Evaluation of the fate of nutrients, antibiotics, and antibiotic resistance genes in sludge treatment wetlands

Azithromycin removal using pine bark, oak ash and mussel shell

Adsorption is considered an interesting option for removing antibiotics from the environment because of its simple design, low cost, and potential efficiency. In this work we evaluated three by-products (pine bark, oak ash, and mussel shell) as bio-adsorbents for the antibiotic azithromycin (AZM). Furthermore, they were added at doses of 48 t ha-1 to four different soils, then comparing AZM removal for soils with and without bio-adsorbents. Batch-type experiments were used, adding AZM concentrations between 2.5 and 600 μmol L-1 to the different bio-adsorbents and soil + bio-adsorbent mixtures. Regarding the bio-adsorbents, oak ash showed the best adsorption scores (9600 μmol kg-1, meaning >80% retention), followed by pine bark (8280 μmol kg-1, 69%) and mussel shell (between 3000 and 6000 μmol kg-1, 25-50% retention). Adsorption data were adjusted to different models (Linear, Freundlich and Langmuir), showing that just mussel shell presented an acceptable fitting to the Freundlich equation, while pine bark and oak ash did not present a good adjustment to any of the three models. Regarding desorption, the values were always below the detection limit, indicating a rather irreversible adsorption of AZM onto these three by-products. Furthermore, the results showed that when the lowest concentrations of AZM were added to the not amended soils they adsorbed 100% of the antibiotic, whereas when the highest concentrations of AZM were spread, the adsorption decreased to 55%. However, when any of the three bio-adsorbents was added to the soils, AZM adsorption reached 100% for all the antibiotic concentrations used. Desorption was null in all cases for both soils with and without bio-adsorbents. These results, corresponding to an investigation carried out for the first time for the antibiotic AZM, can be seen as relevant in the search of low-cost alternative treatments to face environmental pollution caused by this emerging contaminant.

Impact analysis of hydraulic loading rate and antibiotics on hybrid constructed wetland systems: Insight into the response to decontamination performance and environmental-associated microbiota

Hybrid constructed wetlands (HCWs) are a promising solution for water ecology and environmental treatment, not only for conventional types of water pollution but also for antibiotics. Among the critical parameters for wetlands, the hydraulic loading rate (HLR) is especially important given the challenges of antibiotics treatment and frequent extreme rainfall. To investigate the removal performance of different HLRs on nutrients and antibiotics, as well as the response of antibiotics to nutrient removal, and the impact of HLRs on microbial communities, new HCWs with vertical flow constructed wetlands (VFCWs) and floating constructed wetlands (FCWs) in series were built. The results of the study showed that: (1) HCWs are highly effective in removing chemical oxygen demand (COD), NH4+-N, NO2--N, and total phosphorus (TP) at low HLR (L_HLR), with removal efficiencies as high as 97.8%, 99.6%, 100%, and 80.5%. However, high HLR (H_HLR) reduced their removal efficiencies; (2) The average removal efficiency of fluoroquinolones (FQs) under different HLRs was consistently high, at 99.9%, while the average removal efficiency of macrolides (MLs) was 96.3% (L_HLR) and 88.4% (H_HLR). The removal efficiency of sulfonamides (SAs) was susceptible to HLRs, and the removal of antibiotics occurred mainly in the rhizosphere zone of wetland; (3) High concentrations of antibiotics in HCWs were found to inhibit and poison plant growth and to reduce the removal efficiency of TP by 12%. However, they had a minor effect on the removal efficiency of carbon and nitrogen nutrients; (4) H_HLR altered the diversity and abundance of microbial communities in different compartments of the wetland and also reduced the relative abundance of Bacillus, Hydrogenophaga, Nakamurella, Denitratisoma and Acidovorax genera, which are involved in denitrification and phosphorus removal processes. This alteration in microbial communities was one of the main reasons for the reduced performance of nitrogen and phosphorus removal.

