Preparation Of Silicon Aluminum-based Inorganic Organic Hybrid Flocculant And The Enhanced Removal Mechanism Of Contaminants From Complex System By Flocculation

Coagulation-flocculation is one of the most widely used water treatment technology,because it can offer several particular advantages such as easy operation and low cost.It is often used in the treatment of complex wastewater such as coking wastewater.A suitable flocculant is the prerequisite for the process.While the conventional flocculants are quite limited due to the drawback of poor removal efficiency of the contaminants from complex wastewater.With the implementation of“Action Plan for Prevention and Control of Water Pollution”（Water Ten Articles）and“National Discharge Standard of Coking Wastewater”,the discharge standards of the wastewater are reinforced.And less than 0.4 m³ of discharged wastewater for production per ton of coke are strictly required.As pernicious effects of residual contaminants on the discharge and reuse of complex wastewater,it is urgent to remove the contaminants effectively.In order to further improve the removal efficiencies of complex wastewater by coagulation-flocculation,it is pursued urgently to develop new efficient flocculants and to analysize the enhanced removal mechanism.Recently,inorganic–organic hybrid flocculant with“molecular level composition”has been designed.Due to the synergetic effect of different functional groups or components together in one polymer matrix,they could show superior performance than that of individual component.In addition,it can simplify the dosing procedure.It would be a good option for wastewater treatment.In this thesis,ionic bound and covalent bound inorganic-organic hybrid flocculant were prepared with different silicon source.The hybrid flocculants were applied in treatment of the synthetic wastewater and coking wastewater.A number of standardized jar tests and analysis of the organics in coking wastewater samples were conducted to investigate the flocculation performances and enhanced removal mechanism.By coupling hybrid flocculant and Fe₃O₄,magnetic flocculation technology was introduced for enhanced treatment of coking wastewater.The mechanism of flocculation and magnetic flocculation was proposed.（1）Polyaluminum silicate（PASi）was prepared with composite method using Na₂Si O₃as inorganic silicon source.Based on the inorganic component of PASi and organic monomer components of acrylamide（AM）and acryloyloxyethyl dimethylbenzyl ammonium chloride（ADB）,a new kind of ionic bound organic-organic hybrid flocculant named as PASi-P（AM-ADB）was prepared with in-situ hybridization method.The results of characterization showed that the organic component and inorganic component were combined chemically by ionic bound introduced by-SO₄^2-.PASi-P（AM-ADB）exhibited much compact pores surface morphology and three dimensions wires-linked structure,which were beneficial for the flocculation process.For treatment of kaolin/humic acid（HA）synthetic wastewater,the removal ratio of turbidity,UV₂₅₄ and DOC were 99.2%,95.3%and 94.6%,respectively.PASi-P（AM-ADB）showed excellent turbidity removal performance but low phenol（7.6%）removal efficiency in kaolin/phenol synthetic wastewater.The flocculation efficiencies for treatment of raw coking wastewater in terms of turbidity,UV₂₅₄,DOC and COD were 95.3%,19.9%,18.8%,26.2%,and that of biological treated coking wastewater were 96.2%,42.3%,34.1%and 46%,respectively.PASi-P（AM-ADB）showed better flocculation performance compared with composite flocculant PASi,PASi/P（AM-ADB）and conventional polyaluminum chloride（PAC）.（2）To improve the stability of the hybrid system,another new covalent bound organic silicate aluminum hybrid flocculants（PAAP）were prepared with alkalinity titration hydroxylation polymerization method.Here,theγ-aminopropyltriethoxysilane（APTES）,a widely used silane coupling agent,was employed as silicon source.The results of characterization showed that the inorganic component was connected with organic component by covalent bound.The Si/Al molar ratio and basicity showed significant influence on the morphology and flocculation performance of PAAP.PAAP_0.1,0.5 presented the large curl slice surface and the compact chain-net morphology,resulting in the best coagulation properties for kaolin/HA wastewater.The removal ratio of turbidity,UV₂₅₄,DOC were 99.2%、98.5%、93.2%.For treatment of kaolin/phenol synthetic wastewater,the removal ratio of turbidity and phenol were 99.7%and 4.9%.For coking wastewater,PAAP_0.1,0.5 showed better coagulation performance compared with conventional polyaluminum chloride（PAC）.At the optimal dosage,the coagulation efficiencies of turbidity,UV254,DOC and COD were 82.1%,12.1%,9.3%,24.2%.The corresponding flocculation efficiencies for biologically treated coking wastewater were 97.8%、37.7%、29.9%和63.4%.In addition,PAAP_0.1,0.5 showed very high stability over a long period of 18months without sedimentation and gelatinization.And the flocculation efficiency remained high.（3）In order to identify the enhanced removal mechanism of the two prepared hybrid flocculants,the organic content changes in the water samples before and after flocculation treatment were analyzed.The results showed that the organic contaminants with strong hydrophobicity,high aromaticity,humic acid-like substances and fulvic acid-like substances could be removed efficiently by the prepared PASi-P（AM-ADB）and PAAP_0.1,0.5.The removal efficiencies of hydrophobic-acid fraction（HOA）and hydrophobic-neutral fraction（HON）in coking wastewater are much higher than that of hydrophibic-alkalic fraction（HOB）and hydrophilic fraction（HIS）.PASi-P（AM-ADB）tended to remove alcohol,carboxylic acid,heterocyclic compounds containing N and PAHs in raw coking wastewater.While PAAP_0.1,0.5 could remove alcohol,carboxylic acid,and heterocyclic compounds containing N,as well as esters in raw coking wastewater.The hydrophobic and refractory substances removed by hybrid flocculants.It was benefical to the biological treatment of coking wastewater subsequently.The toxic organics such as PAHs and phthalic acid ester in biologically treated coking wastewater were removed by the prepared hybrid flocculants.The environmental hazards of effluent were reduced.（4）To accelerate the sedimentation rate and shorten the time of flocculation process,magnetic flocculation method was used to treat coking wastewater.With the optimal strategy of dosing Fe₃O₄ particles before hybrid flocculant,following sedimentation under magnetic field,the flocculation efficiency and settling ability were improved.During the magnetic enhanced flocculation,the magnetic flocs with much compact morphology were formed.The flcos strength and regrowth ability were also improved.And the recovered Fe₃O₄ particles showed good magnetic coagulation performance.The possible flocculation and magnetic flocculation mechanisms with respect to the hybrid flocculants were imposed.Due to the synergetic effect of different functional group,such as aluminum hydrolysis species,silicon aluminum polymer macromolecule,quaternary ammonium group,amino group,hydrophobic benzyl,long polymer chains and chain-net structure,the prepared inorganic-organic hybrid flocculants showed superior performance in consequence.In the magnetic enhanced flocculation,magnetic particles could be served as nuclei during formation process of the magnetic flocs.In addition,the introduction of magnetic particles could increase the concentration of particles,adsorb organic matters and enhance flocculant.The flocculation performance was improved furtherly.It was demonstrated that PASi-P（AM-ADB）and PAAP_0.1,0.5presented outstanding flocculation properties as well as excellent stability for treatment of coking wastewater.Accordingly,is beneficial to enhance the removal of contaminants from complex wastewater by coagulation-flocculation process.And it could provide strong support and guarantee for reducing the discharge and promoting the utilization of industrial wastewater.