Wash water addition on protein foam for removal of soluble impurities in foam fractionation process

This work evaluates the addition of wash water to a foam fractionation cell in order to remove the soluble impurities from a protein foam. Due to the irreversible adsorption of the proteins at the air interface, the addition of wash water to the foam can displace the entrained substances downward together with the liquid, while the adsorbed proteins are not desorbed from the foam surface. Here, we performed experiments on bovine serum albumin (BSA), as a model protein and NaCl salt, as a model of soluble impurities. The experiments were conducted in a glass foam fractionation cell, where the liquid level was kept constant. The wash water was added on the foam top with different flow rates and BSA and NaCl concentrations were measured at the outlets for further analysis. The influence of initial bubble size and the wash water rate on purification efficiency were investigated. The results show that wash water displaces the entrained liquid in foam and reduces the salt content of the foam. The process shows higher salt removal for higher wash water rates as well as for foams with larger bubble sizes, where up to 93 % of the salt was removed from the main solution. A lower air flow rate can further enhance the washing efficiency. However, it intensifies the foam collapse and hence diminishes the foam outflow.