Irisfan,
Your Starbucks is lying to you...
There's a corporate policy regarding their endeavor to recycle this green product. Print it out, and carry it back to that store manager...if they don't cooperate, threaten to call the corporate office...
https://news.starbucks.com/new...
P.S. CALL your local Health Department to see if it is, in fact, their policy to not let Starbucks save the grounds...