Part II: Mass Transfer of O 3 in Water: Fundamentals & Applications L aboratory of P hysical and A nalytical C hemistry REWARD H. Vankerckhoven

Outline What is mass transfer? Quantitative measure: “k L a” Factors affecting k L a Types of gas-liquid contactors Energy consumption in O 3 contacting Considerations regarding REWARD L aboratory of P hysical and A nalytical C hemistry

Mass transfer = absorption of a gas (O 3 ) in a liquid (water) dispersion of an O 3 -containing gas in water Mass transfer of O 3 in water: an important process Water treatment with O 3 : L aboratory of P hysical and A nalytical C hemistry production mass transfer off-gas treatment

“k L a”: A quantitative measure for the mass transfer performance Mass transfer rate: L aboratory of P hysical and A nalytical C hemistry driving force for mass transfer k L a : measure for mass transfer performance of a system characteristic for the contacting system used allows comparison between different systems volumetric mass transfer coefficient (s -1 or hr -1 )

“k L a”: A quantitative measure for the mass transfer rate k L a L aboratory of P hysical and A nalytical C hemistry a = gas-liquid interfacial area (cm -1 ), surface-to-volume ratio of gas bubbles k L = liquid mass transfer coefficient (cm/s), determined by hydrodynamic pattern k L a: 0 to > hr -1 Improvement of k L a: increasing k L and/or a Determination: directly; chemical and physical methods indirectly; determining

“k L a”: A quantitative measure for the mass transfer rate k L a L aboratory of P hysical and A nalytical C hemistry a = gas-liquid interfacial area (cm -1 ), surface-to-volume ratio of gas bubbles k L = liquid mass transfer coefficient (cm/s), determined by hydrodynamic pattern k L a: 0 to > hr -1 Improvement of k L a: increasing k L and/or a Determination: directly; chemical and physical methods indirectly; determining (k L a) O2 a = gas-liquid interfacial area (cm -1 ), surface-to-volume ratio of gas bubbles

Operating conditions and water quality affect k L a Factors affecting k L a: L aboratory of P hysical and A nalytical C hemistry Type of contactor+++ Energy dissipation+++ Temperature++ Gas & water flow rates+++ pH/ Ionic strength+ Presence of organic compounds - Nature+ ~ ++ - Concentration+ Physical properties - Surface tension- - Viscosity- - Density+ Contactor geometry Operating conditions Water quality

For every application, a suited gas- liquid contactor is available Many different types commercially available: different methods of operation different operating limits (water flow, ozone dose,…) characteristic k L a-range L aboratory of P hysical and A nalytical C hemistry Typek L a (hr -1 ) Bubble column5-50 Stirred vessel Liquid jet reactor Venturi injector Static mixer Membrane contactor …

Ozone transfer efficiency (OTE, in %) = fraction of absorbed O 3 from the gas phase O 3 transfer efficiency < 100 % ! L aboratory of P hysical and A nalytical C hemistry OTE is generally < 100 % Need for additional O 3 input

O 3 contacting can be energy intensive L aboratory of P hysical and A nalytical C hemistry High performance contactors: high energy consumption Exploitation costs: O 3 generation = low efficiency process Contacting:  Operating energy (gas pressure, water pressure, electrical power, …)  Additional amount of O 3 since OTE < 100 % O 3 treatment = energy intensive process Investment costs: purchase of a gas feed system, O 3 generator, contactor, off-gas destruct, … Exploitation costs

O 3 contacting in REWARD: various criteria to take into account Ozone treatment in the REWARD project: importance of O 3 contacting Choice of an O 3 contactor will depend on: Required minimum k L a (water temperature !) Investment costs: purchase of the contactor Exploitation costs: pumping, stirring,… Technical aspects (dimensions of the tank, water flow diagram in the dishwasher, safety issues, …) L aboratory of P hysical and A nalytical C hemistry