Chemical cleaning of microfiltration membranes fouled by whey

Millipore hydrophobic polyvinylidene fluoride (PVDF) microfiltration membra nes were used for whey processing. Fouled membranes were cleaned with acid (HCl), alkaline (NaOH) and surfactant (Triton-X100). The latter resulted in maximum flux recovery and resistance removal. Hydrochloric acid had a mode rate effect and sodium hydroxide was the weakest cleaning agent. This is du e to the cleaning strength of emulsifiers compared to acid or alkali. Howev er acids are more efficient than alkaline solutions for removal of mineral compounds which remain on the membrane surface. Cleaning efficiency depends on the concentration of cleaning agent being hi gher for higher surfactant concentration. For acids and alkali, the efficie ncy increases with increasing the concentration of the reagent reaches a ma ximum (optimum concentration) and then decreases. This can be explained by changes in permeability of the deposit layer with the concentration of the cleaning agent. Another explanation is the breakage of proteins by acid or alkali which produces more fouling materials and causes less cleaning effic iency. Operating conditions affect the cleaning process. At higher stirring speeds (turbulent flow) or longer cleaning time better removal of deposits and hi gher cleaning efficiency were observed. The sequential cleaning process may or may not improve the cleaning efficiency. When acidic cleaning was follo wed by washing with a surfactant an improvement was achieved. This can be a ttributed to the incomplete removal of deposits by acid. However further cl eaning with acid can not improve the cleaning efficiency. During whey processing fouling occurs by deposition of foulants of mostly p roteins and macromolecules on the membrane surface or in the membrane matri x. Large substances (compared to the membrane pores) settle on the membrane surface and the small species penetrate and are adsorbed in the membrane p ores. Cleaning dissolves and removes the adsorbed foulants from the membran e.