Alkaline fermentation of waste sludge causes a significant reduction of antibiotic resistance genes in anaerobic reactors

Deciphering the reduction of antibiotic resistance genes (ARGs) during medium-chain fatty acids production from waste activated sludge: Driven by inhibition of ARGs transmission and shift of microbial community

Medium-chain fatty acids (MCFAs) production from waste activated sludge (WAS) by chain extension (CE) is a promising technology. However, the effects and mechanisms of CE process on the fate of antibiotic resistance genes (ARGs) remain unclear. In this study, the results showed that the removal efficiency of ARGs was 81.15 % in CE process, suggesting its efficacy in reducing environmental risks. Further, the observed decrease in mobile genetic elements (MGEs) indicated that CE process restricted the horizontal gene transfer (HGT). Complementing this, the increase in soluble organic matters and extracellular 16 S rDNA confirmed that MCFAs production caused bacterial damage. Decreased intracellular ARGs and increased extracellular ARGs further revealed that MCFAs production impaired ARGs hosts, thereby limiting the vertical gene transfer (VGT) of ARGs. Shift of microbial community combined with co-occurrence network analysis demonstrated that functional bacteria without host potential for ARGs were enriched, but potential ARGs and MGEs hosts decreased, showing the role of functional bacterial phylogeny and selection pressure of MCFAs in reducing ARGs. Finally, partial least squares path model was used to systematic verify the mechanism of ARGs removal in CE process, which was attributed to the inhibition of ARGs transmission (HGT and VGT) and shift of microbial community.

Affecting factors and mechanism of removing antibiotics and antibiotic resistance genes by nano zero-valent iron (nZVI) and modified nZVI: A critical review

Antibiotics and antibiotic resistance genetic pollution have become a global environmental and health concern recently, with frequent detection in various environmental media. Therefore, finding ways to control antibiotics and antibiotic resistance genes (ARGs) is urgently needed. Nano zero-valent iron (nZVI) has shown a positive effect on antibiotics degradation and restraining ARGs, making it a promising solution for controlling antibiotics and ARGs. However, given the current increasingly fragmented research focus and results, a comprehensive review is still lacking. In this work, we first introduce the origin and transmission of antibiotics and ARGs in various environmental media, and then discuss the affecting factors during the degradation of antibiotics and the control of ARGs by nZVI and modified nZVI, including pH, nZVI dose, and oxidant concentration, etc. Then, the mechanisms of antibiotic and ARGs removal promoted by nZVI are also summarized. In general, the mechanism of antibiotic degradation by nZVI mainly includes adsorption and reduction, while promoting the biodegradation of antibiotics by affecting the microbial community. nZVI can also be combined with persulfates to degrade antibiotics through advanced oxidation processes. For the control of ARGs, nZVI not only changes the microbial community structure, but also affects the proliferation of ARGs through affecting the fate of mobile genetic elements (MGEs). Finally, some new ideas on the application of nZVI in the treatment of antibiotic resistance are proposed. This paper provides a reference for research and application in this field.

The role of water matrix on antibiotic resistance genes transmission in substrate layer from stormwater bioretention cells

Recently, extensive attention has been paid to antibiotic resistance genes (ARGs) transmission. However, little available literature could be found about ARGs transmission in stormwater bioretention cells, especially the role of water matrix on ARGs transmission. Batch experiments were conducted to investigate target ARGs (blaTEM, tetR and aphA) transmission behaviors in substrate layer from stormwater bioretention cells under different water matrices, including nutrient elements (e.g., carbon, nitrogen and phosphorus), water environmental conditions (dissolved oxygen (DO), pH and salinity, etc.) and pollution factors (like heavy metals, antibiotics and disinfectants), showing that ARGs conjugation frequency increased sharply with the enhancement of water matrices (expect DO and pH), while there were obvious increasing tendencies for all ARGs transformation frequencies under only the pollution factor. The correlation between dominant bacteria and ARGs transmission implied that conjugation and transformation of ARGs were mainly determined by Firmicutes, Bacteroidota, Latescibacterota, Chloroflexi and Cyanobacteria at the phylum level, and by Sphingomonas, Ensifer, IMCC26256, Rubellimicrobium, Saccharimonadales, Vicinamibacteraceae, Nocardioides, JG30-KF-CM66 at the genus level. The mentioned dominant bacteria were responsible for intracellular reactive oxygen species (ROS) and cell membrane permeability (CMP) in the substrate layer, where the amplification of intracellular ROS variation were the largest with 144 and 147 % under the condition of TP and salinity, respectively, and the one of CMP variation were the highest more than 165 % under various pollution factors. Furthermore, both increasing DO and reducing salinity could be potential approaches for the inhibition of ARGs transmission in bioretention cells taking into account the simultaneous removal of conventional pollutants.

Large-Scale Biogeographical Shifts of Abundance of Antibiotic Resistance Genes and Marine Bacterial Communities as Their Carriers along a Trophic Gradient

The role of marine environments in the global spread of antibiotic resistance still remains poorly understood, leaving gaps in the One Health-based research framework. Antibiotic resistance genes (ARGs) encoding resistance to five major antibiotic classes, including sulfonamides (sul1, sul2), tetracyclines (tetA, tetB), β-lactams (blaCTX-M, blaTEMblaVIM), macrolides (ermB, mphA), aminoglycosides (aac3-2), and integrase gene (intl1) were quantified by RT-qPCR, and their distribution was investigated in relation to environmental parameters and the total bacterial community in bottom layer and surface waters of the central Adriatic (Mediterranean), over a 68 km line from the wastewater-impacted estuary to coastal and pristine open sea. Seasonal changes (higher in winter) were observed for antibiotic resistance frequency and the relative abundances of ARGs, which were generally higher in eutrophic coastal areas. In particular, intl1, followed by blaTEM and blaVIM, were strongly associated with anthropogenic influence and Gammaproteobacteria as their predominant carriers. Water column stratification and geographic location had a significant influence on ARGs distribution in the oligotrophic zone, where the bacterial community exhibited a seasonal shift from Gammaproteobacteria in winter to Marine group II in summer.

Risk control of antibiotics, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) during sewage sludge treatment and disposal: A review

Sewage sludge is an important reservoir of antibiotics, antibiotic resistance genes (ARGs), and antibiotic resistant bacteria (ARB) in wastewater treatment plants (WWTPs), and the reclamation of sewage sludge potentially threats human health and environmental safety. Sludge treatment and disposal are expected to control these risks, and this review summarizes the fate and controlling efficiency of antibiotics, ARGs, and ARB in sludge involved in different processes, i.e., disintegration, anaerobic digestion, aerobic composting, drying, pyrolysis, constructed wetland, and land application. Additionally, the analysis and characterization methods of antibiotics, ARGs, and ARB in complicate sludge are reviewed, and the quantitative risk assessment approaches involved in land application are comprehensively discussed. This review benefits process optimization of sludge treatment and disposal, with regard to environmental risks control of antibiotics, ARGs, and ARB in sludge. Furthermore, current research limitations and gaps, e.g., the antibiotic resistance risk assessment in sludge-amended soil, are proposed to advance the future studies.

