The Binding Properties And Regulation Between Microbubbles And Flocs In Dissolved Air Flotation

At present,the common methods to improve the flotation removal characteristics is to optimize operating parameters,such as hydraulic load,coagulation time,saturator pressure and recycle ratio.However,there are few studies on improving the removal characteristics of dissolved air flotation through aerated flocs modification.Although the previous studies constructed the kinetic model about collision and combination between flocs and microbubbles in the contact zone and the mathematical model on the rise of aerated flocs in the separation zone,the research was still at the theoretical and conceptual level.The interaction between microbubbles and flocs has never been thoroughly studied.However,the interaction forces between microbubbles and flocs,such as hydrodynamic and electrostatic forces,will directly affect the collision and combination efficiency,thereby changing the removal characteristics of dissolved air flotation.Based on this,this study constructed a dissolved air flotation experimental device with treatment capacity 50 m³?d^-1.Moreover,the physicochemical properties of inorganic and organic flocs were regulated by high molecular polymers,and the effects of coagulation destabilization and different electrical types of polymers on removal characteristics in dissolved air flotation were investigated.By means of microscopic technique and image analysis methods,binding characteristics between floc and microbubble were revealed by aerated floc size and two-dimensional fractal dimension and contact angle.The research results provide a theoretical basis for the optimization treatment effect in the dissolved air flotation.The effects of coagulant and high molecular polymers on flotation removal efficiency in the inorganic and organic systems were investigated by analyzing turbidity,TOC,UV₂₅₄ and color combining with floc Zeta potential analysis.The results showed that the turbidity removal was the highest when the PAC dosage was 200 mg?L^-1??=20mV?for inorganic system,indicating that the removal mechanism was mainly aluminium hydroxide sweeping flocculation.For organic system,when the PAC dosage was 130 mg?L^-1??=0 mV?,the removal of TOC,UV₂₅₄ and color were the highest,which were 63.28%,90.59%and 95.33%,respectively,indicating that charge neutralization is the main coagulation mechanism.Furthermore,the addition of anionic,cationic and non-ionic polymer improved the flotation removal efficiency.In the case of adding high molecular polymer,for inorganic system,turbidity removal was the highest?75.06%?when the PAC dosage was 200 mg?L^-1 and the anionic polymer dosage was 1mg?L^-1.For organic system,when the PAC dosage was 130 mg?L^-1 and the cationic polymer dosage was 1 mg?L^-1,the removal of TOC,UV₂₅₄ and color were the highest,which were 75.05%,94.74%and 99.32%,respectively.Through microscopic technique and image analysis methods,binding characteristics between floc and microbubble were revealed by aerated floc size and two-dimensional fractal dimension and contact angle.The results showed that when the PAC dosage was 200 mg?L^-1??=20 mv?for inorganic system,and when the PAC dosage was 130 mg?L^-1??=0 mv?for organic system,the formed aerated floc size was the best,with the smallest fractal dimension and the largest contact angle.Moreover,when the anionic,cationic and non-ionic polymer were added,aerated floc characteristics changed,with larger floc size,smaller fractal dimension and larger contact angle.When the PAC dosage was 200 mg?L^-1 and the anionic polymer dosage was 1 mg?L^-1 for inorganic system,and when the PAC dosage was 130 mg?L^-1 and the cationic polymer dosage was 1 mg?L^-1 for organic system,the formed aerated flocs size was the best,with the smallest fractal dimension and the largest contact angle.