Hydroxyl-Radical-Induced Degradative Oxidation of β-Lactam Antibiotics in Water: Absolute Rate Constant Measurements

Dorfman L.M., Adams G.E.

Abstract : The reaction rate data of the hydroxyl radical in aqueous solution are compiled and evaluated in this critical review. The values are reported in a series of tables covering addition, hydrogen abstraction, inorganic electron transfer and radical reactions. Rate constants for the hydroxyl radical with biological molecules are included. In addition, the rate constant data for the oxide radical ion are given. Physical properties are listed and the experimental methods employed in OH radical chemistry are reviewed. An analysis involving rate constant data comparisons is made.

Avisar D., Lester Y., Mamane H.

Water and wastewater effluents contain a vast range of chemicals in mixtures that have different chemical structures and characteristics. This study presents a treatment technology for the removal of mixtures of antibiotic residues (sulfamethoxazole (SMX), oxtetracycline (OTC) and ciprofloxacin (CIP)) from contaminated water. The treatment combines pH modification of the water to an optimal value, followed by a photolytic treatment using direct polychromatic ultraviolet (UV) irradiation by medium pressure UV lamp. The pH adjustment of the treated water leads to structural modifications of the pollutant's molecule thus may enhance direct photolysis by UV light. Results showed that an increase of water pH from 5 to 7 leads to a decrease in degradation rate of SMX and an increase in degradation rate of OTC and CIP, when studied separately and not in a mixture. Thus, the optimal pH values for UV photodegradation in a mixture, involve initial photolysis at pH 5 and then gradually changing the pH from 5 to 7 during the UV exposure. For example, this resulted in 99% degradation of SMX at pH 5 and enhanced degradation of OTC and CIP from 54% and 26% to 91% and 96% respectively when pH was increased from 5 to 7. Thus the pH induced photolytic treatment has a potential in improving treatment of antibiotics in mixtures.

Hylton K., Sangwan M., Mitra S.

Antibiotics include a wide range of compounds that in addition to having high solubility in water may be basic, acidic or neutral. Therefore, it is anticipated that no single method would be effective in simultaneously extracting all of these compounds. In recent times, microscale membrane extraction has evolved as a viable sample preparation alternative. The two major approaches are microscale supported liquid membrane extraction (micro-SLME) and microscale liquid-liquid membrane extraction (micro-LLME). An approach that includes micro-LLME as well as micro-SLME for acidic and basic compounds is presented for the extraction and concentration of diverse antibiotics in water. Enrichment factors as high as 2700 were achieved. Relative standard deviations ranged from 1.5% to 2.0%, and detection limits were as low as 92 ng/L.

Prabhakaran D., Sukul P., Lamshöft M., Maheswari M.A., Zühlke S., Spiteller M.

The photodegradation of two fluoroquinolone veterinary antibiotics, difloxacin (DIF) and sarafloxacin (SARA) has been explored for the first time in aqueous systems. The study was performed to evaluate the influence of pH, inorganics, humic substances, and other additives. The drugs followed first-order degradation kinetics in matrix free aqueous medium with a rate constant 'k' value of 0.82 and 0.26 h(-1) for DIF and SARA, respectively. Studies performed at various pH revealed that the photolysis rates dropped sharply at pH >7 for DIF, while SARA dissipated faster with increasing pH. Humic substances acted as light barriers by attenuating the light intensity, to retard the drug degradation process. However, rapid drug dissipation was observed in the presence of additives like acetone, hydrogen peroxide, and phosphates, while inorganics such as fluoride, nitrate, and sulfate did not influence the drug photodegradation. Studies on the photolysis of DIF and SARA in river water revealed that both the drugs degraded rapidly under conditions that were relevant to natural systems, following direct photolysis mechanism. It was observed that SARA was the primary photoproduct of DIF and showed relatively a higher persistence than DIF. The findings were also substantiated by the quantum yield (Phi(c)) calculations. The analytical measurements were carried out with LC-MS/MS.

Beltrán F.J., Aguinaco A., García-Araya J.F., Oropesa A.

