Advanced Materials Research Vol. 777

Abstract: Small mesh grid is mostly used as flocculation equipment in present water plant, and its head loss is closely related to flocculation effect. Flocculation tank installed with several grid groups in different mesh sizes were tested with a view to evaluating its head loss characteristics, including the frictional and local head losses. The tests were carried out at pilot scale, using a steel tank as flocculation basin. The grids are made of plastic material and the cross section size of the grid trips is 7 mm in width and 2 mm in height. The results indicate that relative roughness is most associated with frictional resistance coefficient (FRC), whereas Reynolds number was unrelated to that. The ratio of frictional head loss to total head loss of the basin does not vary with the variation of channel velocity, and the ratio is always less than 6% in this case. Local resistance coefficient (LRC) decreases with the increase of mesh size. In order to improve the utilization rate of head loss, the preferred mesh size of the grid should be 30-40 mm. The optimal space between the neighboring grid layers can maximize the utilization of turbulent kinetic energy loss generated by grids.

Abstract: In order to cope with urban flooding, water scarcity and rainfall-runoff pollution comprehensively, a conceptual tank model of urban storm water system is proposed. Tank model is a multi-layer, multi-objective model, so design of urban storm water system is more complex than that of urban storm sewer system. Some principles of design of urban storm water system are discussed, such as Low Impact Development, Smart storm water management, and so on.

Abstract: The 2-D and 3-D numerical model have been developed to predict flow state and outlet velocity distribution by FLUENT based on the high-sludge setting tank in a large scale water treatment plant in Chongqing, and physical model has been built to verify the rationality and accuracy of the models. With the comparison of the two models, the following results can be found: 3-D model is lower in computing efficiency; both of the flow state are in substantial, but the stream lines of 3-D model are more complex; The velocities of 2-D model are slightly higher, both of the velocity distributions and tendency are approximately identical in 5 to 6 meters and 14 to18 meters, but not the same in 6 to 14 meters. 3-D model is more reasonable and accurate compared with 2-D model.

Abstract: In order to study the effect of salinity wastewater discharging ways on the range of salt content rise nearby the outfall. Two three-dimensional numerical models of discharging ways which were single-port submerged-type and double-port submerged-type in the condition of subcritical flow were researched based on FLUENT. The range of salt content rise of the two discharging ways could be concluded according to the simulation results. The value of maximum salt concentration and average salt concentration of two discharging ways were compared and analyzed. The results showed that double-port submerged-type discharging way was better than single-port submerged-type discharging way.

Abstract: SWMM modeling plays an important role in the urban drainage system management. The paper depicts several modeling steps, including model parameters, dynamic wave options, CFL condition and equivalent pipe and model evaluation. For dynamic wave options, combination of ignore and both is relatively better than others. Impact of friction equation is very tiny. Especially, Froude No. is recommended not to use, while slope can make a good result. For inertial terms, ignore is considered as the best option. Equivalent pipe is used to deal with SWMM numerical instability, and coefficient of correlation, Nash-Sutcliffe efficiency are used to assess modeling performance.

Abstract: At present the majority of studies on constructed wetlands reports are limited to a single wetland and hence the results lack broad representation. In order to study the general effect of treatment of sewage using a horizontal subsurface-flow constructed wetland, a more detailed wetland regression equation needs to be established to guide the design of constructed wetlands. In this study, we used the main pollutant index COD as the indicator and classified 1500 groups of collected data in accordance with the season, hydraulic loading, planting vegetation type and climate type classification in accordance with the "black box model". We analyses different factors affecting pollutant removal by constructed wetlands, using the impact of season and hydraulic loading as the main classification criteria. On this basis, in accordance with the linear regression method, 12 groups of regression equations for COD removal were established. The goodness of fit R² values ranged from 0.65 to 0.95, showing the accuracy had been greatly improved. Using the regression equation in the design process can better estimate the removal effect.

Abstract: Recycling ratio of mixed sludge and properties of raw water (such as pH, turbidity and organic matter concentration) were systematically investigated to optimize coagulation efficiency in current study. It was found that the appropriate recycling ratio of mixed sludge was 6%, effective initial turbidity were below 45.0 NTU, and optimal pH for dissolved organic matter and turbidity removal was 6.5-7.0 and 8.0, respectively. Residual dissolved alum (RDA) in treated water met the drinking water quality standard (<0.2 mg/L). Coagulation efficiency and RDA was not negatively influenced by organic matter concentration of 1.104-3.354mgDOC/L. Under above condition, sludge reuse process could be significant for the low temperature and low turbidity water treatment.

Abstract: Turning can supply oxygen and increase dewatering efficiency during the composting process. This study was conducted to investigate the influence of turning on water removal. In this study, different turning modes were used in different fermentation phases. Results showed that turning in thermophilic phase improve the efficiency of water removal; in cooling phase, higher turning frequency resulted in lower water removal; turning in temperature-increasing phase had no significant effect on water removal. Unturning in the temperature-increasing phase, turning once in the thermophilic phase, and turning every 4 days in the cooling phase achieved the best effects of water removal, the water reduction was 0.566 tonston^-1 matrix.

Abstract: The environmental impacts of the dregs disposal in cement kiln and conventional production were contrastively evaluated by life cycle assessment (LCA) in this study. The results showed that the environmental load ratio of both cement productions followed the order of energy depletion potential (EDP) > depletion potential (ADP) > global warming potential (GWP) > acidification potential (AP) > human toxicity (HT) > photochemical ozone creation potential (POCP). The comprehensive environmental load of disposal dregs was 14.465×10^-12/a, which was 3.98% lower than that of the conventional cement production. Moreover, the reduced percentage of the environmental load followed the order of HT> AP> POCP> EDP> ADP> GWP, which indicated that the reduced percentage of human toxicity and acidification reached 10.62% and 10.06% respectively. Thus, considering the environmental benefits, it would be a better method to dispose dregs instead of limestone in cement kiln.

Abstract: Calcium ions, magnesium ions, and silicate were the main reasons for the high silting density index (SDI) of natural waters. Therefore, they posed serious membrane fouling problems in the nanofiltration (NF) system, which restricted the wide application of this excellent drinking water treatment technology. In this study, the sand filtration and the micro-flocculation/sand filtration hybrid process were investigated as the pretreatment process of NF for SDI reduction. Compared with the sand filtration, the hybrid process of micro-flocculation/sand filtration was more effective for SDI reduction. When polyaluminium chloride (PAC) was used as the flocculant at a dose of 10 mg/L and the filtration rate of the sand filter was controlled at 10 m/h, the SDI value in the effluent of the pretreatment process maintained below 3. As a result, the subsequent NF system stably ran for one year. 68% COD_Mn was removal by NF. The membrane fouling during the operation was quite slight as the transmembrane pressure (TMP) increased by 17% after one-year use. Chemical cleaning with sodium tripolyphosphate (2%) and sodium dodecyl benzene sulfonate (0.25%) at 6 months interval could effectively recover the flux loss of the NF membrane.