Hadas Mamane

Silver nanoparticle-E. coli colloidal interaction in water and effect on E. coli survival.

Silver nanoparticles exhibit antibacterial properties via bacterial inactivation and growth inhibition. The mechanism is not yet completely understood. This work was aimed at elucidating the effect of silver nanoparticles on inactivation of Escherichia coli, by studying particle-particle interactions in aqueous suspensions. Stable, molecularly capped, positively or negatively charged silver nanoparticles were mixed at 1 to 60microgmL(-1) with suspended E. coli cells to examine their effect on inactivation of the bacteria. Gold nanoparticles with the same surfactant were used as a control, being of similar size but made up of a presumably inert metal. Log reduction of 5log(10) and complete inactivation were obtained with the silver nanoparticles while the gold nanoparticles did not show any inactivation ability. The effect of molecularly capped nanoparticles on E. coli survival was dependent on particle number. Log reduction of E. coli was associated with the ratio between the number of nanoparticles and the initial bacterial cell count. Electrostatic attraction or repulsion mechanisms in silver nanoparticle-E. coli cell interactions did not contribute to the inactivation process.

pH induced polychromatic UV treatment for the removal of a mixture of SMX, OTC and CIP from water

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), oxytetracycline (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 pollutants 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.

Photodegradation of the antibiotic sulphamethoxazole in water with UV/H2O2 advanced oxidation process

Photodegradation of the antibiotic sulphamethoxazole (SMX) in water using a medium‐pressure UV lamp combined with H2O2 (UV/H2O2) was used to generate the advanced oxidation process (AOP). The photodegradation process was steadily improved with addition of H2O2 at relatively low to moderate concentrations (5 to 50 mg L−1). However, the addition of H2O2 to the photolysis process at higher concentrations (50 to 150 mg L−1) did not improve the degradation rate of SMX (in comparison with 50 mg L−1 H2O2). Addition of H2O2 to the UV photolysis process resulted in several processes occurring concurrently as follows: (a) formation of HO· radicals which contributed to the SMX degradation, (b) decrease in the available light for direct UV photolysis of SMX, and (c) scavenging of the HO· radicals by H2O2, which was highly dominant at moderate to high concentrations of H2O2. It is clear that these factors, separately and synergistically, and possibly others such as by‐product formation, affect the overall difference in SMX degradation in the AOP process at different H2O2 concentrations.

Treating wastewater from a pharmaceutical formulation facility by biological process and ozone

Wastewater from a pharmaceutical formulation facility (TevaKS, Israel) was treated with a biological activated-sludge system followed by ozonation. The goal was to reduce the concentrations of the drugs carbamazepine (CBZ) and venlafaxine (VLX) before discharging the wastewater to the municipal wastewater treatment plant (WWTP). Both drugs were detected at extremely high concentrations in TevaKS raw wastewater ([VLX]=11.72 ± 2.2mg/L, [CBZ]=0.84 ± 0.19 mg/L), and resisted the biological treatment. Ozone efficiently degraded CBZ: at an O3 dose-to-dissolved organic carbon ratio of 0.55 (O3/DOC), the concentration of CBZ was reduced by >99%. A lower removal rate was observed for VLX, which was decreased by ≈ 98% at the higher O3/DOC ratio of 0.87. Decreasing the pH of the biologically treated effluent from 7 to 5 significantly increased the ozone degradation rate of CBZ, while decreasing the degradation rate of VLX. Ozone treatment did not alter the concentration of the effluents DOC and filtered chemical oxygen demand (CODf). However, a significant increase was recorded (following ozonation) in the effluents biological oxygen demand (BOD5) and the BOD5/CODf ratio. This implies an increase in the effluents biodegradability, which is highly desirable if ozonation is followed by a domestic biological treatment. Different organic byproducts were formed following ozone reaction with the target pharmaceuticals and with the effluent organic matter; however, these byproducts are expected to be removed during biological treatment in the municipal WWTP.

Impact of water quality on removal of carbamazepine in natural waters by N-doped TiO2 photo-catalytic thin film surfaces

Photocatalytic experiments on the pharmaceutical pollutant carbamazepine (CBZ) were conducted using sol-gel nitrogen-doped TiO(2)-coated glass slides under a solar simulator. CBZ was stable to photodegradation under direct solar irradiation. No CBZ sorption to the catalyst surface was observed, as further confirmed by surface characterization using X-ray photoelectron spectroscopic analysis of N-doped TiO(2) surfaces. When exposing the catalyst surface to natural organic matter (NOM), an excess amount of carbon was detected relative to controls, which is consistent with NOM remaining on the catalyst surface. The catalyst surface charge was negative at pH values from 4 to 10 and decreased with increasing pH, correlated with enhanced CBZ removal with increasing medium pH in the range of 5-9. A dissolved organic carbon concentration of 5mg/L resulted in ~20% reduction in CBZ removal, probably due to competitive inhibition of the photocatalytic degradation of CBZ. At alkalinity values corresponding to CaCO(3) addition at 100mg/L, an over 40% decrease in CBZ removal was observed. A 35% reduction in CBZ occurred in the presence of surface water compared to complete suppression of the photocatalytic process in wastewater effluent.

