Research On Improving The Separation Property Of Dredged Sludge By Flocculants

In recent years,with the development of river regulation projects in China,the amount of dredged sludge is increasing.It has been urgent to start the works on dredged sludge treatment.How to deal with the problems of large areas dredged sludge occupied and long drying time has become the technical problem to be solved in the filed of environment protection.Dewatering with flocculants is the most important technology in sludge treatment.In this paper,the dredging sludge from Zhang river of Wuhu,Guxi river of Dangtu and Simashan main canal of MaAnshan is the research object.After pretreatment with Fenton regents,different types of floccluants and compounding flocculants were chosen.Finally,the best plan for fast dehydration of dredging sludge was confirmed through static experiments in measuring cylinder according to the indicators of the suspension solids content,drop speed of clear and sludgedy interface,sludge settling velocity and the volume of remaining sludge.Studies showed that the flocculants in this experiment could significantly expedite the settling velocity of dredging sludge.When the sludge content was 5%,the settling ratio of sludge from Zhang river sludge with Ca?OH?₂ of100mg/L reduced to 28.04%;Sludge from Guxi River with Ca?OH?₂ of 70mg/L and fly ash of 1g/L reduced to 14.33%;Sludge from Simashan main canal with PAFC of160mg/L reduced to 33.57%.When the sludge content risen to 10%and 15%,the best flocculants dosage of 10%and 15%sludge were basically the same as the dosage of 5%sludge.Settlement velocity decreased obviously,and the volume of residual sludge increased significantly.It can be seen from that when the sludge concentration is below15%,the optimal amount of flocculants is not related to the sludge concentration,but with the increase of the sludge concentration,the settlement velocity decreased obviously,and the volume of residual sludge increased significantly.The sludge from Guxi River is a mixture of mud and sands,and the sludge from Zhang River and Simashan main canal are with little or no sands.The results showed that the flocculants had better effect on the dehydration of sludge with a certain amount of sand,while the sedimentation effect of sludge with a little or almost no sands was relatively poor.In this paper,small dynamic sludge dewatering equipment simulated the subsidence condition of sludge-dumping area on the scene of the project so that the mobile modular sludge dewatering process could be explored.Some influencing factors were studied,such as ways of dosing flocculants,baffle setting,different types of flocculants,flocculants dosing quantities and retention time.etc.According to the analysis of suspension solids content and settlement velocity,the optimal parameters of the device in the sludge treatment was determined.The experimental results showed that the minimum value of suspension solids content was 451.8mg/L when the sludge was mixed with Ca?OH?₂ of 70mg/L by pipeline and the retention time reached to50min.Taking Guxi River in Dangtu as an example,the project of adding Fenton reagents and Ca?OH?₂ will reduce the land requisition and cofferdam construction by 40%and reduce the cost of 0.4 million yuan compared with the original dredging program.The results of this study could provide some references for the dewatering process and flocculants selection in dredging projects,and also give important suggestions for the design of dumping-sludge area in the later dredging project.