Study On The Law Of Flocculation And Sedimentation Of Viscous Fine-grained Sediment

Sediment flocculation exists widely in rivers,lakes and other water bodies and affects sediment deposition and transport.In this paper,viscous fine sediment is taken as the research object,and the sedimentation law of mass sediment in natural river is studied from theoretical deduction and physical experiment,as well as the influence of single flocculant and compound flocculant on flocculation sedimentation.The main research contents and results are as follows:(1)Based on the settlement law of single flocs in viscous fine sand,the influence of sediment concentration on the viscosity and settling rate of muddy water is comprehensively considered,and the settling rate formula of viscous fine sand is deduced.According to the existing experimental data of flocculation sedimentation,the formula of effective volume concentration of sediment in muddy water is fitted and substituted into the formula of sedimentation rate of cohesive fine sand,and the formula of sedimentation rate of flocculation with sediment concentration as variable is obtained.Compared with other classical formulas,the results show that the deduced formula has higher calculation accuracy.(2)Self-designed flocculation settling device to observe and analyze the effects of single and compound flocculants on the flocculation settling of viscous fine sand.Based on digital image processing technology,the image data of subsidence experiment is analyzed and processed.The particle size of flocs was determined by image-Pro Plus software.The image of flocs settlement was analyzed and processed with multi-resolution based on wavelet transform,and the approximate component image was extracted to draw the flocs settlement curve and accurately measure the uniform settling velocity of flocs in the constant velocity section.(3)Observation and analysis of different concentrations of sand(60g/L,70g/L,80g/L,90g/L,100g/L),adding different kinds of single flocculant(inorganic polymer flocculant polyaluminum chloride PAC,organic polymer flocculant cationic polyacrylamide CPAM and anionic polymer Acrylamide APAM),different concentrations of flocculant(0.04g/L,0.06g/L,0.08g/L,0.1g/L,0.12g/L,0.14g/L,0.16g/L),the flocculation sedimentation process of viscous fine sediment,determine the optimal concentration of PAC,CPAM,APAM under different sediment concentration conditions.Combined with the adsorption isotherm equation,the flocculant settling velocity formula with flocculant concentration parameter was obtained.By comparing the flocculation effect of three kinds of flocculants,two kinds of flocculants with good flocculation effect were selected for further compound study.(4)According to the results of single flocculant experiment,two cationic flocculants PAC and CPAM were selected for compound study.Under the sand concentration of 70g/L,80g/L and 90g/L,Change flocculant concentration(0.04g/L,0.06g/L,0.08g/L,0.1g/L,0.12g/L)and flocculant ratio(PAC:CPAM=1:1,2:1,3:1,4:1,5:1),the influence of compound flocculant on sedimentation of fine sand floc was studied.The experimental results show that the compound flocculant has good flocculation effect and can significantly improve the flocculation sedimentation rate.After flocculation sedimentation,the upper liquid is clear and transparent,and the sediment particle removal rate is high.When PAC: CPAM complex ratio is 2:1,the flocculation rate is the fastest and the flocculation effect is the best.When the sand content is70-80g/L,the optimal dosage concentration is 0.08g/L.When the sand content is 80-90g/L,the best dosage concentration is 0.1g/L.The compound flocculant significantly enhanced the adsorption bridging effect of the flocs,and the flocs formed were more loose,connected with each other in the water to form loose chains,and quickly settled in the form of flocculant nets.Compared with single flocculant,the flocculant with compound flocculant has larger particle size,lower effective density and smaller fractal dimension.The particle size of flocs plays a dominant role in the sedimentation rate.When the particle size of flocs increases,the sedimentation rate still increases with the increase of particle size,although the density of flocs decreases.