finally, areas requiring further research are determined.© 2002 Society of Chemical Industry
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Activated sludge (AS) contains highly complex microbial communities. In this study, PCR-based 454 pyrosequencing was applied to investigate the bacterial communities of AS samples from 14 sewage treatment plants of Asia (mainland China, Hong Kong, and Singapore), and North America (Canada and the United States). A total of 259 K effective sequences of 16S rRNA gene V4 region were obtained from these AS samples. These sequences revealed huge amount of operational taxonomic units (OTUs) in AS, that is, 1183-3567 OTUs in a sludge sample, at 3% cutoff level and sequencing depth of 16,489 sequences. Clear geographical differences among the AS samples from Asia and North America were revealed by (1) cluster analyses based on abundances of OTUs or the genus/family/order assigned by Ribosomal Database Project (RDP) and (2) the principal coordinate analyses based on OTUs abundances, RDP taxa abundances and UniFrac of OTUs and their distances. In addition to certain unique bacterial populations in each AS sample, some genera were dominant, and core populations shared by multiple samples, including two commonly reported genera of Zoogloea and Dechloromonas, three genera not frequently reported (i.e., Prosthecobacter, Caldilinea and Tricoccus) and three genera not well described so far (i.e., Gp4 and Gp6 in Acidobacteria and Subdivision3 genera incertae sedis of Verrucomicrobia). Pyrosequencing analyses of multiple AS samples in this study also revealed the minority populations that are hard to be explored by traditional molecular methods and showed that a large proportion of sequences could not be assigned to taxonomic affiliations even at the phylum/class levels.
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The purpose of this study was to quantify the occurrence and release of antibiotic resistant genes (ARGs) and antibiotic resistant bacteria (ARB) into the environment through the effluent and biosolids of different wastewater treatment utilities including an MBR (Membrane Biological Reactor) utility, conventional utilities (Activated Sludge, Oxidative Ditch and Rotatory Biological Contactors-RBCs) and multiple sludge treatment processes (Dewatering, Gravity Thickening, Anaerobic Digestion and Lime Stabilization). Samples of raw wastewater, pre- and post-disinfected effluents, and biosolids were monitored for tetracycline resistant genes (tetW and tetO) and sulfonamide resistant gene (Sul-I) and tetracycline and sulfonamide resistant bacteria. ARGs and ARB concentrations in the final effluent were found to be in the range of ND(non-detectable)-2.33 × 10(6) copies/100 mL and 5.00 × 10(2)-6.10 × 10(5) CFU/100 mL respectively. Concentrations of ARGs (tetW and tetO) and 16s rRNA gene in the MBR effluent were observed to be 1-3 log less, compared to conventional treatment utilities. Significantly higher removals of ARGs and ARB were observed in the MBR facility (range of removal: 2.57-7.06 logs) compared to that in conventional treatment plants (range of removal: 2.37-4.56 logs) (p < 0.05). Disinfection (Chlorination and UV) processes did not contribute in significant reduction of ARGs and ARB (p > 0.05). In biosolids, ARGs and ARB concentrations were found to be in the range of 5.61 × 10(6)-4.32 × 10(9) copies/g and 3.17 × 10(4)-1.85 × 10(9) CFU/g, respectively. Significant differences (p < 0.05) were observed in concentrations of ARGs (except tetW) and ARB between the advanced biosolid treatment methods (i.e., anaerobic digestion and lime stabilization) and the conventional dewatering and gravity thickening methods.
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Small subunit rRNA sequence data were generated for 27 strains of cyanobacteria and incorporated into a phylogenetic analysis of 1,377 aligned sequence positions from a diverse sampling of 53 cyanobacteria and 10 photosynthetic plastids. Tree inference was carried out using a maximum likelihood method with correction for site-to-site variation in evolutionary rate. Confidence in the inferred phylogenetic relationships was determined by construction of a majority-rule consensus tree based on alternative topologies not considered to be statistically significantly different from the optimal tree. The results are in agreement with earlier studies in the assignment of individual taxa to specific sequence groups. Several relationships not previously noted among sequence groups are indicated, whereas other relationships previously supported are contradicted. All plastids cluster as a strongly supported monophyletic group arising near the root of the cyanobacterial line of descent.
