Insights into the occurrence, elimination efficiency and ecological risk of antibiotics in rural domestic wastewater treatment facilities along the Yangtze River Basin, China

Prevalence of antibiotics, antibiotic resistance genes, and their associations in municipal wastewater treatment plants along the Yangtze River basin, China

The overuse and misuse of antibiotics have resulted in the pollution of antibiotics and antibiotic resistance genes (ARGs) in municipal wastewater treatment plants (WWTPs), posing threats to ecological security and human health. Thus, a comprehensive investigation was conducted to assess the occurrence, removal efficiency, and ecological risk of antibiotics, along with the diversity, abundance, and co-occurrence of ARGs, and their correlations in 13 WWTPs along the Yangtze River Basin. Among 35 target antibiotics, 23 antibiotics within 6 categories were detected in all the samples. Amoxicillin (AMO), ofloxacin (OFL), and pefloxacin (PEF) were predominant in influents, while AMO exhibited dominance with the highest concentration of 1409 ng/L in effluents. Although antibiotic removal performance varied among different WWTPs, a significant decrease in each antibiotic category and overall antibiotics was observed in effluents compared with that in influents (p < 0.05). Remarkably, ecological risk assessment revealed high risks associated with AMO and ciprofloxacin (CIP) and medium risks linked to several antibiotics, notably including OFL, roxithromycin (ROX), clarithromycin (CLA), and tetracycline (TC). Furthermore, 96 ARG subtypes within 12 resistance types were detected in this study, and the total absolute abundance and diversity of ARGs were significantly decreased from influents to effluents (p < 0.05). Enrichment of 38 ARGs (e.g., blaNDM, ermA, vatA, mexA, and dfrA25) in effluents indicated potential health risks. Various mobile genetic elements (MGEs), exhibited significant correlations with a majority of ARGs in both influents and effluents, such as intⅠ1, tnpA1, tnpA5, and tp614, underscoring the important role of MGEs in contributing to the ARG dissemination. Many antibiotics displayed lower correlations with corresponding ARGs, but exhibited higher correlations with other ARGs, suggesting complex selective pressures influencing ARG propagation. Overall, the incomplete elimination of antibiotics and ARGs in WWTPs is likely to pose adverse impacts on aquatic ecosystems in the Yangtze River Basin.

Potential pathogenic microorganisms in rural wastewater treatment process: Succession characteristics, concentration variation, source exploration, and risk assessment

Pathogenic microorganisms can cause infection, sepsis, and other diseases in humans. Although municipal wastewater plants are important sources and sinks for potential pathogenic microorganisms, data on rural wastewater treatment processes are limited. The proximity of rural wastewater facilities to human settlements and the trend toward wastewater resourcing could pose risks to humans. Here, a typical village in southern China was selected to analyze potential pathogenic microorganisms in wastewater, sewage sludge, and aerosols during the collection, treatment, and discharge of domestic wastewater. The succession characteristics and concentration variations of potential pathogenic microorganisms throughout the wastewater treatment process were identified using high-throughput sequencing and culture methods. Bacteria-associated health risks in facility aerosols were estimated based on average daily dose rates from inhalation and dermal exposure. Lower amounts of pathogenic bacteria and pathogenic fungi were detected in the effluent of the 1-ton treatment scale and the 10-ton treatment scale facilities, compared to those in the influent. Pathogen effluent concentrations were significantly lower than influent concentrations after treatment in rural wastewater facilities. 16 and 29 potential pathogenic bacteria and fungi were detected in aerosols from wastewater treatment facilities, respectively. Furthermore, the potential pathogen concentrations were higher than those in the background air. Aerobic units are the main source of pathogen emissions from aerosols. There were 42 potential pathogenic bacteria and 34 potential pathogenic fungi in the sewage sludge. Biochemical units were the main source of potential pathogens in sewage sludge, and more potential airborne pathogens originated from wastewater. In rural wastewater resourcing processes with greater pollutant exposure, the effluent of rural wastewater treatment facilities (WWTFs), downstream rivers, and facility aerosols, could be important potential sources of microbial risk. Inhalation is the main pathway of human exposure to airborne bacteria. Therefore, more attention should be focused on microbiological risk in rural wastewater treatment processes.

