Amélioration de la qualité microbiologique des eaux de surface dans un bassin versant, dans une zone densément peuplée : scénario des coûts et effets

Colloque avec actes et comité de lecture. Internationale.International audienc

Effects of Thermal Pretreatment of Sewage Sludge on Anaerobic Digestion

The study examines the constraints on thermal pretreatment of sludge at temperatures in excess of 100 °C and its effects on subsequent anaerobic digestion. The table below summarizes the maximum measured increase rates and the corresponding optimum pretreatment temperatures as a function of the type of sludge tested. The influence of the sludge type is considerable.Sludge TypeGas Yield without/with PretreatmentMaximum increase RateOptimum Pretreatment Temperaturel/kg VSinfl%°CDigested Sludge60.4223.0+ 269.2180Excess Sludge SLR = 0.03124.7278.1+ 123.0135Excess Sludge SLR = 0.15314.7546.7+ 73.7170Excess Sludge SLR = 2.00234.7334.2+ 42.4135Primary Sludge259.0326.6+ 20.3170Excess Sludge SLR = 0.60596.8600.0+ 0.5135 Calculation of detailed energy balances for various sludge treatment systems with and without thermal pretreatment revealed a clear economic advantage for thermal pretreatment. The excess heat for an overall system composed of thermal pretreatment, anaerobic stabilisation and digester-gas electricity generation is significantly higher than that for a system without pretreatment. Sludge pasteurisation represents an additional advantage of thermal pretreatment. In general, it may be stated that, provided certain conditions are satisfied, thermal pretreatment of sewage sludge prior to anaerobic stabilisation can positively affect the energy balance of the treatment plant.</jats:p

Amélioration de la qualité des eaux en utilisant des chasses pour nettoyer le réseau

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Impact of the Level of Approximation on Modeling Flushing Waves

Sewer cleaning with the means of flushing offers the possibility to place sewers free of deposit if flushing waves are generated continuously or quasi-continuously by suitable flushing devices. Numerical investigations should be carried out regarding different hydraulic circumstances because sewer networks consist of various compounds with complex geometries e.g. cross-section alignment or special structures. To accomplish a stable and successful operation of flushing devices it seems necessary to use different level of approximation on modelling flushing waves. Thereby both accuracy and running-time of simulations with numerical models will be optimized. This paper presents differences and similarities of the simulation results of a one-dimensional and a three-dimensional model of flushing wave within a big sized sewer. As assumed the one-dimensional model becomes less accurate when the complexity of the geometry increases. The three-dimensional model shows an underestimation of velocity and bottom shear-stress at the flushing head due to energy losses within the water body. Contrary, the one-dimensional model overestimates bottom shear-stress at the flushing head because of a stationary basic approach which is used. However, real highly resolved measurements of bottom shear-stresses are required to confirm the results in detail.</jats:p