Research On Pellet Flocculation Concertrate The River Sediment Dredging Technology

Most city rivers are slow water, with narrow interface of channel, small gradient, weak ability of self-purification. However, the technology of dredging the sediment is mainly used in the large lakes, rivers, for the city’s small rivers, rarely used. The equipment of dredging applied in lakes and large flow channel is very difficult to use in small flow channel, so urgently needing a kind of dredging technology applied in the usual control of sediment pollution in small river. Pellet flocculation technology is suitable for the separation of the solid liquid, with the characteristics of small volume, high efficiency and less cover of land. Using the pellet flocculation as the core technology, the idea of combination of suction underwater, the pellet flocculation and dehydration is a kind of ecological dredging technology, adapting to the need of dredging in the urban river channel. Therefore, this paper focuing on the core technology of the content-pellet flocculation, starts the research of river sediment experiment. Apply the highly efficient solid-liquid separator in the river sediment treatment in Yangzhou, chose the proper condition of the process, finally put forward a new kind of ecological dredging process and introduce a new kind of theory and engineering application for urban ecological river dredging in future.This research topic cintains three aspects:Analyze the characteristics of the river sediment pollution in Yangzhou; Select the best kind of aid coagulant to use in pellet flocculation through the static coagulation experiment; Undertake dynamic experiment of the pellet flocculation. Main research results are as follows:(1) The pH of the sediment is8-9, alkaline, in Yangzhou city rivers; The organic matter of the surface sediment mainly comes from the floating plants, animals and algae for the most rivers, less rivers are from the accumulation of pollutants outside the river; The sediment is pulluted by nutrient seriously; From the analysis of the standard of heavy metals and evaluation of accumulation index shows that Cd and Pb are moderate and mild polluted, meets the "standard of pollutant control in agricultural sludge"(GB4284-84) and the hierarchical order of the three kinds of heavy metal pollution is Cd> Pb> Cr.(2) Choose Shanghai cationic PAM (S2) as coagulant aid.(3)PAM dosing quantity has great effect on the formation of the pellet flocculation; The concentration of water sludge determines the PAM dosing quantity; The PAM dosing quantity increases with the increase of sludge concentration linearly; With the concentration of sludge dosing rate increases, the PAM dosing rate decrease; The concentration of sludge increase from2to9g/L, the best PAM dosing quantity increases from2.0～5.3‰.(4) PAC has the buffering capacity in pellet flocculation process, and turbidity is not sensitive to the change of PAC; The proper PAC dosing quantity is1.0-5.0%.(5) The intensity of mechanical stirring in the suspension layer reflects the direct indicator of the control; The proper stirring intensity increase initial particles and groups of the collision probability, improve the particle capture efficiency on the suspension contact layer, and benefit to the quality of the effluent water; The best speed is8-12r/min and the corresponding velocity gradient G=4.98～9.14s-1.(6) HRT effects the pellet flocculation significantly;As HRT>120s, the turbidity of effluent is less than3NTU and the effect of the treatment has nothing to do with the rise velocity in the reaction zone; As HRT<120s, with the decrease of the HRT, the turbidity of effluent deteriorated rapidly; As the same HRT, adopting the dumpy reation aera with low velocity gets the better treatment effect than the the tall reation aera with high velocity; As the pellet flocculation zone tube0.9m, get highest rising velocity of13.28mm/s, the turbidity of the effluent water<15.21NTU, the rate of particles sinking>4.09cm/s, the moisture content of tail mud<94.35%.(7) As HRT=85s,the turbidity of the effluent water can be stabilized at about15NTU, the speed of the articles sinking is controlled about75mm/s, the moisture content<93.88%, the specific resistance of sludge<1.4×105s2/g, and belongs the easy filtration sludge. CODmn<2.5mg/L, TP<0.15mg/L, NH3<0.23mg/L, TN<0.25mg/L. The river sediment can be concentrated more than10times and the tail water meets the standards of the municipal sewage treatment plant emissions.(8) Applying the technology of pellet flocculation in the sediment concentration is feasible and the process with combination of sediment suction underwater, the pellet flocculation and dehydration has great prospects and application value for urban river sediment treatment in future.