Regeneration of Lyes for Cleaning-In-Place (CIP) Processes in Dairies: Comparison of Recycled Potash and Soda Solutions Cleaning Properties

The regeneration of lyes for their integration in the dairy CIP was investigated applying an original process combining adsorption/coagulation and flocculation operations. Solutions of potassium hydroxide (KOH) and caustic soda (NaOH) soiled with 1% (v/v) of whole milk were submitted up to twenty successive regeneration cycles. The multiple recycling of the regenerated solutions was found to modify their physicochemical characteristics that are an increase of the turbidity, total Chemical Oxygen Demand (COD_t) and Total Nitrogen (TN) content simultaneously with a decrease of surface tension (γ) and equilibrium contact angle (θ_e). Along regeneration cycles, potash solutions exhibit quite a distinct trend from soda, especially a lower TN increase and a faster reduction of γ leading to a significant lower value of the critical micelle concentration (32 Vs. 36 mN.m^-1). These alterations can be correlated with the accumulation of surfactant molecules in the cleaning solutions derived from the saponification of fatty acids and the degradation of amino acids that can originate an improvement of the cleaning efficiency when re-used in CIP process.