Research On Technical Reform And Control Optimization Of Vortex Grit Removal System In Wastewater Treatment Plant

In recent years, the oxidation ditch and sequencing batch activated sludge(SBR) without primary settling tanks(PSTs) is becoming more common. In order to ensure sufficient carbon source for phosphorus and nitrogen removal, the PSTs are also can-celled in A2/O technology. In this case, the removal of inorganic particles can only rely on grit removal system to complete. It is particularly important how to ensure the grit chamber can steadily remove inorganic particles whose size are more than 200?m, while strengthening the removal of fine inorganic particles. Vortex grit chamber is the most common grit removal process in China. According to research, the existing vortex grit chamber has a small amount of grit removal. When air lifting grit, the gas supply pipe and lifting tube is frequently blocked, and inorganic matters in overflow water of grit-water separator are so many. To solve the above problems, domestic wastewater treatment plants occur infrequently technical reform of vortex grit chamber and ways to lift grit, while nearly no attention on grit-water separator. Based on a detailed research of Chongqing region Wastewater Treatment Plants' vortex grit removal system, this paper, combining with research situation at home and abroad, analyzes problems of grit removal, grit lifting and grit-water separation that exit in the system. To rely on a grit removal system of Chongqing wastewater treatment plant, we had a series of technical reforms on grit chamber, based on case studies, further proposals and control measures are made to ensure grit removal system stable and efficient. The main conclusions of this paper are as follows:(1)The inorganic particles whose size is more than 200?m can be stably removed when coming into grit chamber in research wastewater treatment plant. The big size particles that did not enter the pool easily accumulated in the pipe network or lift pump station; The inorganic particles whose size is less than 200?m cannot be removed effectively, this may be attributed to the influent water inorganic particle size is too small, the actual amount of water greater than the design process scale, part of the structure function is canceled in the design. When air lifting grit, the gas supply pipe and lifting tube, frequently blocked, are unable to discharge the grit. The air lifting time and grit-water separator running time is unreasonable, great impact happens when air lifting grit-water mixture come into the separator fiercely, leading to a small amount of draining sand and a high inorganic particle concentration of overflow water in the separator.(2)Technical reform on grit chamber was made as follows:the original air lifting source and tube length was changed, the grit chamber vent pipe was increased, the internal structure and flow field were optimized. After the reform, the amount of daily average grit removal increased 10 times than before. The overall removal rate of inorganic particles increased from 14.6% to 21.05%. 100~200?m particles content increased 15.59%~32.61% than before in the draining grit, which proved fine inorganic particles was removed efficiently. the COD removal rate decreased from 30.2% to 19%, saving some carbon sources for the subsequent biological treatment systems.(3)By the optimization that had been made by desilting automatic control and operation cycle adjustment of air lift and the separator, the suspended solids concentration of gas striping mixture increases from 3.1583g/L to 5.2625g/L, and inorganic particles concentration from 1.4023g/L to 2.4278g/L. The amount of daily average grit removal improves efficiency of 56.2% than before in dry season, 37.8% compared with the last year. Suspended solids and inorganic particles concentration in overflow water of the separator has decreased effectively, and the concentration change tends to accordance after decrease. Therefore, the operation cycle efficiency of grit removal system are closely related to operation cycle adjustment of air lift and the separator.(4)The swash plate and the diversion path settings into internal diversion area and precipitation zone, had a positive impact on the amount of lift desanding. The design of jet water and fluidized stirring blade in grit-water separator is designed to elute organic matter on the surface of inorganic particles.The settings of inclined plate and the diversion path divide internal area into diversion zone and precipitation zone,which has a positive impact on the amount of grit removal.