Modelling and Optimization of the Biological Treatment in the Conception of Water-Treatment Plants Whith Activated Sludge

Abstract

The pond of aeration, or airy biological reactor, is the major element of a water-treatment plant with activated sludge. His functioning packages the quality of the treatment, the network mud and the energy expenditure. The good knowledge of the hydrodynamics of these reactors is an essential stake to improve their conception and thus to optimize their functioning. Our study is interested in the use of the code of calculation FLUENT for the simulation of the flows in ponds of aeration the case of the water-treatment plant of Souk-Ahras, where the functions of aeration and admixture are separated. This software uses the method of the volumes finished to solve the equations of Navier-Stockes in turbulent regime. The final goal lives in the definition of technical capacities to improve the functioning of the work. Finally, we highlight the influence of the aeration on the speeds of circulation and the phenomena of ascending convection of the water (spiral spring-flows), responsible for a decrease of the transfer of oxygen in the pond. The impact of a horizontal speed on certain types of spiralflows is studied. Big spiral spring -flows disappear totally from a speed of 0,3 m.s −1 . These simulations are led for various geometries of ponds KeywordsChannel of oxidation Á Flow Á Hydrodynamics Á Transfer of oxygen Á Agitation IntroductionThe secondary treatment is essentially a biological oxidation of the dissolved materials. The agents of this oxidation are microorganisms, in particular aerobic bacteria, susceptible to feed on present organic matters in waste water. The secondary processing plants thus appear as ponds of culture where we put in touch a bacterial population and the effluent to be treated in the presence of oxygen.These ponds called also ponds of oxidation operate a free bacterial biomass associated in plops. These flakes of muds include heterotrophic microorganisms and autotrophes nitrifiants when the residence time of the mud is self-important so that their multiplication produces an active biomass in the treatment.This reproduction of microorganisms intervenes in favorable conditions, when their growth is important is that bacterium beginning dividing. The exo-polymers which they secrete allow them to gather together in plops settlings.The chosen conditions of operation are the ones which favor the settling of these plops. In this case, the biomass can be separated by a second settling where the extracted mud is recirculate towards the pond of aerobic treatment.The aeration can be assured on surface by turbines or at the bottom by processes of banister of distribution of air bubbles. The efficiency on transfer can be improved by the increase of the height of water.