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Tetracyclines were discovered in the 1940s and exhibited activity against a wide range of microorganisms including gram-positive and gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoan parasites. They are inexpensive antibiotics, which have been used extensively in the prophlylaxis and therapy of human and animal infections and also at subtherapeutic levels in animal feed as growth promoters. The first tetracycline-resistant bacterium, Shigella dysenteriae, was isolated in 1953. Tetracycline resistance now occurs in an increasing number of pathogenic, opportunistic, and commensal bacteria. The presence of tetracycline-resistant pathogens limits the use of these agents in treatment of disease. Tetracycline resistance is often due to the acquisition of new genes, which code for energy-dependent efflux of tetracyclines or for a protein that protects bacterial ribosomes from the action of tetracyclines. Many of these genes are associated with mobile plasmids or transposons and can be distinguished from each other using molecular methods including DNA-DNA hybridization with oligonucleotide probes and DNA sequencing. A limited number of bacteria acquire resistance by mutations, which alter the permeability of the outer membrane porins and/or lipopolysaccharides in the outer membrane, change the regulation of innate efflux systems, or alter the 16S rRNA. New tetracycline derivatives are being examined, although their role in treatment is not clear. Changing the use of tetracyclines in human and animal health as well as in food production is needed if we are to continue to use this class of broad-spectrum antimicrobials through the present century.
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The population dynamics of activated sludge in a pilot plant with two activated sludge systems, both designed for enhanced biological phosphorus removal (EBPR), but one of them with (BNP) and the other without (BP) nitrogen removal, was monitored during a period of 2.5 years. The influent water to the pilot plant was periodically manipulated by external addition of phosphorus (P), acetate and glucose, respectively. The population dynamics and the in situ physiology were monitored by quantitative fluorescence in situ hybridization (FISH) and microautoradiography. Significant P removal was observed in both systems throughout the whole period, with significant increases of the P removal when substrates were dosed. The activated sludge in both systems contained large amounts of dense clusters of gram-negative, methylene-blue staining coccoid rods during the whole period. A large part of the clusters belonged to the beta Proteobacteria, whereas the rest of the clusters belonged either to the Actinobacteria or to the alpha Proteobacteria. The relative abundance of Rhodocyclus-related bacteria in the activated sludge varied significantly in both systems during the whole period (from 6 to 18% in BNP, and from 4 to 28% in BP). However, no statistically significant correlation of the Rhodocyclus-related nor any of the other investigated bacterial groups to the P content of the activated sludge (correlation for all groups investigated was always < 0.5) was observed. A significant 33Pi uptake was observed by the beta Proteobacteria (part of them Rhodocyclus-related, the identity of the rest unknown) and the Actinobacteria. However, not all of the Rhodocyclus-related bacteria showed 33Pi uptake. The P removal in the investigated plants is thus believed to be mediated by a mixed population consisting of a part of the Rhodocyclus-related bacteria, the Actinobacteria and other, yet unidentified bacteria.
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Antimicrobial resistance and class 1 integrons found in Escherichia coli isolates from humans and animals in Korea were characterized. E. coli isolates were examined for susceptibility to antimicrobial agents. Integrase genes were amplified. Gene cassette regions for classes 1 and 2 integrons were amplified and sequenced. Conjugal transfer and Southern hybridization were performed to determine the genetic localization of class 1 integrons. The clonal relationship of E. coli isolates carrying an identical cassette array was analysed by PFGE. Commensal E. coli isolates from animals were highly resistant to commonly used antimicrobial agents such as tetracycline, sulfamethoxazole, streptomycin, ampicillin and carbenicillin. Integrons were most prevalent in commensal E. coli isolates from poultry (44%), followed by clinical isolates from humans (33%), commensal isolates from swine (23%) and humans (13%). dfrA17-aadA5, dfrA12-orfF-aadA2 and aadA1 were found most frequently in E. coli isolates from humans, poultry and swine, respectively. Class 1 integrons were mostly located in conjugative plasmids. E. coli isolates carrying an identical cassette array were phylogenetically unrelated. The use of antibiotics is strongly associated with antimicrobial resistance. E. coli isolates from different sources may select a specific gene cassette by antibiotic selective pressure, which results in differences in class 1 integrons. The horizontal transfer of class 1 integrons through conjugative plasmids seems to be responsible for wide dissemination of a particular type of class 1 integron.