Microbial inoculants enhance the persistence of antibiotic resistance genes in aerobic compost of food waste mainly by altering interspecific relationships

The effects of microbial inoculants on ARG removal in composting are poorly understood. Here, a co-composting method for food waste and sawdust amended with different microbial agents (MAs) was designed. The results show that the compost without MA unexpectedly achieved the best ARG removal. The addition of MAs markedly increased the abundance of tet, sul and multidrug resistance genes (p < 0.05). Structural equation modeling demonstrated that MAs can enhance the contribution of the microbial community to ARG changes by reshaping community structure and altering the ecological niche, causing the proliferation of individual ARGs, an effect related to the MA component. Network analysis revealed that inoculants weakened the correlation between ARGs and community but increased the linkage between ARGs and core species, suggesting that inoculant-induced ARG proliferation may correspond with gene exchange occurring mainly between core species. The outcome provides new insights into MA application for ARG removal in waste treatment.

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.

Determination of the fate of antibiotic resistance genes and the response mechanism of plants during enhanced antibiotic degradation in a bioelectrochemical-constructed wetland system

Chloramphenicol (CAP) has a high concentration and detection frequency in aquatic environments due to its insufficient degradation in traditional biological wastewater treatment processes. In this study, bioelectrochemical assistant-constructed wetland systems (BES-CWs) were developed as advanced processes for efficient CAP removal, in which the degradation and transfer of CAP and the fate of antibiotic resistance genes (ARGs) were evaluated. The CAP removal efficiency could reach as high as 90.2%, while the removed CAP can be partially adsorbed and bioaccumulated in plants, significantly affecting plant growth. The vertical gene transfer and horizontal gene transfer increased the abundance of ARGs under high voltage and CAP concentrations. Microbial community analysis showed that CAP pressure and electrical stimulation selected the functional bacteria to increase CAP removal and antibiotic resistance. CAP degradation species carrying ARGs could increase their opposition to the biotoxicity of CAP and maintain system performance. In addition, ARGs are transferred into the plant and upward, which can potentially enter the food chain. This study provides an essential reference for enhancing antibiotic degradation and offers fundamental support for the underlying mechanism and ARG proliferation during antibiotic biodegradation.

Fate of antibiotic resistance genes and bacteria in a coupled water-processing system with wastewater treatment plants and constructed wetlands in coastal eco-industrial parks

In coastal eco-industrial zones, wastewater treatment plants (WWTPs) and constructed wetlands (CWs) can alleviate the challenge of water shortage and the negative effect of sewage discharge, while the problems of antibiotic resistance genes (ARGs) have not attracted enough attention. In this research, the Wafergen SmartChip system was adopted to investigate the ARG profiles in a coupled system combined WWTPs and CWs in a coastal industrial park. Potential risks of antibiotic resistance in chemical industrial wastewater were confirmed due to the higher abundance of target ARGs (> 10⁷ copies/mL). General decline with partial enrichment in absolute and relative abundance of ARGs from the WWTPs to CWs revealed the effective removal of ARGs in the coupled system, while the fate of different ARG types varied greatly. Aminoglycoside and sulfonamide ARGs were detected with higher abundance (up to 5.34 ×10⁷ and 3.61 ×10⁷ copies/mL), especially aac(6')-Ib and sul1. Denitrification, secondary sedimentation, and acid hydrolysis contributed to the removal of aminoglycoside, sulfonamide, β-lactamase, chloramphenicol, and multidrug ARGs. Catalytic ozonation contributed to the removal of tetracycline and MLSB ARGs. Subsurface CWs worked effectively for the removal of sulfonamide, tetracycline, and multidrug ARGs, especially tetX, cphA, tetG, and strB. Close correlations between ARGs and MGEs emphasized the vital roles of anthropogenic pollutants and horizontal gene transfer on the diffusion of ARGs. Actinobacteria, Bacteroidota, and Cyanobacteria were dominant in the CWs, while Proteobacteria, Firmicutes, and Planctomycetota were prevalent in the WWTPs. Redundancy analysis and variance partitioning analysis indicated that transposase and water quality posed greater influences on the distribution of ARGs. Co-occurrence network revealed that potential multiple antibiotic resistant pathogenic bacteria decreased in the CWs. The coupled system has a limited effect on the reduction of ARGs and potential ARG hosts, providing a comprehensive insight into the fate of ARGs in conventional water-processing systems.

