Condition Technology For Sludge Dewatering Of Construction Slurry In N City

There are lots of shortages about the disposal method of construction slurry, suchas low efficiency, high cost and so on. In order to meet the national environmentalrequirements and reduce the costs, the existing disposal technologies should beimproved. In this research, construction slurry of city N was elected, and correlationratio between slurry properties and dewatering ability was studied. And according tothe key factors, improving the ability of slurry dewatering with chemical method wasstudied.The properties of construction slurry was studied, such as slurry concentration,organic matter content in dry solid, slurry salinity, pH, zeta-potential and particle sizerange. In order to identify the key factors of slurry dewatering, the correlation ratiobetween slurry’s resistance number and slurry’s properties was analyzed. Resultsshowed that the proportion of slurry particle whose size was less than2μm was themost important influence factor; its correlation reached72.45%. If the proportionincreased, the specific resistance increased and the ability of dewatering was worse.The influence of dry solid matter content and surface potential were also important,their correlation were59.76%and57.21%.In order to select the proper flocculant, the effects of single flocculant using forimproving slurry dewatering was studied, such as PAC, PFS, Ca(OH)2, CPAM,ACPAM, HCA, cationic etherified starch and polyving akohol. Results showed that theproportion of slurry particle whose size was less than2μm reduced after dosing HCAof700000molecular weight level; it was the best dosage. And surface potential alsoincreased by a large margin. The pH value and surface potential of slurry increasedafter dosing Ca(OH)2, and the performance of dewatering was also improved, in themeanwhile, organic matter content in dry solid did not increase.According to various flocculants combined use experiments, it was proved thatthe method of combined use could achieve better results. The best dosing method wasthat PAC-HCA-Ca(OH)2was dosed in turn, and their concentrations were200mg/L,1000mg/L,3200mg/L. And the best conditions of slurry were as followed: pH valueof9.0, temperature of0-40℃, salinity of less than0.25%and slurry concentration ofless than170g/L.Applying the best combined method to pilot plant, it was found that the averagesize of slurry particle was increased from7.32μm to90.46μm; it could meet theconditions of vacuum belt dewatering machine. If rolling belt pressure filter was used,dosing ACPAM of100mg/L was needed. The average cost of this technologicalprocess was28.7rmb/t and it was39.1%lower than general methods.