A strategy for xenobiotic removal using photocatalytic treatment, microbial degradation or integrated photocatalytic-biological process

According to the limited natural resources and due to the risks of anthropogenic pollution, it appears necessary to react efficiently in order to remove existing contaminations and avoid the creation of new ones. Therefore, the purpose of this thesis is to propose a sustainable strategy for treating problematic pollutants with the most adequate process. First, an overview of the different treatment processes has been given. In particular, biological, photocatalytic and integrated biological-photocatalytic treatments have been described as efficient methods to remove xenobiotics. Biological treatment of contaminated environments and industrial effluents has been presented as the most attractive method on a cost-benefit extent. But for biorecalcitrant substances, the Advanced Oxidation Processes (AOP) have remained the most efficient methods although expensive. Therefore, the coupling of biological-photocatalytic has emerged as the best compromise for removal of recalcitrant xenobiotics. The first step of the treatment strategy has consisted of evaluating the biotraitability of 19 chemicals: pesticides, pharmaceuticals and volatile organic compounds (VOCs) have been assessed according to three biodegradability methods (Zahn-Wellens, Manometric Respirometry, Closed-Bottle tests), whose official protocols had to be adapted to the compound specificities (volatility, hydrophobicity). Structure-Activity Relationship (SAR) estimation models have also been used to compare and validate the experimental results. For the compounds which have been assessed as biotraitable (VOCs), further biodegradation studies have been led in order to improve the treatment (batch with pulses of substrate): automated monitoring of the biodegradation process, increased degradation yields and biomass productivity have been successfully completed for Toluene, Ethylbenzene, Xylenes, Chlorobenzenze and Dichlorobenzene removal. Conversely, the compounds assessed as biorecalcitrant have been oriented towards the TiO2 and photo-Fenton photocatalytic treatments. Thus, the degradation of four p-halophenols by TiO2 photocatalysis has been investigated and has demonstrated the halogen effect on removal rates, aromatic intermediates and toxicity variations. Finally, the treatment of five bioreacalcitrant pesticides (Alachlor, Atrazine, Chlorfenvinphos, Diuron, Pentachlorophenol) has been studied in order to develop a coupled photocatalytic-biological system: first, enhanced biotreatability has been evaluated using the Zahn-Wellens procedure and then fixed-bed bioreactors have been operated and permitted to find out the best moment for coupling.

Imaging the aerobic granular sludge microbial community using light-sheet fluorescence micros

