Thermal attenuation and lag time in fractured rock: theory and field measurements from joint heat and solute tracer tests

International audienceThe modelling and prediction of heat transfer in fractured media is particularly challenging as hydraulic and transport properties depend on a multiscale structure that is difficult to resolve. In addition to advection and dispersion, heat transfer is also impacted by thermal attenuation and lag time, which results from fracture‐matrix thermal exchanges. Here we derive analytical expressions for thermal lag time and attenuation coefficient in fractured media, which quantify the effect of fracture geometry on these key factors. We use the developed expressions to interpret the results of single‐well thermal tracer tests performed in a crystalline rock aquifer at the experimental site of Ploemeur (H+ observatory network). Thermal breakthrough was monitored with Fiber‐Optic Distributed Temperature Sensing (FO‐DTS), which allows temperature monitoring at high spatial and temporal resolution. The observed thermal response departs from the conventional parallel plate fracture model but is consistent with a channel model representing highly channelized fracture flow. These findings, which point to a strong reduction of fracture‐matrix exchange by flow channeling, show the impact of fracture geometry on heat recovery in geothermal systems. This study also highlights the advantages to conduct both thermal and solute tracer tests to infer fracture aperture and geometry

Urban wastewater treatment by Tetraselmis sp CTP4 (Chlorophyta)

The ability of a recent isolate, Tetraselmis sp. CTP4, for nutrient removal from sewage effluents before and after the nitrification process under batch and continuous cultivation was studied. Biomass productivities in both wastewaters were similar under continuous conditions ( 0.343 +/- 0.053 g L-1 d(-1)) and nutrient uptake rates were maximal 31.4 +/- 0.4 mg N L-1 d(-1) and 6.66 +/- 1.57 mg P-PO43 L- 1 d(-1) in WW before nitrification when cultivated in batch. Among batch treatments, cellular protein, carbohydrate and lipid levels shifted with aging cultures from 71.7 +/- 6.3 to 29.2 +/- 1.2%, 17.4 +/- 7.2 to 57.2 +/- 3.9% and 10.9 +/- 1.7 to 13.7 +/- 4.7%, respectively. In contrast, CTP4 cultivated continuously in Algal medium (control) showed lower biomass productivities ( 0.282 g VSS L-1 d(-1)) although improved lipid content (up to 20% lipids) in batch cultivation. Overall, Tetraselmis sp. CTP4 is promising for WW treatment as a replacement of the costly nitrification process, fixating more nutrients and providing a protein and carbohydrate-rich biomass as by-product. (C) 2016 Elsevier Ltd. All rights reserved.Portuguese Foundation for Science and Technology (FCT) [SFRH/BD/105541/2014]FCT [SFRH/BPD/81882/2011, IF/00049/2012]FCT Investigator Programmeinfo:eu-repo/semantics/publishedVersio