Removal of Antibiotic Resistance Genes from Animal Wastewater by Ecological Treatment Technology Based on Plant Absorption

With the aim of controlling the pollution of antibiotic resistance genes (ARGs) in livestock and poultry wastewater, this paper highlights an ecological treatment technology based on plant absorption and comprehensively discusses the removal effect, driving factors, removal mechanism, and distribution characteristics of ARGs in plant tissues. The review shows that ecological treatment technology based on plant absorption has gradually become an important method of wastewater treatment of livestock and poultry breeding and has a good ARG removal effect. In plant treatment ecosystems, microbial community structure is the main driver of ARGs, while mobile genetic elements, other pollutants, and environmental factors also affect the growth and decline of ARGs. The role of plant uptake and adsorption of matrix particles, which provide attachment sites for microorganisms and contaminants, cannot be ignored. The distribution characteristics of ARGs in different plant tissues were clarified and their transfer mechanism was determined. In conclusion, the main driving factors affecting ARGs in the ecological treatment technology of plant absorption should be grasped, and the removal mechanism of ARGs by root adsorption, rhizosphere microorganisms, and root exudates should be deeply explored, which will be the focus of future research.

Distribution and influencing factors of antibiotic resistance genes of crayfish (Procambarus clarkii) intestine in main crayfish breeding provinces in China

The propagation of antibiotic resistance genes (ARGs) has become a global public health concern. However, the distribution and influencing factors of ARGs, especially high-risk ARGs, in the gut of aquaculture animals remain unclear. Here, we employed 16S rRNA gene sequencing and high-throughput quantitative PCR techniques to determine crayfish gut microbiota and ARGs collected from 40 culture ponds in major crayfish farming provinces of China. We detected 74 ARGs in crayfish gut. Among them, the beta-lactamase and tetracycline resistance genes were dominant. The total ARG abundance was the highest in Hubei Province. High-risk ARGs were also found in crayfish gut, and ermB had the highest abundance and distributed in Anhui, Hubei, Henan and Jiangxi Province. In addition, opportunistic pathogens (Streptococcus, Aeromonas and Acinetobacter) might be potential hosts for ARGs, including high-risk ARGs. Finally, habitat, environmental factors (NO₃-N, pH and temperature), microbial alpha diversity and mobile genetic elements (MGEs) showed significant influence on ARGs profiles. Generally, our results illustrate that ARGs are prevalent in crayfish gut and may pose potential risk to human health, which will help develop targeted strategies for the risk management and assessment of ARGs in the aquaculture.

Removal of pharmaceuticals by vertical flow constructed wetland with different configurations: Effect of inlet load and biochar addition in the substrate

Pharmaceuticals (PCs) residues are considered an emerging threat to the environment due to their persistency, ecotoxicity and bioaccumulative nature. To study the PC (amoxicillin, AMX; caffeine, CF; ibuprofen, IBU) removal efficiency of vertical flow constructed wetland (VFCW), three setups of VFCWs were configured: SB (substrate matrix + biochar (BC)); SBP (substrate matrix + BC + plant); SP (substrate matrix + plant) and changes in effluent PC load was estimated at 24, 48, 72, 96, 120, 144 and 168 h intervals. SBP with an influent load of 1,000 μg L^-1 showed the maximum removals of 75.51% (AMX), 87.53% (CF), and 79.93% (IBU) significantly higher than that of SB and SP (p < 0.00). Results showed an inverse relationship between removal efficacy and influent PCs loading. The average removal (%) by VFCWS (of all studied setups) was in the order: 66.20 > 47.88 > 39.0 (IBU), 56.56 > 42.12 > 34.36 (AMX), and 74.13 > 64.0 > 52.07 (CF) with 1,000, 5,000 > 10,000 μg L^-1 influent load, respectively. The maximum removal of COD, NH₄⁺-N, and NO₃-N was recorded at 88.8%, 83.1%, and 64.9%, respectively in SBP, and their removal was hardly affected by influent PC concentration. In summary, planted VFCW spiked with BC could be a viable approach for the removal of PCs in wastewater. The impact of PC load on plant toxicity in VFCWs can be taken as a research problem for future work in this series.

