Effects of UV and Calcium Perchlorates on Uracil Deposited on Strontium Fluoride Substrates at Mars Pressure and Temperature.

Organic matter is actively searched on Mars with current and future space missions as it is a key to detecting potential biosignatures. Given the current harsh environmental conditions at the surface of Mars, many organic compounds might not be preserved over a long period as they are exposed to energetic radiation such as ultraviolet light, which is not filtered above 190 nm by the martian atmosphere. Moreover, the presence of strong oxidizing species in the regolith, such as perchlorate salts, might enhance the photodegradation of organic compounds of astrobiological interest. Because current space instruments analyze samples collected in the upper surface layer, it is necessary to investigate the stability of organic matter at the surface of Mars. Previous experimental studies have shown that uracil, a molecule relevant to astrobiology, is quickly photolyzed when exposed to UV radiation under the temperature and pressure conditions of the martian surface with an experimental quantum efficiency of photodecomposition (φexp) of 0.30 ± 0.26 molecule·photon-1. Moreover, the photolysis of uracil leads to the formation of more stable photoproducts that were identified as uracil dimers. The present work aims to characterize the additional effect of calcium perchlorate detected on Mars on the degradation of uracil. Results show that the presence of calcium perchlorate enhances the photodecomposition of uracil with φexp = 12.3 ± 8.3 molecule·photon-1. Although some of the photoproducts formed during these experiments are common to those formed from pure uracil only, the Fourier transformation infrared (FTIR) detection of previously unseen chemical functions such as alkyne C ≡ C or nitrile C ≡ N has shown that additional chemical species are formed in the presence of calcium perchlorate in the irradiated sample. This implies that the effect of calcium perchlorate on the photolysis of uracil is not only kinetic but also related to the nature of the photoproducts formed.

Removal of a wide range of emerging pollutants from wastewater treatment plant discharges by micro-grain activated carbon in fluidized bed as tertiary treatment at large pilot scale.

Among the solutions to reduce micropollutant discharges into the aquatic environment, activated carbon adsorption is a promising technique and a large scale pilot has been tested at the Seine Centre (240,000 m(3)/d - Paris, France) wastewater treatment plant (WWTP). While most of available works studied fixed bed or contact reactors with a separated separation step, this study assesses a new type of tertiary treatment based on a fluidized bed containing a high mass of activated carbon, continuously renewed. For the first time in the literature, micro-grain activated carbon (µGAC) was studied. The aims were (1) to determine the performances of fluidized bed operating with µCAG on both emerging micropollutants and conventional wastewater quality parameters, and (2) to compare its efficiency and applicability to wastewater to former results obtained with PAC. Thus, conventional wastewater quality parameters (n=11), pharmaceuticals and hormones (PPHs; n=62) and other emerging pollutants (n=57) have been monitored in µGAC configuration during 13 campaigns. A significant correlation has been established between dissolved organic carbon (DOC), PPHs and UV absorbance at 254 nm (UV-254) removals. This confirms that UV-254 could be used as a tertiary treatment performance indicator to monitor the process. This parameter allowed identifying that the removals of UV-254 and DOC reach a plateau from a µGAC retention time (SRT) of 90-100 days. The µGAC configuration substantially improves the overall quality of the WWTP discharges by reducing biological (38-45%) and chemical oxygen demands (21-48%), DOC (13-44%) and UV-254 (22-48%). In addition, total suspended solids (TSS) are retained by the µGAC bed and a biological activity (nitratation) leads to a total elimination of NO2(-). For micropollutants, PPHs have a good affinity for µGAC and high (>60%) or very high (>80%) removals are observed for most of the quantified compounds (n=22/32), i.e. atenolol (92-97%), carbamazepine (80-94%), ciprofloxacin (75-95%), diclofenac (71-97%), oxazepam (74-91%) or sulfamethoxazole (56-83%). In addition, alkylphenols, artificial sweeteners, benzotriazole, bisphenol A, personal care products (triclocarban and parabens) and pesticides have removals lying in the 50 ->90% range. Overall, the fluidized bed of µGAC allows obtaining performances comparable to PAC at the same activated carbon dose. Indeed, the average removal of the 13 PPHs found at a high occurrence (>75%) in WWTP discharges is similar at 20 g/m(3) of µGAC (78-89%) and PAC (85-93%). In addition, this recycled µGAC operation leads to several operational advantages (no FeCl3, reactivable, higher SRT, higher treated flow) and has a stronger impact on the overall wastewater quality compared to PAC.

