The aquatic fern Azolla, a small-leaf floating plant that lives in symbiosis with a nitrogen fixing cyanobacteria (Anabaena), is an outstanding plant, thanks to its high biomass productivity along with its tremendous rate per unit area for nitrogen-fixation.  The present study investigates the potential growth of Azolla in secondary effluents for removal of COD, phosphorus, and nitrogen. Results have shown that N and P removal at 100 ppm of each component in separate medium turned out to be 36% and 44%, respectively, whereas in case of a mixed solution of these two compounds, N and P removal declined to 33% and 40.5%, respectively. Moreover, results have suggested that in the presence of phosphorus nitrogen absorption decreased. Furthermore, Azolla has revealed a high potential of COD removal by 98.8% in 28 days. Finally, Azolla may be one of the most promising agents to remove COD and treat nitrogen-free and phosphorus-rich wastewaters.

This study systematically explored the effect of humic acid (HA) (as model of natural organic matter) on the kinetics, products and transformation pathway of triclosan (TCS) by laccase-catalyzed oxidation. It was found that TCS could be effectively transformed by laccase-catalysis, with the apparent second-order rate constant being 0.056 U⁻¹ mL min⁻¹. HA inhibited the removal rate of TCS. HA-induced inhibition was negatively correlated with HA concentration in the range of 0–10 mg L⁻¹ and pH-dependent from 3.5 to 9.5. FT-IR and ¹³C NMR spectra showed a decrease of aromatic hydroxyl (phenolic) groups and an increase of aromatic ether groups, indicating the cross-linking of HA via C-O-C and C-N-C bonds during enzyme-catalyzed oxidation. Ten principle oxidative products, including two quinone-like products (2-chlorohydroquinone, 2-chloro-5-(2,4-dichlodichlorophenoxy)-(1,4)benzoquinone), one chlorinated phenol (2,4-dichlorophenol (2,4-DCP)), three dimers, two trimmers and two tetramers, were detected by gas chromatograghy/mass spectrometry (GC-MS) and high performance liquid chromatography/quadrupole time-of-flight/mass spectrometry (HPLC/Q-TOF/MS). The presence of HA induced significantly lesser generation of self-polymers and enhanced cross-coupling between HA and self-polymers via C-O-C, C-N-C and C-C coupling pathways. A plausible transformation pathway was proposed as follows: TCS was initially oxidized to form reactive phenoxyl radicals, which self-coupled to each other subsequently by C-C and C-O pathway, yielding self-polymers. In addition, the scission of ether bond was also observed. The presence of HA can promote scission of ether bond and further oxidation of phenoxyl radicals, forming hydroxylated or quinone-like TCS. This study shed light on the behavior of TCS in natural environment and engineered processes, as well provided a perspective for the water/wastewater treatment using enzyme-catalyzed oxidation techniques.

Sewage sludge from a municipal wastewater treatment facility employing activated sludge process was pre-incubated with varying substrates and mixtures of substrates including metformin (MET), guanylurea (GUA) and glucose. The biomass from enriched cultures separately utilising MET and glucose/GUA was then used to investigate the kinetics of aerobic biodegradation of MET and GUA, respectively, as individual substrates in batch reactors. The results showed that GUA can be completely degraded as a nitrogen source when glucose is provided as a carbon and energy source. On the contrary, MET can be biodegraded as a sole carbon and energy source. However, formation of by-product GUA in solution, which acts as a nitrogen source, rapidly increased the degradation rate of MET resembling autocatalytic behaviour. At low starting concentration of 5 mg/L, the specific substrate utilisation rates of MET and GUA were 0.0033 day⁻¹ and 0.0013 day⁻¹, respectively, which is reported first time in this study. Out of the five biodegradation kinetic models used to describe substrate utilisation, the Quiroga-Sales-Romero (QSR) model was found to predict the measured MET and GUA degradation profile well supported by the goodness of fit parameters. Furthermore, the QSR model was able to describe the autocatalytic degradation of MET and the incomplete biodegradation of GUA in solution.