A review on antibiotics removal: Leveraging the combination of grey and green techniques

Antibiotics are currently a major source of concern around the world due to the serious risks posed to human health and the environment. The performance of the secondary wastewater treatment processes/technologies (representing grey process) and constructed wetlands (CWs) (typical green process) in removing antibiotics and antibiotic resistance genes (ARG) was reviewed. The result showed that the grey process mainly removes antibiotics, but does not significantly remove ARG, and some processes may even cause ARG enrichment. The overall treatment in CWs is better than WWTPs, especially for ARG. Vertical subsurface flow CWs (VFCWs) are more conductive to antibiotics removal, while horizontal subsurface flow CWs (HFCWs) have a better ARG removal. More importantly, this review admits and suggests that the combination of grey process with green process is an effective strategy to remove antibiotics and ARG. The most advantage of the combination lies in realizing complementary advantages, i.e. the grey process as the primary treatment while CWs as the polishing stage. The efficiency of such the hybrid system is much higher than either single treatment process.

The prevalence and removal of antibiotic resistance genes in full-scale wastewater treatment plants: Bacterial host, influencing factors and correlation with nitrogen metabolic pathway

This study investigated the prevalence of antibiotic resistance genes (ARGs) in the influent, effluent, and waste activated sludge (WAS) of eight full-scale municipal wastewater treatment plants (WWTPs) in Shanghai, China. A comprehensive understanding of the correlation between various influencing factors (characteristics of wastewater and WAS, antibiotics, metals, mobile genetic elements) and ARGs was explored. Among the eight full-scale WWTPs, the Unitank process was inefficient in removing typical ARGs compared with continuous-flow anaerobic-anoxic-aerobic and oxidation ditch processes. Antibiotic was identified as the most influential factor affecting the occurrence of ARGs in wastewater, followed by flow rate and nutrients. Positive correlations were observed between antibiotics and their corresponding ARGs in the influent, while this correlation disappeared in the WAS. Class I integron, wastewater characteristics (nitrogen and flow rate), antibiotics (ofloxacin, sulfamethazine, and erythromycin), metals (Mg, Al, Fe, and Mn) were identified as crucial factors comprehensively affecting the distribution of ARGs in WAS. Dissimilatory nitrate reduction profoundly influenced the fate of ARGs during wastewater treatment processes, and K04561 (norB), K02567 (napA), K00262 (gdhA), K00284 (gltS) were identified as the most significant genes in the nitrogen metabolism pathway (ko00910). This study provides a new perspective for comprehensively understanding the occurrence and dissemination of ARGs in WWTPs.

Restriction of biosolids returning to land: Fate of antibiotic resistance genes in soils after long-term biosolids application

