I USA, från EPA :
If you must dispose treated wood, follow these recommendations:
State statute prohibits open burning of treated lumber. Typically, open burning of any kind can only occur at town transfer stations, by permit, involving only clean (untreated) wood and brush. Other limited open burning situations can occur at other sites, but only under a permit from local authorities, and typically only for clean wood and brush, not treated lumber.
Treated wood of all types can be most responsibly disposed of as follows: Homeowners engaged in small projects should take treated wood to their local landfill or transfer station and place it in the designated location (i.e., the non-clean wood pile). Contractors, utilities, and manufacturers should contract directly with a DEEP permitted bulky waste landfill, or send it to an out-of state wood burner facility appropriately equipped and permitted to burn treated wood.
Sawdust, chips, and small wood scraps should never be composted. Treat these items as stated above.