Ibuprofen (IBU), as a commonly used non-steroidal anti-inflammatory drug (NSAID) and pharmaceutical and personal care product (PPCP), is frequently prescribed by doctors to relieve pain. It is widely released into environmental water and soil in the form of chiral enantiomers by the urination and defecation of humans or animals and by sewage discharge from wastewater treatment plants. This study focused on the alteration of metabolism in the adult zebrafish (Danio rerio) brain after exposure to R-(-)-/S-(+)-/rac-IBU at 5 μg L−1 for 28 days. A total of 45 potential biomarkers and related pathways, including amino acids and their derivatives, purine and its derivatives, nucleotides and other metabolites, were observed with untargeted metabolomics. To validate the metabolic disorders induced by IBU, 22 amino acids and 3 antioxidant enzymes were selected to be quantitated and determined using targeted metabolomics and enzyme assay. Stereoselective changes were observed in the 45 identified biomarkers from the untargeted metabolomics analysis. The 22 amino acids quantitated in targeted metabolomics and 3 antioxidant enzymes determined in enzyme assay also showed stereoselective changes after R-(-)-/S-(+)-/rac-IBU exposure. Results showed that even at a low concentration of R-(-)-/S-(+)-/rac-IBU, disorders in metabolism and antioxidant defense systems were still induced with stereoselectivity. Our study may enable a better understanding of the risks of chiral PPCPs in aquatic organisms in the environment.

Several metabolic parameters were assessed in juvenile Chinook salmon (Oncorhynchus tshawytscha) and staghorn sculpin (Leptocottus armatus) residing in two estuaries receiving wastewater treatment effluent and one reference estuary. We also conducted a laboratory study with fish dosed for 32 days with 16 of the most common contaminants of emerging concern (CECs) detected in feral fish. Several blood chemistry parameters and other indicators of health were measured in fish from the field and laboratory study that were used to assess potential metabolic disruption. The blood chemistry values observed in feral juvenile Chinook salmon were relatively consistent among fish collected from effluent-impacted sites and substantially different compared to reference site fish. These responses were more pronounced in Chinook salmon, which is supported by the disparity in accumulated CECs. The blood chemistry results for juvenile Chinook salmon collected at effluent-impacted sites exhibited a pattern generally consistent with starvation because of similarities to observations from studies of food-deprived fish; however, this response is not consistent with physical starvation but may be contaminant induced. The altered blood chemistry parameters are useful as an early indicator of metabolic stress, even though organismal characteristics (lipid content and condition factor) were not different among sites indicating an early response. Evidence of metabolic disruption was also observed in juvenile Chinook salmon that were exposed in the laboratory to a limited mixture of CECs; however, the plasma parameters were qualitatively different possibly due to exposure route, season, or the suite of CECs. Growth was impaired in the high-dose fish during the dosing phase and the low- and medium-dose fish assayed after 2 weeks of depuration. Overall, these results are consistent with metabolic disruption for fish exposed to CECs, which may result in early mortality or an impaired ability to compete for limited resources.

