Determination of minimum inhibitory concentration and half maximal inhibitory concentration of antibiotics and their degradation products to assess the eco-toxicological potential

Abstract

Numerous studies have been reported on today’s ubiquitous presence of antibiotics in surface waters causing the emergence of multidrug-resistant bacteria. Advanced water treatment procedures aim at the complete prevention and elimination of antibiotics from entering natural water bodies. In this study, photoinduced degradation processes using UVC-irradiation were applied toward selected fluoroquinolone, tetracycline, macrolide, and sulfonamide antibiotics. Photodegradation products were elucidated using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). Rate constants and quantum efficiencies were determined for the active substances and their photo-transformation products. As a measure of ecotoxicity, minimum inhibitory and half-maximal inhibitory concentrations were determined against the Gram-negative bacterium Pseudomonas fluorescens and the Gram-positive Bacillus subtilis in a standard assay format. These values were further recorded as a function of UV exposure time. The irradiation time-dependent increase of minimum inhibitory concentration (MIC) values agreed well with the kinetic models. After 10?min of irradiation, the compound solutions ceased to inhibit bacterial cell growth, indicating removal of the pharmaceutical activity. These findings were found in agreement with quantitative structure–activity relationship analysis. The combination of microbiological activity testing, molecular structure analysis, chemical kinetic investigation, and quantitative structure–activity relationship models proved to be able to predict irradiation times and evaluate potential ecotoxicological hazard of the irradiated drugs.     

Photodegradation of the antibiotic spiramycin studied by high-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry

The degradation of spiramycin induced by ultraviolet (UV) irradiation was studied at pH 3–4, 6–7 and 8–9 using high-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry. Furthermore, the influence of hydrogen peroxide and oxygen on the photodegradation was investigated. Three degradation products were observed in the presence of oxygen and four in the absence of oxygen. The degradation kinetics were monitored as mass area-time curves, analyzed and described using subsequent follow-up reaction first-order models. The m/z values of the degradation products were determined to be 160, 322 and 366, the latter representing two separate products, the sugar moieties of spiramycin. Remainders of the macrocycle or the intact lactone ring of spiramycin were not observed, since the conjugated π-electron system was assumed photoexcited and thus undergoing photodegradation and fast destruction of the ring. The kinetic of the degradation of spiramycin itself was described using a first-order model. The degradation was accelerated upon addition of hydrogen peroxide. In contrast, systematic acceleration depending on pH could not be found. The absence of oxygen did not lead to any significant acceleration. The findings are interpreted in terms of the effectiveness of advanced oxidation processes and their potential use as a fourth purification step in wastewater treatment plants.     

Iron-doped copper 1,4-benzenedicarboxylate as photo-Fenton catalyst for degradation of methylene blue

Abstract

A metal-organic framework of iron-doped copper 1,4-benzenedicarboxylate was synthesized and, for the first time, utilized as a heterogeneous photo-Fenton catalyst for degradation of methylene blue dye in aqueous solution under visible light irradiation. The synthesized materials were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. The influence factors, kinetics, and stability of the synthesized catalysts were investigated in detail. Iron-doped copper 1,4-benzenedicarboxylate showed higher degradation efficiency than pure copper 1,4-benzenedicarboxylate. An almost complete degradation was achieved within 70?min under visible light irradiation at a solution pH of 6, a catalyst loading of 1?g?L^?1, a H₂O₂ dosage of 0.05?mol L^?1 and methylene blue concentration of 50?mg?L^?1. Recycling studies demonstrated that the iron-doped copper 1,4-benzenedicarboxylate is a promising heterogeneous photo-Fenton catalyst for long-term removal of methylene blue dye from industrial wastewater.     

Sonocatalytic degradation of tetracycline antibiotic in aqueous solution by sonocatalysis

Tetracycline (TC), one of the most common antibiotics, is often poorly bio-degraded in conventional wastewater treatment plants. In this study, the sonocatalytic degradation of TC was investigated using TiO₂ nano-particles as catalyst. The effect of pH, initial TC concentrations, reaction times, and H₂O₂ concentrations were evaluated. The efficacy of ultrasonic irradiation alone in the removal of this pollutant was negligible but removal efficiency increased upon addition of TiO₂ up to 250 mg L^?1; increase of pH and initial TC concentration attenuated TC degradation. Addition of H₂O₂ raised the removal efficiency so that complete removal of TC was achieved within 75 min.     

