Internal occupational dosimetry for the occupational worker exposed to [18F] FDG from the Cyclotron-PET/CT Laboratory of the Universidad de Costa Rica / Dosimetría ocupacional interna para el personal trabajador expuesto a [18F] FDG del ciclotrón-PET/CT en el Laboratorio de la Universidad de Costa Rica

ABSTRACT: The aim of this work is to provide a methodology for evaluating the committed effective dose E(50) due to the incorporation of [18F] FDG in the occupationally exposed worker (OEW) of the Cyclotron-PET/CT Laboratory of the Centro de Investigación en Ciencias Atómicas, Nucleares y Moleculares (CICANUM) at Universidad de Costa Rica using in vivo measurements. The measurement system was calibrated to perform in vivo measurements and defined as the corresponding bioassay function for the radiopharmaceutical used. The conversion factor was assessed with a known activity of 18F in the geometry and measurement time established. Among the most relevant results, the measurement parameters and the calibration procedure were defined. A value of 1.73 x 103 Bq/cps for in vivo brain measurements was obtained as a conversion factor. This study provides a methodology, to evaluate the committed effective dose due to the incorporation of 18F-FDG in a radionuclide production and diagnostic center

Characterisation and perspectives of energetic use of dissolved gas recovered from anaerobic effluent with membrane contactor.

Biogas is a source of renewable energy, and its production and use has been validated in anaerobic-based sewage treatment plants (STPs). However, in these systems, a large amount of methane is lost as dissolved methane (D-CH4) in the liquid effluent. In this study, the characteristics and potential energetic uses of the gas recovered during the desorption of D-CH4 from anaerobic effluents with hollow fibre membrane contactors were investigated. A pilot-scale experiment was performed using sewage and two types of membrane contactors. The recovered gas contained considerable amounts of CH4, CO2, H2S, N2, and O2; therefore, a gas upgrade is required prior to its use as a biofuel. The recovery process should be energetically self-sustainable, and induce a considerable decrease in the STP carbon footprint. Recovering D-CH4 with membrane contactors could increase the energetic potential of anaerobic-based STPs up to 50 % and allow for more sustainable systems.

Simultaneous removal of dissolved sulphide and dissolved methane from anaerobic effluents with hollow fibre membrane contactors.

Dissolved gases in the effluent of anaerobic reactors, specifically dissolved methane (D-CH4) and sulphide (S2-), are a drawback for anaerobic-based sewage treatment plants (STPs). This article studied the simultaneous desorption/removal of both gases from anaerobic effluents with hollow fibre membrane contactors (HFMCs), evaluating two types of membrane materials (e.g. microporous and dense) at different operating conditions (atmospheric air as sweeping gas or vacuum, and different gas/liquid flows and vacuum pressures). The transfer of other gases, such as O2 and CO2, was studied as well. Desorption/removal efficiencies up to 99% for D-CH4 and 100% for S2- were obtained, with the higher efficiencies reported for the dense HFMC and with air as sweeping gas. It was found that the removal mechanism for S2- was oxidation with O2 from the air. In addition, the use of air as sweeping gas allowed the obtention of a nearly O2 saturated effluent, with more elevated dissolved oxygen concentrations in the microporous HFMC. Finally, it was found that the higher mass-transfer resistance in the dense membrane was compensated by a better performance in the liquid phase (lower mass-transfer resistance) in this unit, which allowed better D-CH4 desorption efficiencies.

Development and performance of a dynamic membrane for anaerobic wastewater treatment - an analysis with different mesh pore sizes and configurations.

Recent studies have focused on proposing materials with larger pores and lower cost to replace conventional membranes. This study aims to investigate the performance of an anaerobic dynamic membrane bioreactor (AnDMBR) at pilot scale, acting as a post-treatment for an Upflow Anaerobic Sludge Blanket (UASB) reactor treating sewage, for the removal of complementary organic matter, focusing on the module design, dynamic layer formation and process performance. The configurations tested on this study were: UASB followed by stone filter and three AnDMBRs in series with polyester pore sizes of 100 µm, 50 µm, and 5 µm; UASB followed by disc filter and the three AnDMBRs in series; UASB followed by the three AnDMBRs in series; and UASB reactor with only one AnDMBR module. Regarding the studied configurations, high removals of total suspended solids, chemical oxygen demand, and turbidity were achieved in all experimental setups. The use of stone and disc filters did not bring clear benefits to the system concerning the direct application of filtration with dynamic membranes, therefore, their removal in the system was favorable. The dynamic membrane formation was faster in the 50 µm mesh, and only a few hours were necessary to obtain a permeate quality with a total suspended solids concentration and a turbidity lower than 15 mg·L-1 and 30 NTU, respectively. Thus, the dynamic membrane technology proved to be a potential solution in the post-treatment of UASB reactor effluents.

Mitigation of diffuse CH4 and H2S emissions from the liquid phase of UASB-based sewage treatment plants: challenges, techniques, and perspectives.

Upflow anaerobic sludge blanket (UASB) reactors are considered to be a sustainable and well-established technology for sewage treatment in warm climate countries. However, gases dissolved in the effluent of these reactors, CH4 and H2S in some instances, are a major drawback. These dissolved gases can be emitted into the atmosphere downstream of the anaerobic reactors, resulting in odour nuisance and, in the case of H2S, corrosion, while in the case of CH4, increasing greenhouse gas emissions with a significant loss of potentially recoverable energy. In this sense, this study aims to provide a critical review of the recent efforts to control CH4 and H2S dissolved in UASB reactor effluents, with a focus on the different available techniques. Different desorption techniques have been tested for the removal/recovery of dissolved CH4 and H2S: diffused aeration, simplified desorption chamber, packed desorption chamber, closed downflow hanging sponge reactor, membrane contactor, and vacuum desorption chamber. Other recent publications addressing the oxidation of these compounds in biological posttreatments with simultaneous nitrification/denitrification of ammonia were also discussed. Additionally, the rationale of CH4 recovery was determined by energy balance and carbon footprint approaches, and the H2S removal was examined by modelling its emission and atmospheric dispersion.