| In the background of china urbanization construction, the amount of sediment concentration in the influent of sewage treatment plant is generally higher than the design value. But in order to save carbon source, most of sweage treatment plant in China has canceled the primary setting tank, and the rotational flow grit chaber was unable to reach design capacity which was designed to remove the fine sediment whose particle size is above 200μm, which let large amount of fine sediment drifted into the biochemical treatment plant. Caused the MLSS/LVSS value reduces unconventionally, influenced the quality of activated sludge, made mechanical aeration equipment insufficient, caused aeration equipment wear and tear, lead to the treatment costs increased. Among the completed sweage treatment plant, few of them paid attention to the effect of desanding. In water treatment industry, there is a demand for evaluation method of desanding system, and intensified removal techniques of fine sediment. We had a national research about Sediment remove capacity in pretreatment unit. What’s more, we compared the amount of sediment in inlet sewage. Based on a water treatment plant in Chongqing, pipe network dredging and particle size of sediment was studied first, in order to make the source and distribution of sediment clear. Second, the operation characteristics and processing capacity of desanding facilities in pretreatment section was analyzed, a systemic evaluation method of desanding ability was built. Finally, in order to improve stability of desanding system and strengthen the removal of fine sediment, the desanding system was reformed, and the change of desanding effect was studied. A scientific and efficient operation mode of desanding system was formed through debugging operation. The main conclusions are as follows:1)The inflow value of SS/ BOD5 of sweage treatment plant in the three gores reservoir area is generally higher than those in plain area in China and exceed 1.1, the average value of sweage treatment plant in developed country. But one of these plant, which is in Chongqing, the middle partial size distribution of influent fine sediment was as low as 45.85μm, voluble average diameter was about 70μm, these were far below the cognitive, above 200μm as usual. After pipe network analysis, we found that the main source of sediment whose diameter above 400μm is traffic area and residential area 1; sediment whose diameter below 50μm mainly comes from catering business district and residential area 1; 65% sediment of secondary pipe network is sediment under 1mm, the reason why inflow sediment content on the low side is large particle size sediment deposited in the terminal of pipe network.2)Based on one sweage treatment plant in Chongqing, Inflow corridor sediment situation, flow pattern of grit chamber, SS and fine sediment removal efficiency of grit chamber, fine sediment removal efficiency, separation efficiency of the segregator of grit and water, stability of the system under impact of the storm have been discussed. Taking measures of sediment estimation, flow test, periodic monitoring of the removal rate, stability analysis under storm impact and so on. Evaluation method of desanding ability has been structured.3)After the grit chamber structure transformation in the sweage treatment plant, daily average removal sediment amount has been improved from 60kg/d to 367kg/d, the removal rate of SS reached 43.58%; average concentration of gas striping mixture was 3.3957g/L, whose median diameter was 157.3μm, meant the sand removal system had the potential to remove fine sediment. The automation transformation of sediment rising control system made the system automatic, the SS、 ISS concentration of gas striping mixture reached 5.9562g/L、2.7260g/L, and the water quality was stable, daily average removal sediment amount reached 483 kg. The byway horizontal flow type grit chamber added on the outflow of segregator of grit and water, whose removal rate of SS、 ISS was 78% and 71%, sediment outlet amount within 24 h was 338 kg, which increased the sediment removal amount to 593 kg; median diameter of the sediment was 117.5μm, fine sediment separation ability of the system was effectively promoted, what’s more, the influence of water inflow rate to the horizontal flow type grit chamber has been researched. Through optimization of the sediment rising system, sediment removal amount reached 821kg/d, mass ratio of which,whose particle size was under 1mm, improved from 8.17% to 11.35%, whose particle size was between 0.1mm and 0.2mm, improved from 20.33% to 32.54%. Fine sediment removal ability got strengthen. |
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