Development Of Inclined Foam Separation Column With Hydrophobic Material And Its Application In Wastewater Treatment

Foam separation is a green separation technology using bubbles as the adsorption medium to achieve the separation of a desired material from its diluted aqueous solution.There are two essential factors of interfacial adsorption and foam drainage,which jointly determined the performance of foam separation（e.g.,enrichment ratio and recovery percentage）.Wang et al.developed a novel column with inclined foam channel（IFC）to strengthen foam drainage.Experimental results indicated that the IFC could reduce the reflux distance and flow resistance between bubbles and interstitial liquid.Consequently,the interstitial liquid quickly drained onto the channel walls and formed a thin liquid film,when the foam was rising along the inclined channel.Then,the drained liquid would flow back to the bulk solution along the thin film,thereby strengthening foam drainage.However,the drainage efficiency of IFC decreased with the accumulation of thin film.In order to overcome this obstacle,the IFC was constructed with hydrophobic material in this work.Firstly,the effects of materials and tilt angle of inclined foam phase on foam drainage were studied,respectively.Then,the novel foam separation column was constructed and used to recover the desired material from the actual wastewater thereby improving the enrichment efficiency of the desired material.Firstly,the effects of materials and tilt angle of inclined foam phase on foam drainage were studied,respectively.Experimental results indicated that liquid holdup of the foam out of the column(ε_out)firstly decreased and then increased with the increase of tilt angle,and the minimum of theε_out was obtained at a tilt angle of 45°.And theε_out decreased with increase of hydrophobicity of wall materials.Since the hydrophobic effect induced the slip phenomena of thin layer on wall of column,the liquid film quickly flowed back into the bulk solution.When the tilt angle was 45°,foam drainage could be significantly strengthened by using IFC with polytetrafluoroethylene（PTFE）for obtaining a high enrichment ratio of the desired material.And then,the IFC with PTFE was used to recover dyes from the printing and dyeing wastewater.A two-stage foam separation technology was developed.In the first stage,the foam separation has been used to recover sweet potato protein（SPP）from the starch producing wastewater.In the second stage,the recovered sweet potato protein in the foamate could be used as the collector to recover crystal violet（CV）.The surface tension of the solution could be significantly reduced by SPP due to its good foaming property.The IFC with PTFE was used to strengthen foam drainage for increasing the enrichment ratio of crystal violet.Under the suitable conditions of p H 5.0,SPP concentration 2.8 g/L,tilt angle45°and volumetric air flow rate 150 m L/min,the enrichment ratio and recovery percentage of CV reached 21.2±1.1 and 87.7±4.4%,respectively.And the concentration of CV in the residual solution was as low as 2.1±0.1mg/L.Finally,the IFC with PTFE was used to recover the antibiotic from its wastewater.Firstly,thiol functionalized silica nanoparticles（t-SNPs）were prepared to enhance their adsorption capacity to streptomycin sulfate（SS）,and they would be used as the collectors in foam separation.Moreover,the IFC with PTFE was used to strengthen foam drainage.A low liquid holdup of the foam was achieved because the PTFE contributed to accelerating the flow of entrained liquid in the exterior channels.Under the suitable conditions of p H 7.0,t-SNPs concentration 500 mg/L,tilt angle 45°and volumetric air flow rate 700 m L/min,the recovery percentage and enrichment ratio of SS reached 90.1±4.5%and 82.4±4.1,respectively.Furthermore,desorption experiments were performed for isolating SS from the t-SNPs and the desorption percentage of SS reached 91.3±4.6%after four cycles.Sum up,this work had significant engineering significance and could supply some new light for the green and recycling treatment of antibiotic-contaminated wastewater.