Advanced oxidation technologies and constructed wetlands in aquaculture farms: What do we know so far about micropollutant removal?

Occurrence, distribution and potential environmental risks of pollutants in aquaculture ponds during pond cleaning in Taihu Lake Basin, China

During the process of cleaning aquaculture ponds, the drainage contributes significantly to antibiotic pollution in the surrounding water environment. Therefore, we conducted a study on the distribution of 26 antibiotics in 57 ponds within the Taihu Lake basin. The results revealed that the detection frequency of antibiotics ranged from 1.75 % to 80.7 %, with the overall detection concentrations ranging from 3.27 to 708.72 ng/L. Among them, the detection rate of 8 antibiotics exceeded 50 %. Regarding the spatial distribution, the concentration of antibiotics was relatively high in aquaculture ponds located in the Changzhou area, with the highest concentration reaching 708.72 ng/L. This observation is likely due to the large size and intensive breeding practices in Changzhou. Fish ponds exhibited a significantly higher total antibiotic concentration of 3.27 to 445.57 ng/L compared to crab ponds (13.01 to 206.30 ng/L) and shrimp ponds (23.17 to 107.40 ng/L). Quinolones and sulfonamides were the predominant antibiotic classes found in fish ponds, accounting for 51.49 % of the total antibiotic concentration. Notably, sulfamethoxazole (SMX) and enrofloxacin (ENR) exhibited the highest antibiotic concentrations. Risk assessments demonstrated that SMX, ENR, and ofloxacin (OFX) contributed significantly to ecological risks. Furthermore, the study found that the tertiary constructed wetland treatment process achieved a remarkable removal rate of 92.44 % for antibiotics in aquaculture wastewater, while other treatment processes displayed limited effectiveness in removing antibiotics. This study addresses the knowledge gap concerning antibiotic pollution during the cleaning process of aquaculture ponds within the Taihu Lake basin.

Exploring the efficiency of tide flow constructed wetlands for treating mariculture wastewater: A comprehensive study on antibiotic removal mechanism under salinity stress

Antibiotic residues in aquaculture environment pose persistent threats to ecology and human health, exacerbated by salt-alkali mariculture wastewater. Yet, little is known about antibiotic removal in tidal flow constructed wetlands (TFCWs) under salinity stress, especially considering TFCW constitution, configuration, and influent water characteristics. Here, the removal performance and mechanism of different TFCWs for sulfonamide antibiotics (SAs: sulfadiazine, sulfamethazine, sulfamonomethoxine, and sulfamethoxazole) and trimethoprim (TMP) from mariculture wastewater (with low, medium, and high salinity) were evaluated alongside comparisons of environmental factors and microbial responses. Results showed substantial reduction in alkalinity (from 8.25-8.26 to 7.65-8.18), salinity (from 3.67-11.30 ppt to 3.20-10.79 ppt), and SAs concentrations (from 7.79-15.46 mg/L to 0.25-10.00 mg/L) for mariculture wastewater using TFCWs. Zeolite and yellow flag configurations exhibited superior performance in SAs removal from mariculture wastewater. Furthermore, the salt-alkali neutralization and oxygen transport capabilities of zeolite, along with the salt-alkali tolerance and biofilm formation characteristics of yellow flag, promoted the development of a biofilm in the rhizosphere dominated by oxidative stress tolerance and facultative anaerobic traits, thereby improving the TFCW microenvironment. Consequently, aerobic (Sulfuritalea and Enterobacter) and salt-tolerant (Pseudomonas) functional bacteria involved in antibiotic degradation were selectively enriched in the zeolite- and yellow flag-TFCWs, contributing to the effective biodegradation of SAs (achieving removal efficiency of 92-97 %). Besides, the high salt-alkali levels of mariculture wastewater and the strong oxygen-enriched capacity of the TFCWs not only enhanced the aerobic oxidation reaction of SAs, but also bidirectionally inhibited the substrate adsorption and anaerobic reduction process of TMP. These findings address a critical gap by investigating the efficacy of TFCWs in removing antibiotics from mariculture wastewater under various salinity conditions, providing essential insights for optimizing wetland design and improving wastewater management in mariculture environments.