In this study, water containing the pharmaceutical compound sulfamethoxazole (SMT) was subjected to the various treatments of different oxidation processes involving ozonation, and photolysis and catalysis under different experimental conditions. Removal rates of SMT and total organic carbon (TOC), from experiments of simple UVA radiation, ozonation (O(3)), catalytic ozonation (O(3)/TiO(2)), ozone photolysis (O(3)/UVA), photocatalytic oxidation (O(2)/TiO(2)/UVA) and photocatalytic ozonation (O(3)/UVA/TiO(2)), have been compared. Photocatalytic ozonation leads to the highest SMT removal rate (pH 7 in buffered systems, complete removal is achieved in less than 5min) and total organic carbon (in unbuffered systems, with initial pH=4, 93% TOC removal is reached). Also, lowest ozone consumption per TOC removed and toxicity was achieved with the O(3)/UVA/TiO(2) process. Direct ozone and free radical reactions were found to be the principal mechanisms for SMT and TOC removal, respectively. In photocatalytic ozonation, with buffered (pH 7) aqueous solutions phosphates (buffering salts) and accumulation of bicarbonate scavengers inhibit the reactions completely on the TiO(2) surface. As a consequence, TOC removal diminishes. In all cases, hydrogen peroxide plays a key role in TOC mineralization. According to the results obtained in this work the use of photocatalytic ozonation is recommended to achieve a high mineralization degree of water containing SMT type compounds.

Song W., Chen W., Cooper W.J., Greaves J., Miller G.E.

Many pharmaceutical compounds and metabolites are being found in surface and ground waters, indicating their ineffective removal by conventional wastewater treatment technologies. Advanced oxidation/reduction processes (AO/RPs), which utilize free-radical reactions to directly degrade chemical contaminants, are alternatives to traditional water treatment. This study reports the absolute rate constants for reaction of three beta-lactam antibiotics (penicillin G, penicillin V, amoxicillin) and a model compound (+)-6-aminopenicillanic acid with the two major AO/RP reactive species: hydroxyl radical ((*)OH) and hydrated electron (e(-)aq). The bimolecular reaction rate constants (M(-1) s(-1)) for penicillin G, penicillin V, amoxicillin, and (+)-6-aminopenicillanic acid for (*)OH were (7.97 +/- 0.11) x 10(9), (8.76 +/- 0.28) x 10(9), (6.94 +/- 0.44) x 10(9), and (2.40 +/- 0.05) x 10(9) and for e(-)aq were (3.92 +/- 0.10) x 10(9), (5.76 +/- 0.24) x 10(9), (3.47 +/- 0.07) x 10(9), and (3.35 +/- 0.06) x 10(9), respectively. To provide a better understanding of the decomposition of the intermediate radicals produced by hydroxyl radical reactions, transient absorption spectra were observed from 1 to 100 micros. In addition, preliminary degradation mechanisms and major products were elucidated using (137)Cs gamma irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

Navalon S., Alvaro M., Garcia H.

This work deals with the chlorine dioxide (ClO(2)) reactivity with three representative beta-lactam antibiotics (penicillin, amoxicillin and cefadroxil) that can be present in natural aquatic resources. Due to the wide use of ClO(2) as disinfection agent our work is of interest to determine the fate of these antibiotics during the water treatment process. Our study shows that antibiotics react stoichiometrically with ClO(2) because increasing amounts of ClO(2) lead to increasing antibiotic disappearance. Concerning the influence of antibiotic structure, penicillin reacts sluggishly with ClO(2), whereas amoxicillin and cefadroxil are highly reactive at either neutral or basic pH. For both reactive antibiotics, hydroquinone together with a wide range of 4-substituted phenols were detected as products. Pretreatment with ClO(2) before chlorination of aqueous solutions of antibiotics reduces the trihalomethane formation as compared with analogous chlorination without ClO(2) pretreatment.

Bailón-Pérez M.I., García-Campaña A.M., Cruces-Blanco C., del Olmo Iruela M.

