The Experimental Study Of Improving Natural Filtering Layer By Back Wash

By combining water filtration project in Longhui, Hunan and using investigation, testing, analysis, research, this paper researches into the impact factors of filter blockage and the experiment which shows that back washing filter can improve the permeability of the natural layer.Filter project area is divided into two layers. The top lay is backfill soil, which is loose and mainly in limestone; the lower is gravel soil, which is slightly dense and filled with medium sand and coarse sand. The key component of the lower is feldspar, quartz and a small amount of mica. The average thickness of the filter is 6.2m, the minimum thickness is 3.5m, the largest thickness is 11m. The majority of the media are coarse particles (strong water permeability),and its infiltration speed is 22.03m/d. Because of the mixture of a small amount of silt and high volume of sand in river water, the filtering layer will be blocked after water-intaken project's long time running.Through the simulation of filter layer's blockage, this paper studies the main impact factor of filter blockage, and analyzes the thickness of filter, the size of particle filter, the turbidity of raw water, the water conditions of filter layer surface on the filter blockage rate. Experiments show that, the speed of filter blockage will quicken with the increase of the thickness, the reduction of media size, and the slowdown of the speed of raw water. In combination with simulation experiments, this paper gets a conclusion that the main factors of the filter blockage are filter layer structure and composition, the water quality of raw water, and the raw water hydrodynamic conditions.Backwashing the filter simulation analyzes the intensity backwashing, backwashing time, filter diameter, filter thickness, the number of recoil effect backwashing. The seepage rate after backwashing will improve with the extension of backwashing time and the buildups of backwashing intension. However, when these two conditions, respectively, enhance to a certain extent, the infiltration rate of the filter tends to balance, and the turning point is the threshold of backwashing intensity and time. After experimenting on different size and different thickness of the filter backwash, the author reaches a conclusion: the smaller particle and the thicker filter layer, the longer time and the stronger strength. The infiltration rate of the filter layer will fall into a decline with the increase of experimental times, but at the same time, the rate of descending rate will degrade. with of increase in the number of recoil and weakening, but the gradual lowering of the rate of decline, according to the measurement results of the fitting curve equation is drawn. Research test results combined with the anti-flushing mechanism, filter backwashing to remove impurities in the major media rely on friction between the collision and flow of the combined effects of shear stress. Empirical formula based on knowledge, backwashing filter strength depends on the maximum size of the minimum flushing flow intensity; backwashing filter depending on the residual level of impurities and backwashing the filter before the cut-off ratio of the total amount of impurities inβ. Backwashing in a reasonable time and intensity of backwash, the filter backwash infiltration can be improved performance.