PPCP Degradation by Chlorine-UV Processes in Ammoniacal Water: New Reaction Insights, Kinetic Modeling, and DBP Formation.

The combination of chlorine and UV (i.e., chlorine-UV process) has been attracting more attention in recent years due to its ready incorporation into existing water treatment facilities to remove PPCPs. However, limited information is available on the impact of total ammonia nitrogen (TAN). This study investigated two model PPCPs, N,N-diethyl-3-toluamide (DEET) and caffeine (CAF), in the two stages of the chlorine-UV process (i.e., chlorination and UV/chlor(am)ine) to elucidate the impact of TAN. During chlorination, the degradation of DEET and CAF was positively correlated with the overall consumption of total chlorine by TAN. Reactive nitrogen intermediates, including HNO/NO- and ONOOH/ONOO-, along with •OH were identified as major contributors to the removal of DEET and CAF. During UV irradiation, DEET and CAF were degraded under UV/chlorine or UV/NH2Cl conditions. •OH and •Cl were the major reactive species to degrade DEET and CAF under UV/NH2Cl conditions, whereas •OCl played a major role for degrading CAF under UV/chlorine conditions. Numerical models were developed to predict the removal of DEET and CAF under chlorination-UV process. Chlorinated disinfection byproducts were detected. Overall, this study presented kinetic features and mechanistic insights on the degradation of PPCPs under the chlorine-UV process in ammoniacal water.

An insight into the removal of fluoroquinolones in activated sludge process: Sorption and biodegradation characteristics.

The detailed sorption steps and biodegradation characteristics of fluoroquinolones (FQs) including ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin, and ofloxacin were investigated through batch experiments. The results indicate that FQs at a total concentration of 500µg/L caused little inhibition of sludge bioactivity. Sorption was the primary removal pathway of FQs in the activated sludge process, followed by biodegradation, while hydrolysis and volatilization were negligible. FQ sorption on activated sludge was a reversible process governed by surface reaction. Henry and Freundlich models could describe the FQ sorption isotherms well in the concentration range of 100-300µg/L. Thermodynamic parameters revealed that FQ sorption on activated sludge is spontaneous, exothermic, and enthalpy-driven. Hydrophobicity-independent mechanisms determined the FQ sorption affinity with activated sludge. The zwitterion of FQs had the strongest sorption affinity, followed by cation and anion, and aerobic condition facilitated FQ sorption. FQs were slowly biodegradable, with long half-lives (>100hr). FQ biodegradation was enhanced with increasing temperature and under aerobic condition, and thus was possibly achieved through co-metabolism during nitrification. This study provides an insight into the removal kinetics and mechanism of FQs in the activated sludge process, but also helps assess the environmental risks of FQs resulting from sludge disposal.

Adsorptive removal of antibiotics from water using magnetic ion exchange resin.

The occurrence of antibiotics in the environment has recently raised serious concern regarding their potential threat to aquatic ecosystem and human health. In this study, the magnetic ion exchange (MIEX) resin was applied for removing three commonly-used antibiotics, sulfamethoxazole (SMX), tetracycline (TCN) and amoxicillin (AMX) from water. The results of batch experiments show that the maximum adsorption capacities on the MIEX resin for SMX, TCN and AMX were 789.32, 443.18 and 155.15µg/mL at 25°C, respectively, which were 2-7 times that for the powdered activated carbon. The adsorption kinetics of antibiotics on the MIEX resin could be simulated by the pseudo-second-order model (R2=0.99), and the adsorption isotherm data were well described by the Langmuir model (R2=0.97). Solution pH exhibited a remarkable impact on the adsorption process and the absorbed concentrations of the tested antibiotics were obtained around the neutral pH. The MIEX resin could be easily regenerated by 2mol/L NaCl solution and maintained high adsorption removal for the tested antibiotics after regeneration. Anion exchange mechanism mainly controlled the adsorption of antibiotic and the formation of hydrogen binding between the antibiotic and resin can also result in the increase of adsorption capacity. The high adsorption capacity, fast adsorption rate and prominent reusability make the MIEX resin a potential adsorbent in the application for removing antibiotics from water.

