Experiments On Short-Time "Coagulation-Sedimentation-Filtration" Of Poly-Silicate-Ferric

The paper explored the short-time"coagulation-precipitation-filtration"process?hereinafter referred to as short-time process?based on the excellent properties of poly-silicate-ferrite?PSF?coagulant.Humic acid simulated water was used as the experimental water sample to investigate the short-time"coagulation-precipitation"effect of PSF,compared with ordinary"coagulation-precipitation"of PSF and that of polyferric aluminum?PFA?,and the fractal dimension was measured to analyze the flocs.In this experiment,the short-time process effect of PSF was explored through a self-made filter device,and the influence of filtration factors was analyzed,and the flocs and filter materials were observed by a camera and a scanning electron microscope?SEM?.In addition,the computational fluid dynamics?CFD?was used to simulate the filter and analyze the pressure drop and velocity change in the flow field.Finally,the mechanism of PSF short-time process was analyzed.?1?Short-time"coagulation-precipitation"process conditions of PSF:dosage,flocculation time and precipitation time were 6 mg/L,4 min and 3 min,respectively.The turbidity and colority removal rates of the PSF short-time"coagulation-precipitation"were both about 92%,which was slightly different from that of PSF ordinary"coagulation-precipitation",but the reaction time was saved by nearly 62%,while the turbidity and colority removal rates of PFA short-time"coagulation-precipitation"was only about 70%.Under the microscope,the flocs of PSF short time and ordinary"coagulation-sedimentation"showed reddish brown color,with larger fractal dimension,while the flocs of PFA had smaller fractal dimension and lighter color.?2?Both the effluent quality and filtration duration of PSF short-time process were better than that of PFA short-time process and the ordinary"coagulation-sedimentation-filtration"process?hereinafter referred to as the ordinary process?,and the advantages were obvious.The filtration duration of PSF short-time process was slightly shorter than that of PSF ordinary process,but the effluent quality was not significantly different.Within the experimental range,the thickness of the filter layer had little effect on the effluent quality of the PSF short-time process,and had an impact on the filtration cycle,and the filtration cycles of 30 cm,70 cm and 50 cm filter layer thickness were 14 h,18 h and 20 h,respectively.The filtration rate had little effect on the removal of turbidity and colority and significant effect on the removal of UV₂₅₄ and COD_Mn in PSF short-time process.The effect of particle size is that the larger the particle size,the longer the filtration cycle.When the particle size was 1² mm and 2³ mm,the filtration cycle was 55 h and 74 h,respectively,and the water quality difference between them was small.?3?It is concluded from the numerical simulation that the filtration flow field with greater filter thickness or filtration velocity had greater internal pressure.Notably,the pressure values in the flow field decreased gradually along the flow direction,and the pressure values of the same horizontal height in the filter layer were approximately equal.The velocity in the filtration flow field?except for the filter layer?was different from the pressure,which was obviously affected by the viscosity of the boundary.The velocity value was not constant on the horizontal plane at the same height of the filter layer,but decreased gradually along the center of the filter column to the wall surface.Because the porous media is more ideal,the velocity in the filter layer is more consistent.?4?The flocs produced by PSF short time and ordinary"coagulation-precipitation"were larger in size,and the difference between them was not obvious from the observation of ordinary camera and SEM.The flocs produced by PFA were smaller in size.The impurities on the surface of the filter material in the PSF short-time process were less attached and the pollution degree was weaker,while in the PFA short-time process and the ordinary process are more attached.Even the surface of the filter material in the middle of the filter layer also appeared the impurity accumulation morphology.Mechanism analysis:In the process of coagulation and precipitation,PSF has high efficiency in destabilization,bridging and net rooling-sweeping based on its advantages in structure and composition,forming floc groups with large fractal dimensions and high precipitation efficiency.Therefore,the flocs can be fully adhered and intercepted by the filter material,so the effluent quality is good and then there is a long filtration period in the case of meeting the water quality requirement.