A generic methodology for determining the required surface area of a final clarifier is presented. Clarification and thickening requirements are integrated to form a unified procedure for final clarifier design. The new method is based on results obtained by Yuen (2002) on the solids flux theory for a secondary clarifier; it does not require the specification of recycle rate, which is computed as an output of the method. The author shows that there is a minimum required surface area (A(m)) for a final clarifier under the thickening requirement when the designed recycle rate is set at the maximum allowable value (FR)m (at the critical state). The designed surface area and the return activated sludge pumping capacity can be determined by applying a safety factor to A(m) and (FR)m, respectively. The method is shown to conform to conventional design criteria under typical design conditions. 相似文献
Objective: To better capture the relationships between lane-changing collisions and explanatory variables, a microscopic model is developed for freeway lane-changing collisions based on the interactions between lane-changing vehicles.
Methods: The model applies an intervehicle interaction structure to account for the occurrence mechanism of lane-changing collisions. The occurrence mechanism can be described as the failure of a vehicle driver of an adjacent lane in avoiding the lane-changing vehicle, which disturbs the smooth movement of the adjacent lane vehicle and requires the driver's brake action to avoid an angle collision. This model is examined using data collected from freeways in Washington State during 2010 to 2011 and validated using lane-changing collision data for the SR 520 freeway.
Results: The findings of this study show that generalized truck percentage has a significant decreasing effect on lane-changing collision risk, whereas average spacing and several roadway characteristics have significant increasing effects. The frequency of slight collisions during peak hours is higher than that during off-peak hours. Young female drivers are more likely to be involved in collisions during lane-changing than young male drivers, but the result for senior drivers is opposite, with older male drivers having a higher probability of lane-changing collisions than female drivers in the same age group.
Conclusion: The process of lane-changing collisions is a complicated maneuver. Truck percentage, average spacing, and good roadway characteristics, such as straight and level segment, in the target lane have a significant effect on the occurrence of lane-changing collisions. Age and gender are also 2 important factors contributing to the relationship between lane-changing collisions and explanatory variables. 相似文献
A fixed bed reactor was used to assess the catalytic incineration of toluene by various transition-metal oxide species supported on gamma-Al(2)O(3). CuO/gamma-Al(2)O(3) was found to be the most active of seven catalysts investigated. The CuO species, with a Cu content of 5% (wt), was hence used with four different supports (CeO(2), gamma-Al(2)O(3), TiO(2) and V(2)O(5)) in order to define the optimal combination. Results of the catalytic incineration of toluene, X-ray diffraction (XRD) analysis, oxygen-temperature programmed desorption (O(2)-TPD), toluene-temperature programmed desorption (toluene-TPD) and hydrogen-temperature programmed reduction (H(2)-TPR) showed that CuO/CeO(2) was the most active catalyst, followed by CuO/gamma-Al(2)O(3). The activity of CuO/CeO(2) with respect to the VOC molecule was observed to follow this sequence: toluen>p-xylene>benzene. The addition of water vapor or CO(2) significantly inhibited the activity of the CuO/CeO(2) and CuO/gamma-Al(2)O(3) catalysts. The inhibiting effect of both was reversible for CuO/gamma-Al(2)O(3). For CuO/CeO(2), the inhibiting effect of CO(2) was reversible and even insignificant at a higher temperature (220 degrees C), but the effect of H(2)O vapor was somewhat irreversible at lower incineration temperatures (220 degrees C). For complete oxidation of toluene, the required reaction temperature increased with gas hourly space velocity (GHSV) and toluene inlet concentration. 相似文献
Three innovations in water and soil conservancy technology in the Pearl River Delta of South China, i.e., dike building, land reclamation, and dike-pond systems, were examined from a historical perspective. They were found to best reflect local farmers' efforts to cope with the challenges of various water disasters and to build a harmonious relationship with the changed environment. These technologies were critical to the agricultural success and sustainability over the past 2000 years, and reflected local farmers' wisdom in balancing land use and environmental conservation. Imprudent use of a new agricultural technology could damage the environment, and could disturb the human-environment relationship, as evidenced by the more frequent flooding that followed inappropriate dike building and premature reclamation. It is suggested that as the urbanization and industrialization process in the delta region continues, the kind of thinking that made the water and soil conservancy sustainable needs to be incorporated into the design of similar technologies for water use and river basin management today. 相似文献
A new type of designed hyperbranched ethylenediamine trazine polymer (HBETP) is successfully synthesized and characterized based upon NMR and GPC. The prepared HBETP is used to modify the poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/poly(butylene adipate-co-terephthalate) (PBAT) blends. The effect of HBETP on the microstructure, mechanical properties and thermal properties of the blends is studied. The results indicate that upon addition of 1.0 wt% of HBETP, the impact strength of the PHBV/PBAT blends is increased by 47.1%; ?Tg of the blends decreases from 53.2 to 49.9 °C. These results, together with the morphology analysis of the fractured surface of the blends, conclude the formation of the transition layer between PHBV and PBAT. Also, the XRD result shows that the addition of HBETP can limit the growth of the PHBV crystals and causes the decrease of both the crystallinity and the grain crystalline size. The DSC result demonstrates that the addition of HBETP mainly affects the crystallization of the HB-HV binary eutectic region within PHBV. The mechanism of PHBV/PBAT toughening is due to the formation of the strong physical hydrogen bonding and the chemical micro-crosslinking between HBETP and PHBV/PBAT, which is proposed based on XPS characterization. 相似文献