Ofloxacin weakened treatment performance of rural domestic sewage in an aerobic biofilm system by affecting biofilm resistance, bacterial community, and functional genes

Ofloxacin (OFL) is a typical fluoroquinolone antibiotic widely detected in rural domestic sewage, however, its effects on the performance of aerobic biofilm systems during sewage treatment process remain poorly understood. We carried out an aerobic biofilm experiment to explore how the OFL with different concentrations affects the pollutant removal efficiency of rural domestic sewage. Results demonstrated that the OFL negatively affected pollutant removal in aerobic biofilm systems. High OFL levels resulted in a decrease in removal efficiency: 9.33% for chemical oxygen demand (COD), 18.57% for ammonium (NH4+-N), and 8.49% for total phosphorus (TP) after 35 days. The findings related to the chemical and biological properties of the biofilm revealed that the OFL exposure triggered oxidative stress and SOS responses, decreased the live cell number and extracellular polymeric substance content of biofilm, and altered bacterial community composition. More specifically, the relative abundance of key genera linked to COD (e.g., Rhodobacter), NH4+-N (e.g., Nitrosomonas), and TP (e.g., Dechlorimonas) removal was decreased. Such the OFL-induced decrease of these genera might result in the down-regulation of carbon degradation (amyA), ammonia oxidation (hao), and phosphorus adsorption (ppx) functional genes. The conventional pollutants (COD, NH4+-N, and TP) removal was directly affected by biofilm resistance, functional genes, and bacterial community under OFL exposure, and the bacterial community played a more dominant role based on partial least-squares path model analysis. These findings will provide valuable insights into understanding how antibiotics impact the performance of aerobic biofilm systems during rural domestic sewage treatment.

Comprehensive evaluation of antibiotics pollution the Yangtze River basin, China: Emission, multimedia fate and risk assessment

Antibiotics have attracted global attention because of their potential ecological and health risks. The emission, multimedia fate and risk of 18 selected antibiotics in the entire Yangtze River basin were evaluated by using a level Ⅳ fugacity model. High antibiotic emissions were found in the middle and lower reaches of the Yangtze River basin. The total antibiotic emissions in the Yangtze River basin exceeded 1600 tons per year between 2013 and 2021. The spatial distribution of antibiotics concentration was the upper Yangtze River > middle Yangtze River > lower Yangtze River, which is positively correlated with animal husbandry size in the basin. Temperature and precipitation increases may decrease the antibiotic concentrations in the environment. Transfer fluxes showed that source emission inputs, advection processes, and degradation fluxes contributed more to the total input and output. High ecological risks in the water environment were found in 2018, 2019, 2020, and 2021. The comprehensive health risk assessment through drinking water and fish consumption routes showed that a small part of the Yangtze River basin is at medium risk, and children have a relatively high degree of health risk. This study provides a scientific basis for the pollution control of antibiotics at the basin scale.

Organophosphate esters in rural wastewater along the Yangtze river Basin: Occurrence, removal efficiency and environmental implications