Although the utilization of biosolids in agricultural lands is widely considered as an effective way to improve resource reuse, the presence of antibiotic resistance genes (ARGs) severely restricts biosolids returning to fields. A 12-year long-term experiment with different biosolids application rates (from 0 to 36 t ha^-1 yr^-1) was conducted to study the effect of biosolids application on shaping ARGs in soil. Biosolids application significantly increased ARGs abundance in the soil, except for MBS treatment (9 t ha^-1 yr^-1 biosolids application). The abundance of ARGs in soil did not increase linearly with the dose of biosolids applied, but they were significantly (P < 0.05) positively correlated. A total of 173 subtypes were detected, among them mobile genetic elements (MGEs), aminoglycoside, and multidrug resistance genes were the most dominant types. Except for MBS treatment, most of the ARGs detected were enriched in amended soils after long-term continuous biosolids application. Specifically, tetPA, sul1, mefA, and IS6100 were highly enriched in all amended soils. In addition, biosolids application increased soil nutrients and heavy metals, and changed the soil microbial community, all of which affected ARGs formation. But MGEs may be a greater factor for shaping ARGs profiles than soil properties. Overall, controlling the rate of biosolid application is the key to reducing the accumulation and horizontal transfer of ARGs in soils.

Antibiotic resistance genes removals in stormwater bioretention cells with three kinds of environmental conditions

Recently, increasing attention has been paid to antibiotic resistance genes (ARGs) in stormwater runoff. However, there is still no available literature about ARGs removals through stormwater bioretention cells. Batch experiments were conducted to investigate target ARGs (bla_TEM, tetR and aphA) removals under three environmental conditions, including substrate (weight ratios of sand to soil), hydraulic loading rate (HLR) and submerged area depth. The target ARGs removals were the largest (more than 5 log in the bottom outlets) in bioretention cells with 8:2 ratio of sand to soil, HLR 0.044 cm³/cm²/min and 150 mm of submerged area depth. The proportion for both iARGs and eARGs had little effect on target ARGs removals (expect extracellular bla_TEM), although distributions of target ARGs were different in substrate layers. Adsorption behavior tests indicated that both kinetics and isotherms of target ARGs adsorption by biofilms were more suitable to explain their best removals for bioretention cells with 8:2 ratio of sand to soil than that by substrate. At phylum and genus levels, there were respectively 6 dominant microflora related significantly to target ARGs levels, and their relationships changed obviously under different environmental conditions, suggesting that regulating the dominant microflora (like Verrucomicrobia and Actinobacteria) could be feasible to change ARGs removals.

Insight into using a novel ultraviolet/peracetic acid combination disinfection process to simultaneously remove antibiotics and antibiotic resistance genes in wastewater: Mechanism and comparison with conventional processes

In this study, the simultaneous removal mechanism of antibiotics and antibiotic resistance genes (ARGs) was investigated using the novel ultraviolet/peracetic acid (UV/PAA) combination disinfection process and conventional disinfection processes were also applied for comparison. The results showed that UV/PAA disinfection with a high UV dosage (UV/PAA-H) was most effective for the removal of tetracyclines, quinolones, macrolides and β-lactams; their average removal efficiencies ranged from 25.7% to 100%, while NaClO disinfection was effective for the removal of sulfonamides (∼81.6%). The majority of ARGs were well removed after the UV/PAA-H disinfection, while specific genes including tetB, tetC, ermA and bla_TEM significantly increased after NaClO disinfection. In addition, β-lactam resistance genes (-35.9%) and macrolides resistance genes (-12.0%) remarkably augmented after UV/NaClO disinfection. The highly reactive oxidation species generated from UV/PAA process including hydroxyl radicals (•OH) and carbon-centered organic radicals (R-C•), were responsible for the elimination of antibiotics and ARGs. Correlation analysis showed that tetracycline, sulfonamide and macrolide antibiotics removal showed a positive correlation with the corresponding ARGs, and a low dose of antibiotic residues played an important role in the distribution of ARGs. Metagenomic sequencing analysis showed that UV/PAA disinfection could not only greatly decrease the abundance of resistant bacteria but also downregulate the expression of key functional genes involved in ARGs propagation and inhibit the signal transduction of the host bacteria, underlying that its removal mechanism was quite different from that of NaClO-based disinfection processes. Our study provides valuable information for understanding the simultaneous removal mechanism of antibiotics and ARGs in wastewater during the disinfection processes, especially for the novel UV/PAA combination process.