Synthesis of carbon-coated magnetic nanocomposite (Fe3O4@C) and its application for sulfonamide antibiotics removal from water.

The occurrence of antibiotics in the environment has recently raised serious concerns regarding their potential threat to human health and aquatic ecosystem. A new magnetic nanocomposite, Fe3O4@C (Fe3O4 coated with carbon), was synthesized, characterized, and then applied to remove five commonly-used sulfonamides (SAs) from water. Due to its combinational merits of the outer functionalized carbon shell and the inner magnetite core, Fe3O4@C exhibited a high adsorption affinity for selected SAs and a fast magnetic separability. The adsorption kinetics of SAs on Fe3O4@C could be expressed by the pseudo second-order model. The adsorption isotherms were fitted well with the Dual-mode model, revealing that the adsorption process consisted of an initial partitioning stage and a subsequent hole-filling stage. Solution pH exerted a strong impact on the adsorption process with the maximum removal efficiencies (74% to 96%) obtained at pH 4.8 for all selected SAs. Electrostatic force and hydrogen bonding were two major driving forces for adsorption, and electron-donor-acceptor interactions may also make a certain contribution. Because the synthesized Fe3O4@C showed comprehensive advantages of high adsorptivity, fast magnetic separability, and prominent reusability, it has potential applications in water treatment.

Adsorption behavior of sulfamethazine in an activated sludge process treating swine wastewater.

Swine wastewater is an important pollution source of antibiotics entering the aquatic environment. In this work, the adsorption behavior of sulfamethazine (SMN), a commonly-used sulfonamide antibiotic, on activated sludge from a sequencing batch reactor treating swine wastewater was investigated. The results show that the adsorption of SMN on activated sludge was an initially rapid process and reached equilibrium after 6hr. The removal efficiency of SMN from the water phase increased with an increasing concentration of mixed liquor suspended solids, while the adsorbed concentration of SMN decreased. Solution pH influenced both the speciation of SMN and the surface properties of activated sludge, thus significantly impacting the adsorption process. A linear partition model could give a good fit for the equilibrium concentrations of SMN at the test temperatures (i.e., 10, 20 and 30°C). The partition coefficient (Kd) was determined to be 100.5L/kg at 20°C, indicating a quite high adsorption capacity for SMN. Thermodynamic analysis revealed that SMN adsorption on activated sludge was an exothermic process. This study could help to clarify the fate and behavior of sulfonamide antibiotics in the activated sludge process and assess consequent environmental risks arising from sludge disposal as well.

Rapid detection of multiple class pharmaceuticals in both municipal wastewater and sludge with ultra high performance liquid chromatography tandem mass spectrometry.

This work described the development, optimization and validation of an analytical method for rapid detection of multiple-class pharmaceuticals in both municipal wastewater and sludge samples based on ultrasonic solvent extraction, solid-phase extraction, and ultra high performance liquid chromatography-tandem mass spectrometry quantification. The results indicated that the developed method could effectively extract all the target pharmaceuticals (25) in a single process and analyze them within 24min. The recoveries of the target pharmaceuticals were in the range of 69%-131% for wastewater and 54%-130% for sludge at different spiked concentration levels. The method quantification limits in wastewater and sludge ranged from 0.02 to 0.73ng/L and from 0.02 to 1.00µg/kg, respectively. Subsequently, this method was validated and applied for residual pharmaceutical analysis in a wastewater treatment plant located in Beijing, China. All the target pharmaceuticals were detected in the influent samples with concentrations varying from 0.09ng/L (tiamulin) to 15.24µg/L (caffeine); meanwhile, up to 23 pharmaceuticals were detected in sludge samples with concentrations varying from 60ng/kg (sulfamethizole) to 8.55mg/kg (ofloxacin). The developed method demonstrated its selectivity, sensitivity, and reliability for detecting multiple-class pharmaceuticals in complex matrices such as municipal wastewater and sludge.

