Effects of influent physicochemical characteristics on air dissolution, bubble size and rise velocity in dissolved air flotation: A review

• Influent physicochemical parameters can have great impacts on dissolved air flotation (DAF) performance. • Effect on air dissolution, bubble size distribution and bubble rise velocity has been discussed for each parameter considered. • This would help to determine changes required at design and operational stages to obtain optimum separation efficiencies. • Some future research prospects are recommended to be investigated further to clarify the identified grey areas. Microbubble (MB) aided clarification is applied in many industries due to its high efficiency, high loading rate and compact unit size over most other conventional technologies. Compared to coarser air bubbles, MBs perform better in fine particle capture due to a high surface area to volume ratio and increased bubble population. The most common method of generating MBs in water/ wastewater treatment and fine particle recovery in the mineral processing industry is dissolved air flotation (DAF). DAF is a proven efficient technology in water treatment and has been regularly used in this industry over the past few decades. Influent physicochemical parameters can have greater impacts on DAF performance when it is applied in high solid content applications. Air dissolution within the saturator, bubble size distribution and rise velocity of air bubbles are key factors that determine the process efficiency of DAF units. Therefore, understanding the effects of various physicochemical parameters of the influent on DAF performance is important as these variations have to be compensated during both the design and operational stages to obtain better separation efficiencies. The current article reviews up to date research findings on the effect of viscosity, salinity, temperature, pH, zeta potential, surface tension, solid content, particle size and hydraulic loading rate on air dissolution, bubble size distribution and bubble rise velocity of MBs. Finally, conclusions have been drawn from the critical analysis and literature survey and the future research prospects are proposed.