Simultaneous Removal of Sulfamethoxazole during Fermentative Production of Short-Chain Fatty Acids

This study explores the simultaneous sulfamethoxazole (SMX) removal and short-chain fatty acids (SCFAs) production by a Clostridium sensu stricto-dominated microbial consortium. SMX is a commonly prescribed and persistent antimicrobial agent frequently detected in aquatic environments, while the prevalence of antibiotic-resistant genes limits the biological removal of SMX. Under strictly anaerobic conditions, sequencing batch cultivation coupled with co-metabolism resulted in the production of butyric acid, valeric acid, succinic acid, and caproic acid. Continuous cultivation in a CSTR achieved a maximum butyric acid production rate and yield of 0.167 g/L/h and 9.56 mg/g COD, respectively, while achieving a maximum SMX degradation rate and removal capacity of 116.06 mg/L/h and 55.8 g SMX/g biomass. Furthermore, continuous anaerobic fermentation reduced sul genes prevalence, thus limiting the transmission of antibiotic resistance genes during antibiotic degradation. These findings suggest a promising approach for efficient antibiotic elimination while simultaneously producing valuable products (e.g., SCFAs).

Surfactant aggravated the antibiotic's stress on antibiotic resistance genes proliferation by altering antibiotic solubilization and microbial traits in sludge anaerobic fermentation

The excessive application of antibiotics and surfactants resulted in their massive accumulation in waste activated sludge (WAS), but the co-occurrent impacts of antibiotics and surfactants on the antibiotic resistant genes (ARGs) fates have seldom reported. This work mainly revealed the roles and critical mechanisms of sodium dodecyl benzene sulfonate (SDBS) on the sulfadiazine (SDZ) stressing for ARGs distribution during WAS anaerobic fermentation. High-throughput qPCR and metagenomic analysis revealed that SDBS aggravated the SDZ selective pressure, and accelerated the proliferation of ARGs. The total abundance of ARGs was increased from 8.81 × 10¹⁰ in SDZ to 1.17 × 10¹¹ copies/g TSS in the SDBS/SDZ co-occurrence system. Specifically, the absolute abundances of ermF (MLSB), mefA (MLSB), tetM-01 (tetracycline), tetX (tetracycline), sul2 (sulfonamide) and strB (aminoglycoside) were risen from 4.60 × 10⁸-7.44 × 10⁹ copies/g TSS in the SDZ reactor to 1.02 × 10⁹-4.63 × 10¹⁰ copies/g TSS in SDBS/SDZ reactor. SDBS was contributed to the SDZ solubilization and simultaneously effective in disintegrating extracellular polymeric substances and improving cell membrane permeability, which would facilitate the SDZ transport and its interactions with ARGs hosts. Consequently, the microbial community structure was evidently altered, and the typical ARGs hosts (i.e., Saccharimonadales and Ahniella) were greatly enriched. Also, the cell signal transduction systems (i.e., glnL, glrK and pilG), oxidative stress response (i.e., frmA and recA) and bacterial secretion systems (i.e., VirB4), which were related with ARGs propagation, were all provoked in the co-occurred SDBS/SDZ reactor compared with that of sole SDZ. PLS-PM analysis suggested that the bacterial community was the predominant factor that determined the ARGs fates, followed by mobile genetic elements and metabolic pathway. This work demonstrated the interactive effects of surfactants and antibiotics on the ARGs fates in WAS fermentation systems and gave insightful implications on the ecological risks of different exogenous pollutants.

Effect of hydrochar on antibiotic-resistance genes and relevant mechanisms during chicken manure composting

The reduction of enhanced antibiotic resistance genes (ARGs) in compost is important to mitigate the risk of ARG transmission in agricultural production. Hydrochar is used in many applications as a functional carbon material with adsorption and catalytic properties. This study investigated the effects of hydrochar addition on bacterial communities, mobile genetic elements (MGEs), and ARGs in chicken manure composting. The addition of 2%, 5%, and 10% hydrochar (dry weight) reduced the total numbers of target ARGs and MGEs in the compost products by 40.13-55.33% and 23.63-37.23%, respectively. Hydrochar changed the succession of the bacterial population during composting, lowering the abundance of potential pathogens and promoting microbial activity in amino acid and carbohydrate metabolism. A significant possible microbial host for ARGs was found to be Firmicutes. Hydrochar was found to affect the host microorganisms and MGEs directly by altering environmental factors that indirectly impacted the ARG profiles, as shown by partial least squares pathway modeling analysis. In conclusion, the addition of hydrochar to compost is a simple and effective method to promote the removal of ARGs.

The role of pretreatments in handling antibiotic resistance genes in anaerobic sludge digestion - A review

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.

Effect of pH on the mitigation of extracellular/intracellular antibiotic resistance genes and antibiotic resistance pathogenic bacteria during anaerobic fermentation of swine manure

Effects of various initial pH values (i.e., 3, 5, 7, 11) during anaerobic fermentation of swine manure on intracellular and extracellular antibiotic resistance genes (iARGs and eARGs) and ARG-carrying potential microbial hosts were investigated. The abundance of almost all iARGs and eARGs decreased by 0.1-1.7 logs at pH 3 and pH 5. The abundance of only three iARGs and eARGs decreased by 0.1-0.9 logs at pH 7 and pH 11. Under acidic initial fermentation conditions (pH 3 and pH 5), the ARG removal effect was more pronounced. Acidic conditions (pH 3 and pH 5) significantly reduced the diversity and abundance of the microbial community, thereby eliminating many potential ARG hosts and antibiotic-resistant pathogenic bacteria (ARPB). Therefore, the study results contribute to the investigation of the effects of swine manure anaerobic fermentation on the removal and risk of contamination of ARGs and ARPB.

Succession and change of potential pathogens in the co-composting of rural sewage sludge and food waste

Composting is an effective way to prevent and control the spread of pathogenic microorganisms which could put potential risk to humans and environment, from rural solid waste, especially sewage sludge and food waste. In the study, we aim to analyze the changes of pathogenic bacteria during the co-composting of rural sewage sludge and food waste. The results showed that only 27 pathogenic bacteria were detected after composting, compared to 50 pathogenic bacteria in the raw mixed pile. About 74% of pathogen concentrations dropped below 1000 copies/g after composting. Lactobacillus, Bacillus, Paenibacillus and Comamonas were the core pathogenic bacteria in the compost, of which concentrations were all significantly lower than that in the raw mixed pile at the end of composting. The concentration of Lactobacillus decreased to 3.03 × 10³ copies/g compared to 0 d with 1.25 × 10⁹ copies/g by the end of the composting, while that of Bacillus, Paenibacillus and Comamonas decreased to 2.77 × 10⁴ copies/g, 2.13 × 10⁴ copies/g and 3.38 × 10² copies/g, respectively, with 1.26 × 10⁷ copies/g, 4.71 × 10⁶ copies/g, 1.69 × 10⁸ copies/g on 0 d. Redundancy analysis (RDA) indicated that physicochemical factors and substances could affect the changes of pathogenic bacteria during composting, while temperature was the key influencing factor. In addition, certain potential pathogenic bacteria, such as Bacteroides-Bifidobacterium, show statistically strong and significant co-occurrence during composting, which may increase the risk of multiple infections and also influence their distribution. These findings provide a theoretical reference for biosafety prevention and control in the treatment and disposal of rural solid waste.

Dynamics of antibiotic resistance genes and microbial community in shortcut nitrification-denitrification process under antibiotic stresses

In this study, the performance of shortcut nitrification-denitrification (SCND) at different TC and SD stress conditions (0 μg/L, 1-97 days; 100 μg/L, 98-138 days; 500 μg/L, 139-175 days) was investigated. Higher level antibiotic stress (500 μg/L) led to the serious deterioration of nitrogen removal, and denitrification was more sensitive to antibiotic stress than nitrification. The dynamics of antibiotic resistance genes (ARGs) and microbial community were revealed by quantitative real-time PCR and 16S rDNA high-throughput sequencing, respectively. Tet-genes (tetA, tetQ, tetW), sul-genes (sulI, sulII), and mobile genetic element (intI1) in activated sludge increased by 1.2 ~ 2.5 logs with long-term exposure of antibiotic stress, and sulI, tetA, tetQ, and tetW were significantly positively correlated with intI1. Long-term antibiotics stress caused the decrease of most denitrifiers, and five genera were identified as the potential host of ARGs. The key impact factors of SCND drove the dynamics of ARGs and microbial community. Except for sulII gene, DO and FA were significantly positively correlated with ARGs, while FNA, NAR, and NO₂^--N showed opposite effects to ARGs. Overall, maintaining relative lower DO, higher FNA, NAR, and NO₂^--N conditions are not only benefit to the stable operation of SCND, but may also conducive to the control of ARG dissemination. This study provides theoretical basis on the control of ARGs in the SCND process.

