The Synthesis Of Poly-diallyldimethyl-Ammonium Chloride And Application In Treating Wastewater

The scope of this thesis was to investigate the application of PDADMAC as a primarycoagulant/composite coagulant in water/wastewater treatment. Firstly, the Taguchi methodof design of experiments was used in synthesizing PDADMAC and determining optimumconditions. In addition, ANOVA determined the influence of the factors on the turbidityremoval efficiency. The evaluation of the PDADMAC treatment efficiency was determinedby measuring both the reduction of residual turbidity and chemical oxygen demand （COD）.For turbidity removal efficiency, the combination of factors selected as optimum conditionsfor synthesis of PDADMAC using the Taguchi method for synthesis temperature, mass ofthe initiator, volume of de-ionized water and synthesis time were50oC,0.20g,10mL and8h respectively. The ANOVA results show the synthesis temperature had the mostsignificant influence on the turbidity removal efficiency, followed by the mass of initiator,synthesis time and volume of deionized water. However, for product viscosity, thecombination of factors selected as optimum conditions using the Taguchi method forsynthesis temperature, mass of the initiator, volume of de-ionized water and synthesis timewere60oC,0.15g,10mL and5h, respectively. The ANOVA results show the synthesistemperature had the most significant influence on the product viscosity, followed by themass of initiator, synthesis time and volume of de-ionized water.The optimum conditions for coagulation-flocculation were12mg/L,9,300rpm and120min for coagulant dosage, coagulation pH, rapid mixing speed and settling timerespectively. At the adopted optimum dosage of12mg/l, the turbidity and COD removalefficiencies were86.56%and57.64%respectively. The wastewater turbidity was reducedfrom70.9NTU to a final level of9.53NTU at optimum dosage while COD was reducedfrom288mg/L to a final level of122mg/L. However, at optimum coagulation pH, theturbidity and COD removal efficiencies were91.06%and57.47%respectively. The CODat optimum pH decreased from an initial value of174mg/L to74mg/L whereas theturbidity was reduced from106NTU to a final level of9.45NTU. However, the turbidityand COD removal efficiency at optimum conditions （coagulant dosage, coagulation pH,rapid mixing time, and settling time） were90.71%and76.54%, respectively. At optimum conditions, the turbidity decreased to a final level of9.15NTU while the COD decreased to42mg/L. The zeta potential value at the optimum condition of-4.97mV was below thepoint of zero charges; thus, charge neutralization （electrostatic patch effect） mechanismplayed a role in the coagulation-flocculation process, but was not the only coagulationmechanism for the synthesized PDADMAC.Secondly, new composite coagulants PFPD₁, PFPD₂and PFPD3were prepared andstudied with PFS. The response surface design was used to investigate the effect changes inthe level of coagulant dose and coagulation pH have on turbidity and COD. In addition, theoptimum combination of dose and pH that yields the best turbidity and COD removal weredetermined. Confirmation experiments were carried to confirm the agreements of theresults achieved from the models and the experiments.Optimizing the fitted models for turbidity removal efficiency, it shows a turbidityremoval efficiency of98.2%could be achieved at a coagulant dosage of390mg/L andcoagulation pH of7.7using PFS. For PFPD₁, the predicted turbidity removal efficiency of98.1%could be achieved at a coagulant dosage of430mg/L and coagulation pH of7.96. Inaddition, the PFPD₂model predicted the turbidity removal efficiency of96.75%could beachieved at a coagulant dosage of320mg/L and coagulation pH of7.24. Lastly, the modelpredicted the turbidity removal efficiency of90.5%could be achieved at a coagulantdosage of390mg/L and coagulation pH of7.28using PFPD3.Optimizing the fitted models for COD removal efficiency, a removal efficiency of66.9%at a coagulant dosage of390mg/L and coagulation pH of7.32was predicted forPFS. For PFPD₁, a removal efficiency of66.2%was predicted at a coagulant dosage of384mg/L and coagulation pH of8.13. In addition, using PFPD₂, the model predicted a removalefficiency of69.4%at a coagulant dosage of450mg/L and coagulation pH of8.14. Lastly,the PFPD3model predicted a removal efficiency of67.6%at a coagulant dosage of390mg/L and coagulation pH of7.49for COD removal using.For simultaneous