A sensitive and reliable method using capillary zone electrophoresis with UV-diode array detection (CZE-DAD) has been developed and validated for trace determination of beta-lactam antibiotics in waste, well and river water matrices. Due to the lack of sensitivity of the UV-vis detection, a solvent extraction/solid-phase extraction (SPE) method applied for off-line preconcentration and cleanup of water samples, in combination with an on-line preconcentration methodology named large volume sample stacking (LVSS) have been applied. The analytes included nafcillin, dicloxacillin, cloxacillin, oxacillin, ampicillin, penicillin G and amoxicillin. Average recoveries for water samples fortified with the studied beta-lactams at different concentration levels (1.0, 2.0 and 4.0 microg/L) were ranging between 94 and 99%, with relative standard deviations (RSDs) lower than 10%. The precision, calculated as intra-day and inter-day standard deviations fell within acceptable ranges (3.3-7.2%). The limits of detection were estimated to range between 0.08 and 0.80 microgL(-1) for the studied compounds. All the samples analyzed were negative for all the analytes at these levels of concentration and the method showed its usefulness for the detection of these widely applied beta-lactam antibiotics in different kinds of waters.

Choi K.‐., Kim S.‐., Kim S.‐.

Removal of sulfonamide (SAs) and tetracycline (TAs) classes of antibiotic compound from deionized water and DOC water by powdered activated carbon (PAC) adsorption was evaluated in this study. According to the study results, TAs were more easily adsorbed than SAs although TAs were more hydrophilic than SAs. The phenolic compounds in TAs might be responsible for their high adsorption. Complex formation of TAs with metal and metal oxide on the surface of activated carbon might also contribute to higher adsorption. The hydrophobic effect was important for removal of SAs. More hydrophobic SAs were removed more easily. The carbon type was not important for adsorption of SAs and TAs. Coal based carbon and coconut based carbon showed similar removal efficiencies for these antibiotics. Dissolved organic materials interfered with adsorption of SAs and TAs. Organic interference was more significant for the antibiotic compound, which was more subject to the PAC adsorption. Self-decomposition of SAs and TAs occurred even after 1 day. TAs were more subject to self-decomposition than SAs. Depending on the antibiotic type, more than 60% of TA was removed through self-decomposition.

Ikehata K., Gamal El-Din M., Snyder S.A.

A vast number of persistent organic pollutants have been found in wastewater effluent, surface water, and drinking water around the world. This indicates their ineffective removal from water and wastewater using conventional treatment technologies. In addition to classical persistent organics such as organochlorine insecticides, solvents, and polychlorinated biphenyls, a growing number of emerging pollutants of both synthetic and natural origins have been identified as major environmental pollutants in recent years. A variety of advanced and conventional treatment options have been suggested for the removal and/or destruction of these persistent organics in water and wastewater, such as chemical oxidation, activated carbon adsorption, and membrane filtration. Of these options, chemical oxidation using ozone, alone or in combination with additional physical/chemical agents (i.e., advanced oxidation), has been proved a highly effective treatment process for a wide spectrum of emerging aqueous organic pollut...

Koyuncu I., Arikan O.A., Wiesner M.R., Rice C.

The removal of several hormones and antibiotics by nanofiltration membranes was studied in mixed solutions. The effects of solution chemistry, organic matter and salinity were investigated on the rejection of tetracycline's and sulfanamides and selected hormones and their adsorption on membranes. Tetracyclines were observed to have a high adsorptive affinity for the membrane. Almost 80% of chlorotetracycline was adsorbed on the membrane surface compared with 50% for doxcycline while the adsorption rates for hormones were lower than those obtained for tetracyclines. Addition of calcium, organic matter and salinity had an influence on the rejections. Rejection of sulfanamides was low compared to hormones and tetracyclines. Addition of antibiotics to hormone solution increased the hormone rejections while almost complete rejections were observed for tetracyclines.

Choi K., Kim S., Kim S.

Treatment of seven tetracycline classes of antibiotic (TAs) from raw waters (synthetic and river) was evaluated using coagulation and granular activated carbon (GAC) filtration in this study. Both coagulation and GAC filtration were effective for removal of TAs, and the removal efficiency depended on the type of TAs. GAC filtration was relatively more effective for removal of tetracycline (TC), doxycycline-hyclate (DXC), and chlortetracycline-HCl (CTC), which were difficult to remove by coagulation. It was speculated that TAs would be removed through the charge neutralization and sweep coagulation when poly-aluminum chloride (PACl) was added into the raw waters. The charge neutralization of zwitterionic or negative TAs by cationic Al (III) species drove removal of TAs from the synthetic water. When sufficient alkalinity was available (river water), aluminum hydroxide precipitates were formed. TAs could be removed by being enmeshed into or adsorbed onto the precipitates when PACl was added to the river water.