Removal of pharmaceuticals using combination of UV/H2O2/O3 advanced oxidation process

Water and wastewater effluents contain a vast range of pharmaceutical chemicals. The present study aims to determine the potential of the advanced oxidation technology UV/H(2)O(2)/O(3) and its sub-processes (i.e. UV, UV/H(2)O(2), UV/O(3), O(3) and H(2)O(2)/O(3)) for the degradation of the antibiotics ciprofloxacin (CIP) and trimethoprim (TMP), and the antineoplastic drug cyclophosphamide (CPD) from water. Creating AOP conditions improved in most cases the degradation rate of the target compounds (compared with O(3) and UV alone). H(2)O(2) concentration was found to be an important parameter in the UV/H(2)O(2) and H(2)O(2)/O(3) sub-processes, acting as (•)OH initiator as well as (•)OH scavenger. Out of the examined processes, O(3) had the highest degradation rate for TMP and H(2)O(2)/O(3) showed highest degradation rate for CIP and CPD. The electrical energy consumption for both CIP and CPD, as calculated using the E(EO) parameter, was in the following order: UV > UV/O(3) > UV/H(2)O(2)/O(3) > O(3) > H(2)O(2)/O(3). Whereas for TMP O(3) was shown to be the most electrical energy efficient. Twelve degradation byproducts were identified following direct UV photolysis of CIP.

Control of biofilm formation in water using molecularly capped silver nanoparticles

Control of biofouling and its negative effects on process performance of water systems is a serious operational challenge in all of the water sectors. Molecularly capped silver nanoparticles (Ag-MCNPs) were used as a pretreatment strategy for controlling biofilm development in aqueous suspensions using the model organism Pseudomonas aeruginosa. Biofilm control was tested in a two-step procedure: planktonic P. aeruginosa was exposed to the Ag-MCNPs and then the adherent biofilm formed by the surviving cells was monitored by applying a model biofilm-formation assay. Under specific conditions, Ag-MCNPs retarded biofilm formation, even when high percentage of planktonic P. aeruginosa cells survived the treatment. For example, Ag-MCNPs (10 microg mL(-1)) retarded biofilm formation (>60%), when 50 percent of the planktonic P. aeruginosa cells survived the treatment. Moreover, stable low value of relative biomass has been formed in the presence of fixed Ag-MCNPs concentrations at various biofilm incubation times. Our results showed that Ag-MCNPs pretreated cells were able to produce EPS although they succeeded to form relatively low adherent biofilm. These pretreated cells appear well preserved and undamaged under TEM HPH/freeze micrographs, yet the intra cellular material seems to be pushed towards the peripheral parts of the cell, possibly indicating a survival strategy to the presence of Ag-MCNPs. The lower value of relative biomass formed in the presence of Ag-MCNPs could be associated with molecular mechanisms related to biofilm formation or continuous release of silver ions in the sample. However, further research is required to examine these factors.

Production of photo-oxidants by dissolved organic matter during UV water treatment.

Dissolved organic matter (DOM) irradiated by sunlight generates photo-oxidants that can accelerate organic contaminant degradation in surface waters. However, the significance of this process to contaminant removal during engineered UV water treatment has not been demonstrated, partly due to a lack of suitable methods in the deep UV range. This work expands methods previously established to detect (1)O2, HO•, H2O2, and DOM triplet states ((3)DOM*) at solar wavelengths to irradiation at 254 nm, typical of UV water treatment. For transient intermediates, the methods include a photostable probe combined with selective scavengers. Quantum yields for (1)O2, (3)DOM* and H2O2 were in the same range as for solar-driven reactions but were an order of magnitude higher for HO•, which other experiments indicate is due to H2O2 reduction. With the quantum yields, the degradation of metoxuron was successfully predicted in a DOM solution irradiated at 254 nm. Further modeling showed that the contribution of DOM sensitization to organic contaminant removal during UV treatment should be significant only at high UV fluence, characteristic of advanced oxidation processes. Of the reactive species studied, (3)DOM* is predicted to have the greatest general influence on UV degradation of contaminants.

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.

Influence of wastewater particles on ozone degradation of trace organic contaminants.

In this Article, we demonstrate the influence of effluent particles (in the range of <50 μm) on ozone degradation of trace organic contaminants (TrOCs) and effluent-quality parameters. Secondary effluent was filtered through different pore-size filters and ozonated at various ozone doses. Degradation of both ozone-reactive and ozone-refractory contaminants improved following ozonation of effluent filtered with smaller pore size filters, indicating that particles in this range may adversely affect ozonation. The inhibitory effect of particles was attributed to their reaction with ozone, reducing available ozone and HO(•) radicals. In addition, increasing filtration level decreased the effluents (instantaneous) ozone demand and increased removal of effluent UV absorbance (UVA254), further establishing that ozone reacts with effluent particles, in competition with dissolved matter. Moreover, ozone was shown to react with particles even during the first seconds of the process, suggesting a high rate of some ozone-particle reactions, comparable to ozone reaction with highly reactive dissolved organic matter moieties. Particle image analysis revealed that particle formation/aggregation and particle disintegration occurs simultaneously during wastewater (WW) ozonation. Our study implies that particles could affect the efficiency of WW ozonation, by increasing the effluents ozone demand and decreasing contaminant degradation.