Can aged microplastics be transport vectors for organic micropollutants? - Sorption and phytotoxicity tests

Microplastics have been investigated over the last decade as potential transport vectors for other pollutants. However, the specific role of plastic aging, in which plastics change their characteristics over time when exposed to environmental agents, has been overlooked. Therefore, sorption experiments were herein conducted using virgin and aged (by ozone treatment or rooftop weathering) microplastic particles of LDPE - low-density polyethylene, PET - poly(ethylene terephthalate), or uPVC - unplasticized poly(vinyl chloride). The organic micropollutants (OMPs) selected as sorbates comprise a diversified group of priority substances and contaminants of emerging concern, including pharmaceutical substances (florfenicol, trimethoprim, diclofenac, tramadol, citalopram, venlafaxine) and pesticides (alachlor, clofibric acid, diuron, pentachlorophenol), analyzed at trace concentrations (each ≤100 μg L^-1). Sorption kinetics and equilibrium isotherms were obtained, as well as the confirmation that the aging degree of microplastics plays a major role in their sorption capacities. The results show an increased sorption of several OMPs on aged microplastics when compared to pristine samples, i.e. the sorption capacity increasing from one or two sorbed substances (maximum 3 μg g^-1 per sorbate) up to nine after aging (maximum 10 μg g^-1 per sorbate). The extent of sorption depends on the OMP, polymer and the effectiveness of the aging treatment. The modifications (e.g. in the chemical structure) between virgin and aged microplastics were linked to the increased sorption capacity of certain OMPs, allowing to better understand the different affinities observed. Additionally, phytotoxicity tests were performed to evaluate the mobility of the OMPs sorbed on the microplastics and the potential effects (on germination and early growth) of the combo on two species of plants (Lepidium sativum and Sinapis alba). These tests suggest low or no phytotoxicity effect under the conditions tested but indicate a need for further research on the behavior of microplastics on soil-plant systems.

Removal of micropollutants through bio-based materials as a transition to circular bioeconomy: Treatment processes involved, perspectives and bottlenecks

The recent increase in micropollutant levels in water bodies is a growing concern globally. The generation of new materials and techniques for wastewater treatment often involves the release of hazardous wastes and the utilization of energy related to it. This can be resolved by the synthesis of bio-based materials through the use of already released wastes and naturally occurring components, adding their value as reusable resources. These bio-based materials find wide applications for micropollutant elimination and energy tapping due to the presence of various functional groups, large surface area, high stability, and reusability. The processes involved in micropollutant elimination through biomaterials generally include adsorption and degradation. These treatment processes are suggested to depend on various operational parameters like pH, temperature, dose, reaction time, presence of other contaminants, ions, etc. in the system, which may influence the process efficiency. Understanding the potential of bio-based materials many steps can be taken towards its large-scale application to upgrade wastewater treatment plants for micropollutant elimination. Furthermore, the recent advances of bio-based materials in energy storage and conversion have widened its scope for implementation in a circular bioeconomy. The bottlenecks towards such a transition and future recommendations are also presented and discussed.

Pesticide degradation in an integrated constructed wetland: Insights from compound-specific isotope analysis and 16S rDNA sequencing

