Preparation Of Cellulose-chitosan Amphoteric Flocculant And Its Application In The Treatment Of Papermaking Wastewater

At present,China's industry is developing rapidly,which not only promotes the rapid development of economy but also produces a series of environmental pollution problems that especially the water pollution problem is the most serious.It arising people's living environment and health issues.The pulping and papermaking industry is an important industrial sector closely related to social and economic development and civilized construction.It is also a major water consumer and one of the main sources of water pollution in China which accounting for the 20-30%of the total industrial wastewater discharge.The papermaking wastewater has complex pollutants.It mainly containing fine cellulose,lignin,organic matter,esters and other pollutants.These are robust pollutants,which are difficult to treat and causes detrimental effect on the natural body of water if the discharge not meet the standard of discharge protocol.At present,the papermaking enterprises mainly use polyacrylamide flocculant(PAM)to coagulate and treat papermaking wastewater.However,the lower efficiency and limited operational features such as single charge carrier,difficulty in biodegradation as well as generation of secondary pollution,restrict the PAM useChitosan and cellulose are natural polymer materials having wide sources.They are low cost with good biocompatibility and a large amount of accessible hydroxyl groups in their molecular chains.Therefore,in this work,a biodegradable amphoteric bio-based composite(HTCC-g-CMC)was synthesized by a one-step cross-linking of glutaraldehyde where cellulose and chitosan are used as raw materials to prepare the carboxymethyl cellulose and quaternized chitosan based flocculant.The flocculation performance and biodegradability of HTCC-g-CMC on Kaolin suspension and papermaking wastewater were investigated,and the flocculation mechanism was studied.The experimental results are as follows:1.Preparation and structural characterization of carboxymethyl cellulose and quaternized chitosanThe cellulose and chitosan were used as raw materials.The preparation process of HTCC and CMC was optimized by orthogonal array design L9(34).The experimental results showed that the optimal preparation parameters for the HTCC are:CTA 10 mL,NaOH 20 mL,reaction time and temperature 8 h × 90?,where for CMC are:chloroacetic acid 4.3 mL,NaOH 1.4 g,reaction time and temperature 1 h × 80?.The HTCC and CMC were fully charactered by SEM,FTIR,XRD,TGA,and BET.The results indicated that HTCC and CMC were successfully prepared with enhanced adsorption site in the surface.The TGA and XRD results exhibited that the crystallinity of the modified cellulose and chitosan reduced and the thermal stability of the HTCC and CMC were lower than before modification which rationalizes the higher surface species for the adsorption sites.2.Preparation and structure characterization of cellulose-chitosan amphoteric flocculantThe HTCC-g-CMC product was obtained after HTCC and CMC grafted by acetal reaction.The preparation process of HTCC-g-CMC is optimized by orthogonal array design experiment.According to the orthogonal results and range analysis,the optimal preparation process are:glutaraldehyde 0.35 g,pH 5,reaction temperature 50? and reaction time 3 h.The FTIR result indicated that the HTCC-g-CMC has both positively charged quaternary ammonium(NH4+)group and negatively charged carboxyl(COOH-)group.The Zeta potential result indicated that HTCC-g-CMC expressed different charging properties under the acidic and alkaline conditions.It was found that,HTCC-g-CMC degraded after 80 days while the degradation rate reached 93.7%,the surface of the degraded HTCC-g-CMC was rough,and more pore size appeared.These results indicated that the HTCC-g-CMC sample has a great biodegradablity.3.Evaluation of flocculation performance of the cellulose-chitosan amphoteric flocculantThe optimal HTCC-g-CMC was employed to flocculate Kao line suspension and papermaking wasterwater,and the flocculation mechanism of the papermaking wasterwater treatment by HTCC-g-CMC was also investigated.The orthogonal experiment showed that the optimum flocculation process for the Kaolin suspension treatment by HTCC-g-CMC under the acidic conditions are:pH 2,coagulant 0 mL,flocculant 10 mL and stirring time 6 min.The alkaline conditions are:pH 12,coagulant 2 mL,flocculant 6 mL,and stirring time 4 min.The turbidity removal rate was calculated by an average of three times of repeatitive cycles,and the rates were 90.4%and 98.9%under acidic and alkaline,respectively.The turbidity and CODCr reduction rate of HTCC-g-CMC flocculation actual papermaking wastewater reached 90.3%and 67.2%,respectively,which is equivalent to the commercial PAM flocculation effect.Hence,this flocculant material can be considered for the flocculation and sedimentation section of the wastewater treatement for the papermaking industries.