In order to improve the hydraulic impact resistance of the polyvinyl alcohol (PVA) hydrogel as microorganism immobilization carrier and meet the requirements of long-time aeration of sewage treatment, the toughening PVA hydrogel beads were prepared by co-crosslinking with polyoxypropylene triol (PPG) through the boric acid (H3BO3)-chemical crosslinking method. It was found that PPG could increase the consumption of H3BO3, participated and accelerated the crosslinking reaction of PVA, and the pore size of the surface layer and core layer of the hydrogel beads can be controlled. With increasing PPG content, the shear storage modulus (G’) and the effective network density (νe) increased first, reached maximum in presence of 2 wt% PPG, and decreased afterwards. A relatively low content of PPG could promote the formation of relatively uniform and dense network structure in PVA hydrogel, resulting in an improvement of the mechanical property and long-term hydraulic stability of the gel beads. By addition of PPG, the capillary water absorption capacity of PVA hydrogel can be enhanced and the high permeability can be kept well. When applying in waste water treatment, the value of the oxygen uptake rate (OUR) and COD removal rate of the PVA hydrogel immobilized with activated sludge had no obvious difference with addition of PPG, and a high microbial activity can be maintained. 相似文献
Understanding of the magnitude of urban runoff toxicity to aquatic organisms is important for effective management of runoff quality. In this paper, the aquatic toxicity of polycyclic aromatic hydrocarbons (PAHs) in urban road runoff was evaluated through a damage assessment model. Mortality probability of the organisms representative in aquatic environment was calculated using the monitored PAHs concentration in road runoff. The result showed that the toxicity of runoff in spring was higher than those in summer. Analysis of the time-dependent toxicity of series of runoff water samples illustrated that the toxicity of runoff water in the final phase of a runoff event may be as high as those in the initial phase. Therefore, the storm runoff treatment systems or strategies designed for capture and treatment of the initial portion of runoff may be inappropriate for control of runoff toxicity. 相似文献
This paper investigates the influence of near-bank vegetation patches on the bed morphological adjustment in open channel flow systems. The 2D depth-averaged hydro-morphological model is adopted for this investigation, which is first validated by laboratory experimental data measured in an open channel with a single near-bank vegetation patch. The validated model is then applied for extensive numerical simulations, with the aim of conducting a systematic analysis of the influence of different geometric controlling parameters on the bed morphological evolution. The controlling parameters taken into account for numerical analysis include the angle of repose value (RAV) of sediment, vegetation density (VD), patch length (PL) and patch width (PW). The numerical results and analysis show that: (1) the RAV of sediment with slope-failure parametrization only influences the shape of the transverse bed topography in the junction region; (2) increase in VD, PL and PW that substantially enhances flow blockage effect encourages the growth of the pool adjacent to the patch in three dimensions; (3) increase in VD, PL and PW produces analogous retrogressive erosion (erosion toward the upstream) in the pool region, presumably due to the increase in flow resistance. Additional numerical experiments suggest that the staggered-order distribution of multiple patches might be an optimal choice for channel restoration and conservation since pools and riffles with larger scales can be produced.