Deciphering changes in the abundance of intracellular and extracellular antibiotic resistance genes and mobile genetic elements under anaerobic fermentation: Driven by bacterial community

Antibiotic resistance genes (ARGs) are considered to be a new environmental pollutant and the removal of ARGs from swine manure by anaerobic fermentation was a crucial topic. This research discusses effects of initial pH values (3, 5, 7, 11) on intracellular and extracellular ARGs (iARGs and eARGs) as well as mobile genetic elements (MGEs) during anaerobic fermentation of swine manure had been examined. The initial pH during fermentation was found to be acidic (pH 3 and 5) in results, which was conducive to the removal of six eARGs and seven iARGs. Similarly, intracellular and extracellular MGEs were effectively eliminated with an initial pH of 3 and 5. The abundance of MGEs and four ARGs were enriched with an initial pH of 7 and 11. Acidic conditions can greatly deduce the diversity as well as abundance of the microbial community, ensuing removal of MEGs and ARGs. These findings are critical for risk assessment and management of ARGs.

Effect of lignin on short-chain fatty acids production from anaerobic fermentation of waste activated sludge

Lignin, a biological resource with great potential, can be as high as ∼16% of the total organics in the waste activated sludge (WAS). This work therefore aims to fill the knowledge gap about the effect of lignin on short-chain fatty acids (SCFAs) production from anaerobic fermentation of sludge. Experimental results showed that lignin promoted rather than inhibited SCFAs production. Specifically, the presence of 15% lignin promoted the SCFAs production from 129.1 ± 6.5 to 223.14 ± 7.8 mg COD/g VSS compared with the control, and the proportion of acetic increased by 61.8%, while that of propionic decreased by 44.9%. Mechanism exploration revealed that lignin improved the solubilization of biodegradable substrates due to its hydrophobic characteristics. In addition, lignin enhanced the acidogenesis process, possibly by perfecting the electron transfer chain in the fermentation system, and the quinone structure in lignin may compete electrons with methanogens to inhibit the consumption of SCFAs. Microbiological analysis showed that the abundance of microorganisms related to acidogenesi, especially the acetogenesis, including Proteiniclasticum sp., Acetoanaerobium sp., in the fermenter with lignin increased, which caused the community to shift towards specialized and diverse SCFAs production.

Optimising mixed aerobic and anaerobic composting process parameters for reducing bacterial pathogenicity in compost-derived products

Although composting techniques are continuously optimised and adjusted, the removal of bacterial pathogen based on the quality of composting products needs further to ensure safe of agricultural use. In this study, we combined aerobic composting and anaerobic process to determine the optimal combination (turning frequency of once a day, the proportion of swine manure to corn straw (3:1), and mixed 6-day anaerobic process) that benefits the reduction of bacterial pathogens, among which the maximum removal efficiency of up to 92.96% was observed for Clostridium_sensu_stricto_1 reached, thereby improving the quality of the compost products. The variation partition analysis and redundancy analysis indicated that physicochemical factors such as temperature, TOC, and pH significantly affected the removal of bacterial pathogens. Therefore, the additive effects of physicochemical factors on bacterial pathogen removal requires further process optimisation. These findings offer powerful technological support for improving agricultural waste recycling and enhancing the safety of fertiliser application.

Mechanism of a double-channel nitrogen-doped lignin-based carbon on the highly selective removal of tetracycline from water

A high-performance nitrogen-doped lignin-based carbon material (ILAC-N) was synthesized using industrial lignin and urea by hydrothermal and activation, as an absorbent of tetracycline hydrochloride (TC). The results showed that the ILAC-N comprises a double-channeled structure with micro and mesopores. It exhibits an excellent adsorption capacity of TC across a wide pH range (pH 2-11), with the highest adsorption capacity of 1396 mg g^-1 at 323 K. Tests in actual wastewater showed that the TC removal rate by ILAC-N exceeded 97.4%. Moreover, it maintained a removal rate of 84% after 10 regeneration cycles, revealing its high reusability. Mechanisms suggested that pore filling and π-π interaction played a critical role in this process. In conclusion, ILAC-N can be broadly applied to livestock manure and pharmaceutical wastewater treatment, owing to its high adsorption capacity, good adsorption properties across a wide pH range, excellent reusability. Furthermore, this research opens a new path for lignin utilization.

Genes associated with antibiotic tolerance and synthesis of antimicrobial compounds in a mangrove with contrasting salinities

Salinity and wastewater pollution in mangrove ecosystems can affect microorganisms and the abundance of genes involved in response to these stressors. This research aimed to identify genes associated with resistance and biosynthesis of antimicrobial compounds in mangrove soils subjected to contrasting salinities and wastewater pollution. Samples of rhizospheric soil were taken from a mangrove at the mouth of the Ranchería River in La Guajira, Colombia. A functional analysis was performed using Illumina HiSeq 2500 sequencing data obtained from total DNA extracted. Increased salt concentration influenced metabolic pathways and differential abundance of genes associated with the synthesis of antimicrobial compounds (e.g., rfbB/rffG, INO1/ISYNA1, rfbA/rffH, sat/met3, asd). Also, among 33 genes involved in intrinsic antibiotic resistance, 16 were significantly influenced by salinity (e.g., cusR/copR/silR, vgb, tolC). We concluded that salt stress tolerance and adaptive mechanisms could favor the biosynthesis of antimicrobial compounds in mangroves contaminated by sewage.

Mechanisms of emerging pollutant Dechlorane Plus on the production of short-chain fatty acids from sludge anaerobic fermentation

The effect of emerging pollutant Dechlorane Plus (DPs), an organochlorine aliphatic flame retardant, on waste-activated sludge anaerobic fermentation was investigated, and the related mechanisms were revealed for the first time. The results of this experiment suggested that the presence of DPs had a significant inhibitory effect on sludge anaerobic fermentation to generate the intermediate valuable product short-chain fatty acids (SCFA), and when the DP content was 3034.1±101.7 mg/kg total suspended solids (TSS), the maximal output of SCFA was only 215.04 mg/g, which was 0.47 times of that in the blank. The underlying mechanism investigation indicated DPs promoted the disintegration of sludge, but inhibited the process of hydrolysis and acidification. DPs inhibited the release of soluble bound extracellular polymers (SB-EPS) in sludge. The analysis of microbial community characteristics indicated that DPs reduced the level of Firmicutes and Actinobacteriathe, which were the key acid producing bacteria. At the genus level, DPs reduced the relative abundance of Proteiniclasticum and Mycobacteriumwas.

