A biofilter is simply a filter media that removes something specific out of water, like Phosphorus for example. An example of a biofilter would be a bag of a granulated Phosphate removal product. Most are iron oxide pellets.
A microfilter filters out certain types of microorganisms, like bacteria. Water is forced through a specific kind of membrane. Better models remove all but viruses. An Ultraviolet Sterilizer can remove more microorganisms than a microfilter, but there are portable microfilters. I have one in my camping supplies to make stream water drinkable.
When a finger points to the moon, the imbecile looks at the finger.
Omnia mutantur nihil interit.
The more you read, the more things you will know. The more that you learn, the more places you'll go