| The proper treatment and disposal of sludge has become a challenge for the development of water treatment industry due to the high volume of residual sludge and the high cost of treatment.Before mechanical dewatering,the sludge needs to be conditioned to improve the dewatering performance.Coagulation is widely used in sludge conditioning because of its low cost,high efficiency,and ease of operation.During coagulation conditioning,treatment efficiencies are deeply influenced by dewatering agents.In this research,polysilicate ferric(PSF),polysilicate aluminum ferric(PSAF),and polysilicate aluminum ferric magnesium(PSAFM)were prepared by copolymerization reaction,then they were applied to sludge dewatering pretreatment.The single factor and response surface method were used to regulate the reaction conditions.The successful preparation of polysilicate was confirmed by Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction analysis(XRD).By studying the effect of the properties of cationic polyacrylamide(CPAM)on sludge dewatering performance,the CPAM type suitable for sludge dewatering pretreatment was screened.Through dewatering conditioning experiments,the prepared polysilicate was used alone and in combination with CPAM to reveal the mechanism of sludge dewatering conditioning.The research results are as follows.The preparation procedures of polysilicate were optimized by single factor and response surface experiments.It was found that the optimal preparation conditions of PSF were as follows:pH=1.0,temperature=20℃,Si/Fe=1.00.The optimum preparation conditions of PSAF were pH=1.0,temperature=20℃,Si/M=0.40,Fe/Al=1.562.The optimum preparation conditions of PSAFM were as follows:pH=1.0,temperature=20℃,Si/M=1.08,Fe/Al=2.00,Fe/Mg=2.00.FTIR and XRD analyses confirmed that Fe3+,Al3+,Mg2+ were polymerized with polysilicic acid to form an amorphous polymer.Results of Fe-Ferron time-by-time complexation colorimetry confirmed that the polysilicate had a higher Feb content compared to polymerized ferric sulfate(PFS).The results of particle size distribution showed that the particle size of polysilicate was improved compared with PFS.The CPAM with the best effect in sludge dewatering conditioning was selected.The results showed that the viscosity of CPAM had the greatest influence on sludge dewatering performance,with a correlation coefficient of 0.92025 between sludge SRF values and viscosity,indicating that the adsorption bridging effect of CPAM played a dominant role in sludge dewatering pretreatment.Among the CPAM selected,9112 showed the strongest application performance.At a dosage of 3‰,the SRF and moisture content of sludge cake were 1.40×1012 m·kg-1 and 84.38%respectively,representing a 90.17%and 7.45%reduction compared to the raw sludge.When used alone,polysilicate could change the sludge floc properties by adsorption bridging,change Zeta potential and viscosity by electro-neutralization,destroy EPS and release bound water.There was also an optimum dosage of polysilicate and PFS:2.5%for PSF,2%for PSAF,1.5%for PSAFM and 2%for PFS.Compared to the commercially available inorganic dewatering agent PFS,polysilicate had a stronger adsorptive bridging effect and therefore achieved better treatment results at low dosages.When polysilicate used in combination with CPAM,the dosage of dewatering agents was significantly reduced,with the dosage of 9112 reduced from 3‰ to 2‰,and the dosage of inorganic dewatering agent reduced from 1.5%to 5‰.In terms of characteristics of the treated sludge,both the polysilicate and CPAM played an adsorptive bridging role,while the combination of PFS and CPAM was a combination of electro-neutralization and adsorptive bridging.Through economic analysis,the preparation cost of inorganic dewatering agents was much lower than that of CPAM.Considering the economic and environmental benefits,it was recommended to use inorganic dewatering agents and CPAM in the sludge dewatering pretreatment. |
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