To evaluate the seasonal distribution of antibiotic resistance genes (ARGs) and explore the reason for their patterns in different seasons and different systems, two wastewater treatment systems were selected and analyzed using high-throughput qPCR. Linear discriminant analysis (LDA) effect size (LEfSe) was used to discover the differential ARGs (biomarkers) and estimate the biomarkers’ effect size. We found that the total absolute abundances of ARGs in inflows and excess sludge samples had no obvious seasonal fluctuations, while those in winter outflow samples decreased in comparison with the inflow samples. Eleven differentially abundant ARGs (biomarker genes, BmGs) (aadA5-02, aac-6-II, cmlA1-01, cmlA1-02, blaOXA10-02, aadA-02, tetX, aadA1, ereA, qacEΔ1-01, and blaTEM) in summer samples and 10 BmGs (tet-32, tetA-02, aacC2, vanC-03, aac-6-I1, tetE, ermB, mefA, tnpA - 07, and sul2) in winter samples were validated. According to 16S rRNA gene sequencing, the relative abundance of bacteria at the phylum level exhibited significant seasonal changes in outflow water (OW), and biomarker bacteria (BmB) were discovered at the family (or genus) level. Synechococcus and vadinCA02 are BmB in summer, and Trichococcus, Lactococcus, Pelosinus, Janthinobacterium, Nitrosomonadaceae and Sterolibacterium are BmB in winter. In addition, BmB have good correlations with BmGs in the same season, which indicates that bacterial community changes drive different distributions of ARGs during seasonal changes and that LEfSe is an acute and effective method for finding significantly different ARGs and bacteria between two or more classes.In conclusion, this study demonstrated the seasonal changes of BmGs and BmB at two wastewater treatment systems.

Knowledge of adsorption behavior of organic contaminants on high heat temperature treated biochars is essential for application of biochars as adsorbents in wastewater treatment and soil remediation. In this study, isotherms of 25 aromatic compounds adsorption on biochars pyrolyzed at 700 °C from biomass including wood chips, rice straw, bamboo chips, cellulose, lignin and chitin were investigated to establish correlations between adsorption behavior and physicochemical properties of biochars. Isotherms were well fitted by Polanyi theory-based Dubinin-Ashtakhov (DA) model with three parameters, i.e., adsorption capacity (Q⁰) and adsorption affinity (E and b). Besides the negative correlation of Q⁰ with molecular maximum cross-sectional areas (σ) of organic compounds, positive correlations of Q⁰ with total pore volume (Vₜₒₜₐₗ) and average diameter of micropore (D) of biochars were observed, indicating that adsorption by biochars is captured by the pore-filling mechanism with molecular sieving effect in biochar pores. Linear solvation energy relationships (LSERs) of adsorption affinity (E) with solvatochromic parameters of organic compounds (i. e., αₘ and π∗) were established, suggesting that hydrophobic effect, π-π interaction and hydrogen-bonding interaction are the main forces responsible for adsorption. The regression coefficient (π₁) and intercept (C) of obtained LSERs are correlated with biochar H/C and Rₘᵢcᵣₒ, respectively, implying that biochars with higher aromaticity and more micropores have stronger π-π bonding potential and hydrophobic effect potential with aromatic molecule, respectively. However, hydrogen-bonding potential of biochars for organic molecules is not changed significantly with properties of biochars. A negative correlation of b with biochar H/C is also obtained. These correlations could be used to predict the adsorption behavior of organic compounds on high heat temperature treated biochars from various biomass for the application of biochars as sorbents and for the estimating of environmental risks of organic compounds in the present of biochars.

The use of reclaimed wastewater for irrigation is foreseen as a possible strategy to mitigate the pressure on water resources in dry regions. However, there is the risk of potential accumulation of contaminants of emerging concern (CECs) in the edaphic environment, their percolation and consequently contamination of aquifers. In the present study, we measured the levels of a wide range of commonly used pharmaceutically active compounds (PhACs) in sewage from a local wastewater treatment plant (WWTP) and in soils irrigated with treated wastewater. Analysis of target compounds showed total concentrations between 73 and 372 μg L⁻¹ in WWTP influents, and from 3 to 41 μg L⁻¹ in effluents. The total concentrations of PhACs detected in surface soil samples were in the range of 2 and 15 ng g⁻¹, with predominance of analgesics and anti-inflammatories (maximum concentration = 10.05 ng g⁻¹), followed by antibiotics and psychiatric drugs (maximum concentration = 5.45 ng g⁻¹ and 3.78 ng g⁻¹, respectively). Both effluent samples and irrigated soils shared similar compositional patterns, with compounds such as hydrochlorothiazide and diclofenac being predominant. Additionally, PhACs were also detected in soil samples at a depth of 150 cm, indicating that these chemical undergo leaching associated with heavy-rain episodes. Their occurrence in soils was affected by temperature too, as maximum concentrations were measured in colder months (up to 14 ng g⁻¹), indicating higher persistence at lower temperatures. Finally, the ecotoxicological risk of PhACs in soil was evaluated by calculating their risk quotients (RQs). The risk was very low as RQ values ranged between <0.01 and 0.07. However, this initial assessment could be improved by future works on toxicity using specific terrestrial organisms.

