Danae Venieri

Detection and fate of antibiotic resistant bacteria in wastewater treatment plants: A review

Antibiotics are among the most successful group of pharmaceuticals used for human and veterinary therapy. However, large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics, which finally find their ways into different natural environmental compartments. The emergence and rapid spread of antibiotic resistant bacteria (ARB) has led to an increasing concern about the potential environmental and public health risks. ARB and antibiotic resistant genes (ARGs) have been detected extensively in wastewater samples. Available data show significantly higher proportion of antibiotic resistant bacteria contained in raw and treated wastewater relative to surface water. According to these studies, the conditions in wastewater treatment plants (WWTPs) are favourable for the proliferation of ARB. Moreover, another concern with regards to the presence of ARB and ARGs is their effective removal from sewage. This review gives an overview of the available data on the occurrence of ARB and ARGs and their fate in WWTPs, on the biological methods dealing with the detection of bacterial populations and their resistance genes, and highlights areas in need for further research studies.

Degradation, mineralization and antibiotic inactivation of amoxicillin by UV-A/TiO2 photocatalysis

The UV-A/TiO(2) photocatalytic decomposition of amoxicillin (AMX) in aqueous suspensions was investigated. Experiments were performed at antibiotic concentrations between 2.5 and 30 mg/L, eight commercially available TiO(2) catalysts at loadings between 100 and 750 mg/L, acidic or near-neutral conditions (pH 5 or 7.5) and two different matrices (ultrapure water and secondary treated effluent) at a photon flux of 8 × 10(-4) E/(L min). Of the various catalysts tested, Degussa P25 was highly active, i.e. complete AMX degradation and 93% mineralization could be achieved after 25 and 90 min of reaction, respectively at 10 mg/L AMX and 250 mg/L titania. In general, mineralization was slower than degradation due to the formation of stable transformation by-products. For the range of concentrations studied, initial degradation rates can be approached by a Langmuir-Hinshelwood kinetic model, while the reaction order with respect to AMX shifts from first to zeroth as initial concentration increases from 2.5 to 5 mg/L to higher values. Degradation in treated effluent was partly impeded compared to pure water due to the inherent presence of organic and inorganic constituents that compete for hydroxyl radicals. Although increasing solution pH from 5 to 7.5 had no effect on degradation, it retarded mineralization. The antibiotic activity of AMX prior to and after photocatalytic degradation was tested to three reference bacterial strains, namely Escherichia coli (ATCC 23716), Klebsiella pneumoniae (NCTC 5056) and Enterococcus faecalis (ATCC 14506). The first two were found to be highly resistant at AMX concentrations up to 25 mg/L, while the latter could partly be inactivated at lower AMX concentrations (i.e. 10 mg/L) and/or in the presence of photocatalytic by-products.

Sonochemical degradation of ethyl paraben in environmental samples: Statistically important parameters determining kinetics, by-products and pathways.

The sonochemical degradation of ethyl paraben (EP), a representative of the parabens family, was investigated. Experiments were conducted at constant ultrasound frequency of 20 kHz and liquid bulk temperature of 30 °C in the following range of experimental conditions: EP concentration 250-1250 μg/L, ultrasound (US) density 20-60 W/L, reaction time up to 120 min, initial pH 3-8 and sodium persulfate 0-100mg/L, either in ultrapure water or secondary treated wastewater. A factorial design methodology was adopted to elucidate the statistically important effects and their interactions and a full empirical model comprising seventeen terms was originally developed. Omitting several terms of lower significance, a reduced model that can reliably simulate the process was finally proposed; this includes EP concentration, reaction time, power density and initial pH, as well as the interactions (EP concentration)×(US density), (EP concentration)×(pHo) and (EP concentration)×(time). Experiments at an increased EP concentration of 3.5mg/L were also performed to identify degradation by-products. LC-TOF-MS analysis revealed that EP sonochemical degradation occurs through dealkylation of the ethyl chain to form methyl paraben, while successive hydroxylation of the aromatic ring yields 4-hydroxybenzoic, 2,4-dihydroxybenzoic and 3,4-dihydroxybenzoic acids. By-products are less toxic to bacterium V. fischeri than the parent compound.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m2/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500μg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