Study of a large scale powdered activated carbon pilot: Removals of a wide range of emerging and priority micropollutants from wastewater treatment plant effluents.

The efficacy of a fluidized powdered activated carbon (PAC) pilot (CarboPlus(®)) was studied in both nominal (total nitrification + post denitrification) and degraded (partial nitrification + no denitrification) configuration of the Seine Centre WWTP (Colombes, France). In addition to conventional wastewater parameters 54 pharmaceuticals and hormones (PhPHs) and 59 other emerging pollutants were monitored in influents and effluents of the pilot. Thus, the impacts of the WWTP configuration, the process operation and the physico-chemical properties of the studied compounds were assessed in this article. Among the 26 PhPHs quantified in nominal WWTP configuration influents, 8 have high dissolved concentrations (>100 ng/L), 11 have an intermediary concentration (10-100 ng/L) and 7 are quantified below 10 ng/L. Sulfamethoxazole is predominant (about 30% of the sum of the PhPHs). Overall, 6 PhPHs are poorly to moderately removed (<60%), such as ibuprofen, paracetamol or estrone, while 9 are very well removed (>80%), i.e. beta blockers, carbamazepine or trimethoprim, and 11 are well eliminated (60-80%), i.e. diclofenac, naproxen or sulfamethoxazole. In degraded WWTP configuration, higher levels of organic matter and higher concentrations of most pollutants are observed. Consequently, most PhPHs are substantially less removed in percentages but the removed flux is higher. Thus, the PAC dose required to achieve a given removal percentage is higher in degraded WWTP configuration. For the other micropollutants (34 quantified), artificial sweeteners and phthalates are found at particularly high concentrations in degraded WWTP configuration influents, up to µg/L range. Only pesticides, bisphenol A and parabens are largely eliminated (50-95%), while perfluorinated acids, PAHs, triclosan and sweeteners are not or weakly removed (<50%). The remaining compounds exhibit a very variable fate from campaign to campaign. The fresh PAC dose was identified as the most influencing operation parameter and is strongly correlated to performances. Charge and hydrophobicity of compounds have been recognized as crucial for the micropollutant adsorption on PAC, as well as the molecular weight. Finally, a PAC dose of 10 mg/L allows an average removal of 72-80% of the sum of the PhPHs in nominal WWTP configuration. The comparaison of the results with those from the scarce other studies tends to indicate that an extrapolation of them to different PAC processes and to other WWTPs could be possible and relevant, taking into account the differences of water quality from WWTP to WWTP.

Micropollutants in urban stormwater: occurrence, concentrations, and atmospheric contributions for a wide range of contaminants in three French catchments.

This study aimed at: (a) providing information on the occurrence and concentration ranges in urban stormwater for a wide array of pollutants (n = 77); (b) assessing whether despite the differences between various catchments (land use, climatic conditions, etc.), the trends in terms of contamination level are similar; and (c) analyzing the contribution of total atmospheric fallout (TAF) with respect to sources endogenous to this contamination. The studied contaminants include conventional stormwater contaminants (polycyclic aromatic hydrocarbons (PAHs), Zn, Cu, Pb, etc.), in addition to poorly or undocumented pollutants such as nonylphenol and octylphenol ethoxylates (NPnEO and OPnEO), bisphenol A (BPA), polybrominated diphenyl ethers (PBDEs), a wide variety of pesticides, and various metals of relevance (As, Ti, Sr, V). Sampling and analysis were performed using homogeneous methods on three urban catchments with different land use patterns located in three distinct French towns. For many of these pollutants, the results do not allow highlighting a significant difference in stormwater quality at the scale of the three urban catchments considered. Significant differences were, however, observed for several metals (As, Cr, Cu, Ni, Sr and Zn), PAHs, and PBDEs, though this assessment would need to be confirmed by further experiments. The pollutant distributions between dissolved and particulate phases were found to be similar across the three experimental sites, thus suggesting no site dependence. Lastly, the contributions of TAF to stormwater contamination for micropollutants were quite low. This finding held true not only for PAHs, as previously demonstrated in the literature, but also for a broader range of molecules such as BPA, NPnEO, OPnEO, and PBDEs, whose high local production is correlated with the leaching of urban surfaces, buildings, and vehicles.