| Paper reviewed the situation about the variation of water quality and quantity of urban sewage and water quality model in domestic and foreign. Because of the lack of sewage water quality data and quite different between reference design parameters and the actual situation, cause some wastewater treatment plants which in middle and small towns can not stable operation. To research the wastewater quality and quantity of middle and small towns in Three Gorges Reservoir area to access to the actual situation data of urban sewage. Based on the current data analysis the characteristics and variation of water quality and quantity of urban sewage in Three Gorges Reservoir area by using mathematical statistical. Further to model and predicte the urban sewage water quality by using ARIMA model. Hope the results can be used as the basis of the design of new wastewater treatment plant reference and optimal operation of wastewater treatment plant control. Paper also studied the characteristics and distribution of the ultra-fine grit in urban sewage in Three Gorges Reservoir area. The results show that:①To conduct research on the urban sewage water of 10 typical towns in Chongqing Three Gorges Reservoir Area, found water quality characteristics of sewage is high nitrogen,medium carbon, medium phosphorus. In most of the urban wastewater, the ratio of BOD5/CODcr is more the 0.45, the sweage has good biodegradability. The ratio of BOD5/TN is between 3 to 5, the carbon for biological nitrogen removal is exile.②The sweage quantity between June to September is much more than it in January to February. Changes of water quality and the change of water quantity is the opposite. Water quality variation within a day is significant, the polution load peak often appears at noon and dusk. Using Kolmogorov-Smirnov (K-S) test to test lognormal distribution of urban sweage, it proved the distribution of pollutions in sweage water is lognormal distribution.Using the paired samples T-test to test the differences of water quantity and quality between dry season and rainy season, the results show that most of the sweage water quantity and quality have seasonal differences.③Establishing the ARIMA(p,d,q) model of urban sweage water quality in Chongqing Three Gorges Reservoir Area. Using the model to predict the water quality of sewage. Most of the average percentage errors of the results are less than 20%. Model effectively.④It's found by analysis samples of dry-weather sweage and wet-weather initial sweage that there is a evident time rule.The polluttion load of dry-weather sweage is lower early in the morning and higher at noon and dusk. There are large differences in dry-weather sweage quality in different functional areas. Concentration of commercial waste water pollution is the highest, residential sewage are lower, sewage pollution load of traffic area is minimum. The time rule of wet-weather initial sweage quality associated with the rainfall intensity. When the rainfall intensity is large, the time rule has one concentration peak and the concentration of contaminants presents the evident index attenuation rule with the increasing of flow time. When the rainfall intensity is small the time rule is different . There are large differences in wet-weather initial sweage quality in different functional areas. The concentration of pollutants in residential area (south) of the initial combined sewage is the highest. Commercial areas sewer less affected by rain, it also has high pollution load. The pollurion of commercial rainwater sewage is also very serious. The concentration of pollutants in wet-weather initial sweage in traffic area is lager then the initial sweage in residential area (east). Comparison of the forms of pollutants in dry-weather sweage and in wet-weather initial sweage, it can be found that the proportion of particulate pollution of the wet-weather initial sweage is higher then dry-weather initial sweage. The major pollutants form in wet-weather initial wastewater is particles.⑤The EMC(event mean concentration) of CSO (Combined Sewage Overflow) can be used to quantitative analysis contaminants in CSO. The EMC of the CSO in fuling city are TSS=477mg/L,TCOD=530mg/L,TP=3.11mg/L,TN=26.2mg/L, which all much higher than the national surface water environmental quality standard V class. Combined overflow of sewage pollution is serious. Using the M (V) curves and b parameters method to analysis the first flush effect of CSO in fuling. The results showed that TCOD, TSS and Sand content had significant first flush effect when rainfall intensity is large.⑥Research on the grit which size is very little. It can be found that the concentration of grit in wet-weather initial sweage is much more than it in dry-weather sweage. The order of the concentration of grit in dry-weather sweage is: Traffic area> Residential area(east)> Residential area(south)> Commercial district. The order of the concentration of grit in wet-weather initial sweage is: Residential area(south) > Residential area(east) > Traffic area≈Commercial district sweage > Commercial district runoff. It can be found by anlysis the particle size distribution of the grit by laser particle size analyzer that the average size of grit in dry-weather sweage is smaller than 200μm, and the average size of grit in wet-weather initial sweage is also smaller than 250μm. Analysised the component of grit in sweage by X-diffraction method, the results show the main component of grit are quartz, albite, microcline, calcite.
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