Machine learning predicts the growth of cyanobacterial genera in river systems and reveals their different environmental responses.

Cyanobacterial blooms are a common and serious problem in global freshwater environments. However, the response mechanisms of various cyanobacterial genera to multiple nutrients and pollutants, as well as the factors driving their competitive dominance, remain unclear or controversial. The relative abundance and cell density of two dominant cyanobacterial genera (i.e., Cyanobium and Microcystis) in river ecosystems along a gradient of anthropogenic disturbance were predicted by random forest with post-interpretability based on physicochemical indices. Results showed that the optimized predictions all reached strong fitting with R2 > 0.75, and conventional water quality indices played a dominant role. One-dimensional and two-dimensional partial dependence plot (PDP) revealed that the responses of Cyanobium and Microcystis to nutrients and temperature were similar, but they showed differences in preferrable nutrient utilization and response to pollutants. Further prediction and PDP for the ratio of Cyanobium and Microcystis unveiled that their distinct responses to PAHs and SPAHs were crucial drivers for their competitive dominance over each other. This study presents a new way for analyzing the response of cyanobacterial genera to multiple environmental factors and their dominance relationships by interpretable machine learning, which is suitable for the identification and interpretation of high-dimensional nonlinear ecosystems with complex interactions.

Virus inactivation by sequential ultraviolet-chlorine disinfection: Synergistic effect and mechanism.

The COVID-19 outbreak has raised concerns about the efficacy of the disinfection process followed in water treatment plants in preventing the spread of viruses. Ultraviolet (UV) and chlorine multi-barrier disinfection processes are commonly used in water treatment plants; however, their effects on virus inactivation are still unclear. In this study, the effects of different disinfection processes (i.e., UV, free chlorine, and their combination) on waterborne viruses were analyzed using bacteriophage surrogates (i.e., MS2 and PR772) as alternative indicators. The results showed that the inactivation rates of PR772 by either UV or free chlorine disinfection were higher than those of MS2. PR772 was approximately 1.5 times more sensitive to UV disinfection and 8.4 times more sensitive to chlorine disinfection than MS2. Sequential UV-chlorine disinfection had a synergistic effect on virus inactivation, which was enhanced by an increase in the UV dose. As compared with single free chlorine disinfection, UV irradiation at 40 mJ cm-2 enhanced MS2 and PR772 inactivation significantly with a 2.7-fold (MS2) and a 1.7-fold (PR772) increase in the inactivation rate constants on subsequent chlorination in phosphate buffered saline. The synergistic effect was also observed in real wastewater samples, in which the MS2 inactivation rate increased 1.4-fold on subsequent chlorination following UV irradiation at 40 mJ cm-2. The mechanism of the synergistic effect of sequential UV-chlorine disinfection was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using MS2 as an indicator. The results showed that the synergistic effect was due to damage to MS2 surface proteins caused by previous UV disinfection, which enhanced the sensitivity of MS2 to chlorination. This study provides a feasible approach for the efficient inactivation of viruses in water supply and drainage.

Simultaneous determination of three classes of antibiotics in the suspended solids of swine wastewater by ultrasonic extraction, solid-phase extraction and liquid chromatography-mass spectrometry.

