Bilan thermique sous climat tempéré des lagunes aérées et naturelles

Abstract

SUMMARYVery few studies hâve ever focused on the thermal balance of a wastewater treatment process, despite its major impact on various aspects of sanitary engineering, such as biological growth, oxygen transfer and, most importantly, purification kinetics. This lack of knowledge is particularly worrying for the design of aerated lagoons and waste stabilization ponds, since thèse two extensive treatment technologies are extremely dépendent on climatic conditions and subject to high thermal variations. In temperate régions, a pond annual température range can even exceed 20°C, while a 10°C variation will induce a more than 60% drop or increase in its removal yield. Our paper intends to présent a comprehensive température prédiction model which accounts for the main beat loss and gain ternis exchanged through the pond surface and walls.Our approach includes six différent energy inputs and outputs, namely: solar radiation, air-water surface convection, atmospheric radiation, back surface radiation, evaporation and ground-water-walls convection. Each of thèse components was described extensively by means of a literature review of ail previous efforts made to predict equilibrium température in lakes, rivers, saitgradient solar ponds, cooling tanks, even outdoor pools. The best aspects of each prédiction model were then incorporated into a new computer model developed as two différent but complementary variants: one for steady-state conditions and the other for continuous and therefore also transient simulations. The main différence between thèse two approaches is that the first one neglects enthalpy variation while the second one takes the form of a differential équation, with basin températures being estimated by an itérative calculation procédure and a numerical intégration method, respectively. Two hypothèses were necessary to develop this model. The first one posits that pond hydrodynamics correspond to completely mixed conditions. Such Eau, 12(1), 1999 T. Namèche etJ.L. Vasel hydraulic behavior is extremely fréquent in aerated lagoons and waste stabilization ponds in temperate climates, but less so in tropical or Mediterranean régions, where thermal balances appear much more complex since stabilization ponds are often thermally stratifled. The second hypothesis is that ail radiation fluxes received by the ponds are completely absorbed by the pond's contents and are never reflected, even partially, by their bottoms or walls.This model, which is in fact the thermal balance of the basins, relies mainly on meteorological factors and pond characteristics. Only two out of the six estimated fluxes -evaporation rates and solar radiation -are measured directly in situ. It seemed too difflcult to estimate them, since prédictive équations found in literature constantly gave unsatisfactory results.To establish the validity of this model, expérimental data were collected at a wastewater treatment plant located in the southem part of Belgium. This plant consists of a séries of two aerated lagoons and four waste stabilization...

Etude expérimentale du traitement par évaporation forcée des lixiviats des déchets ménagers. Cas de la ville de Kasbah Tadla

“…La vitesse moyenne d'évaporation a augmenté d'environ 20 % par rapport à la vitesse d'évaporation initiale, passant de 0,37 mm/j à 0,46 mm/j. La surélévation du bac au-dessus du sol augmente la surface exposée au rayonnement solaire qui est le moteur de la vaporisation (Braconnier et al, 2008, Nameche et Vasel, 1999, Vincon-Leite et al, 1989. La vitesse d'évaporation est ainsi une fonction croissante de la surface d'exposition aux rayonnements solaires.…”

Traitement Par Evaporation Solaire De Lixiviats De Dechets Menagers Au Maroc

“…La technique d'évaporation dans des casiers traditionnels au sol est utilisée dans la majorité des décharges contrôlées au Maroc. Les résultats ne donnent cependant pas entière satisfaction à cause des volumes trop importants de lixiviat à traiter (Nameche et Vasel, 1999). Nos travaux visent donc à améliorer cette technique en caractérisant les facteurs d'influence du traitement par évaporation forcée.…”