Organophosphate esters (OPEs) discharged from rural domestic wastewater were one of the important sources of OPEs in receiving water bodies, which has posed a potential threat to the ecological environment. However, very little information on the characteristics of OPEs in the rural domestic wastewater is available. Herein, the occurrence, removal efficiency and environmental implication of OPEs in rural domestic wastewater treatment facilities (RD-WWTFs) along the Yangtze River Basin were investigated. Results indicated that the median concentrations of ΣAlkyl-OPEs, ΣHalogenated-OPEs, ΣAryl-OPEs and the total OPE (ΣOPEs) in influents were 28.28, 99.25, 10.22 and 136.84 ng/L, while the median concentrations of them in effluents were 25.80, 141.86, 7.98 and 173.31 ng/L, respectively. Undoubtedly, halogenated OPEs were the most abundant in both influent and effluent, followed by alkyl and aryl OPEs, and they accounted for average proportions of 69.50%, 19.96%and 10.54% for influents, and 78.16%, 16.14%and 5.71% for effluents, respectively. Specifically, tris(2-chloroisopropyl) phosphate (TCPP, median: 55.17 ng/L in influents and 85.75 ng/L in effluents) was the dominant contributor to the ΣOPEs concentrations with average proportions of 37.75% and 47.33% for influents and effluents, respectively. Moreover, the concentration ranks for most OPEs except for aryl OPEs from high to low were upper reaches > lower reaches > middle reaches. However, negative values of tris(2-chloroethyl)phosphate (TCEP, -32.4%), TCPP (-55.4%) and tris(1,3-dichloroisopropyl) phosphate (TDCPP, -26.3%) were observed. The removal rates of alkyl OPEs (10-20%) and aryl OPEs (20-30%) were also not sufficient. Ecological risk values of ΣOPEs showed that there were 2.44% of high risk, 31.7% of moderate risk and 41.5% of low risk for effluents; while 0.00%, 48.8% and 46.3% were exhibited in high, moderate and low risk for influents, indicating that very slight reduction in risk was achieved by the RD-WWTFs.

Occurrence, removal, and risk assessment of emerging contaminants in aquatic products processing sewage treatment plants

Emerging contaminants (ECs) in aquatic environments have attracted attention due to their wide distribution and potential ecotoxicities. Sewage treatment plants (STPs) are proven to be the major source of ECs in the aquatic environment, while there remains insufficient understanding of the removal and risk assessment of ECs in STPs. Here, we clarified the degradation and risk impact of 13 ECs in two aquatic product processing sewage treatment plants (APPSTPs) along the southeast coast of China. The concentrations of ECs followed the order: endocrine-disrupting chemicals (1877.85-15,398.02 ng/L in influent, 3.37-44.47 ng/L in effluent) >  > sulfonamide antibiotics (SAs, 75.14-906.19 ng/L in influent, 1.14-15.33 ng/L in effluent) > pharmaceutical and personal care products (PPCPs, 44.47-589.93 ng/L in influent, 2.54-34.16 ng/L in effluent) ≈ fluoroquinolone antibiotic (54.76-434.83 ng/L in influent, 10.75-32.82 ng/L in effluent) > other antibiotics (16.21-51.96 ng/L in influent, 0.68-6.17 ng/L in effluent). Moreover, the concentrations of PPCPs (decreased by 55.33-87.65% in peak fishing season) and antibiotics (increased by 44.99% in peak fishing season) were affected by fishing activities. In particular, the sequencing batch reactor (SBR) process had a better removal effect than the anaerobic-anoxic-oxic (A2/O) process on the treatment of some contaminants (e.g., norfloxacin and nonylphenol). Risk evaluations of ECs demonstrated that nonylphenol and SAs were at high- and low-risk states, respectively. Overall, our results provide important information for the degradation treatment of ECs, which is essential for pollutant management policy formulation.

Occurrence of antibiotics in wastewater: Potential ecological risk and removal through anaerobic-aerobic systems

Antibiotics are intensively used to improve public health, prevent diseases and enhance productivity in animal farms. Contrarily, when released, the antibiotics laden wastewater produced from pharmaceutical industries and their application sources poses a potential ecological risk to the environment. This study provides a discussion on the occurrence of various antibiotics in wastewater and their potential ecological risk in the environment. Further, a critical review of anaerobic-aerobic processes based on three major systems (such as constructed wetland, high-rate bioreactor, and integrated treatment technologies) applied for antibiotics removal from wastewater is performed. The review also explores microbial dynamics responsible for antibiotic biodegradation in anaerobic-aerobic systems and its economic feasibility at wider-scale applications. The operational problems and prospective modifications are discussed to define key future research directions. The appropriate selection of treatment processes, sources control, understanding of antibiotic fate, and adopting precise monitoring strategies could eliminate the potential ecological risks of antibiotics. Integrated bio-electrochemical systems exhibit antibiotics removal ≥95% by dominant Geobacter sp. at short HRT ∼4-10 h. Major process factors like organic loading rate, hydraulic loading rate (HRT), and solid retention time significantly affect the system performance. This review will be beneficial to the researchers by providing in-depth understanding of antibiotic pollution and its abatement via anaerobic-aerobic processes to develop sustainable wastewater treatment technology in the future.