This work describes a systematic approach to the development of a method for simultaneous determination of three classes of veterinary antibiotics in the suspended solids (SS) of swine wastewater, including five sulfonamides, three tetracyclines and one macrolide (tiamulin). The entire procedures for sample pretreatment, ultrasonic extraction (USE), solid-phase extraction (SPE), and liquid chromatography-mass spectrometry (LC-MS) quantification were examined and optimized. The recovery efficiencies were found to be 76%-104% for sulfonamides, 81%-112% for tetracyclines, and 51%-64% for tiamulin at three spiking levels. The intra-day and inter-day precisions, as expressed by the relative standard deviation (RSD), were below 17%. The method detection limits (MDLs) were between 0.14 and 7.14 microg/kg, depending on a specific antibiotic studied. The developed method was applied to field samples collected from three concentrated swine feeding plants located in Beijing, Shanghai and Shandong province of China. All the investigated antibiotics were detected in both SS and liquid phase of swine wastewater, with partition coefficients (logK(d)) ranging from 0.49 to 2.30. This study demonstrates that the SS can not be ignored when determining the concentrations of antibiotics in swine wastewater.

Impacts of wastewater treatment plant upgrades on the distribution and risks of pharmaceuticals in receiving rivers.

Upgrades of wastewater treatment plant (WWTP) and full-scale application of additional advanced oxidation processes have been proven to be effective in reducing the nutrient emissions to the environment; however, the impacts of WWTP upgrades on the receiving waters with regard to the occurrence and ecological risks of pharmaceuticals are still unclear. In this study, 27 pharmaceuticals with diverse physicochemical properties were monitored in four rivers in Beijing, each of which was heavily impacted by a large-scale WWTP. Three-year sampling campaigns were conducted, covering the periods before and after the WWTP upgrades. The results show that the newly added combined treatment processes (e.g., biological filter, ultrafiltration, ozonation, and NaClO disinfection) reduced the total pharmaceutical concentrations in the effluents by 45-74%. The composition profiles reveal that the upgrades of two studied WWTPs resulted in a significant reduction of pharmaceutical concentrations in the receiving rivers, while little impacts were observed for the other rivers. The risk assessment shows that the acute toxic pressures in the studied rivers were generally low and the WWTP upgrades were conducive to reduce the risks for most of pharmaceuticals. However, erythromycin and ofloxacin still posed high risk, indicating the potential adverse effect of pharmaceuticals on aquatic environment.

Machine learning approach identifies water sample source based on microbial abundance.

Water quality can change along a river system due to differences in adjacent land use patterns and discharge sources. These variations can induce rapid responses of the aquatic microbial community, which may be an indicator of water quality characteristics. In the current study, we used a random forest model to predict water sample sources from three different river ecosystems along a gradient of anthropogenic disturbance (i.e., less disturbed mountainous area, wastewater discharged urban area, and pesticide and fertilizer applied agricultural area) based on environmental physicochemical indices (PCIs), microbiological indices (MBIs), and their combination. Results showed that among the PCI-based models, using conventional water quality indices as inputs provided markedly better prediction of water sample source than using pharmaceutical and personal care products (PPCPs), and much better prediction than using polycyclic aromatic hydrocarbons (PAHs) and substituted PAHs (SPAHs). Among the MBI-based models, using the abundances of the top 30 bacteria combined with pathogenic antibiotic resistant bacteria (PARB) as inputs achieved the lowest median out-of-bag error rate (9.9%) and increased median kappa coefficient (0.8694), while adding fungal inputs reduced the kappa coefficient. The model based on the top 30 bacteria still showed an advantage compared with models based on PCIs or the combination of PCIs and MBIs. With improvement in sequencing technology and increase in data availability in the future, the proposed method provides an economical, rapid, and reliable way in which to identify water sample sources based on abundance data of microbial communities.

The profile of antibiotic resistance genes in pig manure composting shaped by composting stage: Mesophilic-thermophilic and cooling-maturation stages.

