The phrase "are treated separately" is correct and usable in written English.
It can be used when discussing items, subjects, or cases that are handled independently from one another.
Example: "In this study, the two variables are treated separately to analyze their individual effects on the outcome."
Alternatives: "are handled independently" or "are considered individually."
Men and women are treated separately in hospitals here.
Waters deeper than 6,000 m are treated separately as the hadal realm by ecologists.
Copper, sulfur, and precious metals remain in the residue and are treated separately.
The literatures of these countries are treated separately under Brazilian literature and African literature.
By creating wholly owned subsidiaries for the parts that are treated separately for tax matters, Amazon is under no obligation to collect sales tax.
Nevertheless, because of their unique processing and application, glasses are treated separately in the article industrial glass.
Almost 2,000 works of significance are treated separately at the end of the appropriate composer entries (in many cases with synopses) and indexed at the back of the book.
Earnings from image rights are treated separately from money earned from playing for a British club, which HMRC says is down to a court ruling in 2000 which stated they should be treated as two separate income streams.
Some literatures are treated separately by language, by nation, or by special subject (e.g., Arabic literature, Celtic literature, Latin literature, French literature, Japanese literature, and biblical literature).
The major literatures written in English outside the British Isles are treated separately under American literature, Australian literature, Canadian literature, and New Zealand literature.
Similarly, because zinc, cadmium, and mercury exhibit few of the properties characteristic of the other transition elements, they are treated separately (see zinc group element).