Improved reduction of antibiotic resistance genes and mobile genetic elements from biowastes in dry anaerobic co-digestion

This study investigated the performance of anaerobic co-digestion (AcoD) of pig manure and food waste on the reduction of antibiotic resistomes under wet and dry AcoD conditions. High-throughput quantitative PCR technology was utilized for a comprehensive assessment of the performances of the two processes. The results show that dry AcoD with a total solids (TS) content of 20% effectively reduced total antibiotic resistance genes (ARGs) by 1.24 log copies/g wet sample, while only 0.54 log copies/g wet sample was reduced in wet AcoD with a TS content of 5%. Dry AcoD was more efficient in reduction of aminoglycosides, multidrug and sulfonamide resistance genes compared with the reduction of other classes of ARGs. Dry AcoD caused a significant reduction of ARGs with resistance mechanisms of efflux pump and antibiotic deactivation. In contrast, there was no obvious difference in reductions of ARGs with different resistance mechanisms in wet AcoD. Network analysis showed that ARGs were significantly correlated with mobile genetic elements (MGEs) (Spearman's r > 0.8, P < 0.05), as well as microbial communities. Enrichment of ARGs and MGEs was found at the early period of AcoD processes, indicating some ARGs and MGEs increased during the hydrolysis and acidogenesis stages. But after a long retention time, their abundances were effectively reduced by dry AcoD in the subsequent stages.

Tracking high-risk β-lactamase gene (bla gene) transfers in two Chinese intensive dairy farms

Extended-spectrum β-lactam antibiotics are critically important antibiotics for humans, but their use in food-animals poses a potential threat for public health. This paper addressed the occurrence of high-risk β-lactamase genes (bla genes) in intensive dairy farms, and assessed the effects of different waste treatment technologies at dairies on the propagation and dissemination of bla genes. Results showed that ESBL genes (bla_TEM-1, bla_OXA-1), ampC β-lactamase genes (bla_ampC) and carbapenemase genes (bla_GES-1, bla_NDM) were prevalent in dairy cow waste, and even prevailed through each processing stage of solid manure and dairy wastewater. Significant levels of bla genes were present in the final lagoon (from 10⁴ to 10⁶ copies/mL, representing from 10% to 151%, of raw influent levels), raising the possibility of dissemination to the receiving environment. This concern was validated by the investigation on farmland that had long-term undergone wastewater irrigation, where causing an increase in bla gene levels in soils (approximately 1-3 orders of magnitude). More troublesomely, considerable levels of certain bla genes were still observed in the bedding material (up to 10⁵ and 10⁷ copies/g), which would directly threaten the dairy cow health. Otherwise, correlation analysis showed that both bacterial community and environmental factors played important roles in the bla genes abundances in dairy farms. This study demonstrated the prevalence of high-risk bla genes in dairy farms, and also underscored that dairy waste was a non-ignored great source of multidrug resistance for their surroundings.

Distinct effects of hypochlorite types on the reduction of antibiotic resistance genes during waste activated sludge fermentation: Insights of bacterial community, cellular activity, and genetic expression

The effectiveness of hypochlorites (NaClO and Ca(ClO)₂) on the reduction of antibiotic resistance genes (ARGs) during waste activated sludge (WAS) fermentation was determined by the quantitative PCR. NaClO and Ca(ClO)₂ exhibited distinct effects on ARGs fates. Ca(ClO)₂ was effective in removing all investigated ARGs, and the efficiency was highly dose-dependent. Unexpectedly, the NaClO treatment attenuated ARGs with lower efficiency and even caused the propagation of certain ARGs (i.e., aadA1 and tetQ) at higher doses. The extracellular polymeric substances dissolution and membrane integrity suggested that unstable NaClO had acute effects on bacteria initially, while it was ineffective to further attenuate ARGs released from hosts due to the rapid consumption of oxidative ClO^-. Without lasting and strong oxidative stress, the microbial activities of tolerant ARGs hosts will partially recover and then contribute to the ARGs dissemination across genera. In contrast, solid-state Ca(ClO)₂ was slowly released and exhibited prolonged effects on bacteria by disrupting cell membranes and removing the susceptible ARGs released from hosts. Furthermore, bacterial taxa-ARG network analysis indicated that Ca(ClO)₂ reduced the abundance of potential hosts, and the metabolic pathway and gene expression related to ARGs propagation were significantly downregulated by Ca(ClO)₂, which contributed to efficient ARGs attenuation.

Improving the treatment of waste activated sludge using calcium peroxide

The treatment and disposal of waste activated sludge (WAS) has become one of the major challenges for the wastewater treatment plants (WWTPs) due to large output, high treatment costs and enriched substantial emerging contaminants (ECs). Therefore, reducing sludge volume, recovering energy and resource from WAS, and removing ECs and decreasing environmental risk have gained increasing attentions. Calcium peroxide (CaO₂), a versatile and safe peroxide, has been widely applied in terms of WAS treatment including sludge dewatering, anaerobic sludge digestion and anaerobic sludge fermentation due to its specific properties such as generating free radicals and alkali, etc., providing supports for sludge reduction, recycling, and risk mitigation. This review outlines comprehensively the recent progresses and breakthroughs of CaO₂ in the fields of sludge treatment. In particular, the relevant mechanisms of CaO₂ enhancing WAS dewaterability, methane production from anaerobic digestion, short-chain fatty acids (SCFA) and hydrogen production from anaerobic fermentation, and the removal of ECs in WAS and role of experiment parameters are systematically elucidated and discussed, respectively. Finally, the knowledge gaps and opportunities in CaO₂-based sludge treatment technologies that need to be focused in the future are prospected. The review presented can supply a theoretical basis and technical reference for the application of CaO₂ for improving the treatment of WAS.

Critical insight into the fate of antibiotic resistance genes during biological treatment of typical biowastes

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.

Alkaline-thermal pretreatment of spectinomycin mycelial residues: Insights on anaerobic biodegradability and the fate of antibiotic resistance genes

Alkaline-thermal (AT) pretreatment is an economical and efficient pretreatment method to improve anaerobic biodegradability of biowaste. This study investigated the effect of AT pretreatment of spectinomycin mycelial residues (SMRs) for promoting anaerobic biodegradability along with the reduction of antibiotic resistance genes (ARGs), and thus obtained the optimal conditions of AT pretreatment. Biomethane potential (BMP) test was conducted to evaluate the anaerobic biodegradability of untreated and pretreated SMRs, and the fate of ARGs was tracked by quantitative polymerase chain reaction. Results showed that the modified Gompertz model fitted the results of BMP tests satisfactorily. Furthermore, AT pretreatment promoted BMP (B₀) and reduced lag phase (λ) effectively. These were attributed to the solubilization of SMRs. The analyses of the changes in dissolved organic matter indicated that AT pretreatment could facilitate the solubilization of both biodegradable (e.g. protein) and recalcitrant matter (e.g. humic-like, analyzing by EEMs-PARAFAC), which had a significant corresponding positive (Person correlation, p < 0.01) and negative (Partial correlation, p < 0.01) influences on anaerobic biodegradability. However, the positive effects surpassed the negative effects, promoting the overall anaerobic biodegradability of SMRs. In addition, a considerable reduction of ARGs (by 0.62-1.36 log units) was observed at pH ≥ 12, attributed to the hydrolysis of phosphodiester bond of DNA in strong alkaline solution. Considering both anaerobic biodegradability and ARGs, the optimal AT condition was concluded as pH 12, temperature 90 °C and time 120 min.