The variation of antibiotic resistance genes (ARGs) and influential factors in pig manure composting were investigated by conducting simulated composting tests using four different supplement materials (wheat straw, corn straw, poplar sawdust and spent mushroom). The results show that the relative abundance of total ARGs increased by 0.19-1.61 logs after composting, and tetX, sulI, sulII, dfrA1 and aadA were the major contributors. The variations of ARG profiles and bacterial communities throughout the composting were clearly divided into mesophilic-thermophilic and cooling-maturation stages in all tests, while different supplement materials did not exert a noticeable influence. Network analysis demonstrated the diversity of bacterial hosts for ARGs, the existence of multiple antibiotic resistant bacteria, and the weak correlations between ARGs and physicochemical factors in the composting piles. Of note, integron intI1 and Mycobacterium (a potential pathogen) were positively correlated with eight and four ARGs, respectively, that displayed increased abundance after composting.

Removal of antibiotic resistance genes in pig manure composting influenced by inoculation of compound microbial agents.

The influence of compound microbial agents on antibiotic resistance genes (ARGs) in pig manure composting was investigated. The results show that the addition of microbial agents promoted the reduction of total ARGs and the maximum removal efficiencies for absolute abundance (77.2%) and relative abundance (64.5%) were observed in the repeated dose and high dose groups, respectively. Four categories of ARGs declined with the reduction of Firmicutes and Tn916/1545, whereas two categories increased with the proliferation of intI1 and various potential hosts in the composting. The ARG profiles and bacterial communities were shaped by composting stages (mesophilic-thermophilic and cooling-maturation stages) in all groups. However, the addition of microbial agents accelerated the variation of composting stages, and may change the potential ARG hosts which influences the removal of ARGs. Of note, intI1 and two potential pathogens (Mycobacterium and Bacillus) correlated positively to several increased ARGs, implying the possible risks of compost products.

Occurrence, source estimation and risk assessment of pharmaceuticals in the Chaobai River characterized by adjacent land use.

This study investigated the occurrence of 27 pharmaceuticals with diverse physicochemical properties in a year-long monitoring campaign in the Chaobai River, China. The correlation between the distribution of pharmaceuticals in the river and the adjacent sources was elucidated. The results indicate that the agriculture area was the most polluted area with a median summed pharmaceutical concentration of 225.3 ng L-1, followed by the urban area and the mountain area with the corresponding values of 136.9 and 29.9 ng L-1, respectively. In terms of individual compounds, 22 out of 27 compounds were detected with concentrations ranging from <1 to 1972 ng L-1. Caffeine, carbamazepine, azithromycin, bezafibrate, metoprolol, sulfadiazine, sulfamethoxazole, clarithromycin, erythromycin, roxithromycin, and trimethoprim were pharmaceuticals with relatively high levels, with median concentrations ranging from 3.3 to 25.6 ng L-1 and detection frequencies ranging from 40% to 97%. Higher concentrations were mainly observed during cold seasons, with mean concentrations 1 to 52 times as high as those during warm seasons. Spatial analysis reveals that the pharmaceutical concentrations in different areas were impacted by different sources. A wastewater treatment plant was an important source in the urban area, while the agriculture area was impacted by various treated and untreated wastewater sources. The species sensitivity distribution model and risk quotient (RQ) method were combined in the ecological risk assessment. The results indicate that the multi-substance potentially affected fraction (msPAF) values of the sampling sites were below 0.04%, whereas nearly half of RQ values were higher than 1. Caffeine was proposed as a priority compound due to its high contribution rate (i.e., 79%) to the cumulative msPAF value, which implies that increased control and management of untreated wastewater sources along the Chaobai River is necessary.

Simultaneous determination of sulfonamides, tetracyclines and tiamulin in swine wastewater by solid-phase extraction and liquid chromatography-mass spectrometry.

