Microfiltration of bovine and ovine milk for the reduction of microbial content in a tubular membrane:a preliminary investigation

摘要

In the present work a preliminary study on bovine and ovine milk microfiltration is reported. The study was aimed at the reduction of milk microbial content through a "cold technology" (i.e. at temperatures not higher than 40degC), with the obvious advantages for the preservation of essential elements. Considering the system's fouling characteristics, membrane washing was firstly optimised: Ultrasil 25 resulted to be more effective than NaOH, which was suggested by the membrane producer. Then, some preliminary tests with skimmed bovine milk evidenced the importance of the back-pulse device used in order to reduce fouling. In fact no permeate flux was observed in the absence of back-pulse, while permeate fluxes of about 350 and 410 L h~(-1)m~~(-2) were observed with back-pulse activated every 4 and 1 min, respectively. After this preliminary study on fouling, some tests with ovine milk were performed. It was previously centrifuged in order to remove fats, and a filtration step prior to microfiltration was demonstrated to be necessary for satisfactory performances. An average permeate flux of about 200 L h~~(-1) m~(-2) was obtained in the same conditions of bovine milk (back-pulse activated every 1 min) and an effective microbial removal was realised in the permeated ovine milk.