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WE have a good article on sumps in the article area. A fuge is simply an aquarium thats dedicated to a specific purpose. Be that growing macro algae, or other wildlife. With a sump the size of 10 gal I would really shy away from making a part of that a refuge. You will be much beter served having a 5 or 10 gal refuge and a 10 gal sump.
Your sump can be as complex (with dividers and seperate sections) or as simple (just a box with water going in and out) as you want/need it to be.