Research review of the tail disposal technology of the standard sewage offshore outfall

Abstract

Water pollution has become an important factor which impacts the national economic development. In order to reduce the pollution, many technologies have been used. Sewage offshore outfall is one of effective technology in reduction the water pollution. This technology is that the sewage was discharged into marine by the pipeline system, and thus the concentration of pollutants in water was dilution. Sewage offshore outfall have been become an important waste water treatment in the coast cities due to many advantages of low鄄cost and high processing rates. In the present study, we reviewed the development of the technology of the sewage offshore outfall, including the outfall location selection, the jet parameter optimization, and the hydraulic structures optimization. For the outfall location selection, the best selection is including both the qualitatively and quantitatively choosing. The qualitatively choosing was mainly to select the suitable area to offshore outfall based on the regional planning, hydrodynamic conditions, coastal terrain features, the distribution of marine resources and water quality conditions. Based on the qualitatively choosing, the further selection is the quantitatively choosing. Such selection is correlated to the movement of sewage pollutants, envelope size and particle trajectories, which is studied by founding numerical and physical model, such as near鄄zone, far鄄zone, overall鄄zone convection鄄diffusion diffuser model and particle tracking model. Particularly, overall鄄zone composited diffuser model can simulate the dilution and dispersion law fully and truly, because it can simultaneously predict turbulent jet and transport diffusion. Meanwhile, the outfall location selection should be considered the sediment deposition and the long鄄term cumulative effects of ecological elements. It is very important to optimize the jet parameter and the hydraulic structures. This optimization can increase the http: / / www.ecologica.cn dilution of sewage, improve the discharge uniformity of the nozzle, and thus ensure the proper and efficient operation of the offshore outfall. In general, jet parameter optimization is mainly to design the jet numbers, jet angle, horizontal angle of the diffuser nozzle based on analyzing dilution and dispersion law of the buoyant jet, mechanism of the cross鄄flow and turbulence jet. Hydraulic parameter optimization is mainly to design the diameter and length of main pipe, riser and nozzle via analyzing flow and pressure of diffuser pipe, the discharge uniformity of the nozzle, loss along the pipe and partial loss, seawater intrusion laws. Through there are many progress in the sewage offshore outfall technology, large of problems are necessary to overcome, for example, how to reduce the ecological impact on the outfall location selection, the sediment invasion, and so on. Such work is significant to improve the effect of sewage offshore outfall technology in the future.