| Due to the special topographical features,climatic conditions,eating habits and imperfect drainage system of the Chongqing section of the Three Gorges reservoir area,the content of sand in the inlet water of the municipal wastewater treatment plant is relatively high,and particle size of sand is small.The existing desanding process is ineffective in removing fine sand from wastewater,causing problems such as wear and tear of wastewater treatment equipment,blocking of sludge disposal pipeline,and lowering of the activated sludge MLVSS/MLSS ratio.The thesis clarifies the migration characteristics of inorganic sand in a municipal wastewater treatment plant in Chongqing through long-term monitoring of wastewater and sludge.This thesis was based on the study of the content and particle size of inorganic sand in the inlet water,and carried out flocculation experiments by using simulated wastewater with different sand concentrations in the dry and rainy seasons.This thesis studied the effect of flocculation to remove inorganic sand with different types and concentrations of flocculants,and formed a technique to remove inorganic sand by using flocculation to enhance the Grit chamber-Primary sedimentation tank system.The flocculants were used in the raw water of wastewater plants to consider the effect on the removal of COD,TN,TP and p H.The main research results of this thesis were presented as follows:(1)The cumulative content of inorganic sand particles with particle sizes below 100μm in the inlet water of a wastewater treatment plant in Chongqing was around 80-90%,and the volume average particle size of inorganic sand ranges from 40 to 70 μm.The volume average particle diameter of inorganic sand in the effluent of the grit chamber was in the range of 29～41 μm,while in the effluent of the primary sedimentation tank dropped to between 20 and 27 μm.Rainfall scouring would increase the inorganic sand content in the inlet water of the municipal wastewater treatment plant.Currently,the removal rate of inorganic sand content in wastewater was 7.5% for the grit chamber and74.2% for the primary sedimentation tank.(2)The inorganic sand content in the primary sludge of the municipal wastewater treatment plant was relatively high and the volume average particle diameter range of inorganic sand was between 30 and 50 μm.Due to the large particle size of inorganic sand being easily deposited in the sludge disposal pipeline,the volume average particle diameter range of inorganic sand in the thickener sludge decreased to between 22 and30 μm.Inorganic sand in activated sludge and excess sludge was concentrated within 33μm and was adsorbed and bound by activated sludge,with the volume average particle size of inorganic sand being around 15 μm.(3)The flocculation sedimentation experiments showed that 30 mg/L chitosan as a single flocculant in the raw wastewater was more effective in the removal of the supernatant sand content,supernatant turbidity and suspended solids with particle size in the range of 56～807 μm,with less effect on the p H of the raw wastewater.The average SS removal rate was 31.3%,the average sand removal rate was 56.2%,the average TN removal rate was 23.4%,the average TP removal rate was 65.5%,the average COD removal rate was 44.9% and the ratio between sand content and total suspended solids decreased by 14.6%.(4)After optimisation with the compound flocculant,the effect of desanding was improved compared to the single flocculant,but also with less effect on the p H of the raw wastewater.Under the treatment with 15 mg/L cationic polyacrylamide and 15mg/L chitosan,the average SS removal rate reached 55.8%,the average sand removal rate increased to 72.7%,the average TN removal rate increased to 41.1%,the average TP removal rate increased to 70.5%,the average COD removal rate increased to 49.7%and the ratio between sand content and total suspended solids decreased by 15.5%. |
PDF Full Text Request