Bi3.64Mo0.36O6.55 nanoparticles anchored in BiOI: A p-n heterojunction photocatalyst to enhance water purification

Selective constructing of heterojunctions enables directional electron-hole migration and favorable charge separation. In this study, a novel p-n junction Bi_3.64Mo_0.36O_6.55 (BMO) nanoparticles anchored in BiOI construct by hydrothermal and subsequent in-situ synthesis. The construction of tight heterojunctions that enhance the characteristic absorption of visible light by Bi_3.64Mo_0.36O_6.55/BiOI (BIMO) and expose more reactive sites can be used to facilitate the rapid degradation of antibiotics (Tetracycline, TC), endocrine disruptors (Bisphenol A, BPA) and dyes in water. In addition, the BIMO catalyst maintained the rapid degradation rate of TC despite the interference of inorganic anions and aqueous substrates. The charge transfer pathways and radical species between the heterojunction components were investigated. In addition, the intermediates and toxicological analysis showed that TC was further mineralized and the small molecule products were generated significantly less toxic and less contaminated. In conclusion, this study synthesized photocatalysts based on p-n heterojunctions, which have potential applications for the degradation of TC.

Integrated photocatalysis and moving bed biofilm reactor (MBBR) for treating conventional and emerging organic pollutants from synthetic wastewater: Performances and microbial community responses

Increasing concern for emerging organic pollutants (e.g. antibiotics) urges improvements in conventional biological wastewater treatment processes. This study examined the performance of an integrated photocatalysis and moving bed biofilm reactor (MBBR) system in treating synthetic wastewater containing sulfamethoxazole (SMX). It was found that the integrated system could remove over 80.5 % of SMX and 67.7-80.7 % of chemical oxygen demand (COD) with a hydraulic retention time of 24 h. The introduction of photocatalysis had no impact on COD removal and significantly enhanced SMX removal. High-throughput analysis indicated that microbial community greatly altered due to photocatalytic oxidation stress, with clostridiaceae and enterobacteriaceae becoming dominant families. Nevertheless, microorganisms maintained metabolic activity, which may be ascribed to the protection of carriers and microbial self-preservation by secreting extracellular polymeric substances and antioxidant enzymes. Collectively, this study sheds light on treating wastewater containing conventional and emerging organic pollutants by integrating photocatalysis with MBBR.

The Current Status and Prevention of Antibiotic Pollution in Groundwater in China

The problem of environmental pollution caused by the abuse of antibiotics has received increasing attention. However, only in recent years have antibiotic pollution and its risk assessment to the environment been deeply studied. Although there has been a large number of reports about the input, occurrence, destination, and influence of antibiotics in the past 10 years, systemic knowledge of antibiotics in the groundwater environment is still lacking. This review systematically expounds the sources, migration and transformation, pollution status, and potential risks to the ecological environment of antibiotics in groundwater systems, by integrating 10 years of existing research results. The results showed that 47 kinds of antibiotics in four categories, mainly sulfonamides and fluoroquinolones, have been detected; antibiotics in groundwater species will induce the production of resistance genes and cause ecological harm. In view of the entire process of antibiotics entering groundwater, the current antibiotic control methods at various levels are listed, including the control of the discharge of antibiotics at source, the removal of antibiotics in water treatment plants, and the treatment of existing antibiotic contamination in groundwater. Additionally, the future research direction of antibiotics in groundwater is pointed out, and suggestions and prospects for antibiotic control are put forward.