Environmental heterogeneity determines the response patterns of microbially mediated N-reduction processes to sulfamethoxazole in river sediments

The widespread occurrence of antibiotics in aquatic ecosystems leads to potential ecological risks to organisms, in turn affecting microbially mediated processes. Here, we investigated the response of dominant N-reduction processes to the frequently detected antibiotic sulfamethoxazole (SMX) along the Chaobai River with regional environmental heterogeneity, including denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), and nitrous oxide (N₂O) release. We found two divergent SMX response patterns for denitrification in contrasting scenarios of geochemical properties. In the context of low nitrate and carbon, SMX weakened denitrification with a slightly stimulation first. Whereas SMX directly inhibited denitrification when nitrate and carbon were sufficient. High SMX concentration suppressed anammox (26-72%) and DNRA activities (48-84%) via restraining the activities of anammox and DNRA bacteria. Notably, SMX increased the contribution of denitrification to N-reduction at the expense of DNRA to N-reduction, leading to a shift in nitrogen conversion towards denitrification. Additionally, SMX stimulated N₂O emission (up to 91%) due to superior restraint on process of N₂O reduction to N₂ and an incline for N-reduction towards denitrification, thereby exacerbating greenhouse effect. Our results advance the understanding of how nitrogen cycling is affected by SMX in aquatic ecosystems with environmental heterogeneity.

Ecological impact of antibiotics on bioremediation performance of constructed wetlands: Microbial and plant dynamics, and potential antibiotic resistance genes hotspots

Constructed wetlands (CWs) are nature-based solutions for treating domestic and livestock wastewater which may contain residual antibiotics concentration. Antibiotics may exert selection pressure on wetland's microbes, thereby increasing the global antibiotics resistance problems. This review critically examined the chemodynamics of antibiotics and antibiotics resistance genes (ARGs) in CWs. Antibiotics affected the biogeochemical cycling function of microbial communities in CWs and directly disrupted the removal efficiency of total nitrogen, total phosphorus, and chemical oxygen demand by 22%, 9.3%, and 24%, respectively. Since changes in microbial function and structure are linked to the emergence and propagation of antibiotic resistance, antibiotics could adversely affect microbial diversity in CWs. The cyanobacteria community seemed to be particularly vulnerable, while Proteobacteria could resist and persist in antibiotics contaminated wetlands. Antibiotics triggered excitation responses in plants and increased the root activities and exudates. Microbes, plants, and substrates play crucial roles in antibiotic removal. High removal efficiency was exhibited for triclosan (100%) > enrofloxacin (99.8%) > metronidazole (99%) > tetracycline (98.8%) > chlortetracycline (98.4%) > levofloxacin (96.69%) > sulfamethoxazole (91.9%) by the CWs. This review showed that CWs exhibited high antibiotics removal capacity, but the absolute abundance of ARGs increased, suggesting CWs are potential hotspots for ARGs. Future research should focus on specific bacterial response and impact on microbial interactions.

Effects of Sulfamethoxazole on Growth and Antibiotic Resistance of A Natural Microbial Community

Diffuse environmental antibiotic and antibiotic resistance gene contamination is increasing human and animal exposure to these emerging compounds with a consequent risk of reduction in antibiotic effectiveness. The present work investigated the effect of the antibiotic sulfamethoxazole (SMX) on growth and antibiotic resistance genes of a microbial community collected from an anaerobic digestion plant fed with cattle manure. Digestate samples were used as inoculum for concentration-dependent experiments using SMX at various concentrations. The antibiotic concentrations affecting the mixed microbial community in terms of growth and spread of resistant genes (sul1, sul2) were investigated through OD (Optical Density) measures and qPCR assays. Moreover, SMX biodegradation was assessed by LC-MS/MS analysis. The overall results showed that SMX concentrations in the range of those found in the environment did not affect the microbial community growth and did not select for antibiotic-resistant gene (ARG) maintenance or spread. Furthermore, the microorganisms tested were able to degrade SMX in only 24 h. This study confirms the complexity of antibiotic resistance spread in real matrices where different microorganisms coexist and suggests that antibiotic biodegradation needs to be included for fully understanding the resistance phenomena among bacteria.

