► Some emerging pollutants are refractory to conventional biological treatment. ► Acclimation, biostimulation and bioaugmentation processes were defined. ► Experimental approach to evaluate ...bioaugmentation's performance is exposed. ► Recently published papers dealing with bioaugmentation are reviewed. ► Some engineered new approaches of bioaugmentation are also noticed.
Water quality is questionable when looking at the emerging pollutants that accumulate in hydrosphere day after day. In terms of water treatments to eliminate organic compounds, biological treatments are the most used technique, especially the conventional activated sludge (CAS) process. Unfortunately, several of these compounds such as petroleum and industrial wastes, some pesticides, pharmaceuticals, and hormonal substances appear to be refractory to such treatments and can join the different water surfaces from other natural environments especially contaminated soils. Physical and chemical treatments, in particularly the advanced oxidation processes (AOPs) are able to degrade some of these pollutants, but the nature and the possible effects of oxidation by-products remain controversial when complete mineralization does not occur. The aim of this article is to shed light on new and renewed biotechnological techniques recently introduced to resolve recalcitrance problem. Amending activated sludge with additional microorganisms able to produce versatile enzymes to enhance biodegradability or “bioaugmentation”, is gradually considered as a possible solution for the recalcitrance of Bio-Refractory Organic Compounds (Bio-ROCs). The use of this technique, traditionally in soil remediation field, and recently in water and sediments treatment is reviewed in this paper.
This work highlights new insights into the performance of TiO2 doped with noble metal catalysts for the photocatalytic degradation of organic water pollutants. Different samples of titanium dioxide ...doped with noble metals (Au and Pd) were successfully synthesized via incipient wet impregnation (IWI) and ultrasound-assisted impregnation (US) methods. X-ray diffraction, scanning electron microscopy and UV-Vis reflectance spectroscopy were used for the characterization of the obtained materials. Their photocatalytic efficiency was investigated in aqueous suspension thorough a series of laboratory tests performed under ultraviolet (UV-A) irradiation conditions using 2,4 dinitrophenol (2,4 DNP) as a target molecule. The results clearly show that the method used for the catalyst synthesis affects its photocatalytic activity. It was found that the samples prepared by the IWI method exhibited high photocatalytic activity, and the removal rate obtained with TiO2-Pd/IWI was higher than that found for TiO2-Au/IWI. Furthermore, for the best catalyst, some extra photocatalytic experiments were conducted with rhodamine 6G (R6G), a highly stable molecule with a very different chemical structure to 2,4 DNP, in order to check the reactivity of this material. Moreover, the recycling experiments carried out with TiO2-Pd/IWI clearly demonstrated the high photocatalytic stability of this material for the degradation of 2,4 DNP. All of the collected data confirmed the interesting photocatalytic potential of the selected catalyst in the elimination of organic pollutants with no obvious change in its reactivity after four reaction cycles, which is very promising for promoting future applications in water depollution.
Mesoporous TiO2 photocatalysts intended for the advanced removal of clofibric acid (CA) from water were synthesized by the sol-gel method in a medium containing cetyl-trimethyl-ammonium bromide ...(CTAB) and urea, using either ethanol or isopropanol to dilute the TiO2 precursor. The activation of the samples was undertaken at 550, 650 and 750 °C. The XRD revealed that the nature of the solvent resulted in significant differences in the anatase-to-rutile ratios obtained at different temperatures. The specific surface area values were situated between 9 and 43 m2·g−1 and the band gap values were similar for all the samples. The photocatalytic activity of the prepared samples was examined for the degradation of CA, an emergent water contaminant. The photocatalytic tests performed under UV-A irradiation revealed that the photo-reactivity of these materials depends on the calcination temperature. The best results were obtained for the samples calcined at 750 °C, which showed high yields of CA elimination, as well as almost complete mineralization (over 95%) after 180 min of reaction. Good results in terms of catalyst reusability in the reaction were found for the catalyst showing the highest photo-reactivity. Therefore, the samples can be considered good candidates for future water remediation applications.
Mixed oxides containing zinc and lanthanum were prepared by coprecipitation in alkaline medium, followed by calcination at 400 °C. The initial precipitation product and the calcined form were ...characterized by Brunauer-Emmett-Teller (BET) method adsorption of nitrogen at -196 °C, Scanning Electron Microscopy/Electron-Probe Microanalysis (SEM/EPM), Ultraviolet-Diffuse Reflectance Spectroscopy (UV-DRS) and Infrared (IR) spectroscopy. The band gap slightly changes from 3.23 eV to 3 eV by calcination. The photocatalytic performance of the solids were investigated in diluted aqueous medium, by using clofibric acid (CA), a stable and toxic molecule used as precursor in some pesticides and drugs, as test compound, possibly found in the wastewaters in low concentrations. The effects of the degradation extent, determined by high performance liquid chromatography (HPLC) and total organic carbon (TOC) measurements, were investigated at different initial concentrations of CA. Within about 60 min the CA degradation is almost total at low concentration values (3 ppm) and reaches over 80% in 180 min for an initial concentration of 50 ppm. Moreover, the CA removal performance of photocatalyst remains excellent after three cycles of use: the removal yield was practically total after 60 min in the first two cycles and reached 95% even in the third cycle.