Treatment Processes for Microbial Resistance Mitigation: The Technological Contribution to Tackle the Problem of Antibiotic Resistance

Advances generated in medicine, science, and technology have contributed to a better quality of life in recent years; however, antimicrobial resistance has also benefited from these advances, creating various environmental and health problems. Several determinants may explain the problem of antimicrobial resistance, such as wastewater treatment plants that represent a powerful agent for the promotion of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG), and are an important factor in mitigating the problem. This article focuses on reviewing current technologies for ARB and ARG removal treatments, which include disinfection, constructed wetlands, advanced oxidation processes (AOP), anaerobic, aerobic, or combined treatments, and nanomaterial-based treatments. Some of these technologies are highly intensive, such as AOP; however, other technologies require long treatment times or high doses of oxidizing agents. From this review, it can be concluded that treatment technologies must be significantly enhanced before the environmental and heath problems associated with antimicrobial resistance can be effectively solved. In either case, it is necessary to achieve total removal of bacteria and genes to avoid the possibility of regrowth given by the favorable environmental conditions at treatment plant facilities.

Variation and distribution of antibiotic resistance genes and their potential hosts in microbial electrolysis cells treating sewage sludge

Microbial electrolysis cells (MECs) system is an emerging pollution control technology. However, information on the variation of antibiotic resistance genes (ARGs) in MECs treating sewage sludge is still very limited. In this study, the fate of ARGs and their correlation with microbes in MECs under different applied voltages (0-1.5 V) were studied. Most target ARGs were effectively removed, but tetB, tetM and tetQ were enriched up to 2.05 log units in suspended sludge. Most ARGs were mainly distributed on electrodes, except tetQ and tetM enriched in suspended sludge. The selective pressure of residual antibiotics in the sewage sludge was negligible. Horizontal gene transfer was validated for the spread of sul1, sul2, tetA and tetC in MECs. Network analysis revealed that the potential hosts of ARGs mainly belonged to Bacteroidetes, Firmicutes and Proteobacteria. Some genera related to electron transfer were newly found to be the potential ARGs hosts in MECs.

Manure pretreatments with black soldier fly Hermetia illucens L. (Diptera: Stratiomyidae): A study to reduce pathogen content

This study aim was to investigate the influence of black soldier fly larvae (BSFL) Hermetia illucens L. (Diptera: Stratiomyidae) on pathogenic bacteria (PB) survival in the chicken manure (CM), pig manure (PM), cow manure (COM) and sewage sludge (SS) compost. Three kinds of manure [chicken (T2), pig (T4) and cow (T6)] and SS (T8) were inoculated with BSFL (1.2:7 ratio on fresh weight basis) and without BSFL (T1, T3, T5 and T7) was used as control and experiment lasted for 9 days. The results indicated that BSFL amendment 90-93% of PB abundances (RAs) was significantly mitigate in CM and COM (T2 and T6), and 86-88% in PM and SS compost. However, relatively greater abundance of PB was recorded in the T4 and T8 treatments. Most of the PB belong to Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes phylum and their community composition varied from phylum to species levels among the all treatments. The PB composition was significantly altered by BSFL amendment and also important role play to enhance in compost quality. Interestingly, Bacillus and Clostridium were significantly very less abundant present in BSFL applied treatments, but considerably higher population of these bacterial genus and its associated species were identifies from control or without BSFL applied treatments. Overall, without BSFL blended-all three kinds of manure-composts have comparatively greater PB abundance than with BSFL applied treatments, as the PB species Listeria_monocytogenes_FSL_R2-503, Staphylococcus_aureus_M0406, Bacillus_anthracis, Listeria_ivanovii, Staphylococcus_aureus_C0673, Salmonella Bacillus_cereus_VD115, Mycobacterium_tuberculosis_FJ05194 and Pseudomonas_aeruginosa has relatively greater RAs, followed by Bartonella_bacilliformis_Ver075; Bordetella_pertussis_2356847; Brucella_melitensis_ADMAS-G1; Klebsiella_pneumoniae_LCT-KP182 and Corynebacterium_jeikeium_K411 respectively. Thus, chicken manure composting with BSFL addition is efficient technology for the organic waste recycling and conversion of sanitized matured compost with significantly less abundance of pathogenic bacteria.

Assessing the effects of tylosin fermentation dregs as soil amendment on macrolide antibiotic resistance genes and microbial communities: Incubation study

Tylosin fermentation dregs (TFDs) are biosolid waste of antibiotics tylosin production process which contain nutritious components and may be recycled as soil amendments. However, the specific ecological safety of TFDs from the perspective of bacterial resistance in soil microenvironment is not fully explored. In the present study, a series of replicated lab-scale work were performed using the simulated fertilization to gain insight into the potential environmental effects and risks of macrolide antibiotic resistance genes (ARGs) and the soil microbial communities composition via quantitative PCR and 16S rRNA sequencing following the TFDs land application as the soil amendments. The results showed that bio-processes might play an important role in the decomposition of tylosin which degraded above 90% after 20 days in soil. The application of TFDs might induce the development of antibiotic-resistant bacteria, change soil environment and reduce the microbial diversity. Though the abundances of macrolide ARGs exhibited a decreasing trend following the tylosin degradation, other components in TFDs may have a lasting impact on both macrolide ARGs abundance and soil bacterial communities. Thus, this study pointed out the fate of TFDs on soil ecological environment when directly applying into soil, and provide valuable scientific basis for TFDs management.

Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities

In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56-1.58 and 0.34-1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.

The role of a newly isolated strain Corynebacterium pollutisoli SPH6 in waste activated sludge alkaline fermentation

Alkaline fermentation has been considered as one of the efficient methods for waste activated sludge (WAS) treatment, but usually limited by microbial fermentation activities under extreme pH condition. One newly isolated alkali-tolerant strain Corynebacterium pollutisoli SPH6 was used to assess its potential role and effect on WAS alkaline fermentation process. Results from response surface method showed that the optimal organic nitrogen degradation rate by SPH6 was obtained under temperature of 35 °C, initial pH of 10, shaking speed of 80 rpm, inoculation ratio of 6.5%. Batch-scale experiments demonstrated that, compared with the control group, the inoculation of SPH6 finally achieved higher productions with 13.4% of carbohydrates, 27.1% of protein and 25.4% of total volatile fatty acids (VFAs), and more predominant functional bacteria characterized by high-throughput sequencing, such as genera Acinetobacter in phylum Proteobacteria, Tissierella and Acetoanaerobium in phylum Firmicutes. The strain SPH6 might play a vital role in maintaining and facilitating the growth and diversity of functional bacteria in WAS alkaline fermentation process. It has implied promising practical application of the present strain in enhancing WAS reduction and utilization.

Microbial community in in-situ waste sludge anaerobic digestion with alkalization for enhancement of nutrient recovery and energy generation

Microbial community in in-situ waste sludge anaerobic digestion with alkalization for enhancement of nutrient recovery and energy generation was studied. Firmicutes, Proteobacteria and Bacteroidetes phylum became the majority in the microbial community, especially Firmicutes showed the predominate role in the community due to its thick cell wall structure, potential ability hydrolysis and hydrogenogenic acidogenesis. Anaerobic digestion with alkalization caused the obvious microbial diversity decrease, and over 50% of minority bacteria grew up in quantity from original sludge. Phylum of Firmicutes developed by themselves having few interactions with other bacteria, partly contributing to its rapid growth in anaerobic digestion with alkalization. The decrease of hydrocarbon degradation, and the increase of both fermentation and reductive acetogenesis in microbial community, indicating the promotion of short chain fatty acids production, especially acetic acid which is the key intermediate products for nutrient recovery and energy generation.

