Microbubble-based methods, in recent times, have been widely used for purification of water and wastewater. Microbubbles have several physicochemi- cal properties, which make them eminently suitable for wastewater treatment. In this review, these properties have been analyzed in detail from the perspective of appli- cation. Various types of microbubble generators and their operation principles have been discussed. The transport of gas into the aqueous phase has been explained, and the correlations to predict the volumetric mass transfer coef- ficient have been presented. Many practical applications using ozone, oxygen and air microbubbles, some of which are currently at various stages of commercialization, have been presented. Other important uses of microbubbles for wastewater treatment, namely, removal of fine solid particulate matter and oil, have also been discussed. In addition, directions for future research of microbubble technology and their potential applications have been identified.

Microbubble-aided water and wastewater purification: a review

Dissolved air precipitation/solvent sublation for oil-field produced water treatment

Hydrophobic compounds in the environment: Adsorption equilibrium at the air-water interface

The solvent sublation technique, one of adsorption bubble separation techniques, is initially proposed by Sebba[1] as an option for ion flotation, in which the material adsorbed on the surface of ascending bubbles and then collected by a solvent in the column upper zone. The technique has advantage over ion flotation or solvent extraction, so it has attracted many attentions in the wastewater treatment and the recovery of many metals. But as to now, the review on the solvent sublation is very sparse. The present paper reviews the theory and application in the solvent sublation.

Solvent sublation: theory and application

The separation of oily contaminants out of aqueous/non-aqueous phases using foam fractionation with a surfactant was investigated. In the separation of the light oil (hexadecane), the eluted amount of oil and the o/w (oil/water) ratio increased with the weight percentage of SDS (sodium dodecyl sulfate); and the ratio actually remained the same above the CMC (critical micelle concentration) point (0.23 wt% of SDS). Most of the oil was eluted even at 49:1 initial o/w ratio with the surfactant. For the heavy oil (carbon tetrachloride), the eluted o/w ratio and the oil recovery had maxima at 0.05 and 0.1 wt% of SDS solution, respectively, even though the overall recovery of 20–30 % was much lower than that of 80–100 % in the light oil. It was speculated that emulsion formation might affect oil entrapment in the foams. Higher gas flow rates, in general, increased the oil recovery, but did not increase the o/w ratio in the effluents.

X. Y. Lu

Papers

Removal of Hydrophobic Organic Compounds from the Aqueous Phase: Continuous Non-Foaming Adsorptive Bubble Separation Processes

Continuous countercurrent solvent sublation for the removal of hydrophobic organics from water