Abstract: When partial nitritation-anammox (PN-AMX) processes are applied to treat the mainstream in wastewater treatment plants (WWTPs), it is difficult to fulfil the total nitrogen (TN) quality requirements established by the European Union (<10g TN/m(3)). The operation of the anammox process was evaluated here in a continuous stirred tank reactor operated at 15 degrees C and fed with concentrations of 50 g TN/m(3) (1.30 +/- 0.23 g NO2- -N/g NH4+-N). Two different aspects were identified as crucial, limiting nitrogen removal efficiency. On the one hand, the oxygen transferred from the air in contact with the mixed liquor surface favoured the nitrite oxidation to nitrate (up to 75 %) and this nitrate, in addition to the amount produced from the anammox reaction itself, worsened the effluent quality. On the other hand, the mass transfer of ammonium and nitrite to be converted inside the anammox granules involves relatively large values of apparent affinity constants (k(NH4+app) : 0.50 g NH4+-N/m(3) ; k(NO2-app) 0.17 g NO2--N/m(3)) that favour the presence of these nitrogen compounds in the produced effluent. The careful isolation of the reactor from air seeping and the fixation of right hydraulic and solids retention times are expected to help the maintenance of stability and effluent quality. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Abstract: Nowadays the application of Anammox based processes in the wastewater treatment plants has given a step forward. The new goal consists of removing the nitrogen present in the main stream of the WWTTPs to improve their energetic efficiencies. This new approach aims to remove not only the nitrogen but also to provide a better use of the energy contained in the organic matter. The organic matter will be removed either by an anaerobic psychrophilic membrane reactor or an aerobic stage operated at low solids retention time followed by an anaerobic digestion of the generated sludge. Then ammonia coming from these units will be removed in an Anammox based process in a single unit system. The second strategy provides the best results in terms of operational costs and would allow reductions of about 28%. Recent research works performed on Anammox based processes and operated at relatively low temperatures and/or low ammonia concentrations were carried out in single-stage systems using biofilms, granules or a mixture of flocculent nitrifying and granular Anammox biomasses. These systems allowed the appropriated retention of Anammox and ammonia oxidizing bacteria but also the proliferation of nitrite oxidizing bacteria which seems to be the main drawback to achieve the required effluent quality for disposal. Therefore, prior to the implementation of the Anammox based processes at full scale to the water line, a reliable strategy to avoid nitrite oxidation should be defined in order to maintain the process stability and to obtain the desired effluent quality. If not, the application of a post-denitrification step should be necessary. (C) 2015 Elsevier Ltd. All rights reserved.

Abstract: Soot volume fractions and soot temperatures have been measured for the first time on candle flames. Measurements on laminar steady flames were carried out using candles with wick diameters of 2, 3 and 4 mm. Wick length was varied between 4 and 10 mm. The shape of the candle flame was obtained from CH* spontaneous emissions. Measured flame heights show an increase with wick dimensions, approaching an asymptotic value for increasing wick lengths. Soot volume fractions were obtained from laser extinction measurements with the Modulated Absorption/Emission (MAE) technique. A deconvolution technique and a regularization procedure were applied to the data. Radial profiles of soot volume fractions increase when varying the wick dimensions; this effect is produced by the greater amount of fuel released by the wick. Radially integrated soot volume fractions were also calculated, presenting a similar behavior to the soot volume fraction radial profiles. The peak integrated soot volume fraction was found at approximately half the flame height, independent of the wick dimensions and burning rates. Soot temperature was obtained from emission measurements at two different wavelengths considering the attenuation of the soot particles in the optical path length. A deconvolution and regularization procedure was carried out in order to obtain temperature profiles for different heights in the flame. The observed increase in soot production and soot temperature profiles was directly related to the higher burning rate experienced by the candle. The results show that peak integrated soot volume fractions are proportional to both the mass loss rates and the flame heights. (C) 2016 Elsevier Inc. All rights reserved.