29 research outputs found

    Rheological Characteristics of Municipal Thickened Excess Activated Sludge (TEAS): Impacts of pH, Temperature, Solid Concentration and Polymer Dose

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    Rheological characterization of sludge is known to be an essential tool to optimize flow, mixing and other process parameters in wastewater treatment plants. This study deals with the characterization of thickened excess activated sludge in comparison to raw primary sludge and excess activated sludge. The effects of key parameters (total solid concentration, temperature, and pH) on the rheology and flow behavior of thickened excess activated sludge were studied. The rheological investigations were carried out for total solid concentration range of 0.9–3.7 %w/w, temperature range of 23–55 °C, and pH range of 3.6–10.0. Different rheological model equations were fitted to the experimental data. The model equations with better fitting were used to calculate the yield stress, apparent, zero-rate, infinite-rate viscosities, flow consistency index, and flow index. The decrease in concentration from 3.7 to 3.1 %w/w resulted in a drastic reduction of yield stress from 27.6 to 11.0 Pa, while a further reduction of yield stress to 1.3 Pa was observed as solid concentration was reduced to 1.3 %w/w. The viscosity at higher shear rate (>600 s−1) decreased from 0.05 Pa·s down to 0.008 Pa·s when the total solid concentration was reduced from 3.7 to 0.9 %. Yield stress decreased from 20.1 Pa down to 8.3 Pa for the Bingham plastic model when the temperature was raised from 25 to 55 °C. Activation energy and viscosity also showed decreasing trends with increasing temperature. Yield stress of thickened excess activated sludge increased from a value of 6.0 Pa to 8.3 Pa when the pH was increased from 3.6 to 10.0. The effect of polymer dose on the rheological behavior of the thickening of excess activated sludge was also investigated, and the optimum polymer dosage for enhanced thickener performance was determined to be 1.3 kg/ton DS

    Les procédés de gazéification comme alternative pour la valorisation de boues de stations d'épuration des eaux usées

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    International audienceThe problem of wastewater treatment plant sewage sludge is becoming crucial. Indeed the quantity of sewage sludge will increase with the population and the economic developments, the rise of the number of treatment plants and their better performance. Sewage sludge treatment is at the moment realized in limited ways. Whatever the future of those ways and without creating polemics, they will not be able, to absorb this increasing volume. It consequently becomes necessary to diversify the methods of treatment to answer the problems arising from the management of this waste. Within this framework, the new thermochemical ways of treatment by valorization seems more interesting. Indeed, they present in addition to the advantage of the possibility of processing, the capacity to easily produce "storable" and valuable compounds. Thus will treat, in this article, the interest to develop the processes of gasification of waste water sewage sludge.Le devenir des boues de stations d'épuration des eaux usées (Step) est un problème crucial posé aux pays industrialisés. En effet la quantité de boues produite en Step ne va cesser d’augmenter avec les croissances démographique et économique, ainsi que le nombre et la performance des Step des eaux usées. Actuellement, le traitement des boues de Step se fait par différentes filières, dont le nombre est limité. Quel que soit le devenir de ces filières et sans créer de polémiques particulières elles ne pourront, dans tous les cas, pas absorber ce volume croissant. Il devient dès lors nécessaire de diversifier les méthodes de traitement pour répondre aux problèmes posés par la gestion de ce déchet. Dans ce cadre, les nouvelles filières de traitement par valorisation thermochimiques semblent des plus intéressantes. En effet, elles présentent en plus de la capacité de traitement, l’avantage de produire des composés « stockables » et facilement «valorisables». Nous traiterons ainsi, dans cet article, de l'intérêt de développer les procédés de gazéification des boues de Step

    Inhibition of activated sludge respiration by sodium azide addition: Effect on rheology and oxygen transfer

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    International audienceAlthough microorganism respiration inhibition by sodium azide (NaN3) is used in some studies to identify activated sludge adsorption capacity, little is known about the effect of this compound on the suspension properties. In this study we have investigated the effect of NaN3 addition on both volumetric oxygen mass transfer coefficient and rheology of activated sludge (AS) suspensions in a 1.9 L bioreactor. The rheological properties (shear thinning one) of AS suspensions with and without NaN3 addition are measured in situ (triphasic conditions). It appears that NaN3 addition leads to a deflocculation of AS suspensions and thus a decrease in apparent viscosity. A small amount of suspended solids was added in order to obtain identical apparent viscosities (under 1.2 or 46.3 s−1) for AS suspensions with and without NaN3 addition. KLa values were then measured in both respiring and non-respiring suspensions for different air flow rates (2, 3 or 4 L/min) and under low or high mechanical shear rate (1.2 or 46.3 s−1). Results show that under high mechanical shear rate, the respiration state for a given air flow rate does not impact the KLa values. On the contrary, under low mechanical shear rate, NaN3 addition induces an increase of KLa values in comparison with those obtained with the respiring biomass. This effect, for a same apparent viscosity, is attributed to the deflocculation observed in the presence of NaN3. Indeed, AS with and without NaN3 addition used for the KLa measurements induce a modification of the floc internal structure, corresponding to smaller floc size in the case of NaN3 addition
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