Little is known about the contamination level of antibiotics in swine wastewater in China. The highly complex matrix of swine wastewater, which generally has a chemical oxygen demand (COD) concentration as high as 15,000 mg/L, makes it difficult to detect antibiotics at trace levels. In this work, a highly selective and sensitive analytical method was developed for simultaneous determination of three classes of commonly used veterinary antibiotics including five sulfonamides, three tetracyclines and one macrolide in swine wastewater using solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (LC-MS). The method detection limits (MDL) in the swine wastewater were determined to be between 5 and 91 ng/L, depending on specific antibiotics. Except sulfamethizole, all the other eight antibiotics were detected in the swine wastewaters collected from three concentrated swine feeding plants located in the Beijing (China) area, showing a concentration range of 0.62-32.67 microg/L. These results reveal the representative concentration levels of selected antibiotics in the swine wastewaters of Beijing area.

[Removal of Antibiotics During In-situ Sludge Ozone-reduction Process].

Two sequencing batch reactors were established at bench-scale, with one used as an in-situ sludge ozone-reduction system and the other as a control system. Both systems were continuously operated for 90 days to comparatively investigate the elimination of nine typical antibiotics (i.e., tetracycline, oxytetracycline, doxytetracycline, norfloxacin, ofloxacin, ciprofloxacin, lomefloxacin, enrofloxacin, and azithromycin) during the in-situ sludge ozone-reduction process. Results indicated that the presence of target antibiotics in the influent (100 µg·L-1 each) had an insignificant influence on the removal of COD, total nitrogen, ammonia, and total phosphorus by the activated sludge. The antibiotic concentrations in the effluent of the reduction system remained fairly stable over the entire operation period, and were similar to those in the effluent of the control system; however, the antibiotic concentrations in the sludge of the reduction system were obviously lower than those in the control system sludge. Mass balance calculations revealed that the input and output of target antibiotics gradually approached balance in both the systems. Ozone degradation and excess sludge discharge were the main pathways for target antibiotic removal in the reduction and the control systems, respectively. The influent antibiotics could be degraded by 83% in the sludge ozonation module of the reduction system, while 82% of the influent antibiotics were discharged with excess sludge in the control system. Therefore, the in-situ sludge ozone-reduction process could greatly reduce the release of antibiotics from the activated sludge system, which is of great importance in practice.

Ozonation of norfloxacin and levofloxacin in water: Specific reaction rate constants and defluorination reaction.

The degradation kinetics and mechanism of two typical fluoroquinolones (FQs), norfloxacin (NF) and levofloxacin (LOF), by ozone in water were investigated. Semi-continuous mode and competition kinetics mode experiments were conducted to determine the reaction rate constants of target FQs with ozone and OH, separately. Results indicate that both NF and LOF were highly reactive toward ozone, and the reactivity was strongly impacted by the solution pH. The specific reaction rate constants of the diprotonated, monoprotonated and deprotonated species were determined to be 7.20 × 102, 8.59 × 103, 4.54 × 105 M-1 s-1 respectively for NF and 1.30 × 103, 1.40 × 104, 1.33 × 106 M-1 s-1 respectively for LOF. The reaction rate constants of target FQs toward OH were measured to be (4.81-7.41) × 109 M-1 s-1 in the pH range of 6.3-8.3. Furthermore, NF was selected as a model compound to clarify the degradation pathways, with a particular focus on the defluorination reaction. The significant release of F- ions and the formation of three F-free organic byproducts indicated that defluorination was a prevalent pathway in ozonation of FQs, while six F-containing organic byproducts indicated that ozone also attacked the piperazinyl and quinolone moieties. Escherichia coli growth inhibition tests revealed that ozonation could effectively eliminate the antibacterial activity of target FQ solutions, and the residual antibacterial activity had a negative linear correlation with the released F- concentration.

Occurrence, removal and risk of organic micropollutants in wastewater treatment plants across China: Comparison of wastewater treatment processes.

