Removal Of Trace High-risk Organics From Water And Control Of Membrane Fouling By Flocculation-sedimentation-ultrafiltration Process Based On Moderately Hydrophobically Modified Flocculants

Trace high risk organic pollutants（such as pesticides,antibiotics）and their associated biological effects have attracted widespread attention due to their safety issues.The conventional water treatment technology is based on coagulation,sedimentation,disinfection and filtration.With the comprehensive implementation of the new Sanitary Standards for Drinking Water and the reduction of the cost of UF membrane,UF technology has been applied more and more in the renovation of old water plants and construction of new water plants in China.However,the ultrafiltration process alone does not guarantee the high quality of produced water.In addition,a variety of organic pollutants in surface water,including humus,polysaccharides,and proteins,often lead to severe membrane fouling and reduce membrane life span.According to the previous studies,which have shown that the short process of flocculation-sedimentation-ultrafiltration can save water plant area and reduce investment,and has more advantages in terms of pollutant removal and membrane fouling control.Due to the low concentration of the above-mentioned high-risk organic pollutants（such as pesticides and antibiotics）in water,the traditional commercial flocculants have limited ability to remove them,and at the same time,the pretreatment with traditional commercial flocculants has very limited ability to control membrane fouling.Membrane fouling is often caused by some small molecule hydrophobic pollutants,according to this reason,this thesis chooses this synthesis of the two kinds of moderate hydrophobic modified flocculant as the pretreatment agents of flocculation-sedimentation-ultrafiltration process,and this process is used to remove the trace organic pollutants（pesticides,antibiotics）with the coexistence of natural organic matter（NOMs）and high risk of suspended particles in water;for the two kinds of flocculants,one is moderately hydrophobic modified chitosan-based flocculant,and the other is moderately hydrophobic modified organic/inorganic composite flocculant;In this paper,after the synthesis of the above two kinds of flocculants,the two kinds of moderately hydrophobic modified flocculants were characterized by Fourier transform infrared spectroscopy,hydrogen nuclear magnetic resonance spectroscopy,X-ray diffraction spectroscopy and Zeta potential and other methods to ensure the success of synthesis.Then,the same simulated surface water as the process of dynamic continuous flow flocculation-sedimentation-ultrafiltration was selected for static flocculation experiment to explore the optimal dosage of two moderately hydrophobic modified flocculants under static conditions,paving the way for the subsequent dynamic continuous flow experiment.Finally disappeared in the flocculating agent under the optimal dosing quantity of continuous flow flocculation-sedimentation-ultrafiltration experiments,through calculation of the TMP,produced water quality,membrane resistance,scanning electron microscopy（SEM）picture,DFT theoretical calculation as well as the quality of each pollutant distribution calculation of continuous flow flocculation-sedimentation-ultrafiltration process of high risk for trace organic pollutants removal efficiency and the mechanism of membrane fouling are easing conducted in-depth research.Some research results are shown as the following statement:（1）For the removal of trace amounts of antibiotics in water,this study selected the four kinds of common and representative of antibiotics in water,and they era tetracycline（TC）,erythromycin（ROX）,norfloxacin（NOR）and sulfamethoxazole（SMZ）,respectively.And then choose the moderate group synthesis hydrophobic modification of chitosan based flocculant（CS-g-PNIAPM）with alum as the pretreatment agents of a continuous flow of flocculation-sedimentation-ultrafiltration experiments.In room temperature,this study found that the removal efficiency of the kaolin and humic acid（the conventional pollutants in water）,regardless of the sedimentation tank or UF produced water,is similar with each other,and the distribution of this process does not reflect a clear advantage.However,compared with the traditional commercial flocculants（such as alum and PAM）,this CS-g-PNIPAM with alum system has obvious advantages in both pre-treatment and post-ultrafiltration effluent