Dose effect of Zn and Cu in sludge-amended soils on vegetable uptake of trace elements, antibiotics, and antibiotic resistance genes: Human health implications

The application of sewage sludge to agricultural fields reduces the need for mineral fertilizers by increasing soil organic matter, but may also increase soil pollution. Previous studies indicate that zinc and copper, as the most abundant elements in sewage sludge, affect plant uptake of other contaminants. This paper aims to investigate and compare the effect of increasing amounts of Zn and Cu in sludge-amended soils on the accumulation of trace elements (TEs), antibiotics (ABs), and antibiotic resistance genes (ARGs) in lettuce and radish. The vegetables were grown under controlled conditions, and the influence on plant physiology and human health were also evaluated. The results show that the addition of Zn and Cu significantly increased the concentration of TEs in the edible tissue of both vegetables. According to the hazard quotient (HQ) of the TEs, the human health risk increased 2 to 3 times and was 3-4 times greater in lettuce than in radish. In contrast to the TEs, the occurrence of ABs and most of the ARGs was higher in radish roots than lettuce leaves. ABs were not detected in lettuce leaves, and the amount of all ARGs except bla_TEM was 10 times lower than in radish roots. On the other hand, the addition of Zn and Cu had no significant effect on the occurrence of ABs and ARGs in the edible part of the vegetables, and no damage was found to plant productivity or physiology. The results show that the consumption of lettuce and radish grown in sewage-sludge-amended soils under tested doses of Cu and Zn does not pose an adverse human health effect, as the total HQ value was always less than 1, and the presence of ABs and ARGs was not found to have any potential impact. Nevertheless, further studies are needed to estimate the long-term effect on human health of crops grown under frequent application of biosolids in arable soil.

Occurrence and distribution of five antibiotic resistance genes during the loading period in sludge treatment wetlands

The objectives of this study were to clarify the distribution as well as the removal mechanism of antibiotic resistance genes (ARGs) within three sludge treatment wetlands (STWs) during a loading period of two years. Three STW units were constructed and run during the loading period: Unit 1 (U1) built with aeration tubes, Unit 2 (U2) built with aeration tubes and reeds, and Unit 3 (U3) built with reeds only. All targeted ARGs, intI1, and 16S rRNA were detected in residual sludge in the order of magnitude: 16S rRNA>sul1>intI1>sul2>tetC>tetA>ermB. The abundance of the five targeted ARGs, intI1, and 16S rRNA increased in residual sludge, during the loading period, which may be due to the increase in bacteria caused by the continuous import of exogenous nutrients. However, STWs can also remove ARGs from sewage during the loading period and the mean removal efficiency of five resistance genes was 73.0%. The removal rates of intI1 and 16S rRNA were 73.5% and 78.6%, respectively. Positive correlations were detected in abundance of most ARGs and intI1, as well as 16S rRNA (P < 0.05), indicating intI1 plays a vital part in the propagation of ARGs. The removal of bacteria harboring these genes also occurs in the STW units.

Catalytic liquefaction of sewage sludge to small molecular weight chemicals

The catalytic hydrotreatment of sewage sludge, the wet solid byproducts from wastewater treatment plants, using supported Ir, Pt, Pd, Ru catalysts had been investigated with different solvent conditions. Reactions were carried out in a batch set-up at elevated temperatures (400 °C) using a hydrogen donor (formic acid (FA) in isopropanol (IPA) or hydrogen gas), with sewage sludge obtained from different sampling places. Sewage sludge conversions of up to 83.72% were achieved using Pt/C, whereas the performance for the others catalysts is different and solvent had a strong effect on the conversion rate and product constitution. The sewage sludge oils were characterised using a range of analytical techniques (GC, GC-MS, GCxGC, GPC) and were shown to consist of monomers, mainly alkanes and higher oligomers.