| In recent years, the level of many city wastewater treatment plants influent inorganic suspended solids(ISS) concentration and SS / BOD5 value are higher than the developed countries, and the median diameter of SS is about 100?m. This phenomenon is more prevalent in the south mountainous city wastewater treatment plants. In the existing national design codes and manuals, grit chamber is to remove above 200?m,density of about 2.65 sand, with no consideration of the fine particles removal in sewage, which makes amount of fine particles streaming into the subsequent processing unit. It also leads to inorganic component increase in setting tank. Activated sludge mixture MLVSS/MLSS in the biochemical pool is low. Biochemical pool bottom silt and equipment badly worn. And wastewater treatment plant operating costs are high.Rotational flow grit chamber is widely used in domestic wastewater treatment plants. As the complete set of foreign patents, its technical parameters are not exhaustively public. And because the depth of localization is still lagging behind. So rotational flow grit chamber in most existing domestic wastewater treatment plants are poor in running performance and stability. On the other hand, the domestic norms lack the technical parameters and design standards for less than 200?m particles. As for the water quality with different characteristics of sand, it still lacks the research and practice of enhancing fine sand removal. Based on similarity criterion, a model of rotational flow grit chamber was created by the basic feature of Pista in this paper. It investigates the effect of sand removal rate by which rotation speed of the windstick, number of the windstick laminas, distance between the windstick and the tank bottom, windstick slope and hydraulic retention time influences through the single factor experiment. Based on the single factor experiment, ISS removal efficiencies with different particle diameters were compared by the orthogonal experiments for artificial water and real wastewater,and the optimal conditions were also determined. Further, according to the sewage impact load test, it discusses the stability and reliability of ISS removal of grit chamber under the experimental conditions.The main contents and conclusions are as follows:(1) There were carried out single factor experiments about rotation speed of the windstick, number of the windstick laminas, distance between the windstick and the tank bottom, windstick slope and hydraulic retention time. It investigated its effect torotational flow grit chamber ISS removal rate and sought the variation of various factors on the impact of the grit removal rate. The results showed that the influence of windstick slope factor was relatively weak, and it obtained the appropriate range of the experimental factors of ISS removal rate.(2) Based on single factor tests, it selected the rotation speed of the windstick,distance between the windstick and the tank bottom, number of the windstick laminas and hydraulic retention time four factors to conduct orthogonal experiments with artificial water and real wastewater, respectively. The results showed that when the median diameter of grit chamber influent ISS is from 108?m to 129?m, the influence degree of various factors on the rotational flow grit chamber ISS total removal rate is that hydraulic retention time> distance between the windstick and the tank bottom>number of the windstick laminas> rotation speed of the windstick. The total removal rate of ISS in artificial water distribution experiment and real wastewater experiment are 77.73% and 75.07%, respectively, under the windstick of 25r·min-1 / 20r·min-1(artificial water/ real wastewater), distance between the windstick and the tank bottom of 40 mm, number of the windstick laminas of 3 and hydraulic retention time of 30 s.Studies suggest that, it can improve removal rate of large size of ISS to some extent by appropriately increase the hydraulic detention time in rotational flow grit chamber,which has little impact on the fine particles.(3) Under the optimum orthogonal conditions, it carried out the grit chamber continuous inflow experiments with real wastewater. Experimental results showed that when the flow rate in the drains was from 0.7m/s to 0.8m/s, the SS concentration of real wastewater was form 400mg/L to 430mg/L and ISS influent concentration was form180mg/L to 205mg/L, the average removal rates of SS and ISS were 37.02%, 76.76%,respectively. Grit chamber has a good cut of inorganic fine particles in wastewater and intercepts carbon. Rotational flow grit chamber model is with good stability under certain optimized conditions.(4) Under optimum orthogonal conditions, it carried out the influent ISS concentration impact load experiments with real wastewater. It investigated the operational characteristics of grit chamber sand removal effectiveness under the short-term ISS concentration surge in sewage condition. Experimental results showed that within 6h, when the influent SS concentration increased from 420mg/L to1410mg/L and ISS concentration increased from 190mg/L to 1160mg/L, the SS and ISS removal rate of grit chamber increased with increasing influent water concentration.When the influent SS and ISS concentration get to the peak, SS and ISS removal rates were 61.69% and 85.00%, respectively. The effluent SS and ISS concentration were559.01mg/L, 171.37mg/L, respectively. When the influent concentration returned to the background values, SS and ISS removal rates were decreased to the background values considerably. It shows that under experimental conditions, rotational flow grit chamber model has the ability of certain anti-SS and ISS shock loading.At present, the research of rotational flow grit chamber sand removal process is aim to remove the grit which its particle size above 200?m, and less research on the fine particles removal technique. It can provide a theoretical reference and data support for the design and development of complete sets of rotational flow grit chamber based on the real wastewater and artificial water by analyzing the removal rate and factors of different particle size ISS with the rotational flow grit chamber model. The research has good theoretical and practical significance. |
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