Fenton degradation of dialkylphthalates: products and mechanism

Contamination of wastewater by organic pollutants is a major worldwide issue. For instance plastic additives such as phthalates are found in wastewater. Efficient techniques are thus needed to clean wastewaters. The Fenton reaction involving H₂O₂ and Fe(II) salts can be used to treat polluted water. During the Fenton reaction pollutants are decomposed directly by hydroxyl radicals. In some cases toxic by-products are produced. Here dimethyl phthalate, diethyl phthalate, and dipropyl phthalate by-products formed during the Fenton reaction were studied. Fenton degradation of selected phthalates yielded numerous transformation products such as hydroxylated phthalates. The hydroxylation reaction occurred at the aromatic ring of phthalates and yielded mono- and dihydroxylated phthalates. For monohydroxylated phthalate, 3-hydroxy- and 4-hydroxydialkylphthalates are the main transformation products. In addition to hydroxylated derivatives, aliphatic chain degraded mono- and dihydroxylated phthalates were also detected.     

Photodegradation of chromophoric dissolved organic matters in the water of Lake Dianchi,China

Water samples were taken from Lake Dianchi, on the Yungui Plateau of southwest China, and experiments were conducted to simulate the photochemical degradation characteristic of chromophoric dissolved organic matter (CDOM) in the lake water. Three groups of experiments under different light conditions: ultraviolet (UV) light, visible light, and dark, were done and variations of fluorescence properties, UV absorbance, and dissolved organic carbon (DOC) concentrations during the experiments were analyzed to study the photodegradation process of CDOM with time. The result showed that light irradiation led to significant photochemical degradation of CDOM, resulting in changes in florescent properties, absorbance losses, decreases in aromaticity and average molecular weight, as well as decline in DOC concentration in the water. It was also observed that UV irradiation had greater effect than visible light did. However, various fluorophores had different sensitivities to the same irradiation condition, that is, protein-like fluorophore at the low excitation wavelengths is more sensitive to UV irradiation than the other fluorophores, and is more readily to undergo photo-degradation. In addition, visible light irradiation did not have significant impact on DOC in the water, with DOC concentration decrease by 5.57% –59.9% during the experiment time. These results may provide new knowledge on the environment behavior of CDOM in the water of Lake Dianchi.     

Sulfamethoxazole removal from polluted water by immobilized photocatalysis

The photocatalytic activity of TiO₂ deposits (Degussa P25 and Millennium PC500) has been studied using sulfamethoxazole (SMX) as a model water pollutant and a UV fluorescent lamp as a light source (365 nm). Both catalysts have shown very similar properties in the photocatalytic degradation of SMX. Special attention has been given to the effect of the irradiation time, pH, and pollutant concentration. No mass-transfer limitations are observed. The degradation of SMX is accelerated at low concentration, and the photocatalytic degradation kinetics obey the Langmuir–Hinshelwood model, allowing the adsorption and apparent rate constants to be determined for both catalysts.     

Microbiological degradation of polycyclic aromatic hydrocarbons: Anthracene,benzo(K)fluoranthene,dibenzothiophene, benzo(H) quinoline and 2‐nitronaphthalene

Biodegradation experiments of various polycyclic aromatic hydrocarbons were studied with mixed bacteria culture under aerobic conditions. An easy‐to‐handle clean‐up procedure was developed for PAH and their metabolites simultaneously as well as a gc‐ms‐method to identify and quantify these compounds.

Anthracene and dibenzothiophene are completely degradable in an aqeous system, whereas biodegradation of benzo(k)fluoranthene and benzo(h)quinoline is possible only in an oil‐in‐water‐system with dodecane as cosubstrate. No degradation of nitronaphthalene was observed in aqueous systems. New metabolites are 2,3‐dihydroxybenzothiophene, hydroxybenzothiophenecarbonic acid and benzothiophenequinone for dibenzothiophene and hydroxyfluoranthenic acid for benzo(k)flouranthene. Whereas the former metabolites are degradable under the experimental conditions, the latter accumulates during the degradation experiment.