Arnaud Michel Gelb, Karen Gemayel, Christof Holliger, Julien Maillard

One of the aims of wastewater treatment is the removal of phosphorus before the water is discharged into the environment. Since phosphorus concentrations in wastewater exceed the requirement of bacterial growth, biological phosphorus removal is based on the ability of a group of microorganisms, named “Polyphosphate Accumulating Organisms” (PAO), to store large quantities of intracellular phosphate in form of polyphosphate. In this study, we are focusing on the PAO actively involved in bioreactors operated with Aerobic Granular Sludge (AGS) technology. This process based on dense microbial biofilms is a cost-effective and landsaving alternative to the conventional biological wastewater treatment with activated sludge. This promising technology has received a significant commercial interest, but questions remain unanswered regarding the system performances in the context of full-scale applications. Like many natural microbial communities, the microbial structure of the AGS is complex. Its spatial organization is shaped by the diffusion of nutrients from the external environment and by the diffusion of microbial by-products formed in the biofilm. Understanding how the AGS microbial community works requires the elucidation of its spatial architecture and development. Light-sheet fluorescence microscopy is a powerful tool for examining microbial communities by overcoming the limitations of the classical three-dimensional confocal fluorescence microscopy. This technique shapes the excitation laser into a thin sheet providing an optical sectioning in order to illuminate the sample on a single plane. Then the emission signal is collected by a perpendicular lens. The large datasets generated are analyzed with a pipeline on the FIJI platform[1] to extract quantitative information. Preliminary results indicate that AGS are composed of heterogeneous biofilm aggregates. Interestingly, our observations are contrasting the AGS model structure previously described[2]. We would like to highlight the necessity of multiple observations when highly variable structures, like AGS, are analyzed in order to capture data which are representative of the studied system. [1] Schindelin et al. in Nat. Methods 28;9(7):676-82 (2012) [2] Winkler et al. in Water Res. 15;46(16):4973-80 (2012) Poster 3 Conférence: Swiss Microbial Ecology Meeting 2019 (Lausanne) Titre: Anaerobic Biodegradation of organohalide pollutants: a crucial step towards the elucidation of proteins involved Auteurs: Lorenzo Cimmino, Adrian Schmid, Christof Holliger, Julien Maillard Abstract: Halogenated organic compounds (so-called organohalides) represent one of the major class of groundwater pollutants. The exploration of how organohalides are used as energy source is important in terms of ecosystem remediation but is also essential for the complete understanding of microbial metabolic interactions in the environment. Organohalide respiration (OHR) is a bacterial anaerobic process in which chlorinated compound, e.g. tetrachloroethene (PCE), is used as terminal electron acceptor. In the present work, Desulfitobacterium hafniense TCE1 and Dehalobacter restrictus, our model organohalide-respiring bacteria (OHRB) harbouring the pceABCT gene cluster, will be considered for the study of PCE respiration. To date, the function of PceA, the key catalytic enzyme in the process, and PceT, the dedicated molecular chaperone for PceA maturation, are well defined. However, the roles of PceB and PceC are not yet elucidated and the biochemistry of OHR electron transfer is still relatively elusive. Based on the genetic composition of the pce gene cluster, the hypothesis of a possible PceABC respiratory complex is tempting but the question remains largely unanswered. The present work represents an evaluation of the stoichiometry of PceA, PceB and PceC proteins via quantitative proteomics applied to the membranes fractions of our model organisms. In a second phase, the use of Blue-Native electrophoresis technology will be considered to investigate whether PceC participates in a membrane-bound protein complex toge.

2019

Degradation of 37 emergent contaminants by UV and neutral fenton and photo-fenton in domestic wastewater effluent previously treated by activated sludge

Luiz Felippe De Alencastro, Natalia de la Cruz, Dominique Grandjean, César Pulgarin

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L␣1, and a real global quantity of micropollutants of 29.5 mg L␣1. The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV254) alone, dark Fenton (Fe2þ,3þ/H2O2) and photo-Fenton (Fe2þ,3þ/H2O2/light). Different irradiation sources were used for the photo-Fenton experi- ences: UV254 and simulated sunlight. Iron and H2O2 concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV254, 50 mg L␣1 of H2O2, with and without adding iron (5 mg L␣1 of Fe2þ added or 1.48 mg L␣1 of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treat- ments. As the H2O2 concentration increased (10, 25 and 50 mg L␣1), best degradations were observed. UV254, Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

