Experimental Study On "Biological Falling Water Aerated Filter" For Wastewater Treatment In Small Towns

With the development of urbanization and the improvement of people’s livingstandards, water pollution of small towns is becoming increasingly prominent.Increasing quantity of sewage to be treated and lack of treatment ability make itnecessary for environment protecter to develop a sewage treatment technology that issuitable for small towns in China.Based on investigation of the sewage characteristics and treatment statustation insmall town of the Three Gorges Reservoir, combining considering the high altitude ofthe mountain town terrain, Our group innovate the traditional tower biofilter, applyingnatural falling water aerated technology to biological filter scientificly, finding a way totake full advantage of the natural terrain elevation, low investment, low running costsand more convenient management of urban sewage treatment technology.In this paper, falling water aeration, the start of biological falling water aeratedfilter, HRT and volumetric loading as well as water quality remove characteristics alongthe biological aerated filter were studied. Experimental studies show:â‘ When the flux of falling water changes from0.03m³/h to0.07m³/h, the value ofK_L.a （20） is increasing. The increasing of the flux of falling water can effectivelyimproved the water aeration effects. In the range of0%to45%, the oxygen transfercoefficient K_L.a （20） increases with fill rate of the filler box filler. When the fill ratereaches45%, K_L.a （20） reaches its maximum0.0716/min. At the range of45%to75%,the oxygen transfer coefficient K_L.a （20） is no longer increases even though the filler fillrate increase, showing a rapid decline trend. Comparative analysis of the oxygenationeffect of the perforated pipe weir plate with serrated weir plate, groups find perforatedpipe weir plate is better than serrated weir plate.â‘¡At the conditions of the width B=580mm, height H=700mm and fallingwater depth L=266mm,0.03m³/h≤Q≤0.07m³/h,0≤D≤0.75.Groups derive theoxygen transfer coefficient K_L.a （20）:K_L.a （20）（Q, D）=636.2182（D²-0.6804D-0.4563）.（Q²-0.0364Q+0.00008）③As the biofilm grows, the effluent pH of biologiacal falling water aerated filterfirstly lower than the influent pH value, and then the pH value difference betweeneffluent and inffuent keep relatively stable until the biofilm formed. In the case of thepoor conditions of water quality monitoring, the reducing and eventually stabiliztion of pH and the removal rate of COD_cr can be used as a simple criterion for sucessedbiofilm. The biofilm formation period of suspended spherical packing is shorter thanceramsite filler, it’s water treatment effect is better than ceramsite filler.â‘£HRT, volume loading affect the removal rate of pollutants in billogical fallingwater aerated filter. Pollutant removal efficiency reduces for the shortening of HRT orthe increase of pollutants volumetric loading. HRT=7.8h, the concentration of COD_cr,NH₃-N, TN, TP, SS in effluent is70.0mg/L,39.0mg/L,63.4mg/L,3.6mg/L,25.6mg/L,COD_cr, SS in effulent can reach the two standards of pollutants for municipalwastewater treatment plant”（GB18918-2002）, the other indexes reach the threestandards of pollutants for municipal wastewater treatment plant”（GB18918-2002）. Atthe same filter layer of the biological falling water aerated filter, the removal rates ofpollutants decreased with the volume load increasing. Different filter media layers havedifferent pollutants removal efficiency, at the same working conditions. The removalrate of NH₃-N, TN increase with the number of the layer increased, while the removalrate of COD_cr, TP decrease. COD_cr, TP are mainly removed at the first filter layer, thesecond filter layer, the third filter layer, while NH₃-N, TN removal mainly at the thirdfilter layer, the fourth filter layer, the fifth filter layer.⑤Biological falling water aerated filter can be used for the wastewater treatmentin small towms, especially suited for upland small towns.