Respirometric evaluation of S 0 /X 0 ratio effect on the kinetic and stoechiometric parameters of activated sludge Mahfoud Sakhraoui * , R. Zamouche-Zerdazi, M. Bencheikh-Lehocine, A.-H. Meniai Laboratoire de l'Ingenierie des Procedes d'Environnement (LIPE), Faculte de Genie des Procedes, Universite Constantine 3, Constantine 25000, Algeria article info Article history: Received 2 August 2016 Received in revised form 1 January 2017 Accepted 16 January 2017 Available online xxx Keywords: Respirometry S 0 /X 0 ratios Stoechiometric-kinetic parametres Activated sludge abstract Respirometry has been used in this work to assess the effect of S 0 /X 0 ratio, knowing that this ratio is a very important operational parameter in the conduct of wastewater treat- ment plant. It affects its design and operation; part of the respirometry calculations, dis- solved oxygen transfer coefficient K L a is calculate for each respirometric experiment, due to the fact that operational condition change. Under endogenous conditions OUR end is calculated using the linear portion of the variation of DO concentration under no aeration conditions. Then the OUR end is used in the endogenous phase at a no oxygen concretion variation to calculate the K L a. Samples of wastewater, with different S 0 /X 0 ratios in the range between 0.01 and 0.23, containing sometimes ATU, a nitrification inhibitor, were injected in the respirometer with DO concentration variation recording. Exogenous OUR exo were calculated from the DO data and they show that as S 0 /X 0 ratio increased total OUR t increased too as well as total oxidation time. However when, COD is present alone the removal kinetics is more rapid than when both substrates (nitrogen and carbonaceous) are present. It has been shown that the use of respirometry in biomass activation assessment is a sound approach because of the celerity, the reliability and the limited cost. Conse- quently it has been extended in to the assessment of biomass activation when it is exposed to antibiotics. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Activated sludge biomass activity has been studied in a batch respirometer [1e4] through DO consumption. This method is one of the most frequently used to optimize biological re- actions and to evaluate kinetic and stoechiometric parame- ters [5e10] such as the substrate affinity constant (K S ), the maximum specific growth rate (m max ), the yield (Y X/S ) [11] etc. This technique consists of measuring biological oxygen con- sumption rate under well-defined conditions [12]. Particular thought has been paid to the influence of the initial substrate to biomass ratio S 0 /X 0 [13] on wastewater treatment perfor- mance [14e18]. This S 0 /X 0 ratio is an important [10,11] parameter in batch experiments because it reflects the initial energy level, to investigate the consumption of * Corresponding author. LIPE, Constantine 3 University, 25000, Algeria. E-mail address: mahfoudsakh@yahoo.com (M. Sakhraoui). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (2017) 1 e10 http://dx.doi.org/10.1016/j.ijhydene.2017.01.097 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Sakhraoui M, et al., Respirometric evaluation of S 0 /X 0 ratio effect on the kinetic and stoechiometric parameters of activated sludge, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.01.097