Carbon isotope analysis and the 16S rDNA sequencing were adopted to investigate the degradation process of chlorpyrifos during its transport in the integrated constructed wetland (ICW). Firstly, the extent of concentration decrease of chlorpyrifos was examined, and the removal efficiency in the first 36 h was found to be the highest. The removal rate reached 96.83 % after 96 h, and this process fit to the first-order kinetic model, with a kinetic constant (k) of 0.066 h^-1. A significant carbon isotope fractionation was observed, with a change of the δ¹³C values from -26.54 ± 0.07 ‰ to -25.41 ± 0.08 ‰. The average chlorpyrifos biodegradation proportion reached 71.23 % (60.42 %-85.04 %), and it was predicted that about 11.79 %-36.41 % of chlorpyrifos removal in the ICW was attributed to abiotic factors. The outlet of the subsurface flow constructed wetland saw the highest D^∗/B^∗ value (1.38-3.88), indicating that the remaining fraction of dilution was much more significant than that of degradation in this period. The top 20 phyla of microbial community were identified in the ICW. Proteobacteria was the most dominant phylum, accounting for >40 % of the bacterial communities in all sampling locations. Acidobacteria and Bacteroidetes were the second and third dominant phyla. At the genus level, the microbial community composition differed more greatly in every stage of the ICW, and the spatial distribution difference was quite significant in the ICW. This study is important to figure out the migration and transformation of chlorpyrifos when the ICW was adopted as a removal tool for organic micro-pollutants, and more similar studies could be carried out in the future to promote the evaluation of pollutant removal capacity of the ICWs, and to further develop the application of stable isotope analysis of compounds in the natural environment.

Influence of chemical structure of organic micropollutants on the degradability with ozonation

The increasing environmental problems due to various organic micropollutants in water cause the search of suitable additional water treatment methods. Gaining experimental data for the large amount and variety of pollutants would consume a lot of time as well as economic and ecologic resources. An alternative approach is predictive quantitative structure-property relationship (QSPR) modeling, which establishes a correlation between the structural properties of a molecules with a biological, physical, or chemical property. Therefore, in this study, QSPR modeling has been conducted using extensive validation techniques and statistical test to investigate the structural influence on the degradability of organic micropollutants with ozonation. In contrast to most of the other studies, the underlying dataset - rate constants for 92 organic molecules - were obtained under standardized conditions with defined experimental parameters. QSPR modeling was executed using a combination of the software PaDEL for descriptor calculation and QSARINS for the modeling process respecting all five OECD-requirements for applicable QSAR/QSPR-models. The final model was selected using a multi-criteria decision-making tool to evaluate the model quality based on all calculated statistical quality parameters. The model included 10 selected descriptors and fingerprints and showed good regression abilities, predictive power, and stability (R² = 0.8221, CCC_tr = 0.9024, Q²_loo = 0.7436, R²_ext = 0.8420, Q²_F1 = 0.8104). The applicability domain of the QSPR model was defined and an interpretation of selected model descriptors has been connected to previous experimental studies. A significant influence of the interpretable descriptors was put into experimental context and compared with previous studies and models. For example, the molar refractivity as a measure of size and polarizability of a molecule and the occurrence of important substructures such as a formamide group seem to decrease the removal rate constant. The contribution of lone electrons entering into resonance as well as the occurrence of fused rings were identified as influences for the increase of the degradability of micropollutants by ozonation.

Antibiotics removal from aquaculture effluents by ozonation: chemical and toxicity descriptors

Antibiotics are often applied in aquaculture to prevent fish diseases. These substances can cause disturbances on receiving waters, when not properly eliminated from the aquaculture effluents. In this work, ozone (O₃) was investigated as a possible oxidizing agent to remove fishery antibiotics from aquaculture effluents: florfenicol (FF), oxytetracycline (OTC), sulfadimethoxine (SDM), sulfamethoxazole (SMX), and trimethoprim (TMP). Batch experiments were performed using ultrapure water and aquaculture effluents spiked with a mixture of target antibiotics at relatively high concentrations (10 mg L^-1 each). OTC, SMX and TMP were fully removed (< 30 min) regardless of the tested conditions, mainly by O₃ direct attack. In contrast, FF was partially removed in 30 min (∼ 10 and 60%, in aquaculture effluents and ultrapure water, respectively), but only in the presence of hydroxyl radicals (HO^•), the FF concentrations reaching levels below the detection limits in ultrapure water after 60 min. In the case of SDM, its degradation was highly influenced by the selected water matrix, but with removals always higher than 68%. In continuous-flow experiments applying more environmentally relevant antibiotic concentrations (100 ng L^-1 each) and low O₃ doses (1.5 mg L^-1), ozonation highly removed (> 98%) all tested antibiotics from aquaculture effluents with a hydraulic retention time (HRT) of 10 min, except FF (68%). Although by-products were detected in treated samples, zebrafish (Danio rerio) embryotoxicity tests did not show a toxicity increase by applying this ozonation treatment. Ozonation is thus a possible solution to remove antibiotics from aquaculture effluents. Still, full-scale studies in aquaculture farms are needed, and generation of HO^• may be favoured to readily oxidize the FF antibiotic.