The discrepant mobility of antibiotic resistant genes: Evidence from their spatial distribution in sewage sludge flocs

The present study stratified excess activated sludge from six municipal wastewater treatment plants into four extracellular fractions including supernatant, slime, slightly-bond extracellular polymeric substances (LB-EPS) and tightly-bond EPS (TB-EPS) and one intracellular fraction (pellet) according to their different degrees of tight binding to sludge microbial aggregates and determined the abundance of seven antibiotic resistance genes (ARGs) (sul-I, sul-II, tet-C, tet-X, blaTEM, mefA and cat) and one mobile genetic elements (MGEs) (IntI-1) in each fraction. Extracellular ARGs were found to make up 0.1% - 74.2% of total ARGs, while the ratio of extracellular DNA to total DNA was only 1.2% - 4.2%, implying that EPS was a major ARG reservoir in sewage sludge. The genes of sul-I, tet-C and mefA have the highest mobility owing to a large proportion ranging from 0.5% to 32.7% in the fractions of LB-EPS, slime and supernatant, which indicates an increased risk of mediating the transfer of ARGs to environment. Comparatively, the proportion of blaTEM in the TB-EPS of sludge accounted for 0.3%-34.9% and caused limited-mobility. Sul-II, tet-X and cat and IntI-1, made up approximately 82.6% - 99.6% proportion in the cells, and were thus less mobile. This study proposes that ARGs and MGEs can have different mobilities. Those located in the outermost layers of sludge have a higher mobility potential of propagation into the natural environment during wastewater treatment and sludge utilization, leading to an increased risk of transferability.

Effects of nanoscale zero-valent iron on the performance and the fate of antibiotic resistance genes during thermophilic and mesophilic anaerobic digestion of food waste

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.

Fate of sulfonamide resistance genes during sludge anaerobic fermentation: Roles of sludge components and fermentation pHs

This study assessed potential effects of two neglected factors (sludge components and pH values) on the fate of sulfonamide (sul) resistance genes during sludge anaerobic fermentation. It was found that sludge with different contents of protein, carbohydrate and humic acid caused no significant changes in the abundances of sul genes. Nevertheless, sul genes were sensitive to pHs (4-10), and the maximum attenuations (0.8-1.1 log unit) were obtained at pH 10. Mechanism exploration indicated that pHs drove the community evolution of sulfonamide resistant bacteria (SRB), most of which were affiliated to the pH-enriched phyla but not the pH-enriched dominant genera. In addition, the relative abundances of SRB were decreased under both acidic and alkaline conditions. Furthermore, the abundances of intI 1 as well as the sul-carrying abilities of plasmid and extracellular DNA were all reduced at test pHs, indicating that the potential of horizontal gene transfer among bacteria was restricted.

Degradation of antibiotics and antibiotic resistance genes in erythromycin fermentation residues using radiation coupled with peroxymonosulfate oxidation

Ionizing radiation coupled with peroxymonosulfate (PMS) oxidation was developed to degrade antibiotics and antibiotic resistance genes (ARGs) from the erythromycin fermentation (EryF) residual wastes. The experimental results showed that the ERY content and ARGs abundance decreased with increase of the absorbed dose and PMS dosage and gamma irradiation was more effective to abate ARGs from the EryF wastes. The removal efficiency of ERY reached 49-55% and more than 96-99% of ARGs (1.32-2.55 log) was eliminated with the absorbed dose of 25-50 kGy and PMS dosage of 50-100 mM. Illumina pyrosequencing revealed that 3 bacterial phyla, Proteobacteria, Firmicutes and Fusobacteria were highly enriched and the ARGs-linked hosts were affiliated to the genera Aeromonas, Enterobacteriaceae and Enterobacter in the phylum Proteobacteria. The abundance of the ARGs-linked bacteria decreased by gamma/PMS treatment. Ionizing radiation/PMS treatment with the doses of 25 kGy and 50 mM PMS is proposed for potential practical application.

More than sulfidation: Roles of biogenic sulfide in attenuating the impacts of CuO nanoparticle on antibiotic resistance genes during sludge anaerobic digestion

Biogenic sulfide (BS) in anaerobic digesters was previously suggested to mitigate the potential impacts of metallic nanoparticles (M-NPs) on antibiotic resistance genes (ARGs) propagation by sulfidation of the M-NPs. In this study, a new role of BS in regulating ARGs responses to M-NPs is reported. It was observed that CuO NPs at environmentally relevant level had no significant effects on the spread of ARGs. However, higher dosage (50 mg/gTSS) contributed to the propagation of ARGs, whose abundances would be effectively reduced by 74-115% if BS production was stimulated. Instead, introduction of EDTA, a metal ion chelator, resulted in much lower attenuation efficiencies (12-40%), indicating that restriction of the bioavailability of CuO NPs might not be the only reason for the buffering of ARG responses in the presence of BS. Further investigation showed that the presence of BS together with activation of key enzymes (O-acetyl serine sulfhydrylase and γ-glutamylcysteine synthetase) supplied and favored the biosynthesis and transformation of cysteine, which mitigated the oxidative stress induced by CuO NPs. Moreover, the amounts of cysteine and its metabolite glutathione in sludge were associated with the abundances of ARGs negatively, implying that in situ generated cysteine was the important ARGs regulator. Exploration of possible mechanisms revealed that the biosynthesized cysteine might limit gene transfer potential via mobile genetic elements, as cysteine restricted the abundances of intI 1, Tn916/1545 and ISCR 1. In addition, the cysteine remarkably alleviated the copper stress and copper resistance, which in turn blocked possible co-selection between copper and antibiotic resistance. This work provides new insight into attenuation of the bio-effects of NPs in digesters.

Low-level free nitrous acid efficiently inhibits the conjugative transfer of antibiotic resistance by altering intracellular ions and disabling transfer apparatus

Recently, the dissemination of antibiotic resistance genes (ARGs) via plasmid-mediated conjugation has been reported to be facilitated by a series of contaminants. This has highlighted potential challenges to the effective control of this principal mode of horizontal transfer. In the present study, we found that low levels (<0.02 mgN/L) of free nitrous acid (FNA) remarkably inhibited (over 90%) the conjugative transfer of plasmid RP4, a model broad-host-range plasmid, between Escherichia coli. The antimicrobial role of FNA at the applied dosages was firstly ruled out, since no dramatic reductions in viabilities of donor or recipient were observed. Instead, FNA appeared to reduce the available intracellular free Mg²⁺, which was confirmed to be triggered by the liberation of intracellular Fe²⁺. These alterations in intracellular Mg²⁺ and Fe²⁺ concentrations were found to significantly limit the available energy for conjugative transfer through suppression of glycolysis by decreasing the activities of glycogen phosphorylase and glyceraldehyde-3-phosphate dehydrogenase and also by diverting the glycolytic flux into the pentose phosphate pathway via activation of glucose-6-phosphate dehydrogenase towards the generation of NADPH rather than ATP. Moreover, RP4-encoding genes responsible for DNA transfer and replication (traI, traJ and trfAp), coupling (traG) and mating pair formation (traF and trbBp) were all significantly down-regulated after FNA treatment, indicating that the transfer apparatus required for plasmid processing and delivery was deactivated. By validating the inhibitory effects of FNA on conjugation in real wastewater, this study highlights a promising method for controlling the dissemination of ARGs in systems such as wastewater treatment plants.