optimizing of the turbidity and COD removal efficiency models, theresults reveal the optimum conditions for PFS were coagulant dosage of388mg/L andcoagulation pH of7.6while the predicted turbidity and COD removal efficiencies were98.1%and66.8%. For PFPD₁, optimum conditions were coagulant dosage of384mg/L andcoagulation pH of7.75while the predicted turbidity and COD removal efficiency were 97.8%and65.8%. The optimum conditions for PFPD₂were coagulant dosage of444mg/Land coagulation pH of8.05while the predicted turbidity and COD removal efficiency were93.65%and69.05%. For PFPD3, optimum conditions were coagulant dosage of390mg/Land wastewater initial pH of7.48while the predicted turbidity and COD removal efficiencywere90.5%and67.6%. The models show for turbidity removal the effectiveness of thecoagulants in decreasing order was PFS>PFPD₁>PFPD₂>PFPD3while for COD removal,the order was PFPD₂>PFPD3>PFS>PFPD₁.Confirmation experiments using optimum conditions for PFS shows the residualturbidity was reduced from an initial level of67.3NTU to a final level of2.66NTU whilethe COD was reduced from an initial level of200mg/L to a final level of65mg/L. ForPFPD₁, the residual turbidity was reduced from an initial level of74.0NTU to a final levelof2.70NTU while the COD was reduced from an initial level of194mg/L to65.2mg/L atoptimum conditions. However, using PFPD₂, the residual turbidity was reduced from aninitial level of70.4NTU to a final level of5.25NTU while the COD was reduced from aninitial level of192mg/L to60.9mg/L. Lastly, using PFPD3, the residual turbidity wasreduced from an initial level of63.1NTU to a final level of6.10NTU while the COD wasreduced from an initial level of199mg/L to63.8mg/L. The results of verificationexperiments demonstrated RSM approach was appropriate for optimizing the coagulation-flocculation process.Lastly, composite coagulants PFPD₁, and PFPD₂were prepared and studied with PFSin treating micro-polluted surface water. The response surface design was used to designand investigate the effect changes in the level of coagulant dose and coagulation pH haveon the residual turbidity and TOC. In addition, the optimum combination of dose and pHthat yields the lowest residual turbidity and TOC were determined. Confirmationexperiments were carried to confirm the agreements of the results achieved from themodels and the experiments.Optimizing the fitted models for residual turbidity, the residual turbidity could bereduced from an initial turbidity of8.01NTU to a final turbidity of0.924NTU at acoagulant dosage of200mg/L and coagulation pH of8.13using PFS. For PFPD₁, themodel predicted the residual turbidity could be reduced from an initial turbidity of8.01NTU to a final turbidity of0.907NTU at a coagulant dosage of140mg/L and coagulation pH of7.52. Furthermore, the model for PFPD₂predicted the residual turbidity could bereduced from an initial turbidity of14.40NTU to a final turbidity of1.08NTU at acoagulant dosage of100mg/L and coagulation pH of7.34for.Optimizing the fitted model for TOC, the model predicted the TOC could be reducedfrom an initial level of3.17mg/L to a final level of2.03mg/L at a coagulant dosage of200mg/L and coagulation pH of7.98using PFS. For PFPD₁, the model predicted the residualTOC could be reduced from an initial level of3.17mg/L to a final level of1.83mg/L at acoagulant dosage of180mg/L and coagulation pH of7.97. Furthermore, the fitted modelfor PFPD₂predicted the residual TOC could be reduced from an initial level of2.53mg/Lto a final level of1.51mg/L at a coagulant dosage of140mg/L and coagulation pH of7.94.For simultaneous optimization of the residual turbidity and TOC models, the resultsreveal the optimum conditions for PFS were coagulant dosage of204mg/L and coagulationpH of8.06while the predicted residual turbidity and TOC were0.924NTU and2.025mg/L. For PFPD₁, optimum conditions were coagulant dosage of179mg/L and coagulationpH of7.99while the predicted residual turbidity and TOC were1.09NTU and1.829mg/L.The optimum conditions for PFPD₂, were coagulant dosage of112mg/L and coagulationpH of7.65while the predicted residual turbidity and TOC were1.7NTU and1.64mg/L.The models show for residual turbidity, the effectiveness of the coagulants indecreasing order was PFS>PFPD₁>PFPD₂while for residual TOC, the order wasPFPD₂>PFPD₁>PFS. The verification experiments demonstrated RSM approach wasappropriate for optimizing the coagulation-flocculation process.