Preparation Of Starch Grafted Flocculant(SBF) And Its Sludge Dewatering Performance

Sludge resource utilization requires sludge to have a lower moisture content.Nonetheless,the extracellular polymer substance（EPS）in sludge is a highly hydrophilic and compressible network structure,which makes it problematic to dewater sludge.Therefore,the development of high efficiency and environment friendly of the novel flocculant pretreatment of sludge is one of the methods of sludge dewatering.In this paper,natural starch was selected as the main chain of graft,acrylamide（AM）containing C=C bond and amide group,methylacryloxyethyl trimethylammonium chloride（DMC）as the graft monomer,ammonium persulfate（APS）as the initiator,and starch-grafted flocculant（SBF）was synthesized by hydrothermal initiation.The structure of SBF was characterized and the effect of SBF dosage on sludge dewatering efficiency was studied.The main findings of the study are as follows:In this paper,starch,AM,DMC as monomers,ammonium persulfate（APS）as initiator,hydrothermal preparation of SBF.The effects of total monomer mass fraction,initiator mass fraction,monomer mass ratio,polymerization temperature and polymerization time on the graft efficiency and intrinsic viscosity of SBF were investigated by single-factor experiment.The synthetic conditions of SBF were optimized by orthogonal test.The structure of SBF was characterized in many aspects,and the results showed that SBF was successfully synthesized.Synthetic SBF and market cationic polyacrylamide flocculant（CPAM）were used in the dewatering experiment of urban excess sludge,respectively.The results indicated that SBF could effectively improve the performance of sludge dewatering.When the SBF dosage was40 mg/L,the filter cake moisture content,specific resistance to filtration,capillary suction time and compression coefficient of sludge were 66.76%,5.68×10¹¹m/kg,20.80s and 0.78,respectively.However,when the CPAM dosage was 40mg/L,the filter cake moisture content,specific resistance to filtration and capillary suction time were 71.65%,6.55×1011m/kg and23.5s,respectively.Therefore,the sludge conditioning efficiency of SBF was higher than that of CPAM when the dosage was 40mg/L.Only surface adsorbed water and intracellular bound water were found in sludge cake,indicating that inter-capillary water was released under SBF conditioning into supernatant.The floc structure showed that the size of sludge floc increased from 86.40μm to 212.30μm,and the Zeta potential decreased obviously,which provided a guarantee for improving the sludge dewatering efficiency.EPS analysis before and after conditioning showed that SBF could effectively crack part of LB-EPS and TB-EPS into supernatant,thus releasing bound water wrapped by them and further improving the content of SB-EPS.EPS sludge is effectively destroyed and the proteins in EPS are decomposed and further released.3D-EEM showed that EPS in the sludge was cracked,resulting in the release of fluorescent substances in EPS.FT-IR and XPS analysis of EPS showed that SBF interacted with C-O,O=C-OR in EPS protein to change the secondary structure of protein molecule and increased the hydrophobic component of the molecule,which contributes to the improvement of sludge dehydration performance.Thus,sludge skeleton channel construction,charge neutralization and hydrophobic association effect are the mechanisms of SBF conditioning sludge dewatering.