The results are important for microbiological wastewater treatment, since knowledge of biodegradation processes is indespensable for the successful treatment of PAH‐containing wastewater.     

Effect of acetate and propionate on the production and characterization of soluble microbial products (SMP) in aerobic granular sludge system

It is well known that soluble microbial products (SMP) derived from biological systems found in wastewater treatment plant effluent are responsible for chemical oxygen demand (COD). Aerobic granular sludge (AGS) is recognized as an efficient and innovative approach for wastewater treatment. Acetate and propionate as two dominant organic substances in wastewater need to be effectively removed before discharge. The aim of this study was to investigate the effectiveness of acetate and propionate to interfere with the accumulation, molecular weight (MW) distribution and composition of SMP in aerobic granular sludge (AGS) system using two identical sequencing batch reactors (SBR) named R1 and R2, respectively, thus reducing the COD. The results demonstrated that more SMP accumulated in R1 in presence of acetate compared to R2 treated with propionate. A positive correlation for SMP formation was detected as evidenced by aeration rates, but a negative correlation with hydraulic retention time (HRT). The MW distribution analysis suggested that small molecules (MW <3?kDa) were the dominant fraction of SMP in R1 and R2, accounting for 57–79% and 39–61%, respectively. In addition, gas chromatography-mass spectrometry (GC-MS) demonstrated that esters, alkanes, alkenes and alcohols were the predominant low-MW SMP in R1 and R2. More peaks were present in R2 (61) than R1 (46). Esters were the predominant SMP (39%) in R1, while alkanes were the predominant SMP (31%) in R2. Further, microbial community analysis indicated that more α- and γ-Proteobacteria groups which readily utilize low-MW SMP were found in R2 compared to R1-granules which may have contributed to less SMP accumulated in R2. The abundant genera in the granules were Zoogloea and Azoarcus, in particular, a greater quantity of Azoarcus was detected in R2 than R1-granules, which may be associated with higher degradation of aromatics in SMP.     

城市污水中典型卤代苯酚分布及其光降解行为研究

卤代苯酚(HPs)是一类广泛存在于水体中的污染物,其在污水处理厂出水中的存在及迁移转化会产生一定的健康和生态风险。探究卤代苯酚在环境中的转化行为非常重要。光降解反应是酚类物质在水体中迁移转化的重要途径,实际水体中的有机质等对卤代苯酚的光降解会产生一定的影响。对大连市区6家污水处理厂出水中卤代苯酚的污染状况进行了调查,结果显示在所有出水中总HPs的浓度范围为77.2~168.6 ng·L-1。在所有检出的卤代苯酚中,五氯酚和2,6-二氯酚浓度较高,且检出频率均为100%,检出浓度范围分别为10.8~166.7 ng·L-1和0.1~72.2 ng·L-1。在模拟太阳光照射条件下,选取2种氯酚和2种溴酚研究它们在污水样品与纯水中光降解行为,从卤原子取代的程度和种类两方面对不同卤代苯酚光降解的规律进行类比,分析了其光降解特性。此外,对比分析了不同污水厂出水的对同种卤代苯酚降解速率的影响,发现出水的p H值、溶解性有机质等因素,都可能影响卤代苯酚的光降解。     

The toxic and environmental evaluation of pyrolytic liquids by Allium cepa test

In this study, liquid products obtained from the pyrolysis of hazelnut shell (HS), with and without ultra-high molecular weight polyethylene (UHMWPE), were subjected to the Allium cepa test system. Pyrolysis in conjunction with the A. cepa test is a promising technology not only from the perspective of energy savings and a source of precious material, but in terms of the removal of hazardous material from the environment in safe manner. Dosages of pyrolytic liquids dissolved in water were determined according to lethal dose (LD₅₀), with three different solution concentrations. The preparates were dyed with acetocarmine. The mitotic index decreased and chromosomal aberration, especially stickiness and c-mitosis, increased with dosage and time. The addition of UHMWPE to HS in the pyrolysis process resulted in less harmful chemical agents, as observed by the relatively higher mitotic index and lower levels of chromosomal aberration.     