Clofibric acid (CLF) is the main pharmacologically active metabolite in composition of the pharmaceutical products used for controlling blood lipid content. This xenobiotic compound is highly ...persistent in the aquatic environment and passes unchanged or poorly transformed in wastewater treatment plants. A white-rot fungal strain of Trametes pubescens was previously selected, for its ability for clofibric acid biodegradation (up to 30%) during cultivation in submerged system under aerobic conditions at an initial CLF concentration of 15 mg L−1. Plackett-Burman design (PBD) and response surface methodology (RSM) were used for experimental planning, mathematical modelling and statistical analysis of data of the biotechnological process of CLF biotransformation by Trametes pubescens fungal strain. After optimization, the capacity of the selected Trametes pubescens strain to degrade CLF was increased by cultivation in a liquid medium containing 3 g·L−1 yeast extract, 15 g·L−1 peptone, 5 g·L−1 glucose and mineral salts, inoculated at 2% (v/v) vegetative inoculum and cultivated at pH 5.5, during 14 days at 25 °C and 135 rpm. In these optimized biotechnological conditions, the CLF biotransformation yield was 60%.
Recently, environmental scientists have been focused their attention on the occurrence of emerging contaminants in water, such as disinfection by products (DBPs), including chlorophenols. These ...pollutants can be a public health problem due to their carcinogenic properties. In this work, ultra-high pressure liquid chromatography (UHPLC) coupled to a photodiode array detector (PDA) was used for the development of an analytical method capable of simultaneous identification and quantification of two chlorophenols namely, 2-chlorophenol and 2,4-dichlorophenol in water samples. In addition, a solid phase extraction (SPE) procedure for the extraction of these compounds was optimized. The chlorophenols were separated by an Acquity BEH C18 (100×2.1mm, 1.7μm) column with a mobile phase of acetonitrile/ultrapure water/formic acid (55/45/0.1, v/v/v). The flow rate of the mobile phase was 0.4mLmin−1. The optimized SPE–UHPLC/PDA technique was evaluated in terms of robustness, considering the enrichment factor for all of the studied chlorophenols. Linear calibration was obtained with correlation coefficients r2⩾0.998. Intra-day and inter-day precision was less than 5% and accuracy ranged from 99.95% to 103.32%, respectively. The obtained extraction recoveries were higher than 98%. The pre-concentration factor was 2.500 for the both analytes. Under optimized conditions, the detection limits of the overall SPE–UHPLC/PDA method were in the ngL−1 level. The excellent performance of the developed method, as well as the short analysis time makes it a promising analytical tool for the screening of chlorophenols in environmental water samples.
A low-cost adsorbent was prepared by using cherry stones powder and chitosan and used to retain Reactive Black 5 dye from aqueous solution. Then, the spent material was submitted to a regeneration ...process. Five different eluents (water, sodium hydroxide, hydrochloric acid, sodium chloride and ethanol) were tested. Among them, sodium hydroxide was selected for an advanced investigation. Values of three working conditions, namely the eluent volume, its concentration and the desorption temperature, were optimized by Response Surface Methodology-Box-Behnken Design. In the established settings (NaOH volume: 30 mL, NaOH concentration: 1.5 M, working temperature: 40 °C), three successive cycles of adsorption/desorption were conducted. The analysis performed by Scanning Electron Microscopy and by Fourier Transform Infrared Spectroscopy revealed the evolution of the adsorbent throughout the dye elution from the material. Pseudo-second-order kinetic model and Freundlich equilibrium isotherm were able to accurately describe the desorption process. Based on the acquired results, our outcomes sustain the suitability of the synthesized material as dye adsorbent and the possibility of efficaciously recycling and reusing it.
An innovative “domino” process, based on an arene hydrogenation followed by a photocatalytic step, was designed for the remediation of endocrine disrupting compounds, in highly concentrated aqueous ...effluents. The novelty relies on the use of TiO2-supported zerovalent Rh nanoparticles as multicatalytic materials (MCMs) for this two-step treatment, applied on diethyl phthalate, which is a model aromatic pollutant frequently present in aquatic environments. This nanocomposite advanced material, which was easily prepared by a green, wet impregnation methodology, proved to be active in the successive reactions, the reduction in the aromatic ring, and the photodegradation step. This sustainable approach offers promising alternatives in the case of photoresistive compounds.
PDF