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This mini-review summarizes the changes in the field of bacterial acquired tetracycline resistance (tet) and oxytetracycline (otr) genes identified since the last major review in 2001. Thirty-eight acquired tetracycline resistant (Tc(r)) genes are known of which nine are new and include five genes coding for energy-dependent efflux proteins, two genes coding for ribosomal protection proteins, and two genes coding for tetracycline inactivating enzymes. The number of inactivating enzymes has increased from one to three, suggesting that work needs to be done to determine the role these enzymes play in bacterial resistance to tetracycline. In the same time period, 66 new genera have been identified which carry one or more of the previously described 29 Tc(r) genes. Included in the new genera is, for the first time, an obligate intracellular pathogen suggesting that this sheltered group of bacteria is capable of DNA exchange with non-obligate intracellular bacteria. The number of genera carrying ribosomal protection genes increased dramatically with the tet(M) gene now identified in 42 genera as compared with 24 and the tet(W) gene found in 17 new genera as compared to two genera in the last major review. New conjugative transposons, carrying different ribosomal protection tet genes, have been identified and an increase in the number of antibiotic resistance genes linked to tet genes has been found. Whether these new elements may help to spread the tet genes they carry to a wider bacterial host range is discussed.
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The development and proliferation of antibiotic resistance in pathogenic, commensal, and environmental microorganisms is a major public health concern. The extent to which human activities contribute to the maintenance of environmental reservoirs of antibiotic resistance is poorly understood. In the current study, wastewater treatment plants (WWTPs) were investigated as possible sources of tetracycline resistance via qualitative PCR and quantitative PCR (qPCR). Various WWTPs and two freshwater lakes were surveyed for the presence of an array of 10 tetracycline resistance determinants (tet(R)): tet(A)-(E), tet(G), tet(M), tet(O), tet(Q), tet(S). All WWTP samples contained more different types of tet(R) genes, as compared to the lake water samples. Gene copy numbers of tet(G) and tet(Q) in these samples were quantified via qPCR and normalized to both the volume of original sample and to the amount of DNA extracted per sample (a proxy for bacterial abundance). Concentrations of tet(Q) were found to be highest in wastewater influent while tet(G) concentrations were highest in activated sludge. Investigation of the effects of UV disinfection on wastewater effluent showed no reduction in the number of detectable tet(R) gene types.
Article
Rice straw biochar (RSB) and mushroom biochar (MB) were added to lab-scale chicken manure composting to evaluate their effects on the behaviors of antibiotic resistance genes (ARGs) and on total and bio-available heavy metals (Cu, Zn and As). The associated bacterial community was characterized by 16SrRNA high-throughput sequencing. The abundance of pathogenic bacteria was also calculated. At the end of the control composting experiment, the average removal rate of ARGs was 0.86log units and the removal rate of pathogenic bacteria was 57.1%. MB addition resulted in a higher removal rate than that in the control composting experiment. However, RSB addition yielded opposite results, which may be due to the higher abundance of Erysipelotrichaceae, Lactobacillaceae, Family_XI_Incertae_Sedis (belonging to Firmicutes carrying and disseminating ARGs) and pathogenic bacteria carrying ARGs. Furthermore, the correlations between bio-available heavy metals and ARGs were more obvious than those between total heavy metals and ARGs.
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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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A temperature-phased anaerobic digestion system with the thermophilic digester acidified by acidogenesis products (referred to as AT-TPAD) was evaluated to treat high-strength dairy cattle manure at a 15-day retention time. Three temperatures (50, 55, and 60°C) were tested on the thermophilic digester, and 50°C was found to be the optimal temperature for overall performance of the AT-TPAD system, achieving 31% VS removal and 0.22Lmethane/g VS fed. The mesophilic digester contributed significantly more to the overall system performance than the thermophilic digester. The thermophilic and the mesophilic digesters had different microbial communities under all conditions, and both microbial communities exhibited dynamic changes in response to different conditions. Certain microbial groups were found significantly correlated with the system performance. Methanosarcina was the most important methanogen genus of the AT-TPAD system and its population abundance was inversely correlated with high concentrations of volatile fatty acids (VFA).
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Small subunit rRNA sequence data were generated for 27 strains of cyanobacteria and incorporated into a phylogenetic analysis of 1,377 aligned sequence positions from a diverse sampling of 53 cyanobacteria and 10 photosynthetic plastids. Tree inference was carried out using a maximum likelihood method with correction for site-to-site variation in evolutionary rate. Confidence in the inferred phylogenetic relationships was determined by construction of a majority-rule consensus tree based on alternative topologies not considered to be statistically significantly different from the optimal tree. The results are in agreement with earlier studies in the assignment of individual taxa to specific sequence groups. Several relationships not previously noted among sequence groups are indicated, whereas other relationships previously supported are contradicted. All plastids cluster as a strongly supported monophyletic group arising near the root of the cyanobacterial line of descent.
