Preparation And Properties Of Modified Chitosan Flocculant

Flocculation method has been widely used based on the advantages of simple operation,fast treatment time and low cost.It can be applied to the pretreatment,post-treatment and main treatment process of wastewater.The type of flocculant plays an important role in flocculation performance.Due to the accumulation of inorganic salts and the non-environmental friendliness of residual monomers,traditional flocculants have gradually failed to meet the demand.The characteristic of natural polymer flocculants are non-toxic,biodegradable and abundant in resources.Among them,chitosan(CTS)is a kind of natural alkaline polysaccharide,which has the problems of poor solubility and low cation degree.In this study,acrylyl oxyethyl trimethyl ammonium chloride(DAC)and dimethyl diallyl ammonium chloride(DMDACC)were selected for quaternization modification of CTS,then two kinds of modified chitosan flocculants were successfully prepared.The characterization analysis and performance test were carried out,explore the influence on the post-treatment process and the utilization of chemical sludge resources.The main research contents and conclusions are as follows:(1)FTIR,XRD and SEM proved that DAC and DMDACC were grafted and copolymerized with CTS in aqueous solution system,and modified chitosan flocculants CTS-DAC and CTS-DMDACC were successfully prepared.The Zeta potential,solubility test and viscosity test proved that the modified chitosan flocculant had high charge strength and good water solubility.According to Jar-test experiment,which showed that when the optimum dosage of CTS-DAC was 16 mg/L,and the removal rate of turbidity was 98.30%and COD was 71.13%.When the optimum dosage of CTS-DMDACC was 18 mg/L,and the removal rate of turbidity and COD was 98.86% and 68.92%.The modified chitosan flocculant had a larger floc size,better flocculation performance and wider dosing range than chitosan during the flocculation process.The quaternization modification enhanced the charge neutralization,bonding bridging and net sweeping of the flocculant,which made it has better flocculation performance.(2)The effects of modified chitosan flocculant on activated sludge characteristics and membrane filtration performance were investigated through sequencing batch activated sludge reactor and constant pressure filtration experiment.Continuous monitoring of activated sludge characteristic parameters showed that the modified chitosan flocculants could reduce effluent COD and supernatant turbidity which improved effluent quality.It was helpful to improve MLSS and MLVSS/MLSS value.Moreover,the modified chitosan flocculants also increased the particle size of activated sludge,reduced the SVI and improved sludge settleability.In the constant pressure filtration experiment,the addition of modified chitosan flocculant reduced the permeation flux attenuation rate of activated sludge mixture.At the same time,it could enhance the permeability of the filter cake layer and reduce membrane pore blockage,which was beneficial to alleviate membrane fouling.(3)The chemical sludge(Sludge-1,Sludge-2)produced by CTS-DAC and CTS-DMDACC treating simulated papermaking wastewater was used as adsorbent to treat methylene blue(MB)and methyl violet(MV)in printing and dyeing wastewater.When the dosage is 0.15 g,the contact time is 1 h,and the temperature is 25 °C,the removal rate of MB and MV with a concentration of 50 mg/L by chemical sludge is above 97 %,showing a faster adsorption rate and higher removal effect.