I have not attempted to recycle PLA, as the raw material is so cheap (~$2/lb) that it is not worth the time or money to purchase a shredder/grinder, in my opinion. However, virgin PLA can be extruded just fine: http://www.soliforum.com/topic/4108/my-filastruder-and-results-so-far-abs-and-pla/
Tim here, from Filastruder. With the melt filter, dirt and other contaminants are not a concern. The nozzles I provide are closer to 2.9mm output, depending on extrusion temperature. If you need a slightly smaller diameter, you can up the temperature. If you are really worried about hitting 2.8mm, you could buy a 1.75mm nozzle and drill it out in increments, or email me through the FIlastruder website and I'll custom drill a nozzle for you. Happy printing!