Article
Wastewater treatment processes are of growing interest as a potential means to limit the dissemination of antibiotic resistance. This study examines the response of nine representative antibiotic resistance genes (ARGs) encoding resistance to sulfonamide (sulI, sulII), erythromycin (erm(B), erm(F)), and tetracycline (tet(O), tet(W), tet(C), tet(G), tet(X)) to various laboratory-scale sludge digestion processes. The class I integron gene (intI1) was also monitored as an indicator of horizontal gene transfer potential and multiple antibiotic resistance. Mesophilic anaerobic digestion at both 10 and 20 day solids retention times (SRTs) significantly reduced sulI, suII, tet(C), tet(G), and tet(X) with longer SRT exhibiting a greater extent of removal; however, tet(W), erm(B) and erm(F) genes increased relative to the feed. Thermophilic anaerobic digesters operating at 47 °C, 52 °C, and 59 °C performed similarly to each other and provided more effective reduction of erm(B), erm(F), tet(O), and tet(W) compared to mesophilic digestion. However, thermophilic digestion resulted in similar or poorer removal of all other ARGs and intI1. Thermal hydrolysis pretreatment drastically reduced all ARGs, but they generally rebounded during subsequent anaerobic and aerobic digestion treatments. To gain insight into potential mechanisms driving ARG behavior in the digesters, the dominant bacterial communities were compared by denaturing gradient gel electrophoresis. The overall results suggest that bacterial community composition of the sludge digestion process, as controlled by the physical operating characteristics, drives the distribution of ARGs present in the produced biosolids, more so than the influent ARG composition.
Article
Activated sludge was sampled from 15 sewage treatment plants (STPs) across China and other global locations to investigate the occurrence, abundance and diversity of tetracycline resistance genes (tet) in the STPs. Occurrence and abundance of 14 tet genes were determined using polymerase chain reaction (PCR) and quantitative real time PCR. Six genes (tet(A), tet(C), tet(G), tet(M), tet(S), and tet(X)) were detected in all the STPs, while no sludge sample contained tet(Q). Total concentration of the 14 genes was significantly different among the STPs and average tet abundance of the STPs varied greatly among the tet types (p<0.05). Tet(G) had the highest concentration in the STPs, followed by tet(C), tet(A) and tet(S). Phylogenetic diversity of the genes was investigated using DNA cloning. BLAST analysis showed that all of the 450 cloned sequences matched known tet genes, except for tet(G). The 56 tet(G) clones were grouped into 14 genotypes, among which type G24 had an identical sequence to tet(G) carried by Salmonella enterica or Acinetobacter baumannii, while the other sequences had low similarity to the known genes in GenBank. The results of this study might be useful to understand the diversity of these resistance genes in STPs.
Article
The present study investigated a two-stage anaerobic hydrogen and methane process for increasing bioenergy production from organic wastes. A two-stage process with hydraulic retention time (HRT) 3d for hydrogen reactor and 12d for methane reactor, obtained 11% higher energy compared to a single-stage methanogenic process (HRT 15 d) under organic loading rate (OLR) 3 gVS/(L d). The two-stage process was still stable when the OLR was increased to 4.5 gVS/(Ld), while the single-stage process failed. The study further revealed that by changing the HRT(hydrogen):HRT(methane) ratio of the two-stage process from 3:12 to 1:14, 6.7%, more energy could be obtained. Microbial community analysis indicated that the dominant bacterial species were different in the hydrogen reactors (Thermoanaerobacterium thermosaccharolyticum-like species) and methane reactors (Clostridium thermocellum-like species). The changes of substrates and HRT did not change the dominant species. The archaeal community structures in methane reactors were similar both in single- and two- stage reactors, with acetoclastic methanogens Methanosarcina acetivorans-like organisms as the dominant species.