Elsevier2012

Fate of volatile fluorinated compounds in the subsurface

Christian Balsiger

Since their discovery around 1930, the synthetic compounds of the class of chlorofluorocarbons (CFCs) have been produced and used worldwide at very large scale. Their physico-chemical properties (non-flammability, chemical inertia, miscibility with water and oil, compatibility with many metals and plastics, solvent capacity) have made them ideal candidates for several applications, such as refrigerant fluids, aerosol propellants, foam blowing agents, or as solvents or intermediates of chemical synthesis. In the 70', it was demonstrated that following their release in the atmosphere, they are implicated in the process leading to the commonly called stratospheric ozone hole. The governments of several industrialised country have thus signed a protocol with the objective to stop the production and use of CFCs. CFCs have been increasingly replaced by compounds with similar structure, the hydrochlorofluorocarbons (HCFCs), but whose reactivity in the lower layers of the atmosphere is quite different from that of CFCs. Due to their chemical inertia, CFCs has been used as tracers for surface and groundwater datation. During such investigations, the biodegradability of these compounds and the existence of punctual pollution sources in soil and groundwater have been evidenced. It has been demonstrated that some of these compounds can be dechlorinated under anoxic conditions producing other compounds with sometimes higher toxicity and higher water solubility, and resulting in a risk linked to the consumption of natural groundwater. The goal of this thesis was to get indications about reductive transformations of CFCs and especially HCFCs in Swiss aquifers and landfills, on the potential of different microbial communities to reductively dechlorinate certain compounds, and under which redox conditions the transformations occur in aquifer systems. Data concerning the production, use, emission, regulation, as well as the biodegradability and toxicity of these compounds are presented in chapter 1 and in the appendix. The analytical methods developed and used during this work are presented in chapter 2. Particularly, a versatile analytical system allowing the measure of trace but also higher concentrations in different media, solid or aqueous, has been set up and used during this work. CFCs and HCFCs were analyzed at 3 sites in Switzerland. Samples were collected from a natural groundwater in which a chloroethene plume had been observed, from an old landfill closed in 1980, and from a more recent bioactive landfill constructed in horizontal layers. In addition, the behaviour of different CFCs and HCFCs was studied in microcosms inoculated with sludge originating from several sewage treatment plants in the canton of Vaud, and with a sediment originating from a contaminated aquifer in Holland. The studied CFCs and HCFCs were furthermore injected at the inlet of a 1.2 m height column filled with the aquifer sediment from Holland. In this quasi natural aquifer, the oxido-reductive conditions were modified during the experiment in order to investigate the conditions at which the biodegradation occurred. The field studies showed that CFCs and HCFCs are present in aquifers and landfills, and there were indications that their transformation also occurs there. Estimations of half-life times indicated that the reductive dechlorination occurred at slow rates. This could be due to the low temperatures of natural groundwater systems and other factors linked to the hydro-geological properties of the natural environment such as dispersion, sorption or partitionning. In the microcosms inoculated with sludge, CFC-11 was transformed to HCFC-21, the latter being further dechlorinated to HCFC-31. HCFC-123a and chlorotrifluoroethene (CTFE) were produced simultaneously from CFC-113. Inhibition of methanogesis with 2 bromoethane sulfonate decreased significantly the degradation rate of CFC-11, emphasizing the importance of the role of methanogens in the degradation process. In the microcosms inoculated with the contaminated sediment, the transformation of CFC-11 also occurred, but was not accompanied with methane production, as it was the case in the suldge microcosms. Moreover, the presence of acetate, lactate and butyrate in the microcosms containing CFC-11 suggested that methanogens were inhibited in the presence of CFC-11. CFC-113 was transformed in the same way as in the microcosms inoculated with the sludge; however, the produced CTFE was further transformed to trifluoroethene (TFE). Production of HCFC-151b from HCFC-141b was also observed. In the column filled with aquifer material, only the transformations of CFC-11 and CFC-113 were observed, which is probably due to the short residence time in the column (~10 days), during which the transformation of the other compounds was not sufficiently pronounced. The increasingly reducing conditions in the column were accompanied with an increase of the degradation rates of CFC-11 and CFC-113, with a maximum reached in presence of methanogenesis. The addition of sulfate in the artificial groundwater decreased the biodegradation rates of the two compounds, and the concentration of their transformation products was simultaneously increased. This suggests that these products become more persistent under sulfate-reducing conditions. Natural attenuation designates all the processes leading to the decrease of the concentration of organic compounds migrating from a pollution source throughout a natural environment. Whereas natural attenuation or enhanced natural attenuation seem adequate for several classes of compounds, the absence of defluorination reaction of CFCs and HCFCs reported in this work suggests the use of other remediation techniques for the decontamination of sites polluted with these compounds. Indeed, the transformation products of CFCs and HCFCs still contain a fluorine atom and are not less harmfull to the environment than the parent compounds. In addition, the use of CFCs as age-dating tracers in groundwater is not recommended under anoxic conditions, as it was demonstrated here that they are not stable in such environments. The HCFCs on the other hand seem to be more persistent, and it is primordial to decrease rapidly their production and release in the environment.