This study investigated the occurrence, removal and risk of 42 organic micropollutants (MPs), including 30 pharmaceuticals and personal care products and 12 endocrine disrupting chemicals, in 14 municipal wastewater treatment plants (WWTPs) distributed across China. The composition profiles of different MP categories in the influent, effluent, and excess sludge were explored and the aqueous removal efficiencies of MPs were determined. Quantitative meta-analysis was performed to compare the efficacies of different wastewater treatment processes in eliminating MPs. Results indicate that different MP categories showed quite similar distributions among the studied WWTPs, with phenolic estrogenic compounds (PEs), macrolides, and fluoroquinolones being always dominant in the influent, effluent and excess sludge. Tetracyclines, bezafibrate, caffeine, steroid estrogens, and PEs showed high and stable aqueous removal efficiencies, whereas other MPs showed considerably varied aqueous removal efficiencies. Anaerobic/anoxic/oxic process combined with a moving-bed biofilm reactor achieved the highest aqueous removal of MPs among various secondary treatment processes. A combined process consisting of ultrafiltration, ozonation and ClO2 disinfection resulted in the highest removal of MPs among the tertiary treatment processes. Sulfamethoxazole, ofloxacin, ciprofloxacin, clarithromycin, erythromycin, estrone, and bisphenol A in the effluent, as well as ß-estradiol 3-sulfate in the excess sludge could pose high risks. This study draws an overall picture about the current status of MPs in WWTPs across China and provides useful information for better control of the risks associated with MPs.

Behavior of tetracycline and macrolide antibiotics in activated sludge process and their subsequent removal during sludge reduction by ozone.

Ozonation is a promising means for the reduction of excess sludge in wastewater treatment plants. However, little information is available on the removal of antibiotics during sludge ozonation. Therefore, this study investigated first the behavior of four commonly-used hydrophobic antibiotics, including three tetracyclines (tetracycline, oxytetracycline, and doxycycline) and one macrolide (azithromycin) in activated sludge process and then their removal during sludge reduction by ozone. Results indicate that the studied antibiotics were primarily transferred into the solid phase of activated sludge via sorption, which was a reversible, spontaneous, and exothermic process governed by surface reactions. Sludge ozonation could effectively remove 86.4-93.6% of the antibiotics present in the sludge at an ozone dose of 102 mg per gram of mixed liquor suspended solids and pH 7.2. The removal of studied antibiotics mainly proceeded through desorption and subsequent oxidation. Increasing the initial pH from 5.0 to 9.5 obviously enhanced the antibiotic removal during sludge ozonation. This study demonstrated that the activated sludge process coupled with sludge ozonation can simultaneously reduce excess sludge and eliminate antibiotics.

Dissemination of antibiotic resistance genes and their potential removal by on-farm treatment processes in nine swine feedlots in Shandong Province, China.

This work investigated the dissemination of antibiotic resistance genes (ARGs) encoding resistance to sulfonamide and tetracycline antibiotics in nine swine feedlots located in Shandong Province of China, and examined their potential removal by various on-farm treatment processes. Results indicate that the target ARGs were widely distributed in swine wastes, with mean relative abundances ranging from 3.3 × 10-5 (tetC) to 5.2 × 10-1 (tetO) in swine manure and from 7.3 × 10-3 (tetC) to 1.7 × 10-1 (tetO) in swine wastewater. The mean relative ARG abundances ranged from 9.9 × 10-5 (tetW) to 1.1 × 10-2 (tetO) in soils and from 3.1 × 10-4 (tetW) to 1.1 × 10-2 (sul2) in receiving river sediments, indicating that the farmland application of swine manure compost and the discharge of swine wastewater promoted the dissemination of ARGs into adjacent environments. Microbial fermentation bed (MFB) could reduce the relative ARG abundances by 0-1.18 logs. However, septic tank, biogas digester and natural drying methods were relatively ineffective for ARG removal, and the relative abundances of some ARGs (i.e., tetC, tetG, sul1, and sul2) even increased by 0.74-3.90 logs in treated wastes. Bacterial diversity analysis indicates that the evolution of bacterial communities in the MFB played a crucial role in eliminating the ARGs. This study helps the effective assessment and management of ecological risks arising from ARGs in swine feedlots.