Impact Of Fine Sediment On Sewage Treatment System And The Energy Consumption

In recent years, the operation data of some urban sewage treatment plant at home ;how that:there is a serious sediment deposition in biochemical pool after the cancellation of primary settling tank, the silt height usually accounts for 15%～40% of he effective height, at the same time, accompanied by the activated sludge concentration (MLSS) increasing and the MLVSS/MLSS reducing sharply. The mixture VILVSS/MLSS ratio is 0.3～0.5 in many sewage treatment plant, far less than the experience value of 0.75, and the sludge concentration is often as high as 5000～7000 ng/L, also much higher than the traditional cognition of 2000～4000 mg/L. Maybe this s the reason that high influent SS/BOD5 value and small SS size in China, which also lave closely relations with the backward drainage system and poor effect of the bretreatment system. Based on the comprehensive reviewing present situation of norganic materials and sediment accumulation in wastewater treatment system, the auhor use quartz sand which volume mean diameter(D[4,3]) were 19.8μm,72.0μm, 18.6μm (correspond to 2#,3# and 4# systems respectively, and 1# systems was the blank control) simulate the fine sediment in influent. The effects of different sized Fine sediment on activated sludge properties, sludge yield and sewage treatment effect were studied by laboratory SBR reactor. And the effect of fine sediment on sewage reatment system operation cost and energy consumption is analyzed from the perspective of economictheory, the negative effects of fine sediment on the sewage reatment system which can not be ignored is revealed. The main conclusions are as ollows:① According to the ascending order of particle size.the sludge concentration ncreased from 3450 to 7898,5389,3742 mg/L respectively and the MLVSS/MLSS atio of activated sludge decreased from 0.67 to 0.33,0.48,0.59 respectively after 36 lays. With the increase of MLSS and the decline MLVSS/MLSS ratio, the mixed liquid sludge volume index (SVI) and capillary suction time (CST) values also fell significantly, the changes of 2# reaction sludge characteristics which add 19.8μm sediment grain were the most obvious, the SVI and CST values compared with the blank control group were decreased by 70.1% and 57.1% respectively after running 36d.② The small size sediment has a certain effect on effluent turbidity, background ind they was changed to 6.1,13.3,9.8 and 5.6NTU respectively after 36 days. Fine sediment have no obvious effect on the concentration and the removal rate of COD,TP, TN in water.③ In view of the high and unstable SS/BOD5 value of our country’s sewage uality, the paper modify Germany ATV sludge yield formula which is widely used by ’sediment fate characteristics". Based on the introduction of suspension coefficient ω, sludge yield formula he 1#-4# systems relative errors of correction formula calculated value and measured value are 5.2%,8.4%,8.9% and 3.5% respectively. Based on the modified sludge yield rmula and the dismantling of the organic and inorganic parts, f value prediction ;quation he 1#-4# systems relative errors of prediction value and measured value are .7%,18.3%,12.6%,4.4% respectively. Compared with the domestic outdoor drainage design specifications and the German ATV formula calculation of YT and f, the error of wo correction formula calculation is smaller, which is more in line with the actual situation.④ Oxygen transfer coefficient decreased as the traditional activated sludge concentration which is microbial and EPS as the main body increased. when the raditional sludge concentration is 5500mg/L,7900mg/L, 10000mg/L,12000mg/L, compared with the blank sludge 3685mg/L, the oxygen transfer coefficient dropped by 5.8%,22.5%,42.3% and 54.4% respectively; The improve of activated sludge comcentration by fine sediment (when sediment concentration is less than 4213mg/L as no obvious effect on the oxygen transfer coefficient. When the concentration of sludge which have sediment in it is 7898,5389,3742mg/L (MLVSS≈2506mg/L), compared with the blank sludge 3685mg/L, the oxygen transfer coefficient dropped by .7%,3.6%,—0.9% respectively.⑤ The effective volume of biochemical reactor decreases after sedimentation. Based on the constant of sludge load, the method of improving traditional sludge concentration to ensure the sewage treatment effect is applied. System oxygen transfer coefficient KLa is falling during the process of sedimentation, it increases the energy consumption of aeration system directly. At the same time, a small test of mixing proved that:compared with 1# and 4# systems, the mixing energy consumption of 2# and 3# systems which have much suspended sediment is increased by 25%.⑥ Large grain size sediment mainly improve energy consumption of aeration system and dredging costs in biochemical unit, particle size of sediment is mainly to improve the stirred,plug flow and mixed energy consumption in biochemical unit.