Clarification and Purification of Drinking Water

In addition, bacterias need to be removed from well, river or lake water before water can be rendered potable. A properly selected microfiltration ceramic membrane is effective for bacteria decontamination. When used preceding a reverse osmosis or an ion-exchange unit, the microflltiaiion membrane protects the downstream separation process from bacteria contamination and possible fouling due to colloids. 

Furthermore, ultrafiltration ceramic membranes have been found to be effective in removing some heavy metal pollutants. 

Surface water can also be processed to become drinking water but it requires some pretreatment prior to the microfiltration step. A filtrate flux of 1,000-1,500 L/hr-m can be realized [Guibaud, 1989]. 

Both microfiltration (02 m) and ultrafiltration (4 nm) alumina membranes are very effective in removing bacterias. For example, the bacteria level of a lagoon water is reduced from 1,000-5,000/cm to 0.03-0.4/cm and 0.03-0.1/cm with the microHltration and ultrafiltration membrane, respectively [Castelas et al., 1984]. The total coliform level drops from 50-500/cm to zero for both types of membranes. The accompanying permeate flux is 600-1,200 L/hr-m for 70 hours for the microfiltration membrane when the water contains a low level of colloids and only 200 L/hr-m for 20 hours when the concentrations of colloids and organic materials are high. The ultrafiltration flux varies between 100 and 250 L/hr-m for 1,000 hours of operation. 

In addition to bacteria decontamination, the ultrafiltration membranes also reduce some ions such as sulfates (118 to 1.5 mg/L) and nitrites (0.22 to 0.02 mg/L). This is attributable to complexation of these ions with the humic and fulvic acids which are retained by the membranes. On the other hand, the non-complexed ammonium and chloride ion concentrations are essentially the same before and after ultrafiltration. 

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