Importance of sludge conditioning in attenuating antibiotic resistance: Removal of antibiotic resistance genes by bioleaching and chemical conditioning with Fe[III]/CaO

Conditioning can drastically improve the dewaterability of sewage sludge and thus it is widely practiced in most wastewater treatment plants (WWTPs). In WWTPs, various antibiotic resistance genes (ARGs) present in sewage are concentrated in the sewage sludge, but the effect of sludge conditioning on ARGs in sewage sludge remains unclear. Here, we evaluated and compared the effectiveness of four sludge conditioning methods (namely chemical conditioning with polyacrylamide (PAM), chemical conditioning with Fe[III]/CaO, bioleaching conditioning, and chemical acidification conditioning) and an aerobic incubation control in removing 46 target ARGs and intI1 from a municipal sewage sludge. The damage of sludge microbial cells and the change in the sludge bacterial community during the various sludge conditioning treatments were also characterized. The results suggested that the chemical conditioning with PAM and aerobic incubation treatment did not remove ARGs and intI1 from the sewage sludge. The chemical acidification reduced the absolute abundances of most ARGs and intI1, but increased their relative abundances. However, the chemical conditioning with Fe[III]/CaO and bioleaching conditioning reduced both the absolute and relative abundances of most ARGs and removed a majority of extracellular ARGs in the sludge. During sludge conditioning treatments, the sludge microbial cells were severely damaged to decrease the total bacterial biomass in sludge, and accordingly the bacterial hosts carrying ARGs and intI were effectively damaged to reduce the absolute abundances of most ARGs and intI1. In addition, the sludge bacterial community in conditioned sludge determined the relative abundances of residual ARGs. Our findings suggest that sludge conditioning can be an important sludge treatment process in attenuating antibiotic resistance in sewage sludge, and bioleaching and chemical conditioning with Fe[III]/CaO can be employed as effective conditioning ways to reduce ARGs in sewage sludge, potentially limiting their release to the environment.

An assessment of the persistence of pathogenic bacteria removal in chicken manure compost employing clay as additive via meta-genomic analysis

The aim was to evaluate pathogenic bacteria (PB) survival during the composting of chicken manure (CM) amended with five different dosages of clay compared to CM without clay-applied treatment. The results showed that 85-87% of PB relative abundances (RAs) were significantly reduced in lower dosages of applied clay (T2 and T3). However, the maximum survival of PB was noticed in the T6 and T5 treatments, but most of the PB belong to Firmicutes, Actinobacteria and Proteobacteria phylum and their derivative bacterial species. The changes in PB during the composting were not only strongly influenced by clay amendment but also significantly associated with the succession of bacterial species in compost. Bacillus, Clostridium, Mycobacterium and Klebsiella were the dominant spore-forming bacteria identified in higher dosages of clay (i.e., T4, T5 and T6) treatments, but very low abundance of these bacterial genus and its species were recovered from lower dosages of clay (T2 and T3)-applied treatments. Overall, without clay, amended-CM-derived compost contained a relatively higher PB abundance than other treatments, as the anaerobic bacterial species Clostridium_difficile_AA1, Vibrio_cholerae, and Acinetobacter_calcoaceticus had relatively greater RAs, followed by Klebsiella_oxytoca_10-5248, Paenibacillus_Bacillus_cereus and Bartonella_quintana_RM-11. Thus, CM composting with 4% clay amendment is considered a useful method for the efficient recycling of CM, as this process produced sanitized compost with less survival of PB.

Degradation of antibiotics and antibiotic resistance genes in fermentation residues by ionizing radiation: A new insight into a sustainable management of antibiotic fermentative residuals

Antibiotic fermentative residues are categorized into hazardous wastes in China due to the existence of antibiotic resistance genes (ARGs) and residual antibiotics How to treat and manage these wastes is a new challenge. This paper investigated the treatment of erythromycin thiocyanate fermentation (EryTcF) residues using ionizing radiation technology for removing ARGs and antibiotics from the fermentation residues. The results showed that as exposed the EryTcF residues to gamma radiation, the abundance of four macrolide resistance genes (ereA, ermB, mefA and mpfB) decreased 1.0-1.3 log with 90-95% removal, and around 56% of erythromycin was removed at absorbed dose of 30&#x202F;kGy and room temperature (19-22&#x202F;°C). Direct action of γ-ray radiation contributed to 42-53% of ARGs removal and indirect action (radicals' reaction) was mainly responsible for erythromycin removal (84%). The positive correlation between total ARGs and Shannon index was observed. The potential ARGs-linked hosts were assigned to genera Aeromonas and Enterobacteriaceae and their abundance decreased by 36-43% at 30&#x202F;kGy. Radiation has not obvious influence on the nutrient components of residues, such as protein content, suggesting that the radiation treated fermentative residues can be used as fertilizer, which is favorable for the development of recycling economy in antibiotic pharmaceutical factory. The results could provide a new insight into a sustainable management of antibiotic fermentative residuals.

Effects of individual and combined zinc oxide nanoparticle, norfloxacin, and sulfamethazine contamination on sludge anaerobic digestion

This work investigated the individual and combined effects of zinc oxide, norfloxacin, and sulfamethazine on sludge anaerobic digestion-associated methane production, protein and carbohydrate metabolism, and microbial diversity. Norfloxacin and sulfamethazine (500 mg/kg) did not inhibit methane production, but inhibited its production rate. Zinc oxide nanoparticles with antibiotics inhibited hydrolysis, fermentation, and methanogenesis over varying digestion periods. Complex pollution had a greater impact on methane production than zinc oxide alone, with acute, synergistic toxicity to methanogenesis over short periods. Complex pollution also had varying effects on bacterial and archaeal communities during digestion. These results aid understanding of the toxicity of emerging contaminants in sludge digestion, with the potential to improve pollution removal and reduce associated risks.

Comparative network analysis revealing the mechanisms of antibiotic resistance genes removal by leachate recirculation under different hydraulic loadings

The wide dissemination of antibiotic resistance is a pervasive global health threat, and landfill leachate has been an important hotspot of antibiotic resistance genes (ARGs). This study aimed to investigate the removal performance and mechanism of ARGs from leachate under different hydraulic loadings. ARGs removal efficiencies were dependent on hydraulic loadings and ARGs types other than operating time, and reactors operated with hydraulic loadings of 25 and 50 L·m^-3·d^-1 exhibited greater removal potential than 100 L·m^-3·d^-1. ARGs removal patterns varied from different subtypes, for genes sul2, tetQ, aadA1 and bla_CTX-M were eliminated from both leachate and refuse, and tetM, ermB, mefA, and strB were removed from leachate but enriched in refuse. Under different hydraulic loadings, bacterial communities shift shaped ARGs fates in leachate, but refuse had more stable antibiotic resistome and community structure. The topology comparison analysis of co-occurrence network suggested a closer hosting relationship between ARGs and genera in refuse than leachate. Furthermore, taxonomic category of host bacteria other than diversity of host genera determined the ARGs removal, and the ARGs harbored in phyla Cyanobacteria, Tenericutes and Acidobacteria were more likely to be removed. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes under different operating conditions.

Microbial community evolution and fate of antibiotic resistance genes along six different full-scale municipal wastewater treatment processes

The evolution of microbial community and the fate of ARGs along different full-scale wastewater treatment processes (i.e., Anaerobic-Anoxic-Oxic, Oxidation Ditch, and Cyclic Activated Sludge System) were investigated in this study. We found that the sludges of bioreactors treating similar influent showed the similar microbial communities, independent of the treatment technologies. The horizontal gene transfer (HGT) mainly occurred in aeration tank rather that anaerobic/anoxic tank. More co-occurrence of potential pathogens and ARGs was found in wastewater than in sludge. Microbial biomass was the key driver for the fate of ARGs in wastewater, while mobile genetic elements (MGEs) was the key factor for the fate of ARGs in sludge. Combination of wastewater characteristics, microbial diversity, microbial biomass, and MGEs contributed to the variation of ARGs. Finally, it was found that enhanced nutrients removal process and tertiary treatment would benefit ARGs removal.