Mezyk S.P., Neubauer T.J., Cooper W.J., Peller J.R.

Absolute rate constants and degradation efficiencies for hydroxyl radical and hydrated electron reactions with four different sulfa drugs in water have been evaluated using a combination of electron pulse radiolysis/absorption spectroscopy and steady-state radiolysis/high-performance liquid chromatography measurements. For sulfamethazine, sulfamethizole, sulfamethoxazole, and sulfamerazine, absolute rate constants for hydroxyl radical oxidation were determined as (8.3 +/- 0.8) x 10(9), (7.9 +/- 0.4) x 10(9), (8.5 +/- 0.3) x 10(9), and (7.8 +/- 0.3) x 10(9) M(-1) s(-1), respectively, with corresponding degradation efficiencies of 36% +/- 6%, 46% +/- 8%, 53% +/- 8%, and 35% +/- 5%. The reduction of these four compounds by their reaction with the hydrated electron occurred with rate constants of (2.4 +/- 0.1) x 10(10), (2.0 +/- 0.1) x 10(10), (1.0 +/- 0.03) x 10(10), and (2.0 +/- 0.1) x 10(10) M(-1) s(-1), respectively, with efficiencies of 0.5% +/- 4%, 61% +/- 9%, 71% +/- 10%, and 19% +/- 5%. We propose that hydroxyl radical adds predominantly to the sulfanilic acid ring of the different sulfa drugs based on similar hydroxyl radical rate constants and transient absorption spectra. In contrast, the variation in the rate constants for hydrated electrons with the sulfa drugs suggests the reaction occurs at different reaction sites, likely the different heterocyclic rings. The results of this study provide fundamental mechanistic parameters, hydroxyl radical and hydrated electron rate constants, and degradation efficiencies that are critical for the evaluation and implementation of advanced oxidation processes (AOPs).

Leclair C., Yargeau V.

Increasing concern in recent years over the occurrence and fate of low-level concentrations of pharmaceuticals in the aquatic environment stimulates research on alternative treatment methods. This paper presents a study of the degradation of sulphamethoxazole, an antibiotic used on humans and animals in order to treat various bacterial infections, by ozonation. After 4.5 min of treatment, the concentration of sulphamethoxazole was below the HPLC detection limit of 0.6 mgL−1, indicating degradation efficiency higher than 99.24%. This value is comparable and in some cases higher than published data on the degradation in drinking water. Kinetic analysis of the data indicated an overall first-order reaction with a rate constant of 1.0594 min−1 at 20 °C. The reaction order differs with the second-order reaction observed by other researchers. This change of reaction order could be explained by the different treatment conditions used. Preliminary analysis using the FT-IR technique was also performed in order to obtain information on the structure of the degradation products. Further analysis using a GC-MS is needed in order to elucidate the structure of the degradation products. Finally, based on the experiments performed, ozonation seems to be a promising technique for the degradation of antibiotics, even in wastewater.

Ikehata K., Jodeiri Naghashkar N., Gamal El-Din M.

A vast number of pharmaceuticals have been detected in surface water and drinking water around the world, which indicates their ineffective removal from water and wastewater using conventional treatment technologies. Concerns have been raised over the potential adverse effects of pharmaceuticals on public health and aquatic environment. Among the different treatment options, ozonation and advanced oxidation processes are likely promising for efficient degradation of pharmaceuticals in water and wastewater. Recent progress of advanced oxidation of aqueous pharmaceuticals is reviewed in this paper. The pharmaceuticals and non-therapeutic medical agent of interest include antibiotics, anticonvulsants, antipyretics, beta-blockers, cytostatic drugs, H2 antagonists, estrogenic hormone and contraceptives, blood lipid regulators, and X-ray contrast media.

Hadavand N., Khazalpour S., Fotouhi L., Nematollahi D.

Zhu J., Huang Y., Bu L., Wu Y., Zhou S.

Ostrovskii Vladimir A., Chernova Ekaterina N., Zhakovskaya Zoya A., Pavlyukova Yulia N., Ilyushin Mikhail A., Trifonov Rostislav E.