Microcosm evaluation of autochthonous bioaugmentation to combat marine oil spills

Oil spills can be disastrous to any ecosystem. Bioremediation through bioaugmentation (addition of oil-degrading bacteria) and biostimulation (addition of nutrients N&P) options can be a promising strategy for combating oil spills following first response actions. However, bioaugmentation is one of the most controversial issues of bioremediation since nutrient addition alone has a greater effect on oil biodegradation than the addition of microbial products that are highly dependent on environmental conditions. There is increasing evidence that the best way to overcome the above barriers is to use microorganisms from the polluted area, an approach proposed as autochthonous bioaugmentation (ABA) and defined as the bioaugmentation technology that uses exclusively microorganisms indigenous to the sites (soil, sand, and water) to be decontaminated. In this study, we examined the effectiveness of an ABA strategy for the successful remediation of polluted marine environments. A consortium was enriched from seawater samples taken from Elefsina Gulf near the Hellenic Petroleum Refinery, a site exposed to chronic crude oil pollution. Pre-adapted consortium was tested alone or in combination with inorganic nutrients in the presence (or not) of biosurfactants (rhamnolipids) in 30-day experiments. Treatment with fertilizers in the presence of biosurfactants exhibited the highest alkane and PAH degradation and showed highest growth over a period of almost 15 days. Considering the above, the use of biostimulation additives in combination with naturally pre-adapted hydrocarbon degrading consortia has proved to be a very effective treatment and it is a promising strategy in the future especially when combined with lipophilic fertilizers instead of inorganic nutrients. Such an approach becomes more pertinent when the oil spill approaches near the shoreline and immediate hydrocarbon degradation is needed.

Solar Photocatalytic Degradation of Bisphenol A on Immobilized ZnO or TiO2

The removal of bisphenol A (BPA) under simulated solar irradiation and in the presence of either TiO2 or ZnO catalysts immobilized onto glass plates was investigated. The effect of various operating conditions on degradation was assessed including the amount of the immobilized catalyst (36.1–150.7 mg/cm2 for TiO2 and 0.5–6.8 mg/cm2 for ZnO), initial BPA concentration (50–200 μg/L), treatment time (up to 90 min), water matrix (wastewater, drinking water, and pure water), the addition of H2O2 (25–100 mg/L), and the presence of other endocrine disruptors in the reaction mixture. Specifically, it was observed that increasing the amount of immobilized catalyst increases BPA conversion and so does the addition of H2O2 up to 100 mg/L. Moreover, BPA degradation follows first-order reaction kinetics indicating that the final removal is not practically affected by the initial BPA concentration. Degradation in wastewater is slower than that in pure water up to five times, implying the scavenging behavior of effluent’s constituents against hydroxyl radicals. Finally, the presence of other endocrine disruptors, such as 17α-ethynylestradiol, spiked in the reaction mixture at low concentrations usually found in environmental samples (i.e., 100 μg/L), neither affects BPA degradation nor alters its kinetics to a considerable extent.

Single stage treatment of saline wastewater with marine bacterial-microalgae consortia in a fixed-bed photobioreactor.