Tertiary treatment of municipal wastewater using isolated algal strains: treatment efficiency and value-added products recovery

ABSTRACT

Two microalgal strains (Chlorella sorokiniana, A&B,) grown optimally at pH 9 (A) and 7 (B) were isolated from a municipal wastewater treatment plant. These strains were used to check their efficacy for nutrients and organic carbon removal capacities from the tertiary wastewater. The strains were characterised using 18S rDNA sequencing method and both the strains closely related to Chlorella sorokiniana. Different inoculum doses (IDs) of both the strains were tried to check their efficacy on wastewater treatment. Due to the increase in the IDs, hydraulic retention time decreased from 6 d to 1?d. On an average, 12–100% of total kjeldahl nitrogen, 53–96% NO₃–N, and 59–92% PO₄–P, were removed. Despite the same growth environment, strain A with the highest ID (700?mg/L) showed the best performance in terms of overall organic carbon removal, nutrient removal, and value-added products recovery. Strain A showed an increase in carbohydrate and protein content by 42% and 13%, respectively. Both the strains showed luxury phosphorus uptake and found suitable for advanced wastewater treatment.     

Accumulation, distribution and transformation of DDT and PCBs by Phragmites australis and Oryza sativa L.: II. Enzyme study

Two wetland plant species, Phragmites australis and Oryza sativa, were grown in a glasshouse under hydroponics conditions. Enzyme extracts from different parts of the plants were used to determine the transformation rate of o,p′-DDT, p,p′-DDT and PCBs. The organic pollutants were directly spiked into the enzyme extracts, and samples were collected every 30 min and analyzed with a GC-ECD. Root extracts of P. australis readily degraded and transformed DDT and some PCB congeners with a low degree of chlorination. In contrast, crude extracts of O. sativa showed no appreciable degradation or transformation of DDT or PCBs. Inhibition studies indicated that the degradation and transformation of both DDT and PCBs by P. australis enzymes were partly mediated by peroxidase and the plant P-450 system. PCBs with a high degree of chlorination were highly resistant to transformation or degradation by plant enzymes. Both wetland plant species accumulated substantial quantities of the persistent organic chemicals but had different degradation capacities. The enzyme systems in P. australis were much more effective that those in rice in the degradation and transformation of the organic pollutants.     

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S₂O ₈ ^2? ) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01?C0.15 mol·L^?1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L^?1 at 90°C and 0.06 mol·L^?1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.     

Electrochemical treatment of wastewater to remove contaminants from the production and disposal of plastics: a review

Wastewater is major source of contaminants originating from the production, usage, and disposal of plastic materials. Due to their poor biodegradability of these contaminants in municipal wastewater treatment plants, additional advanced oxidation processes such as electrochemical treatments have been developed to improve the standard biological treatment. Here we review the applications of electrochemical treatments of wastewater for the removal of the following plastic contaminants: bisphenol A, phthalic acid esters, and benzotriazoles. We present the effectiveness of treatment in terms of contaminant removal and mineralization; the identification of transformation products; toxicity assessment; and process energy requirements. In the present review, we have focused on the applications of electrochemical treatments of wastewater for the removal of three important groups of contaminants originating mainly from plastics: bisphenol A, phthalic acid esters, and benzotriazoles. The review focuses on the research of electrochemical treatments for these contaminants from the last five years. The papers are assessed from the point of i) effectiveness of treatment in terms of contaminant removal and mineralization; ii) identification of transformation products; iii) toxicity assessment; iv) processes’ energy requirements. Electrochemical treatments were confirmed to be a viable option for the removal of selected contaminants from wastewater.

