Analysis On Overflow Pollution In Rainy Days And Technical Research On Hydrocyclone Separation Process

The phenomenon of drainage system hybridj unction was serious on the upper reaches of Nanfeihe River, in particular of its southern bank, where there were two freeing ports. And it was difficult to implement separate sewage system in the short term. During drought flow or less rainfall period, the sewage in the two gullies was sent to the sewage treatment plant for processing by the pump station nearby. When there was bigger rainfall, the overflow sewage was directly discharged into Nanfeihe River without any processing. The sewage overflowed from pipe networks in the rainy days contained lower deliquescent COD and higher SS, which was different from the general sanitary sewage. The hydrocyclone could take advantage of the centrifugal force field to speed up the sedimentation of solid particles from the suspension, which strengthened the separation process. Therefore, hydrocyclone separation process was applied to deal with the overflow sewage from Qingchong Ⅰ/Ⅱ which contained many pollutants.It was so important to master the condition of city rainfall and local runoff rain water quality that it was the foundation to design and operate the hydrocyclone safely and effectively as a productive device. For this reason, the water quality of Qingchong Ⅰ/Ⅱ was monitored. Meanwhile, the change rules of pollutant concentrations from Qingchong Ⅰ/Ⅱ were discussed in a single rain of different rainfall patterns. The experiments showed that the water quality of drought flow in Qingchong Ⅰ/Ⅱ was relatively stable, but each pollutant concentration in Qingchong Ⅱ was a little higher than that in Qingchong I. The contaminants concentrations of the overflow sewage in Qingchong Ⅰ were relatively low:74～552mg/L,25～491mg/L,0.76～10.75mg/L and0.21～1.25mg/L for SS, COD, NH3-N and TP respectively. The contaminants concentrations of the overflow sewage in Qingchong Ⅱ were363-2169mg/L,193～884mg/L,2.14～21.5mg/L and0.25～5.46mg/L respectively. The contaminants concentration change rules of the overflow sewage in Qingchong Ⅰ/Ⅱ showed that the contaminant concentrations reduced as the hours passed away, sometimes fluctuated. But they would reduced gradually along with the rain continued, flattened finally. Generally speaking, each index in Qingchong II was significantly higher than that in Qingchong I, such as initial concentration, crest value and the ultima stable value, the change trends of which were more obvious, and the rangeabilities higher.However, on-site processing of overflow sewage in rainy days was a relatively complex engineering which involved all aspects of decision-makings, considerations, and some details. The determination of the solution to dispose the overflow sewage using a hydrocyclone especially should be verified by the laboratory research. Hydrocyclones should be chosed on the basis of the water quality conditions. Eventually, the type of KLBS-HD manufactured by Wuhu Hongda Co., Ltd was purchased:D for100mm, di for40mm, do for40mm, ds for8mm,θ for20°, ho for60mm and H for120mm. The research showed that the separating effects of Kaolin Water with particle size for325mesh were significantly better than one with particle size for40-80mesh. And the removal rates of SS reached58.9%and40.5%respectively. The SS and COD removal rates of Sediment Water were the same with Overflow Sewage, and the removal rates for approximately50%and40%respectively under the pressure of0.03MPa.The processing scale of hydrocyclone productive device was55mJ/h:D for0.5m, H for1m,0for12°, cone length for2.2m, the inlet for DN125, do for15cm, ho for68cm. The productive experimental research showed that the average removal rate of COD and SS could amount to35%and50%respectively. At the same time, the capacities of annual pollution load processed were1974.32kg for SS and750.07kg for COD. Reckoning results showed that the total capacities of annual pollution load generated from rainfall runoff were3927.5t for SS and1965.5t for COD, NH4+-N for35.4t and TP for5.8t in Qingchong Ⅰ and Qingchong Ⅱ. Under the construction and operation of runoff pollution control engineering, the cut rates of annual pollution load in rainy days were32.53%for SS and32.21%for COD, which satisfied the expected research goal.