Cyclophosphamide (CP) and Ifosfamide (IF) are two nitrogen mustard drugs widely prescribed in cancer therapy. They are continuously released via excreta into hospital and urban wastewaters reaching wastewater treatment plants. Although CP and IF, their metabolites and transformation products (TPs) residues have been found in the aquatic environment from few ng L⁻¹ to tens of μg L⁻¹, their environmental toxic effects are still not well known. The present study aimed to investigate the acute and chronic ecotoxicity of CP and IF and their commercially available human metabolites/TPs, i.e. carboxy-CP, Keto-CP and N-dechloroethyl-CP on different organisms of the aquatic trophic chain. The experiments were performed using the green alga Pseudokirchneriella subcapitata, the rotifer Brachionus calyciflorus and the crustaceans Thamnocephalus platyurus and Ceriodaphnia dubia. Moreover, to assess the treatment conditions in regards to parent compound removal and formation of new TPs, CP and IF were UV- irradiated for 6 h, 12 h, 24 h, 36 h and 48 h, followed by toxicity evaluation of treated samples by algae, rotifers and crustaceans. Between the parent compounds, IF resulted as more toxic drug under tested conditions, exerting both acute and chronic effects especially on C. dubia (LC50:196.4 mg L⁻¹, EC50:15.84 mg L⁻¹). Among the tested metabolites/TPs, only carboxy-CP inhibited the reproduction in the rotifer. However, LOEC and NOEC values were calculated for CP and IF for all organisms. In addition, despite a low degradation of CP (28%) and IF (36%) after 48 h UV-irradiation, statistically significant effect differences (p < 0.05) from not-irradiated and irradiated samples were observed in both acute and chronic assays, starting from 6 h UV-irradiation. Our results suggest that the toxic effects found in the aquatic organisms may be attributable to interactions between the parent compounds and their metabolites/TPs.

The urban water ecosystems, such as the landscape ponds are commonly considered under the influence of anthropogenic disturbances, which can lead to the deterioration of the water quality. The prokaryotic communities are considered as one of the best indicators of the water quality. However, there are significant gaps in understanding the ecological processes that shape the composition and function of prokaryotic communities in the urban water ecosystems. Here, we investigated the biogeographic distribution of prokaryotic assemblages in water environments including landscape ponds, drinking water reservoirs, influents (IFs) and effluents (EFs) of wastewater treatment plants of a coastal city (Xiamen), China, by using 16S rDNA amplicon sequencing. Our results indicated that the ponds had higher α-diversity of prokaryotic communities than those in the reservoirs, while there were significant variations in the community compositions among ponds, reservoirs, IFs and EFs. Moreover, ponds harbored a significantly higher proportion of sewage- and fecal-indicator taxa than those in the reservoirs, suggesting the occurrence of exogenous pollution in the urban ponds. Null model analysis revealed that dispersal limitation was the main ecological processes resulting in the divergence of prokaryotic community compositions between ponds and other environments, while dispersal limitation and variable selection played an essential role in the formation of unique prokaryotic assemblages in the reservoirs. Function predication analysis demonstrated that the ponds shared more similar functional profiles with IFs or EFs (e.g., chemoheterotrophy, fermentation, chlorate reducers, nitrate reduction and respiration) than the reservoirs, whereas dominance of photoautotrophy was observed in the reservoirs. Overall, this study provides a profound insight of the ecological mechanisms underlying the responses of prokaryotic communities in the urban landscape ponds to the anthropogenic disturbances.