Study On Micro Flocculation Variable-void Deep Filter For Advancd Treating Secondary Treated Effluent From Urban Waste Water Plants

Water resource shortage will be the focus all over the world in 21st century.Water resource shortage has become one of important factors which restrict the economic development of China.China has a low per-capita of water resource and the irregular distribution for time and space.The water supply and demand problems are increasing seriously with growing population and economic development. Therefore,the urban sewage treatment and recycling would be more economic and efficient approaches to solve water resource shortage.In order to solve problems caused by deep treatment of the secondary effluent in urban waste water plants,this study used secondary effluent from Qingdao Li River Waste Water Plant to operate small site tests and semi-production tests and research variable-void deep filter technology.It also explored the appropriate operating conditions and parameters of micro flocculation variable-void deep filter based on organic combination of micro flocculation filter and variable-void deep filter technology,which applied in deep treatment of secondary treated effluent in urban waster water plants.Meanwhile,combining micro flocculation variable-void deep filter with no-valve filter technique,the feasibility of recycled water was studied to select and develop appropriate technologies for the deep treatment of secondary treated effluent in Chinese urban waste water plants,and provided literatures for treatment equipments used in water recycling.The conclusions are following:(1) The comparative experiments of traditional anthracite,quartz sand double-layer filter and multiple size ratio variable-void filter to treat the secondary treated effluent from urban waste water plant showed that the retention effect of 4% and 6%small particle filter was more efficient than the traditional double-filter,and the average removal rates of turbidity,COD_Cr,TP were 78%and 80%,31%and 34%, 26%and 30%,the average effluent parameters were 1.12NTU and 0.88NTU,and the concentration were 33.2mg/L and 32.8mg/L,0.97mg/L and 0.98mg/L,respectively. Removal efficiency of color by variable-void deep filter system was not obvious and the average removal rate was below 10%.The filtration cycle of 4%small particle filter system was up to 18h.(2) The study of combining micro flocculation filter with variable-void deep filter technology showed that PAC was the best coagulant.The overall treatment effect was best while the PAC concentration was 4mg/L and small particle filter volume ratio was 4%.The average removal rates of Turbidity,COD_Cr,TP and color respectively were 85%,46%,40%and 24%,increased 7%,15%,14%and 15% compared with direct filter.The filtration cycle of system was up to 14h.(3) The best strength for backwashing of micro flocculation and variable-void deep filter system was 14～16L/sm² and the filter bed expansion was 40%～50%if the lasting backwashing time was 4～6min,which developed the best backwashing effect.(4) The study of combining micro flocculation variable-void deep filter with no-valve filter technique showed that the overall treatment effect was best when the PAC concentration was 4mg/L and small particle filter volume ratio was 4%.The average removal rate of turbidity was 92%and the effluent turbidity was less than 0.5NTU;The average removal rate of COD_Cr was 51%and the concentration of COD_Cr in final effluent was 27.98mg/L;The average removal rate of TP was 50%and the concentration of TP in final effluent was 0.76mg/L;Although the average removal rate of color was lower than the traditional double-layer filter by 7%,but it could reach 35%and the final effluent color was 16.86 degree.The filtration cycle of no-valve filter was up to 24h and the production of recycling water increased apparently.