Ozone mass transfer in water and wastewater treatment: Experimental observations using a 2D laser particle dynamics analyzer

Ozone mass transfer in water and wastewater was studied by using a 2D laser particle dynamics analyzer (PDA) to simultaneously measure bubble size dis tribution and mixing intensity. Three types of water samples, including dei onized water, tap water and pulp mill effluents were tested to demonstrate the enhancement of ozone absorption with the presence of chemical reactions . Bubble size distribution and apparent mass transfer rates were used to es timate individual mass transfer parameters and examine the effects of opera ting conditions and selected gas spargers. II was shown that gas bubbles in ozonation systems varied over a broad range of sizes and their distributio ns usually deviated From a simple normal distribution. Among the factors ex amined, the gas sparger and water types were identified as the most importa nt factors affecting mean bubble size, whereas the impacts of ozone dose an d gas flow rate on bubble size distribution were minor. Due to the higher g as holdup, however, the specific surface area was strongly dependent on the gas Row rare as well. Consequently, the mass transfer coefficient increase d as the gas flow rate increased. A further enhancement of mass transfer wa s observed for pulp mill wastewarers as compared to tap and deionized water samples, because the occurrence of chemical reactions depleted the dissolv ed ozone within the gas-liquid film. (C) 2000 Elsevier Science Ltd. All rig hts reserved.