Currently, the treatment of aquaculture-origin effluents is mainly performed through land-based recirculating aquaculture systems (RAS). In this study, we evaluate and introduce a novel immobilized/packed bed bioreactor which uses a synthetic textile as the support medium. A marine microbial consortium was developed on the textile by its inoculation with the microalgae Picochlorum sp. The bioreactor was tested with variable loadings of C and N and showed outstanding performance approaching removal rates up to 95% within a few hours (4-5h) of operation. Pyrosequencing analysis revealed a novel microbial consortium consisting mainly of chitrinomycetes, Pseudomonas sp. and the absence of β-proteobacteria, which is the Class encompassing autotrophic nitrifiers. Quantitative polymerase chain reaction further confirmed these findings suggesting heterotrophic nitrification and aerobic denitrification as the principal mechanisms of N-removal from the bioreactor. Overall our findings reveal the potential of the AdvanTex System for the treatment of marine aquaculture effluents-COD reduction and N-removal, in a single stage.

Bisphenol-A removal by the halophyte Juncus acutus in a phytoremediation pilot: Characterization and potential role of the endophytic community.

A phytoremediation pilot emulating a shallow aquifer planted with Juncus acutus showed to be effective for remediating Bisphenol-A (BPA) contaminated groundwater. Biostimulation with root exudates, low molecular weight organic acids, of J. acutus did not improve BPA-degradation rates. Furthermore, the endophytic bacterial community of J. acutus was isolated and characterized. Many strains were found to possess increased tolerance to metals such as Zn, Ni, Pb and Cd. Moreover, several endophytic bacterial strains tolerated and even used BPA and/or two antibiotics (ciprofloxacin and sulfamethoxazole) as a sole carbon source. Our results demonstrate that the cultivable bacterial endophytic community of J. acutus is able to use organic contaminants as carbon sources, tolerates metals and is equipped with plant-growth promoting traits. Therefore, J. acutus has potential to be exploited in constructed wetlands when co-contamination is one of the restricting factors.

Photoelectrocatalytic disinfection of water and wastewater: Performance evaluation by qPCR and culture techniques

Photoelectrocatalytic oxidation (PEC) was evaluated as a disinfection technique using water and secondary treated wastewater spiked with Escherichia coli and Enterococcus faecalis. PEC experiments were carried out using a TiO(2)/Ti-film anode and a zirconium cathode under simulated solar radiation. Bacterial inactivation was monitored by culture and quantitative polymerase chain reaction (qPCR). Inactivation rates were enhanced when the duration of the treatment was prolonged and when the bacterial density and the complexity of the water matrix were decreased. E. coli cells were reduced by approximately 6 orders of magnitude after 15 min of PEC treatment in water at 2V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to about 5 log reduction, while electrochemical oxidation alone resulted in negligible inactivation. The superiority of PEC relative to PC can be attributed to a more efficient separation of the photogenerated charge carriers. Regarding disinfection in mixed bacterial suspensions, E. coli was more susceptible than E. faecalis at a potential of 2V. The complex composition of wastewater affected disinfection efficiency, yielding lower inactivation rates compared to water treatment. qPCR yielded lower inactivation rates at longer treatment times than culture techniques, presumably due to the fact that the latter do not take into account the viable but not culturable state of microorganisms.

Disinfection of Waters/Wastewaters by Solar Photocatalysis

A light source and a semiconducting material comprise a powerful duo that may offer several photocatalytic applications for environmental remediation; in recent years, photocatalytic disinfection based on sunlight has gained considerable attention as an efficient and sustainable technology to control the population of various microorganisms in several aqueous matrices. This chapter highlights recent developments in the field both from an engineering and a microbiological point of view. Advances in photocatalytic materials include the modification of all-time classic titania to perform better in the visible part of the electromagnetic spectrum, as well as synthesize novel catalysts such as silver phosphate or robust Fenton-like materials. Measuring disinfection efficiency correctly is critical in designing proper treatment systems. Disinfection kinetics are affected by several factors including reactor configuration, the water matrix, possible synergy with other oxidation processes, the selection of the test microorganism, and, most importantly, the way the population of microorganisms is measured; the latter is crucial since disinfection efficiency can easily be overestimated. All these, alongside the mechanisms of microbial structure destruction upon photocatalytic illumination and the perspectives and constraints of process scale-up, are dealt with in this chapter.