Rapid processes of tetrazole decomposition serve as sources of chemical energy stored in the five-membered ring, as well as gaseous products, primarily molecular nitrogen. Due to these properties, energetic tetrazole derivatives have found applications in various fields of science, engineering and technology, for example as components of energetic materials and products, as well as in emergency rescue equipment. The review presents an alternative view of the processes of tetrazoles decomposition, focusing on the diversity, differences, and similarities of the mechanisms and degradation products formed under the action of external energy sources. Some of these products are valuable reagents for the synthesis of previously inaccessible substances, as well as promising objects of analytical, medical, and bioorthogonal chemistry.The bibliography includes 140 references.

Liang X., Lei Y., Yang X.

Quantitative structure–activity relationships (QSARs) can be effective ways to understand the reactivity between trace organic contaminants (TrOCs) and radicals involved in advanced oxidation processes (AOPs).

Lei Y., Yu Y., Lei X., Liang X., Cheng S., Ouyang G., Yang X.

Lu H., Wang X., Li G., Liao B., Gu Z., Zhang X., Yuan F., Tong J., Chen L.

Combining molecular transition-metal complexes and semiconductors is an effective way to create high-performance hybrid photocatalysts based on improvement of solar energy harvesting ability and photogenerated charge carrier separation efficiency.

Aydogdu S., Hatipoglu A.

Ampicillin (AMP) is a penicillin-class beta-lactam antibiotic widely used to treat infections caused by bacteria. Therefore, due to its widespread use, this antibiotic is found in wastewater, and it contains long-term risks such as toxicity to all living organisms. In this study, the degradation reaction of ampicillin with hydroxyl radical was investigated by the density functional theory (DFT) method. All the calculations were performed with B3LYP functional at 6-31G(d,p) basis set. The thermodynamic energy values and reaction rates of all possible reaction paths were calculated. The addition of the hydroxyl radical to the carbonyl group of the beta-lactam ring is thermodynamically the most probable reaction path. The calculated overall reaction rate constant is 1.36 × 1011 M−1 s−1. To determine the effect of temperature on the reaction rate, rate constants were calculated for all reaction paths at five different temperatures. The subsequent reaction kinetics of the most preferred primary route was also examined, and the toxicity values of the intermediates were estimated. The acute toxicity of AMP and its degradation product were calculated using the Ecological Structure Activity Relationships (ECOSAR) software. The degradation product was found to be more toxic than AMP.

Luo X., Yu S., Xu D., Ding J., Zhu X., Xing J., Wu T., Zheng X., Aminabhavi T.M., Cheng X., Liang H.

Catalytic membrane based oxidation-filtration processes (AOP-CM), a derivative concept of membrane process that combines physical separation and chemical oxidation, offers a high-efficient water purification strategy. However, the application of AOP-CM was still hampered by the low heterogeneous AOPs efficiency of catalytic membranes. In order to improve the heterogeneous AOP efficiency, an isoporous AlOx/La2CoMnO6-δ ceramic membrane (IAPCM) with nano-confinement characteristics was prepared via sol–gel based block copolymer self-assembly route. Benefiting from the well-designed pore structure, IAPCM exhibited excellent pure water permeance (313 L·m−2·h−1·bar−1) and size-exclusion performance (complete rejection of MS2 phages with a diameter of ∼ 20 nm). With the addition of peroxymonosulfate (PMS), IAPCM achieved ultrafast degradation of organic micropollutants (e.g. atrazine, carbamazepine and sulfamethazine) at 0.5 bar (equivalent to a retention time of 4.3 × 10−4 s). Finite-Element analysis confirmed that high-concentration radical fields were generated in the confined nanoscale-pores within the isoporous La2CoMnO6-δ layer. The boosted mass transfer rates and high-concentration radical fields induced ultrafast degradation of micropollutants in IAPCM based oxidation-filtration system. This work highlights the significance of pore structure design for high-performance AOP-CM processes.

Chen X., Yang J., Zeng R.J., Qin S., Liu X., Zhang Y., Zhou S., Chen M.

Lu Z., Ling Y., Sun W., Liu C., Mao T., Ao X., Huang T.