Environmental impacts of antibiotics addition to algal-bacterial-based aquaponic system

Antibiotics usage is a double-edged sword among the production promotion and environmental aggravation of aquaculture system. In this study, the effects of sulfadiazine addition on algal-bacterial-based aquaponic (AA) system were thoroughly investigated. Results showed that sulfadiazine addition increased the nitrogen (N) and carbon (C) recovery of AA system by 1.3 times and 2.9 times, respectively. Meanwhile, the global warming potential was increased by 63% due to aggravated nitrous oxide (N₂O) emission. This was mainly because sulfadiazine increased the abundance of nirS genes and decreased the abundance of nosZ genes, which subsequently led to higher N₂O accumulation. Furthermore, resistance gene (sul-1, sul-2, and intI-1) abundance in the treatment group was an order higher than that of the control group, which would give rise to the environmental risk for agroecological system. KEY POINTS: • Sulfadiazine addition increased NUE at expense of aggravated GHG emissions. • Sulfadiazine disrupted the balance between the abundance of nirS and nosZ genes. • Sulfadiazine addition increased the resistance gene abundance of AA system.

Optimal Allocation of Water Resources and Eco-Compensation Mechanism Model Based on the Interval-Fuzzy Two-Stage Stochastic Programming Method for Tingjiang River

In this work, based on the upper line of water resources utilization and the bottom line of water environmental quality of "Three Lines, Single Project", a fuzzy optimization method was introduced into the Tingjiang River water resources optimal allocation and eco-compensation mechanism model, which is based on the interval two-stage (ITS) stochastic programming method. In addition, a Tingjiang River water resources allocation and eco-compensation mechanism model based on the interval fuzzy two-stage (IFTS) optimization method was also constructed. The objective functions of both models were to maximize the economic benefits of the Tingjiang River. The available water resources in the basin, the water environmental quality requirements, and regional development requirements were used as constraints, and under the five hydrological scenarios of extreme dryness, dryness, normal flow, abundance, and extreme abundance, the water resources allocation plan of various sectors (industry, municipal, agriculture, and ecology) in the Tingjiang River was optimized, and an eco-compensation mechanism was developed. In this work, the uncertainty of the maximum available water resources in each region and the whole basin was considered. If the maximum available water resources were too high, it would lead to a large waste of water resources, whereas if the maximum available water resources were too low, regional economic development would be limited. Therefore, the above two parameters were set as fuzzy parameters in the optimization model construction in this work. The simulation results from the IFTS model showed that the amount of water available in the river basin directly affects the water usage by various departments, thereby affecting the economic benefits of the river basin and the amount of eco-compensation paid by the downstream areas. The average economic benefit of the Tingjiang River after the optimization of the IFTS model simulation was [3868.51, 5748.99] × 10⁸ CNY, which is an increase of [1.67%, 51.9%] compared to the economic benefit of the basin announced by the government in 2018. Compared to the ITS model, the economic benefit interval of the five hydrological scenarios of extreme dryness, dryness, normal flow, abundance, and extreme abundance was reduced by 28.54%, 44.9%, 31.49%, 40.37%, and 36.43%, respectively, which can improve the economic benefits of the basin and provide more accurate decision-making schemes. In addition, the IFTS simulation showed that the eco-compensation quota paid by downstream Guangdong Province to upstream Fujian Province is [28,116.4, 30,738.6] × 10⁴ CNY, which is a reduction of [8461.404, 110,836] × 10⁴ CNY compared to the 2018 compensation scheme of the government. Compared to the ITS model, the range of eco-compensation values was observed to increase by 9.94%, 54.81%, 15.85%, 50.31%, and 82.90%, respectively, under the five hydrological scenarios, which reduces the burden of ecological expenditure downstream and provides a broader decision-making space for decision-makers and thus enables improved decision-making efficiency. At the same time, after the optimization of the IFTS model, the additional water consumption of the second stage of the Tingjiang River during the extremely dry year decreased by 62.11% compared to the results of the ITS model. The additional water consumption of the industrial sector decreased by 68.39%, the municipal sector decreased by 59.27%, and in the first phase of water resources allocation for 14 districts and counties in the Tingjiang River, industrial and municipal sectors are the main two sectors. After introducing the fuzzy method into the IFTS model, the difference in the water consumption by these two sectors in the basin under different hydrological scenarios can be alleviated, and the waste of water resources caused by too low water allocation or excessive water allocation can be avoided. The national and local (the downstream region) eco-compensation quotas can be indirectly reduced, and the risk of water resources allocation and eco-compensation decision-making in the basin can be effectively reduced.

Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review

In the last decades photocatalysis has become one of the most employed technologies for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are transition metal oxides, in which the band structure allows charge carrier separation upon solar irradiation. The photoinduced charge carrier can thus cause oxidative and reductive redox reactions at the surface, inducing the formation of the radical species able to initiate the AOPs. Despite the great advantages of this process (non-toxic, cheap and environmentally clean), the main drawback lies in the fact that the most efficient semiconductors are only able to absorb UV irradiation, which accounts for only 5% of the total solar irradiation at the Earth’s surface and not enough to generate the required amount of electron-hole pairs. On the other hand, many efforts have been devoted to the sensitization of wide band gap transition metal oxides to visible light, which represents a higher percentage (almost 45%) in the solar electromagnetic spectrum. Among all the strategies to sensitize transition metal oxides to visible irradiation, doping with lanthanides has been less explored. In this regard, lanthanides offer a unique electronic configuration, consisting in 4f orbitals shielded by a 5s5p external shell. This occurrence, coupled with the different occupation of the localized 4f orbitals would provide an astounding opportunity to tune these materials’ properties. In this review we will focus in depth on the modification of two promising photocatalytic transition metal oxides, namely ZnO and ZrO2, with cerium, europium and erbium atoms. The aim of the work is to provide a comprehensive overview of the influence of lanthanides on the structural, optical and electronic properties of the modified materials, emphasizing the effect of the different 4f orbital occupation in the three considered doping atoms. Moreover, a large portion of the discussion will be devoted to the structural-properties relationships evidencing the improved light absorption working mechanism of each system and the resulting enhanced photocatalytic performance in the abatement of contaminants in aqueous environments.

Potential of Bacterial Strains Isolated from Coastal Water for Wastewater Treatment and as Aqua-Feed Additives

Bacteria have various and sustained effects on humans in various fields: molecular biology, biomedical science, environmental/food industry, etc. This study was conducted to evaluate the wastewater treatment capacity and feed-additive fish-growth effect of four strains of bacteria: Pseudoalteromonas mariniglutinosa, Psychrobacter celer, Bacillus albus, and Bacillus safensis. In a wastewater degradation experiment, (i) nitrate-N and nitrite-N were removed within 1 h in all of the 4 bacterial strains; (ii) the removal rates of TAN and TN were higher in all of the strains relative to the B. subtilis. In a feed-additive experiment (5% Kg-1), (i) the growth of fish was higher in all of the 4 bacterial strains with the B. subtilis relative to the commercial feed; (ii) there was no significant growth difference for B. albus and B. safensis relative to the B. subtilis, but growth was higher in P. mariniglutinosa and P. celer. The results indicated that the 4 bacterial strains can be effectively utilized for biological wastewater treatment processes and as aqua-feed.