Optimization of Flocculation in Dairy Industry Wastewaters Treatment

Treatment of milk industry wastewaters by separation techniques often requires a flocculation stage to increase the efficiency of particle removal in the pretreatment and filtration stages. Flocculation efficiency is determined by the nature and characteristics of the flocculant, mainly molecular weight and charge density. Flocculant selection has been traditionally based on settling trials, electrokinetic properties of the particles and results from mill trials, which are time and resource consuming methods. This paper presents the optimization of the flocculation stage for the treatment of dairy wastewater based on both the degree of flocculation and the floc properties, which were determined by using a methodology based on real-time particle chord size distribution monitoring. Eleven polyacrylamides (PAMs) were studied and compared. Anionic PAMs (A-PAMs) with a very high molecular weight and medium charge density induced the fastest flocculation and formed the largest flocs, but these flocs were unable to reflocculate if broken by hydrodynamic forces when high dosages of A-PAM were used. Flocs induced by cationic PAMs (C-PAMs) were smaller, but they were able to reflocculate. The dosage of the most efficient PAM was optimized by this technique. The reflocculation ability of the system was higher when the dose was lower than optimal.