Antibiotics are emerging contaminants in aquatic environments which pose serious risks to the ecological environment and human health. Advanced oxidation processes (AOPs) based on ultraviolet (UV) light have good application prospects for antibiotic degradation. As new and developing UV-AOPs, UV/chlorine and derived UV/chloramine processes have attracted increasing attention due to the production of highly reactive radicals (e.g., hydroxyl radical, reactive chlorine species, and reactive nitrogen species) and also because they can provide long-lasting disinfection. In this review, the main reaction pathways of radicals formed during the UV/chlor (am)ine process are proposed. The degradation efficiency, influencing factors, generation of disinfection by-products (DBPs), and changes in toxicity that occur during antibiotic degradation by UV/chlor (am)ine are reviewed. Based on the statistics and analysis of published results, the effects caused by energy consumption, defined as electrical energy per order (EE/O), increase in the following order: UV/chlorine < UV/peroxydisulfate (PDS)< UV/H2O2 < UV/persulfate (PS) < 265 nm and 285 nm UV-LED/chlorine (EE/O). Some inherent problems that affect the UV/chlor (am)ine processes and prospects for future research are proposed. The use of UV/chlor (am)ine AOPs is a rich field of research and has promising future applications, and this review provides a theoretical basis for that.

Yang X., Rosario-Ortiz F.L., Lei Y., Pan Y., Lei X., Westerhoff P.

Advanced oxidation processes (AOPs) can degrade a wide range of trace organic contaminants (TrOCs) to improve the quality of potable water or discharged wastewater effluents. Their effectiveness is impacted, however, by the dissolved organic matter (DOM) that is ubiquitous in all water sources. During the application of an AOP, DOM can scavenge radicals and/or block light penetration, therefore impacting their effectiveness toward contaminant transformation. The multiple ways in which different types or sources of DOM can impact oxidative water purification processes are critically reviewed. DOM can inhibit the degradation of TrOCs, but it can also enhance the formation and reactivity of useful radicals for contaminants elimination and alter the transformation pathways of contaminants. An in-depth analysis highlights the inhibitory effect of DOM on the degradation efficiency of TrOCs based on DOM's structure and optical properties and its reactivity toward oxidants as well as the synergistic contribution of DOM to the transformation of TrOCs from the analysis of DOM's redox properties and DOM's transient intermediates. AOPs can alter DOM structure properties as well as and influence types, mechanisms, and extent of oxidation byproducts formation. Research needs are proposed to advance practical understanding of how DOM can be exploited to improve oxidative water purification.

Wojnárovits L., Wang J., Chu L., Tóth T., Kovács K., Bezsenyi A., Szabó L., Homlok R., Takács E.

Due to the spread of antibiotic resistant bacteria, elimination of antibiotics from purified wastewater is a highly important task. Purified wastewater contains large variety of organic/inorganic compounds that strongly influence the efficiency of advanced oxidation processes (AOP). In this work, we investigate the radiation-induced degradation of selected antibiotic contaminants (oxacillin and cloxacillin from the β-lactams; tetracycline and chlortetracycline from the tetracyclines) in four matrices: pure water, tap water, synthetic wastewater and purified wastewater received from a wastewater treatment plant. Changes in technically important parameters, such as COD, TOC, BOD, OUR, acute toxicity and antibacterial activity, were investigated at 0.1 mmol dm −3 (40–48 mg dm −3 ) antibiotic concentration. None of the four antibiotics were biodegradable in any of the four matrices, however, after irradiation with relatively low doses the obtained products were biodegradable. Oxacillin and cloxacillin were not toxic in Vibrio fischeri test, while tetracycline and chlortetracycline showed toxicity that was strongly reduced by the irradiation treatment. Both COD and TOC decreased after irradiation, their ratio shifted towards TOC indicating an increase in the average oxidation state (AOS). The increase in AOS was lower in purified wastewater matrices: this matrix may contain various small, highly oxidized molecules in high concentration, which degrade very slowly in AOP. The antibacterial activity in most of matrices was greatly reduced or completely disappeared at around 2–4 kGy. However, in purified wastewater matrices some antibiotic activity remained even at 4 kGy. Here the degradation of antibiotic is slow (small ΔCOD/dose value) because a large fraction of the reactive radicals is scavenged presumably by small, highly oxidized molecules in the solution. Although the water radiolysis product H 2 O 2 affected some of the bioassays, this phenomenon was absent in purified wastewater. The purified wastewater after ionizing radiation treatment can be safely released into the receiving lakes or rivers. • The antibacterial activities greatly decreased or completely vanished at 2–4 kGy. • The degradation products did not show antibacterial activity. • The AOP increased the TOC/COD ratio implying enhanced average oxidation state (AOS). • The increase in AOS was lower in purified wastewater matrices. • After irradiation treatment all the four antibiotics became biodegradable.

