Study On Preparation And Removal Of Dissolved Organic Carbon/Nitrogen By Aluminum-based Composite Coagulant

The surface water environment dissolved organic matter?DOM?pollution is seriously threatening the safety of water supply quality.DOM is mainly dissolved in organic carbon/nitrogen?DOC/DON?,and its pollution control has received extensive attention.Conventional aluminum salt and iron salt coagulants have very limited effect on DOC/DON reduction.As the core of drinking water treatment,coagulation method has important practical significance to study the removal of DOC/DON in water by coagulation.Polyaluminum chloride?PAC?is the most widely used and most common coagulant.The market demand is huge,but its effect on DOC/DON removal is not ideal.It is necessary to use some means to increase the efficiency of PAC coagulation to remove DOM.Organic-inorganic complex coagulants are a class of polymers that contain a variety of high polymer forms and are of interest because of their excellent coagulation performance.In this dissertation,PO₄^3-and polydimethyldiallylammonium chloride?PDMDAAC?were introduced on the basis of PAC,and the new organic-inorganic composite coagulant?PPAC-PDMDAAC?was prepared by optimizing the synthesis conditions.Using a series of advanced methods for microscopic morphology,chemical structure,aluminum morphology distribution and transformation characterization.To study the efficacy mechanism and aluminum mitigation of PPAC-PDMDAAC in the process of coagulation and DOM removal under different significant influence factors,and to explore the relationship between aluminum form reduction rate and DOM removal.The new PPAC-PDMDAAC was applied to eight typical surface water bodies to verify the effectiveness and mechanism of DOM removal.The main research contents and conclusions of the paper are as follows:?1?In the optimized preparation of PPAC-PDMDAAC,the optimal synthesis conditions of PPAC-PDMDAAC were obtained through single factor experiments such as synthesis temperature,PDMDAAC addition,phosphorus-aluminum molar ratio,alkalinity,and response surface optimization design experiments.The optimal preparation conditions were to dissolve 72.45 g of AlCl₃·6H₂O in 75 mL of pure water to ensure that PDMDAAC was added in an amount of 6 mL,the molar ratio of phosphorus to aluminum was 0.3,the alkalinity was 0.09,the reaction temperature was 90?,and the maturation time was 24 h.A polyhydroxy aluminum is bridged with phosphoric acid to form a polymer of high polymer form,and the degree of alkalization is adjusted with sodium carbonate.The introduction of appropriate amount of PO₄^3-and PDMDAAC into the composite system is beneficial to improve PAC coagulation to remove DOM performance.?2?During the characterization of PPAC-PDMDAAC,electron micrographs show that PDMDAAC envelops the PPAC in a microscopic appearance,with a lumpy structure on the surface.Both the Fourier infrared analysis and the X-ray diffraction pattern indicate that the introduction of PDMDAAC caused some new peaks in PPAC,while part of the old peak of PPAC was lost.Al-Ferron timed complex colorimetry was used to analyze the distribution and transformation of aluminum in PPAC-PDMDAAC.PDMDAAC produced more Al_b and Al_c in the composite coagulant,especially the Al_c fraction increased significantly.PDMDAAC and PPAC are chemically complexed to generate PPAC-PDMDAAC.?3?In the PDMDAAC enhanced PPAC coagulation removal DOM efficacy,the Zeta potential indicates that the introduction of PDMDAAC greatly enhance the PPAC electricity neutralizing ability.Dynamic particle size results indicate that PPAC-PDMDAAC has better flocculation ability,faster aggregation and settling properties,and regeneration ability than PPAC.PPAC-PDMDAAC is superior to PPAC and commercial PAC in the removal of DOM by coagulation and has a wider pH application range.The introduction of PDMDAAC enhanced PPAC coagulation to remove DOM performance.?4?In the PPAC-PDMDAAC process to remove water DOM and mechanism,the best coagulation hydraulic conditions were obtained through single-factor experiments.The optimum coagulation hydraulic conditions are 120 s for fast stirring,15 min for slow stirring,250 r/min for fast stirring and 100 r/min for slow stirring.PPAC-PDMDAAC obtained optimal turbidity,UV₂₅₄,DOC,DON comprehensive removal effect at a pH of 8 and a speculative dose of 20 mg/L.PPAC-PDMDAAC works better in neutral and alkaline.The turbidity removal mainly depends on the electricity neutralization effect.The mechanism of action of removing DOC and DON is not consistent.Better dosing of DOC needs to be higher than better dosing of DON.The main mechanisms for removing UV₂₅₄,DOC,and DON are adsorption bridges and web traps.?5?The correlations between Ala,Alb,Alc depletion rate and turbidity,UV254,DOC,DON removal rate of PPAC-PDMDAAC under different significant factors were studied.The effects of different dosages,4 different hydraulic conditions,different pH values,different initial turbidity,and different initial DOC concentrations on the removal relationship of aluminum form reduction and water quality indicators were investigated.Because PAC-PDMDAAC accounted for the highest proportion of Al_c,followed by Al_b,and the least for Al_a,Al_b and Al_c contributed more to the removal of water quality indicators,and Al_a contributed the least.The correlation between Al_b reduction rate and the removal rate of water quality index was the highest under different factors,showing a strong positive correlation,and the combined effect of Al_b and Al_c was the main reason for DOM reduction.?6?PPAC-PDMDAAC uses different surface waters?Xiangjiang water,constructed wetland water,sewage plant effluent,aquaculture water,pond water,algae water,and artificial lake water?for surface water DOM removal.The removal rate of turbidity,UV₂₅₄,DOC,and DON were all significantly higher than those of conventional treatments.The aluminum species Al_a,Al_b,and Al_c were almost completely reduced during the coagulation process.Therefore,PPAC-PDMDAAC can treat different surface waters better.The use of three-dimensional fluorescence technology to evaluate the removal of DOM by coagulation can excavate more DOM component information.PPAC-PDMDAAC is superior to other three components in the removal of soluble microbial products and humic acid components in DOM.