This study investigated the use of biological powdered activated carbon {PAC) for the removal of natural organic matter {NOM) and ammonia from drinking water. The impact of soiids retention time (SRT), hydraulic retention time (HRT), PAC diameter and PAC concentration on the process efficiency was evaluated. Five bioreactors were filled with a slurry using two PAC concentrations {5or25gr^), two PAC mean diameters (25 or 200um) and two SRTs (30 or 100-160 days).The bioreactors were operated during 161 days using post-ozonated water as influent. It was determined that the PAC concentration in the bioreactors was a key parameter for the improvement of biciogical removal. The higher PAC concentration {25 g I ^) was more efficient for the removal of ammonia, dissolved organic carbon (DOC) and biodegradable dissolved organic carbon (BDOC). Full nitrification vi/as observed after 90 days in bioreactors with 25gl of PAC.The PAC diameter (25 vs. 200 jim) did not significantly influence BDOC, DOC and N-NH4 removals under stable conditions, although nitrification was initiated faster using a 25-jLm diameter PAC.increasing HRT from 15 to 30 minutes improved NOM and ammonia removals. Reducing SRT from 100-161 to 30 days improved DOC removals but reduced BDOC and ammonia removals.The overall performances observed during this study demonstrate the efficiency of biological PAC.Its combination with Ultrafiltration in a hybrid membrane process appears promising but the feasibility from an operational standpoint still has to be demonstrated
In recent years several parallel bridges were designed and built in North America. These bridges have been selected to replace existing structures and to meet the ever-increasing demands of vehicle traffic. To meet the demands of increased traffic, the parallel configuration is often selected where each bridge deck carries traffic of opposite direction. This pair of decks, even when remaining dynamically independent, become coupled aerodynamically due to their proximity. In this configuration the aerodynamic forces can be enhanced by the similar cross-sections of each bridge and by the close dynamic properties of the twin structures. Becoming aerodynamically coupled, these twin-deck systems have been found to display aerodynamic behavior noticeably different to what could be expected from a single deck of the same cross-section. Typical known aerodynamic solutions to cure instabilities such as vortex shedding and flutter may not be as efficient for these cases. The conventional strategy to study each deck dynamically suspended upwind or downwind of the other statically-mounted deck section showed limited application given the new and complex motion-driven aerodynamic behavior that appeared only in a tandem dynamic arrangement of testing. Generally, there are slight geometrical differences in the twin sections (e.g., a walkway on one of the decks) and these difference lead to asymmetries in the combined cross-section. Therefore, finding an aerodynamic solution for one wind direction will not necessarily work for the opposite direction. Given that known solutions of a single section may not be efficient, and vice versa when considering bridge's construction, an extensive circle of trials was required until appropriate aerodynamic solutions were found applicable in all conditions. This paper presents results of the aerodynamic studies for three different bridges, and of particular solutions found when required. Useful suggestions for future twin-bridge configurations of similar arrangements are also given.
This article deals with an experimental determination of the relative phase angle between the shedding of vortices and motion in the case of the Aeolian vibrations of a flexible circular tube. The objective is to compare and determine if the phase value of a transient regime differs from that measured in a steady vibrating state. For each mode of vortex shedding (Von Ka´rma´n, 2S and 2P), the results show that the value of the phase angle in the unsteady and steady regimes is relatively similar if an appropriate dependency is selected: in the cases of the 2P and 2S modes of vortex shedding, this dependency is either the dimensionless amplitude or the ratio of the velocity of the structure motion to the oncoming flow velocity; in the case of the Von Ka´rma´n regime, at the onset of the instability, the usual reduced velocity is a better dependent variable. The analysis of jumps occurring in the instruments output reveals a boundary between the Von Ka´rma´n and the 2P modes of vortex shedding.
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