Takács E., Wang J., Chu L., Tóth T., Kovács K., Bezsenyi A., Szabó L., Homlok R., Wojnárovits L.

The chemical changes caused by electron beam and γ irradiations and the biochemical characteristics of degradation products of a frequently used antibiotic oxacillin were investigated and compared with those of cloxacillin by applying pulse radiolysis, chemical and biochemical oxygen demand, total organic carbon content, oxygen uptake rate, toxicity and antibacterial activity measurements. Oxacillin was found to be non-toxic, but poorly biodegradable by the mixed microbial population of the activated sludge of a wastewater treatment plant. Therefore, it can significantly contribute to the spread of β-lactam antibiotic resistant bacteria. However, the products formed by γ-irradiation were more easily biodegradable as they were utilized as nutrient source by the microbes of the activated sludge and the products did not show antibacterial activity. During irradiation treatment of aerated aqueous solutions mainly hydroxyl radicals induce the elimination of antimicrobial activity by making alterations at the bicyclic β-lactam part of these antibiotics. Since the β-lactam part is the same in oxacillin and cloxacillin, the biochemical characteristics of products of the two antibiotics are similar. The attack of hydrated electron takes place on the carbonyl groups. When the irradiation is made under anoxic conditions these reactions may also contribute considerably to alterations at the β-lactam part and thereby to the loss of antibacterial activity. • Oxacillin biodegradability is improved by irradiation. • OH induces elimination of antimicrobial activity altering the bicyclic part. • Oxacillin and degradation products are non-toxic to microbes in a WWT plant. • The microbes in a WWT plant cannot use oxacillin as nutrient source. • Degradation products are utilized by microbes.

Ali Noman E., Al-Gheethi A., Saphira Radin Mohamed R.M., Talip B.A., Hossain M.S., Ali Hamood Altowayti W., Ismail N.

In this article, the removal of cephalexin (CFX) antibiotic from non-clinical environment is reviewed. Adsorption and photocatalytic degradation techniques are widely used to remove CFX from waters and wastewaters, the combination of these methods is becoming more common for CFX removal. The treatment methods of CFX has not been reviewed before, the present article aim is to organize the scattered available information regarding sustainable approaches for CFX removal from non-clinical environment. These include adsorption by nanoparticles, bacterial biomass, biodegradation by bacterial enzymes and the photocatalysis using different catalysts and Photo-Fenton photocatalysis. The metal-organic frameworks (MOFs) appeared to have high potential for CFX degradation. It is evident from the recently papers reviewed that the effective methods could be used in place of commercial activated carbon. The widespread uses of photocatalytic degradation for CFX remediation are strongly recommended due to their engineering applicability, technical feasibility, and high effectiveness. The adsorption capacity of the CFX is ranging from 7 mg CFX g −1 of activated carbon nanoparticles to 1667 mg CFX g −1 of Nano-zero-valent iron from Nettle. In contrast, the photo-degradation was 45% using Photo-Fenton while has increased to 100% using heterogeneous photoelectro-Fenton (HPEF) with UVA light using chalcopyrite catalyst. • The removal of nickel ions by sustainable approaches was reviewed. • Adsorption takes place by electrostatic repulsion, attraction and interaction. • The elimination of nickel ions need a selective biomass adsorbent. • The artificial neural networks could help to understand the behaviour of Ni 2+ ions for adsorption.

Lei Y., Lei X., Yu Y., Li K., Li Z., Cheng S., Ouyang G., Yang X.

Bromine radicals can pose great impacts on the photochemical transformation of trace organic contaminants in natural and engineered waters. However, the reaction kinetics and mechanisms involved are barely known. In this work, second-order reaction rate constants with Br• and Br2•- were determined for 70 common trace organic contaminants and for 17 model compounds using laser flash photolysis and steady-state competition kinetics. The kBr• values ranged from