Physiochemical Characteristics Of Urban Retarded River Sediment And Key Control Factors For Dewaterability

Most urban retarded rivers have small environmental capacity and poor self-purification capacity.As the main accumulation place of pollutants,river sediment is pollution endogenous sources.It is an effective way to ensure water quality to implement normalized sediment dredging and dewatering.However,research on control factors for its dewaterability and treatment technology in small and micro water body like urban retarded river is still in infancy in China.Therefore,physiochemical characteristics of urban retarded river sediment and key control factors for dewaterability was studied through field investigation,laboratory test,pressure filtration model machine test and engineering practice,which provide theoretical support for the treatment technology and reduction control of sediment produced by normalized sediment dredging.The main research work and achievements are as follows:(1)Physiochemical characteristics of urban retarded river sediment in the Slender West Lake river network area of Yangzhou were analyzed.The analysis shows that large-scale flowing sediment slurry with high water content and very low strength will be produced in normalized sediment dredging,and it contains a considerable proportion of particles with poor dewaterability.Thus optimization and control of key technical such as flocculation conditioning and mechanical dehydration in reduction disposal process is the key to realize normalized sediment dredging of urban retarded river.Dredging effect under the existing dredging technology was evaluated based on physiochemical characteristics of urban retarded river sediment.The evaluation shows that source-sink relationship in the river network area should be taken into account in normalized sediment dredging,long-term mechanism of rotational dredging should be constructed scientifically,standard on rotational dredging should be determined according to local conditions,siltation monitoring of urban retarded river should be carried out in an all-round way.The dredging frequency should be once every 1～2 year and the rotational dredging control thickness should be 30 cm.(2)Flocculation conditioning tests of river sediment with different initial water content and different liquid limit were carried out.Taking specific resistance to filtration,capillary suction time and particle size scale as the characterization indexes,the dewaterability variation law of sediment slurry before and after flocculation conditioning was revealed.Sediment slurry with different liquid limit has the most suitable flocculant dosage and initial water content for flocculation conditioning.Synergistic flocculation mechanism of PAC-CPAM composite flocculant for sediment slurry conditioning was confirmed based on fractal theory,infrared spectroscopy and water hinge hypothesis.The quantitative relationship between optimal dosage of PAC-CPAM composite flocculant and flocculation control factors such as initial water content,liquid limit and particle content with particle size less than 0.01 mm of sediment slurry was constructed.(3)Belt pressure filtration model machine tests of river sediment after optimal flocculation conditioning with different initial water content and different liquid limit were carried out.Taking processing capacity as the characterization index,the effect of flocs particle size after optimal flocculation conditioning and filter belt speed on the dewaterability of sediment slurry after optimal flocculation conditioning under belt pressure filtration was revealed.Sediment slurry with different liquid limit has the most suitable belt speed for belt pressure filtration.The quantitative relationship between maximum cake dry output,critical cake water content,critical cake thickness,best belt speed and belt pressure filtration control factors such as liquid limit and constrained grain size of flocs after optimal flocculation conditioning was constructed.Then,Water-based integrated equipment suitable for normalized sediment dredging and dewatering was expounded,which solves the problem that it is difficult to set up reduction disposal site in urban retarded river.Based on engineering practice of the integrated equipment,the efficiency and feasibility of the research results was verified.