Article
The objective of this research was to investigate the ability of anaerobic and aerobic digesters to reduce the quantity of antibiotic resistant bacteria in wastewater solids. Lab-scale digesters were operated at different temperatures (22 °C, 37 °C, 46 °C, and 55 °C) under both anaerobic and aerobic conditions and fed wastewater solids collected from a full-scale treatment facility. Quantitative PCR was used to track five genes encoding tetracycline resistance (tet(A), tet(L), tet(O), tet(W), and tet(X)) and the gene encoding the integrase (intI1) of class 1 integrons. Statistically significant reductions in the quantities of these genes occurred in the anaerobic reactors at 37 °C, 46 °C, and 55 °C, with the removal rates and removal efficiencies increasing as a function of temperature. The aerobic digesters, in contrast, were generally incapable of significantly decreasing gene quantities, although these digesters were operated at much shorter mean hydraulic residence times. This research suggests that high temperature anaerobic digestion of wastewater solids would be a suitable technology for eliminating various antibiotic resistance genes, an emerging pollutant of concern.
Article
Given the potential for a variety of bacterial pathogens to occur in variably stabilized sewage sludge (biosolids), an understanding of pathogen diversity and abundance is necessary for accurate assessment of infective risk when these products are land applied. 16S rDNA was PCR amplified from genomic DNA extracted from municipal wastewater residuals (mesophilic- and thermophilic-phased anaerobic digestion (MAD and TPAD), composting (COM)), and agricultural soil (SOIL), and these amplicons were sequenced using massively parallel pyrosequencing technology. Resulting libraries contained an average of 30,893 16S rDNA sequences per sample with an average length of 392 bases. FASTUNIFRAC-based comparisons of population phylogenetic distance demonstrated similarities between the populations of different treatment plants performing the same stabilization method (e.g. different MAD samples), and population differences among samples from different biosolids stabilization methods (COM, MAD, and TPAD). Based on a 0.03 Jukes-Cantor distance to 80 potential bacterial pathogens, all samples contained pathogens and enrichment ranged from 0.02% to 0.1% of sequences. Most (61%) species identified were opportunistic pathogens of the genera Clostridium and Mycobacterium. As risk sciences continue to evolve to address scenarios that include multiple pathogen exposure, the analysis described here can be used to determine the diversity of pathogens in an environmental sample. This work provides guidance for prioritizing subsequent culturable and quantitative analysis, and for the first time, ensuring that potentially significant pathogens are not left out of risk estimations.
Article
To study the frequency and diversity of class 1 integrons lacking the 3'-conserved segment (CS) in intI1-positive Escherichia coli isolates of different origins. The presence of intI1 was previously detected in 84 E. coli isolates of food (21 isolates), animal (32) and healthy-human volunteer (31) origins. The qacEDelta1-sul1 genes were analyzed by PCR and those isolates that lacked these genes were included in this work. The genetic structure of class 1 integrons was determined, using the PCR and sequencing primer-walking strategy. Isolates and plasmids were typed. Class 1 integrons lacking the 3'-CS were found in 13 of the 84 intI1-positive E. coli isolates (15.5%) of food, animal, and human origins. All 13 isolates showed unrelated patterns by REP-PCR. The following gene cassette arrangements were identified inside the class 1 integrons of these 13 strains: dfrA1; dfrA5; dfrA12-orfF-aadA2-cmlA1-aadA1-qacH-IS440-sul3; dfrA12-orfF-aadA2-cmlA1-aadA1-IS440-sul3; estX-psp-aadA2-cmlA1-aadA1-qacH-IS440-sul3; and a new arrangement estX-psp-aadA2-cmlA1Delta-IS1294-DeltacmlA1-aadA1-qacH-IS440-sul3 that contain the IS1294 into the cmlA1 gene (included in GenBank, number EU704128). Complete or truncated mef(B) gene was detected upstream of sul3 gene in this type of integrons. Plasmids were identified in four of the studied strains by PCR-replicon-typing, detecting different combinations of IncY, I1, FIC, FII, FIB plasmids. Non-classic integrons were located into plasmids of 100-150 kb in four studied strains. Occurrence and diversity of class 1 integrons lacking 3'-CS among the studied intI1-positive E. coli isolates of different origins were relatively high. The sul3 gene was detected in most of class 1 integrons lacking 3'-CS.
