| Wastewater treatment plant effluent contains high content and complex matrix of residue organic matters, which made conventional treatment process(coagulation-sedimentation-filtration) become more and more limited in wastewater reclamation recently. Therefore, pre-ozonation was often applied to enhance the treatment performance of coagulation. However, pre-ozonation-coagulation process was always limited by ozone dosage control and raw water organic matter characteristics. Based on this, effluent from some wastewater treatment plant with A2 O process was selected to analyze the effluent dissolved organic matter(EfOM) characteristics and ozonation of EfOM was also investigated. Based on the effect of pre-ozonation on conventional treatment process, hybrid ozonation-coagulation(HOC) system was proposed. According to the mutual enhancement mechanism in HOC system, dissolved ozone flotation(DOF) process was developed in this study and was applied in wastewater reclamation. The results provide theoretical and application basis for advanced wastewater treatment process and improvement of wastewater reclamation. The main results was summarized as follows:(1) XAD-8 resin was used in this study to fractionate the EfOM, the results indicated that HOA(hydrophobic acid) and HON(hydrophobic neutral) was the major component of EfOM. They contained mainly humic-like substances and aromatic, aliphatic and carboxyl carbon. The molecular weight distributed mainly between 500-1000 Da. The content of HOB(hydrophobic base) and HI(hydrophilic fraction) was low and mainly contained protein-like substances with aliphatic carbon. The molecular weight was between 0.01-100 kDa.(2) Hydrophobic fractions especialy HOA and HON was transformed into HI during ozonation and HOA will transform to HON first then converted into HI fraction. Ozonation can reduce the humic-like and protein-like fluorescence intensity and destroy the aromatic structures to increase the aliphatic and carbonyl carbon content. The results implied that there was obvious selectivity during organic matter ozonation. Ozone will preferentially react with HON and then react with HOA. Ozone tend to react with hydrophobic fluorescent protein-like substances with molecular weight lower than 10 kDa.(3) Aiming at the limited dissolved organic matter removal efficiency of conventional coagulation-sedimentation-filtration process and sensitive influence of ozone dosage control on pre-ozonation-coagulation process, Hybrid ozonation-coaguation(HOC) system was developed, in which coagulation and ozonation could synchronize in one unit. The metal ions in coagulant can accelerate the decomposition of ozone into hydroxyl radicals(?OH) and improve the efficiency of organic matter ozonation. The results indicated that HOC system with polyaluminium chloride(PAC) can generate more ?OH than AlCl3?6H2O. For two kinds of coagulant, the content of Alb increased, which mainly contained Al13. The increase of Al13 will improve the removal efficiency of organic matter in coagulation. Therefore, there is mechanism of synergism between ozonation and coagulation in HOC system.(4) Based on mechanism of synergism between ozonation and coagulation, DOF process was put forward. DOF combined ozonation and flotation together, and ozonation, coagulation, flotation and disinfection can occur in one single reactor. In order to further improve the treatment efficiency of organic matter, turbidity as well as disinfection, and make full use of ozone gas and waterhead in the flotation column, Dual step ozone-induced flotation(DOIF) and membrane dissolved ozone flotation(MDOF) was developed without increasing the space consumption and using high-pressure pump. These two processes decreased the energy consumption during treatment, and increased disinfection performance and turbidity removal. Because of addition of ozone, membrane fouling rate was reduced and the cleaning period of membrane module was extended. |
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