Fermentation liquor of CaO2 treated chemically enhanced primary sedimentation (CEPS) sludge for bioplastic biosynthesis

Chemically enhanced primary sedimentation (CEPS) technology has been widely applied in Hong Kong, exhibiting excellent performance in contaminants removal from sewage. The generated CEPS sludge contains abundance of organics which could be recovered as volatile fatty acids (VFAs) by fermentation for further utilization. In this work, the effect of calcium peroxide (CaO₂) on the fermentation of FeCl₃ based CEPS sludge was investigated. The feasibility of utilizing the fermentation liquor as substrate for polyhydroxyalkanoates (PHAs) biosynthesis was also evaluated. Results demonstrated that CaO₂ addition facilitated the disintegration of CEPS sludge and enhanced VFAs production. The maximum VFAs yield of 455.8 mg COD/g VSS was obtained with the dosage of 0.1 g CaO₂/g SS, improving by 44.7% compared with the control sludge. Acetic and propionic acid were the predominant components of the VFAs. Microbial analysis indicated that CaO₂ induced microbial reduction of Fe(III), accelerating the initial disintegration of FeCl₃ based CEPS sludge. Microbial communities with hydrolysis and acidogenesis functions were enriched effectively. CaO₂ treatment had no significant influence on the release of ammonia nitrogen (NH₄⁺-N), while reduced the concentration of orthophosphate (PO₄^3--P) and ferrous (Fe²⁺) in fermentation liquor, that was beneficial to the further utilization as substrate for PHAs biosynthesis. The VFA-rich fermentation liquor was proved to be a suitable substrate for PHAs biosynthesis. After cultivation, the PHAs content in activated sludge reached 22.3%, which was comparable to those obtained using waste materials as carbon source. This integrated technology could be a superior alternative of realizing sludge disposal and bioplastic production simultaneously.

Factors influencing the fate of antibiotic resistance genes during thermochemical pretreatment and anaerobic digestion of pharmaceutical waste sludge

The prevalence of antibiotic resistance genes (ARGs) in waste sludge, especially for the pharmaceutical waste sludge, presents great potential risks to human health. Although ARGs and factors affecting their spreading are of major importance for human health, the factors influencing the fate of ARGs during sludge treatment, especially for pharmaceutical sludge treatment are not yet well understood. In order to be able to minimize ARGs spreading, it is important to find what is influencing their spreading. Therefore, certain factors, such as the sludge characteristics, bacterial diversity and community composition, and mobile genetic elements (MGEs) during the advanced AD of pharmaceutical sludge with different pretreatments were studied, and their affinity with ARGs was elucidated by Spearman correlation analysis. Furthermore, multiple linear regression was introduced to evaluate the importance of the various factors. Results showed that 59.7%-88.3% of the variations in individual ARGs and total ARGs can be explained by the corresponding factors. Bacterial diversity rather than specific bacterial community composition affected the fate of ARGs, whereas alkalinity was the most important factor on ARGs among all sludge characteristics investigated in this study. Besides, 66.4% of variation of total ARGs was driven by the changes of MGEs. Multiple linear regression models also reveal the collective effect of these factors on ARGs, and the contributions of each factor impact on ARGs. This study provides more comprehension about the factors impact on the fate of ARGs during pharmaceutical sludge treatment, and offers an approach to evaluate the importance of each factor, which method could be introduced for evaluation of factors influencing ARGs during other types of sludge or wastewater treatment.

Influence of zeolite and superphosphate as additives on antibiotic resistance genes and bacterial communities during factory-scale chicken manure composting

Factory-scale chicken manure composting added with zeolite (F), superphosphate (G), or zeolite and ferrous sulfate (FL) simultaneously, were evaluate for their effects on the behaviors of antibiotic resistance genes (ARGs) and bacterial communities. After composting, ARGs in manure decreased by 67.3% in the control, whereas the reductions were 86.5%, 68.6% and 72.2% in F, G and FL, respectively. ARGs encoding ribosomal protection proteins (tetO, tetB(P), and tetM) were reduced to a greater extent than tetG, tetL, sul1 and sul2. Bacteria pathogens were also effectively removed by composting. Network analysis showed that Firmicutes were the important potential host bacteria for ARGs. The bacterial communities and environmental factors, as well as the intI gene, contributed significantly to the variation of ARGs. The ARGs and integrons were reduced more when zeolite was added than when superphosphate was added; thus, it may be useful for reducing the risks of ARGs in chicken manure.

Biodegradation of the sulfonamide antibiotic sulfamethoxazole by sulfamethoxazole acclimatized cultures in microbial fuel cells

Microbial fuel cells (MFCs) are known for their ability to enhance the removal rate of toxins while generating power. This research presents a performance assessment of MFCs for power generation and sulfamethoxazole (SMX) degradation using SMX acclimatized cultures. Experiments were performed in MFC batch mode using different SMX concentrations in synthetic wastewater. The experimental results showed that voltage generation was >400mV up to the SMX concentration of 0.20mM (at 400Ω external resistance). Control experiments supported the inference that biodegradation was the main process for SMX removal compared to sorption by SMX acclimatized cultures and that the process results in efficient removal of SMX in MFC mode. The specific removal rates of SMX in MFC with SMX acclimatized sludge were 0.67, 1.37, 3.43, 7.32, and 13.36μm/h at initial SMX concentrations of 0.04, 0.08, 0.20, 0.39, and 0.79mM, respectively. Moreover, the MFC was able to remove >90% of the TOC from the wastewater up to SMX concentrations of 0.08mM. However, this TOC removal produces negative effects at higher SMX concentrations due to toxic intermediates. Microbial community analysis revealed large changes in bacterial communities at the phylum, class, and genus levels after SMX acclimatization and MFC operation. Thauera, a well-known aromatic-degrading bacteria, was the most dominant genus present in post-acclimatized conditions. In summary, this study showed that acclimatized sludge can play an important role in the biodegradation of SMX in MFCs.

Effect of diclofenac on the production of volatile fatty acids from anaerobic fermentation of waste activated sludge

In this study, the impact of diclofenac (DCF), an antiinflammatory drug being extensively used in human health care and veterinary treatment, on the production of volatile fatty acids (VFAs) from anaerobic fermentation of waste activated sludge (WAS) was investigated for the first time. Experimental results showed that when DCF concentration increased from 2.5 to 25 mg/kg total suspended solid (TSS), the maximum production of VFAs increased from 599 to 1113 mg COD/L, but further increase of DCF to 47.5 mg/kg TSS decreased VFAs yield to 896 mg COD/L. The mechanism investigation revealed that DCF had no effect on the hydrolysis process, promoted the process of acidogenesis, acetogenesis, and homoacetogenesis, but severely inhibited methanogenesis, leading to the accumulation of VFAs. Microbial community analysis showed that the addition of DCF could promote the relative abundance of VFAs (especially acetic acid) producers, which was well consistent with the results obtained above.

Pilot-scale investigation of sludge reduction in aerobic digestion system with endospore-forming bacteria

A pilot-scale investigation of membrane-based aerobic digestion system dominated by endospore-forming bacteria was evaluated as one of the potential sludge treatment processes (STP). Most of the organic matter in the sludge was removed (90.1%) by the particular bacteria in the STP, which consisted of mixed liquor suspended solid (MLSS) contact reactor (MCR), MLSS oxidation reactor (MOR), and membrane bioreactor (MBR). The sludge was accumulated in the MBR without wasting, and then the effluent in STP was fed into the first step in water resource recovery facility (WRRF). According to the analysis of microbial communities in all reactors, various Bacillus species were present in the STP, mainly due to their intrinsic resistance to the extreme conditions. As the surviving Bacillus species might consume degraded microorganisms for their growth, these endospore-forming bacteria-based STP could be suitable for the sludge reduction when they operated for a long time.