Article
In this study, the abilities of two anaerobic digestion processes used for sewage sludge stabilization were compared for their ability to reduce the quantities of three genes that encode resistance to tetracycline (tet(A), tet(O), and tet(X)) and one gene involved with integrons (intI1). A two-stage, thermophilic/mesophilic digestion process always resulted in significant decreases in the quantities of tet(X) and intI1, less frequently in decreases of tet(O), and no net decrease in tet(A). The thermophilic stage was primarily responsible for reducing the quantities of these genes, while the subsequent mesophilic stage sometimes caused a rebound in their quantities. In contrast, a conventional anaerobic digestion process rarely caused a significant decrease in the quantities of any of these genes, with significant increases occurring more frequently. Our results demonstrate that anaerobic thermophilic treatment was more efficient in reducing quantities of genes associated with the spread of antibiotic resistance compared to mesophilic digestion.
Article
Activated sludges were sampled from five sewage treatment plants (STPs) distributed in three geographically isolated areas, i.e., Hong Kong (Shatin, Stanley), Shanghai (Minhang) in China, and the bay area in California (Palo Alto and San Jose) of the United States. Among the tested 14 tetracycline resistance (tet) genes, nine genes encompassing efflux pumps (tetA, tetC, tetE, and tetG), ribosomal protection proteins (tetM, tetO, tetQ, and tetS), and enzymatic modification (tetX) were commonly detected in the STP sludge samples, whereas five genes encompassing efflux pumps [tetB, tetD, tetL, tetK, and tetA(P)] were not detected in any sludge sample. Additionally, 109 lactose-fermenting Enterobacteriaceae (LFE) strains were isolated from the activated sludge of the Shatin STP. Tetracycline-resistant (TR) LFE accounted for 32% of the total 109 LFE strains. The occurrence frequencies of tet genes among all TR-LEF strains varied from 0 to 91%, i.e., tetC (91%), tetA (46%), tetE (9%), tetG (6%), and tetD (6%). Finally, quantitative real-time polymerase chain reaction was used to quantify the change of tetC and tetA genes as the indicator of TR-LEF in the Shatin and Stanley STPs. The results showed that the concentrations of tetC and tetA genes in STP effluent ranged from 10(4) to 10(5) copies/mL, significantly lower than those in the influent by 3 orders of magnitude.
Article
Extended-spectrum beta-lactamases (ESBLs) are considered to be one of the most important antibiotic resistance mechanisms. This study reported the ESBL-producing genes in 53 randomly selected clinical bacterial isolates from the Steve Biko Academic Hospital. The presence of the bla(SHV), bla(TEM) and bla(CTX-M) genes was determined, and the overall prevalence of these genes detected in this study was 87% (46/53) in comparison with the literature; these results were higher when compared with 33% for Escherichia coli in Europe and 0.8% in Denmark for similar pathogens. These research findings indicated that it is crucial to routinely monitor the prevalence of these resistance genes.
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Two- phase stabilization involves a provision for primary proliferation of acid forming organisms and secondary, and separate, proliferation of methane forming organisms with provision for pH value control in the latter stage when required. If maximum specific growth rates are attained in the first reactor, the results will be almost complete conversion of substrates to volatile acids and other intermediates acceptable to the methane formers.
Article
Tetracycline resistance is common among isolates of the animal commensal and opportunistic pathogen Arcanobacterium pyogenes. The tetracycline resistance determinant cloned from two bovine isolates of A. pyogenes was highly similar at the DNA level (92% identity) to the tet(W) gene, encoding a ribosomal protection tetracycline resistance protein, from the rumen bacterium Butyrivibrio fibrisolvens. The tet(W) gene was found in all 20 tetracycline-resistant isolates tested, indicating that it is a widely distributed determinant of tetracycline resistance in this organism. In 25% of tetracycline-resistant isolates, the tet(W) gene was associated with a mob gene, encoding a functional mobilization protein, and an origin of transfer, suggesting that the determinant may be transferable to other bacteria. In fact, low-frequency transfer of tet(W) was detected from mob+ A. pyogenes isolates to a tetracycline-sensitive A. pyogenes recipient. The mobile nature of this determinant and the presence of A. pyogenes in the gastrointestinal tract of cattle and pigs suggest that A. pyogenes may have inherited this determinant within the gastrointestinal tracts of these animals.
Article
A new gene, sul3, which specifies a 263-amino-acid protein similar to a dihydropteroate synthase encoded by the 54-kb conjugative plasmid pVP440 from Escherichia coli was characterized. Expression of the cloned sul3 gene conferred resistance to sulfamethoxazole on E. coli. Two copies of the insertion element IS15Δ/26 flanked the region containing sul3. The sul3 gene was detected in one-third of the sulfonamide-resistant pathogenic E. coli isolates from pigs in Switzerland.