Experiment Research Of Air Water Backwashing And Filtration Of Sand Layer In Micro-Irrigation

Sand filter is one of the most widely used filtering equipment in micro-irrigation engineering, andit has great interception capability of particles and is easy to be backwashed. Based on the unique wayof three-dimensional filter, it can effectively filter the organic and inorganic impurities in the water, andthe effect of filtration and backwashing is very stable, it is generally used as the fine filter of watersource. Water backwashing is the main backwashing way, and many scholars have already conductedextensive research. To solve the problem emerged in water backwashing such as large waterconsumption, low cleanliness of filters and a high backwashing frequency, we develop air waterbackwashing trials, the purpose of which is to find the most efficient way of backwashing.Firstly, we compared the effects of three different kinds of air water backwashing modes, andfound out the factors and levels of the most appropriate mode. Secondly, the factors of air waterbackwashing by orthogonal experiment were studied in detail to deter mine the significance of factorsand the primary and secondary order of the factors. Finally, the effects of water backwashing and airwater backwashing were compared, and the phenomenon of surface layer filtration and the distributionof impurities were analyzed.The research contents include:(1) Taking water quality turbidity as the evaluation index tocompare the effects of three different kinds of air water backwashing modes, we found the mode whichis firstly air water backwashing confusing secondly single water backwashing has the best effect, theoperation of which is the most convenient. As a result, we studied further factors under thisbackwashing mode. We studied the four factors which may greatly affect the results of backwashing,namely, intensity of gas, flow magnitude, filter layer thickness and size of mean filter granule. Each ofthem has four levels.(2) The analysis results of orthogonal test shows that，taking sewage solidsaccumulation as the index，flow magnitude approaches to be significant at F0.01an dF0.05test, and theintensity of gas is a significant indicator. Taking the time when the sewage turbidity accumulationreached90%as an index, we found that flow magnitude approached to be significant at F0.01and F0.05test. The air water backwashing is a complex process. There is no simple direct ratio relationshipbetween various factors.(3) By comparing the effects of air water backwashing and water backwashing,we found the former could prolong the filtration cycle, reduce backwashing frequency as well as reducethe consumption of water used during backwashing process. None of the backwashing model changesfiltering quality of the filters because all filtered water has similar quality.(4) Different filteringconditions show that smaller size of filter material with great concentration of rare water is easy to bringsurface layer filtration. The appropriate measure should enlarge the size of filter material. After filtrationthe dirt mainly spread within300mm below the surface of filter layer, which account of90%of totaldirt intercepted. Measuring particle content, turbidity and particle size distribution to deter mine theparameters of air water backwashing is applied in sand filters. The paper focuses on the summarizationand analysis of the experiment, which provide parameter and theoretical foundation for the applicationof air water backwashing in the sand filter.