A dramatic increase in plastic waste has resulted in a strong need to increase plastic recycling accordingly. A selective flotation has been highlighted due to its outstanding efficiency for the separation of mixed plastics with analogous physicochemical characteristics. In this study, the effects of design and operational factors on the bubble’s hydrodynamic and mixing parameters in induced air flotation (IAF) with a mixing device were investigated through a design of experiment method (DOE) analysis for improving the plastic separation efficiency (i.e., PS and ABS). As a result of DOE analysis, the increase in the induced air tube diameter together with the rotational speed could generate a smaller bubble size. This led to the enhancement of the ratio of interfacial area to velocity gradient (a/G), which was interestingly found to be a significant factor affecting plastic recovery apart from the chemical agents. It demonstrates that operating IAF with a mixing device at a greater a/G ratio improved the plastic separation performance. These findings suggest that operating an IAF process with a mixing device at suitable a/G conditions could be a promising technique for separating plastic wastes, which have similar physicochemical characteristics as PS and ABS.
The use of appropriate flotation agents is mandatory to effectively separate plastic mixtures with analogous physicochemical characteristics by flotation. In this study, both virgin and post-consumer ABS and PS plastics were chosen as research objects to investigate the effects of flotation agents in ABS – PS flotation and an appropriate condition was then identified for effective separation. The wetting behaviors of wetting agents on ABS and PS surfaces were further studied. As a result, TA demonstrated better selective performance than LS in ABS – PS flotation due to its selective wettability on the ABS surface, referring to a greater surface free energy and a stronger repulsive interfacial interaction. Additionally, laureth-5 was found to be used potentially as a frother in ABS – PS flotation as well as MIBC; however, its application was limited at high concentrations due to its tendency to rapidly reduce surface tension. These findings suggest that the selection of a suitable frother for ABS – PS flotation should not only consider the ability to produce fine bubbles and stabilize the froth but also the ability to reduce the surface tension of the liquid medium. Overall, high recovery and purity of both virgin and post-consumer ABS – PS flotation were achieved by more than 90% under the conditions of TA concentration of 5 mg/L, MIBC concentration of 5 mg/L, and conditioning time of 15 minutes.
a b s t r a c tIn this study, fouled reverse osmosis (RO) membranes from the full-scale low pressure reverse osmosis (LPRO) plant were autopsied in March (RO-M) and September (RO-S), and investigated before and after the chemical cleaning. The characteristics of residual matters on LPRO membrane surfaces were then determined via several analysis methods including excitation-emission matrix, molecular weight distribution, thermogravimetric analysis, and organic analyses. The foulants were predominantly composed of hydrophobic organic matters with dense structures on RO-S, while loose structure of CaSO 4 and BaSO 4 scaling dominantly covered membrane surfaces on RO-M. Interestingly, loose structure of scaling provided more significant growth of biofilm and subsequently higher organic mass per unit area on RO-M. The order of basic-acidic cleaning showed improved flux recovery (87%) than acidic-basic cleaning (79%) due to the dense structure of biofilm layer on RO-S. In case of RO-M, foulants were easily removed without regarding the order of chemical cleaning (higher than 93% of initial flux recovery) due to the loose structure of fouling layer. The results proposed that the membrane foulants might have seasonal differences, and the cleaning order of basic-acidic chemicals would provide higher flux recovery in the case of the fluctuation in influent quality.
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