     

地表水中抗生素复合残留对水生生物的毒性及其生态风险评价

针对上海地区地表水中混合并持久残留的抗生素对水生态的危害,测试了3种主要被使用的抗生素(磺胺甲恶唑,SMZ;土霉素,OTC;氟苯尼考,FF)对4个不同营养级的水生生物代表种(蛋白核小球藻、费氏弧菌、大型蚤和斑马鱼胚胎)的单一毒性和联合毒性,并进一步对生态风险进行评估来探究抗生素对水生态系统的综合作用。研究表明:水生生物对单一抗生素暴露的毒性敏感顺序为:蛋白核小球藻斑马鱼胚胎费氏弧菌大型蚤。用联合指数(CI)来评价抗生素二元混合物之间的相互作用时发现对于不同水生模式生物,抗生素之间的相互作用方式以拮抗作用(CI1)为主。通过与浓度加和(CA)和独立作用(IA)2个传统模型的预测效果比较,发现CI模型能准确预测到抗生素联合毒性偏离相加作用。由于养殖废水中这3种抗生素的含量均远高于其他水体(如黄浦江、长江口、工厂废水),其对不同营养级的水生生物均表现出较高的风险性,需要对养殖废水采取相应的风险削减措施;相比之下,其他水体中抗生素对费氏弧菌、斑马鱼胚胎、大型蚤均表现出低风险,但是对蛋白核小球藻仍具有一定的风险性,需要警惕抗生素对水体初级生产者的风险性。     

Effect of humic acids,nitrate and oxygen on the photodegradation of the flubendiamide insecticide: identification of products

Flubendiamide is a ryanodine insecticide that shows a strong insecticidal activity and is relatively safe for non-target organisms. Actually only flubendiamide and its product desiodo-flubendiamide have been studied during catalytic degradation using TiO₂ and ZnO. Therefore, here we tested the photocatalytic removal of flubendiamide in the presence of nitrates or humic acids. Degradation kinetics were monitored using high-performance liquid chromatography ultraviolet–visible detector. Product identification was done using a high-resolution time-of-flight mass spectrometer coupled to a gas chromatograph (GC-HRMS). Results show that the addition of humic acids at 10 mg l^?1 increased the removal of flubendiamide more than five times. The addition of nitrate ions at 10 mg l^?1 had no influence. The removal of flubendiamide was more than ten times faster in experiments with oxygen purging. Fourteen degradation products were identified, which can be classified into three groups: phthalimide and related phthalic acid derivatives, fluorinated species related to the second amide moiety, and advanced transformation products.     

First approach of the selective treatment of water by heterogeneous photocatalysis

Photocatalytic reactions using titanium dioxide are of great interest due to their possible applications to solar energy storage and detoxification of wastewater. However, TiO₂ has usually given a very poor selectivity. Here we show that, using binary mixtures, it is possible to selectively degrade one molecular substance without any concentration change of another substance. We have studied the influence of the pH and TiO₂ concentration on the selectivity of the degradation of benzamide and 4-hydroxybenzoic acid. With appropriate modifications of both parameters, the selectivity can be improved.     

Optimal parameters for Phanerochaete chrysosporium degradation of terephthalic acid wastewater

The optimal parameters for the degradation of pure terephthalic acid (PTA) wastewater by the white rot fungus Phanerochaete chrysosporium were investigated. The relative mathematical model, objective function equation, constraint equations, constraint conditions and computer program were established in the optimal method. The results showed that the optimal value of the reactor volume needed was 9798 m³. It could save 83.82% of the reactor volume, which was needed for the native bacterium YZ1. This optimal method is simple, useful and economical for average treatment plants. Using the optimal parameters and P. chrysosporium to design and operate the treatment process of PTA wastewater would increase the treatment efficiency and decrease the cost.     

Degradation of dye rhodamine B under visible irradiation with Prussian blue as a photo-Fenton reagent

Rhodamine B can be degraded using Prussian blue as a photo-Fenton like reagent under λ > 420 nm visible irradiation. Kinetic studies show ln(C _o/C _t ) is linearly proportional to the reaction time during the photo-degradation process; thus, the degradation reaction obeys a pseudo-first order kinetic law. It is very interesting that the presence of salinity such as 0.1 M KCl can speed up greatly the degradation rate: the time to achieve 90.0% degradation ratio is shortened from 120.0 to 40.0 min under comparable conditions, which is very useful in the treatment of wastewaters with high content of salinity.