RESUMEN
Sinking marine particles drive the biological pump that naturally sequesters carbon from the atmosphere. Despite their small size, the compartmentalized nature of particles promotes intense localized metabolic activity by their bacterial colonizers. Yet the mechanisms promoting the onset of denitrification, a metabolism that arises once oxygen is limiting, remain to be established. Here we show experimentally that slow sinking aggregates composed of marine diatoms-important primary producers for global carbon export-support active denitrification even among bulk oxygenated water typically thought to exclude anaerobic metabolisms. Denitrification occurs at anoxic microsites distributed throughout a particle and within microns of a particle's boundary, and fluorescence-reporting bacteria show nitrite can be released into the water column due to segregated dissimilatory reduction of nitrate and nitrite. Examining intact and broken diatoms as organic sources, we show slowly leaking cells promote more bacterial growth, allow particles to have lower oxygen, and generally support greater denitrification.
RESUMEN
Degradation of PPCPs by AOPs has gained major interest in the past decade. In this work, theophylline (TP) oxidation was studied in thermally (TAP) and chemically (CAP) activated persulfate systems, separately and in combination (TCAP). For [TP]0 = 10 mg L-1, (i) TAP resulted in 60% TP degradation at [PS]0 = 5 mM and T = 60 °C after 60 min of reaction and (ii) CAP showed slight degradation at room temperature; however, (iii) TCAP resulted in complete TP degradation for [PS]0 = [Fe2+]0 = 2 mM at T = 60 °C following a pseudo-first order reaction rate with calculated k obs = 5.6 (±0.4) × 10-2 min-1. In the TCAP system, the [PS]0 : [Fe2+]0 ratio of 1 : 1 presented the best results. A positive correlation was obtained between the TP degradation rate and increasing temperature and [PS]0, and a negative correlation was obtained with increasing pH. Both chloride and humic acid inhibited the degradation process, while nitrates enhanced it. TP dissolved in spring, sea and waste water simulating real effluents showed lower degradation rates than in DI water. Waste water caused the highest inhibition (k obs = 2.6 (±0.6) × 10-4 min-1). Finally, the TCAP system was tested on a real factory effluent highly charged with TP, e.g. [TP]0 = 160 mg L-1, with successful degradation under the conditions of 60 °C and [PS]0 = [Fe2+]0 = 50 mM.
RESUMEN
H2O2 is one of the most commonly used oxidants for the degradation of recalcitrant organic contaminants in advanced oxidation processes (AOPs). However, most research aiming to optimize AOPs is missing the monitoring of the remaining H2O2, an important parameter to assess the efficiency of the process. In this work, a novel method for [H2O2] quantification was developed using simple modifications of an HPLC-DAD setup that is available in most analytical chemistry laboratories. The modifications include the use of acidified potassium iodide solution as mobile phase and replacing the reverse phase column with a series of capillary columns. This instrument configuration allowed also the quantification of organic contaminants using the same H2O2 containing sample. The method's LOD and LOQ were calculated to be as low as 8.29â¯×â¯10-4â¯mM and 2.76â¯×â¯10-3â¯mM, respectively with an LDR range of 0.01-150â¯mM. The cost per analysis ranged between 0.8 and 1.8 USD cents depending on the concentration tested. This analytical method was validated by a statistical comparison to a well-known titrimetric method that is commonly used for H2O2 quantification. It was also tested using standards prepared in natural matrices such as spring and seawater, and in media containing high concentration of several spectator species such as chlorides, bicarbonates, humic acids, fumaric acids and micro pollutants. The method showed excellent robustness by maintaining high regression coefficient and excellent sensitivity in all calibration curves regardless of the matrix content.