quality at room temperature for the removal of trace antibiotics in water,and the membrane fouling is also significantly reduced.For the removal of four kinds of antibiotics,in the sedimentation tank,the removal efficiency of the four kinds of antibiotics in the CS-g-PNIPAM with alum system were:SMZ（76.62%）,NOR（67.65%）,TC（62.21%）and ROX（71.98%）,which were too much higher than that in the alum or polyacrylamide system,and in alum system:SMZ（45.87%）,NOR（36.47%）,TC（31.62%）and ROX（43.88%）.In PAM system:SMZ（46.22%）,NOR（40.14%）,TC（38.32%）and ROX（42.28%）);Moreover,the corresponding membrane fouling control is also better for the moderately hydrophobic modified flocculant system than for the commercial flocculant system.The calculation of reversible and irreversible membrane fouling resistance shows that the reversible and irreversible membrane fouling resistance of CS-G-PNIPAM with alum system is much less than that of the two commercial flocculant systems.In addition,the moderately hydrophobic modified chitosan-based flocculant synthesized in this group can hydrophilic modify the membrane surface,which is also a reason for reducing membrane fouling.To further improve combined process,considering the CS-g-PNIPAM is thermosensitivity,（temperature switch:32℃）,and also mentioned above on the membrane surface modification,this paper further to do the research on flocculation-sedimentation-ultrafiltration process,using different temperature of in-situ and ex-situ cleaning water to study its effects on membrane fouling control and produced water quality.It was found that compared with the room temperature,for the produced water,the removal efficiency of trace organic pollutants was further improved when both the in-situ and the ex-situ cleaning water temperature was 45℃,and the membrane fouling was also further improved.（2）For the removal of trace pesticides in water,moderate hydrophobic modified organic/inorganic composite flocculant（long hydrophobic carbon chain modified metal hydroxides,such as CSA,CSF and CST）was selected as the pretreatment agent of flocculation-sedimentation-ultrafiltration process in this paper to study its removal efficiency of four kinds of pesticides:Glyphosate（GPS）,carbendazim（CBZ）,totally insect amidine（AAP）as well as the removal of the four gather acetaldehyde（MET）,and in the process of membrane fouling control,the study found that compared with the traditional commercial flocculant,this group of moderate hydrophobic modification of synthetic organic/inorganic composite flocculant for pesticides have strong combined ability,and the CSA has the best performance in above three flocculants,in sedimentation tank,for the four kinds of pesticides,the removal efficiency is as follows:GPS（72.28%）,CBZ（74.36%）,AAP（84.12%）and MET（78.86%）;For membrane fouling,the corresponding reversible and irreversible membrane fouling at the first and second stages were 2.5×10¹¹ m^-1（reversible membrane fouling）,4.2×10¹⁰ m^-1（Irreversible membrane fouling）.In the second stage,reversible membrane fouling was 2.9×10¹¹ m^-1,and the irreversible membrane fouling was 1.09×10¹¹ m^-1.Much lower than commercial flocculant system(AlCl₃:phaseⅠ,reversible membrane fouling was 2.83×10¹¹ m^-1 and the irreversible membrane fouling was 1.27×10¹¹ m^-1.phaseⅡ,reversible membrane fouling was3.95×10¹¹ m^-1 and the irreversible membrane fouling was 2.57×10¹¹ m^-1).It can also be identified by scanning electron microscopy that the cake layer on the membrane surface corresponding to the modified flocculant is relatively loose and porous.The results showed that the moderate hydrophobic modified organic/inorganic composite flocculant had excellent performance in the removal of pesticides and the control of membrane fouling.Through the study of two systems,continuous flow flocculation-sedimentation-ultrafiltration water treatment process in using this group of moderate hydrophobic modification of synthetic flocculant as pretreatment agents,compared to the traditional commercial flocculants,the removal efficiency of conventional pollutants（such as kaolin and humic acid）for the modified flocculants are higher,and at the same time,this kind of flocculants can also be effective in the removal of the trace high-risk organic pollutants in water,such as pesticides and antibiotics.and can effectively control the membrane fouling;To some extent,this deal with the two problems:one is membrane fouling,and the other is the difficulty of removing the trace organic matter in water.